Thiol Redox and pKa Properties of Mycothiol,the Predominant Low‐Molecular‐Weight Thiol Cofactor in the Actinomycetes

The thiol pK_a and standard redox potential of mycothiol, the major low‐molecular‐weight thiol cofactor in the actinomycetes, are reported. The measured standard redox potential reveals substantial discrepancies in one or more of the other previously measured intracellular parameters that are relevant to mycothiol redox biochemistry.     

缩醛/酮的无气味硫缩醛/酮化反应

在甲醇介质中,氯化乙酰存在下,易制备和稳定的2-（1,3-二噻）亚甲基-3-氧代丁酸作无气味代硫醇试剂能与缩醛/酮有效进行硫缩醛/酮化反应。该反应条件温和,操作简单,产率高,且反应和后处理过程中,无硫醇的恶臭气味。     

Blood Thiol Redox State in Chronic Kidney Disease

Thiols (sulfhydryl groups) are effective antioxidants that can preserve the correct structure of proteins, and can protect cells and tissues from damage induced by oxidative stress. Abnormal levels of thiols have been measured in the blood of patients with moderate-to-severe chronic kidney disease (CKD) compared to healthy subjects, as well as in end-stage renal disease (ESRD) patients on haemodialysis or peritoneal dialysis. The levels of protein thiols (a measure of the endogenous antioxidant capacity inversely related to protein oxidation) and S-thiolated proteins (mixed disulphides of protein thiols and low molecular mass thiols), and the protein thiolation index (the molar ratio of the S-thiolated proteins to free protein thiols in plasma) have been investigated in the plasma or red blood cells of CKD and ESRD patients as possible biomarkers of oxidative stress. This type of minimally invasive analysis provides valuable information on the redox status of the less-easily accessible tissues and organs, and of the whole organism. This review provides an overview of reversible modifications in protein thiols in the setting of CKD and renal replacement therapy. The evidence suggests that protein thiols, S-thiolated proteins, and the protein thiolation index are promising biomarkers of reversible oxidative stress that could be included in the routine monitoring of CKD and ESRD patients.     

庚烯与H2S在酸性催化剂上反应机理研究I-硫醇等生成机理

 为了研究催化裂化汽油中硫化物的生成机理,在小型固定流化床(FFB)装置中考察了不同质量分数的庚烯与H₂S在固体酸催化剂上的反应.结果表明, 庚烯与H₂S的反应主要生成噻吩类硫化物、部分硫醇、少量硫醚和痕量四氢噻吩等硫化物；庚烯质量分数越高,生成硫化物的量越多; 噻吩类硫化物中生成量最大的甲基苯并噻吩的生成量也随着庚烯质量分数增加而线性增长.烯烃在催化剂B酸活性中心上吸附形成正碳离子, 正碳离子与H₂S结合生成硫醇,硫醇的生成遵循正碳离子机理.硫醇与烯烃反应生成硫醚.当反应温度为400～500℃,庚烯与H₂S反应中,生成硫醇、硫醚的反应均为放热反应,硫醇的平衡收率较低,硫醚的平衡收率更低一些.     

Synthesis and thermal properties of polythioether‐based liquid‐crystalline polymers containing azobenzene in the side chain

BACKGROUND: Owing to the unusual structural rearrangement of polychloromethylthiirane (PCMT) at room temperature, it has not been used as the main‐chain backbone of side‐chain liquid‐crystalline polymers (SLCPs). However, it has been observed that PCMT has a relatively stable and clear structure under special conditions. Therefore, we attempted to synthesize SLCPs using PCMT as main‐chain backbone and investigated their thermal behavior. RESULTS: New polymers, poly[1‐({(4‐methoxyazobenzene‐4′‐oxy)alkyl}thio)‐2,3‐epithiopropane], in which the number of methylene units in the alkyl group is 4, 5 or 6, were prepared by means of reactions of corresponding (4‐methoxyazobenzene‐4′‐oxy)alkylthiols with PCMT. The structures of these compounds were confirmed using elemental analysis and ¹H NMR spectroscopy. The substitution ratios of the copolymers with 4, 5 and 6 methylene units in the alkyl group were 56, 75 and 80%, respectively. Differential scanning calorimetry measurements and polarized optical microscopy observations showed that the resulting copolymers exhibited thermotropic liquid‐crystalline mesomorphism with nematic phase except for the copolymer with a 56% substitution ratio. The decomposition temperature of all the synthesized copolymers was near 195 °C. CONCLUSION: This investigation has demonstrated that PCMT polymerized for 8 h has the ability to act as a suitable main‐chain backbone for SLCPs. Moreover, SLCPs could be obtained only by the reaction of PCMT with thiolate salt containing mesogenic groups. The substitution ratios increased with increasing number of methylene groups in the spacer. Copyright © 2009 Society of Chemical Industry     

Catalytic Asymmetric Conjugate Addition of Mercaptans to β‐Substituted‐β‐Trifluoromethyl Oxazolidinone Enoates: Access to Chiral Trifluoromethylated Tertiary Thioethers and Thiols

The first asymmetric conjugate addition of mercaptans to β‐substituted‐β‐trifluoromethyl oxazolidinone enoates has been developed. The opposite enantiomers of adducts, containing a trifluoromethylated hetero‐quaternary stereogenic centers, could be obtained by utilizing two pseudo‐enantiomeric Cinchona alkaloid‐derived tertiary amine/squaramides as catalysts. Potassium dihydrogen phosphate was found to accelerate the reaction rate without compromising the enantioselective excess. A variety of chiral trifluoromethylated tertiary thioethers and thiols were readily prepared with excellent enantioselectivity.

