No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Reaction of 2,2?-azinobis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) derived radicals with hydroperoxides. Kinetics and mechanism
Abstract
Tert-Butyl hydroperoxide and hydrogen peroxide readily react with the radical cation derived from 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The reaction is inhibited by ABTS and protons, and can be interpreted in terms of a mechanism comprising a partially reversible electron transferROOH+ABTS•+↔ ROO · + ABTS + H+ (1)followed by the self-reactions of the hydroperoxide derived radicals and reactions between them and another ABTS derived radical. A complete kinetic analysis allows an evaluation of the rate constant for reaction (1). A value of 0.2 M−1 s−1 was obtained for both compounds. The back reaction of process (1) is more relevant when tert-butyl hydroperoxide is employed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 565–570, 1998
... The antioxidant activity assay was estimated using an ABTS free radical scavenging activity assay (2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) [42]. Inhibition free radical ABTS in percent (I %) was calculated as per the equation: ...
... The antioxidant activity assay was estimated using an ABTS free radical scavenging activity assay (2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid) [42]. Inhibition free radical ABTS in percent (I %) was calculated as per the equation: ...
The present work reports the preparation of twelve new heterocyclic scaffolds containing an antipyrinyl-thiazole hybrid through the reaction of 4-antipyrinyl-2-chloroacetamido-thiazoles 1 and 6 with various types of nucleophiles, namely; ethyl thioglycolate, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, ammonium thiocyanate, malononitrile, and salicylaldehyde. The constructed compounds were characterized by conventional spectroscopic techniques (IR, 1H NMR, 13C NMR, and mass analysis). A DFT method (material studio package) was used to predict the geometry, bond lengths, bond angles, and dipole moments as well as other global chemical reactivities of the constructed antipyrinyl-thiazole compounds. Also, their semi-core pseudopods calculations (dspp) were carried out with DNP (double numerical basis sets plus polarization functional) to predict the properties of materials. In addition, the antioxidant activity of these antipyrinyl-thiazole scaffolds has been screened by the ABTS method. The results indicated that 2-(4-antipyrinylthiazolylamino)-5-substituitedbenzylidene-thiazol-4(5H)-ones 10b and 10c exhibited the best antioxidant activity with a percentage inhibition of 85.74% and 83.51%, respectively.
... As we know, ABTS + • scavenging is an electron (e) transfer process. 28 In the process, e transfer is always accompanied by deprotonation, so it is termed a sequential electron proton transfer (SEPT) mechanism, 29 or proton coupled electron-transfer (PCET) mechanism, 30 sequential proton loss single electron transfer (SPLET). 31 The SEPT mechanism for [6]-gingerol to scavenge ABTS + • was proposed as described in Figure 6. ...
... This may be the HAT mechanism for [6]-gingerol to directly scavenge •OH. This mechanism agrees with the previous findings that the dopamine reaction towards •OH is mainly via HAT at physiological pH 7.4.28 To quantitatively evaluate the relative antioxidant level of[6]-gingerol, the ratio value was defined as IC 50,Trolox /IC 50,[6]gingerol . ...
[6]-Gingerol is known as the major bioactive constituent of ginger. In the study, it was observed to effectively. protect against center dot OH-induced DNA damage (IC50 328.60 +/- 24.41 mu M). Antioxidant assays indicated that [6]-gingerol could efficiently scavenge various free radicals, including center dot OH radical (IC50 70.39 +/- 1.23 mu M), center dot O-2(-) radical (IC50 228.40 +/- 9.20 mu M), DPPH center dot radical (IC50 27.35 +/- 1.44 mu M), and ABTS(+)center dot radical (IC50 2.53 +/- 0.070 mu M), and reduce Cu2+ ion (IC50 11.97 +/- 0.68 mu M). In order to investigate the possible mechanism, the reaction product of [6]-gingerol and DPPH center dot radical was further measured using HPLC combined mass spectrometry. The product showed a molecular ion peak at m/z 316 [M+Na](+), and diagnostic fragment loss (m/z 28) for quinone. On this basis, it can be concluded that: (i) [6]-gingerol can effectively protect against center dot OH-induced DNA damage; (ii) a possible mechanism for [6]-gingerol to protect against oxidative damage is center dot OH radical scavenging; (iii) [6]-gingerol scavenges center dot OH radical through hydrogen atom (H center dot) transfer (HAT) and sequential electron (e) proton transfer (SEPT) mechanisms; and (iv) both mechanisms make [6]-gingerol be oxidized to semi-quinone or quinone forms.
... In the reaction between trolox and ABTS • , trolox quinone is formed, that does not react with ABTS • . It has been reported that in the reaction of trolox with ABTS • a trolox radical is formed as intermediate product [8]. The stoichiometry of this reaction is 1. ...
... This suggests that the trolox radical, formed as a product of the reaction of trolox and ABTS • , reacts fast with a second ABTS • . The observed stoichiometry is not exactly 2. This may be due to competing reactions e.g. between two trolox radicals [8,9]. The trolox radical has to be qualified as a potent antioxidant in this assay. ...
The Trolox Equivalent Antioxidant Capacity (TEAC) assay is based on the scavenging of the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical (ABTS(*)) converting it into a colorless product. The degree of decolorization induced by a compound is related to that induced by trolox, giving the TEAC value. The assay is frequently used for constructing structure activity relationships (SARs). HPLC analysis of the reaction mixture, obtained after scavenging of ABTS(*) by the flavonoid chrysin, shows that a product is formed that also reacts with ABTS(*). The product has a higher antioxidant capacity and reacts faster with ABTS(*) than the parent compound, chrysin. In contrast to the reaction product of chrysin, the reaction product of trolox, which is formed during scavenging of ABTS(*), i.e. trolox quinone, does not react with ABTS(*). The experiments show that the TEAC is the antioxidant capacity of the parent compound plus the potential antioxidant capacity of the reaction product(s). This means that the TEAC assay does not necessarily reflect the antioxidant effect of only one structure. This hampers the applicability of the assay for the construction of SARs and for ranking antioxidants.
... With appropriate oxidant action, ABTS will be oxidized into green cations. Relevant studies have shown that ABTS can react quickly with hydroxyl radicals to form colored ABTS •+ [11][12][13][14] . Cu 2+ reacts with H 2 O 2 to form hydroxyl radicals, which can be used to catalyze the oxidation of ABTS [15][16][17] . ...
... The EDC values of the ten model compounds at pH 7.0 are shown in Fig. 2 The EDC values of the amino acids (PHE, tryptophan, tyrosine, and cysteine) are closely related to their structures. The amino acids with aromatic rings or a hydroxyl, amino or sulfhydryl functional groups on the side chain had higher EDC values because these functional groups can act as electron donators (Campos A M, 1997; Aliaga C, 1998;Wang et al., 2006;Deborde and von Gunten, 2008). Cysteine is an aliphatic amino acid with active substituent groups (-COOH, eNH 2 , and eSH); in particular, eSH is very easily oxidized by ABTS $þ (de Vera et al., 2017). ...
Electron donating capacity (EDC) is a promising parameter to characterize the antioxidant properties and oxidant consumption of dissolved organic matter (DOM). To assess the potential of EDC in rapidly predicting the chlorine demand during chlorination, the EDC values were measured for ten DOM model compounds, including phenol, quinol, resorcinol, vanillin, tannic acid, L-phenylalanine, L-tryptophan, L-tyrosine, L-cysteine, and reduced glutathione. The EDC values varied according to the functional moieties present in the model compounds and the pH. At pH 7.0, the order of EDC values of the ten model compounds was (mol e⁻/mol C): 0.843 (cysteine) > 0.538 (tyrosine) > 0.522 (tannic acid) > 0.516 (resorcinol) > 0.452 (phenol) ≈ 0.450 (tryptophan) > 0.257 (vanillin) > 0.226 (reduced glutathione) > 0.160 (quinol) > 0.00035 (phenylalanine). The EDC values correlated well (R² = 0.93) with the 24 h Cl2 demand of the model compounds (except for phenol and tannic acid). By contrast, there was poor correlation between the EDC values and the 24 h formation potentials of chlorination byproducts (trihalomethanes, haloacetic acids and haloacetonitriles). The levels and variation of the EDC values were not significantly correlated with the total organic carbon, specific UV absorbance at 254 nm, or assimilable organic carbon of the model compounds.
... The antioxidant activity test [33] is a methodology used to measure stable free radicals consumption. The electron donation capacity of the investigated compounds was evaluated by bleaching of purple color of diphenyl picryl hydrazyl (DPPH) in methanolic solution. ...
