Oxygen activation by non-heme iron complexes and proteins

OXYGEN

DO12 OXYGEN COMPLEXES

ACTIVATION BY AND PROTEINS

NON-HEME

279

IRON

Stephen J. Lippard Department of Chemistry, Massachusetts Insfitute of Technology, Cambridge, MA, 02139, USA. A dinuclear iron center bridged by at least one protein derived carboxylate ligand comprises the functional core of hemerythrin, the R2 protein of ribonucleotide reductase, and the hydroxylase of methane monooxygenase (MMO). A comprehensive study of the structure, physical properties, and reaction chemistry of the MM0 hydroxylase has been carried out. In addition, we have prepared model complexes for the diiron cores in the diiron carboxylate proteins and have investigated their physical and chemical properties. Results to be discussed include stopped flow kinetics results for the reaction of the reduced hydroxylase with dioxygen in the presence and absence ofits natural partner proteins; ENDOR experiments that establish a bridging hydroxide ligand for the mixed valence form of the hydroxylase; progress on the crystal structure determination of the hydroxylase protein; radical clock experiments

that address mechanistic questions concerning the

hydroxylation characterization

reaction

mechanism;

the

synthesis

and

of a bioinorganic chip for kinetically stabilized

diiron carboxylate-bridged

cores; preparation of a Qt.-oxo)diiron

complex having pendant phenoxyl radical ligands as a model for the R2 protein core; and kinetics and mechanistic investigations of the reaction of dioxygen with a variety of diiron(II) model complexes. Many co-workers

and collaborators

have contributed

to these

investigations, which were supported by a grant from the National Institute of General Medical Sciences.