Multiparameter kinetic analysis of alkaline hydrolysis of a series of aryl diphenylphosphinothioates: models for P=S neurotoxins

Alkaline hydrolysis of a series of X‐substituted‐phenyl diphenylphosphinothioates ( 2a‐i ) in 80 mol%/20 mol% DMSO at 25.0 ± 0.1°C has been studied kinetically and assessed through a multiparameter approach. Substrates 2a to 2i are approximately 12 to 22 times less reactive than their P=O analogues 1a to 1i (ie, the thio effect). The Brønsted‐type plot for the reactions of 2a to 2i is linear with β_lg = ?0.43, consistent with a concerted mechanism. Hammett plots correlated with σ^o and σ^? constants also support a concerted mechanism; the Yukawa‐Tsuno plot results in an excellent linear correlation with ρ_X = 1.26 and r = 0.30, indicating that expulsion of the leaving group occurs in the rate‐determining step (RDS). The ΔH^? value increases from 10.5 to 11.7 and 13.9 kcal/mol as substituent X in the leaving group changes from 3,4‐(NO₂)₂ to 4‐NO₂ and H, in turn, while TΔS^? remains constant at ?6.0 kcal/mol. The strong dependence of ΔH^? on the electronic nature of substituent X also indicates that the leaving group departs in the RDS. The reaction mechanism and origin of the thio effect are discussed by comparison of the current kinetic results with those reported for the reactions of 1a to 1i . The results suggest that for useful OP neurotoxins the mechanism of abiotic hydrolysis is concerted (with varying degrees of asynchronicity) when the substrate bears good leaving groups.     

Cd对纤锌矿ZnO极化特性的影响以及Zn0.75Cd0.25O/ZnO界面能带偏差的第一性原理研究

基于第一性原理GGA+U方法研究了Zn1-xCdxO合金的品格常数以及自发极化随Cd组分x的变化关系,其中极化特性的计算采用Berry-phase方法,同时计算了禁带宽度随Cd组分x的变化关系,并得到了能隙弯曲参数0.69.此外,通过计算宏观平均静电势的方法得到了(5 +3)Cd0.25Cd0.750/ZnO超晶格界面处的价带偏差为0.13 eV,导带偏差与价带偏差的比值为4/13,并且Zn1-xCdxO/ZnO界面两侧能带呈现Ⅰ型排列,这些研究结果将对Zn1-xCdxO/ZnO界面二维电子气的设计与优化起到重要作用.     

第二类Feigenbaum函数方程凸解的构造

考虑第二类Feigenbaum函数方程{f（x）=1/λf（f（λx））,0〈λ〈1,f（0）=1,0≤f（x）≤1,x∈[0,1]对于给定的初始函数,利用构造性方法讨论上述方程的连续凸解、C^1-凸解和C^2-凸解的存在性及唯一性.     

Modification of both the electrophilic center and substituents on the nonleaving group in pyridinolysis of O-4-nitrophenyl benzoate and thionobenzoates

A kinetic study is reported for reactions of 4-nitrophenyl benzoate (1c) and O-4-nitrophenyl X-substituted thionobenzoates (2a-e) with a series of pyridines in 80 mol % H2O/20 mol % dimethyl sulfoxide (DMSO) at 25.0 +/- 0.1 degrees C. O-4-Nitrophenyl thionobenzoate (2c) is more reactive than its oxygen analogue 1c toward all the pyridines studied. The Br?nsted-type plot is linear with beta(nuc)=1.06 for reactions of 1c but curved for the corresponding reactions of 2c with beta(nu)c decreasing from 1.38 to 0.38 as the pyridine basicity increases, indicating that the reaction mechanism is also influenced on changing the electrophilic center from C=O to C=S. The curvature center of the curved Br?nsted-type plots (defined as pK(a)(o)) occurs at pKa = 9.3 regardless of the electronic nature of the substituent X in the nonleaving group. The Hammett plot for reactions of 2a-e with 4-aminopyridine is nonlinear, i.e., the substrates having an electron-donating substituent exhibit negative deviations from the Hammett plot. However, the Yukawa-Tsuno plot for the same reactions exhibits good linear correlation, indicating that the negative deviations shown by these substrates arise from stabilization of the ground state through resonance interaction between the electron-donating substituent X and the C=S bond.     

Synthesis of Pure <Emphasis Type="Italic">meso</Emphasis>-2,3-Butanediol from Crude Glycerol Using an Engineered Metabolic Pathway in <Emphasis Type="Italic">Escherichia coli</Emphasis>

