POTENTIOMETRIC AND SPECTROSCOPIC STUDY OF SELENOMETHIONINE COMPLEXES WITH COPPER(II) AND ZINC(II) IONS

The stepwise stability constants of 1:1 and 2:1 complexes of selenomethionine (SeMet) with Cu-II and Zn-II ions have been determined in NaNO3 (0.1 M) supporting electrolyte by potentiometric titration at 25 degrees C. The overall log stability constant (log beta ML(2) = [ML(2)]/[M(2+)][L(-1)](2)) for Cu-II and Zn-II complexes are 14.50 and 8.75, respectively. Two new solids were prepared and identified by elemental microanalysis as (SeMet)(2)Cu and (SeMet)(2)Zn. I.r. and Raman spectral studies indicated metal coordination with the nitrogen and oxygen atoms of the amino acidato group of SeMet. The corresponding stretching bands were assigned at 341.1 cm(-1) for Cu-O, 352.9 cm(-1) for Zn-O, 497.3 cm(-1) for Cu-N and 375.2 cm(-1) for Zn-N bonds.