Anions disulphide

Tin disulphide has the same dangerous reactions as sulphides, for which sulphide anion is very sensitive to the effect of oxidants. So the effect of chloric acid and chlorates gives rise respectively to violent detonations and the formation of spectacular showers of sparks. Dichlorine oxide detonates, but this is to be expected. 

Dichromate anions are readily absorbed under acidic conditions by wool that has been dyed with chrome dyes. The chromium(VI) on the fibre is then gradually reduced by the cystine residues in wool keratin to chromium(III) cations, which react with the dye ligands to form a stable complex. In this way the cystine disulphide bonds are destroyed, resulting in oxidative degradation of the wool fibres [71]. 

A rather complex mixture of products is obtained from the reaction of benzyl-idenetriphenylphosphorane and CS2.48 The major product from the reaction of diphenyl disulphide with methylenetriphenylphosphorane is tris(phenylthio)-methane (44) and only a trace of the insertion product bis(phenylthio)methane is isolated.49 Presumably the salt (45) is deprotonated before it can react with the phenylthioate anion (Scheme 12). a-Thiocarbonyl-stabilized ylides (46) are obtained from the reaction of ylides with S-alkyl thiolcarboxylates.50... 

Trifluoromethyl thioethers are produced in a fluoride-catalysed one-pot reaction of alkyl or aryl thiocyanates with trifluoromethyl silanes [37]. The reaction is initiated by fluoride ion displacement of the trifluoromethyl anion from the silane the thioether is formed from the thiocyanate by displacement by the trifluoromethyl anion of the cyanide ion, which then perpetuates the reaction. Trifluoromethyl selenoethers are obtained by an analogous route. In a similar manner, disulphides can be converted into trifluoromethyl thio- or selenoethers [38],... 

As indicated above, the traditional base-catalysed hydrolysis of 0,5-dialkyl thio-carbonates for the synthesis of thiols is generally unsatisfactory, as oxidation leads to the formation of disulphides. Under phase-transfer conditions, the procedure produces thioethers to the virtual exclusion of the thiols, as a result of the slow release of the thiolate anions in the presence of the electrophilic ester. However, a simple modification of the reaction conditions provides an efficient one-pot reaction [50] from haloalkanes (Table 4.15) via the intermediate formation of the thermally labile (9-/ert-butyl-5-alkyl dithiocarbonates (Scheme 4.8). 

In conclusion, structures containing polyiodide anions, with cationic aromatic ligands as counter parts of formulae [(L)(HL+)] (I ) are known to be synthesized by the treatment of the appropriate amide with HI [26-28], In contrast, the complexes with PYOH, in the present case, were formed by the direct reaction of 2-hydroxypyridine with di-iodine in a molar ratio of 2 1 and 1 2. This is a redox reaction, where 2-hydroxy-pyridine firstly is oxidized to pyridinone-2 radical cation. In the case of 2-hydroxy-pyridine however, peroxide structures are not formed like disulphides in the case of PYSH. Polyiodide anions are simultaneously produced in this case This should be a consequence of redox differences between -SH and OH groups and may be proven a useful pathway for the synthesis of polyiodide materials. 

Substrate analogues containing the mercaptan functionaUty have been extensively investigated as collagenase inhibitors, and some other sulphur-based functionalities have also been explored [1,161,172-185]. The mercap-tans tend to be very potent inhibitors of all of the MMP, presumably due to the strong interaction between the active site Zn(II) and the mercaptide anion. Unfortunately, these compounds tend to undergo inactivation by oxidative disulphide formation. However, the rate at which this occurs varies widely and depends on the structure of the inhibitor. The most common synthetic route to these derivatives again leads to a diastereomeric mixture. 

Homogeneous reductive cleavage of the sulphur-sulphur bond in some diphenyl disulphides by electron transfer from added radical-anions in the solution illustrate points from the two previous paragraphs [32], Rate data for two diphenyl disulphides are given in Figure 4.6. The variation in electron transfer rate with electron... 

Figure 4.6. Homogeneous dissociative electron transfer reaction between aromatic radical-anions and (a) di-(4-cyanophenyl) disulphide, (b) diphenyl disulphide in dimethyl formamide. Data from ref [31J.

Substances undergoing redox reactions (such as quinone-hydroquinone, sulphide-disulphide, metal complexes, redox couples) may serve as electron carriers and allow the coupling of oxidation-reduction processes across membranes (see, for instance, [6.44-6.46]) to cation or anion transport. 

The neutral sulphur compounds include sulphides or thioethers, disulphides, sulphoxides and sulphones, sulphate and sulphonate esters, and isothiocyanates. Acidic sulphur compounds, i.e. sulphonic and sulphinic acids, thiols and thio-phenols, and the primary sulphonamides have already been discussed. The sulphates of amines are converted by aqueous sodium hydroxide into the free bases the sulphate anion can be detected in the resulting aqueous solution as barium sulphate in the usual manner. 

Prutz WA (1989) Chemical repair in irradiated DNA solutions containing thiols and/or disulphides. Further evidence for disulphide radical anions acting as electron donors. Int J Radiat Biol 56 21-33... 

The resulting thiyl radical (RS ) reacts with further thiolate to form a relatively stable disulphide radical anion (Equation 10.24) which in turn completes the chain reaction by SET to the starting material, Me2C(X)N02 (Equation 10.25). 

Beer and co-workers have investigated this concept using self-assembled monolayers of the l,l -bis(alkyl-iV-amido)ferrocene 106 on gold electrodes [72]. The pendant disulphide groups serve to covalently anchor the receptor to the gold surface. In electrochemical experiments on 106 in acetonitrile/dichloro-methane solution, anion-induced cathodic shifts of the ferrocene/ferrocenium... 

