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Antibacterial activity of N-quaternary chitosan derivatives: Synthesis, characterization and structure activity relationship (SAR) investigations
Abstract
Quaternary N-(2-(N,N,N-tri-alkyl ammoniumyl and 2-pyridiniumyl) acetyl) derivatives of chitosan polymer, chitooligomer, and glucosamine (monomer) were synthesized for the purpose of investigating the structure activity relationship (SAR) for the antibacterial effect. Novel methods were used in the synthesis. The final chitosan and chitooligomer derivatives could thus be obtained in two steps without prior protection of the hydroxyl groups. However, in order to obtain chitosan derivatives with the bulky N,N-dimethyl-N-dodecyl- and N,N-dimethyl-N-butyl side chains three steps were needed, starting from 3,6-O-di-tert-butyldimethylsilyl chitosan (3,6-O-di-TBDMS chitosan) as the key intermediate. The quaternary ammoniumyl acetyl derivatives of glucosamine were synthesized from glucosamine or tetra-O-acetylglucosamine. N,N,N-trimethyl chitosan (TMC) was used as reference compound for investigation of antibacterial activity. Clinical Laboratory Standard Institute (CLSI) protocols were used to determine MIC and MLC for activity against clinically important Gram-positive strains Staphylococcus aureus (ATCC 25923), and S. aureus (MRSA) (ATCC 43300), and Gram-negative strains of Escherichia coli (ATCC 25922), P. aeriginosa (ATCC 27853) and Enterococcus facialis (ATCC 29212). The MIC values for the compounds ranged from 8 to ⩾8192 mg/L. In general the N-(2-(N,N-dimethyl-N-dodecyl ammoniumyl) acetyl) derivatives of chitooligomer and glucosamine monomer were more active against bacteria than derivatives with shorter alkyl chains. In contrast the N-(2-(N,N-dimethyl-N-dodecyl ammoniumyl) acetyl) derivatives of chitosan were less active than derivatives with N-(2-N,N,N-trimetylammoniumyl) acetyl or N-(2-(N-pyridiniumyl) acetyl) quaternary moiety. N,N,N-trimethyl chitosan (TMC) was the most active compound in this study.
... As a result of this, TMC normally presents a higher bactericidal potential than that of its parent chitosan, increasing as its cationic charge density is augmented with presence of quaternary groups. TMC has been demonstrated to have antibacterial activity against Gram-negative bacteria: Escherichia coli [19,62,63], Enterococcus facialis, Pseudomonas aeruginosa [62], Salmonella enterica [64] and Gram-positive bacteria: Staphylococcus aureus [62,63,65], Listeria innocua [66], Bacillus subtilis [64]. Regarding TMC's activity against Gram-positive bacteria, Sadeghi et al. [67] reported that the TMC derivatives with the highest zeta potentials were the ones that presented the higher value of minimum inhibitory concentration (MIC). ...
... As a result of this, TMC normally presents a higher bactericidal potential than that of its parent chitosan, increasing as its cationic charge density is augmented with presence of quaternary groups. TMC has been demonstrated to have antibacterial activity against Gram-negative bacteria: Escherichia coli [19,62,63], Enterococcus facialis, Pseudomonas aeruginosa [62], Salmonella enterica [64] and Gram-positive bacteria: Staphylococcus aureus [62,63,65], Listeria innocua [66], Bacillus subtilis [64]. Regarding TMC's activity against Gram-positive bacteria, Sadeghi et al. [67] reported that the TMC derivatives with the highest zeta potentials were the ones that presented the higher value of minimum inhibitory concentration (MIC). ...
... As a result of this, TMC normally presents a higher bactericidal potential than that of its parent chitosan, increasing as its cationic charge density is augmented with presence of quaternary groups. TMC has been demonstrated to have antibacterial activity against Gram-negative bacteria: Escherichia coli [19,62,63], Enterococcus facialis, Pseudomonas aeruginosa [62], Salmonella enterica [64] and Gram-positive bacteria: Staphylococcus aureus [62,63,65], Listeria innocua [66], Bacillus subtilis [64]. Regarding TMC's activity against Gram-positive bacteria, Sadeghi et al. [67] reported that the TMC derivatives with the highest zeta potentials were the ones that presented the higher value of minimum inhibitory concentration (MIC). ...
Chitosan, a chitin-derivative polysaccharide, known for its non-toxicity, biocompatibility and biodegradability, presents limited applications due to its low solubility in neutral or basic pH medium. Quaternization stands out as an alternative to modify this natural polymer, aiming to improve its solubility over a wide pH range and, consequently, expand its range of applications. Quaternization occurs by introducing a quaternary ammonium moiety onto or outside the chitosan backbone, via chemical reactions with primary amino and hydroxyl groups, under vast experimental conditions. The oldest and most common forms of quaternized chitosan involve N,N,N-trimethyl chitosan (TMC) and N-[(2-hydroxy-3-trimethyl ammonium) propyl] chitosan (HTCC) and, more recently, quaternized chitosan by insertion of pyridinium or phosphonium salts. By modifying chitosan through the insertion of a quaternary moiety, permanent cationic charges on the polysaccharide backbone are achieved and properties such as water solubility, antimicrobial activity, mucoadhesiveness and permeability are significantly improved, enabling the application mainly in the biomedical and pharmaceutical areas. In this review, the main quaternized chitosan compounds are addressed in terms of their structure, properties, synthesis routes and applications. In addition, other less explored compounds are also presented, involving the main findings and future prospects regarding the field of quaternized chitosans.
... The research attention was directed to specific grafting groups, which can improve or bring new properties to chitosan, when precise applications were targeted [27,28]. Thus, many grafting groups were used along the time: Ncarboxyalkl [29][30][31]; O-carboxyalkyl [32][33][34][35]; N,O-carboxyalkyl [30][31][32]34,[36][37][38]; sulfate [39][40][41]; N-, O-, N,O-alkyl [42,43]; polyethylenglycol [44,45]; thiolate [46]; phosphate [47]; quaternary ammonium salts [48,49]. Each derivatization technique brought advantages and disadvantages, and researchers adopted them to prepare valuable products for specific bio-applications. ...
... However, no information about the depolymerization was given, it can be supposed that it was not suppressed. This method was further applied by other groups, but not to the same extent as other quaternization methods [48,113,114]. ...
The quaternary ammonium salts of chitosan are water soluble derivatives which keep the promise for real life applications in a large realm of biomedical fields, such as antimicrobial products, gene therapy, drug delivery, wound healing, tissue engineering and cosmetics. The increased potential for such applications is gained by a beneficial combination of the intrinsic properties of chitosan with those of the quaternary ammonium units. Since the first report of the synthesis of the quaternary ammonium salts of chitosan, many synthetic routes were developed, each of them with advantages and disadvantages which influence the product's properties. The aim of this review was to systemize these synthetic procedures and the properties of the resulted products, highlighting these advantages and disadvantages, in the desire to help the researchers working in this productive domain to choose the most suitable synthetic pathway when specific properties are targeted.
... Benediktsdottir et al. [105] & Runarsson et al. [116] synthesized Quaternary chitosan alternatives putting in their mind to investigate the structure activity relationship for the antibacterial effect [105,116]. Novel methods using protection strategies were used in such synthesis as illustrated in Figure 29. ...
... Benediktsdottir et al. [105] & Runarsson et al. [116] synthesized Quaternary chitosan alternatives putting in their mind to investigate the structure activity relationship for the antibacterial effect [105,116]. Novel methods using protection strategies were used in such synthesis as illustrated in Figure 29. ...
There is no doubt that, chitosan is considered as one of the most important biopolymers that can easily extracted from nature resources or synthesized in the chemical laboratories. Chitosan also display a suitable number of important properties in different fields of applications. Recently, chitosan has been reported as a perfect candidate as a trestle macromolecule for variable biological fields of study. This include, tissue engineering. cell culture and gene delivery, etc. Furthermore, chitosan has widely used in different types of industries which include: food, agriculture, fragrance, and even cosmetic industries. Besides that, chitosan derivatives is treated as excellent tool in waste water treatment. Therefore, the present work gives a simple selective overview for different modifications of Chitosan macromolecule with a special attention to its biological interest. Prior that, a closer look to its resources, chemical structure as well as general properties has been also determined which include its solubility character and its molecular weight. Furthermore, the chemistry of chitosan has been also mentioned with selected examples of each type of interaction. Finally a brief for sulfone based modified chitosan has been reported including classical methods of synthesis and its experimental variants.
... On the other hand, the low M w COS (M w = 0.77 kDa) remained inactive towards S. aureus at both pH values. In a further study N-(2-(N,N,N-trimethylammoniumyl)acetyl and N-(2-(N-pyridiniumyl)acetyl) derivatives of glucosamine, chitooligomer, and chitosan were investigated for activity against S. aureus (MRSA), E. faecalis and P. aeruginosa [15]. It was found that the glucosamine derivatives were inactive (MIC ≥ 8192 µg/mL), the COS derivatives had low to moderate activity (MIC = 4096 to 512 µg/mL) and the chitosan derivatives had moderate to high activity (MIC = 512 to 32 µg/mL). ...
... Hence, the purpose of the current study was to investigate a wider M w range for an antimicrobial chitosan derivative. TMC, with a high degree of quaternization and low O-methylation, was chosen for this study as previous investigations have shown this derivative is highly active, especially against the Gram-positive bacteria S. aureus [14][15][16]18,19]. ...
N,N,N-trimethyl chitosan (TMC) with 93% degree of trimethylation was synthesized. TMC and the chitosan starting material were subjected to acidic hydrolysis to produce 49 different samples with a reduced average molecular weight (Mw) ranging from 2 to 144 kDa. This was done to allow the investigation of the relationship between antibacterial activity and Mw over a wide Mw range. NMR investigation showed that hydrolysis did not affect the degree of trimethylation (DSTRI) or the structure of the polymer backbone. The activity of TMC against Staphylococcus aureus (S. aureus) increased sharply with Mw until a certain Mw value (critical Mw for high activity, CMW) was reached. After the CMW, the activity was not affected by a further increase in the Mw. A similar pattern of activity was observed for chitosan. The CMW was determined to be 20 kDa for TMC and 50 kDa for chitosan.
... 23, 28,29 C2 CH1 CH2 CT1 Figure 4: POM images of representative fibers studied It is well known that the quaternary units improve the antimicrobial activity of chitosan due to the presence of the permanent positive charge, making it more prone to develop intermolecular forces with the negatively charged bacterial membrane, compared to the amine units of chitosan. 15,30,31 This is especially true of nanofibers, which have an increased area-tovolume ratio, augmenting their specific surface and thus their properties. 7,17,32,33 All the tested samples, containing or not quaternary chitosan, showed very high antibacterial activity against the gram-positive bacterial strain S. aureus, with more than 90% bacterial inhibition. ...
The paper reports about binary chitosan/quaternized chitosan nanofibers obtained by direct electrospinning of their solution, without using co-spinning polymers. Both quaternary salts, N,N,N-trimethyl chitosan chloride and N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride, were used in the electrospinning process and provided nanofibers with a mean diameter lower than 100 nm. A morphological evaluation of the nanofibers prepared with quaternized chitosan and chitosan of different molecular weights indicated that chitosan of lower molecular weight yielded fibers of higher diameter, due to the necessity to increase the concentration of the electrospinning solution in order to reach chain entanglement. Polarized light microscopy suggested that the fibers were semicrystalline in nature, in line with the ability of the macromolecular chains to align in an electrical field. Furthermore, the investigation of the antimicrobial and antifungal activities against relevant gram-positive and gram-negative bacteria, as well as yeast strains, revealed the strong effects of the nanofibers, improved by the presence of quaternary chitosan and the lower diameter of the fibers.
... The objective of this study was to synthesize water-soluble chitotriazolan derivatives containing quaternary tetra-alkyl ammonium groups, aromatic alkyl ammonium groups, and basic protonable trialkyl amines using the CuAAC (copper-catalyzed azide-alkyne cycloaddition) method. The synthesized chitotriazolan derivatives (1, 2, 4, 5, 7, 8) included quaternized groups such as N,N,N-trimethyl and triethyl ammonium, as well as quaternary dialkyl piperazine and aromatic pyridinium groups, which have previously been found in antimicrobial N-alkyl and N-acyl chitosan derivatives [59][60][61][62] (Scheme 1). Previous research also investigated N-acyl chitosan derivatives with protonable piperazine and N-methyl piperazine groups [63]. ...
