Kinetic and thermodynamic parameters for Schiff's base formation between pyridoxal 5′-phosphate and n-hexylamine

Abstract

The kinetic and thermodynamic parameters for the reaction between pyridoxal 5′-phosphate and n-hexylamine in aqueous medium as a function of pH, at constant ionic strength (0.1) and temperatures of 10, 15, 20, and 30 °C have been calculated. The variation observed in the overall kinetic formation and hydrolysis constants of the corresponding Schiff's base can be accounted for on the basis of the protonation and reactivity of the substrates present (pyridoxal 5′-phosphate, n-hexylamine, and Schiff's base) in the medium as a function of pH. The first protonation, both of pyridoxal 5′-phosphate and of the Schiff's base, modifies the energies of activation corresponding to the formation and hydrolysis processes, respectively. The less negative charge the pyridoxal 5′-phosphate molecule bears, the more negative the ΔH and ΔS values become.