Very recently Beer and co-workers have developed a surface-enhanced optical anion sensor based on gold nanoparticles [78]. Dodecanethiol-stablised gold nanoparticles were modified by ligand substitution with a disulphide-substituted zinc porphyrin 113 to provide 30 and 80 receptors per nanoparticle. Titration of both the free receptor and the modified nanoparticles with various... 

A sustained drug release is favourable for drugs with short elimination half-life. It can be controlled by hydration and diffusion mechanisms or ionic interactions between the drug and the polymeric carrier. In the case of diffusion control the stability of the carrier system is essential, as its disintegration leads to a burst release. Therefore, the cohesiveness of the polymer network plays a crucial role in order to control the release over several hours. Due to the formation of disulphide bonds within the network thiomers offer adequate cohesive stability. Almost zero-order release kinetics could be shown for insulin embedded in thiolated polycarbophil matrices (Clausen and Bernkop-Schnurch 2001). In the case of peptide and protein drugs release can be controlled via ionic interactions. An anionic or cationic polymer has to be chosen depending... 

The conformational dependence of the 33S isotropic a in dimethyldisulphide, (CH3)2S2, has been studied by HF calculations using the IGLO method.121 (CH3)2S2 is a good model for the disulphide linkage in polypeptides and proteins. 33S a has been calculated as a function of the dihedral angle C-S-S-C. Predicted chemical shifts vary between —84.4 ppm (< C-S-S-C = 0°) and —42.3 ppm (Calculated values refer to CS2 and cannot be converted to the SO4 scale, since the absolute shielding of the SQj anion has not been reported... 

Polarisation lowers the energy of anions in layer and chain structures because generally in these the anions are in asymmetric environment and they experience a strong net electric field from neighbouring ions. In such a situation polarisation stabilises an ion. This is not possible in compounds with coordination symmetry. The occurrence in layer structure of disulphide and dichloride may be attributed to stabilisation effect. The stabilisation is not possible in oxides and fluorides (smaller anions). 

Judging from the decreasing metallic properties in the series, Pb, Sn, Si, C, we should expect the tetrachlorides to hydrolyze more readily as we progress in this order. Two factors modify this effect the tendency to form a complex acid such as H SnCle with the anion SnCle--, and the insolubility or total lack of ionization of the tetrachloride. Explain from this point of view why carbon tetrachloride and carbon disulphide are without perceptible action with water. 

The photostimulated reactions of thiolate anions with 2-halo-2 -nitropropane derivatives yield both oc-nitrosulphides via an S l pathway and disulphides (equation 71a)282 284. In contrast with the case of the oxidative dimerisation products of the mono-enolates, the disulphides are formed via an ionic mechanism nucleophilic attack by the thiolate anion on the a-halogen and subsequent reaction of a second thiolate with the sulphenyl halide. As expected for such a process, disulphide formation is favoured (and thus a-nitrosulphide formation is disfavoured) the more nucleophilic the thiolate (i.e. derived from a less acidic thiol) and the easier the abstraction of the halo-substituent (i.e. I > Br > Cl). Use of the protic solvent methanol instead of the usual dipolar aprotic solvents for the reaction of equation 71a is detrimental to the yield of the S l substitution products exclusively disulphides are formed285 (equation 71b). Methanol solvation probably retards the dissociation of the radical anion intermediate in the SRN reaction, into radical and anion, and hence retards the chain reaction relative to the ionic reaction. The non-nucleophilic methylsulphinate ion gives only an S l reaction product with 2-bromo-2-nitropropane286. 

The reactivity of halogen compounds, of course, strongly depends on the halogen. Fluoroaliphatic compounds are nonreactive unless they contain another reactive functional group. Chloro-compounds are fairly reactive, k > 108 M 1 s 1, and their reactivity increases in the presence of neighbouring electron withdrawing groups. Bromo-and iodo-compounds are more reactive in that order. Thiols and disulphides are very reactive, whereas thiol anions and thioethers are only fairly reactive. Nitro- and nitroso-compounds are very reactive toward eaq. 

In this case two anions unite to form xanthic disulphide. On the other hand, in the electrolysis of sodium acetate, the anions are united, but carbonic acid is simultaneously split off ... 

Radicals formed from thiols and disulphides may play important roles in cellular function and malfunction, the RS radical, and RS-SR T radical anions being particularly implicated. The pKa values for many thiols, in the region of 9 to 10, are such that there are low, but possibly significant concentrations of RS- anions at pH.7. Thus RSH may act as an H-atom donor or, via RS-, as an electron donor. As with other radicals of this type, RS radicals have not been detected by ESR spectroscopy in aqueous solution, nor do they have intense absorption bands in the near-UV. However, they have a high affinity for RSH and RS- (Reactions [1.17]—[1.18]) which act as spin-traps provided they are present in fairly high concentrations. 

Probably the most frequently used spectrophotometric method to detect thiol groups, both for non-protein and protein sulphydryl groups involves the use of Ellman s reagent (Scheme 7.5). 5,5 -Dithiobis(2-nitrobenzoic acid), (DTNB) (Ellman 1959) undergoes disulphide exchange with thiol groups and the formation of 5-thio-2-nitrobenzoate anion (TNB) (Scheme 7.6). 

FIGURE 3. Consecutive radical intermediates observed in the suicidal reaction between E. coli E441Q, wild type R2 and substrate (A), including EPR spectra for the transient tyrosyl radical in R2 presumably at Tyr356 (B), the disulphide anion radical at Cys225nCys462 in R1 (C), and the nucleotide-derived radical (D). The arrows in B-D indicate g = 2.005. 

---