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Isothermal titration calorimetry (ITC) and batch calorimetry techniques have been used to evaluate the effect of added antioxidant
(Quercetin, QN) on the binding between a polymer/surfactant complex, namely the sodium salt of polystyrene sulfonate (PSS)
and typical anionic surfactant sodium dodecylsulfate (SDS). An indirect isotherm approximation m...
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... are polyphenolic compounds that occur in many species in the plant kingdom [9,10]. Flavonoids have attracted attention recently due to the fact that these com- pounds have been shown to possess excellent therapeutic characteristics, including acute high potency and low sys- temic toxicity. Quercetin (3,5,7,3 0 ,4 0 -pentahydroxyflavone; see Fig. 1) is one of the most common flavonoids present in nature. Quercetin is well known for its potent antioxidant behavior and metal ion chelating capacity; hence, it pos- sesses a variety of biological and biochemical effects including anti-inflammatory, antineoplastic, and cardio- protective activities [11][12][13][14][15]. However, in ...
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... Common methods employed to determine QR are chromatography, chronocoulometry, HPLC, controlled potential coulometry, UV-Vis spectroscopy, emission and absorption spectroscopy, mass spectroscopy and microcalorimetric determination [14][15][16][17][18][19][20][21]. These methods suffer from specificity and sensitivity. ...
The fabrication of differential pulse voltametry (DPV) sensor for the effective detection of Quercetin (QR) was achieved by modifying carbon paste electrode (CPE) with Iron decorated multi walled carbon nano tubes (Fe-MWCNTs) followed by drop casting of hexadecyltrimethylammonium bromide onto the surface for optimal results. Cyclic voltammetry and DPV techniques were used for qualitative and quantitative analysis of QR Quercetin respectively. The sensor revealed impressive electro-catalytic behavior towards oxidation of QR Quercetin with almost 6.4 times increase in current compared to bare carbon paste electrode CPE and also decrease in the energetics. Under optimum conditions, a wide linear dynamic range of 0.06 to 3000 μM, with a lower limit of detection, 1.20 nM with S/N = 3 was observed. Absence of peak for the interfering molecules such as Folic acid and Ascorbic acid makes it a unique sensor with significant analytical advantage. The quantification of QR Quercetin at this sensor was not affected by the presence of 1000 fold Uric Acid implying that the sensor is capable of specifically identifying QR Quercetin in a mixture of interfering molecules. In this paper, we demonstrate that with minimal use of modifiers and simple procedures of fabrication, the fabricated sensor exhibits excellent stability, reproducibility and swift responses. Application of the developed electrode was demonstrated by detecting QR Quercetin in wine and coconut water samples with satisfactory recoveries.
... Quercetin (3,5,7,3 0 ,4 0 -pentahydroxyflavone) is one of the most abundant flavonoids in the human diet and has become associated with a myriad of biological activities, many of which may contribute to the prevention of human disease. Quercetin is well known to be a potent antioxidant behaviour and metal ion chelating capacity; hence, it possesses a variety of biological and biochemical effects including antioxidative, free radical scavenging, antitumour, anti-inflammatory and cardioprotective activities (Cook & Samman, 1996; Singh & Marangoni, 2010). In recent years, the food industry has been faced with an increasing demand for active ingredients for food formulation. ...
The interactions of β-lactoglobulin (BLG) with total Acacia gum (TAG) in presence of quercetin have been investigated in aqueous solutions at pH 4.2 and 25 °C. Isothermal titration calorimetry (ITC) has been used to determine the type and magnitude of the energies involved in the complexation process. Dynamic light scattering (DLS), electrophoretic mobility (μE), turbidity measurements (τ), optical microscopy and Fourier transform infrared spectroscopy in total attenuated reflection mode (ATR-FTIR) were used as complementary methods to better understand the sum of complicated phenomena at the origin of thermodynamic behaviour.
