Solvent Effect on Tautomeric and Microscopic Protonation Constants of Glycine in Different Aqueous Solutions of ۱,۴-Dioxane

Depending on the pH values of the media, an amphiprotic compound (such as glycine) may exist in four different microforms. Although, the neutral form of an amino acid is more lipophilic and hence more effective in diffusing through the cellular membrane as compared with the charged forms, the macroscopic protonation constants can provide no information about the equilibrium that produces HLo (with no charge) species. The tautomeric and the protonation microconstants can describe the amount of various microforms of an amino acid at different pH values. Aqueous-organic solvents, mainly ۱,۴-dioxane, mixtures have been widely used due to sparingly or insolubility of many compounds in pure water as solvent. Further, any physicochemical property of solution can be easily varied by changing the composition of water or the organic solvent in the mixtures. However, chemists have usually attempted to understand solvent effects in terms of polarity, defined as the overall solution capabilities that depend on all possible (specific and non-specific) intermolecular interactions between solute and solvent molecules. Many reports on solvent polarity scales have been published in the last few decades [۱]. Previously, the solvent effect on the protonation equilibrium was believed to be guided chiefly by electrostatic interactions (Born model) [۱]. However, recent studies have revealed that the change in macroscopic properties such as the dielectric constant of the solvent, cannot be the sole factor [۱]. It is desirable to develop other empirical functions to take into account the complete picture of all intermolecular forces acting between solute and solvent molecules.

کلیدواژه ها:

Solvent effect ، Kamlet-Taft ، Glycine