Disulfides reversibility

Allyl propyl disulfide Reverse mutation" S. typhimurium TM7, TA98, TA100, TA1535 and TA1537 Up to 333 pg/plate Negative Zeigeretal. (1988)... 

Allyl propyl disulfide Reverse mutation S. typhimurium TMOO Not specified Negative Ederetal. (1982)... 

Rayon. Viscose rayon is obtained by reacting the hydroxy groups of cellulose with carbon disulfide in the presence of alkali to give xanthates. When this solution is poured (spun) into an acid medium, the reaction is reversed and the cellulose is regenerated (coagulated). 

Fillers. Materials used as fillers (qv) in mbber can also be classified as acidic, basic, or neutral. Furnace blacks, ie, HAF, FEF, or SRF, are somewhat basic. As such, they can have an activating effect on sulfur cure rates. Furthermore, carbon blacks have been found to promote formation of mono/disulfide cross-links thereby helping minimize reversion and enhance aging properties. 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

Zirconium monochloride reacts with sodium ethoxide to form additional adducts which hydrolyze in water. The monochloride does not react with benzene in a Friedel-Crafts reaction, and does not enter into intercalation reactions similar to those of zirconium disulfide. Both monohaUdes add hydrogen reversibly up to a limiting composition of ZrXH (131). 

Lysozyme from bacteriophage T4 is a 164 amino acid polypeptide chain that folds into two domains (Figure 17.3) There are no disulfide bridges the two cysteine residues in the amino acid sequence, Cys 54 and Cys 97, are far apart in the folded structure. The stability of both the wild-type and mutant proteins is expressed as the melting temperature, Tm, which is the temperature at which 50% of the enzyme is inactivated during reversible beat denat-uration. For the wild-type T4 lysozyme the Tm is 41.9 °C. 

These reactions are reversible by changing the system temperature. ME A also reacts with carbonyl sulfide (COS) and carbon disulfide (CSi) to form heat-stable salts that cannot be regenerated. At temperatures above 245°F a side reaction with CO2 exists that produces oxazolidone-2. a heat-stable salt, and consumes MEA from the process. 

TliCNC reactions are reversible. DEA reacts with carbonyl sulfide (CUS) and carbon disulfide (CS2) to form compounds that can be regenerated in the stripping column. Therefore, COS and CS2 are removed without a loss i)f DEA. Typically, DEA systems include a carbon filter but do not include a reclaimer. 

The disulfide is a moderately strong oxidant and liberates iodine on addition of an acidified iodide solution. As usual there is a reversible... 

Figure 12.12 Coupled SEC-RPLC separation of Plioflex rubber stock (a) SEC (b) RPLC ti ace of fraction 1, Wingstay 100 (Eive-peak pattern is representative of diarylphenylenedi-amine isomers) (c) RPLC ti ace of fraction 2, mixed disulfide and MBTS (2,2 -thiobis (ben-zothiazole)). Obtained under the same conditions as given for Eigure 12.11. Reprinted from Journal of Chromatography, 149, E. L. Johnson et al, Coupled column chromatography employing exclusion and a reversed phase. A potential general approach to sequential analysis , pp. 571-585, copyright 1978, with permission from Elsevier Science.

Thiols can be oxidized by Br2 or I2 to yield disulfides (RSSR )- The reaction is easily reversed, and a disulfide can be reduced back to a thiol by treatment with zinc and acid. 

The sulfanes are soluble in carbon disulfide, benzene, tetrachloromethane, and dry diethylether (decreasingly so in that order) while alcohols and aqueous systems initiate rapid decomposition. For this reason a report on the chromatographic separation of the sulfanes H2S by reversed-phase HPLC using methanol as an eluent [35] was shown to be in error The peaks observed in the chromatogram have to be assigned to bismethoxy oligosulfanes... 

In 2000, the first example of ELP diblock copolymers for reversible stimulus-responsive self-assembly of nanoparticles was reported and their potential use in controlled delivery and release was suggested [87]. Later, these type of diblock copolypeptides were also covalently crossUnked through disulfide bond formation after self-assembly into micellar nanoparticles. In addition, the encapsulation of l-anilinonaphthalene-8-sulfonic acid, a hydrophobic fluorescent dye that fluoresces in hydrophobic enviromnent, was used to investigate the capacity of the micelle for hydrophobic drugs [88]. Fujita et al. replaced the hydrophilic ELP block by a polyaspartic acid chain (D ). They created a set of block copolymers with varying... 

These structures show that RpII essentially consists of the small core of four-stranded )9-sheet and three relatively large loops. Residues 6-16, 23-30, and 35-40 form loops 1, 2, and 3, respectively, and the chain reversals are accomplished by tight turns involving residues D8-D11, E28-E31, and V36-P39. Segments involved in )5-sheet strands and loops alternate in the primary sequence of Rp toxins. As mentioned above, these structures indicate that the )5-sheet is highly twisted in order to form the correct disulfide bonds. Comparison of different refined structures of RpII indicate that the structure of loop 1 in RpII is less well defined than... 

Thannhauser, T. W., McWherter, C. A., and Scheraga, H. A., Peptide mapping of bovine pancreatic ribonuclease A by reverse-phase high-performance liquid chromatography. II. A two-dimensional technique for determination of disulfide pairings using a continuous-flow disulfide detection system, Anal. Biochem., 149, 322, 1985. 

The interaction of carbon disulfide as a substrate in carbonic anhydrase model systems has been studied using density functional theory methods. A higher activation energy of CS2 compared to C02 in the reaction with [L3ZnOH]+ was due to the reduced electrophilicity of CS2. The reversibility of the reaction on the basis of these calculations is questionable with [L3ZnSC(0)SH]+ as intermediate.572... 

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