MODELING FOR THE ACTIVE-SITE OF SULFITE OXIDASE - SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF [(MOO2)-O-VI(MNT)(2)](2-) (MNT(2-)=1,2-DICYANOETHYLENEDITHIOLATE)
Sk. Das et al., MODELING FOR THE ACTIVE-SITE OF SULFITE OXIDASE - SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF [(MOO2)-O-VI(MNT)(2)](2-) (MNT(2-)=1,2-DICYANOETHYLENEDITHIOLATE), Journal of the American Chemical Society, 116(20), 1994, pp. 9061-9070
The complexes, [Bu(4)N](2)[(MoO2)-O-VI(mnt)(2)] (1), [Bu(4)N](2)[(MoO)
-O-IV(mnt)(2)] (2), and [Ph(3)PNPPh(3)][Et(4)N][(MoOCl)-O-V(mnt)(2)] (
3) (mnt(2-) = 1,2-dicyanoethylenedithiolate) have been synthesized as
possible models for active sites of sulfite oxidase which is proposed
to contain molybdenum cofactor with dithiolene coordination around mol
ybdenum. The structure of the [Bu(4)P](+)l salt of complex anion of 1
has been determined by X-ray crystallography. The compound crystallize
s in space group P2(1)/c, with a = 14.200(3) Angstrom, b = 19.402(4) A
ngstrom, c = 18.967(3) Angstrom, beta = 95.48(1)degrees, and Z = 4. [(
MoO2)-O-VI(mnt)(2)](2-) is a distorted octahedron with the oxo groups
cis to each other and trans to the dithiolene sulfur atoms. The comple
xes 1-3 have been characterized by IR, UV-visible, C-13 NMR, and negat
ive ion FAB mass spectra. Complex 1 shows a quasireversible reduction
and proton coupled electron transfer reaction. Complex 2 undergoes an
one-electron reversible oxidation; but on the coulometric time scale i
t disproportionates to a tris dithiolene complex, [Mo-IV(mnt)(3)](2-)
and MoO3. Complex 2 in the presence of Cl- is oxidized irreversibly wi
th the appearance of a new quasireversible couple corresponding to the
electrochemical detection of (MoOCl)-O-V(mnt)(2)](2-)/[(MoOCl)-O-IV(m
nt)2](3-). The EPR parameters of 3 and [(MoO)-O-V(mnt)(2)](1-) are rep
orted. The Cl-35,Cl-37 superhyperfine splitting of the chloro complex
3 is shown in relevance to Mo-Cl interaction in native sulfite oxidase
. Complex 1 oxidizes HSO3- to HSO4- with the formation of 2 and withou
t forming the biologically irrelevant mu-oxo Mo(V) dimer. This reactio
n follows enzymatic substrate saturation kinetics with apparent K-M (M
ichaelis-Menten constant) = 0.010(+/-0.001) M and k(2) (k(Obs) at subs
trate saturation concentration and is proportional to V-max) = 0.87(+/
-0.04) s(-1) in MeCN/H2O(1:1) medium at 20 degrees C.