Interaction between Glyglu and Ca2+, Pb2+, Cd2+ and Zn2+ in solid state and aqueous solution. Crystal structures of poly[aqua-1,2-kappa-O-di[lead(glygluH)]bis(perchlorate)] and poly[bisglycylglutamic-cadmium(II) tetrahydrate]

Abstract

Glycylglutamic acid (GEH(2)) is a peptide usually present in calcium binding sites. The interaction between the peptide and the cations Ca2+ Pb2+, Cd2+, and Zn in aqueous solution and in the solid state is described. Six compounds were isolated with different protonation states of the ligand. Potentiometric equilibrium studies, C-13 and Cd-111 solid state CP MAS NMR and IR spectroscopy were performed. Two crystal structures are reported: [Pb(GEH)(H2O)](1/2)]ClO4 and [Cd(GEH)(2)].3H(2)O. Both constitute 3D polymers, where only carboxylate groups are coordinated to the cations. The crystalline lead compound shows a hemidirected coordination sphere due to its stereochemically active lone pair. In deprotonated derivatives, it is possible to assign a metal-amino interaction to a far IR signal (340-370 cm(-1)). (C) 2002 Elsevier Science B.V. All rights reserved.