Modeling Hydrogen Bonds in Proteins with Transition Metal Imidazole Carboxylate Complexes, [M(C3H4N2)](RCOO)2

Center for Environmental and Life Sciences Atrium

Hydrogen bonds are essential in the active site of many metalloproteins. Metals are often bound to the amino acid histidine which in turn hydrogen bonds to other groups in the protein. Histidine contains an imidazole ring. We are modeling the metal bound imidazole to carboxylate hydrogen bonding interaction in proteins with small molecular weight compounds containing transition metal-imidazole complexes. These compounds were prepared by reacting transition metal acetates with imidazole followed by substitution of an aromatic carboxylate for acetate. Metals used were manganese, cobalt, and nickel. In some case, a mixture of two metals was used. Six equivalents of imidazole were used per metal atom. Both water and low molecular weight alcohols were used as solvents. The crystals were grown by slow evaporation. Infrared spectroscopy confirmed the presence of a metal to imidazole bond. Suitable crystals were sent for single crystal X-ray diffraction analysis. The hydrogen bond in the crystal structures were compared to see the effects of changing the metal and changing the carboxylic acid on the metal-imidazole to carboxylate hydrogen bond.