Morteza Jabbari

The solid–liquid equilibria of a poorly water-soluble antioxidant agent namely naringoside were assayed to determine solubility in binary liquid mixtures of water + isopropanol (iso-PrOH) between 298.15 K and 320.15 K under atmospheric pressure. The mole fraction solubilities of naringoside in the saturated solution were determined using a combination of static shake-flask and ultraviolet spectrophotometry techniques. The dissolution behavior of naringoside was correlated with three solution models consisting of the van’t Hoff equation, the modified Apelblat equation and the Buchowski-Ksiazczak λH equation. The modified Apelblat equation was more consistent than the two other correlation models. Apparent thermodynamic analysis of naringoside dissolution was also performed at the mean harmonic temperature using the model parameters of the modified Apelblat equation. Furthermore, the Kamlet, Abboud and Taft Linear Solvation Energy Relationship (KAT-LSER) model was applied to analyze the effect of the solute–solvent intermolecular interactions on the solubility of this natural bioactive product. © 2018, Iranian Chemical Society.

The radical scavenging performance and antioxidant activity of γ-alumina nanoparticles towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical were investigated by spectroscopic and computational methods. The radical scavenging ability of γ-alumina nanoparticles in the media with different polarity (i.e. i-propanol and n-hexane) was evaluated by measuring the DPPH absorbance in UV–Vis absorption spectra. The structure and morphology of γ-alumina nanoparticles before and after adsorption of DPPH were studied using XRD, FT-IR and UV–Vis spectroscopic techniques. The adsorption of DPPH free radical on the clean and hydrated γ-alumina (1 1 0) surface was examined by dispersion corrected density functional theory (DFT-D) and natural bond orbital (NBO) calculations. Also, time-dependent density functional theory (TD-DFT) was used to predict the absorption spectra. The adsorption was occurred through the interaction of radical nitrogen N[rad] and NO2 groups of DPPH with the acidic and basic sites of γ-alumina surface. The high potential for the adsorption of DPPH radical on γ-alumina nanoparticles was investigated. Interaction of DPPH with Brønsted and Lewis acidic sites of γ-alumina was more favored than Brønsted basic sites. The following order for the adsorption of DPPH over the different active sites of γ-alumina was predicted: Brønsted base < Lewis acid < Brønsted acid. These results are of great significance for the environmental application of γ-alumina nanoparticles in order to remove free radicals. © 2018[/accordion]
AUTHOR KEYWORDS: Adsorption; Antioxidant; DFT; DPPH; Radical scavenger; γ-Alumina
INDEX KEYWORDS: Adsorption; Alumina; Aluminum oxide; Antioxidants; Chemical bonds; Computation theory; Density functional theory; Electromagnetic wave absorption; Hexane; Nanoparticles; Scavenging, 2 ,2-diphenyl-1-picrylhydrazyl; Dispersion-corrected density functional; DPPH; Environmental applications; Radical scavengers; Spectroscopic technique; Structure and morphology; Time dependent density functional theory, Free radicals
PUBLISHER: Elsevier B.V.

Jabbari, M., Teymoori, F. An insight into effect of micelle-forming surfactants on aqueous solubilization and octanol/water partition coefficient of the drugs gemfibrozil and ibuprofen (2018) 262, pp. 1-7.