Thiosemicarbazide copper (II) complexes; [Cu2(HL¹)2(H2O)2Cl2].H2O (1) and [Cu2(HL²)2(H2O)2Cl2].2H2O (2) (where H2L¹ = 2‐picolinoyl‐N‐(pyridin‐2‐yl)hydrazine‐1‐carbothioamide and H2L² = 2‐(2‐(2‐aminothiazol‐4‐yl)acetyl)‐N‐(pyridin‐2‐yl)hydrazine‐1‐carbothioamide) have been synthesized and characterized. Analytical and spectroscopic data revealed that ligands behaves as monobasic tetradentate with octahedral geometry. In addition, the optimized geometry of the ligands and their complexes was approved with the Jaguar 9.1 program in the Schrödinger set using DFT (density functional theory) to predict chemical processes and to estimate the properties of the material made by the hybrid functional density system B3LYP. Furthermore, the thermal degradation curves of complexes were discussed in order to determine the kinetic and thermodynamic parameters by various approaches. Additionally, the antioxidant (using the DPPH and SOD methods) and the antibacterial potency of the compounds were examined. Also, docking study of ligands and their complexes was carried out against Staphylococcus aureus gram +ve, gram ‐ve bacterial strains of Escherichia coli and Candida albicans using the XP glide protocol of Schrödinger suite.
... DPPH free radical scavenging activity. The antioxidant activity assay [23] is a technique used in measuring the consumption of stable free radicals. The electron donation ability of the investigated compounds was measured from the bleaching of purple color of methanolic solution of diphenyl picryl hydrazyl (DPPH) [24]. ...
Two copper (II) complexes of ligands H2L¹ and H2L² have been prepared and investigated. The ligands were prepared by the individually addition of picolinic acid hydrazide and 2-(2-aminothiazol-4-yl) acetohydrazide into benzoyl isothiocyanate. The results of analytical and spectroscopic equipments revealed that H2L¹ act as monobasic bidentate with square planner environment. While H2L² behaves as monobasic tetradentate with Oh geometry. The geometries of ligands and their complexes being carefully studied using Jaguar 9.1 program based on the density functional theory (DFT) to predict properties of materials performed by the hybrid density functional method B3LYP. Additionally, thermal degradation data were evaluated to determine the kinetic and thermodynamic parameters by different methods. Moreover, the anti-oxidant (using DPPH and SOD methods), and anti-bacterial activities of the compounds have been studied. Furthermore, the docking study of ligands and their complexes were applied against gram-positive S. Aureus, negative E. Coli bacterial and C. Albicans fungal strains by Schrödinger suite program using XP glide protocol.
... ABTS will be oxidized to green cation under the action of appropriate oxidants. Relevant studies have shown that ABTS can react quickly with hydroxyl radicals To form colored ABTS •+ [17][18][19][20]. Cu 2+ reacts with H2O2 to form hydroxyl radical, which can be used to catalyze the oxidation of ABTS [21][22][23]. ...
The reaction between sulfite and hydrogen peroxide causes the absorbance decrease, which provides the basis to determine the sulfite content that is sensitive to the absorbance change. Cu ²⁺ can catalyze the chemical reaction between hydrogen peroxide (H 2 O 2 ) and the 2,2’-Azinobis-(3-ethylbenzothiazoline-6-sulphonate) (ABTS) effectively, which will cause the change of absorbance. In this paper, we presented an experiment system to study the influence of pH value, H 2 O 2 content, Cu ²⁺ content and reaction time on the reaction system. The comparison of experiment system results indicated that the optimal condition was pH value of 7.0, H 2 O 2 of 500 μM, Cu ²⁺ of 250 μM and 5 minutes reaction time. Under the optimal conditions, the absorbance (Y) and SO 3 ²⁻ content (C) have a linear relationship Y=-861.35C+0.8923. The coefficient of determination (R ² ) in the linear relationship is 0.9983, which indicates a strong correspondence between C and Y. Then, the established method was used to detect the sulfite in wine. The recovery rate was between 96.01% and 106.90%, which proves this method is efficient for sulfite determination.
... The ABTS •+ is rather stable and can be used even if not prepared the night before, but one should take into account that in storage, the ABTS •+ gradually decomposes, and thus appropriate blanks should be recorded before each measurement; however, the decomposition rate sufficiently decreases provided that storage temperature is kept below 5 • C [3,45,46,52]. As ABTS •+ partly turns back to ABTS, which is evidenced by the absorbance increase at 340 nm, the ABTS •+ /ABTS ratio changes, which can sometimes affect the measured antioxidant capacity [53][54][55][56]. ...
The 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS •+) radical cation-based assays are among the most abundant antioxidant capacity assays, together with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-based assays according to the Scopus citation rates. The main objective of this review was to elucidate the reaction pathways that underlie the ABTS/potassium persulfate decolorization assay of antioxidant capacity. Comparative analysis of the literature data showed that there are two principal reaction pathways. Some antioxidants, at least of phenolic nature, can form coupling adducts with ABTS •+ , whereas others can undergo oxidation without coupling, thus the coupling is a specific reaction for certain antioxidants. These coupling adducts can undergo further oxidative degradation, leading to hydrazindyilidene-like and/or imine-like adducts with 3-ethyl-2-oxo-1,3-benzothiazoline-6-sulfonate and 3-ethyl-2-imino-1,3-benzothiazoline-6-sulfonate as marker compounds, respectively. The extent to which the coupling reaction contributes to the total antioxidant capacity, as well as the specificity and relevance of oxidation products, requires further in-depth elucidation. Undoubtedly, there are questions as to the overall application of this assay and this review adds to them, as specific reactions such as coupling might bias a comparison between antioxidants. Nevertheless, ABTS-based assays can still be recommended with certain reservations, particularly for tracking changes in the same antioxidant system during storage and processing.
(This article belongs to the Special Issue Redox Modulation: Restoring Homeostasis with Antioxidants, Special Issue Editors: Prof. Dr Guido R.M.M. Haenen, Dr Mohamed Moalin, Ms Ming Zhang).
... As previously discussed, during the antioxidant process of phenolics, ET is usually accompanied by proton (H + ) transfer to form several antioxidant mechanisms [24], such as hydrogen-atom transfer (HAT) [23,[25][26][27], sequential electron-proton transfer (SEPT) [26,27], sequential proton loss single-electron transfer (SPLET) [26], and proton-coupled electron transfer (PCET) [24][25][26]28]. For example, ABTS + •-scavenging, a reaction dominated by single-electron transfer (SET) [29], has also been proven to be affected by H + levels recently [30]. ABTS + •-scavenging is therefore a multi-pathway-based antioxidant assay [21,31]. ...
The study tried to explore the role of sugar-residues and mechanisms of phenolic phenylpropanoid antioxidants. Acteoside, along with its apioside forsythoside B and rhamnoside poliumoside, were comparatively investigated using various antioxidant assays. In three electron-transfer (ET)-based assays (FRAP, CUPRAC, PTIO•-scavenging at pH 4.5), the relative antioxidant levels roughly ruled as: acteoside >forsythoside B > poliumoside. Such order was also observed in H+-transfer-involved PTIO•-scavenging assay at pH 7.4, and in three multiple-pathway-involved radical-scavenging assays, i.e., ABTS+•-scavenging, DPPH•-scavenging, and •O2−-scavenging. In UV-vis spectra, each of them displayed a red-shift at 335→364 nm and two weak peaks (480 and 719 nm), when mixed with Fe2+; however, acteoside gave the weakest absorption. In Ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC−ESI−Q−TOF−MS/MS) analysis, no radical-adduct-formation (RAF) peak was found. MTT assay revealed that poliumoside exhibited the highest viability of oxidative-stressed bone marrow-derived mesenchymal stem cells. In conclusion, acteoside, forsythoside B, and poliumoside may be involved in multiple-pathways to exert the antioxidant action, including ET, H+-transfer, or Fe2+-chelating, but not RAF. The ET and H+-transfer may be hindered by rhamnosyl and apiosyl moieties; however, the Fe2+-chelating potential can be enhanced by two sugar-residues (especially rhamnosyl moiety). The general effect of rhamnosyl and apiosyl moieties is to improve the antioxidant or cytoprotective effects.
... properties of ABTS and its oxidation by HRP-C have been extensively studied (Childs and Bardsley, 1975;Wolfenden and Willson, 1982;Scott et al., 1993;Campos and Lissi, 1997;Aliaga and Lissi, 1998). In the presence of HRP-C and hydrogen peroxide this substrate readily undergoes a single electron oxidation to produce a cation radical species with distinctive green colour ( Figure 5.1). ...
