Disulfide units

M. Pox, Chemical Economics Handbook, Carbon Disulfide—United States, SRI International, Menlo Park, Calif., Aug. 1988, pp. 625.5030A-G J. Sheehy of SRI International, personal communication, Oct. 11, 1991. 

Electrochemistry of disulfide unit present in cytochrome c (cyt c) molecules on gold electrodes has also been reported [169]. Disulfide unit in cytochrome c is strongly adsorbed on Au electrodes and this slows down the electron-transfer rate to the heme group. More recently, Krylov et al. [170] have immobilized cytochrome c by self-assembling on the surface-modified Au electrodes. CV was applied to study how denaturation and renaturation of cytochrome c depend on the solution composition. 

The interaction between two disulfide units in a 2,3,5,5-tetrathiabicyclo[2.2.2] oct-7-ene type radical cation with transannular delocalization between the four sulphur atoms was established by ESR. This radical cation was persistent enough to be crystallized and analyzed by X-ray crystallography. Remarkably, this species was formed after oxidation of 3,4,5,6-bis(bicyclo[2,2,2]octeno)-l,2-... 

We have noted previously (see Section 2.1) the role played in biochemistry by the thiol disulfide interconversion, and the disulfide unit is a fundamental feature of the structure of peptides and proteins. The sulfur-sulfur bond between two cysteins link remote parts of a peptide chain or cross-link two such chains. Cleavage of these bonds in the hair protein keratin, followed by reoxidation, gives hair its desired shape. 

A number of naturally occurring compounds with a disulfide unit have shown interesting biological activity [28, 29]. Nereistoxin, charatoxin, asparagusic acid, a plant growth inhibitor, and lipoic acid, a key co-factor in the oxidative decarboxylation of pyruvate, are examples taken in the 1,2-dithiolan series. 

As an example of a rr system involving a disulfide unit we briefly consider naphthalene-1,8-disulfide (55). Also this species belongs to a series of rr donors with remarkable electric properties The tt MO energy diagram can be constructed... 

Fig. 32. Diagram indicating the derivation of the highest occupied a orbitals of naphthalene-l,8-disuliide from a orbitals of naphthalene and ng and ng orbitals of the disulfide unit l...

The amino acid sequence in bovine insulin. The A chain is joined to the B chain by two disulfide units (shown in green). There is also a disulfide bond linking cysteines 6 and 11 in the A chain. Human insulin has threonine and isoleucine at residues 8 and 10, respectively, in the A chain and threonine as the C-terminal amino acid in the B chain. 

The bifunctional material having an acidic framework and basic pores was obtained by appropriate chemical transformations of the resulting material, that is, reduction of disulfide units into SH groups followed by their oxidation into SO3H groups and deprotection of amino groups by thermal treatment under vacuum. 

Scheme 12.14. Self-organization of bridged organosilica with disulfide units and subsequent...

Disulfide units also appear in dithiolopyrrolones, e.g., holomycin (57), which exhibits broad-spectrum antibiotic activity against many grampositive and gram-negative bacteria, as well as strains of Mycobacterium tuberculosis (2014NPR905). 

Ribonucleotide Reductase. The ribonucleotide reductases catalyze the reduction of ribonucleoside-diphosphates (or triphosphates) to the corresponding 2 -deoxyribonucleoside-diphosphates (or triphosphates), processes of preeminent importance for the biosynthesis of DNA (see Table 2, entry 4) (65,86). A variety of metal-containing cofactors have been discovered in the ribonucleotide reductases investigated to date (eg, a binuclear iron center in the mammalian and in the E. coli ribonucleoside diphosphate reductase) and the oxidation of two protein thiols to a disulfide unit is indicated as the direct source of the two reduction equivalents. The reductase from Lactobacillus leichmanii employs coenzyme B12 as cofactor in its (normal) base-on form and acts on purine- or pyrimidine-based ribonucleoside-triphosphates. Its crystal structure reveals not only the arrangement of the bound corrinoid cofactor, but also how the enzyme is... 

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