The azide transfer reaction and copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) can be used to convert the amino groups in chitosan to triazole 1,2,3-moieties. The resulting polymer has been named chitotriazolan. This synthesis was performed with six different quaternary ammonium alkynes and three amine alkynes to obtain a series of nine water-soluble chitotriazolan derivatives. The structure and complete conversion of the azide were confirmed by FT-IR and proton NMR spectroscopy. The derivatives were investigated for antibacterial activity against S. aureus, E. faecalis, E. coli, and P. aeruginosa. The activity of the quaternized chitotriazolan derivatives varied depending on the structure of the quaternary moiety and the species of bacteria. The basic protonable derivatives were less active or inactive against the bacteria.
... Multiple techniques have been used to improve the bacterial inhibitory effects of CHOS. Due to an increase in the quaternary amine's alkyl chain length, N-quaternization increased the antibacterial activities of CHOS [140,141]. Generally, quaternary ammonium salt augments the electro-positivity and water solubility of CHOS [142]. Thus, highly electropositive CHOS might more strongly adhere to negatively charged bacterial surfaces. ...
Chitooligosaccharide (CHOS), a depolymerized chitosan, can be prepared via physical, chemical, and enzymatic hydrolysis, or a combination of these techniques. The superior properties of CHOS have attracted attention as alternative additives or bioactive compounds for various food and biomedical applications. To increase the bioactivities of a CHOS, its derivatives have been prepared via different methods and were characterized using various analytical methods including FTIR and NMR spectroscopy. CHOS derivatives such as carboxylated CHOS, quaternized CHOS, and others showed their potential as potent anti-inflammatory, anti-obesity, neuroprotective, and anti-cancer agents, which could further be used for human health benefits. Moreover, enhanced antibacterial and antioxidant bioactivities, especially for a CHOS-polyphenol conjugate, could play a profound role in shelf-life extension and the safety assurance of perishable foods via the inhibition of spoilage microorganisms and pathogens and lipid oxidation. Also, the effectiveness of CHOS derivatives for shelf-life extension can be augmented when used in combination with other preservative technologies. Therefore, this review provides an overview of the production of a CHOS and its derivatives, as well as their potential applications in food as either additives or nutraceuticals. Furthermore, it revisits recent advancements in translational research and in vivo studies on CHOS and its derivatives in the medical-related field.
... However, chitosan becomes water insoluble around physiological pH, because its amino groups (pKa ≈ 6.5) lose their positive charge upon deprotonation [12,17]. Therefore, most studies with chitosan are performed under acidic conditions (pH < 6.5), but exceptions include chitosan derivatives (e.g. with permanent positive charges) and chitosan oligomers (which remain water soluble in the physiological pH range) [18,19]. Although the literature on chitosan's antimicrobial activity is relatively dense, the molecular details of its interaction with biomembranes remain unclear, [15,17] partly due to the complexity of cell membranes and of in vivo studies. ...
Chitosan is a versatile and biocompatible cationic antimicrobial polymer obtained from sustainable sources that is effective against a wide range of microorganisms. Although it is soluble only at low pH, chitosan oligomers (ChitO) are soluble in pure water and thus more appropriate for antibacterial applications. Although there is a vast literature on chitosan’s antimicrobial activity, the molecular details of its interaction with biomembranes remain unclear. Here we investigate these molecular interactions by resorting to phospholipid Langmuir films (zwitterionic DPPC and anionic DPPG) as simplified membrane models (for mammalian and bacterial membranes, respectively), and using SFG vibrational spectroscopy to probe lipid tail conformation, headgroup dynamics and interfacial water orientation. For comparison, we also investigate the interactions of another simple cationic antimicrobial polyelectrolyte, poly(allylamine) hydrochloride – PAH. By forming the lipid films over the polyelectrolyte solutions, we found that both have only a very small interaction with DPPC, but PAH adsorption is able to invert the interfacial water orientation (membrane potential). This might explain why ChitO is compatible with mammalian cells, while PAH is toxic. In contrast, their interaction with DPPG films is much stronger, even more so for ChitO, with both insertion within the lipid film and interaction with the oppositely charged headgroups. Again, PAH adsorption inverts the membrane potential, while ChitO does not. Finally, ChitO interaction with DPPG is weaker if the antimicrobial is injected underneath a pre-assembled Langmuir film, and its interaction mode depends on the time interval between end of film compression and ChitO injection. These differences between ChitO and PAH effects on the model membranes highlight the importance of molecular structure and intermolecular interactions for their bioactivity, and therefore this study may provide insights for the rational design of more effective antimicrobial molecules.
... 30 Other studies proved that the antibacterial activity is affected not only by the chemical nature of the group but also by the position of the positive charges. 30,128 Oxanthonyl-chitosan ( Figure 12, compound 3) is an example of a quaternary derivative of chitosan with promising antibacterial activity. 129 This compound compared to its starting materials showed a better solubility in water and a better antibacterial activity, being these improvements associated with the positive charges of the quaternary ammonium groups and with the multi-hydroxy planar benzene structure. ...
Polysaccharides arouse great interest due to their structure and unique properties, such as biocompatibility, biodegradability, and absence of toxicity. Polysaccharides from marine sources are particularly useful due to the wide variety of applications and biological activities. Chitosan, a deacetylated derivative of chitin, is an example of an interesting bioactive marine‐derived polysaccharide. Moreover, a wide variety of chemical modifications and conjugation of chitosan with other bioactive molecules are responsible for improvements in physicochemical properties and biological activities, expanding the range of applications. An overview of the synthetic approaches for preparing chitosan, chitosan derivatives, and conjugates is described and discussed. A recent update of the biological activities and applications in different research fields, mainly focused on the last 5 years, is presented, highlighting current trends.
... Although COS is efficient to inhibit the bacterial growth, various methods have been employed to enhance those inhibitory activities. For example, N-quaternization of COS enhanced antimicrobial activity, and higher efficiency of antimicrobial activity was noticed when alkyl chain length of the quaternary amine was increased (Rúnarsson et al. 2007(Rúnarsson et al. , 2010. Generally, quaternary ammonium salt increases the electropositivity and water solubility of COS (Hui et al. 2020). ...
Chitooligosaccharide (COS) is the hydrolyzed product of chitosan (CS). Various chemical, physical, and enzymatic methods have been employed to produce COS. COS has higher water solubility than the CS, which is an aqueous acid soluble biopolymer. In general, COS has a molecular weight (MW) varied between 3 and 10 kDa with a degree of depolymerization (DP) ranging from 2 to 20. However, both DP and MW fluctuate, depending on sources as well as the method of preparation. COS possesses excellent antioxidant and antimicrobial activities and those activities have been exploited to inhibit oxidation of lipids/proteins and microbial growth in foods that are prone to deterioration such as fatty fish, etc. In recent times, consumers are more oriented towards health-related issues, leading to increased consumption of food with high nutraceutical values. Apart from preservative efficacy, COS has been widely studied for its anti-diabetic, anti-obesity, digestive enzyme inhibitory activities as well as other nutraceutical properties. COS shows positive results in controlling glucose levels, serum lipid levels, or weight gain as confirmed in both in vivo and in vitro studies. Overall, COS has tremendous potential to act as a nutraceutical, which can provide health-related benefits for the consumers and can improve the quality as well as extend shelf life of various foods.
... Chitosan (polyglucosamine), a deacetylated derivative of natural polymer chitin, is known for its intrinsic antimicrobial properties (Kalantari, Afifi, Jahangirian, & Webster, 2019). Quaternization of chitosan has been shown to enhance antibacterial activity of this biopolymer, due to increased electrostatic interaction between positively charged quaternary ammonium moieties and negatively charged components of bacterial cells (Vidar Rúnarsson et al., 2010). In addition, quaternization helps to overcome solubility limitations of chitosan which requires an acidic environment (Chivangkul et al., 2014). ...
A series of quaternary dimethyl-(alkyl)-ammonium chitosan derivatives (QACs) was synthesized and studied for physicochemical properties and bioactivity. The QACs tended to spontaneously self-assembly into nanoaggregates. Antimicrobial activity was examined in vitro on Gram-negative Escherichia coli (E. coli) and Gram-positive Listeria innocua (L. innocua) bacteria as well as phytopathogenic fungus Botrytis cinerea. The hexyl chain-substituted QAC-6 demonstrated the highest potency causing 3.0- and 4.5-log CFU mL-1 reduction of E. coli and L. innocua, respectively. QAC-6 was tested for antimicrobial activity on stainless steel coupons and fresh spinach leaves. A traditional ‘wet’ application (spray) and dry engineered water nanostructure (EWNS) approach were used for spinach decontamination. With both approaches, significant reduction of microbial load on the treated produce was achieved. The wet application showed a greater reduction of microbial load, while the advantages of EWNS were reaching the antimicrobial effect with miniscule dose of active agent leaving treated surface visibly dry.
... They will reduce the number of quaternized primary amino groups and this will reduce their activity similar to the effect of an increase in the degree of acetylation (DA) on the antibacterial activity of chitosan (Younes et al., 2014) and chitosan derivatives (Rathinam, Ó lafsdóttir, et al., 2020c;Sahariah, Snorradóttir, Hjálmarsdóttir, Sigurjónsson, & Másson, 2016). Highly lipophilic substituents, similarly to cinnamic acid, can reduce the activity (Rúnarsson et al., 2010), possibly by causing self-association on the polymer chains. Our investigation has also shown that hydroxypropyl substituents, which are hydrophilic and can form hydrogen bonds similar to the caffeic moiety, will also have a strong negative effect on the antibacterial activity (Másson, 2021a;Rathinam et al., 2020). ...
A new synthesis method was developed and optimized by a full factorial design for conjugating hydroxycinnamic acids (HCA-s) to chitosan. Cinnamic acid and tertbutyldimethylsilyl protected HCA-s were converted to their corresponding acyl chlorides and reacted with tertbutyldimethylsilyl-chitosan to selectively form amide linkages, resulting in water-soluble conjugates after deprotection. Nineteen conjugates were obtained with various degrees of substitution (DS) ranging from 3% to 60%. The conjugates were found to be bactericidal against Staphylococcus aureus and Escherichia coli, with their activities equal to chitosan at low DS but an increase in the DS correlated with reduced activity. DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging assay was performed to determine the EC50 values. Chitosan only exhibited low antioxidant activity, whereas the HCA-chitosan conjugates exhibited higher antioxidant activities correlating with the DS. One caffeic acid conjugate (21%) was 4000 times more active than chitosan and more active than free caffeic acid.
... The modification of the Ch backbone improves the antibacterial activity [26,57]. This improvement may be the result of the interaction between the amphiphilic chain and cell membrane components (phospholipids) [60,61] and cytoplasmic constituents [62] leading to the fungal plasma membrane permeabilization [63]. Several factors contribute to the degradation of fungal cells, such as the concentration, molecular weight (MW), degree of deacetylation (DD), and the local pH [64]. ...
Chitosan (Ch) was reacted with seven benzaldehyde analogs separately through reductive amination in which the corresponding imines were formed and followed by reduction to produce N-(benzyl) chitosan (NBCh) derivatives. ¹H NMR spectroscopy was used to characterize the products. The nanoparticles (NPs) of Ch and NBCh derivatives were prepared according to the ionotropic gelation mechanism between Ch products and sodium tripolyphosphate, followed by high-energy ultrasonication. Scanning electron microscopy, particle size, polydispersity index, and zeta potential were applied for the NPs examination. The particle size was ranged from 235.17 to 686.90 nm and narrow size distribution (PDI <1). The zeta potential of NPs was varied between −1.26 and −27.50 mV. The antimicrobial activity was evaluated against bacteria (Erwinia carotovora subsp. atroseptica, Erwinia carotovora subsp. carotovora, and Ralstonia solanacearum), fungi (Aspergillus flavus and Aspergillus niger), and yeast (Candida albicans). The action of NBCh derivatives was significantly higher than Ch. The NPs had considerably higher than the Ch and NBCh derivatives. The activity was directly proportional to the chemical derivatization of Ch and the zeta potential of the NPs. The antimicrobial efficacy of these derivatives formulated in a greener approach could become an alternative to using traditional antimicrobial applications in an environmentally friendly manner.
... The most important derivative of chitin is chitosan, obtained through partial deacetylation of chitin under alkaline conditions or enzymatic hydrolysis in the presence of a chitin deacetylase [162]. Several studies proved that chitosan and its derivatives have antioxidant, anti-microbial and anti-viral activities [163][164][165][166]. Chitin, chitosan, and their derivatives also act as inhibitors of ACE, an enzyme associated with hypertension. ...
