Formation constants of metal complexes of N3-benzyl-L-histidine and NαN3-dibenzyl-L-histidine and stereoselectivity in the ternary complexes with D- and L-histidine

Abstract

Formation constants for the complexes of Ni^II. Cu^II, and Zn^II with N³-benzyl-L-histidine and N^αN³-dibenzyl-L-histidine, and of the ternary complexes of these metals and ligands with D- and L-histidine, have been measured potentiometrically at 25 °C and I= 0.10 mol dm^–3(K[NO₃]). Stabilization of the ternary complexes is small, but there is significant stereoselectivity between the ternary complexes with Ni^II and Zn^II, the meso complexes being preferred in all cases. With Cu^II, stereoselectivity is small or absent in the unprotonated ternary complexes, but significant in the monoprotonated ternary species {[Cu(D/L-His)(L-Ligand)H]}, the optically active complex being the more stable.