Thiol disulfides

Thiol—Disulfide Interchange Reactions. The interchange between thiols and disulfides has been reviewed (50). This reaction is base-catalyzed. It involves the nucleophihc attack of a thiolate ion on a disulfide. This is shown in equations 35, 36, and 37. 

The free-radical chemistry of fluoroalkanesulfenyl chlorides with hydrocarbons was also investigated [S, 9], Depending upon the structures of the sulfenyl chloride and the hydrocarbon, these reactions yield as major products up to three of the following four types of organic compounds thiols, disulfides, sulfides, and chlorohydrocarbons (equation 6), Perfluoroisobutanesulfenyl chloride is unique m that the only major products detected are the thiol and chlorohydrocarbon [ ] (equation 6) (Table 3). 

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. 

The following sections detail the chemistry undergone by specific transfer agents that react by atom or group transfer by a homolytic substitution mechanism. Thiols, disulfides, and sulfides arc covered in Sections 6.2.2.1,6.2.2.2 and 6.2.2.3 respectively, halocarbons in Section 6.2.2.4, and solvents and other agents in Section 6.2.2.5. The transfer constant data provided have not been critically... 

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... 

Simanek el al. investigated the structure dependence of the kinetics of thiol-disulfide exchange reactions.[44] In general, the rate of exchange decreased as the size of the dendrimers increased. Dendrimers with disulfides attached near the core undergo exchange more slowly than dendrimers with disulfides at the periphery. No evidence was found for intramolecular macrocyclization (cooperative) exchange. 

Rate Constants of Reactions of Sulfides, Thiols, Disulfides, and Sulfoxides with Hydroperoxides (Experimental Data)... 

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 sulfenic acids formed thereby are known to be highly unstable and were presumed to disproportionate to 2/3 thiol disulfide equivalent and 1/3 sulfinic acid38,74-77. 

Keire, D.A., Strauss, E., Guo, W., Noszal, B., Rabenstein, D.L. Kinetics and equilibria of thiol/disulfide interchange reactions of selected biological thiols and related molecules with oxidized glutathione. J. Org. Chem. 1992, 57, 123-127. 

Shaked, Z. Szajewski, R. R Whitesides, G. M. Rates of thiol-disulfide interchange reactions involving proteins and kinetic measurements of thiol pKa values. Biochemistry 1980,19,4156-4166. 

Scheme 7.3 (a) Anchor fragments equipped with two thiol moieties (F-J). (b) Thiol partner fragments (4-22). (c) DCC ntilizing thiol-disulfide exchange and targeting metallo-P-lactamase (Bell). 

A well researched and popular class of monolayers is based on the strong adsorption of thiols (R - SH), disulfides (R - S - S - R) and sulfides (R - S - R) onto metal surfaces. Although thiols, disulfides, and sulfides strongly align with a number of different metals Hke gold, silver, platinum, or copper, gold is usually the substrate of choice because of its inert properties and the formation of a well-defined crystal structure. 

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