DOI: 10.1016/j.molliq.2018.04.054

Aqueous micellar solubilization of ibuprofen and gemfibrozil drugs was investigated at constant temperature (25.0 ± 0.1) °C and atmospheric pressure using shake-flask and UV–vis spectrophotometric techniques. The solubility measurement was done in presence of three surfactants possessing different head groups, namely sodium dodecylsulfate (anionic SDS), cethyltrimethylammonium bromide (cationic CTAB) and polyethylene glycol dodecyl ether (non-ionic Brij 35) as well as their binary mixtures. The micellar solubility descriptors of χ (molar solubilization capacity), K (micelle–water partition coefficient), and ΔGs ∘ (standard free energy of solubilization) were obtained to estimate quantitatively the solubilization efficiency of the surfactant systems. Moreover, the octanol-water partition coefficient of these drugs was also evaluated in the micellar solutions. The results obtained in the aqueous micellar system demonstrate that, irrespective of the surfactant type, the solubility of drugs increases with increasing the concentration of micelles. It was found that the solubility of ibuprofen and gemfibrozil in Brij 35 and CTAB solutions, respectively is higher compared to that in the other surfactants. However, the partition coefficients of these drugs show an inverse trend with solubility data. Finally, the effect of the surfactant type on solubility enhancement of the drugs is explained in terms of possible interactions between the drug and the micelle. © 2018 Elsevier B.V.

The autoprotolysis process in aqueous co-solvent mixtures containing 0–60% (v/v) acetonitrile (ACN) was investigated at constant temperature 25.0 ± 0.1°C by using a high-precision and rapid potentiometric technique. During all measurements, the ionic strength was adjusted to 0.25 mol dm−3 with one of the supporting electrolytes KNO3, NaNO3 or KNO3/NaNO3 mixture (1:1) and the autoprotolysis constants (pKap) were calculated from potentiometric data. In the present study, the variation of the pKap values with co-solvent composition was analysed based on non-specific and specific solute–solvent interactions using the Kamlet, Abboud and Taft (KAT) approach. The experimental results obtained show that the general trend of autoprotolysis constants in different ionic media is as follows: KNO3 > NaNO3/NaNO3 > NaNO3, and these variations increase with increasing the amount of co-solvent ACN. The effect of ionic media used on the pKap values is discussed in terms of the weak interactions between the solvent system and the anionic and cationic components of the background electrolytes. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

In this research, the acid-base properties of two glycosilated flavanones namely naringoside and hesperidin were thermodynamically studied using spectrophotometric and potentiometric techniques at various temperatures (293.15–313.15) K. Because of very low solubility of these flavanones in aqueous solution, the protonation constants were obtained in ethanol-water mixtures (60–90% v/v) containing 0.10 mol dm− 3 tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte for naringoside and DMSO-water mixed solvents (50–95% v/v) containing 0.10 mol dm− 3 NaCl for hesperidin. Data process for the calculation of the protonation constants was done using the computer program STAR. The thermodynamic quantities (ΔG°, ΔH°, and ΔS°) of the protonation process were obtained by means of modified van't Hoff equation. It was found that the acid dissociation reaction is exothermic and the entropic contribution is low for both the flavanones. Finally, the influence of solute-solvent interactions on the protonation equilibria in various temperatures was modelled using Kamlet, Abboud and Taft (KAT) solvatochromic parameters and Hildebrand's solubility index. © 2017

This study describes the thermodynamics of dissolution of flavonoid naringin in different aqueous solutions of dimethyl sulfoxide (DMSO) containing 0-100% (w/w) under atmospheric pressure and over a temperature range of 298.15 to 325.15 K. The temperature dependence of solubility of naringin was analyzed using the modified Apelblat equation model, ideal model, and the λH equation model. In a mean harmonic temperature, the dissolution thermodynamic parameters of naringin containing , and were also calculated. Furthermore, the effects of solvent composition on the solubility of this flavonoid were analyzed in terms of Hildebrand's solubility parameter (δH) and Kamlet, Abboud and Taft (KAT) solvatochromic parameters (α, β, and π*). Finally, the preferential solvation parameters of the flavonoid naringin by DMSO (δxDMSO,S) were determined from experimental solubility data using the inverse Kirkwood-Buff integrals (IKBIs). It was found that water preferentially solvates naringin in water-rich mixtures while DMSO forms local solvation shells in compositions from 50% (w/w) or xDMSO = 0.19 up to pure co-solvent. Moreover, the structure of solvation shells of naringin in the under study mixtures was obtained by molecular dynamics (MD) simulations. The computational results showed that in the compositions xDMSO > 0.20, the probability of presence of the DMSO molecules in vicinity of naringin is more than water molecules. These findings are compatible with the available IKBI data. © The Royal Society of Chemistry.