Seafood by-products, produced by a range of different organisms, such as fishes, shellfishes, squids, and bivalves, are usually discarded as wastes, despite their possible use for innovative formulations of functional foods. Considering that “wastes” of industrial processing represent up to 75% of the whole organisms, the loss of profit may be coupled with the loss of ecological sustainability, due to the scarce recycling of natural resources. Fish head, viscera, skin, bones, scales, as well as exoskeletons, pens, ink, and clam shells can be considered as useful wastes, in various weight percentages, according to the considered species and taxa. Besides several protein sources, still underexploited, the most interesting applications of fisheries and aquaculture by-products are foreseen in the biotechnological field. In fact, by-products obtained from marine sources may supply bioactive molecules, such as collagen, peptides, polyunsaturated fatty acids, antioxidant compounds, and chitin, as well as catalysts in biodiesel synthesis. In addition, those sources can be processed via chemical procedures, enzymatic and fermentation technologies, and chemical modifications, to obtain compounds with antioxidant, anti-microbial, anti-cancer, anti-hypertensive, anti-diabetic, and anti-coagulant effects. Here, we review the main discards from fishery and aquaculture practices and analyse several bioactive compounds isolated from seafood by-products. In particular, we focus on the possible valorisation of seafood and their by-products, which represent a source of biomolecules, useful for the sustainable production of high-value nutraceutical compounds in our circular economy era.
... They will reduce the number of quaternized primary amino groups and this will reduce their activity similar to the effect of an increase in the degree of acetylation (DA) on the antibacterial activity of chitosan (Younes et al., 2014) and chitosan derivatives (Rathinam, Ó lafsdóttir, et al., 2020c;Sahariah, Snorradóttir, Hjálmarsdóttir, Sigurjónsson, & Másson, 2016). Highly lipophilic substituents, similarly to cinnamic acid, can reduce the activity (Rúnarsson et al., 2010), possibly by causing self-association on the polymer chains. Our investigation has also shown that hydroxypropyl substituents, which are hydrophilic and can form hydrogen bonds similar to the caffeic moiety, will also have a strong negative effect on the antibacterial activity (Másson, 2021a;Rathinam et al., 2020). ...
Antioxidants are natural or synthetic substances that prevent or reduce oxidative stress, an imbalance between antioxidant activity and reactive oxygen species. This chapter discusses several anti‐oxidant conjugates of chitosan, including, gallic acid conjugates, caffeic acid conjugates, ferulic acid conjugates, cinnamic acid conjugates, coumaric acic conjugates, chlorogenic acid conjugates, salicylic acid conjugates, and catechin conjugates. It describes the three main methods to synthesize chitosan–antioxidant conjugates: free radical grafting method, enzyme mediated synthesis, and activated ester‐mediated synthesis. The antioxidant activity of the antioxidant‐chitosan conjugates is most commonly investigated by the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) method. Susceptibility testing of the synthesized conjugates is most commonly carried out by disk diffusion assay and minimum inhibitory concentration determination. Antioxidant–chitosan conjugates are promising for a novel multifunctional food packaging material due their filmforming property and antioxidant activity. Antioxidant grafted chitosan can be utilized as drug delivery systems to provide controlled release.
... In the synthesis of N-acyl chitosan derivatives (N-acylation of chitosan is illustrated in Fig. 3), different methods were studied. N-(2-quaternary ammoniumyl) acyl chitosan derivatives have either aromatic ammonium or a quaternary N-tri-alkyl on the N-acetyl group [32]. In a five-step protection group method, Holappa et al. [33] stated the synthesis of chitosan N-betainates N-(2-(N,N,N-trimethyl-ammoniumyl) acetyl) chitosan. ...
In this era, there is a global concern in the use of bioactive molecules such as chitosan in the field of antimicrobial and antioxidant benefits. Because of its biodegradability, biological compatibility, antimicrobial, antioxidants activity, and high safety, chitosan could be used in a large number of applications. It could exist in many forms, such as fibers, gels, films, sponges, nanoparticles, and beads. The different biological activities of chitosan and its products are extensively investigated to broaden the application fields in several areas. Chitosan's natural properties depend strongly on water and other solvent solubility. Consequently, the chitosan oligosaccharides with a low polymerization degree are getting significant attention in the pharmaceutical and medical applications because they have lower viscosity and higher water solubility than chitosan. The objective of this review article is to put the antioxidant and antimicrobial properties of chitosan and its derivatives under the spotlight. The impacts of chitosan on physicochemical parameters like molecular weight and deacetylation degree on its bioactivities are also identified. Additionally, other applications of chitosan and its derivatives, including wound healing products, wastewater treatment, and cosmetics, have also been highlighted.
... In order to solve this problem, the structural trialkyl quaternary ammonium chitosan is considered because it not only increases its water solubility, but also enhances other favorable properties [22]. The antibacterial activity of trialkyl quaternary ammonium chitosan is due to a strong interaction with the cytoplasmic membranes, because there is a hydrophobic affinity between the alkyl chain and the phospholipids, so it causes remarkable antibacterial effects [23][24][25]. ...
Inthiswork,inorderto preparebiocomposites ofciprofloxacin- montmorillonite/N,N,N-triethyl chitosan(CMC/ TEC and CMC׳/TEC), ciprofloxacin was intercalated into the Na+-montmorillonite layers in two different pHs and coated with N,N,N-triethyl chitosan. XRD and FT-IR data demonstrated that ciprofloxacin (CIP) diffused among the layers of montmorillonite. The prepared biocomposites were further characterised by TG, SEM, BET, DSC, and disk diffusion method to investigate antibacterial activity against Staphylococcus aureus as well. Coated composites with N,N,N-triethyl chitosan possessed efficiency of the drug encapsulation, and controlled the release of drug from the biocomposites in comparison with composites without N,N,N-triethyl chitosan. Study of antibacterial activities of two biocomposites of CMC1/TEC and CMC2/TEC with lower release rates and lower concentrations of CIP than other biocomposites revealed that likely N,N,N-triethyl chitosan could considerably help to reduce the consumption of ciprofloxacin. By doing more researches on other bacterial strains and performing advanced tests on our own biocomposites, N,N,N-triethyl chitosan can probably be proved as a suitable candidate for a substitute in biomedical activities.
... Therefore, it is reasonable to improve the positive charge on these polymers by endowing them with more cationic groups to improve their antimicrobial properties and water solubility. Based on this concept, different modification techniques have been developed including the introduction of amino groups Klaykruayat et al. 2010) and quaternary ammonium moieties (Morkaew et al. 2017;Rúnarsson et al. 2010;Sajomsang et al. 2010) and metal/metal oxide nanoparticles (Ifuku et al. 2015;Youssef et al. 2015;Yu et al. 2018). ...
The bacterial infections have always a serious problem to public health. Scientists are developing new antibacterial materials to overcome this problem. Polysaccharides are promising biopolymers due to their diverse biological functions, low toxicity, and high biodegradability. Chitin and chitosan have antibacterial properties due to their cationic nature, while cellulose/bacterial cellulose does not possess any antibacterial activity. Moreover, the insolubility of chitin in common solvents, the poor solubility of chitosan in water, and the low mechanical properties of chitosan have restricted their biomedical applications. In order to solve these problems, chemical modifications such as quaternization, carboxymethylation, cationization, or surface modification of these polymers with different antimicrobial agents, including metal and metal oxide nanoparticles, are carried out to obtain new materials with improved physiochemical and biological properties. This mini review describes the recent progress in such derivatives and composites with potential antibacterial applications.
... We thought that bromoacetyl bromide would be an appropriate candidate that easily joins the terminal amino group of the amino-PVC to the Cs amino group. Therefore, bromoacetylated chitosan was first prepared according to a modified procedure [52][53][54]. Thus, chitosan was soaked in dry DMF overnight. ...
We herein describe the synthesis of four Cs-PVC conjugates three of them were functionalized with benzothiazole (BTh) derivative as an antibacterial agent. Two of these BTh-functionalized conjugates, namely Cs2 and Cs3, comprise silver nanoparticles (AgNPs) and Ag/TiO2 NPs, respectively. The structureswere characterized
via FTIR spectroscopic analysis,morphological investigation such as scanning (SEM) and transmission (TEM) electron microscopy, and thermal gravimetric analysis (TGA). Spectral data confirmed the introduction of the BTh to the Cs backbone as well as the coupling between the two polymers. SEMdata showed homogenous polymer
surfaces with well-distributed Ag nanoparticles. The Ag contents in the prepared samples Cs2 and Cs3were, respectively, 0.61 and 0.21%, however, TEManalysis showed that the sizes of AgNPs and Ag/TiO2 NPswere in the range of 3–7 nmand15–22nmfor the prepared conjugates, respectively. The antibacterial activity of the synthesized conjugates was investigated against two Gram-negative (E. coli, and S. typhimurium) and two Grampositive (S. aureus, and L. monocytogenes) bacteria. The antibacterial assay showed that all three Cs-PVC (Cs1, Cs2, and Cs3) conjugates modified with BTh exhibited excellent bacterial inhibition after 30, 60, and 120 min.
... We thought that bromoacetyl bromide would be an appropriate candidate that easily joins the terminal amino group of the amino-PVC to the Cs amino group. Therefore, bromoacetylated chitosan was first prepared according to a modified procedure [52][53][54]. Thus, chitosan was soaked in dry DMF overnight. ...
... Chitosan contains one -NH 2 and two −OH in its constitutional unit [10], and these sites can be easily reacted to acquire various of quaternary ammonium salt derivatives. For example, the -NH 2 was directly turned into a -N + (CH 3 ) 3 [11][12][13][14][15] or a quaternary phosphonium salt group [16,17]. Also, on the other hand, -NH 2 and −OH were simultaneously substituted by -N + (CH 3 ) 3 or quaternary phosphonium salt group, resulting in improved water solubility and antibacterial activity [18,19]. ...
The positionally substituted 2′-O-hydroxypropyl trimethyl ammonium chloride chitin (2′-O-HTACCT) with different substitution degree of quaternary ammonium salt were synthesized directly from β-chitin, after that these 2′-O-HTACCT were then deacetylated to obtain corresponding 2′-O-hydroxypropyl trimethyl ammonium chloride chitosan (2′-O-HTACCS) with different deacetylation degree. The antibacterial activity and mechanism against E. coli and S. aureus of these 2′-O-HTACCT and 2′-O-HTACCS were investigated with various techniques. The results demonstrated that the 2′-O-HTACCT had antibacterial effect against S. aureus, but it had negligible antibacterial effect against E. coli, maybe due to the lack of anionic compound such as teichoic acid on the E. coli's cell wall. Impressively, the high antibacterial effect against E. coli of the 2′-O-HTACCS was derived only from its -NH2, but the ultra high antibacterial effect against S. aureus of the 2′-O-HTACCS was derived both from its -NH2 and -N⁺(CH3)3, and enhanced as its pH value decreased. Thus, the positionally substituted 2′-O-HTACCS played an important role as a high-performance antibacterial bio-resource polymer against E. coli and S. aureus.
... Lower pH value and higher polymerization were also reported to be beneficial due to the antimicrobial activity of COS [86]. Rúnarsson et al. proved that N-quaternization of COS contributes to antimicrobial activity under neutral conditions, and the efficiency of its antimicrobial activity could be enhanced with increasing alkyl chain length of the quaternary amine [87,88]. With addition of enteropathogenic Escherichia coli (EPEC) to the surface of the human HEp-2 cell line, Quinterovillegas et al. reported that COS could suppress the adherence of EPEC to HEp-2 by more than 90% [89]. ...
Chitooligosaccharide (COS), which is acknowledged for possessing multiple functions, is a kind of low-molecular-weight polymer prepared by degrading chitosan via enzymatic, chemical methods, etc. COS has comprehensive applications in various fields including food, agriculture, pharmacy, clinical therapy, and environmental industries. Besides having excellent properties such as biodegradability, biocompatibility, adsorptive abilities and non-toxicity like chitin and chitosan, COS has better solubility. In addition, COS has strong biological functions including anti-inflammatory, antitumor, immunomodulatory, neuroprotective effects, etc. The present paper has summarized the preparation methods, analytical techniques and biological functions to provide an overall understanding of the application of COS.
... The limitation of chitosan use in various applications is due to its low solubility [12]. Therefore, its low solubility at physiological pH limits its biological activity [13]. Accordingly, chemical modifications of chitosan are required to enhance its solubility and broaden the spectrum of its applications, including as biocide. ...
