Solubility and dissolution thermodynamics of L-histidine and L-tryptophan in aqueous ethanol solution at five equidistant temperatures

Abstract

This study highlights the saturated solubilities and dissolution thermodynamical properties of two very important amino acids viz. L-histidine and L-tryptophan having various roles in many field in pure aqueous and aqua-ethanol medium at particular as well as range of temperature employing static gravimetric method which is very systematic and error free. Finding confirms that L-histidine shows more solubility in water rich region and L-tryptophan shows more solubility in organic rich region. L-tryptophan has an extra benzene ring which makes L-tryptophan more covalent than L-histidine moiety. Consequently, solubility of former in water rich region becomes low. In connection with those mentioned properties other various physiochemical parameters like co-solvent diameter, apparent dipole moment, apparent molar volume, solvent diameter etc. are also estimated. All observations are explained clearly on the ground of several solution related interactions namely cavity forming, solvent-solvent, solvent-solute interactions etc. Both total and chemical transfer Gibbs energies as well as entropies are calculated and explained to give support to stability and variation of solubility in both aqueous and aqua-ethanol media.