Mercaptoethanol, mediation

The most widely appHed colorimetric assay for amino acids rehes upon ninhydrin-mediated color formation (129). Fluorescamine [38183-12-9] and (9-phthalaldehyde [643-79-8] are popular as fluorescence reagents. The latter reagent, ia conjunction with 2-mercaptoethanol, is most often used ia post-column detection of amino acids separated by conventional automated amino acid analysis. More recently, determiaation by capillary 2one electrophoresis has been developed and it is possible to determine attomole quantities of amino acids (130). 

The presence of permanent [Fe2S2] clusters in holo-NifU impeded spectroscopic characterization of transient clusters assembled in a NifS-mediated process. However, unambiguous evidence for NifS-directed assembly of oxidatively and reductively labile [Fe2S2] " clusters on NifU-1 was obtained using the combination of UV-visible absorption and resonance Raman spectroscopies (Yuvaniyama et al. 2000). The anaerobic reaction mixture involved NifU ferric ammonium citrate P-mercaptoethanol l-cysteine NifS in a 50 100 5000 1000 1 ratio. The presence of catalytic amounts of NifS facilitated meaningful UV-visible absorption results and monitoring the time course of cluster assembly. Although ferric ammonium citrate was used for these cluster assembly studies, control experiments... 

It has been proposed that 8-aminodcoxyguanosinc is formed from the nitronate tautomer of 2-nitropropane either by base nitrosation followed by reduction, or via an enzyme-mediated conversion of the nitronate anion to hydroxyiam ine-O-sulfonate or acetate, which yields the highly reactive nitrenium ion NHj (Sodum et al., 1993). Sodum et al. (1994) have provided evidence for the activation of 2-nitropropane to an aminating species by rat liver aryl sulfotransferase in vitro and in vivo. Pretreatment of rats with the aryl sulfotransferase inhibitors pentachlorophenol or 2,6-dichloro-4-nitrophenol significantly decreased the levels of nucleic acid modifications produced in the liver by 2-nitropropane treatment. Partially purified rat liver aryl sulfotransferase activated 2-nitropropane and its nitronate at neutral pH to a reactive species that aminated guanosine at the position. This activation was dependent on the presence of the enzyme, its specific cofactor adenosine 3 -phosphate 5 -phosphosulfate, and mercaptoethanol. It was inhibited... 

Hydrogenase, HyD, includes a Fe-S cluster as active site. Photogenerated N,A -dimethyl-4,4 -bipyridinium radical cation, MV+, mediates H2-evolution in the presence of HyD [201-203], see Fig. 40. Different photosensitizers such as Ru(bpy) +, Zn-TMePyP4+ or acridine orange and sacrificial electron donor, i.e. ethylenediamine tetraacetic acid, EDTA, mercaptoethanol or cysteine, have been... 

Ru(II)tris(bipyridine) [Ru(bpy)3 +] as a photosensitizer, triammonium ethylene-diaminetetraacetic acid [(NH4)3EDTA] as a sacrificial electron donor and the enzyme ferredoxin NADP+ reductase (FDR) [215, 216]. Oxidative electron-transfer quenching of the excited Ru(bpy)3 + yields the A,A -dimethyl-4,4 -bipyridinium radical cation (reduced methylviologen, MV+), which mediates the reduction of NADP+ in the presence of FDR as a biocatalyst (Figure 32A). The quantum efficiency for NADH production corresponds to = 1.9 x 10 . A related system that includes Zn(II)wc50-(A-tetramethylpyridinium)porphyrin (Zn-TMPyP +) as a photosensitizer, mercaptoethanol as a sacrificial donor and lipoamide dehydrogenase (LipDH) as a biocatalyst has been applied for the photochemical reduction of NAD+ to NADH (Figure 32B). 

In summary, manganese bleomycin is able to mediate DNA degradation in the presence of ascorbate (but not with 2-mercaptoethanol for an unknown reason) or iodosylbenzene. It is less efficient than its iron bleomycin congener. The detailed mechanism of the DNA damage by manganese bleomycin as well as the reason for its lower efficiency were not investigated. 

Ballarin et al. used sonogel-carbon composite electrodes containing CoPc for the oxidation of cysteine The catalytic process is mediated by the generation of the Co Pc species. Oxidation of sulfide ion was catalyzed by microcrystals of CoPc immobilized at a surface of paraffin impregnated graphite electrode. Filanovsky reported the use of a carbon electrode prepared by hand pressing carbon powder mixed with CoPc and a polymer solution (poly(methyl methacrylate)) in dichloromethane, followed by evaporating the dichloro-methane, for the analysis of mercaptoethanol in petroleum and cysteine in human urine with detection limits of 8 x 10 M for the former and 2 x 10 M for the latter . 

Double Michael addition of RNHj (1 equiv.) to divinyl sulfones CH2=CHS02CH= CHR, mediated by mercaptoethanol (HSCH2CH2OH) and its analogues, such as HSCH2CH(Y)0H, has been reported to produce the corresponding nitrogen heterocycles. ... 

One of the first approaches of analyte-mediated changes in the surface of QDs has been reported by He and coworkers. They used CdSe QDs modified with mercaptoacetic acid for the selective determination of Ag+. The changes in the emission properties of the QDs were attributed to the chemical displacement of Cd + by Ag+ in the outermost cluster atom layers of the QDs with subsequent formation of Ag2Se. In an analogous way, mercaptoethanol-capped CdSe/CdS QDs were utilized for the detection of Cu " through the displacement of Cd " " and formation of... 

Reduction-mediated technetium-99m labelling of antibodies with 2-mercaptoethanol... 

Copper(I)-catalyzed tandem reaction of isothiocyanates and iodophenols in ionic liquids produced 95 (13JOM(723)137) iodine-mediated electrophilic cychzation of osmabenzene resulted in the isolation and characterization the osmabenzene-fused oxathiole 96 (13AGE9251) and nickel chloride-catalyzed reaaion of aromatic aldehydes with 2-mercaptoethanol produced 97 only as a minor product together with the bis(2-hydroxyethyl)dithioac-etals (13TL5839). Lamivudine 98 and its enantiomer 99 have been efficiently asymmetrically synthesized via enzymatic dynamic kinetic resolution (13CC10376). The deprotection of 1,3-oxathiolanes 100 promoted by a range of bases has been examined (13TL2217). 

Indium-111 labelling of antibodies using cyclic DTPA anhydride 221 Reduction-mediated technetium-99m labelling of antibodies with 2-mercaptoethanol 226... 

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