The stability constants of copper(II) complexes with some alpha-amino acids in dioxan-water mixtures

In this study, the overall stability constants of copper(II) complexes with some a-amino acids (glycine, DL-alanine, DL-valine, L-leucine, L-asparagin e, L-glutamine) were determined by potentiometric titration in water, 25% d ioxan-75% water, 35% dioxan-65% water, 50% dioxan-50% water, and 60% dioxan -40% water. The titrations were performed at 25 degreesC, under nitrogen at mosphere, and the ionic strength of the medium was maintained at 0.10 M by using sodium perchlorate. The formation curves of their complexes ((n) over barp[L]) were obtained by means of the titration data. Then the stability constants were determined in relation to these curves. The mol ratio of cop per(II) to a-amino acid was also determined and it was found that the compl exes were CuL2 type. Another important result obtained was that the tendenc y of amino acids to form complexes with copper(II) was greater in dioxan-wa ter mixtures compared to water. (C) 2001 Academic Press.