Sulphur, binding

It may appear rather strange to measure a strictly inorganic compound. However, there is one important correlation to biopolymers. In proteins the polypeptide chain imposes considerable strain on metal-sulphur binding centres which may lead to sulphur radical species. Such species have been discussed for cytochrome c oxidase and plastocyanin Likewise the polysilicates could take over the same role. They are capable to polarize the sulphur species and the existence of sulphur radicals are debated. 

The thiocyanate K2[Pt(SCN)6].2H20 contains octahedrally coordinated platinum, confirming the readiness of platinum(IV) to bind to a soft donor atom like sulphur [182]. 

Linear S-Au-S (but non-linear Au-S-C) is found in PhAs+Au(SCN)2 [96] related phosphine complexes (R3P) AuSCN have been made (section 4.10.3). Sulphate and thiosulphate bind through sulphur Na3Au(S203)2.2H20 has linear 2-coordinate gold in contrast to tetrahedral coordination of silver by sulphur and oxygen. 

The X-ray photoelectron spectra of metal complexes of sulphur-containing ligands sulphur 2/ -binding energies. R. A. Walton, Coord. Chem. Rev., 1980, 31, 183-220 (88). 

Complex II contains four peptides, the two largest form succinate dehydrogenase, the largest has covalently boiuid flavin adenine dinucleotide (FAD) which reacts with succinate, and the other has three iron-sulphur centers. Smaller subunits anchor the two larger subunits to the membrane and form the UQ binding site. Ubiquinone is the electron acceptor but complex II does not pump protons (see below). 

It is known that chlorine acts as severe poison for NH3 synthesis [20,21]. Hence recent kinetic studies used chlorine-free Ru precursors like Ru3(CO)i2 [8,22] or Ru(N0)(N03)3 [7]. In addition to chlorine, the presence of sulphur was found to poison Ru catalysts. Fig. 2A demonstrates that both poisons may originate from the Ru precursor. The binding energies for the Cl 2p peak and of the S 2p peak observed for Ru prepared form RUO3 are typical for chloride and sulfide anions, respectively [23]. Ru prepared from Rus(CO)i2 was found to have a significantly higher purity. As shown in fig. 2B, sulphur and chlorine impurities can also originate from the support. The XPS data of MgO with a purity of 98 % reveal the presence... 

Most protic solvents have both protogenic and protophilic character, i.e. they can split off as well as bind protons. They are called, therefore, amphiprotic. These include water, alcohols, acids (especially carboxylic), ammonia, dimethylsulphoxide and acetonitrile. Solvents that are protogenic and have weak or practically negligible protophilic character include acid solvents, such as sulphuric acid, hydrogen fluoride, hydrogen cyanide, and formic acid. 

In ribonuclease-S [PtClJ2- binds to the sulphur of methionine (63). In this case however greater interest centres on the use of cis-[PtenCl2] which is one of the best anti-tumour agents. The conditions of application of the reagent were sulphate media s pH 5.5. This is a more favourable attacking medium than that used in the experiments with lysozyme. We quote results from the original paper (63). 

The closely related dichloroethylenediamine platinum(II) was found to be slightly better than PtCll- as a heavy atom. A platinum-sulphur bond to methionine 29 is formed according to current analysis (now confirmed). The platinum cannot be removed by washing the crystal in sharp contrast to the reversible binding of other metal complexes. ... 

Whilst chloramines are less reactive than HOC1, they are longer-lived and so can diffuse away from their site of production. Those formed from lipophilic amines are especially toxic because they can permeate membranes. Chloramines are toxic for a number of reasons they can oxidise sulphydryl or sulphur-ether groups, they are unstable and can be hydrolysed to release chlorine in the form of HOC1 or NH2C1, they can react with iodide to form iodine and they can covalently bind proteins. 

The aqueous solution of methylene blue is not decolorised by sodium hydroxide the blue water-solubie ammonium base is formed. The dye is converted by reducing agents into the easily oxidisable leuco-base. The following experiment, which demonstrates the formation of methylene blue by the introduction of sulphur between the rings of Bind-schedler s green, is very instructive. 

The carcinogenic and mutagenic effects of 1,2-dibromoethane is due to its ability to bind to DNA and RNA with metabolic activation. The mechanism of action for the antispermatogenic effects is probably related to the removal of sulphur from cysteine in the nucleus of the spermatozoa. Clinical intervention to interfere with these mechanisms has yet to be developed. 

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