Showing papers by "Nankai University published in 2003"

Recent Developments in the Catalytic Asymmetric Synthesis of α- and β-Amino Acids

Abstract: The stereoselective synthesis of amino acids is of great importance for the construction of optically active natural products and pharmaceuticals Apart from enzymes, a broad repertoire of chiral reagents, auxiliaries, and catalysts can be used for the formation of amino acids Asymmetric reactions using catalytic amounts of chiral molecules provide efficient methods for the generation of optically active proteinogenic and nonproteinogenic amino acids This minireview collects recent work on catalytic asymmetric synthesis of α- and β-amino acids

An evaluation on feature selection for text clustering

Abstract: Feature selection methods have been successfully applied to text categorization but seldom applied to text clustering due to the unavailability of class label information. In this paper, we first give empirical evidence that feature selection methods can improve the efficiency and performance of text clustering algorithm. Then we propose a new feature selection method called "Term Contribution (TC)" and perform a comparative study on a variety of feature selection methods for text clustering, including Document Frequency (DF), Term Strength (TS), Entropy-based (En), Information Gain (IG) and χ2 statistic (CHI). Finally, we propose an "Iterative Feature Selection (IF)" method that addresses the unavailability of label problem by utilizing effective supervised feature selection method to iteratively select features and perform clustering. Detailed experimental results on Web Directory data are provided in the paper.

Observation of a near-threshold enhancement in the pp mass spectrum from radiative J/psi-->gammapp decays.

Abstract: We observe a narrow enhancement near 2m(p) in the invariant mass spectrum of pp pairs from radiative J/psi-->gammapp decays. No similar structure is seen in J/psi-->pi(0)pp decays. The results are based on an analysis of a 58 x 10(6) event sample of J/psi decays accumulated with the BESII detector at the Beijing electron-positron collider. The enhancement can be fit with either an S- or P-wave Breit-Wigner resonance function. In the case of the S-wave fit, the peak mass is below 2m(p) at M=1859(+3)(-10) (stat)+5-25(syst) MeV/c(2) and the total width is Gamma<30 MeV/c(2) at the 90% confidence level. These mass and width values are not consistent with the properties of any known particle.

Synthesis of spiro diphosphines and their application in asymmetric hydrogenation of ketones.

Abstract: Synthesis of chiral diphosphine ligands containing a spiro scaffold was described. The ruthenium complexes of these spiro ligands were found to have extremely high activities (S/C up to 100 000) and enantioselectivities (ee up to 99.5%) in the asymmetric hydrogenation of aromatic, heteroaromatic, and α,β-unsaturated ketones.

Modified Friedmann equations in R−1-modified gravity

Abstract: Recently, corrections to the Einstein-Hilbert action that become important at small curvature have been proposed. We discuss the first-order and second-order approximations to the field equations derived by the Palatini variational principle. We work out the first- and second-order modified Friedmann equations and present the upper redshift bounds when these approximations are valid. We show that the second-order effects can be neglected in the cosmological predictions involving only the Hubble parameter, e.g. the various cosmological distances, but the second-order effects cannot be neglected in the predictions involving the derivatives of the Hubble parameter. Furthermore, the modified Friedmann equations fit the SNe Ia data at an acceptable level.

Adjusting the frameworks of silver(I) complexes with new pyridyl thioethers by varying the chain lengths of ligand spacers, solvents, and counteranions.