Both mammalian and bacterial peroxidases contain novel covalent linkages. In the former a sulfonium linkage to a critical Met residue is thought to modify the normal planarity of the haem affecting the functional properties. Following on from the work of Metcalfe et al., 2004 which showed that such links could be engineered in ascorbate peroxidase, horseradish peroxidase (HRP) has been used as convenient model system to try and understand the structural and electronic effects of engineered covalent linkages. Previous work in the group (Cali, 2008) had shown that mutation of Ser167 to Met in HRP-C* resulted in autocatalytic cross-linking on incubation with hydrogen peroxide. In this thesis, two additional HRP variants, S167Y and S167W were studied and a new novel structural linkage discovered.
The UV/Vis spectrum of the S167Y variant suggested a more 6-coordinate high spin character. The molar extinction coefficients were markedly increased, 180 mM-1 cm-1 for S167Y and 135 mM-1 cm-1 for S167W, compared to 100 mM-1 cm-1 for the WT enzyme, consistent with a more 6 coordinate high spin character normally seen in lignin peroxidase. In contrast, the dissociation constant (Kd) of the S167W variant mutant for the aromatic donor BHA was hardly affected, whilst that of the S167Y variant increased two-fold relative to the WT, implying a significant perturbation of the aromatic donor binding site and / or the associated haem-linked hydrogen bonding network.
After peroxide treatment the haem group of the S167Y variant could not be extracted into acid butanone in contrast to the WT. Only a proportion of the haem could be extracted even from the untreated S167Y variant, implying that a substantial fraction of the protein had formed the haem-protein linkage during folding and purification. These results were confirmed during reverse phase HPLC and MALDI-TOF / ESI mass spectroscopy measurements. The haem and protein completely co-eluted in the case of peroxide treated S167Y, while only ~50% of the haem was linked to the protein in the untreated as isolated enzyme. The MALDI-TOF and ESI mass spectrum showed that there was a large increase (614 Da) in the mass of the linked S167Y protein, compared to that of the unlinked enzyme. Unlike the sulfonium linkage obtained earlier, treatment with hydrogen peroxide was unnecessary to observe this increase. Interestingly, the 100% unlinked S167Y protein could only be isolated if enzyme was prepared in the presence of an efficient peroxidase substrate as an antioxidant scavenger. It appears that a Tyr residue at position 167 is highly reactive with respect of the haem vinyl side chain forming a spontaneous covalent link not otherwise seen in nature.
Pre steady-state comparison of the intermediates has shown that Compound I was formed essentially normally at near WT rates, however its stability was greatly affected in the S167Y variant (linked or unlinked), the life time being decreased to ~0.04 s, compared to of the WT enzyme, where it was ~80 s. The substrate preference of the cross-linked S167Y variant was also altered. Stopped-flow measurements of the individual rate constants for the partial reactions of the catalytic cycle with luminol as reducing substrate revealed an increase in the rate of reduction of Compound I to Compound II (k2).
The X-ray crystal structure of S167Y variant was solved to 1.7 Å resolution and the structure has been modelled and determined by x-ray crystallography. The x-ray structure reveals an unanticipated linkage containing an additional ring structure bonded to the engineered Tyr. ESI mass measurements supported this structure.
... Unlike the DPPH radical, ABTS + radical needs an electron to neutralize its positive charge. The scavenging of ABTS + is therefore considered as an electron transfer reaction [25]. ...
Objective: The present study was aimed at establishing the antioxidant, free radical scavenging, anti-lipid peroxidative and antimicrobial properties of the plant Pyrrosia heterophylla (L.) M. G. PRICE.Methods: Standard protocols were used to estimate the antioxidant potential of the hexane, ethyl acetate and methanolic extracts of the plant. Radical scavenging ability of the extracts was assayed for 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulphonicacid) (ABTS), 1,1-diphenyl-2-picryl-hydrazil (DPPH) and hydroxyl radicals. Total antioxidant activity assay was done following the phospho- molybdenum method. The reductive potential was measured by ferric reducing antioxidant power (FRAP) assay. Lipid peroxidation assay was done in vitro. Total phenolic content was measured by the Folin-Ciocalteu method. Antimicrobial activity was identified by well diffusion method, and minimum inhibitory concentration (MIC) was determined by serial dilution method.Results: Results revealed that the ethyl acetate extract (PHE) exhibited the highest antioxidant capacity followed by the methanolic extract (PHM) whereas the hexane extract (PHH) had the lowest activity. The percentage radical scavenging by PHE was found to be 86.63±0.85, 89.48±2.08 and 70.89±1.46 for DPPH, ABTS and hydroxyl radicals respectively, at a concentration of 800μg/ml. The total antioxidant activity of PHE, PHM and PHH was found to be 538.33±3.51, 283.33±7.57and 13.76±3.95 ascorbic acid equivalents/g of extract respectively. Phenolic content of PHE was the highest (207.22±1.95 gallic acid equivalents (GAE)/g of extract), followed by PHM and PHH (197.92±2.00 and 37.50±2.18 GAE/g respectively). Total reducing power was also found to be the highest in PHE followed by PHM and PHH as per the FRAP assay. All the extracts were found to possess inhibitory activity against the tested microorganisms. MIC50 value of all the extracts was below 40 µg/ml.Conclusion: The results of this study confirmed the antioxidant, antimicrobial and anti-lipid peroxidation potentials of the plant P. heterophylla (L.) M. G. PRICE.
... For example, kaempferol which occurred in Radix bupleuri [23], may scavenge DPPH• via the following proposed mechanism [24,25] (Figure 5). However, ABTS + • scavenging is regarded as an electron (e) transfer reaction [26]. In a word, the fact that ERB can effectively scavenge DPPH• and ABTS + •, suggests that ERB exerted radicalscavenging action by donating hydrogen atom (H•) and electron (e). ...
... Our assumption is further supported by the results from the ABTS• + assay, in which AS displayed lower IC 50 value than RS (Table 1) and a similar trend of dose response curve to that in FRAP assay (Fig. 4e). ABTS• + scavenging, however, was interrupted to comprise a partially reversible ET mechanism [37]. ...
Background
Sarcandra glabra (Caoshanhu) is a traditional Chinese herbal medicine used for treating various oxidative-stressed diseases. The present work evaluated its protective effect on mesenchymal stem cells (MSCs) from oxidative stress and then discussed possible mechanisms underlying this observation. Methods
Ethanolic extract of S. glabra (ESG) was investigated by chemical methods for its content of total phenolics, rosmarinic acid, and astilbin. ESG, along with rosmarinic acid and astilbin, was investigated for the effect on the viability of Fenton-treated MSCs using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl (MTT) assay. The observed cell protective effect was further explored by mechanistic chemistry using various antioxidant assays, including DNA protection, •OH-scavenging, •O2−-scavenging, FRAP (ferric ion reducing antioxidant power), ABTS+•-scavenging, DPPH•-scavenging, and Fe2+-chelating assays. ResultsAnalysis of ESG revealed a content of 46.31 ± 0.56 mg quercetin/g total phenolics, 0.78 ± 0.01 % rosmarinic acid, and 3.37 ± 0.01 % astilbin. Results from the MTT assay revealed that three compounds (rosmarinic acid>astilbin>ESG) could effectively increase the survival of Fenton-treated MSCs. Similarly, in •O2−-scavenging, DPPH•-scavenging, and Fe2+-chelating assays, rosmarinic acid exhibited more activity than astilbin; while in FRAP, ABTS+•-scavenging assays, astilbin was stronger than rosmarinic acid. ConclusionS. glabra can prevent MSCs from •OH-induced oxidative stress. Such protective effect can be attributed to its antioxidant ability and the presence of two kinds of phytophenols, i.e. caffeoyl derivatives and flavonoids. As the respective representatives of caffeoyl derivatives and flavonoids, rosmarinic acid and astilbin may exert the antioxidant action via direct ROS-scavenging and indirect ROS-scavenging (i.e. Fe2+-chelating). The direct ROS-scavenging ability involves hydrogen atom transfer (HAT) and/or electron transfer (ET) pathway. Astilbin engages the latter pathway more, which can be attributed to the larger planar conjugation in A/C fused rings. Rosmarinic acid, on the other hand, shows more HAT and Fe2+-chelating potential, which may be due to rosmarinic acid bearing one more catechol moiety whereas astilbin has steric-hindrance from 3-α-L-rhamnose and an H-bonding between 4,5 sites. The antioxidant features of rosmarinic acid can be generalized to other caffeoyl derivatives, while that of astilbin cannot be generalized to other flavonoids because of the difference in chemical structures.
