Synthesis, linear, and quadratic-nonlinear optical properties of octupolar D3 and D2d bipyridyl metal complexes

A series of D3 (Fe(II), Ru(II), Zn(II), Hg(II)) and D2d (Cu(I), Ag(I), Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands has been synthesized, and their thermal, linear (absorption and emission), and nonlinear optical (NLO) properties were determined. Their quadratic NLO susceptibilities were determined by harmonic light scattering at 1.91 microm, and the molecular hyperpolarizability (beta0) values are in the range of 200-657 x 10(-30) esu for octahedral complexes and 70-157 x 10(-30) esu for tetrahedral complexes. The octahedral zinc(II) complex 1 e, which contains a 4,4'-oligophenylenevinylene-functionalized 2,2'-bipyridine, exhibits the highest quadratic hyperpolarizability ever reported for an octupolar derivative (lambdamax=482 nm, beta1.91(1 e)=870 x 10(-30) esu, beta0(1 e)=657 x 10(-30) esu). Herein, we demonstrate that the optical and nonlinear optical (NLO) properties are strongly influenced by the symmetry of the complexes, the nature of the ligands (donor endgroups and pi linkers), and the nature of the metallic centers. For example, the length of the pi-conjugated backbone, the Lewis acidity of the metal ion, and the increase of ligand-to-metal ratio result in a substantial enhancement of beta. The contribution of the metal-to-ligand (MLCT) transition to the molecular hyperpolarizability is also discussed with respect to octahedral d6 complexes (M=Fe, Ru).     

Enantioselective Rhodium‐Catalyzed Atom‐Economical Macrolactonization

A highly attractive route toward macrolactones, which form the cyclic scaffold of a multitude of diverse natural compounds, is described. Although many chemical approaches to this structural motif have been explored, an asymmetric variant of the cyclization is unprecedented. Herein we present an enantioselective macrolactonization through an intramolecular atom‐economical rhodium‐catalyzed coupling of ω‐allenyl‐substituted carboxylic acids. The use of a modified diop ligand, chiral DTBM‐diop, led to high enantioselectivity (up to 93 % ee). The reaction tolerated a large variety of functionalities, including α,β‐unsaturated carboxylic acids and depsipeptides, and provided the desired macrocycles with very high enantio‐ and diastereoselectivity.     

Application of Central Composite Design for the Determination of Exfoliating Agents in Cosmetics by Capillary Electrophoresis with Electroosmotic Flow Modulation

Multivariate analysis within central composite design is applied to simplify an optimization procedure and explore the interactions among experimental parameters in analytical chemistry. In this study, central composite design was used to identify the optimal capillary electrophoresis conditions with electroosmotic flow modulation to determine seven exfoliating agents in cosmetics. The influence of phosphate concentration, cetyltrimethylammonium bromide concentration, and methanol percentage on the response was evaluated by the use of the chromatographic exponential function to simultaneously investigate the resolution and separation under sixteen sets of capillary electrophoresis conditions. The optimized conditions were 150 mM phosphate solution (pH = 7) containing 0.5 mM cetyltrimethylammonium bromide, 3 mM γ-cyclodextrin, and 25% methanol as the running buffer. To shorten the analysis time, an electroosmotic flow modulating agent (cetyltrimethylammonium bromide) was added to the separation buffer. Calibration plots were linear (r ≧ 0.998) with high precision and accuracy in the homemade cosmetic matrix. The exfoliating agents in two commercial cosmetic products were determined using the optimized conditions, and the results correlated well with results obtained by high-performance liquid chromatography–mass spectrometry.     

颗粒内传质参数作为工具用于催化剂颗粒的设计(英文)

A chromatographic method and a dynamic Wicke-Kallenbach method (DMWK) were used to determine the diffusion characteristics of two industrial copper containing catalysts. The first catalyst was used in nitrobenzene hydrogenation to aniline and the second was used in a low temperature water-gas shift reaction. Experimental results show that application of these two methods leads to similar results. Experimental data obtained allow for monitoring changes in the texture of the catalyst grains and intraparticle diffusivity of gaseous reagents at different states of the catalyst activity and use, which can be used as criteria for designing optimal industrial catalyst pellets.     

