Sulfido-ligands

Interesting new sulfido complexes of tin have been prepared by the reaction of styrene sulfide with the N-alkylated tin(II) amidinate complexes Sn[RC(NCy)2]2 (Cy = cyclohexyl R = Me, Bu ). The products exhibit two very different bonding modes for the sulfido ligands in one case, S = Sn[RC(NCy)2]2/ a terminal Sn = S moiety was found while in the other case the bridging... 

Y Y = Ph2AsCFl2AsPh2 or Ph2PCH2PPh2 X = Cl, Br) which react with carbon disulfide at room temperature with formation of thiocarbonyl and sulfido ligands. ... 

The molybdenum complex of the molybdopterin prosthetic group (ligand). In the molybdenum cofactor the minimal coordination of the Mo atom is thought to be provided by the chelating dithiolenato group of the molybdopterin and either two oxo or one oxo and one sulfido ligands. 

As with xanthine oxidase, the sulfido ligand of the active form of aldehyde oxidoreductase is readily replaced by an oxido ligand to yield a cofactor with a structure that resembles that of oxidized sulfite oxidase and assimilatoiy nitrate reductase. Both x-ray and EXAFS data are available for the bis(oxido) form, and, with the exception of the oxido replaced sulfido ligand, few changes are obvious in the overall structure of the oxidized form of the desulfo cofactor. Upon reduction of the enzyme the oxido ligand is presumably reduced to hydroxido, an observation that is supported by EPR data for the Mov state. 

Over the course of study of xanthine oxidase, proposals for the mechanism by which the metal functions have ranged from hydride transfer to oxo transfer to CEPT linked to water activation [226,233-235], The latter proposal is presently favored, given what is known about (1) the source of the oxygen atom incorporated into product, (2) the fate of the substrate C(8)—H bond, (3) the role of the sulfido ligand, and (4) substrate binding. 

Since the oxido ligand is not the source of the oxygen atom incorporated into product, simple oxo transfer does not appear to be viable mechanism. Rather, some form of CEPT seems more likely and, as discussed in the next section, appears to involve the sulfido ligand of the (MPT)MoVI(0)(S)(L) cofactor where L = OH or H20. 

The xanthine dehydrogenase/xanthine oxidase family (XDH/XO) is characterized by the presence of oxo and sulfido ligands in the Mo(VI) state, a single dithiolene ligand, an oxygen-donor ligand such as water or hydroxide, and the... 

The history of CODH crystallography is one illustration of how the limitations of protein X-ray crystallography can lead to erroneous interpretation. The initial structural report of CODH (19) described the active site of CODH as having several important differences from the other members of its family. It did not possess the apical sulfido ligand but instead a second oxo ligand. Second, a... 

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