Mercaptide ligands

Fig. 2. Yellowness index vs two-roU mill heat stabiUty, where the mercaptide ligands, — SCH2COOR (A), —SCH2CH2COOR ( ), and —SCH2CH2C00R + HSCH2CH2C00R ( )) IT 9, and 6% Sn, respectively. R = CgH. R = H33. ...

The performance of organotin mercaptides is not only based on the amount of tin metal content, but on the organotin species, mercaptide ligand chemistry and organic co-stabiliser (453). The mechanism of organothiotin stabilisation has been studied extensively (221,347, 348, 387, 388). 

The phosphane ligand can be removed in 18% aqueous hydrochloric acid and subsequently replaced by pyridine [281], The complex then features two mercaptide ligands on the paUadium(II) atom confirming that sulfur coordination on the transition metal is indeed preferred over nitrogen coordination. 

The reduced cytochrome P450 has been determined to be high spin in the case of the camphor-5-exo-monooxygenase Its coordination sphere is probably 5-coor-dinated, but there is no definite proof that the mercaptide ligand is still in the fifth position. Like all ferrous hemoproteins with an open ligand position cytochrome P450 reacts rapidly and with a value of about 10 M with dioxygen to form... 

This points to an important function of the heme and the protein in cytochrome P4S0 monooxygenases the mercaptide as the fifth ligand has to be completely separated from the active oxygen, otherwise a rapid oxidation of this ligand would take place. In terms of this property of the enzyme, which will be also a critical requirement for a tme model system, more sophisticated heme sulfur complexes with shielded mercaptide ligands have to be synthesized. 

Some of the most recent developments in liquid gold precursors involve the synthesis of water-soluble gold(I) mercaptides as reported by Bishop [24]. The mercaptide ligands in these compounds contains a water-solubilizing functional group, having the general formula... 

The water/polar solvent solubility is achieved for these compounds by the generation of an ammonium or quaternary ammonium salt, for example, triethyl-ammonium, via the carboxylate group within the mercaptide ligand (Equation 15.4). 

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