Tasumatrols P – T,Five New Taxoids from Taxus sumatrana

The phytochemical investigation of the more polar fractions from the leaves and twigs of Taxus sumatrana (Taxaceae) afforded five new taxane diterpene esters, tasumatrols P–T ( 1 – 5 ) possessing an 11(15→1),11(10→9)‐diabeotaxane skeleton. Compounds 1, 4 , and 5 contain an α‐hydroxy group at C(14), while 3 has no OH group at either C(13) or C(14). Compound 2 is a natural 4,5‐acetonide derivative, while 4 has an unusual spiro‐connected 2‐hydroxy‐2‐phenyl‐1,3‐dioxolane ring. Ten known taxoids, were also isolated in the course of the chromatographic fractionation. Five additional new O‐acetyl derivatives 3a, 4a, 4b, 5a , and 5b were prepared from the taxanes 3 – 5 . The structures of all new compounds were established on the basis of their spectroscopic analyses. Compound 1 showed mild cytotoxic activity against human Hela and Daoy tumor cells.     

Multilayer films of cationic surfactants incorporating polyoxometalate on electrodes

A new kind of multilayer of didodecyldimethylammonium bromide (DDAB) and 1:12 phosphomolybdic anions (PMo₁₂) was achieved on the surface of a wax-impregnated graphite (WIG) electrode by ion exchange and electrostatic interaction. The characterization and electrochemical behavior of the multilayer films of DDAB/PMo₁₂ is described in detail. The chemically modified electrode was shown to exhibit an excellent electrocatalytic activity toward the reduction of BrO₃ ^– anion in 0.5 M H₂SO₄ and possesses several attractive features, such as simple preparation, fast response, good stability, etc. Electronic Publication     

Liquid chromatographic studies of the effect of phosphate on the binding properties of silica-immobilized bovine serum albumin

High-performance liquid chromatography has been used to examine how phosphate ions affect the binding properties of bovine serum albumin (BSA) immobilized to porous silica. In doing this, the time dependence of the protein to reach conformational equilibrium is measured as a function of the concentration of phosphate in the eluent using the D- and L-isomers of tryptophan and kynurenine as solutes. The overall binding and chiral selectivity (alphaD,L) of the protein toward these solutes appear to be related to two types of effects: one being those that are site-selective and only influence the retention of the L-isomers and the other being those that are nonselective and influence the retention of both enantiomers. An interesting feature of the concentration-dependent data is a maximum in alphaD,L at intermediate phosphate concentrations (i.e., 10 to 50mM phosphate) indicative of both cooperative and antagonistic binding effects. Phosphate eluents within this concentration range provide selectivity advantages, and those at higher concentrations decrease the time required for the protein or column to reach equilibrium. A final set of studies has also been carried out using four alternate buffer systems (i.e., borate, carbonate, acetate, and arsenate eluents). Although the borate eluents affect the BSA's binding properties and alphaD,L similar to the phosphate eluents, the other buffers result in poor separations. Observations from this study are useful in helping to optimize separations carried out on immobilized BSA as well as addressing biological and mechanistic questions related to how anions influence the native binding properties of serum albumins.     

Mathematical Correction for Polyatomic Isobaric Spectral Interferences in Determination of Lanthanides by Inductively Coupled Plasma Mass Spectrometry

The determination of lanthanides by Inductively Coupled Plasma Mass Spectrometry (ICP‐MS) is complicated by several spectral overlaps from M⁺, MO⁺ or MOH⁺ ions formed in the ICP. Especially, it is essential to avoid the spectral interferences from lighter lanthanide and Ba polyatomic ions on middle or heavier lanthanides. To tackle this problem, we have developed a mathematical correction method, which reduces all the spectral overlaps from oxide species of Pr, Nd, Ce and Sm over Gd, Tb, Dy and Ho, and Gd, Tb over Yb and Lu. It can also successfully correct the oxide and hydroxide interference of Ba over Eu. The effectiveness of the proposed the mathematical correction scheme is demonstrated for the USGS Standard Rock samples AGV‐1 and G‐2. The results show that the experimental data obtained by applying the mathematical correction scheme for lanthanides is in good agreement with the reported values, using pneumatic and ultrasonic nebulisation methods, for their ICP‐MS analysis.     

Magnetic, electronic, and structural characterization of nonstoichiometric iron oxides at the nanoscale

We have investigated the structural, magnetic, and electronic properties of nonstoichiometric iron oxide nanocrystals prepared by decomposition of iron(II) and iron(0) precursors in the presence of organic solvents and capping groups. The highly uniform, crystalline, and monodisperse nanocrystals that were produced enabled a full structural and compositional survey by electron microscopy and X-ray diffraction. The complex and metastable behavior of nonstoichiometric iron oxide (wüstite) at the nanoscale was studied by a combination of Mossbauer spectroscopy and magnetic characterization. Deposition from hydrocarbon solvents with subsequent self-assembly of iron oxide nanocrystals into superlattices allowed the preparation of continuous thin films suitable for electronic transport measurements.     