Herein, the interaction of an antidiabetic drug, metformin hydrochloride (MHCl), and a cationic surfactant, cetylpyridinium bromide (CPB) is investigated in an aqueous medium. The critical micellar concentration (CMC) of CPB is estimated through conductivity experiments and found to be reduced on adding MHCl and further decreased in the presence of NaCl. The reduced CMC is attributed to the solubilization of MHCl by CPB through micellization and the micellization is found to be thermodynamically spontaneous that experiences an augmentation in the presence of NaCl. This is identified from the negative value of standard free energy (ΔG0m). The higher negative value of ΔG0m (-55.41 kJ mol-1) for CPB + MHCl + NaCl than CPB (-37.89 kJ mol-1) and CPB + MHCl (-34.08 kJ mol-1) is suggestive of the above phenomenon. The positive values of ΔS0m in all three cases confirm that the micellization is entropy driven. The binding of MHCl on CPB is quantified by estimating binding constant using the Benesi-Hildebrand (B-H) plot through UV-visible spectral methods. The binding constant values were calculated to be 2.70 M-1 for CPB + MHCl + NaCl compared to 1.258 M-1 for CPB + MHCl predicting a favoring of micellization in the presence of NaCl which is higher than that in the presence of co-solvents. The molecular interaction of MHCl and CPB is justified using FT-IR and NMR techniques. The surface properties of drug surfactant interactions are assessed using SEM techniques. The point of interaction between the drug and surfactant is visualized through the molecular docking approach. The results suggest that CPB would be an effective solubilizer for developing MHCl drug formulations.Communicated by Ramaswamy H. Sarma.
Isothermal titration calorimetry is a widely used biophysical technique for studying the formation or dissociation of molecular complexes. Over the last 5 years, much work has been published on the interpretation of isothermal titration calorimetry (ITC) data for single binding and multiple binding sites. As over 80% of ITC papers are on macromolecules of biological origin, this interpretation is challenging. Some researchers have attempted to link the thermodynamics constants to events at the molecular level. This review highlights work carried out using binding sites characterized using x-ray crystallography techniques that allow speculation about individual bond formation and the displacement of individual water molecules during ligand binding and link these events to the thermodynamic constants for binding. The review also considers research conducted with synthetic binding partners where specific binding events like anion-π and π-π interactions were studied. The revival of assays that enable both thermodynamic and kinetic information to be collected from ITC data is highlighted. Lastly, published criticism of ITC research from a physical chemistry perspective is appraised and practical advice provided for researchers unfamiliar with thermodynamics and its interpretation. Copyright © 2016 John Wiley & Sons, Ltd.
Quercetin is a flavonoid very well studied and has already entered clinical trials emerging as prospective anticancer drug candidate. In addition, quercetin has being reported to its free-radical scavenging activity and suggests potential uses for the prevention and treatment of pathologies as atherosclerosis, chronic inflammation, and others. However, quercetin is sparingly soluble in water, which may be responsible for its limited absorption upon oral administration. The solid dispersion of quercetin with polyvinylpyrrolidone Kollidon® 25 (PVP K25) suggests an interesting way to increase quercetin solubility, antioxidant activity, and consequently bioavailability. Then, the purpose of this study was to prepare solid dispersions of quercetin with PVP K25 and evaluate their thermal characterization, antioxidant activity and quercetin improvement solubility. For this purpose, quercetin-PVP K25 solutions were dried and quercetin-PVP K25 solids were obtained. The formation of quercetin-PVP K25 solid dispersion was evaluated by solubility studies, powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetry (TG), and antioxidant activity. It was observed that PVP K25 was able to provide quercetin clear aqueous solutions and that quercetin solubility was increased in a PVP K25 concentration dependent manner, improving solubility even 436-fold the pure quercetin. The results obtained with XRD, FT-IR, DSC, and TG demonstrated possible quercetin-PVP K25 solid dispersion formation. Besides, the antioxidant activity of the quercetin-PVP K25 solid dispersions dissolved in aqueous solution and pure quercetin dissolved in methanol showed IC50 value of 0.61 ± 0.03 and 1.00 ± 0.02 μg/mL, respectively, demonstrating that the solid dispersions presented a significant increase in antioxidant activity (P < 0.05). Putting results together, it was possible to conclude there was the formation of quercetin-PVP K25 solid dispersion.
