Effect of the Chain Length of N-Alkyl-β-alanine on Their Copper Complex Formation in Aqueous Solution

Abstract

Abstract The effects of the chain length of N-alkyl-β-alanine (NAA) (the number of carbon atoms in the alkyl chains; n=0, 2, 4, 6, 8, 10, 12) on the copper(II) complex formation and its properties were investigated. The complex formation constants for two-step reactions were determined by potentiometry using the selective electrodes of copper(II) and hydrogen ions. The values of the complex formation constants decreased with increasing chain length of the alkyl substituents, and became constant for the substituents longer than the butyl group. These results could be explained in terms of a steric hindrance effect of the N-alkyl substituents on these coordination reactions. Each logarithmic function of the solubility and of the solubility product of the 1(Cu):2(NAA)-complexes was found to be expressed, respectively, as a linear function of the number of carbon atoms in the alkyl group. From these data, the standard free energies of the formation and the precipitation of the 1:2-complexes from these constituent ions have been estimated, and a standard free energy diagram was constructed for 1:2-complex formation. It was concluded that the hydrophobic interaction is a driving force which promotes crystalline complex formation from the constituent ions.