... (Childs and Bardsley, 1975) and has been shown to be rapidly oxidised by MnPs (Paice et al., 1993;Martinez et al., 1996;Hofrichter et al., 1999). The chemical properties of ABTS and its oxidation by peroxidases, particularly HRPC, have been intensively studied (Aliaga and Lissi, 1998;Campos and Lissi, 1997;Childs and Bardsley, 1975;Scott et al., 1993). ABTS undergoes a single electron oxidation in the presence of peroxidase and hydrogen peroxide to produce a long-lived cation radical. ...
Manganese peroxidase 3 (MnP3) is an extracellular peroxidase from the white-rot fungus, P. radiata that is a well-studied wood/lignin degrader from Scandinavian forest (Hilden et al., 2005). Unlike the Phanerochaete chrysosporium MnP's previously characterised, the P. radiata MnP3 is a 'short' MnP with a truncated C-terminus evolutionarily more related to the newly characterised versatile peroxidase. The cDNA for the full length MnP3 from P. radiata was optimised at the 5' end for E.coli expression and cloned into the expression vector pFLAG1. Five site-directed mutants targetting the Mn binding site (E40H, E44H, E40H/E44H, D186H and D186N) were constructed and characterised. The recombinant MnP3‘s, both wild-type and variants were isolated from E.coli inclusion bodies after expression in W3110 and active soluble proteins recovered after in vitro refolding and extensively characterised. In this work, the characteristics of the P. radiata wild type MnP3 were compared with those of the mutant enzymes and the 'classical' Phanerochaete enzyme described in the literature. The molecular weight of the enzymes was 36kDa with UV/Vis absorption spectra typical of a six-coordinate high spin haem peroxidase. In contrast to the literature on these enzymes, the Phlebia MnP3 was found to have a maximum efficacy (kcat/Km) at pH 5.0 rather than the more typical optimum at 4.5. Consistent with the high oxidation potential of these enzymes, the Compound I form of the enzyme was found to be unstable decaying rapidly to a Compound II-like intermediate. Mutations to the manganese (II)-binding ligands change the catalytic properties of the Phlebia MnP3 dramatically and reactivity towards Mn (II) were greatly decreased particularly at lower pH. Interestingly, much of the activity in the higher pH region was maintained, showing that carboxylate Mn ligands are not essential at higher pH when tighter binding of Mn2+ is favoured. The pKa‘s for the activity dependence matches those expected for the deprotonation of the surrogate His ligands. The results confirm that the mutated Mn (II) binding site is the only productive catalytic site for Mn (II) oxidation. The specificity of metal binding by MnP3 was examined; Cu ions were found to be strongly inhibitory and Zinc ions bound particularly tightly and somewhat nonspecifically to MnP3 with stoichiometries as high as 5:1 suggestive of multiple metal-binding sites other than the specific manganese-binding site. Use of Zn ions in crystallisation media clearly has the potential to complicate metal ion assignment in the structures of these enzymes. Interestingly, Cobalt ions were able to enhance the activity of MnP3 but were not rapidly oxidised by the enzyme itself. The P. radiata enzymes have been found to be active in acidic and alkaline regions, being stable over a large pH range (5.0 – 8.5) and are readily additionally stabilised by addition of excess Ca2+, both desirable features in such an enzyme that could be applied to the 'biorefinery' concept.
... The antioxidant activity [14] employed a technique depending on measuring the reducing of stable free radicals. The ...
Two thiosemicarbazide ligands were derived from the addition of 2-(2-aminothiazol-4-ylaceto) hydrazid to both ethyl isothiocynate (H2TAET) and allyl isothiocynat (H2TAAT) where their Cd (II) and Hg (II) complexes were synthesized and characterized by traditional techniques. The complexes were assigned the formulas, [Cd(HTAET)(H2O)Cl](H2O)2, [Hg(TAET)(H2O)2]2, [Cd(HTAAT)(H2O)Cl]H2O and [Hg(H2TAAT)(H2O)Cl2], respectively. In Cd (II) complexes, the IR spectra show that the ligands behave as monobasic bidentate through (C = N) thiazol ring and deprotonated enolized (CO). In Hg (II) complexes, H2TAET acts as dibasic tridentate (NSO) via thiol (CS), enolized (CO) and new azomethine, (N = C)* groups, while H2TAAT act as neutral tridentate (NNO) through (C = N) of thiazol ring, (CO) and new (C = N) due to (SH) formation. A tetrahedral for Cd (II) complexes, square pyramidal for [Hg(TAET)(H2O)2]2 and octahedral for [Hg(H2TAAT)(H2O)Cl2] geometries were proposed. The data of theoretical and experimental vibrational frequencies of ligands are comparable. The data calculated of HOMO– LUMO energies gap decided the possibility of charge transfer within the molecule. The binding energies calculations showed the higher stability of complexes than that of ligands. The kinetic and thermodynamic parameters of the Cd(II) complexes have been calculated by Coats–Redfern and Horowitz–Metzger methods. Moreover, the antimicrobial activities of the compounds have been discussed using a wide spectrum of bacterial and fungal strains. Representative of the synthesized compounds were tested and evaluated for anti-oxidant and antitumor activities. All the complexes [Hg(HTAET)(H2O)2]2, Cd(HTAET)(H2O)Cl](H2O)2 and [Hg(H2TAAT)(H2O)Cl2] have higher toxicity with perivascular leukocytic infiltration effect on the rats but in the complex [Cd(HTAAT)(H2O)Cl]H2O has low effect of toxicity when the rats treated with the same dose lead to mitotic figures and sinusoid dialated .
... Unlike DPPH· scavenging, ABTS· + scavenging is an electron (e) transfer process [11]. In the reaction, THA produced two electrons (e) and H + cations. ...
(2S,2″S )-Tetrahydroamentoflavone (THA) is a typical biflavonoid. In this study, we systematically evaluated its antioxidant activity by various antioxidant assays in vitro. The IC50 values of THA were 4.8±0.3, 743.2±49.5, 35.5±1.9, 165.7±22.8, 4.4±0.2, and 77.1±2.2 μg/mL, respectively, for superoxide (•O2-) radical-scavenging, Fe2+-chelating, Cu2+-chelating, DPPH• (1,1-diphenyl-2-picrylhydrazyl radical) scavenging, ABTS•+ (3-ethylbenzthiazoline-6-sulfonic acid radical) scavenging, and Cu2+-reducing power. The average ratio value of IC50,Trolox:IC50,THA was calculated as 2.54, suggesting that THA possesses 2.54 times the total antioxidant level than the standard antioxidant Trolox. THA exerts its antioxidant activity in vitro through metal-chelating, and radical-scavenging, which is via donating a hydrogen atom (H•) and an electron (e). Its antioxidant activity can be responsible for its pharmacological effect and make it an attractive natural antioxidant.
... Unlike DPPH· radical, ABTS• + radical cation needs only an electron (e) to neutralize the positive charge. Therefore, ABTS• + scavenging is an electron (e) transfer process [19]. In the reaction, amentoflavone produced electron Here dAMP• radical has been repaired and converted into a stable dAMP molecule without cytotoxicity. ...
Objective: Oxidative DNA damage is involved in mutation, cell death, carcinogenesis, and aging. Since biflavonoid amentoflavone exhibited beneficial effects on DNA, we therefore investigated its protection against center dot OH-induced DNA oxidative damage then discussed the mechanism. It will enhance the understanding of interaction between biflavonoid vs DNA mediated by free radicals. Methods: The protective effect of amentoflavone against center dot OH-induced DNA damage was measured using our method. To explore the mechanism, it was further determined by center dot OH-induced bases damage, deoxyribose damage, and various antioxidant assays. Results: Amentoflavone increased dose-dependently its protective percentages against center dot OH-induced damage on DNA, bases, and deoxyribose; The IC50 were 31.85 +/- 4.75, 198.75 +/- 33.53, 147.14 +/- 20.95, 75.15 +/- 10.52, 93.75 +/- 16.36, 167.69 +/- 13.90, and 137.95 +/- 19.86 mu M, respectively for DNA, cytosine, uracil, adenine, thymine, guanine, and deoxyribose damages. Radical-scavenging assays suggested that amentoflavone could effectively scavenge center dot O-2(-), DPPH center dot, ABTS center dot(+) radicals (IC50 values were respectively 8.98 +/- 0.23, 432.25 +/- 84.05, 7.25 +/- 0.35 mu M). Conclusions: Based on the mechanistic analysis, it is concluded that amentoflavone can effectively protect against center dot OH-induced oxidative damage DNA (including base & deoxyribose moieties), via deoxynucleotide radical repairing, and reactive oxygen species (ROS) scavenging approaches which may be mediated by donating hydrogen atom (H center dot) and electron (e). Further analysis indicated that both scavenging and repairing approaches can be primarily attributed to its antioxidant mechanism which may ultimately arise from to the stability of its oxidized product semi-quinone form. Its protection against DNA damage may be generally responsible for the radioprotective and anti-inflammation effects.