Chitosan is a biopolymer that has antifungal activity against C. albicans. Chemical modification of chitosan can provide it with new functional properties for a wide range of biological and biomedical applications. Carboxymethyl chitosan is a derivative of chitosan obtained by etherification of alkaline chitosan with monochloroacetic acid. Carboxymethyl chitosan has a higher solubility than chitosan; therefore it is more readily applicable for use in various fields. Chitosan also has antifungal activity against C. albicans. This study evaluated carboxymethyl chitosan as a gauze-coating material to be used for its antifungal properties. This study also optimized the coating process. Gauze was coated with carboxymethyl chitosan then characterized by Fourier Transform Infra-Red Spectrophotometer (FTIR), X-ray diffraction and scanning electron microscopy (SEM). The antifungal activities of gauze-coated samples were then tested by the diffusion method. The results show that the optimum conditions for the process of coating gauze with carboxymethyl chitosan are dipping ten times at a concentration of 1% for 50 s. Antifungal activities of carboxymethyl chitosan-coated gauze as measured by the diameter of the growth inhibition area are 0.30 cm higher than chitosan-coated gauze, which has a growth-inhibition diameter of 0.12 cm.
... Thus, the incorporation of organobentonite synthesized with CTAB impregnated chitosan into the blend of HDPE/chitosan can result in good interfacial adhesion between chitosan and the polymer matrix. In addition, it is established in the literature that the combination of ammonium salts with chitosan retains its properties and improves its natural antibacterial and antifungal properties [41][42][43]. ...
In this study, blends based on a high density polyethylene (HDPE) and chitosan (CS) were successfully prepared by melt processing, in a laboratory internal mixer. The CS biopolymer content effect (up to maximum of 40%), and, the addition of bentonite clay modified with quaternary ammonium salt (CTAB) impregnated chitosan as a compatibilizing agent, on the properties of the blends was analyzed by Fourier transform-infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analyses (TG), tensile strength, and scanning electron microscopy (SEM). The use of clay modified with CTAB impregnated chitosan, employing a method developed here, improved the compatibility of HDPE with chitosan, and therefore the thermal and some of the mechanical properties were enhanced, making HDPE/chitosan blends suitable candidates for food packaging. It was possible to obtain products of synthetic polymer, HDPE, with natural polymer, chitosan, using a method very used industrially, with acceptable and more friendly properties to the environment, when compared to conventional synthetic polymers. In addition, due to the possibility of impregnated chitosan with quaternary ammonium salt exhibit higher antibacterial activity than neat chitosan, the HDPE/chitosan/organobentonite blends may be potentially applied in food containers to favor the preservation of food for a longer time in comparison to conventional materials.
... After N-methylation of 1,2,3-triazole and pyridine with iodomethane, the characteristic peak considered as 1,2,3-triazolium moiety of cationic chitosan derivative c is observed at 1581 cm −1 . Besides, other new peaks for pyridinium at 3058, 1519, and 809 cm −1 are also clearly detected (Rúnarsson et al., 2010). ...
In this paper, novel cationic chitosan derivative possessing 1,2,3-triazolium and pyridinium groups was synthesized conveniently via cuprous-catalyzed azide-alkyne cycloaddition (CuAAC) and methylation. FTIR, ¹H NMR, and elemental analysis examined the structural characteristics of the synthesized derivatives. The antifungal efficiencies of chitosan derivatives against three plant-threatening fungi were assayed by hypha measurement in vitro. The determination showed that chitosan derivative bearing 1,2,3-triazolium and pyridinium displayed tremendously enhanced antifungal activity as compared with chitosan and chitosan derivative bearing 1,2,3-triazole and pyridine. Notably, the inhibitory indices of it against Colletotrichum lagenarium attained 98% above at 1.0 mg/mL. The results showed that N-methylation of 1,2,3-triazole and pyridine could effectively enhance antifungal activity of the synthesized chitosan derivatives. Besides, the prepared chitosan derivatives showed non-toxic effect on cucumber seedlings. This synthetic strategy might provide an effective way and notion to prepare novel cationic chitosan antifungal biomaterials.
Processing of crustaceans such as shrimp, crab, etc., or molluscs, e.g., squid generates large amounts of byproducts, especially shells and squid pens. Improper disposal of those byproducts may cause deleterious implications on environment and human health. The valorization of shells or squid pens via conversion to several high-value bioactive compounds could pave a way for sustainable utilization of marine resources. Crustacean shells and squid pens serve as a potential source of chitin, which can further be deacetylated into chitosan (CS), a positively charged polysaccharide that exhibits biocompatibility and biodegradability. Derivatization or degradation of CS can enhance bioactivities including antioxidant, antimicrobial, antitumor activities, etc. The present chapter covers the established methods of chitin and CS extraction from seafood processing waste. Moreover, the methods for preparation of various CS derivatives, e.g., chitooligosaccharides or chemically modified CS are also revisited. Recent trends in applications of CS derivatives in the food sector are also explored. Furthermore, CS derivatives for biomedical uses are addressed.
Chitosan (CS)-based anion exchange membranes (AEMs) have gained significant attention in fuel cell applications owing to their numerous benefits, such as environmental friendliness, flexibility for structural alteration, and improved mechanical, thermal and chemical durability. This study aims to enhance the cell performance of CS-based AEMs by addressing key factors including mechanical stability, ionic conductivity, water absorption and expansion rate. While previous reviews have predominantly focused on CS as a proton-conducting membrane, the present mini-review highlights the advancements of CS-based AEMs. Furthermore, the study investigates the stability of cationic head groups grafted to CS through simulations. Understanding the chemical properties of CS, including the behaviour of grafted head groups, provides valuable insights into the membrane’s overall stability and performance. Additionally, the study mentions the potential of modern cellulose membranes for alkaline environments as promising biopolymers. While the primary focus is on CS-based AEMs, the inclusion of cellulose membranes underscores the broader exploration of biopolymer materials for fuel cell applications.
There is plenty of scope for modifying chitosan, an only polycationic natural polysaccharide, owing to its reactive functional groups, namely hydroxyl and amino groups. Although innumerable numbers of chitosan derivatives have been synthesized by modifying these groups and reported elsewhere, in this review article, an attempt has been exclusively made to demonstrate the syntheses of various chitosan-based Schiff bases (CSBs) simply by allowing the reactions of reactive amino groups of chitosan with different aldehydes/ketones of interest. Due to their very peculiar and unique characteristics, such as biodegradability, biocompatibility, metal-binding capability, etc., they are found to be very useful for diversified applications. Thus, we have also attempted to showcase their very specific biomedical fields, including tissue engineering, drug delivery, and wound healing, to name a few. In addition, we have also discussed the utilization of CSBs for industrial applications such as wastewater treatment, catalysis, corrosion inhibition, sensors, etc.
Partially substituted N,N,N-trimethyl chitosan (TMC), N-(2-(N,N,N-trimethylammoniumyl))acetyl chitosan (TAC), 2-hydroxy-3-(N,N,N-trimethylammoniumyl)propyl chitosan (HTC), N-(2-hydroxy)propyl chitosan (HPC), and N-carboxymethyl chitosan (CMC) were reacted with the diazo transfer reagent, imidazole-1-sulfonyl azide, to convert the 2-amino groups to azides. Subsequent reaction via copper-catalyzed azide-alkyne cycloaddition (CuAAC) with N-propargyl-N,N,N-trimethylammonium bromide provided water-soluble “mixed” chitotriazolan derivatives. The NMR data was generally consistent with the complete conversion of all primary amines in the polymer to triazole moieties, except in the case of TAC, where the conversion was ∼50%. The mixed chitotriazolans derived from cationic TMC, TAC, and HTC and neutral HPC were active against Gram-positive S. aureus and E. faecalis and Gram-negative bacteria E. coli and P. aeruginosa, but chitotriazolans derived from anionic CMC were inactive.
In this study, an antimicrobial packaging material was successfully developed with blends of high-density polyethylene (HDPE) and chitosan (CS) made by melt processing. In the different HDPE/CS composites, the CS content effect (up to 40%), and the addition of quaternary ammonium salt functionalized chitosan (CS-CTAB) as an additive were evaluated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analyses (TG), tensile strength, scanning electron microscopy (SEM) and antimicrobial activity. When analyzing the effect of the additive in the different HDPE/CS composites, it was observed that the compositions with 10 and 20 %wt of chitosan showed better elongation values (~13% and 10%) as well as a higher decomposition temperature at 20% mass loss (T20) varying from (321–332 °C and 302–312 °C), respectively, in relation to the other compositions, regardless of the type of additive used, it acted as an antimicrobial agent, promoting inhibition of microbial growth against the strains gram-positive and gram-negative used in this work, making the different HDPE/CS composites suitable candidates for use in food packaging.
Large surface area, rich vascularisation, well defined mucous membrane, balanced pH and relatively low enzymatic activity makes vagina a suitable site for drugs associated with women's health issues like Urinary tract infection (UTI) and vaginal infections. Therapeutic performance of intravaginal dosage forms largely depends on the properties of polymers and drugs. Chitosan (CS) because of its unique physical, chemical, pharmaceutical and biopharmaceutical properties have received a great deal of attention as an essential component in vaginal drug delivery systems. Further the presence of free amino and hydroxyl groups on the chitosan skeleton allows easy derivatization under mild conditions to meet specific application requirements. Moreover, CS-based nanopharmaceuticals like nanoparticles, nanofiber, nanogel, nanofilm, liposomes and micelles are widely studied to improve therapeutic performance of vaginal formulations. However, susceptibility of CS to the acidic pH of vagina, poor loading of hydrophobic drugs, rapid mucosal turn over are the key issues need to be addressed for successful outcomes. In this review, we have discussed the application of CS and CS derivatives in vaginal drug delivery and also highlight the recent progress in chitosan based nanocarrier platforms in terms of their limitations and potentials.
Analyzing and finding solution for the natural deformities from the natural sources is the need of the hour for the scientific community. One such natural source that is the target for the researchers is chitin. This is obtained from the crustaceans, invertebrates, insects, etc. Chitin on deacetylation produced an important derivative chitosan. Both chitin and chitosan exhibits remarkable properties such as nontoxic, biocompatible, biodegradable, antimicrobial, etc. In spite of this, there are some limitations. To remove these limitations, they are mostly combined with organic or inorganic fillers to enhance the properties. Chitosan readily undergoes modification or combination with other substances than chitin to form different nanocomposites which can be applied for variety of applications from wound healing to biosensors. Thus, chitin/chitosan forms a versatile polymer in the hands of researchers to be tailor-made into a desired function by combining with suitable fillers.
In recent years, there has been enormous search and demand for naturally sourced polymers and excipients in the healthcare sector. Chitosan is a very important marine-derived natural polymer being a current topic of interest as the anti-infective for wound care. It is obtained through the process of deacetylation having β-(1–4)-linked D-glucosamine and N-acetyl-D-glucosamine units and considered as a linear polysaccharide derived from chitin. Few studies showed that the chitosan exhibits nontoxic, biocompatible, low immunogenic, and biodegradable properties which ultimately favors pharmaceutical dosage delivery. Chitosan-based formulations are successfully being used in the cosmetic industry, antimicrobial activity, biomedical tissue engineering, and gene delivery for wound care. Researchers successfully fabricated chitosan-based sponges utilizing suitable techniques for biomedical applications. Sponges made from chitosan are lightweight and capable of soaking extra liquid and drug solution on topical application. Additionally, osteoblastic differentiation and bone regeneration are successfully observed in the application of the chitosan matrix scaffold. Moreover, this chapter discusses various biomedical applications of marine-based chitosan and in drug delivery for anti-infective activities.
In recent years, the textile industry has been seeking to develop innovative products. It is a good choice to organically combine materials with superior functional characteristics and commercial textiles to form products with excellent performance. In particular, textiles made of biological functional materials are often beneficial to human health, which is an interesting research direction. As a biopolymer material, chitosan has the advantages of strong availability, low cost, excellent safety, outstanding performance, etc., particularly the antibacterial property, and has broad application prospects in the textile field. This review provides an overview of the latest literature and summarizes recent innovations and state-of-the-art technologies that can add value to textiles. To this end, preparation of chitosan fiber, synthesis of chitosan nanofiber, antibacterial activity of chitosan fiber, antibacterial activity of chitosan nanofiber, etc., will be discussed. Furthermore, the challenges and prospects of chitosan-based materials used in textiles are evaluated. Importantly, this review can not only help researchers understand the development status of antibacterial textiles, but also help researchers discover and solve problems in this field through comparative reading.
