Volume Effects in Interactions between L-Histidine and Pyridine Monocarboxylic Acid Isomers in an Aqueous Buffer Solution

Abstract

Densimetry is used to study the interaction between L-histidine (His) and nicotinic (NA), isonicotinic (INA), and picolinic acids (PA) in an aqueous buffer solution in the 288.15–313.15 K range of temperatures. Data on density are used to determine the apparent molar volumes and limiting apparent molar volumes of pyridine monocarboxylic acid (PyCOOH) isomers at infinite dilution, along with their temperature derivatives in a buffer solution containing the amino acid. Unlike the linear concentration dependences of the apparent molar volume of PyCOOH isomers in a buffer solution, the analogous dependences of ternary systems (PyCOOH–His–buffer) are nonlinear, indicating the formation of a molecular complex between the solutes. Limiting apparent molar expansibilities and their temperature derivatives are determined. Their values suggest that the ordering of the solvent grows in the series of isomers PA → NA → INA upon adding the amino acid to a buffer solution of PyCOOH. It is shown that the limiting apparent molar volumes of transferring PyCOOH from a buffer to a His-containing buffer solution have positive values and grow in the studied range of temperatures. The discussion of the results is based on the dominant types of molecular interactions between the solute and solvent using the Gurney model.