Order parameter description of walk-off effect on pattern selection in degenerate optical parametric oscillators

Degenerate optical parametric oscillators can exhibit both uniformly translating fronts and nonuniformly translating envelope fronts under the walk-off effect. The nonlinear dynamics near threshold is shown to be described by a real convective Swift-Hohenberg equation, which provides the main characteristics of the walk-off effect on pattern selection. The predictions of the selected wave vector and the absolute instability threshold are in very good quantitative agreement with numerical solutions found from the equations describing the optical parametric oscillator.     

Four Novel Phenanthrene Derivatives with α-Glucosidase Inhibitory Activity from Gastrochilus bellinus

Four new phenanthrene derivatives, gastrobellinols A-D (1–4), were isolated from the methanolic extract of Gastrochilus bellinus (Rchb.f.) Kuntze, along with eleven known phenolic compounds including agrostophyllin (5), agrostophyllidin (6), coniferyl aldehyde (7), 4-hydroxybenzaldehyde (8), agrostophyllone (9), gigantol (10), 4-(methoxylmethyl)phenol (11), syringaldehyde (12), 1-(4′-hydroxybenzyl)-imbricartin (13), 6-methoxycoelonin (14), and imbricatin (15). Their structures were determined by spectroscopic methods. Each isolate was evaluated for α-glucosidase inhibitory activity. Compounds 1, 2, 3, 7, 9, 13, and 15 showed higher activity than the drug acarbose. Gastrobellinol C (3) exhibited the strongest α-glucosidase inhibition with an IC₅₀ value of 45.92 μM. A kinetic study of 3 showed competitive inhibition on the α-glucosidase enzyme. This is the first report on the phytochemical constituents and α-glucosidase inhibitory activity of G. bellinus.     

Continuous solid-phase extraction and preconcentration of bisphenol A in aqueous samples using molecularly imprinted columns

A bisphenol A (BPA) molecularly imprinted polymer, the composition of which was optimised using a chemometric approach, has been applied to the selective preconcentration of the template from aqueous samples. The selectivity of the polymer toward BPA and related compounds was evaluated chromatographically. The BPA-imprinted polymer was packed in a column and used for continuous on-column solid-phase extraction (MISPE) of aqueous samples followed by subsequent analysis by HPLC with fluorescence detection of the eluted fractions. The composition of the washing solvent applied in the MISPE procedure was optimised to favour the specific interactions of the MIP with BPA and to remove the non-selectively bound matrix components. The MISPE method has proven to be effective for selective preconcentration of BPA in aqueous samples (recoveries >84% obtained in the eluate for 10–100 mL sample volumes) enabling detection and quantification limits of 1.0 and 3.3 ng mL^–1, respectively (based on 25 mL sample size). Analytical recoveries were between 92 and 101% for river water samples spiked with known amounts of BPA (30, 60, and 80 ng mL^–1); relative standard deviations (RSD) were lower than 5.0%.     

Structure and stability of high‐spin Aun(n = 2–8) clusters

The structures and relative stability of the maximum‐spin ⁿ⁺¹Au_n and ⁿAu (n = 2–8) clusters have been determined by density‐functional theory. The structure optimizations and vibrational frequency analysis are performed with the gradient‐corrections of Perdew along with his 1981 local correlation functional, combined with SBKJC effective core potential, augmented in the valence basis set by a set of f functions. We predicted the existence of a number of previously unknown isomers. The energetic and electronic properties of the small high‐spin gold clusters are strongly dependent on sizes. The high‐spin clusters tend to holding three‐dimensional geometry rather than planar form preferred in low‐spin situations. In whole high‐spin Au_n (n = 2–8) neutral and cationic species, ⁵Au₄, ²Au, and ⁴Au are predicted to be of high stability, which can be explained by valence bond theory. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

New Quenching Procedure for Preservation of Initial Polymer/Catalyst Particle Morphology in Ziegler–Natta Olefin Polymerization

Preservation of initial polymer/catalyst particle morphology under air, was examined using stopped‐flow Ziegler–Natta polymerization with various quenching conditions and post‐chemical treatments. The exposure of the initial particles to air caused the fast formation of cracks on the surface, finally leading to significant reformation of the particle shape, when polymerizing particles were washed with heptane at ?65 °C under N₂ or under CO₂. On the other hand, when the particles were washed with heptane containing an appropriate amount of tetrahydrofuran under CO₂, the particle morphology under air was almost completely maintained even after 1 h exposure. The present results are useful for various ex situ characterizations of unstable initial polymer/catalyst particles.