This chapter provides a review of the properties and application of chitin and chitosan. In the first two sections role of chitin and chitosan in nature, as well as the sources for commercial production are discussed. These sections also go into structural and physicochemical properties of these biopolymers. The following section introduces the analytical techniques used for the characterization of chitin and chitosan. Chemical modification of chitosan is then discussed with some emphasis on the more common chemical derivatives. Industrial application is discussed as well as the application for water purification as well as agricultural uses and food preservation among others. The application in health care and pharmaceutical field is covered in the final sections. This includes the use of chitosan as a food supplement, a material for wound care products, and the use in drug delivery.
The relationship between the degree of substitution and antibacterial activity was studied for six common chitosan derivatives N, N,N-trimethyl chitosan (TMCNH2/TM and TMCTM/DM) N-(2-(N,N,N-trimethylammoniumyl)acetyl)-chitin (TACin), N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan (HTC), hydroxypropyl chitosan (HPC), thioglycolic chitosan (TGC) and carboxymethyl chitosan (CMC). The degree of substitution (DS) in the 36 studied samples ranged from 0.02 to 1.1 as determined by ¹H NMR. The activity was determined as the minimum inhibitory concentration (MIC) against S. aureus and E. coli at pH 7.2 and 5.5.
The antibacterial effect of TMC and TACin increased with DS. Samples of these derivatives with high DS were more active than chitosan at pH 7.2. HTC was more active than chitosan against S. aureus, but this activity was not affected by DS. In other cases, the activity of HTC decreased with an increase in DS. The DS for the TGC was very low and the activity was similar to unmodified chitosan. The activity of HPC decreased with DS. CMC was not active in this study.
Chitosan has fascinating antibacterial activity, good biodegradation, outstanding biocompatibility, non-toxicity and excellent physical and chemical properties. As a result, chitosan has been widely used in the field of antibacterial. Chitosan and its derivatives show antibacterial activity against fungi, gram-positive bacteria and gram-negative bacteria. In recent years, there have been some reviews about the antibacterial activity of chitosan and its derivatives. This review adds many valuable concerns on the basis of those previous reviews. For example, composite of chitosan and metal, composite of chitosan and metal oxide, etc. This review will systematically analyze various influencing factors of chitosan, so as to clearly summarize the antibacterial mechanism of chitosan. Finally, the challenges and prospects of chitosan-based materials as antimicrobial agents are assessed and commented.
In this contribution, a novel soluble and antibacterial polymer, O-xanthonyl-chitosan (CTMC-Xan), was synthesized successfully by grafting 1,3-dihydroxy-xanthone (Xan) to the side chains of O-carboxymethyl-N, N, N-trimethyl chitosan (CTMC). The chemical structure and physical properties of the polymer were analyzed by ¹H NMR, FT-IR spectra, UV spectra and XRD. The results showed that Xan could covalently bond with the carboxyl groups of CTMC by esterification at a grafting ratio of 9.1%. XRD patterns indicated that CTMC-Xan does not exhibit crystallization. The solubility tests showed that CTMC-Xan was completely dissolved and stable in neutral solution but unstable in acid or basic conditions. Moreover, it was found that the antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) of CTMC-Xan was much stronger than that of Xan and CTMC, and the minimal bactericidal concentration (MBC) was 125 μg·mL⁻¹. Due to the enhanced solubility and antibacterial activity, CTMC-Xan could potentially serve as a desirable biomaterial for food and pharmaceutical applications.
The solubility of chitosan is one of the most important properties that must be well understood and controlled if chitosan is to realize its full potential in the biomedical industry. In this chapter, a comprehensive look at the solubility behavior of chitosan has been presented. Establishing a relationship between the macromolecular structure and solubility behavior of chitosan is of the utmost importance in the development of useful chitosan.
New chitosan derivatives bearing guanidinium functions were synthesized following different synthesis strategies. N-guanidinium chitosan acetate and N-guanidinium chitosan chloride were synthesized by direct reaction between chitosan and cyanamide in the presence of scandium(III) triflate. The synthesis of N-guanidinium chitosan (N,N′-dicyclohexyl) chloride and N-guanidinium chitosan (N-(3-dimethylaminopropyl)-N'-ethyl hydrochloride) chloride involved the reaction of chitosan with carbodiimides in ionic liquid. The chitosan derivatives were characterized by analytical techniques including ¹³C solid state NMR, FT-IR spectroscopies, thermogravimetry and elemental analysis. The antimicrobial properties of chitosan and the new derivatives were investigated using the minimal inhibitory concentration (MIC) technique. All new guanylated chitosan derivatives displayed high antimicrobial activity in comparison with neat chitosan. The N-guanidinium chitosan acetate reduced the time required for killing to half in comparison with chitosan and recorded MIC values less than 3.125 mg/ml against all assayed microorganisms. This work opens new perspectives for using chitosan derivatives as antimicrobial surfaces.
In the current study, a self-nanoemulsifying drug delivery system (SNEDDS) containing N-trimethyl chitosan chloride (TMC) was developed and evaluated for its potential to deliver amphotericin B (AmpB) via the gastrointestinal tract. SNEDDS comprising Captex 355, Kolliphor RH40 and Propylene Glycol were optimized and characterized for their formation spontaneity, droplet size and drug loading. Investigations on the effects of the application SNEDDS containing TMC to a model intestinal epithelium (Caco-2 monolayer) indicated the capability of the formulations to induce the transient opening of tight junctions. Caco-2 cell viability studies confirmed the safety of the SNEDDS, whereas in vitro transport studies of AmpB through Caco-2 cell monolayers showed the permeation enhancing ability of TMC. Our results suggest that chitosan derivative TMC combined with a SNEDDS may be used as permeation enhancer to facilitate oral delivery of AmpB.
Amongst the natural polymers, chitin is the second most abundant, present mainly in fungi and exoskeleton of crustaceans. It forms a major part of the seafood waste as compiled and presented in this review and is de-acetylated to produce chitosan. Structure and properties of chitosan have been described. Biocompatible and biodegradable characteristics of chitosan have been well studied. In addition to the environmental sustainability associated with its use, the malleability of chitosan, due to its reactive amino and hydroxyl groups, adds to its wide repertoire in usage through various modifications. Recent publications of chitosan and derivatives have been classified into its various applications in food, pharmaceutical, biotechnology, medical, textile, paper, agriculture and environmental applications. The abundance of chitosan and diversity in modifications can be effectively utilized in various applications leading to environmental friendly solutions as highlighted in this review.
In view of rapidly growing interest in the amino polysaccharide chitosan/chitin and its oligosaccharides as functional biopolymer, a recent progress of basic and application studies in chitosan/chitin oligosaccharides chemistry is reviewed as well as some basic aspects of this specialty biomass resource. A special emphasis is placed on the controlled modification reactions to prepare chitin derivatives with well-defined structures and thereby to construct sophisticated molecular architecture having various advanced functions. The reactions discussed here include acylation, quaternary ammonium salt, carboxyalkylation, graft copolymerization, quaternary salt formation, Schiff base formation, reductive alkylation, microwave modification. For conducting modification reactions in a facile and controlled manner, some soluble chitosan/chitin oligosaccharides derivatives are convenient. To fully explore the high potential of these specialty biopolymers, basic and application researches are being made extensively.
The emergence of new pathogenic strains together with continuous rise of antimicrobial resistance and the death of new antibiotics in the clinical pipeline raise an urgent call for the development of potent antimicrobial agents. There has been growing interest in the use of new agents, such as antimicrobial polymers, as alternatives for therapy and disinfection. Cationic chitosan derivatives, N-(2-hydroxypropyl)-3-trimethylammonium chitosan chlorides (HTCC), have been widely studied as potent antibacterial agents. However, their systemic structure-activity relationship (SAR), activity toward drug resistant bacteria and fungi, and mode of action are very rare. Herein, we investigated antibacterial efficacies of the HTCC polymer derivatives against multidrug resistant bacteria, including clinical isolates. The polymers were found to be active against a variety of bacterial pathogens (MIC = 32−128 μg/mL). Interestingly, these polymeric materials were active against Streptococcus Gram-positive bacteria, which are a predominant cause of hospital-acquired infections (HAIs).
A novel quaternary ammonium chitosan hydrogel modified by poly(amidoamine) (PAMAM) dendrimer was prepared by using glutaraldehyde as a cross-linker. The hydrogel was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results confirmed its highly porous three-dimensional network structure. The swelling test of hydrogel proved that it had excellent swelling and pH-sensitive properties. The increasing PAMAM content or quaternization degree led to the increase in swelling properties. And the hydrogel with lower cross-linking agent concentration or quaternary ammonium chitosan concentration exhibited better swelling properties. The antibacterial results indicated that with the increase in the PAMAM content, quaternary ammonium chitosan concentration or cross-linking agent concentration, the hydrogels showed better antibacterial activities against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Thus, the hydrogel could serve as a promising antibacterial material in the future.
In order to improve the bioactivity of lactose, a novel lactose derivative was designed and synthesized by introducing an amino group to the C-6 of lactose. The in vitro antioxidant activities of synthesized lactose derivatives were assessed. It showed better scavenging activity against hydrogen peroxide (IC50 < 0.1 mg/ml), hydroxyl radicals (IC50 0.55 mg/ml), and DPPH radicals (IC50 0.37 mg/ml) than lactose. Based on these data, it is reasonable to propose that the introduction of amino group through chemical modification is significant to enhance the free antioxidant activity of lactose. This derivatization strategy might provide an effective tool to broaden utilization of lactose.
The antimicrobial activity of chitosan and derivatives to human and plant pathogens represents a high-valued prospective market. Presently, two low molecular weight derivatives, endowed with hydrophobic and cationic character at different ratios were synthesized and characterized. They exhibit antimicrobial activity and increased performance in relation to the intermediate and starting compounds. However, just the derivative with higher cationic character showed cytotoxicity towards human cervical carcinoma cells. Considering cell membranes as targets, the mode of action was investigated through the interaction with model lipid vesicles mimicking bacterial, tumoral and erythrocyte membranes. Intense lytic activity and binding are demonstrated for both derivatives in anionic bilayers. The less charged compound exhibits slightly improved selectivity towards bacterial model membranes, suggesting that balancing its hydrophobic/hydrophilic character may improve efficiency. Observing the aggregation of vesicles, we hypothesize that the "charge cluster mechanism", ascribed to some antimicrobial peptides, could be applied to these chitosan derivatives.
The preparation of chitosan-coated alginate fibers by a wet spin process is presented and the characterization of the antibacterial activities of these fibers is discussed. Preformed calcium alginate fibers were passed in chitosan acetate solutions. The coagulation method of the coating consisted in the immersion of fibers in a bath of calcium dihydroxide solution (0.1 M). The antibacterial evaluation was achieved by a CFU (Colony-Forming Units) counting method after 6 h of incubation at 37 °C. The incorporation of chitosan on calcium alginate fibers brings antibacterial activities against Staphylococcus epidermidis, Escherichia coli and various Staphylococcus aureus strains namely MSSA (Methicillin Sensitive Staphylococcus aureus), CA-MRSA (Community Associated Methicillin Resistant Staphylococcus aureus) and HA-MRSA (Healthcare Associated Methicillin Resistant Staphylococcus aureus) which make these chitosan-coated fibers potential candidates for wound dressing materials. Developing a wound dressing with the haemostatic and healing properties of alginate combined with antibacterial properties of chitosan is envisioned for fighting against the infections and more particularly nosocomial diseases.
This review gives an updated overview of the current state-of-the-art for antimicrobial chitosan and chitosan derivatives and the effects of structural modifications on activity and toxicity. The various synthetic routes introduced for chemical modification of chitosan are discussed and the most common functional groups are highlighted. Different analytical techniques used for structural characterization of the synthesized chitosan derivatives are discussed and critically evaluated. For the purpose of this review, the antimicrobial chitosan derivatives have been classified on the basis of the type of functional group conjugated to the polymer backbone. In each case, the influence of the degree of substitution on the biological properties has been examined. Finally, we have summarized the collective information and suggested future directions for further research in order to improve our understanding of the bioactivity and to develop more useful chitosan conjugates.
Glucosamine hydrochloride was transformed into an orthogonally protected intermediate in seven steps and 34% over- all yield. The synthesis includes an optimized preparation of N- phthaloyl- -D-glucosamine tetraacetate, a commonly used precur- sor in carbohydrate chemistry.