... Unlike DPPH• radical, ABTS + • radical cation, however, needs only an electron (e) to neutralize the positive charge and ABTS + • scavenging is regarded as an electron (e) transfer process (Aliaga and Lissi 1998). Therefore, in the reaction of aloe-emodin with ABTS + • radical, aloe-emodin was thought to produce an electron (e) and H + ion. ...
In the study, Folium Sennae (FS) was firstly extracted by various solvents to obtain five FS extracts. Then, five FS extracts were evaluated for the protective effects against •OH-induced DNA damage, antioxidant abilities in vitro, and chemical contents using various methods. On this basis, the correlation graphs between the pharmacological effects and chemical contents were plotted to obtain the correlation coefficients (R values). Finally, in order to obtain biological evidence, ethyl acetate extract of FS (EAFS) was investigated for the protective effect against •OH-induced MSCs (mesenchymal stem cells) damage using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl) assay.
The pharmacological assays indicated that five FS extracts could effectively protect against •OH-induced DNA damage. The correlation analysis suggested that the average R values of total phenolics, total anthraquinones, aloe-emodin, rhein, and emodin were respectively 0.843, 0.833, 0.753, 0.820, and 0.784, while those of total sugars and total saponins were respectively 0.103 and 0.0068. The mechanistic analysis revealed that five FS extracts could also scavenge •OH, •O2
–, DPPH• & ABTS•+ radicals, and reduce Cu2+ to Cu+. MTT assay revealed that the viability of MSCs which were treated with •OH radicals has been effectively protected by EAFS (3 and 30 μg/mL).
On this basis, it can be concluded that: (i) Folium Sennae exhibits a protective effect against •OH-induced damages to DNA and MSCs; (ii ) The effects may be attributed to phytophenols (especially aloe-emodin, rhein, and emodin), not sugars or saponins; (iii) They exert the protective action via hydrogen atom transfer (HAT) and/or sequential electron proton transfer (SEPT) mechanisms which make phenolic –OH moiety be oxidized to stable semi-quinone form; (iv) The stability of semi-quinone form can ultimately be responsible for the protective or antioxidant effect of phytophenols.
... In the study, we used several methods to systematically evaluate the antioxidant ability of Yin-Huang, including DPPH• scavenging assay, ABTS+• scavenging assay, metal reducing power assay, and metal chelating assay. DPPH• scavenging, however, has been demonstrated to be a donation of hydrogen atom (H•) process, while ABTS + • radical-scavenging is regarded as an electron (e) transfer process [15]. In the study, Yin-Huang could effectively inhibit DPPH• and ABTS + • radicals, suggesting that Yin-Huang exerts its radical-scavenging action via donating hydrogen atom (H•) and electron (e) approaches. ...
... For example, kaempferol could transfer H· to DPPH• and then transform into a semiquinone, even stable quinine (Dimitrios and Vassiliki, 2006;Khanduja and Anjana, 2003). However, ABTS• + scavenging is considered an electron (e) transfer reaction (Aliaga and Lissi, 1998). The fact that both SJFH and QXFH can effectively scavenge DPPH• and ABTS• + suggests that H. undatus flower exerts radical scavenging action by donating hydrogen atoms (H•) and electrons (e). ...
Hylocereus undatus flower is commonly used as food or for medicinal purposes in south China. To study its antioxidant activity and mechanism we used antioxidant and chemical assays to compare two commercial samples from different locations (Shenjing, Qixing). The difference in antioxidant levels corresponded with differences in chemical content (including total phenolics, total flavonoids, kaempferol and quercetin) between Shenjing and Qixing. The antioxidant ability of H. undatus flower seems attributable to total phenolics (mainly total flavonoids). Kaempferol is one of the main bioactive components. H. undatus flower exerts its antioxidant effects through metal chelation and radical scavenging via hydrogen atom (H•) and electron (e) donation.
... Similarly, EBFH could also scavenge ABTS• + effectively. However, ABTS• + scavenging is regarded as an electron (e) transfer reaction [20]. Therefore, the possible mechanism for cyanidin-3-Oglucoside to scavenge ABTS• + may be via the proposed reaction in Equation 3 to yield cyanidin-3-O-glucoside radical which can also further converted to semi-quinone or quinone under excessive exposure to ABTS• + . ...
... Therefore, ABTS· + scavenging is an electron (e) transfer process. 22 In the reaction, magnolol was assumed to give an electron (e), accompanied by H + transfer. The elec- tron (e) was then donated to ABTS· + to form stable ABTS molecule. ...
As a Chinese herbal medicine used in East Asia for thousands years, Cortex Magnoliae Officinalis (CMO) was observed to possess a protective effect against OH-induced DNA damage in the study. To explore the mechanism, the antioxidant effects and chemical contents of five CMO extracts were determined by various methods. On the basis of mechanistic analysis, and correlation analysis between antioxidant effects & chemical contents, it can be concluded that CMO exhibits a protective effect against OH-induced DNA damage, and the effect can be attributed to the existence of phenolic compounds, especially magnolol and honokiol. They exert the protective effect via antioxidant mechanism which may be mediated via hydrogen atom transfer (HAT) and/or sequential electron proton transfer (SEPT). In the process, the phenolic-OH moiety in phenylpropanoids is oxidized to the stable quinine-like form and the stability of quinine-like can be ultimately responsible for the antioxidant.
... To test further the possibility of SEPT mechanism of maclurin, it was investigated for ABTS +Å scavenging which has been proved to be an electron (e) transfer process [39,40]. As seen in Supplemental Fig. S6 and Table 1, maclurin increased linearly (R = 0.98748) the inhibition percentages on ABTS +Å radical and IC 50 was 0.97 ± 0.070 lM. ...
Maclurin, an exceptional member of phytophenol family, was found to effectively protect against mesenchymal stem cells (MSCs) oxidative damage induced by hydroxyl radical (•OH) at 62.1-310.5 μM. Antioxidant assays indicated that maclurin could efficiently protect DNA from •OH-induced damage at 114.6-382.2 μM, and scavenge •OH, DPPH• (1,1-diphenyl-2-picrylhydrazyl radical), ABTS•(+) (2,2'-azino-bis(3-ethylbenzothiazoline -6-sulfonic acid radical), and bind Cu(2+) (IC50 values were respectively 122.87±10.14, 10.15±0.85, 0.97±0.07, and 133.95±11.92 μM). HPLC-DAD and HPLC-ESI-MS/MS analyses of the end-product of maclurin reaction with DPPH• clearly suggested that maclurin (m/z = 261.12 [M-H](-)) donated two hydrogen atoms to DPPH• (m/z = 394.06 [M](+)) to form ortho-benzoquinone moiety (λmax = 364 nm; m/z=259.06 [M-H](-), loss of m/z=28) and DPPH2 molecule (m/z=395.03, 396.01), via hydrogen atom transfer (HAT) or sequential electron (e) proton transfer (SEPT), not radical adduct formation (RAF) mechanisms. Therefore, we concluded that: (i) maclurin can effectively protect against •OH-induced damages to DNA and MSCs, thereby it may have a therapeutic potential in prevention of many diseases or MSCs transplantation; (ii) a possible mechanism for maclurin to protect against oxidative damages is •OH radical-scavenging; (iii) maclurin scavenges •OH possibly through metal-chelating, and direct radical-scavenging which is mainly via HAT or SEPT mechanisms; and (iv) the protective and antioxidant effects of maclurin can be primarily attributed to ortho-dihydroxyl groups, and ultimately to the relative stability of the ortho-benzoquinone form.
... Therefore, ABTS + · scavenging is an electron (e) transfer process. 21 For example, γ-mangostin scavenged ABTS + · possiblyvia the following mechanism. At first, γ-mangostin produced electron (e) and H + cation. ...
Purpose:
The aim of this study was to evaluate antioxidant ability of mangosteen shell and explore the non-enzymatic repair reaction and possible mechanism of xanthones in mangosteen shell.
