Sensitivity of Positive Ion Mode Electrospray Ionization Mass Spectrometry in the Analysis of Thiol Metabolites

High signal intensities of glutathione (GSH), [GSH+H]⁺ (m/z 308), cysteine (CySH), [CySH+H]⁺ (m/z 122), and homocysteine (hCySH), [hCySH+H]⁺ (m/z 136), are observed in ESI MS with on‐line electrochemistry (EC). Dimers formed by H‐bonding, which are not electrochemical products, are detected as [2GSH+H]⁺ (m/z 615), [2CySH+H]⁺ (m/z 243) and [2hCySH+H]⁺ (m/z 271) together with disulfide dimers GSSG, CySSCy and hCySSCyh, [GSSG+H]⁺ (m/z 613), [CySSCy+H]⁺ (m/z 241) and [hCySSCyh+H]⁺ (m/z 269). When dopamine is present a thiol/dopamine quinone (DAQ) adduct is observed. Formation of this adduct is proposed to occur by an electrochemical mechanism during ESI. Catalysis of thiol oxidation and analysis of thiol mixtures is addressed.     

Comparative evaluation of antioxidant capacities of thiol-based antioxidants measured by different in vitro methods

Thiol-type compounds are an important class of strong antioxidants and main determinants of total antioxidant capacity (TAC) of cellular homogenates. The TAC of thiol mixtures and the corresponding TEAC (trolox equivalent antioxidant capacity) values of individual thiols were determined by the CUPRAC (CUPric Reducing Antioxidant Capacity) method, and the results were compared with those found by reference assays for method validation. Synthetic mixtures of thiols were prepared, and the expected and found TAC values (in mM trolox (TR) equivalents) of these mixtures showed a good agreement. The technique of standard additions was performed for thiol mixtures and human serum, and the absorbance results confirmed that apparent chemical deviations from Beer's law were absent in the system. The CUPRAC results were compared with those of reference methods, namely 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)/persulphate and Ferric Reducing Antioxidant Power (FRAP). As being a most important thiol (-SH) peptide at in vivo conditions, glutathione (GSH) showed a TEAC value of 0.57 in the CUPRAC method, as opposed to the corresponding value (1.51) in the ABTS/persulphate method. The ABTS/persulphate result was not in accordance with the reversible 1-e oxidation of GSH to the corresponding disulfide that is expected to occur under physiological conditions. FRAP did not give consistent results, and even at relatively high concentrations of GSH, the TEAC_FRAP value was only 0.07. The thiol-type antioxidant-bearing pharmaceuticals of Brunac eye drop, Trom and Mentopin effervescent tablets containing N-acetyl-l-cysteine (NAC) were assayed with HPLC for comparison, and the obtained results for NAC were in accordance with those found with CUPRAC.     

新型芳基硫醇的合成及在聚芳醚砜紫外交联中的应用

通过假高稀反应和芳香亲核取代反应成功制备了一种新型芳基三硫醇,其与烯丙基聚醚砜(c-PAES)的混合体系在光引发剂 TPO 的作用下能极大地增强聚醚砜体系的紫外交联速度.研究结果表明,按官能团摩尔比1:1的比例添加芳基三硫醇的聚醚砜体系在紫外交联情况下,其最终双键转化率提高了1倍左右,而且体系的光反应速率有了极大的提高...     

Reaction between l-cysteine and 10-methylphenothiazine cation radical released from droplet-modified electrodes

The electrochemical oxidation of 10-methylphenothiazine (PMe) dissolved in 1,2-trans-dibromocyclohexane oil droplets immobilised on a basal plane pyrolytic graphite (BPPG) electrode and bathed by an aqueous electrolyte is a one-electron quasi-reversible process which occurs with the expulsion of the electro-generated cation radical from the oil phase. In the presence of l-cysteine in the aqueous phase, the electro-released cation mediates the redox catalytic oxidation of the thiol. The peak catalytic current is observed to increase linearly with increasing cysteine concentration over the range analysed (10–100 mM).     

A simple acylation of thiols with anhydrides

Different thiols were efficiently acylated at room temperature with different anhydrides in the presence of potassium carbonate. Chemoselective protection of thiol in the presence of hydroxy group was achieved using di-tert-butyl dicarbonate and isatoic anhydride.     

Efficient Aerobic Oxidative Synthesis of Benzimidazoles with Fe(III) based PEG1000 Dicationic Imidazolium Ionic Liquid/toluene Temperature‐dependent Biphasic System

A green protocol for the synthesis of benzimidazoles with Fe(III) based PEG1000 dicationic imidazolium ionic liquid ([PEG₁₀₀₀mim₂][FeCl₄]₂)/toluene temperature‐dependent biphasic system was described. Conformed by IR analysis, FeCl₄⁻ is the dominating anion species. It could be seen that aldehydes aryla mines and aromatic aldehydes bearing electron‐deficient group ( Cl,  Br,  NO₂) and electron‐rich groups ( OH,  N(CH₃)₂) on the aromatic rings gave good yields (78–96 %). Moreover, the Fe(III) based PEG1000 dicationic imidazolium ionic liquid could be recycled and reused without significant loss of catalytic activity after seven runs.     

Electrochemical Biosensor Based on Nanocomposites Film of Thiol Graphene‐Thiol Chitosan/Nano Gold for the Detection of Carcinoembryonic Antigen

In this paper, a thiol graphene‐thiol chitosan‐gold nanoparticles (thGP‐thCTS‐AuNPs) nanocomposites film with porous structure was fabricated by electrochemically depositing on glassy carbon electrode (GCE), which exhibited good biocompatibility and improved conductivity, to construct immunosensor free label for detection of carcinoembryonic antigen (CEA). The electrochemical behavior of this immunosensor was investigated by cyclic voltammetry. Under the optimum conditions, the immunosensor revealed a good amperometric response to CEA in two linear ranges (0.3–8.0 ng mL^?1 and 8.0–100 ng mL^?1) with a detection limit of 0.03 ng mL^?1. The results indicated that the immunosensor has the advantages of good selectivity, high sensitivity, and good stability for the determination of CEA.     

Green and reusable homogeneous oxidative system with ceric ammonium nitrate/[Imim‐PEG1000‐TEMPO] for efficient aerobic oxidation of alcohols and one‐pot synthesis of benzimidazoles from alcohols under ambient conditions

An efficient and reusable catalytic system for aerobic oxidation of alcohols and one‐pot synthesis of benzimidazoles from alcohols with ceric ammonium nitrate and PEG₁₀₀₀–ionic liquid‐immobilized 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) is described. This system shows excellent activity and selectivity, affording the target products with good yields. Moreover, the catalytic system can be recycled and reused without significant loss of catalytic activity after seven runs. Copyright © 2014 John Wiley & Sons, Ltd.