Copper -thiolate bond

The structure of pseudoazurin from A. faecalis strain S-6 was determined in two laboratories (in part, because it crystallizes so readily excellent crystals are formed in a matter of hours ) (Petratos et al., 1987, 1988a Adman et al, 1989). The crystals, space group P6j, have the interesting property that they are intensely blue when viewed along the sixfold axis, but are nearly colorless when viewed normal to this axis. This is assumed to be due to the fact that the plane of the Cu-Sy-C/3 atoms is perpendicular to the sixfold axis, consistent with the fact that the copper— thiolate bond is responsible for the blue color of the protein. 

Class I and/or II MTs have been described in all animals examined. Mammalian MTs have been some of the most extensively studied of the 61 or 62 amino acids, 20 are cysteine residues. Metal ions are bound to the MT exclusively through thiolate bonds involving all 20 cysteines (see Hamer, 1986). They associate with a wide range of metals in vitro, 18 different metals in the case of rat liver MT (Nielson etal., 1985). Divalent and trivalent metals exhibit saturation binding at 7 mole equivalents forming M7-MT, whereas copper (Cu(I)) and silver (Ag(I)) bind as monovalent ions forming M12-MT. The structure of these molecules is such that two metal-binding domains are formed an a-cluster from the carboxy-terminal portion of the protein, contains 11 cysteines which bind either 4 divalent or 6 monovalent ions the (3-cluster, the amino-terminal... 

The main difficulty in synthesizing an accurate model for type I copper comes from the instability of the copper(II)-thiolate bond. This bond easily undergoes homolysis, causing reduction of the copper(II) ion with formation of disulfide as follows ... 

The consequent delocalization reduces the interaction of the electron with the copper nuclear spin and generates the small A. So, according to this model, the spectroscopic properties of the site are largely due to the particular constrained geometry of the Cu-thiolate bond. 

Copper(I) thiolate complexes show remarkable diversity of structure, and the most common structural unit in the known thiolate is a three-coordinate copper atom bonded to /u.2-bridging thiolates (15). Parish has recently reported a novel compound in which the thiolate sulfur atom involves unusual four-way bridging (255). The compound with composition [Cui3C1i3(SR)8] H20 (R = CH2CH2NH3) was obtained by reaction of CuCl and cysteamine hydrochloride in an aqueous solu-... 

Phytochelatin a plant peptide produced in response to lieavy metals, e.g. cadmium, copper, mercury, lead and zinc. The structure is (Y-Glu-Cys) -Gly (n = 3-7). Like Metallothionein (see), P. form metal-thiolate bonds and thus sequester toxic metal ions. They are probably derived from glutathione rather than RNA-directed protein synthesis. 

The choice of the active orbital space for the CASSCF calculations is a crucial step, and has turned out to be especially difficult in these proteins and similar systems containing a Cu-thiolate bond. From earlier studies it is known that in complexes with copper (and other first-row transition metal ions with many 3d electrons) it is necessary to include in the... 

Konopka, M., Rousseau, R., Stich, I. and Marx, D. (2004) Detaching Thiolates from Copper and Gold Clusters Which Bonds to Break Journal ofthe American Chemical Society, 126, 12103-12111. 

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