Omar Houache

Reversed phase High Performance Liquid Chromatography used for the physicochemical and thermodynamic characterization of piceatannol/β-cyclodextrin complex

Piceatannol is one of resveratrol derivatives having health promoting potential. However, its low water-solubility and bioavailability could limit its use in both food and pharmaceutical fields. The aim of this work is the study of piceatannol complexation by β-cyclodextrin (β-CD) in aqueous media. The complex formed could improve the bioavailability, the solubility and the stability of piceatannol. The method used was based on RP-HPLC in which, β-CD was added to methanol/water mixtures mobile phases. The apparent formation constant of piceatannol/β-cyclodextrin complex was determined. Within the concentration interval studied (0-4 mM), whenever the concentration of β-CD increased, retention time of piceatannol decreased; indicating an enhancement of solubility due to the formation of the piceatannol/β-CD complex. The formation constants (KF) of the piceatannol/β-CD complex varied significantly with both the methanol concentration in the water-methanol mixture and the temperature. Moreover, in all the physicochemical conditions tested, the stoichiometry of piceatannol/β-CD complex was 1:1. Finally, the thermodynamic parameters were determined: ΔG°=-13.123 kJ mol(-1), ΔH°=-33. 265 kJ mol(-1) and ΔS°=-67.559 J mol(-1) K(-1).

A DFT method for the study of the antioxidant action mechanism of resveratrol derivatives

Quantum-chemical calculations using DFT, have been performed to explain the molecular structure antioxidant activity relationship of resveratrol (RSV) (1) analogues: 3,4-dihydroxy-trans-stilbene (3,4-DHS) (2); 4,4′-dihydroxy-trans-stilbene (4,4′-DHS) (3); 4-hydroxy-trans-stilbene (4-HS) (4); 3,5-dihydroxy-trans-stilbene (3,5-DHS) (5); 3,3′-dimethoxy-4,4′-dihydroxy-trans-stilbene (3,3′-DM-4,4′-DHS) (6); 2,4-dihydroxy-trans-stilbene (2,4-DHS) (7) and 2,4,4′-trihydroxy-trans-stilbene (2,4,4′-THS) (8). It was found that all compounds studied were effective antioxidants with the exception of 3, 5-DHS. The high antioxidant activity of both 3, 3′-DM-4, 4′-DHS and 3, 4-DHS may be due to the abstraction of the two hydrogen atoms of the para and ortho-position hydroxyls respectively, to form a quinone structure. Our results revealed that the antioxidant pharmacophore of 2,4-DHS and 2,4,4′-THS, exhibiting higher antioxidant activity than resveratrol, is the 2-hydroxystilbene, rather than 4-hydroxystilbene. Experimental observations were satisfactorily explained and commented.

Effect of Temperature and Solids on the Rheology of Water-in-Oil Emulsions

Abstract This article reports on an experimental study on the effect of temperature on the viscosity behavior of water-in-oil emulsions with added solids. The experimental conditions consisted of combinations of values of temperature (T) and solids volume fraction (φ s ). The temperature had the values of 10, 20, 30, 40, 50, and 70°C; whilst the solids volume fraction had values between 0 and 0.025. All the treatments had been chosen such that each value of φ s was used once in conjunction with each value of T. In order to obtain an estimate of the experimental error in the experiment, it was necessary to replicate the entire set of experiments a total of three times. Statistical analysis of the experimental data pointed to the existence of an interaction of solids and temperature and to the relative viscosity being a function of these two factors. A model based on the data has been developed to evaluate the relative viscosity as a function of T and φ s for shear rates above 270 s−1.