2,2 -Dithiobis derivatives

The remainder of this chapter deals, in the main, with the preparation of a number of derivatives of the cysteinyl residue such as the acidic compounds, cysteic acid, S-carboxymethylcysteine, S-sulfo-cysteine, and the S-sulfenylthiosulfate of cysteine, the basic derivative S-aminoethylcysteine and S-carboxamidomethylcysteine. Procedures are also presented for the application of N-ethylmaleimide, p-mercuribenzoate, 5,5 -dithiobis(2-nitrobenzoate), and azobenzene-2-sulfenyl bromide to the spectrophotometric determination of sulfhydryl groups. 

The vulcanization accelerators include the thiazole 2-mercaptobenzothiazole (MBT) (169), and its derivative benzothiazole disulfide (dibenzoythiazyl disulfide, 2,2 -dithiobis (benzothiazole), MBTS) (170). Organic accelerators enable reduction in time of vulcanization, more effective use of sulfur in formation of cross-links and use of low processing temperatures. MBTS delays vulcanization, when compared with MBT alone. They are used in production of conveyor belts, footware, etc. The 2-mercaptobenzothiazole zinc salt (MBTZ) (171) is also important, and is used in latex products. Other sulfur donors include 2-morpholinodithiobenzothiazole, 2-(4-morpholinyldithio)benzothiazole (MBSS, MORFAX) (172). 

The method of Fan and Dasgupta (1994) relics on tlie reaction of formaldehyde with 1,3-cyclohexane-dione in acidified ammonium acetate to form the fluorescent dihydropyridine derivative in a flow injection analysis system. Formaldehyde trapped in water can be reacted with pararosaniline and sodium sulfite under mild conditions (neutral pH, room temperature equilibration) to produce a colored product that is measured at 570 nm (Petreas et al. 1986). The presence of bisulfite is an interference in this reaction so the method cannot be used to sample atmospheres that contain sulfur dioxide. In addition, the method is reported to suffer from interferences resulting from the presence of other aldehydes and phenol (Hoogenboom et al. 1987). The indirect method of Hoogenboom et al. (1987) relies on the reaction of excess bisulfite in an aqueous solution of formaldehyde with 5,5 -dithiobis(2-nitrobenzoic acid) to form a colored product, the absorbance of which is measured at 412 nm. The method reported by Naruse et al. (1995) relies on the formation of a colored product obtained by reacting the aqueous formaldehyde with acetylacetone and ammonium acetate in acetic acid. Absorbance is measured at 414 nm. 

Cyclization of 2,2 -Dithiobis(Benzaldehyde) and-(Benzamide) Derivatives via Sulfenylhalides... 

Assays of residual AChE were made by the Ellman spectrophotometric procedure based on acetylthiocholine and the cleavable indicator, 5,5 -dithiobis-2-nitrobenzoic acid (17). The negative logarithm of the molar concentration causing 50% inhibition, pI50, is derived from the inhibition-concentration plot. 

Ch. 10 S-Substituted Thio-, Sulfinyl-, or Suffonyl- 1,2, 4-thiazoles, 3,3 -Dithiobis[l,2,4]triazoles, and 1,2,4-Triazolesulfonic Acids and Iheir Functional Derivatives Ch. 11 Mono-, Di-, and Trihalo-1,2,4-triazoles... 

Serum pseudo-cholinesterase (referred to hereafter as serum cholinesterase) activities were determined from a five minute reaction period at room tenperature with a modification of the method of EUman et 2Q. ( ). Briefly, a 10 pi 2d.iguot of serum ves added to both a reference and sample cuvette ocxitaining 3.0 ml of 5,5-dithiobis-(2-nltrobenzoate) (DDO buffer (0.25 mM in ph 8.0, 0.1 M sodium phos te buffer) and mixed with a micro-stirring rod. Die reaction ves steurted in the sample cuvette by the addition of 20 pi of aoetylthiochollne iodide (78 nM) and stirred. The reference cuvette received 20 pi of distilled water in place of substrate. Absorbance was measured at 412 im over a five minute period and the rate calculated from the slope of the derived curve. 

SERS biosensors have also been used in conjunction with reporter molecules which have strong, distinct Raman spectra as labels. Some such molecules are thiophenol (TP), 2-naphthalenethiol (NT) [39], 5,5-dithiobis(succinimidyl-2-nitro-benzoate) (DSNB, a derivative of dithiobis (benzoic add)) [40], (4-mercaptobenzoic acid, 4MBA) [41], etc. Because the Raman signal is usually quite weak, high-power lasers are required to elicit a measurable signal. However, it is not easy to miniaturize such lasers. Hence, enhancement of the signal by surface modification (ie, SERS) and/or using reporter molecules makes this technique more amenable to use in POC scenarios. 

Thiirane derivatives with thiophosphate and thiocarbamates Dithiobis(thiadiazole thiol)... 

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