Spatial structure, thermodynamics and kinetics of formation of hydrazones derived from pyridoxal 5′-phosphate and 2-furoic, thiophene-2-carboxylic hydrazides in solution

Abstract

© 2019 Elsevier B.V. The spatial structure of pyridoxal 5′-phosphate hydrazones of 2-furoic hydrazide; thiophene-2-carboxylic hydrazide in aqueous solution was studied by means of quantum chemical calculations and NOE experiment. The hydrazones could exist as a mixture of different conformers; however, the specific ones could be suggested from experimental and calculated data. The stability constants of hydrazones at pH of 1.9; 6.6; 7.0; 7.4 were determined using UV–Vis spectroscopy. Rate constants of the hydrazone formation and hydrolysis reaction within the range of 6.6–7.4 pH were obtained. Isothermal calorimetric titration was performed in order to determine the change in the free Gibbs energy, enthalpy and entropy of hydrazones formation at pH of 6.6. Hydrazones were synthesized and characterized by means of 1 H, 13 C, 31 P NMR, IR, UV–Vis, fluorescent, MS-spectroscopy as well as DSC and elemental analysis.