The methods of three-dimensional X-ray crystal structure determination will be applied to determine various aspects of metalloporphyrin stereochemistry. The iron porphyrins are related to the important class of biomolecules, the hemoproteins, which carrry out a wide range of biological functions including oxygen utilization and transport, electron transport, drug metabolism, and other enzymatic processes. The overall objective of the research is to establish possible stereochemical features of a metalloporphyrin group in its biological environment and to model specific prosthetic group behavior of selected hemoproteins. These studies should provide an understanding of how protein structure might modulate metalloporphyrin geometry and allow a multitude of processes to be carried out using the same fundamental iron porphyrin unit. Metalloporphyrins to be studied include iron(II) and iron(III) complexes with a variety of axial ligands. Synthetic analogues of cytochrome c and b will be studied to probe what structural features lead to their redox properties. Other complexes will utilize ligands designed to produce unusual magnetic properties to examine how a protein can effect particular magnetic states. Other studies will focus on metalloporphyrins having oxidized or reduced cores and the electronic communication between the ring and the central metal atom. Such species are of interest in understanding the catalytically important intermediates of the peroxidases and catalases. Synthetic studies examining the axial interaction of potential substrates of nitrite and sulfite redactases will be pursued.