Pectinate beads containing trimethyl chitosan chloride (TMC) as an absorption enhancer were prepared using Coomassie Brilliant Blue G 250 (CB) as a relatively high molecular weight water-soluble model drug. Effects of different formulation variables, such as cross-linker type, cross-linking time, cross-linker concentration, TMC: pectin ratio, pectin concentration and voltage of the bead generator, were assessed on in vitro bead characteristics by release and swelling–erosion studies. The bead formulation was optimized by factorial design. Some measures were taken to improve the bead characteristics and prolong their integrity during the gastrointestinal transit, such as biomineralization of the beads or coating them with high-methoxy pectin (PHM) or Eudragit L30-D 55 (EU). Possible CB-TMC complexation was investigated by Job's Plot method. The suitable system was obtained by coating the optimized core formulation with PHM or EU. TMC was found to form a complex with CB as a model anionic drug. Therefore, TMC-drug interactions can be used to modify the release characteristics of dosage forms.
La barriere de permeabilite, la membrane exterieure qui entoure les bacteries gram-negatives peut etre traversee par des solutes hydrophiles a travers les canaux porine. Ces canaux peuvent etre etroits et entraver la penetration de medicaments hydrophobes et creer differents degres de resistance intrinseque aux antibacteriens
Poly(vinyl alcohol) (PVA) and N-(2-hydroxy)propyl-3-trimethylanunonium chitosan chloride (HTCC), a water soluble chitosan derivative synthesized by the reaction of quaternary ammonium compound with chitosan, were blended using water as a solvent and the PVAMTCC blend films with various compositions were prepared by solution casting method. The miscibility between the two polymers and the thermal properties of the blend films were investigated using FT-IR, DSC, DMA, and TGA. Single glass transition temperatures and single melting temperatures of the blend films along with the strong and clear film state for the whole composition of blending ratios suggest the miscibility between PVA and HTCC. The PVA/HTCC blend films with HTCC content of 1% and greater showed excellent antimicrobial activity.
A simple procedure to prepare water-soluble chitosan (partially N-acetylated chitosan) was developed, and the water-solubility of N-acetylated chitosan was investigated in detail, preparing a series of chitosan samples with various molecular weights. To reduce the molecular weight, chitosan was treated with NaBO3 under a homogeneous condition where chitosan was previously dissolved in an aqueous acetic acid. Weight-average molecular weights of chitosan samples obtained were determined by means of GPC equipped with a low angle laser light scattering photometer. Then each chitosan sample was N-acetylated with acetic anhydride under a homogeneous condition where chitosan was dissolved in a simple aqueous acetic acid. The degree of N-acetylation was estimated by 1H NMR spectroscopy. As a result, the water-solubility of N-acetylated chitosan with about 50% substitution increased as the molecular weight decreased. The sequence of N-acetylglucosamine and glucosamine residues was also determined by 1H NMR spectroscopy.
A novel synthetic route has been developed for the preparation of 1-carboxymethyl-1,4,4-trimethylpiperazinium diiodide and 4-carboxymethyl-1,1-dimethylpiperazinium iodide salts. These quaternary piperazinium acids have potential, for example, in the development of novel water-soluble prodrugs or polymer derivatives.
Potentiometric properties of a fully deacetylated chitosan have been investigated using pH and c.d. measurements. The same studies have also been performed in the presence of copper II ions in order to determine the mode of interaction and to deduce the stoichiometry of the complex formed under these conditions.
Regioselective chemical modifications of chitosan were successfully carried out in homogeneous solution under mild condition using phthalimido chitosan as a key starting material. Discrimination between the primary and secondary hydroxyl groups were also examined by O-tritylation or O-tosylation. As anticipated, the new chitosan derivatives exhibited a much improved solubility in common organic solvents.
An efficient five-step synthetic route was developed for full N-substitution of chitosan with a quaternary betaine moiety. The developed synthetic procedure can also be controlled to produce chitosan N-betainates having lesser degrees of substitution. 6-O-Triphenylmethylchitosan, which is highly soluble in organic solvents, was used as an intermediate for N-acylation reactions. Intermediate products were characterized by 13C CP/MAS NMR, FT-IR, and elemental analysis. The water-soluble quaternary chitosan N-betainates were thoroughly characterized by 1H NMR and 13C NMR and by 2D 1H−1H COSY NMR and 13H−1H HSQC NMR. Degrees of substitution were determined from the 1H NMR spectra. A significant degradation of the polysaccharide backbone during the synthetic procedure was determined by GPC with a light scattering detector.
E. coli and Staphylococcus aureus are used to study the antimicrobial activity of chitosan of different molecular weights (MW). The effect of the concentration and MW of chitosan were investigated, respectively, and the antimicrobial mechanism was discussed. For chitosan with MW below 300 kDa, the antimicrobial effect on S. aureus was strengthened as the MW increased. In contrast, the effect on E. coli was weakened.
Chemical modification on solid N-α-chloropropionyl and N-chloroacetyl derivatives of chitosan was performed. The N-alanyl derivative was prepared by treating the N-α-chloropropionyl derivative with aqueous 25% ammonia at room temperature for 18 h. N-(N′-Phenyl)glycyl, N-(N′-o-tolyl)glycyl and N-(N′-p-methoxyphenyl)glycyl derivatives were prepared by treating the N-chloroacetyl derivative with each of aniline, o-toluidine and p-anisidine at 100° to 150°C for 2 days.
Treatment of O-acetyl-protected sugars with a methanolic solution of guanidine/guanidinium nitrate caused the removal of the acetyl groups (91–99% isolated yield), without affecting other protecting groups. Removal of O-benzoyl groups required a longer reaction time. Of special merit is the stability of the 2,2,2-trichloroethoxycarbonylamino (N-Troc) group under these weakly basic reaction conditions.
The purpose of this study was to synthesize series of methylated chitosaccharide derivatives, possessing various degree of methylation, and to determine their structure activity relationship (SAR) with regard to their antibacterial effect against Staphylococcus aureus. Chitosan polymer and chitooligomers were used as starting materials and were methylated by reaction with methyl iodide. Depending on the reaction conditions the degree of N-quaternization ranged from 0% to 74%, with varying degree of N,N-dimethylation, N-monomethylation and O-methylation. More selective N-quaternization could be obtained with protection group strategy. At pH 5.5 the chitosaccharide polymers and their methylated derivatives were active against S. aureus with minimal inhibitory concentration (MIC) ranging from 16 to 512μg/mL. At pH 7.2 the non-quaternized derivatives were inactive but their highly N-quaternized derivatives showed MIC as low as 8μg/mL. The chitooligomers, as well as their derivatives, were inactive at both pH’s. The SAR studies revealed that N-quaternization was mainly responsible for the antibacterial effects at pH 7.2, whereas it did not contribute to the antibacterial activity under acidic conditions.
Rochelle salt, normally present in the dinitrosalicylic acid reagent for reducing sugar, interferes with the protective action of the sulfite, but is essential to color stability. The difficulty may be resolved either by eliminating Rochelle salt from the reagent and adding it to the mixture of reducing sugar and reagent after the color is developed, or by adding known amounts of glucose to the samples of reducing sugar to compensate for the losses sustained in the presence of the Rochelle salt. The optimal composition of a modified dinitrosalicylic acid reagent is given.
Because of the importance of the chloroacetyl group to carbohydrate synthesis, the objective of this work is to disclose a method that has been found useful for the heterogeneous chloroacetylation of chitosan powder in which sodium bicarbonate is used as the base for the neutralization of the acid byproduct. A series of reactions were conducted to determine the more optimal conditions under which to perform acylation. The three varied aspects of the reaction were the acylating reagent (chloroacetyl chloride and chloroacetic anhydride), the solvent (methylene chloride and N,N-dimethylformamide), and the temperature (0 or 44 °C). According to Fourier transform infrared (FTIR), the chitosan powder being refluxed in methylene chloride in the presence of chloroacetic anhydride constituted the best conditions. By incorporating these conditions and increasing the amount of the base, we obtained a chloroacetylated chitosan powder that, characterized by FTIR, solid-state cross-polarity/magic-angle spinning 13C NMR, and elemental analysis, had degrees of N- and O-chloroacetylation of 0.32 and 0.15, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4174–4181, 2001
Trimethylated chitosan (TMC) is a well-studied N-quaternary chitosan derivative that is promising for various pharmaceutical applications. The most commonly-used procedure today to obtain these derivatives is based on the reaction with methyl iodide as reagent and N-methylpyrrolidone as solvent. This procedure is not N-selective and significant O-methylation is observed in highly trimethylated material. The O-methylation reduces solubility of the TMC derivatives and therefore limits the use of highly N-quaternised products. Here we report a study of a ‘one-pot’ synthesis procedure based on a new solvent system. We obtained readily-soluble TMC derivatives with a degree of N-quaternisation between 0.81 and 0.88 without any O-methylation. The uniformity of these compounds was confirmed with 1D, 2D NMR and IR spectroscopy.
Chitin, chitosan and the newly synthesized and fully characterized N-lauryl chitosan and N-dimethylaminopropyl chitosan, endowed with higher hydrophobicity and cationicity, respectively, were tested for their capacity to alter the composition of olive oil upon percolation of the latter through a bed of their respective powders. The oil samples were extracted, saponified and submitted to gas-chromatography. Results indicated that the percentages of 12 fatty acids were not modified, but the diacylglycerol and steroid concentrations were greatly altered. The percolated oil was depleted of C34 and C36 diacylglycerols (lowered to 42% of the control) when the oil was contacted with chitosan and N-lauryl chitosan, whilst the oil fraction percolated through chitin became 30% enriched. N-Dimethylaminopropyl chitosan was also effective in retaining diacylglycerols. The direct analysis of the unsaponifiable fraction revealed that campesterol, stigmasterol and avenasterol were enriched in the oil fraction retained by chitin and N-lauryl chitosan, while β-sitosterol increased slightly in the fraction retained by chitosan and N-lauryl chitosan. Triterpene alcohols were higher in the oil fraction retained by chitin. This work indicates that chitin might be more suitable than chitosan for sequestering steroids, and that, in general, the chitin derivatives discriminate among the various lipids.
Chitosan was trimethylsilylated, and some properties of the product such as solubility and reactivity were examined. Trimethylsilylation proceeded efficiently with a mixture of hexamethyldisilazane and chlorotrimethylsilane in pyridine; chitosan prepared from β-chitin underwent substitution more facilely than that from α-chitin. The degree of trimethylsilylation per pyranose unit reached 2.9. The resulting silylated derivative was almost soluble in pyridine and swelled considerably in common organic solvents. Though the product was hydrolytically stable in neutral and weakly alkaline media, it was deprotected readily with acid. As a typical example of modification reactions, acetylation of silylated chitosan was examined, and highly acetylated derivatives were obtained under mild conditions, indicating a high potential of the silylated chitosan as a precursor for chemical modifications of chitosan in organic solvents.
Finite element analysis of the strain localization behaviors of a voided ductile material has been performed using a non-local
plasticity, in which the yield strength depends on both an equivalent plastic strain measure (hardening parameter) and Laplacian
equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the
strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the
strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the
load-strain curves of the voided ductile material subjected to plane strain tension converges to one curve, regardless of
the mesh size. In addition, the results using non-local plasticity also showed that the dependence of the deformation behavior
of the material on the mesh size was much less sensitive than with classical local plasticity and could be successfully eliminated
through the introduction of a large value for the characteristic length.
Well characterized methylpiperazine, mono-quaternary dimethylpiperazine and di-quaternary trimethylpiperazine derivatives of chitosan, with different degrees of substitution, were investigated for antibacterial activity against five strains of Gram-positive and Gram-negative bacteria. Some of the methylpiperazine and the dimethyl piperazine derivatives of chitosan, with low degree of substitution, were active against bacteria at pH 5.5 with minimum inhibitory concentration (MIC) ⩾64 μg/ml. Chitosan derivatives with the di-quaternary substituents were active against bacteria with MIC as low as 8 μg/ml and in general more active at pH 7.2 than at pH 5.5. The minimum lethal concentrations (MLC) were the same as the MIC within 1–2 dilutions. The most active compound induced gradual decrease in the count of viable bacteria over 8 h at 8× MIC. The results are consistent with the interpretation that methylpiperazine and mono-quaternary dimethylpiperazine substituents do not contribute to activity against bacteria, whereas di-quaternary trimethylpiperazine moiety, will contribute to antibacterial activity.