     

Synthesis and Characterization of New M‐Triazole Complexes (M = Co,Cu, Zn)

Three new complexes with the ligand 3,5‐diamino‐1,2,4‐triazole (Hdatrz), [Co₃(μ₂‐Hdatrz)₆(H₂O)₆]·(NO₃)₈·4H₂O ( 1 ), [Cu₃(μ₂‐Hdatrz)₄(μ₂‐Cl)₂(H₂O)₂Cl₂]·Cl₂·4H₂O·2C₂H₅OH ( 2 ) and {[Zn₂(μ₂‐SO₄) (μ₃‐datrz)₂]·2H₂O}_n ( 3 ) have been synthesized and structurally characterized. Complex 1 has a linear trinuclear mixed‐valence cobalt structure with six neutral triazole ligands in the N(1), N(2)‐bridging mode. The central cobalt atom, Co(1), is coordinated to six nitrogen atoms (octahedral) whereas the terminal cobalt atom, Co(2), is coordinated to an N₃O₃ moiety (octahedral). In complex 1 , the uudd cyclic water clusters, nitrate anions and the trimeric cations are linked to a supramolecular structure. Complex 2 features a linear trinuclear copper(II) core, with four N(1), N(2)‐bridging triazole ligands and two chlorido bridges. The central copper atom is coordinated to an N₄Cl₂ moiety (octahedral) whereas the terminal copper is coordinated to an N₂Cl₂O moiety (square‐pyramidal). In complex 2 , tetrahedral hydrogen bonding interactions play an important role to form a supramolecular network. Complex 3 exhibits a polymeric structure, with N(1), N(2), N(4)‐bridging triazolate ligands and sulfate bridges, in which zinc is coordinated to an N₃O moiety (tetrahedral). In complex 3 , water molecules and sulfate anions construct the sulfate‐water supramolecular chain with hydrogen bonding interactions. In addition, the complexes were investigated by elemental analyses, IR spectroscopic, and thermogravimetric measurements.     

Using support vector machines for prediction of protein structural classes based on discrete wavelet transform

The prediction of secondary structure is a fundamental and important component in the analytical study of protein structure and functions. How to improve the predictive accuracy of protein structural classification by effectively incorporating the sequence‐order effects is an important and challenging problem. In this study, a new method, in which the support vector machine combines with discrete wavelet transform, is developed to predict the protein structural classes. Its performance is assessed by cross‐validation tests. The predicted results show that the proposed approach can remarkably improve the success rates, and might become a useful tool for predicting the other attributes of proteins as well. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

2-溴丙酸气相热消除反应的机理

用密度泛函（DFT）方法,在B3LYP/6-31G**水平上对2-溴丙酸气相消除反应机理进行了研究.计算表明,反应主要是通过半极化五元环结构过渡态进行的,羧基上的氢原子协助溴原子离去,羧基氧原子帮助稳定过渡态.在B3LYP/6-311＋＋G(3df,3pd)水平上对B3LYP/6-31G**优化的几何构型进行了单点能计算,计算所得反应的速度控制步骤的活化能为189.461 kJ•mol－1,偏离实验值((180.3±3.4) kJ•mol－1)5.08％.     

Chemical constituents of the bark of Dipteryx alata vogel, an active species against Bothrops jararacussu venom

The effect of four sub-extracts prepared from the lyophilized hydroalcoholic bark of Dipteryx alata (Leguminosae-Papilionoideae) dissolved in a methanol-water (80:20) mixture through a liquid-liquid partition procedure has been investigated against the neuromuscular blockade of the venom of the snake Bothrops jararacussu. The active CH?Cl? sub-extract has been extensively analyzed for its chemical constituents, resulting in the isolation of four lupane-type triterpenoids: lupeol, lupenone, 28-hydroxylup-20(29)-en-3-one, betulin, nine isoflavonoids: 8-O-methylretusin, 7-hydroxy-5,6,4'-trimethoxyisoflavone, afrormosin, 7-hydroxy-8,3',4'-trimethoxyisoflavone, 7,3'-dihydroxy-8,4'-dimethoxyisoflavone, odoratin, 7,8,3'-trihydroxy-4'-methoxyisoflavone, 7,8,3'-trihydroxy-6,4'-dimethoxyisoflavone, dipteryxin, one chalcone: isoliquiritigenin, one aurone: sulfuretin and three phenolic compounds: vanillic acid, vanillin, and protocatechuic acid. Their chemical structures were elucidated on the basis of spectroscopic analysis, including HRMS, 1D- and 2D-NMR techniques.