Nano-structural particles of silica were synthesized from low-cost rice husk by acid leaching and further annealing at different temperatures. The surface of the nanoparticles was then functionalized using amino-silane to improve their adsorption properties. The structure of the nano-absorbent was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and thermal gravimetric analysis (TGA). The efficiency of the formed absorbent for the adsorption of quercetin, a plant flavonoid with potent antioxidant activity, was examined in different compositions of water-ethanol mixture (0-100% by v/v). In the batch experiments, the effect of variation of initial concentration of quercetin, pH of solution, and solvent composition was explored on the adsorption behavior. The equilibrium adsorption data were better represented by the Freundlich isotherm model rather than the Langmuir model. In addition, the optimum conditions for quercetin adsorption were achieved at alkaline pH ranges. Furthermore, a significant relationship was found between the adsorption capacity and the extent of preferential solvation of quercetin by ethanol in the binary mixture. Modeling the rate of adsorption was done through different kinetic equations. The results indicated that the adsorption kinetics was well described by the pseudo-second-order model. © 2017 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

The solubility of the antioxidant flavonoid naringenin as well as its preferential solvation was studied in different aqueous solutions containing 0–100 % (v/v) of acetonitrile (ACN) and 1,4-dioxane (DOX) at temperature 25.0 ± 0.1 °C. From the solubility data, both the Gibbs energy changes involved with the solublization process, ΔGs o, and the preferential solvation parameters of the solute naringenin by these co-solvents, δxcosolv,S, were determined. The results show that the equilibrium solubility increases with increasing co-solvent concentration. Moreover, it became clear that the preferential solvation of naringenin is sensitive to changes in solvent composition, so the preferential solvation parameters δxACN,S and δxDOX,S are negative in water-rich mixtures but positive in compositions from 50 % (v/v) ACN (xACN = 0.25) and DOX (xDOX = 0.17) up to the pure co-solvents. Possibly, in water-rich mixtures the structuring of water molecules around the non-polar groups by hydrophobic hydration contributes to lowering of the net δxcosolv,S to negative values. The preferential solvation by the co-solvent in the range 50–100 % (v/v) could be related to the greater basicity of the co-solvents and its interactions with hydroxyl groups of the flavonoid. © 2016, Springer Science+Business Media New York.

The equilibrium solubility of flavonoid chrysin was evaluated using UV-Vis spectrophotometric method in various mixed solvents comprising 0-100% (v/v) dimethylformamide (DMF) and tetrahydrofuran (THF) in water and constant temperature (25.0 ± 0.1) °C. From solubility data, the Gibbs free energy changes involved with the dissolution process of chrysin were also determined. The obtained results showed that the solubility of chrysin increases by increasing the DMF and THF proportion in solution. Furthermore, the preferential solvation parameters of the solute chrysin by co-solvents DMF and THF, δxcosolv,S, were derived using the inverse Kirkwood-Buff integrals (IKBI) approach. From the δxcosolv,S data, it was found that water is the preferred solvent in the solvation shell of chrysin in water-rich mixtures but the co-solvents DMF and THF are preferred in intermediate compositions to pure co-solvent. The variation of this parameter in the binary mixtures studied is discussed based on types of intermolecular solute-solvent interactions and structural characteristics of flavonoid chrysin. © 2016 Elsevier B.V. All rights reserved.

