Molybdenum(V) Sites in Xanthine Oxidase and Relevant Analogue Complexes: Comparison of Molybdenum-95 and Sulfur-33 Hyperfine Coupling

Abstract

95Mo (I = 5/2) hyperfine matrices have been defined from multifrequency (2–4 and 9 GHz) electron spin resonance spectra of the Rapid Type 1, Rapid Type 2, and Slow centers of milk xanthine oxidase. For comparison, 95Mo hyperfine matrices were similarly extracted for the synthetic species [MoOXL]− and [MoO(XH)L] (X = O, S; LH2 = N,.N′-dimethyl-N,N′-bis(2-mercaptophenyl)-l,2-diaminoethane). In addition, 33S (I = 3/2) hyperfine matrices were derived for the thio ligand of [MoOSL]− and for the mercapto ligand SH of [MoO(SH)L] for comparison with the 33S coupling observed in a number of EPR signals of xanthine oxidase. Detailed examination confirms [MoVO(SH)], [MoVO(SH)(OH)], and [MoVO(OH)] as th..