Methods:
Mangosteen shell was extracted by methanol to obtain the extract of mangosteen shell. The extract was then determined by various antioxidant assays in vitro, including protection against DNA damage, •OH scavenging,DPPH• (1,1-diphenyl-2-picryl-hydrazl radical) scavenging, ABTS(+)• (2,2'-azino-bis(3-ethylbenzo- thiazoline-6-sulfonic acid diammonium) scavenging, Cu(2+)-chelating, Fe(2+)-chelatingand Fe(3+) reducing assays.
Results:
Mangosteen shell extract increased dose-dependently its percentages in all assays. Its IC50 values were calculated as 727.85±2.21,176.94±19.25, 453.91±6.47, 84.60±2.47, 6.81±0.28, 1.55±0.10, 3.93±0.17, and 9.52±0.53μg/mL, respectively for DNA damage assay, •OH scavenging assay, Fe(2+)-Chelating assay, Cu(2+)-Chelating assay, DPPH• scavenging assay, ABTS(+)•scavenging assay, Fe(3+) reducing assay and Cu(2+) reducing assay.
Conclusion:
On the mechanistic analysis, it can be concluded that mangosteen shell can effectively protect against hydroxyl-induced DNA oxidative damage. The protective effect can be attributed to the xanthones. One approach for xanthones to protect against hydroxyl-induced DNA oxidative damage may be ROS scavenging. ROS scavenging may be mediated via metal-chelating, and direct radical-scavenging which is through donating hydrogen atom (H·) and electron (e). However, both donating hydrogen atom (H·) and electron (e) can result in the oxidation of xanthone to stable quinone form.
... However, ABTS· + scavenging is regarded as an electron (e) transfer reaction. 24 The fact that ECRP can effectively scavenge both DPPH· and ABTS + ·radicals, suggests that: (1) the protective effect of ECRP against DNA oxidative damage was associated with its radical-scavenging ability; (2) ECRP exerted its radical-scavenging action by donating hydrogen atom (H·) and electron (e). Although a reductant is not necessarily an antioxidant, an antioxidant is commonly a reductant. ...
Purpose:
As a typical Chinese herbal medicine, Citri reticulatae pericarpium (CRP) possesses various pharmacological effects involved in antioxidant ability. However, its antioxidant effects have not been reported yet. The objective of this work was to investigate its antioxidant ability, then further discuss the antioxidant mechanism.
Methods:
CRP was extracted by ethanol to obtain ethanol extract of Citri reticulatae pericarpium (ECRP). ECRP was then measured by various antioxidant methods, including DNA damage assay, DPPH assay, ABTS assay, Fe(3+)-reducing assay and Cu(2+)-reducing assay. Finally, the content of total flavonoids was analyzed by spectrophotometric method.
Results:
Our results revealed that ECRP could effectively protect against hydroxyl-induced DNA damage (IC50 944.47±147.74 μg/mL). In addition, it could also scavenge DPPH· radical (IC50349.67±1.91 μg/mL) and ABTS(+)• radical (IC5011.33±0.10 μg/mL), reduce Fe(3+) (IC50 140.95±2.15 μg/mL) and Cu(2+) (IC50 70.46±1.77 μg/mL). Chemical analysis demonstrated that the content of total flavonoids in ECRP was 198.29±12.24 mg quercetin/g.
Conclusion:
Citri reticulatae pericarpium can effectively protect against hydroxyl-induced DNA damage. One mechanism of protective effect may be radical-scavenging which is via donating hydrogen atom (H·), donating electron (e). Its antioxidant ability can be mainly attributed to the flavonoids, especially hesperidin and narirutin.
... However, ABTS· + scavenging is considered as an electron (e) transfer reaction. 25 The fact that ERG can effectively scavenge both DPPH· and ABTS + · radicals, suggests that: (1) the protective effect of ERG against DNA oxidative damage was relevant to its radical-scavenging ability; (2) ERG exerted radical-scavenging action by donating hydrogen atom (H·) and electron (e). ...
Purpose:
As a typical Chinese herbal medicine, Radix Glycyrrhizae (RG) possesses various pharmacological effects involved in antioxidant ability. However, its antioxidant has not been explored so far. The aim of the study was to investigate its antioxidant ability, then further discuss the antioxidant mechanism.
Methods:
RG was extracted by ethanol to obtain ethanolic extract of Radix Glycyrrhizae (ERG). ERG was then determined by various antioxidant methods, including DNA damage assay, DPPH assay, ABTS assay, Fe(3+)-reducing assay and Cu(2+)-reducing assay. Finally, the contents of total phenolics and total flavonoids were analyzed by spectrophotometric methods.
Results:
Our results revealed that ERG could effectively protect against hydroxyl-induced DNA damage (IC50 517.28±26.61μg/mL). In addition, ERG could scavenge DPPH· radical (IC50165.18±6.48μg/mL) and ABTS(+)• radical (IC507.46±0.07μg/mL), reduce Fe(3+) (IC50 97.23±2.88 μg/mL) and Cu(2+) (IC50 59.21±0.18 μg/mL). Chemical analysis demonstrated that the contents of total phenolics and flavonoids in ERG were 111.48±0.88 and 218.26±8.57 mg quercetin/g, respectively.
Conclusion:
Radix Glycyrrhizae can effectively protect against hydroxyl-induced DNA damage. One mechanism of protective effect may be radical-scavenging which is via donating hydrogen atom (H·), donating electron (e). Its antioxidant ability can be mainly attributed to the flavonoids or total phenolics.
... 8.1.1.1 Cyclovoltammetrie Die Geschwindigkeit der Oxidation des Nukleotid-Kofaktors wurde einerseits cyclovoltammetrisch nach der Methode von Nicholson und Shain 40[189] und andererseits über photometrische Messungen[242,244] bestimmt. ...
In the last decades, the beneficial influence of green tea on human health has been related to the antioxidant capacity (AC) of its phenolic constituents. The latter has originated systematic studies of the AC of green tea and/or its pure antioxidants. Different methodologies have been used with this purpose. The methods are based on: i) Estimation of the consumption by additives of stable free radicals (DPPH, and ABTS radical cation). ii) Evaluation of the protection given by antioxidants to a target being oxidized by free radicals (ORAC, TOSC, LDL oxidation assay). iii) Estimation of the steady state of free radicals before and after addition of additives (TAR). iv) Estimation of the reducing power capacity of the additives (FRAP, CUPRAC). The assays differ in the experimental conditions and their chemistry. Therefore, different conclusions could be obtained depending on the methodology used. For example, green tea presents a lower AC than peumus boldus by ORAC (oxygen radical absorbance capacity) method when fluorescein is used as target molecule. However, if pyrogallol red is used as probe, green tea appears with an ORAC index six times higher than peumus boldus. In the present review, we discuss the advantages, and disadvantages of the different methodologies employed to evaluate the AC of green tea.
In the present study, five nonphenolic (E)-N′-benzylidenebenzohydrazides including three new compounds were synthesized and evaluated for their free radical scavenging activities using 2,2-diphenyl-1-picrylhydrazyl (DPPH). X-Ray analysis of a single crystal of (E)-N′-(4-chlorobenzylidene)benzohydrazide (3c) revealed a triclinic, space group P-1 structure with a trans configuration around the azomethine (-C2=N2-) double bond. The three-dimensional Hirshfeld surfaces and the related two-dimensional fingerprint plots were also drawn to study the plausible intermolecular interactions. Density functional calculations of structures, electronic densities, frontier molecular orbitals modeling, and Mulliken charge analysis of all compounds were performed at the B3LYP/6-311G level of theory. Theoretical vibrational frequencies were predicted and compared with experimental values, and results supported the validity of optimized geometry of noncrystalline compounds. All synthesized compounds showed significant DPPH radical scavenging activity, although compound 3d exhibited greatest antioxidant activity with an IC50 value of 11 μM. The results of DFT analysis were used to explain the proposed antioxidant mechanism of (E)-N′-benzylidenebenzohydrazide analogs. This analysis revealed that protons attached to N, O, and C atoms possessing high negative charge are involved in the production of free radicals that scavenge DPPH. Moreover, the antioxidant activities of (E)-N′-benzylidenebenzohydrazide analogs correlated well with HOMO-LUMO energy difference of molecules. © 2015 Korean Chemical Society, & Wiley-VCH Verlag GmbH & Co. KGaA.
