A SPECTROSCOPIC MODEL FOR THE HIGH PH FORM OF SULFITE OXIDASE

The syntheses and spectroscopic properties of two monomeric oxo-Mo(V) complexes [NMe4][MoO(SC6H4-CH=N-C6H4O)(SAr)2] (Ar=Ph (2a), PhCH3 (2b)) exhibiting a novel S3NO coordination site are described. The EPR parameters of the Mo(V) complexes are almost identical with the parameters for the high pH form of sulfite oxidase, allowing further predictions for the unknown coordination site of the molybdenum cofactor in such molybdenum-containing enzymes. The Mo(V) compounds react with water to form a mu-oxo-bridged Mo(V) dimer, which is readily oxidized by oxygen to give the monomeric dioxo-Mo(VI) complex MoO2(SC6H4-CH=N-C6H4O)(sol) (4) (sol=acetonitrile; dimethyl sulfoxide (DMSO)). The structure of 4 has been determined by X-ray crystallography (space group P1BAR (No. 2), a = 7.855(4), b = 9.530(3), c = 11.676(6) angstrom, alpha = 103.96(3), beta = 99.03(3), gamma = 100.73(3)-degrees, V = 814.5 angstrom3, rho(calc) = 1.79 g cm-3, Z = 2, R(F) = 0.026, R(wF) = 0.026). The geometry about the molybdenum is distorted octahedral, with two terminal oxo groups cis to each other.