The proton dissociation equilibria of ascorbic acid were investigated using a combination of spectrophotometric/potentiometric techniques at constant temperature 25.0 ± 0.1 °C. The study was carried out over a wide range of ionic strengths of 0.1-3.0 mol dm-3 NaClO4 in ethanol-water mixture (1:1). The Gran's method was used for glass electrode calibration to obtain pH readings based on the concentration scale (pcH). Data process for calculation of the protonation constants was done using the STAR (stability constants by absorbance reading) computer program. The dependence on ionic strength of the constants was analyzed by means of the SIT approach (specific ion interaction theory). In addition to the specific interaction parameters of the ionic species, the protonation constants at infinite dilution (zero ionic strength) were obtained. Finally, the thermodynamic functions ΔG0 (standard Gibbs free energy change) for the protonation processes were also calculated at different ionic strengths. © 2016 Sociedade Brasileira de Química.

The acid-base equilibria of two water-insoluble flavonoids, chrysin and daidzein, were studied using combined spectrophtometric/potentiometric measurements at constant temperature (25.0 ± 0.1) °C. The investigation was performed over a wide range of ionic strengths of 0.101-3.503 mol kg-1 NaClO4 medium in ethanol-water mixture (1:1 v/v). The Gran's method was used for glass electrode calibration to obtain pH readings based on the concentration scale (pcH). Data process for calculation of the protonation constants was done using the STAR computer program. The dependence on ionic strength of the constants was successfully modeled by means of the Brönsted-Guggenheim-Scatchard Specific Ion Interaction Theory (SIT). Other than the specific interaction parameters of the ionic species, the protonation constants at infinite dilution (zero ionic strength) were obtained. The thermodynamic functions ΔG0 (standard Gibbs free energy change) for the protonation processes were also calculated at different ionic strengths. © 2016 Elsevier B.V. All rights reserved.

The antioxidant performance of flavonoid naringenin was investigated in terms of the DPPH free radical scavenging activity (RSA) in different aqueous micellar media using UV-vis spectrophotometric technique. The DPPH assay was done at (25.0 ± 0.1). °C and various concentrations of anionic amphiphile of sodium dodecylsulfate (SDS) and cationic amphiphile of cethyltrimethylammonium bromide (CTAB). The kinetics of the antioxidant behavior of naringenin was also evaluated in the micelle systems. The RSA values and kinetic data obtained in the model self-assembled system demonstrate that activity and rate of the DPPH radical scavenging increase with increasing concentration of micelles SDS and CTAB. It was found that these abilities in SDS solution are higher compared to that in the colloidal aggregated CTAB surfactant. Finally, the micellar effects on the antioxidant efficiency were explained in terms of possible interaction modes between naringenin and the micellar surfaces. © 2015.

The antioxidant ability of bioactive agent hesperidin was assessed in terms of radical-scavenging activity (RSA) against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical in aqueous colloidal media containing micelle using UV-vis spectrophotometry. The DPPH assay was carried out at 25.0 ± 0.1°C and cationic surfactant CTAB and anionic surfactant SDS at various concentrations above the critical micelle concentration (CMC). The rates of the antioxidant reaction (Rs) of hesperidin were also measured in the micelle systems. The activity and rate of the DPPH radical scavenging by hesperidin were found to depend on concentration and nature of the surfactants used, so that both RSA and Rs values increase with increasing concentration of micelles CTAB and SDS. Finally, the micelle effects on the antioxidant efficiency were explained based on possible interaction modes between hesperidin and the micellar surfaces. © 2016 The Chemical Society of Japan.

The stoichiometric dissociation constants (pK) of gallic acid were determined in water and several mixed solvents comprising 10-90% (v/v) acetonitrile in water at a temperature of 24.0 ± 0.5 °C and an ionic strength of 0.10 mol dm- 3 KCl medium. In this study, the protonation equilibrium values were calculated from potentiometric measurements and the influence of organic solvent composition on the equilibria was correlated with Born electrostatic model and the Kamlet, Abboud and Taft (KAT) solvatochromic parameters of acetonitrile-water mixtures. The pK values obtained increase when the amount of acetonitrile solvent increases in system investigated. The KAT single and multiple correlation analysis suggest that the specific and non-specific solvent interactions including hydrogen-bond donor ability (α), hydrogen-bond acceptor ability (β) and dipolarity/polarizability (π∗) are dominating factors which control the protonation equilibria in system under study. © 2015 Elsevier B.V. All rights reserved.

