Solvent and pH Dependences of Mixing Enthalpies of <i>N</i>‑Glycylglycine with Protocatechuic Acid

Abstract

Protocatechuic acid (PA) is a natural phenolic compound which has been proven to have chemopreventive property against chemically induced carcinogenesis. The mixing enthalpies of PA with <i>N</i>-glycylglycine in sodium phosphate and potassium phosphate buffer solutions with different pH values have been investigated by mixing-flow isothermal microcalorimetry at <i>T</i> = 298.15 K. The heterotactic enthalpic interaction coefficients (<i>h</i>_<i>xy</i>) in the pH range of phosphate buffer solution from 3.0 to 8.0 have been calculated according to the McMillan–Mayer theory. Trends of the enthalpic pairwise interaction coefficients (<i>h</i>_<i>xy</i>) with increasing pH in both phosphate buffer solutions were obtained. The solvent and pH dependence of the <i>h</i>_<i>xy</i> were discussed in terms of molecular interactions between solvated solute molecules