Photocatalytic and antifouling properties of TiO2-based photocatalytic membranes

Photocatalysis has been extensively studied due to its potential ability to avoid the excessive use of chemical reagents and reduce the energy consumption by employing solar energy. Moreover, to alleviate the reduction in the membrane permeation selectivity, separation efficiency, and membrane service life caused by the emerging micro-pollutants and membrane fouling, membrane technology is often coupled with microbial, electrochemical, and catalytic processes. However, although physical/chemical cleaning and membrane module replacement can overcome the inherent limitations caused by membrane fouling and other membrane separation processes, high operating costs limit their practical applications. In this review, common preparation methods for TiO₂ photocatalytic membranes are described in detail, and the main approaches to enhancing their photocatalytic performance are discussed. More importantly, the mechanism of the TiO₂ photocatalytic membrane antifouling process is elucidated, and some applications of photocatalytic membranes in other areas are described. This review systematically outlines future research directions in the field of photocatalytic membrane modification, including metal and non-metal doping, fabrication of heterojunction structures, control over reaction conditions, increase in hydrophilicity, and increase in membrane porosity.     

New azabenzoquinones by ring‐expansion reactions

Ozonolysis of the pyrrolidinediones 4 afforded the pyrrolidinetriones 5 , which in the presence of Lewis acids were converted into maleimide 6 . Analogously, ozonolysis of the pyrrolidinones 7 gave the pyrrolidinediones 8 , which were converted into the pyridinetriones 11a, b via Lewis acid catalyzed isomerization to yield the trihydroxypyridones 10 and ensuing air oxidation. In solution two tautomeric forms of the pyridinetriones 11 may exist both of which represent hydroxy‐azabenzoquinones. In two steps compounds 11 were transformed into the azaquinone derivatives 19 . Representatives of another type of azaquinones are compounds 28a, b. These were generated in two steps from the pyridones 25 . The azaquinone 28a reacted easily with acidic compounds yielding the adducts 26, 27 and 29 or with 2‐butenal forming the cycloadduct 30 .     

Cu-ZSM-5分子筛上[Cu-O-Cu]2+物种的原位红外光谱研究

通过原位监测Ｃｕ－ＺＳＭ－５分子筛的振动动红外光谱随温度及不同处理条件的变化情况,观察到［Ｃｕ－Ｏ－Ｃｕ］＾２＋物种的形成过程,即两个Ｃｕ（ＯＨ）＾＋在脱水过程中经二聚形成［Ｃｕ－Ｏ－Ｃｕ］＾２＋,低交换度样品开始产生［Ｃｕ－Ｏ－Ｃｕ］＾２＋物种所需脱水温度较高,通过观察不同处理条件对［Ｃｕ－Ｏ－Ｃｕ］＾２＋的影响,说明Ｃｕ＾２＋是通过脱出［Ｃｕ－Ｏ－Ｃｕ］＾２＋中的超各氧而被还原为Ｃｕ＾＋,较高     

Effect of Ce<Superscript>3+</Superscript> on spectral characteristic of D1/D2/Cytb559 complex from spinach

It was studied by spectroscopy that PSII reaction center complex consisting of three polypeptides, D₁, D₂ and Cytb559, were purified from PSII particle of CeCl₃ treated spinach. The results of the experiment show that Ce³⁺ could improve the growth of spinach, and accelerate electron transport of PSII particles. Of chl-a of UV-Vis spectrum of D1/D2/Cytb559 complex, Soret band was blue-shifted by 3 nm and Q band by 2 nm, respectively, and the fluorescence emission peak was blue-shifted by 5 nm in CeCl₃-treated spinach compared with the one in control. By the extended X-ray absorption fine structure (EXAFS) spectroscopy methods, it has been found that Ce³⁺ is coordinated with 8 nitrogen atoms in the first coordination shell with Ce-N bond length of 0.253 nm, and Ce³⁺ with 6 oxygen atoms in the second coordination shell with Ce-O bond length of 0.32 nm. However, the secondary structure of D1/D2/Cytb559 complex by circular dichroism (CD) spectroscopy has no significant change after CeCl₃ treated. It might be that Ce³⁺ binds to porphyrin rings of chlorophyll and oxygen of amino acid residue of polypeptide in D1/D2/Cytb559 complex, and then accelerates the primary reaction of PSII, intensifies function of P680⁺ primary electron donor of D1/D2/Cytb559, but there is little change in conformation of PSII reaction center complex.     

A Line Search SQP-type Method with Bi-object Strategy for Nonlinear Semidefinite Programming

We propose a line search exact penalty method with bi-object strategy for nonlinear semidefinite programming. At each iteration, we solve a linear semidefinite programming to test whether the linearized constraints are consistent or not. The search direction is generated by a piecewise quadratic-linear model of the exact penalty function. The penalty parameter is only related to the information of the current iterate point. The line search strategy is a penalty-free one. Global and local converg...