Spectral and Polarographic studies of ternary complexes of copper [II] with amino acids

ABSTRACT

Ternary complexes [Cu[thr] [hist] [H2O]], [Cu [thr] [val]], [Cu [thr] [alan]], [Cu [thr] [ser]] and [Cu [thr] [gly]] [where thr, hist, val, alan, ser, gly stand for threonine, histidine, valine, alanine, serine, glycine residues respectively] have been isolated and characterized by elemental analysis, infra-red and electronic spectral studies. These studies show the complexes to be of tetragonally distorted octahedral structure. On the basis of the ligand field strength values, v max, the strength of these ligands is in the decreasing order as shown below hist > val > alan > ser > gly In 0. 1 M aqueous sodium perchlorate medium all of the complexes undergo single step two electron irreversible reduction at the dropping mercury electrode [dme]. From the characteristics of the irreversible waves, the rate constant, Kr, at a certain reference potential, -0.30V vs. SCE, have been calculated. The mechanism of the electro-reduction of these complexes does not change with temperature except that of [Cu [thr] [hist] [H2O]. The values of E1/2 of these complexes shift toward more positive values and Kr values increase with the rise of temperature, showing facile electro-reduction at higher temperatures. A correlation has been made between spectral and polarographic behaviour by comparing the polarographic characteristics [E1/2, Kr etc] with spectral parameters, v max. All of the complexes except [Cu [thr] [gly]] follow the trend that the higher the value of v max, the more negative will be the values of E1/2 and lower the value of Kr. On the basis of micro symmetry D2h and orientation of the depolarizer at the electrode surface, and attempt has also been made to rationalize the data by proposing a mechanism for the electro-reduction of the depolarizer at the electrode surface