Structure‐based ligand design by a build‐up approach and genetic algorithm search in conformational space

Program to engineer peptides (PEP) is a build‐up approach for ligand docking and design with implicit solvation. It requires the knowledge of a seed from which it iteratively grows polymeric ligands consisting of any type of amino acid, i.e., natural and/or nonnatural from a user‐defined library. At every growing step, a genetic algorithm is used for conformational optimization of the last added monomer in the rigid binding site. Pruning is performed at every growing step by selecting sequences according to binding energy with electrostatic solvation. PEP is applied to three members of the caspase family of cysteine proteases using Asp at P₁ as seed. The optimal P₄–P₂ peptide recognition motifs and variants thereof are docked correctly in the active site (backbone root‐mean‐square deviation < 0.9 Å). Moreover, for each caspase, the P₄–P₂ sequences of potent aldehyde inhibitors are ranked among the 15 hits with the most favorable PEP energy. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1956–1970, 2001     

Incidence properties of cosets in loops

We study incidence properties among cosets of infinite loops, with emphasis on well‐structured varieties such as antiautomorphic loops and Bol loops. While cosets in groups are either disjoint or identical, we find that the incidence structure in general loops can be much richer. Every symmetric design, for example, can be realized as a canonical collection of cosets of a infinite loop. We show that in the variety of antiautomorphic loops the poset formed by set inclusion among intersections of left cosets is isomorphic to that formed by right cosets. We present an algorithm that, given a infinite Bol loop S, can in some cases determine whether |S| divides |Q| for all infinite Bol loops Q with S?Q, and even whether there is a selection of left cosets of S that partitions Q. This method results in a positive confirmation of Lagrange's Theorem for Bol loops for a few new cases of subloops. Finally, we show that in a left automorphic Moufang loop Q (in particular, in a commutative Moufang loop Q), two left cosets of S?Qare either disjoint or they intersect in a set whose cardinality equals that of some subloop of S.     

A wide-field relay optics system for the Caltech Submillimeter Observatory

Relay optics designed for use with imaging arrays at the Caltech Submillimeter Observatory are described. An off-axis ellipsoidal mirror with foci displaced from the conjugate planes is used to achieve a Strehl ratio >0.88 over a 2′ square field of view (corresponding to a far field of 15 × 15 diffraction beams) at a wavelength of 350μm. The mirror also provides an aperture-stop image just prior to focus which allows compact entry into cryogenic camera dewars. Using a compensating ellipsoid in subsequent camera optics, the Strehl ratio can be improved to >0.95 at all points across the field, even for off-axis chop angles of the telescope’s secondary mirror as large as 2′.     

Factorial analysis optimization of a Diltiazem kinetic spectrophotometric quantification method

A Diltiazem kinetic spectrophotometric method was optimized by factorial analysis. The experimental method is based on a two-stage reaction of Diltiazem with hydroxylamine and a ferric salt: in the first stage there is a hydroxamic acid formation; and, in the second stage there is a red colour complex ferric hydroxamate formation. The variables under investigation were: solvent; hydroxylamine, sodium hydroxide and ammonium ferric sulphate concentrations; volume of perchloric acid; and, temperature. The responses of the reactional system were the maximum absorbance, the wavelength and the reaction time at maximum absorbance. Experimental design methodologies were used in the optimization. Fractional and full factorial designs followed by optimization Box-Behnken and central composite experimental designs were used. The observed optimum conditions were: methanol as reaction solvent; hydroxylamine concentration of 9.375%; sodium hydroxide concentration of 18.750%; ferric reagent concentration of 2.000%; minimum volume of perchloric acid to neutralize the sodium hydroxide; and, room temperature as reaction temperature. With this set of experimental conditions a reaction time of 10.5 s with maximum colour development at 512 nm wavelength was achieved.     

Speciation of Arsenic in Drinking Water by Dispersive Liquid–Liquid Microextraction,Graphite Furnace Atomic Absorption Spectrometry,and Orthogonal Array Design

Orthogonal array design was used to optimize arsenic speciation in drinking water in contact with materials by dispersive liquid–liquid microextraction followed by graphite furnace atomic absorption spectrometry. Arsenic speciation was achieved by the formation of an arsenic(III) hydrophobic complex with a new chelating agent, 1,2,6-hexanetriol trithioglycolate, at neutral pH. The complex was extracted into the organic phase, while arsenic(V) remained in aqueous solution. The concentration of As(V) was determined by subtracting As(III) from the total arsenic following the reduction of As(V) to As(III) by L-cysteine. Orthogonal array design with OA₁₆ (44) and OA₉ (33) matrices was used to optimize the efficiency of dispersive liquid–liquid microextraction and the reduction of As(V) to As(III), respectively. Under the optimal conditions, the detection limit was 0.03?µg?L^?1 for As(III) and the relative standard deviation was 5.9% with an enhancement factor of 87. The calibration curve was linear from 0.19 to 3.0?µg?L^?1 with a correlation coefficient of 0.9996. The developed method was used for arsenic speciation in solutions of drinking water that contacted materials. The recoveries of fortified samples were in an acceptable range from 92.0 to 113.3%.     

浅谈机械设计基础与学生创新思维的培养

机械设计基础是一门承前启后的专业基础课,但学生在学习过程中有不少的困难。教师在讲授过程中应改进教学方法,主抓教学内容,努力提高学生的学习积极性和主动性,培养创新思维和创新意识．