The protonation equilibria for the flavonoid naringenin were studied at 25C using combined multi-wavelength spectroscopic and pH-potentiometric methods as a function of the ionic strength. Over a wide range of ionic strengths, 0.10-3.00 mol dm-3, the investigation was performed in different aqueous solutions of NaClO4 as the background electrolyte. The dependence on ionic strength of protonation constants was modeled by the Brönsted-Guggenheim-Scatchard Specific Ion Interaction Theory (SIT) and Pitzer approaches. Apart from the values of SIT interaction coefficients and Pitzer parameters, the protonation constants at infinite dilution (zero ionic strength) were obtained. On the basis of these results, it was found that Pitzer mode l gives more satisfactory results rather than the SIT method. [Figure not available: see fulltext.] © 2015 Indian Academy of Sciences.

Scavenging ability of three kinds of natural flavonoid antioxidants including chrysin, naringenin, and quercetin against the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical was evaluated by the UV-vis spectrophotometric technique in different aqueous mixtures of methanol (50%-90% v/v) at physiological pH. The studied flavonoids showed their activity to be comparable with ascorbic acid (vitamin C), which is used as a standard reference material in most testing methods. Our findings indicated that an increase in the organic solvent percentage (v/v) has different effects on the radical scavenging efficiency of flavonoids presumably due to solute-solvent interactions. These variations were analyzed in light of various simple and multiple regression equations using the normalized polarity parameter (ETN) and Kamlet, Abboud, and Taft solvatochromic parameters. Moreover, The IC50 values of the samples were then obtained by the Yasuda-Shedlovsky extrapolation procedure in pure water. © 2015 Published by NRC Research Press.

Kinetic study of the reaction of flavonoid naringenin with the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) was performed in different percentage compositions of aqueous ethanol (50-90% v/v) using spectrophotometric method. The reaction, which follows the mixed second-order rate law, was investigated under pseudo first-order conditions with respect to the DPPH radical, at (25.0 ± 0.1) °C and an ionic strength of 0.1 mol dm - 3. The rate of reaction was found to decrease with increasing organic solvent content in binary mixture. The reaction mechanism was inferred from the stoichiometry, kinetics, and product identification. Furthermore, the effects of solvent composition on the reaction rate in the mixed solvents were analyzed in terms of Reichardt parameter (ETN), and Kamlet, Abboud and Taft (KAT) solvatochromic parameters (α, β, and π*). To further investigate the solvent effects we theoretically studied the three antioxidant action mechanisms of naringenin using density functional theory (DFT) method. Reaction enthalpies related to these mechanisms were calculated in gas-phase, water, ethanol and 50-90% (by v/v) ethanol-water. It was found that theoretical findings are in good agreement with experimental results. © 2014 Elsevier B.V.

The antioxidant activity of three different classes of flavonoids including naringenin (flavanon), chrysin (flavone), and daidzein (isoflavone) as well as their complexes with Ce(IV) were assayed in different aqueous solutions of DMSO (50-80% v/v) at physiological pH using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method. The radical scavenging activity (RSA) of the samples was influenced by changes in solvent composition, and their variations were analyzed using the normalized polarity parameter (E T N) and Kamlet, Abboud, and Taft (KAT) equation. A very good linear correlation of the RSA versus E T N and also two parameters of KAT including π* (dipolarity/polarizability) and α (hydrogen-bond donating acidity) was obtained. The RSA values of the samples are also determined by the Yasuda-Shedlovsky extrapolation method at 0% of the organic solvent. Furthermore, it was found that the metal chelation enhances the RSA of the flavonoids. © 2012 Elsevier B.V. All rights reserved.