A homogeneous label free colorimetric sensing strategy for bleomycin (BLM) assay was developed on the basis of BLM enhanced Fe(II)-H2O2-ABTS reaction. Fe(II) exhibits a catalytic effect on H2O2-mediated oxidation of ABTS by Fenton chemistry. BLM•Fe(II) complex possessed a much higher catalytic ability than Fe(II) probably due to the further formation of more active “activated oxo-iron-bleomycin complex”. The present method was convenient without any complicated chemical synthesis, modification, or tedious experimental procedures. And the analysis results can be seen with the naked eye and monitored by UV-vis spectra. The peak absorbance exhibits a linear relationship with BLM concentrations from 25 nM to 1 μM and a detection limit of 16 nM can be achieved. The designed colorimetric strategy may provide a promising alternative for the BLM detection in clinical samples.
Flos Chrysanthemi Indici (FCI) is a Chinese herbal medicine used in China for over 2000 years. In the study, its ethanol extract (EFCL) was found to protect against hydroxyl radical (•OH) induced oxidative damages to mesenchymal stem cells (MSCs) and DNA. To explore the mechanism, EFCL was further determined by chemical and antioxidant assays. Folin-Ciocalteu colorimetric assay suggested that content of total phenolics was 93.85±3.56 mg catechin/g and HPLC analysis indicated a content of 10.05±1.44 mg/g as chlorogenic acid in EFCI. Antioxidant assays revealed that EFCI could also scavenge •O2− radical (IC50 58.74±1.30 μg/mL), DPPH• radical (IC50 46.46±1.35 μg/mL) and ABTS+• radical (IC50 20.59±0.52 μg/mL), bind Fe2+ (IC50 364.27±19.57 μg/mL) and Cu2+ (IC50 734.77±34.69 μg/mL), reduce Fe3+ (IC50 147.11±11.09 μg/mL) and Cu2+ (IC50 35.69±3.14 μg/mL). On the basis of mechanistic analysis, we concluded that FCI can effectively protect against hydroxyl-induced damages to DNA and MSCs, therefore FCI shows promise as a possible therapeutic reagent for many diseases; The effect may be mainly attributed to phenolics especially chlorogenic acid, which exert the antioxidant action possibly through metal-chelating, and radical-scavenging which is via hydrogen atom transfer (HAT) and/or sequential electron proton transfer (SEPT) mechanisms.
Hg(II), Cd(II) and binuclear Zn(II) complexes derived from the tetradentate N(1)-ethyl-N(2)-(pyridine-2-yl) hydrazine-1, 2-bis (carbothioamide) ligand (H2PET) have been prepared and characterized by conventional techniques. The isolated complexes acquired the formulas, [Hg(HPET)(H2O)2Cl]⋅H2O, [Cd(HPET)Cl] and [Zn2(HPET)(PET)(OAc)]⋅H2O, respectively. IR data revealed that the ligand behaves as monobasic tridentate through (CN)py, (C-S) and new (NC)azomethine(∗) groups in both Hg(II) and Cd(II) complexes. In the binuclear Zn(II) complex, the behavior of ligand contains two types, where H2PET acts as dibasic tetradentate via (CN)py, both deprotonated (C-SH) and the new (NC)azomethine(∗) towards two Zn atoms and also it acts as monobasic tridentate via (CS), deprotonated (C-SH) and (CN)py towards the same Zn atoms. An octahedral geometry for Hg(II) complex and tetrahedral geometry for both Cd(II) and Zn(II) complexes were proposed. The bond lengths, bond angles, HOMO, LUMO and dipole moment have been calculated by DFT using materials studio program to confirm the geometry of ligand and its metal complexes. The association constant of the ligand and the stability constants of its complexes as well as the thermodynamic parameters were calculated by pH metric measurements at 298, 308 and 318K in 50% dioxane-water mixture, respectively. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats-Redfern and Horowitz-Metzger methods. Moreover, the anti-oxidant (using ABTS and DPPH methods), anti-hemolytic, and cytotoxic activities of the compounds have been tested.
Excessive reactive oxygen species (ROS) can oxidatively damage DNA to cause severe biological consequences. In the study, a natural flavonoid, myricitrin (myricetin-3-O-α-L-rhamnopyranoside), was found to have a protective effect against hydroxyl-induced DNA damage (IC50 159.86 ± 54.24 μg/mL). To investigate the mechanism, it was determined by various antioxidant assays. The results revealed that myricitrin could effectively scavenge ·OH, ·O2−, DPPH· (1,1-diphenyl-2-picrylhydrazyl radical), and ABTS+· (2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals (IC50 values were respectively 69.71 ± 5.93, 69.71 ± 5.93, 25.34 ± 2.14, and 1.71 ± 0.09 μg/mL), and bind Cu2+ (IC50 27.33 ± 2.36 μg/mL). Based on the mechanistic analysis, it can be concluded that: (i) myricitrin can effectively protect against hydroxyl-induced DNA oxidative damage via ROS scavenging and deoxynucleotide radicals repairing approaches. Both approaches can be attributed to its antioxidant. From a structure-activity relationship viewpoint, its antioxidant ability can be attributed to the ortho-dihydroxyl moiety, and ultimately to the stability of its oxidized form ortho-benzoquinone; (ii) its ROS scavenging is mediated via metal-chelating, and direct radical-scavenging which is through donating hydrogen (H·) and electron (e); and (iii) its protective effect against DNA oxidative damage may be primarily responsible for the pharmacological effects, and offers promise as a new therapeutic reagent for diseases from DNA oxidative damage.
A new series of Zn(II), Cd(II) and Hg(II) complexes of
(1E,5E)-1,5-bis(1-(pyridin-2-yl)ethylidene)carbonohydrazide
(H2APC) have been prepared and characterized by elemental
analyses, spectral (IR, UV-visible, mass and 1H NMR) as well
as magnetic and thermal measurements. The data revealed that the ligand
acts a monobasic hexadentate, neutral tri- and monodentate in Zn(II),
Cd(II) and Hg(II) complexes, respectively. An octahedral geometry is
proposed for Zn(II) complex, a trigonal bi-pyramid for Cd(II) complex
and a tetrahedral one for Hg(II) complex. The bond length, bond angle,
HOMO, LUMO and charges on the atoms have been calculated to confirm the
geometry of the ligand and the investigated complexes using material
studio program. Kinetic parameters were determined for each thermal
degradation stage of some complexes using Coats-Redfern and
Horowitz-Metzger methods. The antioxidant, anti-hemolytic, and cytotoxic
activities of the compounds have been screened. H2APC showed
moderate antioxidant activity using ABTS and DPPH methods. With respect
to erythrocyte hemolysis and in vitro Ehrlich ascites assay,
H2APC exhibited the potent antioxidative activity followed by
Cd(II) and Zn(II) complexes while Hg(II) complex showed very weak
activity.
General introduction
Free radicals play a crucial role in the pathogenesis of several human
diseases and ageing. They are (by)products of various endogenous
processes or a result of external factors, such as irradiation and
xenobiotics. In food products free radicals are also known to cause
damage, resulting in off taste or a reduced shelf-life.
Antioxidants protect against free radicals and they are therefore essential
in obtaining and preserving good health. In food products they act as
preservatives. Much attention has been given to the flavonoids, a class of
polyphenols with strong antioxidant activities, which are ubiquitously
present in a broad range of dietary products.
In order to identify the most potent antioxidants, the antioxidant profiles of
numerous compounds are frequently compared. For this purpose a wide
array of antioxidant assays is available. One of the most frequently
applied assays is the Trolox Equivalent Antioxidant Capacity (TEAC)
assay.
The aim of this thesis is to study antioxidant activity and to examine the
factors that describe and determine this activity of antioxidants.
Outline of this thesis
• Chapter 2 critically evaluates the assessment of antioxidants in
vitro and in vivo.
• Chapter 3 focuses on the applicability of the TEAC assay to
predict the antioxidant activity of a compound. A comparison of
the TEAC with other antioxidant screenings assays is made.
• The contribution of reaction products to the TEAC is examined,
as described in Chapter 4. Based on this, the applicability of the
TEAC assay for the construction of structure activity relationships
(SARs) is evaluated.
• The antioxidant activity of reaction products is further studied in
Chapter 5. A modified TEAC procedure, that includes the
scavenging effect of oxidation products, is presented.
• Chapter 6 describes the effect of interactions between different
ingredients in complex mixtures on the TEAC.
• In Chapter 7, the effect of the interaction between flavonoids and
proteins on the antioxidant capacity is examined. The possible
consequences of masking are discussed.
In Chapter 8 the protection against reactive glucose-derived
species (RGS) and reactive oxygen species (ROS) is compared.
A suggestion for the protection against RGS is made.
