Effects of Structural Isomerism of Pyridine Monocarboxylic Acids on the Volume Properties of Their Buffer Solutions

The intermolecular interactions of the structural isomers of pyridine monocarboxylic acid (PA, NA, INA) in aqueous buffer solutions were studied by densimetry over the temperature range from 288.15 to 313.15 K. The apparent molar volumes of picolinic (PA), nicotinic (NA), and isonicotinic (INA) acids in a buffer solution (pH 7.4) were determined from the experimental densities of solutions; the concentration dependences of the apparent molar volumes are linear. The partial molar volumes and expansibilities at infinite dilution, as well as their temperature derivatives, were determined. Their values suggest the destructive behavior of PyCOOH isomers in the buffer solutions. It was revealed that this effect on the structure of the buffer solution decreases in the series PA → NA → INA, the INA buffer solution being the best-structured system among the given solutions.