Coacervation in mixtures of polyelectrolytes and surfactants with opposite charge is common in nature and is also technologically important to consumer health care products. To understand the complexation behavior of these systems better, we combine multiple experimental techniques to systematically study the polymer/surfactant binding interactions and the phase behavior of anionic sodium dodecyl sulfate (SDS) surfactant in cationic JR 400 polymer aqueous solutions. The phase-behavior study resolves a discrepancy in the literature by identifying a metastable phase between the differing redissolution phase boundaries reported in the literature for the surfactant-rich regime. Isothermal titration calorimetry analyzed within the framework of the simple Satake-Yang model identifies binding parameters for the surfactant-lean phase, whereas a calculation for polymer-bound micelles coexisting with free micelles is analyzed in the surfactant-rich redissolution regime. This analysis provides a preliminary understanding of the interactions governing the observed phase behavior. The resulting thermodynamic properties, including binding constants and the molar Gibbs free energies, enthalpies, and entropies, identify the relative importance of both hydrophobic and electrostatic interactions and provide a first approximation for the corresponding microstructures in the different phases. Our study also addresses the stability and metastability of oppositely charged polyelectrolytes and surfactant mixtures.
Isothermal titration calorimetry (ITC) is a biophysical technique for measuring the formation and dissociation of molecular complexes and has become an invaluable tool in many branches of science from cell biology to food chemistry. By measuring the heat absorbed or released during bond formation, ITC provides accurate, rapid, and label-free measurement of the thermodynamics of molecular interactions. In this review, we survey the recent literature reporting the use of ITC and have highlighted a number of interesting studies that provide a flavour of the diverse systems to which ITC can be applied. These include measurements of protein-protein and protein-membrane interactions required for macromolecular assembly, analysis of enzyme kinetics, experimental validation of molecular dynamics simulations, and even in manufacturing applications such as food science. Some highlights include studies of the biological complex formed by Staphylococcus aureus enterotoxin C3 and the murine T-cell receptor, the mechanism of membrane association of the Parkinson's disease-associated protein α-synuclein, and the role of non-specific tannin-protein interactions in the quality of different beverages. Recent developments in automation are overcoming limitations on throughput imposed by previous manual procedures and promise to greatly extend usefulness of ITC in the future. We also attempt to impart some practical advice for getting the most out of ITC data for those researchers less familiar with the method.
The solubilization of four phenolic antioxidants, namely p-hydroxybenzoic acid (PHBAA), syringic acid, sinapic acid, and quercetin in micelles of an ethylene oxide (EO)-propylene oxide (PO) triblock copolymer Pluronic® P104 (EO27-PO61-EO27, PPO mol wt=3540, % PEO=40) was examined at different temperatures, pHs, and in the presence of sodium chloride. The nano-size core-shell micelles of P104 characterized by dynamic light scattering had hydrodynamic diameter of about 18-20 nm with low polydispersity. Antioxidants induced micellization and micellar growth were observed. The critical micellar concentration (CMC), critical micellar temperature (CMT), cloud point (CP) of P104 decreased due to solubilization and interactions of antioxidants. The solubilization was favored at higher temperature, pH and in the presence of salt and follows the order PHBA>syringic acid>sinapic acid>quercetin which corresponds to the trend in their aqueous solubility. The location of antioxidant in micelles observed from NOESY spectra. Structure and hydrophobicity of antioxidants were found to be governing factors for their interaction and location in the micelles.
The interaction between hydrophobically modified cationic polysaccharides based on dextran and a flavonoid drug (Rutin) was studied by isothermal titration calorimetry (ITC) and fluorescence spectroscopy, in order to assess the factors responsible for the interaction and characterize its energetics, as well as for evaluating their encapsulation capacity, for possible applicability of these polymers as drug delivery vectors. To address the importance of the hydrophobic pendant groups in the solution behavior of these polymer/drug systems, we also studied the interaction of Rutin with a cationic surfactant, cetyltrimethylammonium chloride (CTAC). The interaction enthalpies and drug binding constants for D40R30/Rutin systems were derived from ITC through a simple binding model. The binding constants were independently derived from fluorescence results, with fair agreement between the parameters obtained from both methods. By changing the Rutin concentration, we were able to get evidence for a solubility enhancement induced by the presence of the polymers, a promising effect regarding its use to improve bioavailability.