• An evaluation on the role of oxidative lipid degradation during
mashing is made in Chapter 9. Suggestions are made in order to
minimize oxidative damage and preserve antioxidants in this
phase of the brewing process.
With the current upsurge of interest in the function, measurement of efficacy and use of natural antioxidants, testing of antioxidant activity has received much attention. Several methods are being used, both in vitro and in vivo, to determine the antioxidant activity of natural antioxidants. Although, there is a great multiplicity of the methods used for the determination of antioxidant activity, there is no approved standardized in vitro method to evaluate the antioxidants of interest. This article presents a critical review of the various in vitro methods used for the determination of antioxidant activity and their merits and limitations.
Cr(III), Mn(II) and Fe(III) complexes derived from the quadruple potential dithione heterocyclic thiosemicarbazide ligand (H(2)PET) have been prepared and characterized by conventional techniques. The isolated complexes were assigned the formulae, [Cr(HPET)(H(2)O)(2)Cl(2)]·3H(2)O, [Mn(HPET)(H(2)O)Cl](2) and [Fe(HPET)(H(2)O)(2)Cl(2)]·H(2)O, respectively. IR data revealed that the ligand behaves as monobasic bidentate through (CN)(py) and (CS) groups in both Cr(III) and Fe(III) complexes. In the binuclear Mn(II) complex, H(2)PET acts as NSNS monobasic tetradente via (CN)(py), (CS), (CS) and the new azomethine, (NC)(*) groups. An octahedral geometry for all complexes was proposed. The bond lengths, bond angles, HOMO, LUMO and dipole moment have been calculated by DFT using materials studio program to confirm the geometry of H(2)PET and its metal complexes. The ligand association constant and the stability constants of its complexes in addition to the thermodynamic parameters were calculated from pH metrically at 298, 308 and 318°K in 50% dioxane-water mixture, respectively. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats-Redfern and Horowitz-Metzger methods. Moreover, the anti-oxidant (using ABTS and DPPH methods), anti-hemolytic, and cytotoxic activities of the compounds have been tested.
Binuclear Cu(II), Co(II) and Ni(II) complexes derived from N(1)-ethyl-N(2)-(pyridin-2-yl) hydrazine-1,2-bis(carbothioamide) (H(2)PET) have been prepared and characterized by elemental analysis, spectral (IR, UV-vis, EI mass, ESR and (1)HNMR) and magnetic measurements. The isolated complexes assigned the general formula, [M(HPET)(H(2)O)(n)Cl](2)·xH(2)O where M=Cu(II), Co(II) and Ni(II), n=2, 1, 0 and x=0, 0.5 and 0, respectively. IR data revealed that the ligand behaves as monobasic tridentate through (CN)(py), (C-S) and new azomethine, (NC)(∗) groups in the Co(II) complex but in Cu(II) complex, the ligand coordinate via both (CS) groups, one of them in thiol form as well as the new azomethine group. In Ni(II) complex, H(2)PET acts as NSNS monobasic tetradente via (CN)(py), (C-S), (CS) and the new azomethine, (NC)(∗) groups. An octahedral geometry is proposed for all complexes. pH- metric titration was carried out in 50% dioxane-water mixture at 298, 308 and 318 °K, respectively and the dissociation constant of the ligand as well as the stability constants of its complexes were evaluated. Also the kinetic and thermodynamic parameters for the different thermal decomposition steps of the complexes were determined by Coats-Redfern and Horowitz-Metzger methods. Moreover, the anti-oxidant, anti-hemolytic, and cytotoxic activities of the compounds have been tested.
Electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) proceeds very effectively at 0.585 V versus Ag ∣ AgCl in pH 9.0 buffered solution at ambient temperature using ABTS2− (2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) as an electron transfer mediator. The electrochemistry of ABTS2− and its oxidized form ABTS−, as well as the coupled homogeneous reactions were studied, and the rate constants were estimated using cyclic voltammetry and photometric methods (kapp,NADH=5.6–6.45×103 M−1 s−1). The mediated electrochemical oxidation was successfully coupled to horse liver alcohol dehydrogenase catalyzed oxidation of a meso-diol to a chiral lactone (yield 93.5%, ee>99.5%).
The currently reported values of the heat of formation of hydroperoxyl radical have been reviewed. A best value, ..delta..H/sub f//sup 0/(HO/sub 2/) = 3.5/sub -0.5//sup +1/ /sup 0/ kcal/mol, is recommended. 1 table.
The kinetics of reactions of t-butylperoxyl radicals in aqueous solution have been measured using electron paramagnetic resonance, ultraviolet absorption spectroscopy and gas chromatography. The rate constants for the overall self-reaction, the separate terminating and non-terminating reactions are very similar to those observed in non-polar solvents and the gas phase. The t-butoxyl radicals, formed by the non-terminating reaction, can either undergo scission, which leads to methylperoxyl radicals, or react with further t-butyl hydroperoxide to regenerate t-butylperoxyl radicals. The cross-termination reaction between methylperoxyl and t-butylperoxyl radicals is an important route in the overall termination sequence. The propagation reaction occurs significantly only at high concentrations of t-butyl hydroperoxide, ([ButOOH] > 0.3 mol dm–3) and its rate constant is much lower than that in non-polar solutions.
ESR equilibrium measurements in radical buffer systems yield a value of 76.0 kcal/mol for the OH bond energy in α-tocopherol.
In a recent letter by Sawyer, it was suggested that new values of the bond dissociation energies (BDE), defined for bond-breaking processes in the gas phase at 298 K, for a number of hydrogen- and oxygen-containing species could be determined from half-cell potentials. Discrepancies with accepted values for HO{sub 2} and HO{sub 2}{sup {minus}} were noted. We wish to point out that the bond dissociation energies for H-OO and H-OO{sup {minus}} that were derived by Sawyer are in serious disagreement with those established in the past decade by gas-phase chemical kinetics and photoelectron spectroscopy. These results were not cited by Sawyer. Moreover, computations utilizing half-cell potentials for the derivation of bond dissociation energies must account for substantial solvation effects. When properly calculated, these BDEs are, in fact, in accord with established values.
The total antioxidant-activity (TAA) has been evaluated as a marker of the deterioration of apple juice during storage. Unfortified juice, juice fortified with vitamin C, and an apple ''drink'' (6% juice), to which vitamin C (300 ppm) is added during manufacture, were evaluated. Vitamin C activity represented a minor fraction of the TAA (ca. 1%) of ''longlife'' apple juice, with chlorogenic acid and phloretin glycosides as the major identifiable antioxidants (ca. 32% and 11% of the TAA, respectively). Antioxidant activity ascribable to these substances was stable under the storage conditions examined, whereas ascorbic acid added into the juice was unstable; in fortified whole apple juice the TAA value correlated significantly with the decline in the ascorbic acid concentration, while in the apple drink there was a direct relationship between TAA and ascorbate.
A value of the enthalpy of formation of the phenoxy radical in the gas phase, Δ H ° ,298K (ϕO·, g) = 11.4 ± 2.0 kcal/mol, has been obtained from the kinetic study of the unimolecular decompositions of phenyl ethyl ether, phenyl allyl ether, and benzyl methyl ether Trivial names for ethoxy benzene, 2‐propenoxy (allyloxy) benzene, and α‐methoxytoluene, respectively
at very low pressures. Bond fission, producing phenoxy or benzyl radicals, respectively, is the only mode of decomposition in each case. The present value leads to a bond dissociation energy BDE(ϕO—H) = 86.5 ± 2 kcal/mol, 1 kcal = 4.18674 kJ (absolute)
in good agreement with recent estimates made on the basis of competitive oxidation steps in the liquid phase. A comparison with bond dissociation energies of aliphatic alcohols, BDE(RO—H) = 104 kcal/mol, reveals that the stabilization energy of the phenoxy radical (17.5 kcal/mol) is considerably greater than the one observed for the isoelectronic benzyl radical (13.2 kcal/mol). Decomposition of phenoxy radicals into cyclopentadienyl radicals and CO has been observed at temperatures above 1000°K, and a mechanism for this reaction is proposed.
The total reactive antioxidant potential (TRAP) of white and red wines is evaluated by a procedure based on the bleaching of pre-formed 2,2′-azinodi-(3-ethylbenzothiazoline-6-sulfonic acid radical cations. All the red wines considered presented TRAP values between 25.1 and 33.3 mM. The values obtained for the white wines were considerably smaller, ranging from 2.9 to 5.2 mM. The antioxidant potential measured in the wines is associated to the presence of compounds of low hydrophobicity.