Journal
JOURNAL OF CHEMICAL THERMODYNAMICS
Volume 161, Issue -, Pages -Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jct.2021.106552
Keywords
Calorimetry; Volume; Basic amino acids; Nicotinic acid; Complex formation
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Funding
- Russian Foundation for Basic Research [1843370018]
- G.A. Krestov Institute of Solution Chemistry of the Russian Academy of Science [01201260481]
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The interactions between the polar basic amino acids Lys and His with the heterocyclic ligand NA were studied in different solutions, with His showing more efficient stabilization with NA in buffer media. The affinity of Lys to binding with NA decreases with increasing pH.
Interactions of the polar basic amino acids, L-lysine (Lys) and L-histidine (His), with heterocyclic ligand, nicotinic acid (NA), in pure water and in phosphate buffer solution (pH 7.4) were studied by calorimetry and densimetry. Under the experimental conditions chosen, thermodynamic parameters of complex formation (lgK(c), Delta(c)G, Delta H-c, Delta S-c) as well as the hydration enthalpies of different ionized forms of amino acids have been calculated at 298.15 K. The stoichiometry of complexes between Lys/His and NA was determined. The affinity of Lys to binding with NA decreases with increasing pH, the association process being less favorable. The more efficient stabilization of complexes between His and NA was exhibited in buffer media than in water. The apparent molar volumes, partial molar volumes and partial molar volume of transfer of NA from pure solvent (water/buffer) to mixed amino acid solution at infinite dilution have been evaluated. Their values obtained are lower for aqueous solutions than buffer systems. The dependence of thermodynamic characteristics obtained on molecular structure, ionization and hydration state of the solutes was analyzed. The dominant types of driving forces in the complex formation process of polar basic amino acids (Lys, His) with nicotinic acid were found for water and buffer solution. (C) 2021 Elsevier Ltd.
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