1 Di- sulfide

Mono- and di-thiocyanato-1,2,4-thiadiazoles, obtained by the stepwise action of cyanogen bromide on barium 3,5-dimercapto-l,2,4-thiadiazole, and on 5-chloro- and 5-hydroxy-3-mercapto-1,2,4-thiadiazole, are somewhat labile. The structures of certain of their transformation products (e.g. mono- and di-sulfides), which may have one of several isomeric forms, are not fully elucidated. The reactivity of their cyano group, resembling that in cyanogen halides, is noteworthy it is easily removed by the action of alkalis, the parent thiol being regenerated.202... 

Insulin is composed of 51 amino acids arranged in two polypeptide chains, designated A and B, which are linked together by two di- sulfide bridges (Figure 23.3A). The insulin molecule also contains an j intramolecular disulfide bridge between amino acid residues of the A chain. Beef insulin differs from human insulin at three amino add positions, whereas pork insulin varies at only one position. 

In the formation of SAMs, the film-forming molecules order themselves by chemical interaction with neighbouring molecules and with the substrate surface. This technique has been applied for a large variety of modifier/substrate combinations. Various sulphur compounds, like alkanethiols and (di)sulfides have been deposited on metals such as silver, copper and gold isocyanides on platinum and carboxylic acids on aluminum oxide and silver oxide.75 Alkyltrichlorosilanes have been deposited on gold, mica, aluminum, tin oxide and silicon oxide. The latter combination is of interest here. 

The Npys group is readily introduced under Schotten-Baumann conditions using Npys-Q, e.g. protection of Fmoc-Lys-OH (20) with Npys-Q to give Fmoc-Lys(Npys)-OH (21) (Scheme 7).P This reagent is prepared by chlorination of bis(3-nitro-2-pyridyl) di-sulfide it is also commercially available, but it is worthy to note that it is extremely sensitive to moisture. 

The actions of these proteolytic enzymes on proinsulin resull in the formation of equimolar quantities of insulin and the connecting C-pcpiide. The resulting insulin molecule consists of chains A and B. with 21 and 31 amino acid residues. respectively. The chains are connected by two disulfide linkages, with an additional di.sulfide linkage within chain A (Fig. 25-6). 

The amino acid sequence of insulins from various animal species has been examined. Details of these are shown in Table 25-6. Il is apparent from the antilysis that frequent changes in sequence occur within the inlerehain di.sulfide ring (positions 8, 9, and 10). The hormonal. sequence fur porcine insulin is the closest lo lhal of humans, differing... 

Chemical Operation or Reagent Mer- captans Di- sulfides Poly- sulfides Sulfides Thio- phene Elemental sulfur Hydrogen sulfide Sulfur dioxide... 

Figure 2. Time-resolved absorption changes induced by reaction of pulse radiolytically produced C02 radicals with P. aeruginosa azurin. (a) Reduction of Cu(II) followed at 625 nm. (b). Formation and decay of the di sulfide radical anion measured at 410 nm. Protein concentration is 1 OpAf, where T = 298 K pH 7.0 0.1M formate 10 mM phosphate N2O saturated pulse width 0.4 ps optical path 12.3 cm. Time is in seconds the left panel shows the faster phase, while the right one shows the reaction taking place at the slower phase. The lower panels show the residuals of the calculated fits to the data.

For many who study the chemistry of venoms, the neurotoxins hold particular interest. One example would be the polypeptide toxin cobrotoxin that was isolated from the Formosan cobra and analyzed in 1965 by Chen-Chung Yang, a distingmshed chair professor at Tsing Hua University in Taiwan. The primary structure of this neurotoxin is indicated in Figure 1, along with some components of its secondary structure. There are sixty-two residues in the primary structure and four di-sulfide bonds in the secondary structure. If even one of these di-sulfide bonds is somehow disrupted, the polypeptide is rendered nontoxic. This points to the fact that secondary structure is important even in small polypeptides, not only full-size proteins. 

Needles from sard NaQ soln. mp 82°. Deteriorates on storage and should be used promptly. Sol in 50 parts cold, in 10 parts hot water. Freely sol in alcohol, ether, carbon di sulfids, chloroform, hot benzene, dil mineral acids, acetic arid. Slightly sol in petr ether. The oxalate is more stable. 

SYNONYMS 4,5-dithia-l-octene, onion oil, 2-propenyl propyl di-sulfide, propyl allyl disulfide... 

Friction and Wear. Graphite, molybdenum di-sulfide, and PTFE filled PABMs exhibit peirticularly low wear rates in dry friction vs metal at high PV s and, in particular, at high pressures applied at low velocities. 

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