Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine, diethylenetriamine or N,N,N ',N '',N '''-pentamethyldiethylenetriamine in aqueous solution

摘要

Solution equilibrium studies on the Cu(II)-polyamine-histidine ternary systems (polyamine: ethylenediamine (en). diethylenetriamine (dien), N,N,N',N",N'"-pentamethyidiethylenetriamine (Me(5)dien)) have been performed by pH-potentiometry, UV-Vis spectrophotometry and EPR methods. The obtained results suggest the formation of the mixed-ligand complexes with [Cu(A)(His)](+) stoichiometry in all studied systems. Additionally, in the systems with then and Me(5)dien protonated [Cu(A)(H-His)](2+) species also exists in acid solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(His)(+), the geometry slightly deviated from square pyramidal for the [Cu(dien)(His)](+) and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me(5)dien)(His)](+) species. The coordination modes in these mixed-ligand complexes are discussed. (c) 2008 Elsevier Ltd. All rights reserved.