The effects of molecular weight, degree of acetylation and ionic strength on surface tension of chitosan in dilute aqueous solution were studied systematically using the maximum bubble pressure (MBP) technique. The results show that the surface tension decreases slightly with increasing chitosan concentration in the high dilution (<0.01010−2 kg l−1), above the critical aggregation concentration (0.01×10−2 kg l−1), the surface tension increases apparently for the high molecular weight chitosans or in the lower ionic strength solutions; whereas the degree of acetylation has little effect on the surface tension of chitosans especially in hydrochloric acid solution. It is considered that the changes of surface tension are attributed to the molecules conformation transition in dilute solution, resulting in a variation of intra/inter molecular interactions, i.e. hydrogen bonding, hydrophobic interaction and electrostatic interaction.
In view of rapidly growing interest in the amino polysaccharide chitin as a functional biopolymer, a recent progress of basic and application studies in chitin chemistry is reviewed as well as some basic aspects of this specialty biomass resource. A special emphasis is placed on the controlled modification reactions to prepare chitin derivatives with well-defined structures and thereby to construct sophisticated molecular architecture having various advanced functions. The reactions discussed here include hydrolysis of main chain, deacetylation, acylation, N-phthaloylation of chitosan, tosylation, alkylation, Schiff base formation, reductive alkylation, O-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Of soluble precursors reported, N-phthaloyl-chitosan has proved particularly useful and made possible series of regioselective and quantitative substitutions thus far difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone.
Two chitosan samples (fraction of acetylated units (FA) 0.15 and 0.52) were fractionated by preparative size exclusion chromatography (SEC). The molecular weights and molecular weight distributions of the fractions were analyzed by analytical size exclusion chromatography coupled to an on-line low angle laser light scattering detector and a differential refractive index detector (SEC-LALLS-DRI), and their intrinsic viscosities were determined. The exponent (a) of the Mark-Houwink-Kuhn-Sakurada (MHKS) equation was found to be 0.92 ± 0.07 and 1.1 ± 0.1, respectively, at I = 0.1 and pH 4.5. No variation in FA related to molecular weight was found. Reversible interaction between chitosans and different column packings strongly influenced the log M-V relationships. This interaction was generally most pronounced for the low-FA chitosan, suggesting that the protonated amino groups are involved. Ammonium acetate buffer reduced this effect and the use of a new type of SEC-packing seemed to eliminate it. The more highly acetylated chitosan also had a more pronounced tendency towards concentration dependent self-association, which most probably involve intermolecular hydrophobic interactions between the acetyl groups.
N,N,N-Trimethyl chitosan chloride (TMC) is a chemically modified chitosan with improved aqueous solubility, compared with the native chitosan. It is essential to follow a synthesis procedure in which the degree of substitution of the final product can be controlled by means of the number of reaction steps, the duration of each reaction step and the amount of methyl iodide as reagent. A two-step reaction yields products with high degrees of substitution (40–80%). Comparison of the NMR spectra of the product TMC, after a two-step reaction, indicates that there is a peak assigned to the substituted amino group that shifts from 2.5 to 3.1 ppm upon acidification. This peak must be assigned to N(CH3)2 and not to N(CH3)+3. A three-step reaction procedure yields products with a degree of substitution > 80%, but with substantially decreased water-solubility.
Different molecular weight (MW) chitosans (5.5×104 to 15.5×104 Da) with the same degree of deacetylation (80%±0.29), were obtained by the method of acetic acid hydrolysis. The effect of antimicrobial activities of chitosan and acetic acid against Escherichia coli were investigated. All of the chitosan samples with MW from 5.5×104 to 15.5×104 Da had antimicrobial activities at the concentrations higher than 200 ppm. The growth of E. coli was promoted at concentration lower than 200 ppm. The antibacterial activity of chitosan had relationship to the MW at the concentration range from 50 to 100 ppm. The antibacterial activity of low MW chitosan is higher than that of the high MW samples. But the chitosan sample with the middle MW (9.0×104 Da) could promote the growth of bacteria. In the different stages of cultivation, the earlier chitosan was added the greater effect it did. And the mechanism of antibacterial activity was that E. coli was flocculated.
The effect of degree of substitution on the antimicrobial activity of water-soluble quaternary chitosan N-betainates was determined against Escherichia coli and Staphylococcus aureus. Chitosan N-betainates showed low antimicrobial activity in neutral conditions and the glucosamine N-betainate prepared as a reference compound showed low activity also in acidic conditions. However, the antimicrobial activity increased with decreasing degrees of substitution in acidic conditions (pH 5.5), which suggests that for efficient antimicrobial action, the positive charge should be situated in the amino group of chitosan, rather than in the quaternary substituent.
Chitosan with excellent biodegradable and biocompatible characteristics has received attention as an oral drug delivery vehicle. A quaternized chitosan (i.e., N-diethylmethyl chitosan, DEMC) was prepared based on a modified two-step process via a 22 factorial design to optimize the preparative conditions. DEMC was fully characterized using FTIR and 1H-NMR spectroscopies. As calculated using NMR-based data, high degree of quaternization was achieved through the optimized two-step process. The highly quaternized biopolymeric derivative was subjected to microbial experiments. The antimicrobial activities of chitosan and DEMC against Escherchia coli were compared by calculation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Our data indicates that although the antimicrobial activity of DEMC is higher than that of chitosan in acetic acid medium, the both compounds are pH dependent and an increase in concentration of acetic acid results in a significant decrease in both MIC and MBC.
An efficient and chemoselective procedure for preparing highly organosoluble 3,6-di-O-tert-butyldimethylsilyl (TBDMS)-chitosan and chitooligosaccharides is reported. The selective modification of the chitooligosaccharides with 0.50 degree of N-acetylation was achieved by using TBDMSCl as the reagent in combination with DMF/imidazole. These protocols yielded partly TBDMS-substituted chitooligosaccharides that were subsequently reacted with TBDMSOTf in dichloromethane in order to silylate the remaining, more sterically hindered hydroxyl groups. In the case of the chitosan polymer, a mesylate salt of chitosan was silylated using TBDMSCl in DMSO, yielding full silylation of the hydroxyl groups without using N-protection groups. The silyl-protected polymers displayed excellent solubility in a number of common organic solvents. The 3,6-di-O-TBDMS-chitosan and chitooligosaccharides were reacted with acetic anhydride, and deprotected to obtain the corresponding N-acetyl derivatives (chitin and chitinoligosaccharide). Our results show that the readily prepared 3,6-di-O-TBDMS-chitosan and chitooligosaccharides are useful precursors for selective N-modifications in common organic solvents.
N-Formyl, N-chloroacetyl, N-glycyl, N-isobutyryl, and N-pentanoyl derivatives of chitosan have been prepared. N-Acetylchitosan was the derivative most susceptible to chitinase from Streptomyces griseus and lysozyme from chicken egg-white, but with respect to R in the RCOHN group were CH3 > CH3CH2 > H > CH3CH2CH2 > (CH3)2CH > NH2CH2 > CICH2. Neither enzyme hydrolysed chitosan or its N-methylene. N-benzylidene, N-benzoyl, N-nicotinyl, and N-fatty acyl (C5-C18) derivatives, and lysozyme did not hydrolyse N-butyrychitosan. N-Acetylhexanoyl-chitosans, which had d.s. ratios of approximately 0.7: approximately 0.3 and approximately 0.3: approximately 0.7, were hydrolysed at approximately 0.75 and approximately 0.004 of the rate of N-acetylchitosan (powder) by chitinase. O-Acylation of N-acylchitosans caused a decrease in the rates of hydrolysis by chitinase. N-Acetylchitosan gels were hydrolysed at 8-13 times the rate for crab-shell chitin. These results indicate that not only N- and O-substituents but also the physical form of the substrates influence the rates of hydrolysis by these enzymes.
A nasal solution formulation of the cationic material chitosan was shown to greatly enhance the absorption of insulin across the nasal mucosa of rat and sheep. The absorption promoting effect was concentration dependent with the optimal efficacy obtained for concentrations higher than 0.2% and 0.5% in rats and sheep, respectively. The absorption promoting effect was reversible with time in a "pulse-chase" study. Histological examination of the nasal mucosa of rats exposed to a chitosan solution for 60 minutes showed little change.
Lipopolysaccharides isolated from the polymyxin-resistant Klebsiella pneumoniae O3 mutant OM-5 and its polymyxin-sensitive parent LEN-1 were analyzed for chemical composition, and their lipid A portions were structurally characterized. The lipopolysaccharide of OM-5 contained approximately five times more 4-amino-4-deoxy-L-arabinopyranose than that of LEN-1. Other saccharide and phosphate components exhibited no significant differences. Structural characterization, including analyses by phosphorus magnetic resonance spectroscopy and by fast atom bombardment mass spectrometry, revealed a novel type of lipid A. In the OM-5 lipopolysaccharide, both phosphates of lipid A were almost totally present as phosphodiesters with 4-amino-4-deoxy-L-arabinopyranose. In the sensitive-type LEN-1 lipid A, the extent of this substitution was much lower, especially in the glycosidically linked phosphate. Phosphate in these K. pneumoniae lipopolysaccharides was almost exclusively found in lipid A. These results show that cationic substituents of phosphates of lipid A play a decisive role in determining polymyxin reactivity. OM-5 was also found to contain a large proportion of heptaacyl lipid A, which represented only a small fraction of lipid A in LEN-1.
As part of a cartilage targeting program based on the affinity of the quaternary ammonium (QA) moiety for cartilage, QA derivatives of D-glucosamine (DG), an antirheumatic drug exhibiting a natural tropism for cartilaginous tissues, were designed and evaluated by pharmacokinetic studies. Two QA-DG conjugates were synthesized and labeled with (14)C by cross-linking the QA entity (trimethylammonium or pyridinium) to [(14)C]DG via an amide bond in a two-step procedure. After intravenous injection to male Sprague-Dawley rats, the two (14)C-labeled conjugates exhibited similar pharmacokinetic profiles, but their behavior clearly differed from that of unconjugated DG in several ways. (i) The tissue distribution for the conjugates was more restricted, with a decreased radioactivity level for whole tissues except for kidney, cartilage, and skin. (ii) The radioactivity concentrated more rapidly and strongly in cartilage for the conjugates than for DG for the short times after injection; on the other hand, 1 h after administration, the radioactivity level in cartilage was higher for DG, this result being consistent with the tropism already observed for this compound. (iii) Both conjugates were eliminated predominantly by the urinary route (85%); the radioactivity level in urine for DG was lower (45% of the injected dose), and significant (14)CO(2) was found in expired air, indicating metabolization and utilization of DG for energy-consuming processes. (iv) Blood and plasma kinetics studies displayed an enterohepatic cycle for DG, whereas for the QA conjugates, a rapid disappearance was observed. (v) HPLC analyses of plasma and urine indicated a low degree of metabolization for the conjugates, most of the radioactivity recovered in urine and plasma corresponding to the unchanged molecule. This study demonstrates that the introduction of the QA moiety on DG modifies its biodistribution and lends it a greater specificity for cartilage, at least for short times after injection. These findings justify further work on QA derivatives of other antirheumatic agents.
A simple and improved method of preparing highly soluble chitosan (half N-acetylated chitosan) was developed using a series of chitosan samples of low molecular weights, and the solubility of the half N-acetylated chitosan in water and organic solvents was investigated in detail. To reduce the molecular weight, chitosan was treated with NaBO3 under the condition that chitosan was homogeneously dissolved in aqueous acetic acid. Weight-average molecular weights of the obtained chitosan samples were determined using a size-exclusion chromatography system equipped with a low-angle laser light-scattering photometer. Each chitosan sample was then N-acetylated with acetic anhydride under the condition that chitosan was homogeneously dissolved in aqueous acetic acid again. The water solubility of the half N-acetylated chitosan thus prepared increased with decreasing molecular weight. From 1H NMR spectroscopy, it was suggested that the sequence of N-acetylglucosamine and glucosamine residues was random. The solubility of the half N-acetylated chitosan of low molecular weight was rather high even in aqueous dimethylacetamide and dimethylsulfoxide.
Chitosan derivatives with quaternary ammonium salt, such as N,N,N-trimethyl chitosan, N-N-propyl-N,N-dimethyl chitosan and N-furfuryl-N,N-dimethyl chitosan were prepared using different 96% deacetylated chitosan of M(v) 2.14x10(5), 1.9x10(4), 7.8x10(3). Amino groups on chitosan react with aldehydes to from a Schiff base intermediate. Quaternized chitosan were obtained by reaction of a Schiff base with methyl iodide. The yields, degree of quaternization and water-solubility of quaternized chitosan were influenced by the molecular weight of the chitosan sample. The antibacterial activities of quaternized chitosan against Escherichia coli were explored by calculation of the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) in water, 0.25 and 0.50% acetic acid medium. Results show the antibacterial activities of quaternized chitosan against E. coli is related to its molecular weight. Antibacterial activities of quaternized chitosan in acetic acid medium is stronger than that in water. Their antibacterial activities is increased as the concentration of acetic acid is increased. It was also found that the antibacterial activity of quaternized chitosan against E. coli is stronger than that of chitosan.
