Thermodynamic Characteristics of Complex Formation of L-Lysine With Isomers of Pyridinemonocarboxylic Acid in Aqueous Solution

The interactions of the polar basic amino acid L-lysine (Lys) with structural isomers of pyridine monocarboxylic acid: picolinic (PA), nicotinic (NA) and isonicotinic (INA) acids in an aqueous solution were studied by solution calorimetry at 298.15 K. The experimental data allowed us to establish the formation of Lys complexes with the indicated isomers with a stoichiometry of 1:1. The thermodynamic parameters were determined: binding constants, enthalpies of complex formation, Gibbs energies and entropies. The stability of the formed complexes depends on the structural isomerism of pyridine carboxylic acid and increases in the series: PA NA INA. It was shown that the main contribution to the stabilization of the formed complexes is made by the enthalpic component of the Gibbs free energy of complex formation.