The disulfide of

The telluride TcTe2 has been found to crystallize in a monoclinic layer structure. The disulfides of Re and Tc, unlike the pyrite-type Mn S2, contain monoatomic units. 

NO 3-Reducing. Fig. 9.15 shows data on groundwater below agricultural areas. The sharp decrease of 02 and NO3 at the redox cline indicate that the kinetics of the reduction processes are fast compared to the downward water transport rate. Postma et al., 1991 suggest that pyrite, present in small amounts is the main electron donor for NO3 reduction (note the increase of SOJ immediately below the oxic anoxic boundary). Since NO3 cannot kinetically interact sufficiently fast with pyrite a more involved mechanism must mediate the electron transfer. Based on the mechanism for pyrite oxidation discussed in Chapter 9.4 one could postulate a pyrite oxidation by Fe(III) that forms surface complexes with the disulfide of the pyrite (Fig. 9.1, formula VI) subsequent to the oxidation of the pyrite, the Fe(II) formed is oxidized direct or indirect (microbial mediation) by NO3. For the role of Fe(II)/Fe(III) as a redox buffer in groundwater see Grenthe et al. (1992). 

L-Proline also reacts with 2-hydroxy-6-methylacetophenones in boiling DMF to give racemic pyrrolo[2,l-h][l,3]benzoxazines 138 (79JOC4005). For the synthesis of pyrrolo[2,l-c][l,4]benzothiazepines 139, three different syntheses from L-Pro and 2-methylthiobenzoic acid or the disulfide of o-mercaptobenzoyl chloride have been described (88JHC1007). 

Ei catalyzes first the decarboxylation of pyruvate, producing hydroxyethyl-TPP, and then the oxidation of the hydroxyethyl group to an acetyl group. The electrons from this oxidation reduce the disulfide of lipoate bound to E2, and the acetyl group is transferred into thioester linkage with one —SH group of reduced lipoate. 

The disulfides of Cys and Pen, formed by oxidation, chelate through the (N,0) donor groups at each end of the molecule, with weak or no interaction of the disulfide moiety with first row transition elements. However, with softer metal centres, e.g. Pd11, there is evidence from CD and H NMR studies that a strong metal-sulfur bond can form.25,26... 

Ellman s reagent, 5,5 -dithio-bis-(2-nitrobenzoic acid), or DTNB, is a compound useful for the quantitative determination of sulfhydryls in solution (Ellman, 1958,1959). The disulfide of Ellman s reagent readily undergoes disulfide exchange with a free sulfhydryl to form a mixed disulfide and release of one molecule of the chromogenic substance 5-sulfido-2-nitrobenzoate, also called 5-thio-2-nitrobenzoic acid (TNB). The intense yellow color produced by the TNB anion can be measured by its absor-... 

The much higher reactivity of polysulfide ions, compared with HS, towards organic Michael acceptors suggests that, in coastal marine sediments and salt marshes, polysulfide 10ns could be more important than HS for organosulfur formation. In fact, preliminary studies indicate that TBP treatment of anoxic sediment slurries or extracted pore water from Biscayne Bay (Florida) releases substantial amounts of 3-MPA (22), suggesting the presence of polysufido-propionic acids or the disulfide of 3-MPA This aspect is currently under study. 

That the N-terminal methionine is exposed to the solvent was also concluded from studies directed toward the reduction and alkylation of the disulfides of rhGH. The conditions that were found to be optimal for the derivatization of the four sulfhydryls of rhGH resulted in the production of a side reaction when the procedure was applied to the methionyl analog. This side product was identified as containing carboxymethyl-S-methionine at the amino terminal residue. 

Approximately 150 different amino acid residues have been reported in proteins (1 5). At least half of these could undergo chemical deteriorations under the conditions of stress usually encountered. Many of these deteriorative reactions involve hydrolytic scissions, not only of peptide bonds but of the many different nonprotein substances added covalently to proteins postribosomally. These susceptible side chain groups are indole, phenoxy, thioether, amino, imidazole, sulfhydryl, and derivatives of serine and threonine (such as 0-glycosyl or O-phosphoryl), the disulfides of cystine, and, of course, the amides (such as asparagine and glutamine). With strong acid or alkali, other residues, such as serine and threonine, also are less stable. 

