Copper(II) complexation by 6-(alkylamino)methyl-2-hydroxymethylpyridines with varying alkyl chain length in aqueous solutions. Kinetics and thermodynamics

Kinetic parameters have been obtained from stopped-flow experiments for the complexation of copper(II) by a series of 6-(alkylamino)methyl-2-hydroxymethylpyridines with alkyl chains varying from C1 to C-14, in aqueous solutions (T = 25-degrees-C, pH 2.0-5.0). The apparent rate constants for complex formation at pH 3.5 were found to be weakly dependent on the alkyl chain length. A kinetic model has been proposed which is in excellent agreement with the experimental data, especially the change of the reciprocal relaxation time (or observed rate constant) with pH. Even in a fairly acidic pH range, the contribution of the unprotonated ligand species cannot be neglected. Equilibrium measurements were carried out in parallel using UV-visible spectrophotometry and potentiometric titrations in order to determine the values of thermodynamic parameters such as ionization and stability constants.