Five TMC polymers with different degrees of quaternisation (12-59%) were synthesised and administered together with [14C]-mannitol in the nasal route of rats at a pH of 6.20 and 7.40, respectively. All the TMC polymers increased the nasal absorption of [14C]-mannitol significantly at pH 6.20, but only TMC polymers with higher degrees of quaternisation (>36%) were able to increase the absorption of this hydrophilic model compound at pH 7.40. The absorption of [14C]-mannitol at pH 7.40 increased with an increase in the degree of quaternisation of TMC until a maximum absorption value was reached with TMC with a degree of quaternisation of 48%. The absorption of [14C]-mannitol did not increase further, even when TMC with a higher degree of quaternisation (59%) was used. This can probably be explained by steric effects caused by the attached methyl groups and changes in the flexibility of the TMC molecules with an increase in the degree of quaternisation above an optimum value for absorption enhancement in a neutral environment. It was concluded that the degree of quaternisation of TMC plays an important role in the absorption enhancement properties of this polymer across nasal epithelia in a neutral environment.
Antibacterial activities of six chitosans and six chitosan oligomers with different molecular weights (Mws) were examined against four gram-negative (Escherichia coli, Pseudomonas fluorescens, Salmonella typhimurium, and Vibrio parahaemolyticus) and seven gram-positive bacteria (Listeria monocytogenes, Bacillus megaterium, B. cereus, Staphylococcus aureus, Lactobacillus plantarum, L. brevis, and L. bulgaricus). Chitosans showed higher antibacterial activities than chitosan oligomers and markedly inhibited growth of most bacteria tested although inhibitory effects differed with Mws of chitosan and the particular bacterium. Chitosan generally showed stronger bactericidal effects with gram-positive bacteria than gram-negative bacteria in the presence of 0.1% chitosan. The minimum inhibitory concentration (MIC) of chitosans ranged from 0.05% to >0.1% depending on the bacteria and Mws of chitosan. As a chitosan solvent, 1% acetic acid was effective in inhibiting the growth of most of the bacteria tested except for lactic acid bacteria that were more effectively suppressed with 1% lactic or formic acids. Antibacterial activity of chitosan was inversely affected by pH (pH 4.5-5.9 range tested), with higher activity at lower pH value.
Chitin/chitosan oligosaccharides composed of 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc) and/or 2-amino-2-deoxy-D-glucopyranose (GlcN) were prepared by chemical degradation of chitin or chitosan and separated by gel permeation chromatography. Oligosaccharides obtained after enzymatic hydrolysis of chitosan [F(A) 0.19] with a fungal chitinase were derivatized by reductive amination with 2-aminoacridone and sequenced by matrix-assisted laser desorption ionization time-of-flight postsource decay (PSD) mass spectrometry (MS). The sequence of a trimer, D1A2, was established as D-A-A. The composition of a hexamer D3A3 was ca. 65% D-A-D-D-A-A and 35% D-D-A-D-A-A. The PSD MS of a nonamer D5A4-amac revealed four isobaric species D-X-Y-D-X-Y-D-A-A, where A is GlcNAc, D is GlcN, and X and Y (X not equal Y) are mutually either D or A. This structure motif was also observed in a dodecamer D7A5 which was composed of eight isobaric sequences of the general formula (D-X-Y)(3)-D-A-A.
2-Acetamido-2-deoxy-D-glucose hydrochloride (D-glucosamine hydrochloride) has been used for the preparation of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-trifluoroacetamido-beta- (4) and 2-tetrachlorophthalimido-alpha,beta-D-glucopyranose (6), which have been transformed into the appropriate bromides and the chloride. Both bromo and chloro sugars were used as a glycosyl donors for the glycosylation of diosgenin [(25R)-spirost-5-en-3beta-ol]. These condensations were conducted under mild conditions, using silver triflate as a promoter, and gave diosgenyl glycosides 9 and 12. Each of them was converted into diosgenyl 2-amino-2-deoxy-beta-D-glucopyranoside hydrochloride (11) and N-acylamido derivatives. The structures of all new glycosides were established by 1H and 13C NMR spectroscopy. These diosgenyl glycosides are the first saponins containing the D-glucosamine residue that have been synthesized. These compounds show promising antitumor activities. The synthetic saponins increase the number of apoptotic B cells, in combination with cladribine (2-CdA), that are isolated from chronic lymphotic leukemia (B-CLL) patients.
A derivative of chitooligosaccharide (COS) with quaternary ammonium functionality was synthesized and characterized by means of FT-IR and NMR spectroscopy. Its amtimicrobial activity was evaluated against Streptococcus mutans, which is a principal etiological agent of dental caries in humans. Introduction of quaternary ammonium group to COS has been easily accomplished by coupling of glycidyl trimethylammonium chloride (GTMAC) to COS in aqueous solution without an additional catalyst. The degree of substitution (%), as determined by (1)H NMR, of GTMAC to the COS increased up to 116% at 70 degrees C for 24h. The resulting COS-GTMAC exhibited the growth inhibition of above 80% against S. mutans after 5h, whereas the COS showed the growth inhibition of about 10%. It was found that antimicrobial activity of the COS could be considerably enhanced by the introduction of quaternary ammonium functionality.
A series of soft quaternary ammonium antimicrobial agents, which are analogues to currently used quaternary ammonium preservatives such as cetyl pyridinium chloride and benzalkonium chloride, were synthesized. These soft analogues consist of long alkyl chain connected to a polar headgroup via chemically labile spacer group. They are characterized by facile nonenzymatic and enzymatic degradation to form their original nontoxic building blocks. However, their chemical stability has to be adequate in order for them to have antimicrobial effects. Stability studies and antibacterial and antiviral activity measurements revealed relationship between activity, lipophilicity, and stability. Their minimum inhibitory concentration (MIC) was as low as 1 microg/mL, and their viral reduction was in some cases greater than 6.7 log. The structure-activity studies demonstrate that the bioactive compounds (i.e., MIC for Gram-positive bacteria of <10 microg/mL) have an alkyl chain length between 12 and 18 carbon atoms, with a polar headgroup preferably of a small quaternary ammonium group, and their acquired inactivation half-life must be greater than 3 h at 60 degrees C.
A novel fiber-reactive chitosan derivative was synthesized in two steps from a chitosan of low molecular weight and low degree of acetylation. First, a water-soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium)propyl]chitosan chloride (HTCC), was prepared by introducing quaternary ammonium salt groups on the amino groups of chitosan. This derivative was further modified by introducing functional (acrylamidomethyl) groups, which can form covalent bonds with cellulose under alkaline conditions, on the primary alcohol groups (C-6) of the chitosan backbone. The fiber-reactive chitosan derivative, O-acrylamidomethyl-HTCC (NMA-HTCC), showed complete bacterial reduction within 20 min at the concentration of 10ppm, when contacted with Staphylococcus aureus and Escherichia coli (1.5-2.5 x 10(5) colony forming units per milliliter [CFU/mL]).
The water-soluble quaternary ammonium salt of chitosan was synthesized by reaction of chitosan with glycidyl trimethylammonium chloride. It was characterized by Fourier transform infrared and carbon-13 magnetic resonance spectra. Its microbiostatic effects against Staphylococcus aureus, Escherichia coli and Candid albicans were explored by microcalorimetry. The antimicrobial activity of the quaternized chitosan was stronger in alkaline condition than that in weak acidic condition.
Compounds that alter endothelial cell growth are of interest in the development of angiogenesis modulators. A structurally diverse series of saccharide derivatives (glycosylamide conjugates) have been synthesized and evaluated for their effects on bovine aortic endothelial cell (BAEC) growth. Heparin-albumin (HA) reduced BAEC growth by 32% at 10 mug/mL and a number of the novel saccharide conjugates from the library were found to mimic the effect of HA as they also inhibit endothelial cell survival under identical conditions. Two thiophene conjugates, thioglucamide (24% inhibition at 35 muM) and a related glucuronide (26% inhibition at 33 muM) were the most potent inhibitors of BAEC growth, as determined using a methylthiazol tetrazoliurn (MTT) assay. The effects of thioglucamide and HA on absolute cell number were also studied using cell counting experiments; thioglucamide (47% after 24 h) was more potent than indicated by the MTT assay and initially reduced the BAEC number to a greater extent than HA (30% after 24 h); however, its actions were over more rapidly than were HA's as cell growth had returned to levels of the control after 72 h where HA still caused 25% inhibition. The binding of the monosaccharide conjugates to fibroblast growth factor (FGF-2) in competition with heparin-alburnin by ELISA was investigated to establish the possible mechanism by which glycoconjugates could alter growth but there was no general correlation between reduction in viable cell population and binding to FGF-2. No glycoconjugate reduced the proliferation of mouse mammary epithelial cells, nor did any alter gross cell morphology, supporting a proposal that the reduction in BAEC survival by monosaccharide conjugates such as thioglucamide is a result of the inhibition of cell proliferation rather than being an induction of cytotoxicity. These studies indicate that cell biological studies to determine the mechanism of action of the simple monosaccharide conjugates may be worthwhile.
Low-molecular-weight chitosans with a viscosity-average molecular weight (Mv) of 5 to 27 kDa and equal degree of deacetylation (DD, 85%) were highly active against Pseudomonas aureofaciens, Enterobacter agglomerans, Bacillus subtilis, and Bifidobacterium bifidum 791, causing death of 80 to 100% of cells. An exception to this tendency was Escherichia coli, for which the rate of cell death, induced by the 5-kDa chitosan, was 38%. The antibacterial effect was manifested as early as 10 min after incubation of 12-kDa chitosan with B. subtilis or E. coli cells. Candida krusei was almost insensitive to the above crab chitosans. However, Candida krusei was highly sensitive to chitosans with Mv 5, 6, 12, 15.7, and 27 kDa: the minimum inhibitory concentration (MIC) varied from 0.06 to 0.005%. Chitosans with M, 5, 12, and 15.7 kDa exerted an antibacterial effect on Staphylococcus aureus. Chitosans with Mv 5, 15.7, and 27 kDa had no effect on Bifidobacterium bifidum ATCC 14893. The antibacterial effect of the 4-kDa chitosan on E. coli and B. bifidum 791 increased with DD in the range 55-85%.
Quaternary ammonium surfactants, such as benzalkonium chloride and cetylpyridinium chloride, are commonly used as antibacterial agents for disinfectants and for general environmental sanitation, as well as in surfactants, penetration enhancers and preservatives in pharmaceutical and cosmetic formulations. However, these agents are known to cause various side-effects and toxic reactions that are believed to be associated with their chemical stability. Soft analogues of the long-chain quaternary ammonium compounds were synthesized according to the soft drug approach and their physicochemical properties investigated, such as their hydrolytic rate constant, surface activity and lipophilicity. Structure-activity studies showed that the antimicrobial activity of the compounds was strongly influenced by their lipophilicity and chemical stability, the activity increasing with increasing lipophilicity and stability. However, in soft drug design structure-activity relationships are combined with structure-inactivation relationships during the lead optimization. The safety index (SI) of compounds was defined as the hydrolytic rate constant divided by the minimum inhibitory concentration. The SI of the soft antibacterial agents was found to increase with increasing lipophilicity but optimum SI was obtained when their hydrolytic t1/2, at pH 6 and 60 degrees C, was about 11 h. Optimization of the soft antibacterial agents through SI optimization resulted in potent but chemically unstable quaternary ammonium antibacterial agents.
Novel synthesis methods for the preparation of quaternary piperazine derivatives of chitosan were developed. Quaternary ammonium moiety can be selectively inserted into either one or both of the piperazine nitrogens, yielding structurally uniform chitosan derivative structures. Water-soluble end products were thoroughly characterized with FT-IR, 1H NMR, 13C NMR and 2D 1H-13C HSQC NMR. The molecular weights of the end products were determined by GPC with triple detection.
Various quaternary chitosan derivative structures were synthesized by reacting N-chloroacyl-6-O-triphenylmethylchitosans with tertiary amines. Full substitutions were obtained from the quaternization reactions and the obtained water-soluble quaternary chitosan derivatives were thoroughly characterized with (1)H NMR, (13)C NMR, (1)H-(13)C HSQC NMR, and FT-IR.