Sulfur-containing donors

Donors. Common selenium and sulfur-containing donors such as tetrathiafulvalene [31366-25-3]> tetramethyltetraselenafiilvalene [55259-19-9] and bis-(ethylenedithio)tetrathiafulvalene [66946-17-3] are commercially available, as are other common donors such as tetramethyl-/)-phenylenediamine [100-22-1]. TeUurium-containing donors can be prepared using a variety of synthetic routes. Tetratellurafiilvalene, for example, is prepared in good yield using tin—lithium exchange (22) (Fig. 5). 

Chelate-forming ligands are widely represented amongst oxygen- and sulfur-containing donors [1, vol.2 112,934]. On their basis the following complexes have been isolated monothiocarboxylates 537 [1, vol.2], thio-oxalates 538 [934], and monothio-p-diketonates 539 [1, vol.2 935-937] ... 

Among other sulfur containing donors, thiocarbonates also cleave, and electron transfer from cysteine leading to decarboxylation involves the sulfur atom at all pHs. Electron transfer photosensitization of some 2,2-diarylthietanes causes retrocycloaddition and yields 1,1-diarylethylenes (see Equation 4.27, DCA = 9,10-dicyanoanthracene). ... 

Sulfur-containing chemicals such as dimorpholinyl disulfide (DTDM) and tetraethylthiuram disulfide (TMTD) are not only effective accelerators, but they can also be used as sulfur donors. As such, they are effective ia controlling sulfur cross-link length to form primarily moao- and disulfide cross-links. These short cross-links are more thermally stable than conventional sulfur curing and thereby provide better heat and set resistance. 

Other ligands containing sulfur as donor atom... 

On the other hand, one of the first chiral sulfur-containing ligands employed in the asymmetric transfer hydrogenation of ketones was introduced by Noyori el al Thus, the use of A-tosyl-l,2-diphenylethylenediamine (TsDPEN) in combination with ruthenium for the reduction of various aromatic ketones in the presence of i-PrOH as the hydrogen donor, allowed the corresponding alcohols to be obtained in both excellent yields and enantioselectivities, as... 

Sulfur-containing ligands. Macrocyclic effects have also been documented in mixed donor systems. The Cu(ii) complex of the 14-mem-bered (cis) N2S2-donor analogue of cyclam exhibits a substantial macrocyclic effect with a log K difference of 4.6 relative to the corresponding open-chain species (Figure 6.2) (Micheloni, Paoletti, Siegfried-Hertli Kaden, 1985). The effect in this case is mainly due to a favourable... 

The dissociation kinetics of the nickel chloride complex of the 15-mem-bered, S2N2-macrocycle of type (279) has also been investigated in the presence of hydrochloric acid (Lindoy Smith, 1981). This complex has a similar trans-octahedral structure to that of the 02N2-donor systems just discussed. For the sulfur-containing complex, two consecutive (acid-independent) first-order steps were observed, with the second being slower than the first. The data are in accordance with the scheme ... 

As would be expected, the chemistry is complex. Unpleasant, off flavor odors usually derive from sulfur compounds, such as MT, DMS, DMDS, and DMTS, formed either enzymatically or non-enzymatically from sulfur-containing amino acids.35 Enzymatic routes to MT are essentially those previously considered (Section 11.1.2.4.5). Some DMS may derive by methylation of MT (Equation 8) with the donor, 5-adenosylmethionine, AdoMet ... 

HCN is detoxified to thiocyanate (SCN ) by the mitochondrial enzyme rhodanese rhodanese catalyzes the transfer of sulfur from thiosulfate to cyanide to yield thiocyanate, which is relatively nontoxic (Smith 1996). The rate of detoxification of HCN in humans is about 1 pg/kg/min (Schulz 1984) or 4.2 mg/h, which, the author states, is considerably slower than in small rodents. This information resulted from reports of the therapeutic use of sodium nitroprusside to control hypertension. Rhodanese is present in the liver and skeletal muscle of mammalian species as well as in the nasal epithelium. The mitochondria of the nasal and olfactory mucosa of the rat contain nearly seven times as much rhodanese as the liver (Dahl 1989). The enzyme rhodanese is present to a large excess in the human body relative to its substrates (Schulz 1984). This enzyme demonstrates zero-order kinetics, and the limiting factor in the detoxification of HCN is thiosulphate. However, other sulfur-containing substrates, such as cystine and cysteine, can also serve as sulfur donors. Other enzymes, such as 3-mercapto-pyruvate sulfur transferase, can convert... 

Sulfur-containing allenes can be subdivided into donor-functionalized allenes such as allenyl thioethers and into acceptor-functionalized allenes such as allenyl sulfoxides and sulfones. In this section only the synthesis and chemistry of donor-substituted sulfur-containing allenes will be summarized. 

Sulfur-containing acyclic and cyclic compounds have been prepared from allenyl sulfides in numerous transformations such as substitutions, additions, cydoaddi-tions and other cyclization reactions. Like the other donor-substituted allenes, allenyl sulfides are suitable substrates for regioselective lithiation and substitutions as exemplified in Scheme 8.86 [168, 169,175]. 

Methionine (Met or M) ((5)-2-amino-4-(methylsulfanyl)-butanoic acid) is a nonpolar, neutral, amino acid with the formula HOOCCH(NH2)CH2CH2SCH3. Together with Cys, Met is one of the two sulfur-containing proteinogenic amino acids and a great antioxidant. Its derivative 5-adenosyl methionine (SAM) serves as a methyl donor. ... 

Methionine, another sulfur-containing amino acid, is part of S-adenosylmethionine (SAM), a methyl donor in biochemical pathways. 

X.X Acting on reduced flavodoxin as donor. 2. 8. X.X Transferring sulfur-containing groups. 

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