Stereoselectivity and proton binding in copper(II) complexes of aspartic acid, glutamic acid and some N‐methyl or N‐benzylhistidine derivatives

Abstract

AbstractStability constants and stereoselective effects are measured for copper(II) complexes with aspartate (asp), glutamate (glut), histidinate (his) and some N‐alkylhistidinate derivatives: N‐methyl‐ (mhis), N,N‐dimethyl‐ (dimhis) and N‐benzylhistidinate (bhis). For the dicarboxylic amino acids the predominant species in solution are CuA, CuHA and CuA2 *; for histidine and its derivatives:CuA, CuHA, CuA2 and CuHA2. By comparison of competition constants (vide infra) it is found that the ligand is bound via its glycine‐locus in all complexes CuHA. For complexes CuHA2, the mono‐protonated ligand, HA, is also bound to copper by its glycine‐locus if A = his and bhis, and mainly so if A = mhis, but, if A = dimhis, HA, possibly, is monodentate and bound to copper by its imidazole group. No stereoselective effects are found in complexes CuA2 for A = asp, glut, his and mhis; for A = dimhis a significant positive effect (i.e. in favour of the meso complex Cu(DA)(LA)) is found, in contrast to the case for A = bhis. In the protonated copper complexes CuHA2, small negative effects are found for A = his, mhis and bhis, but no effect for dimhis.