Highly chemoselective lipase from Candida sp. 99-125 catalyzed ring-opening polymerization for direct synthesis of thiol-terminated poly(ε-caprolactone)

Lipase from Candida sp. 99-125 catalyzed ring-opening polymerization of ε-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly(ε-caprolactone). Remarkably, high chemoselectivity of lipase from Candida sp. 99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved. The tedious protecting/deprotecting steps for thiol and metal residue were avoided. The polymerizations with around 70% monomer conversion were conducted in bulk and toluene at relative low temperature of 40 ℃. Number-average molecular weight of resulted polymers ranged from 3000 to 4700 Da by changing the feed ratio between monomer and initiator. The structures of obtained thiolterminated poly(ε-caprolactone) were demonstrated by combining NMR and SEC analyses.     

Quasiadiabatisches Differentialkalorimeter zur Darstellung der Einheit der Energiedosis für Quantenstrahlung

Zur Darstellung der Einheit der Energiedosis von Quantenstrahlung für Energien oberhalb von 0,4 MeV wurde im ASMW eine Normalmeßeinrichtung geschaffen, deren Hauptbestandteil ein quasiadiabatisches Differentialkalorimeter ist. Der Aufbau und die Wirkungsweise der Normalmeßeinrichtung werden erläutert. Als Bezugsmaterial für die absolute Bestimmung der Energiedosis dient Graphit. Die Korrektionsfaktoren, die in die Bestimmungsgleichung für die Energiedosis eingehen, werden kurz diskutiert. Die untere Meßgrenze der Einrichtung liegt bei 10^?1 Gy, wobei die Meßunsicherheit 1,4% betrāgt.     

Spectrophotometric determination of sulfhydryl concentration on the surface of thiol-modified chromatographic silica particles using 2,2′-dipyridyl disulfide reagent

This article describes a straightforward method for the quantification of thiol groups on the surface of chromatographic particles such as 3-mercaptopropyl silica gel. The method is based on a thiol-disulfide exchange reaction with 2,2′-dipyridyl disulfide (DPDS) reagent and spectrophotometric or HPLC-UV determination of the liberated 2-pyridyl thione. Linearity was obtained over the sulfhydryl concentration range of 0.02-0.5 μmol ml⁻¹ for the spectrophotometric determination and 0.2-5 μmol ml⁻¹ for the HPLC-UV measurement, with r² values of 0.9975 and 0.9981, respectively. The results were validated using elemental analysis as independent control method. The agreement between the results of both methods indicates that the sulfur of the thiol-modified silica particles is available as reactive sulfhydryls. The repeatability study indicated a higher precision for the DPDS method compared to the elemental analysis.     

Convenient Synthesis of Thiol Esters from Acyl Chlorides and Disulfides Using Zn/AlCl3

Summary.  Various thiol esters were prepared by condensation of acyl chlorides with disulfides in the presence of Zn/AlCl₃. The advantages of this method are high yields under relatively mild conditions, simple work-up, lack of toxicity, and low costs. Received July, 20, 2001. Accepted September 24, 2001     

高效液相色谱法测定香铃草子中还原型谷胱甘肽和总巯基含量

以5,5′-二硫双-2-硝基苯甲酸为衍生化试剂,使用细胞破壁、衍生化为一体的同步衍生化法,采用高效液相色谱法测定了香铃草子中还原型谷胱甘肽(GSH)和总巯基(-SH)含量。结果表明:香铃草子中GSH和总巯基含量均值分别为4.07μmol/g和6.06μmol/g。总巯基含量中扣除GSH含量大致为巯基蛋白含量,达1.99μmol/g,说明香玲草子富含GSH和巯基蛋白。优化色谱条件下GSH和总疏基的回收率分别为100.43%和101.79%,检测限分别为5.31μmol/L和6.18μmol/L。     

Asymmetric conjugate addition of thiols to (E)-3-crotonoyloxazolidin-2-one by iron or cobalt/pybox catalyst

The enantioselective conjugate addition of thiols to (E)-3-crotonoyloxazolidin-2-one was effectively catalyzed by the Fe(BF₄)₂·6H₂O/(S,S)-ip-pybox catalyst, and the addition product was obtained with up to a 95% ee. Furthermore, the Co(ClO₄)₂·6H₂O/(S,S)-ip-pybox catalyst also catalyzed the same reaction with a high enantioselectivity.     

A simple, base-free preparation of S-aryl thioacetates as surrogates for aryl thiols

A mild method for the preparation of S-aryl thioacetates by hetero cross-coupling reactions of aryl bromides or aryl triflates with potassium thioacetate is described. The reaction proceeded smoothly in toluene at 110 °C, mediated by catalytic Pd₂(dba)₃ in combination with CyPF-tBu as the ligand. Neither the presence of a base nor microwave conditions were required. The formed S-aryl thioacetate proved to be stable under flash chromatographic conditions and could be rapidly converted into the corresponding thiol under mildly basic conditions.     

Bismuth(III) Chloride (BiCl3); An Efficient Catalyst for Mild,Regio- and Stereoselective Cleavage of Epoxides with Alcohols,Acetic Acid and Water

Epoxides can be cleaved in a regio- and stereoselective manner with alcohols, acetic acid and water in the presence of catalytic amounts of bismuth(III) chloride, affording the corresponding β-alkoxy and β-acetoxy alcohols and diols in high yields.     

Emission spectroscopy from optically thick laboratory acetylene samples at high temperature

Recently, a high temperature source has been used to produce high temperature emission spectra of acetylene in the 3 μm spectral range, under Doppler limited resolution, and the complete spectral assignment has been performed using a global rovibrational Hamiltonian [Amyay B, Robert S, Herman M, Fayt A, Raghavendra B, Moudens A et al. Vibration-rotation pattern in acetylene (II): Introduction to Coriolis coupling in the global model and analysis of emission spectra of hot acetylene around 3 μm. J Chem Phys 2009;131:114301]. The present investigation focuses on the relative emission line intensities which are observed to be affected. The strongest lines intensity may be considerably reduced for high column density acetylene samples, hence affecting the 3:1 ortho:para intensity ratio. A radiative model is developed to take into account the effects generated by the strong opacity of the acetylene samples including self-absorption and absorption of the radiation emitted by the hot environment. The model is used to extract the absolute concentration of the high temperature acetylene samples from the observed relative spectral intensities. The relevance of the procedure for infrared remote sensing in high temperature astrophysical environments, such as circumstellar envelopes of cool carbon rich evolved stars, is discussed.     

Protease-catalysed synthesis of Z-l-aminoacyl-l-caprolactam amides from Z-protected amino acid esters and dl-α-amino-ε-caprolactam

The enzymatic synthesis of Z-l-aminoacyl-l-caprolactam amides from Z-protected amino acid esters and dl-α-amino-ε-caprolactam (ACL) was accomplished by the thiol proteases papain, bromelain and ficin in aqueous-organic media. Product yields of 96% and 87% for Z-Gly-l-ACL and Z-Ala-l-ACL, respectively, could be obtained. The products were purified and characterised by polarimetry, NMR and LC-MS. The suitability to accept a bulky 1,2-amino ketone as a nucleophile expands the general knowledge of thiol proteases and their catalytic potential.