Titanium disulfide, like the disulfides of Zr, Hf, V, Nb, and Ta, has a layer structure two adjacent close-packed layers of S atoms have Ti atoms in octahedral interstices. These sandwiches are then stacked so that there are adjacent layers of S atoms. Lewis bases such as aliphatic amines can be intercalated between these adjacent sulfur layers similar intercalation compounds can be made with M and MSe2 compounds for M = Ti, Zr, Hf, V, Nb, and Ta. Many of these have potentially useful electrical properties, including use as cathode material for lithium batteries, and superconductivity, and may be compared with the intercalation compounds of... 

The results in Table XII show that self-activated platinum oxide exchanges in both a and /3 positions of thiophene, whereas self-activated ruthenium oxide catalyzes deuteration almost exclusively in the a. position. A similar type of selectivity has been observed for the exchange of thiophene on the disulfides of tungsten (both a and /3 deuteration) and molybdenum (predominantly a) using evaporated metal films.116... 

The second electron acceptor in these enzymes is the disulfide of a cystine residue. The disulfide in EHz is also partially reduced. Several lines of evidence support this, but one crucial experiment with pig heart lipo-amide dehydrogenase should be described in some detail [27, 55). Arse-nite complexes quite specifically with vicinal dithiols as shown in Eq. (1). 

Some of the catalytic and structural properties of thioredoxin reductase as they relate to analogous properties of lipoamide dehydrogenase and glutathione reductase have been covered in Section II. The flavoprotein, thioredoxin reductase, catalyzes the electron transfer from NADPH to thioredoxin, a protein of 12,000 molecular weight containing a single disulfide. The reductase has a reactive disulfide in addition to FAD. Thus, electron flow is from NADPH to the PAD-disulfide system of thioredoxin reductase, to the disulfide of thioredoxin, and finally to a variety of acceptor systems. 

To a solution of 0.285 g (0.002 mol) of 2-mercaptobydroquinone in 10 parts of alcohol is added 3.5 mL (0.007 mol) of a 2 N solution of ferric chloride. The disulfide of /r-benzoquinone deposits in the form of a yellow precipitate. It is collected and recrystallized from glacial acetic add to give yellow crystals, mp 178 °C, in quantitative yield. 

Potentiometric Methods. - Potassium trithiocarbonate has been used as a reductant (-S-S- reduction cleavage) for the potentiometric (and spectrophoto-metric) determination of the disulfides of dithio-phosphinic acids in DMF-H2O medium at millimolar levels.The protonation equilibria for N,N -diethylami-nomethylenephosphonic acid (88) were elucidated from both potentiometric titration and determination of the pH dependence of the NMR chemical shift (83 ip), and protonation constants for aminoalkanephosphonates RCH(NH2)P(0)(0Et)2 and the acidity constant of di(2-ethylhexyl)thiopho-sphoric acid (111) have also been obtained potentiometrically. 

Figure 4 (a) Analysis of dansyl-Ile-Thr(0 Bu -Pro-Gln-Trp-LysCBocFWang-linker-resin, giving peptide dansyl-Ile-Thr-Pro-Gln-Trp-Lys (MH+, 1006.0). The peak at 772.6 represents a small amount of undansylated material, (b) Analysis of Fmoc-Cys(Trt)-Lys(Boc)-Ile-HMPB-linker-resin, giving Fmoc-Cys-Lys-Ile (MH+, 585.5), Fmoc-Cys(Trt)-Lys-Ile (MH+, 849.8), and Fmoc-Cys-Lys-Ile disulfide [(M-S-S-M)H+, 1168.3], (c)Analysis of the disulfide of Fmoc-Cys-Asn-Cys-Lys(Boc)-Ile-FIMPB-linker-resin giving the disulfide of Fmoc-Cys-Asn-Cys-Lys-Ile (MH+, 801.0). (Reprinted from Ref. 64.)... 

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