Mercaptoacetic acid, effect

As mentioned above, it is not necessary for the metal ion itself to be an oxidising agent, and co-ordinated thiolates also undergo rapid oxidation by dioxygen. Very often, in these cases, only catalytic amounts of metal ion are required for the oxidation of the thiols by dioxygen. Examples are seen in the oxidation of mercaptoacetic acid or cysteine in the presence of metal ions (Fig. 9-12). This reaction has obvious implications for the effects of transition metal ions upon proteins containing cysteine residues. 

Other CTAs and inhibitors also tried (about 0.05 M) were anionic mer-captoacetate and mercaptosuccinate and cationic isopropylamine, 1-dimeth-ylamino-2-propanol, cysteamine hydrochloride, and copper sulfate. The pH was adjusted as necessary to yield the desired ions. None of the ionic CTAs reduced the measured PLMA MW, although mercaptoacetic acid at a pH of 2.2 (mixed anionic and neutral species) reduced the molecular weight almost to that obtained with mercaptoethanol. The ionic CTAs may increase the micelle aggregation number (electrolyte effect). Cu(II) precipitated surfactant, but the other solutions were clear. 

A luminescence of quantum size core-shell CdSe/ZnS nanocrystals solubilized with hydrophilic organic mercaptocompounds was studied. The long-chain molecules of mercaptoundecanoic acid effectively protect the surface of CdSe/ZnS nanocrystals, promote a high luminescence output and photostability of nanocrystals in contrast to short-chain molecules of mercaptoacetic acid. 

Fig. 1 shows PL spectra of as-synthesized CdSe/ZnS nanorystals in chloroform and solubilized in water by 2-aminoethanethiol hydrochloride, cysteine, mercaptoacetic acid and 11-mercaptoundecanoic acid. The general effect of water solubilization results in a noticeable decrease of PL intensity as compared to the original nanocrystals in chloroform. 

Water molecules are well known PL quenchers due to the energy transfer or charge capturing. A short-chain hydrophilic molecule like 2-aminoethanethiol, cysteine, mercaptoacetic acid does not shield the surface of nanocrystals from physi- or chemisorption of water molecules. By contrast, long-chain mercaptoundecanoic acid more effectively protects the surface of nanocrystals which results in less than twofold decrease of PL intensity during the solubilization. 

The effect of surfactants on the autooxidation of different thiols such as 2-mercaptoethanol (ME), 3-mercapto-1,2-propanediol (MPD), mercaptoacetic acid (MAAc) and dodecylmercaptan (DDM) in the presence of a polymeric catalyst, has been studied [155,156]. Fig. 20 illustrates the change in the initial rate of ME oxidation and the change in solution turbidity as a function of the concentration of the added anionic surfactant, sodium dodecylsulfate (DDS). The strong drop in the reaction rate and the increase in the turbidity of the system are apparently due to the formation of a complex between the polyion and the surfactant. However, the nonionic surfactant, oligoethylene oxide, does not influence ME oxidation. 

Strutural and electronic effects should play an important role in the electrocatalytic processes described above which appear to require the presence, in the thiol substrate molecule, of an activating -COOH (in cysteine) or of a derived ester group (in cysteine methyl ester[6]). In fact, not only the replacement of -SH at the cysteine molecule (e.g., by -OH or -SMe to form serine or methionine, respectively), but also the elimination of the -COOH group (to give 2-aminoethanethiol) results in complete loss of the electrocatalytic effect which, however, is maintained upon abstraction of the amino group (to form mercaptoacetic acid). Moreover, the replacement of the -COOH moiety in the mercaptoacetic acid formula, e.g,, by NH, CH, -CH SH or -OH (to give... 

Lai JY. Biodegradable in situ gelling delivery systems containing pilocarpine as new antiglaucoma formulations effect of a mercaptoacetic acid/N-isopropylacrylamide molar ratio. Dmg Des Dev Ther 2013 7 1273—85. 

Herzog G, Beni V, Dillon PH, Barry T, Arrigan DWM (2004) Effect of humic acid on the underpotential deposition-stripping voltammetry of copper in acetic acid soil extract solutions at mercaptoacetic acid-modified gold electrodes. Anal Chim Acta 511 137-143... 

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