Influence of Sodium Salicylate on Self-Aggregation and Caffeine Solubility in Water-A New Hypothesis from Experimental and Computational Data.

The present study analyzed experimental data from volumetric and viscosimetric measurements and computational simulations to understand caffeine hydration and aggregation properties in 0.1 mol∙kg-1 of sodium salicylate aqueous solution. Sodium salicylate reduces the bitter taste and increases the solubility of caffeine in water, which is the main reason for their combination in food products. The results noted in volumetric and viscosimetric measurements indicate that sodium salicylate promotes the self-aggregation of caffeine in water. After self-aggregation, the hydration number of caffeine significantly increases. Molecular simulations have allowed us to hypothesize how salicylate increases caffeine solubility. At the molecular level, relocating salicylate moiety from the parallel stacking (π-π) aromatic complex with caffeine and its hydration could be the main reason for increasing the solubility of caffeine in water. The presented study provides clear guidelines on the choice of additives to increase caffeine's solubility in aqueous media. The choice of salicylate as an additive to increase the solubility of caffeine is very important because caffeine and salicylate are found in combination in a large number of formulations.

Studies of the Formation of Inclusion Complexes Derivatives of Cinnamon Acid with α-Cyclodextrin in a Wide Range of Temperatures Using Conductometric Methods.

The electrical conductivities of aqueous solutions of sodium salts of trans-4-hydroxycinnamic acid (trans-p-coumaric acid), trans-3,4-dihydroxycinnamic acid (trans-caffeic acid), trans-4-hydroxy-3-methoxycinnamic acid, (trans-ferulic acid) and trans-3-phenylacrylic acid (trans-cinnamic acid) with α-cyclodextrin were measured in the temperature range of 288.15 K-318.15 K. For the first time in the literature, using the limiting molar conductivity (Λmo) obtained from conductivity measurements, the values of the complexation constants (Kf) of the salts of phenolic acid derivatives with α-cyclodextrin were determined using a modified low concentration chemical model (IcCM). An attempt was also made to analyze the individual thermodynamic functions ΔGo, ΔHo and ΔSo describing the complexation process as a function of temperature changes. The obtained results show that the process of formation of inclusion complexes is exothermic and is spontaneous.

Neutral glycoconjugated amide-based calix[4]arenes: complexation of alkali metal cations in water.

Cation complexation in water presents a unique challenge in calixarene chemistry, mostly due to the fact that a vast majority of calixarene-based cation receptors is not soluble in water or their solubility has been achieved by introducing functionalities capable of (de)protonation. Such an approach inevitably involves the presence of counterions which compete with target cations for the calixarene binding site, and also rather often requires the use of ion-containing buffer solutions in order to control the pH. Herein we devised a new strategy towards the solution of this problem, based on introducing carbohydrate units at the lower or upper rim of calix[4]arenes which comprise efficient cation binding sites. In this context, we prepared neutral, water-soluble receptors with secondary or tertiary amide coordinating groups, and studied their complexation with alkali metal cations in aqueous and methanol (for the comparison purpose) solutions. Complexation thermodynamics was quantitatively characterized by UV spectrometry and isothermal titration calorimetry, revealing that one of the prepared tertiary amide derivatives is capable of remarkably efficient (log K ≈ 5) and selective binding of sodium cations among alkali metal cations in water. Given the ease of the synthetic procedure used, and thus the variety of accessible analogues, this study can serve as a platform for the development of reagents for diverse purposes in aqueous media.

Viscosity B-Coefficient for Sodium Chloride in Aqueous Mixtures of 1,4-Dioxane at Different Temperatures.

Viscosities of sodium chloride solutions in water-1,4-dioxane binary mixtures with mole fractions of 1,4-dioxane, x(D) = 0.05, 0.10, 0.15 and 0.20, in the temperature range from 278.15 to 318.15 K were determined. The relative viscosity data have been analyzed and interpreted in terms of the rearranged Jones-Dole equation, (η(r) - 1) - Ac(1/2) = Bc. The viscosity A-coefficients were calculated from Falkenhagen and Vernon theory by help of the literature limiting ionic conductivity data and B-coefficients were estimated from linear plots. All B-coefficients obtained for NaCl water-1,4-dioxane binary mixtures are positive at all temperatures. These data were compared with the data for NaCl in aqueous medium at different temperatures reported in literature. The ion-ion, ion-solvent and solvent -solvent interactions have been discussed.

Ion-Association Reaction of Rb+ and Br- in 2-Methylpropan-2-ol + Water Mixtures.

The molar conductivity of RbBr solutions in 2-methylpropan-2-ol (tert-butanol) + water mixtures at alcohol mass fractions of 0.70, 0.80 and 0.90 was measured at temperatures from 288.15 to 308.15 K at 5 K intervals. The limiting molar conductivity (Δo) and the ion-pair formation constant (KoA) were determined by the Lee-Wheaton conductivity equation. Thermodynamic quantities, Gibbs energy (ΔGo), enthalpy (ΔHo) and entropy (ΔSo), for the ion-association reaction were derived from the temperature dependence of KoA; the activation energy of the ionic movement (ΔH*) was derived from the temperature dependence of Λo. These values were compared with those obtained earlier for HBr and NaBr in the same mixtures.