meso-2,3-Butanediol (meso-2,3-BDO) is essential for the synthesis of various economically valuable biosynthetic products; however, the production of meso-2,3-BDO from expensive carbon sources is an obstacle for industrial applications. In this study, genes involved in the synthesis of 2,3-BDO in Klebsiella pneumoniae were identified and used to genetically modify Escherichia coli for meso-2,3-BDO production. Two 2,3-BDO biosynthesis genes—budA, encoding acetolactate, and meso-budC, encoding meso-SADH—from K. pneumoniae were cloned into the pUC18 plasmid and introduced into E. coli. In 2 l batch culture, the SGSB03 E. coli strain yielded meso-2,3-BDO at 0.31 g/g_glucose (with a maximum of 15.7 g/l_culture after 48 h) and 0.21 g/g_{crude glycerol} (with a maximum of 6.9 g/l_culture after 48 h). Batch cultures were grown under optimized conditions (aerobic, 6% carbon source, 37 °C, and initial pH 7). To find the optimal culture conditions for meso-2,3-BDO production, we evaluated the enzyme activity of meso-SADH and the whole cell conversion yield (meso-2,3-BDO/acetoin) of the E. coli SGSB02, which contains pSB02. meso-SADH showed high enzyme activity at 30–37 °C and pH 7 (30.5–41.5 U/mg of protein), and the conversion yield of SGSB02 E. coli was highest at 37–42 °C and a pH of 7 (0.25–0.28 g _meso-2,3-BDO/g_acetoin).     

Rectification of spatial disorder

We demonstrate that a large ensemble of noiseless globally coupled-pinned oscillators is capable of rectifying spatial disorder with spontaneous current activated through a dynamical phase transition mechanism, either of first or second order, depending on the profile of the pinning potential. In the presence of an external weak drive, the same collective mechanism can result in an absolute negative mobility, which, though not immediately related to symmetry breaking, is most prominent at the phase transition. Our results apply to a tug-of-war by competing molecular motors for bidirectional cargo transport.     

Nuclear magnetic resonance-based metabolomics for prediction of gastric damage induced by indomethacin in rats

Non-steroidal anti-inflammatory drugs (NSAIDs) have side effects including gastric erosions, ulceration and bleeding. In this study, pattern recognition analysis of the ¹H-nuclear magnetic resonance (NMR) spectra of urine was performed to develop surrogate biomarkers related to the gastrointestinal (GI) damage induced by indomethacin in rats. Urine was collected for 5 h after oral administration of indomethacin (25 mg kg⁻¹) or co-administration with cimetidine (100 mg kg⁻¹), which protects against GI damage. The ¹H-NMR urine spectra were divided into spectral bins (0.04 ppm) for global profiling, and 36 endogenous metabolites were assigned for targeted profiling. The level of gastric damage in each animal was also determined. Indomethacin caused severe gastric damage; however, indomethacin administered with cimetidine did not. Simultaneously, the patterns of changes in their endogenous metabolites were different. Multivariate data analyses were carried out to recognize the spectral pattern of endogenous metabolites related to indomethacin using partial least square-discrimination analysis. In targeted profiling, a few endogenous metabolites, 2-oxoglutarate, acetate, taurine and hippurate, were selected as putative biomarkers for the gastric damage induced by indomethacin. These metabolites changed depending on the degree of GI damage, although the same dose of indomethacin (10 mg kg⁻¹) was administered to rats. The results of global and targeted profiling suggest that the gastric damage induced by NSAIDs can be screened in the preclinical stage of drug development using a NMR based metabolomics approach.     

Cu3V2O7(OH)2·2H2O纳米线的制备及光吸收性能

以CuSO4·5H2O和 NH4VO3为原料,采用水热法制备了Cu3V2O7(OH)2·2H2O纳米线.采用X射线衍射(XRD)和场发射扫描电子显微镜(FE-SEM)对样品的组成和表面形貌进行了表征,结果显示:Cu3V2O7(OH)2·2H2O纳米线直径约80 nm,长度达到几个微米.对纳米线形成机理研究表明:该纳米线的形成主要取决于反应温度和反应体系pH值等因素.紫外-可见光吸收测试显示Cu3V2O7(OH)2·2H2O纳米线具有较宽的紫外-可见光吸收范围,计算其带隙宽度为1.94 eV.     

载Ag二氧化钛纳米线的制备及其光催化性能

利用水热合成法,制备出了二氧化钛纳米线,通过葡萄糖还原Ag(NH3)+2,在制备出的二氧化钛纳米线表面负载了 Ag纳米颗粒.利用透射电镜(TEM)、高分辨透射电镜(HRTEM)、X射线光电子能谱(XPS)和紫外-可见光谱(UV-Vis)对产物进行了表征.结果表明:该Ag/TiO2纳米线在可见光区域表现出较强的吸收性能.测试了样品降解酸性红3R溶液的活性.结果表明,TiO2纳米线表面负载Ag纳米颗粒对提高其光催化性能具有积极的作用.     

β-AgVO3一维材料的制备及其光学性能

以AgNO3和 NH4VO3为原料,采用水热法,通过调控反应体系pH值,制备了β-AgVO3纳米线、亚微米线及微米棒.采用X射线衍射(XRD)和场发射扫描电子显微镜(FE-SEM)对样品的组成和表面形貌进行了表征.紫外-可见光吸收测试表明所制得的不同尺寸的β-AgVO3一维材料均具有较宽的紫外-可见光吸收范围,通过计算得出β-AgVO3纳米线、亚微米线及微米棒的光学带隙分别为2.21 eV,2.17 eV和2.12 eV.