Thiol disulfides from

Ethyleneamines are used in certain petroleum refining operations as well. Eor example, an EDA solution of sodium 2-aminoethoxide is used to extract thiols from straight-mn petroleum distillates (314) a combination of substituted phenol and AEP are used as an antioxidant to control fouling during processing of a hydrocarbon (315) AEP is used to separate alkenes from thermally cracked petroleum products (316) and TEPA is used to separate carbon disulfide from a pyrolysis fraction from ethylene production (317). EDA and DETA are used in the preparation and reprocessing of certain... 

This thiol-disulfide interconversion is a key part of numerous biological processes. WeTJ see in Chapter 26, for instance, that disulfide formation is involved in defining the structure and three-dimensional conformations of proteins, where disulfide "bridges" often form cross-links between q steine amino acid units in the protein chains. Disulfide formation is also involved in the process by which cells protect themselves from oxidative degradation. A cellular component called glutathione removes potentially harmful oxidants and is itself oxidized to glutathione disulfide in the process. Reduction back to the thiol requires the coenzyme flavin adenine dinucleotide (reduced), abbreviated FADH2. 

Thiol (s), 652, 667-668 disulfides from, 668 electrostatic potential map of, 75 from alkyl halides, 667 hybridization of, 20 naming, 667 odor of, 667 oxidation of, 668 pKa of, 604... 

Sulfiir-anchored SAMs and thin films, mostly from organosulfiir precursors, have been discussed at length by a number of authors [10, 181]. SAMs of organosulfiir compounds (thiols, disulfides, sulfides) form on gold substrates by spontaneous adsorption from either the liquid or the vapor phase. A number of experimental factors can affect the formation and structure of SAMs such as choice of solvent, temperature, concentration, immersion time, purity of adsorbate, oxygen concentration in solution, cleanliness, and structure of the adsorbate. Interestingly, the... 

The second activity, termed denitrosation (Eq. (15)), is catalyzed by the reduced form of the same active site thiols that are involved in the thiol-disulfide exchange activity of the enzyme (Zai et al, 1999 Ramachandran et al. 2001 Raturi and Mutus, 2004). In this process csPDI catalyzes the release of NO from RSNOs. 

The disulfide forms in the thiol oxidation from the recombination of the two RS radicals... 

The formation of benzothiazole-2-thiol (386) from aniline (385), carbon disulfide, and sulfur af 230 °C has been shown fo occur by a sequence of fhree principal steps. Labelling experiments confirmed fhaf bofh sulfur afoms originafed from carbon disulfide. An initial polar reaction to form thiocarbanilide (389) via phenylcarbamic acid... 

Researchers at Sunesis pharmaceuticals have developed a fragment-based drug discovery method termed tethering [25]. The approach, which is illustrated in Scheme 2.6, shares a number of features with DCC. Whereas protein-directed DCLs equilibrate small molecules via disulfide formation, say, in the presence of a protein that acts as a thermodynamic trap, tethering uses a cysteine residue on the protein surface to reversibly capture small-molecule thiol fragments from solution. Tethering is designed... 

Drugs coupled via a disulfide bond like, captopril, are rapidly released from the protein-spacer moiety of the conjugate, enzymatically by 3-lyase and/or non-enzymatically by thiol-disulfide exchange with endogenous thiols [68]. 

These early studies clearly revealed the inherent problems of the chemistry for site-directed formation of unsymmetrical disulfides that has to avoid formation of homodimers. These can result from (i) slow rates of activation of the cysteine peptide, (ii) disproportionation of the activated cysteine species, (in) weak activation and thus slow thiolysis by the second cysteine component and thus its oxidation to the homodimer as well as thiol/ disulfide exchange reactions on the unsymmetrical disulfide present in the reaction media. The latter side reactions are partly controlled by operating in degassed argon-saturated buffers or in organic solvents and preferably under acidic conditions where thiol/disulfide exchange reactions on the nonactivated disulfides, i.e. on the target unsymmetrical cystine peptide occurs at slow rates. 

Scheme 13.13 Formation of 2-methylfirran-3-thiol and its disulfide from xylose...

In addition to the sulfur compounds listed above, hydrogen sulfide has been found in many crude petroleums. Elemental sulfur has been definitely found in several crude petroleums by API Research Project 48 (23). Although Birch and Norris (5) isolated several disulfides from the spent caustic used in treating gasoline from Iranian petroleum, these compounds may have resulted from the oxidation of the thiols and their presence in the original petroleum is regarded as doubtful. Other types of sulfur compounds, such as thiophenes and aromatic thiols, have been identified in cracked petroleum products, but the presence of such compounds in naturally occurring petroleums has not yet been established. 

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