     

THE ESTIMATION OF THIOLS AND DISULPHIDES IN BARLEY

Methods are described for the extraction and quantitation of endogenous barley thiols and disulphides. Thiols and disulphides, together with added internal standards, are extracted from ground barley tissues (embryos or degermed grains) and the thiols in the extract are trapped on columns of beaded p-hydroxymercuribenzoyl-agarose (p-HMB-agarose). After elution they are derivatised with 5,5′-dithiobis (2-nitrobenzoic acid) and the derivatives are separated and quantified by hplc. The disulphides in the effluent from the p-HMB-agarose column are collected on a silica-based ion exchange material. After elution they are reduced to thiols and, after derivatisation, they are assayed by hplc. Dry barley embryos contain substantial quantities of glutathione, progressively lesser quantities of oxidised glutathione, cystine and cysteine and traces of γ-glutamyl cysteine and cysteinyl glycine.     

RELEASE AND ACTIVATION OF BARLEY β-AMYLASE

The aim of this study was to determine the role of low molecular weight thiols both in the release and activation of β-amylase during grain germination. In quiescent barley grains (Hordeum vulgare L. cv. Torrent) about 55% of the β-amylase was extracted with buffer, the remaining 45% was in the bound form. During micromalting the bound form was progressively solubilised between germination days 1 and 4. When free β-amylase, extracted from ungerminated grains, was incubated with dithiothreitol the enzymic activity increased by 15%-20%. This activation did not occur when free β-amylase, from grain germinated for 3 days or more, was incubated with DTT. The release of bound β-amylase with thiols was pH dependant, occurring most rapidly at and above pH 8.0. At the onset of germination the embryo released soluble thiol (approximately 5 nmol per embryo) into the endosperm. Degermed grains were dosed with reduced glutathione and incubated for 72 h. The addition of 60 nmol glutathione caused the release of about 80% of the bound β-amylase. When less glutathione was used, 5 nmol (an amount similar to that released by the embryo in vivo) no significant release of the bound enzyme was detected. When degermed grains were dosed with oxidised glutathione (60 nmol), no bound β-amylase was released. However, addition of the disulphide bis-hydroxyethyldisulphide (60 nmol) did cause the release of about 90% of the bound enzyme. The aleurone layer reduced the bis-hydroxyethyldisulphide to a thiol, presumably 2-mercaptoethanol. Oxidised glutathione and cystine were not significantly reduced to thiols by isolated aleurone layers. The aleurone layer did cause the disappearance of cysteine from solution. When preparations of bound β-amylase were incubated with extracts from the endosperms of grains germinated for three days, the bound enzyme was released. This release was due to the high molecu lar weight material (>5 kDa) in the extract and not to low molecular weight thiols. It seems unlikely that simple thiols, such as glutathione, are solely responsible for the release of bound β-amylase.     

Effects of chain lengths,molecular orientation,and functional groups of thiols adsorbed onto CF surface on interfacial properties of CF/epoxy composites

In this article, a new treatment method based on molecular self‐assembly on carbon fiber (CF) surface was proposed for obtaining a controlled interface between CF and epoxy matrix in composite system. To form the controlled interfacial region, the surfaces of CF were first metallized by electroless Ag plating, then were reacted with a series of thiols (alkanethiols, aromatic thiol, and heterocyclic thiol) to form self‐assembly (SA) films, which further reacted with epoxy resin to generate a strong adhesion interface. The structure and composition of untreated and treated CF surface were investigated by surface‐enhanced Raman scattering spectroscopy (SERS) and X‐ray photoelectron spectroscopy (XPS), respectively. SERS study showed that thiols chemisorbed on Ag‐plated CF in the form of thiolate species via the strong S? Ag coordinative bond. Moreover, adsorbate orientation of thiols SA films on Ag‐plated CF surfaces was revealed on the basis of SERS selection rules. The XPS study further confirmed the well organized alignment and the chemisorption of thiols. To understand the interfacial adhesion mechanism, the interfacial shear strength of CF/epoxy microcomposites was evaluated by the microbond technique. The results showed that among the parameters such as chain lengths, molecular orientation, and types of functional groups, the chemical nature of functional groups is most important for the improvement of interfacial properties in CF/epoxy composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009