Aqueous Solubility of Some Natural Phenolic Compounds

Abstract

In this work, the aqueous solubilities of two hydroxybenzoic acids (gallic and salicylic acid) and three phenylpropenoic acids (trans-cinnamic, ferulic, and caffeic acids) are addressed. Measurements were performed, as a function of temperature, between 288.15 and 323.15 K, using the shake-flask method for generating the saturated aqueous solutions, followed by compositional analysis by spectrophotometric and gravimetric methods.The pH values of the saturated aqueous solutions were measured by potentiometry. Additional thermodynamic properties, which are fundamental for a better understanding of the solubilization process, as well as necessary for the modeling studies, such as melting temperatures and fusion enthalpies were determined by differential scanning calorimetry (DSC). Apparent acid dissociation constants (K a ) were obtained by potentiometry titration. The measured data were modeled with the cubic-plus-association (CPA) equation of state (EoS). This EoS is applied, for the first time, for multifunctional associating molecules, and the results indicate that it can adequately be used to represent the measured and other literature data with satisfactory accuracy.

Hypoglycemic and anti–hyperglycemic study of Gynura procumbens leaf extracts

“…Overall, the phenolic and flavonoid contents appear to decrease with increase in water content of the extraction solvent, contrary to the observed anti-hyperglycaemic activity of the extracts. It was noted earlier that the presence of a certain amount of water in an extraction solvent is necessary to enhance interaction of hydroxyl and/or carboxylic groups with water, to promote the dissolution of phenolics in the solvent [17] , but that as the amount of water is increased, the interaction is decreased by the benzene ring present in the structure hence restricting the solubility of phenolic compounds. Whole plant extracts are known to contain numerous compounds whose net observed pharmacological actions or inactions largely depend on synergistic or antagonistic interactions among these compounds [18] .…”

Pressurized liquid extraction of phenolic compounds from rice (Oryza sativa) grains

“…High pressure leads to greater contact between the extracting liquid and the solid matrix (Wang & Weller, 2006), while high temperature breaks the phenolic-matrix bonds and increases the solubility of the compounds in the extraction solvent (Mota, Queimada, Pinho, & Macedo, 2008). The efficiency of the PLE process therefore depends on the extraction temperature, pressure, time and solvent.…”

A calorimetric and equilibrium investigation of the reaction {methyl ferulate(aq)+H2O(l)=methanol(aq)+ferulic acid(aq)}

“…Indeed, the thermochemical literature on ferulic acid and methyl ferulate is sparse. In addition to the pK and D r H°vales given in table 4, the only other thermochemical data in the literature is that of Mota et al [15], who report the melting temperature, the molar enthalpy of fusion, and the solubility of ferulic acid in water from T = (288 to 323) K. At T = 298.15 K, the solubility of ferulic acid is 0.78 g Á dm À3 [15]. This corresponds to a saturation molality m(sat) = 0.00403 mol Á kg À1 .…”

“…Adjustment of these values gives pK = 4.30 for reaction (9) and pK = 8.81 for reaction (10) at I = 0. Mota et al [15] report pK = 4.61 for reaction (9) at T = 298.15 K but do not give the ionic strength. The selected pK values are the averages of the pK values at I = 0 obtained from the studies of Nordström and Lindberg [11], Casolaro et al [13], and Fazary and Ju [14].…”