Abstract: In our efforts to systematically investigate the effects of the linker units of flexible ligands and other factors on the structures of Ag(I) complexes with thioethers, five new flexible pyridyl thioether ligands, bis(2-pyridylthio)methane (L(1)()), 1,3-bis(2-pyridylthio)propane (L(3)()), 1,4-bis(2-pyridylthio)butane (L(4)), 1,5-bis(2-pyridylthio)pentane (L(5)), and 1,6-bis(2-pyridylthio)hexane (L(6)), have been designed and synthesized, and the reactions of these ligands with Ag(I) salts under varied conditions (varying the solvents and counteranions) lead to the formation of eight novel metal-organic coordination architectures from di- and trinuclear species to two-dimensional networks: [Ag(3)(L(1)())(2)(ClO(4))(2)](ClO(4)) (1), [[AgL(3)](ClO(4))]( infinity ) (2), [[Ag(2)(L(4))(2)](ClO(4))(2)(CHCl(3))]( infinity ) (3), [[AgL(4)](ClO(4))(C(3)H(6)O)]( infinity ) (4), [[Ag(2)L(4)](NO(3))(2)]( infinity ) (5), [Ag(2)L(4)()(CF(3)SO(3))(2)]( infinity ) (6), [[AgL(5)](ClO(4))(CHCl(3))](2) (7), and [[AgL(6)()](ClO(4))]( infinity ) (8). All the structures were established by single-crystal X-ray diffraction analysis. The coordination modes of these ligands were found to vary from N,N-bidentate to N,N,S-tridentate to N,N,S,S-tetradentate modes, while the Ag(I) centers adopt two-, three-, or four-coordination geometries with different coordination environments. The structural differences of 1, 2, 3, 7, and 8 indicate that the subtle variations on the spacer units can greatly affect the coordination modes of the terminal pyridylsulfanyl groups and the coordination geometries of Ag(I) ions. The structural differences of 3 and 4 indicate that solvents also have great influence on the structures of Ag(I) complexes, and the differences between 3, 5, and 6 show counteranion effects in polymerization of Ag(I) complexes. The influences of counterions and solvents on the frameworks of these complexes are probably based upon the flexibility of ligands and the wide coordination geometries of Ag(I) ions. The results of this study indicate that the frameworks of the Ag(I) complexes with pyridyl dithioethers could be adjusted by ligand modifications and variations of the complex formation conditions.

Determination of the C4-H bond dissociation energies of NADH models and their radical cations in acetonitrile.

Abstract: Heterolytic and homolytic bond dissociation energies of the C4-H bonds in ten NADH models (seven 1,4-dihydronicotinamide derivatives, two Hantzsch 1,4-dihydropyridine derivatives, and 9,10-dihydroacridine) and their radical cations in acetonitrile were evaluated by titration calorimetry and electrochemistry, according to the four thermodynamic cycles constructed from the reactions of the NADH models with N,N,N',N'-tetramethyl-p-phenylenediamine radical cation perchlorate in acetonitrile (note: C9-H bond rather than C4-H bond for 9,10-dihydroacridine; however, unless specified, the C9-H bond will be described as a C4-H bond for convenience). The results show that the energetic scales of the heterolytic and homolytic bond dissociation energies of the C4-H bonds cover ranges of 64.2-81.1 and 67.9-73.7 kcal mol(-1) for the neutral NADH models, respectively, and the energetic scales of the heterolytic and homolytic bond dissociation energies of the (C4-H)(.+) bonds cover ranges of 4.1-9.7 and 31.4-43.5 kcal mol(-1) for the radical cations of the NADH models, respectively. Detailed comparison of the two sets of C4-H bond dissociation energies in 1-benzyl-1,4-dihydronicotinamide (BNAH), Hantzsch 1,4-dihydropyridine (HEH), and 9,10-dihydroacridine (AcrH(2)) (as the three most typical NADH models) shows that for BNAH and AcrH(2), the heterolytic C4-H bond dissociation energies are smaller (by 3.62 kcal mol(-1)) and larger (by 7.4 kcal mol(-1)), respectively, than the corresponding homolytic C4-H bond dissociation energy. However, for HEH, the heterolytic C4-H bond dissociation energy (69.3 kcal mol(-1)) is very close to the corresponding homolytic C4-H bond dissociation energy (69.4 kcal mol(-1)). These results suggests that the hydride is released more easily than the corresponding hydrogen atom from BNAH and vice versa for AcrH(2), and that there are two almost equal possibilities for the hydride and the hydrogen atom transfers from HEH. Examination of the two sets of the (C4-H)(.+) bond dissociation energies shows that the homolytic (C4-H)(.+) bond dissociation energies are much larger than the corresponding heterolytic (C4-H)(.+) bond dissociation energies for the ten NADH models by 23.3-34.4 kcal mol(-1); this suggests that if the hydride transfer from the NADH models is initiated by a one-electron transfer, the proton transfer should be more likely to take place than the corresponding hydrogen atom transfer in the second step. In addition, some elusive structural information about the reaction intermediates of the NADH models was obtained by using Hammett-type linear free-energy analysis.

Antioxidant activity of compounds from the medicinal herb Aster tataricus.

Abstract: A number of compounds were isolated from the medicinal plant Aster tataricus including shionone, epifriedelinol, quercetin, kaempferol, scopoletin, emodin, aurantiamide acetate and 1,7-dihydroxy-6-methyl-anthraquinone. The compounds were compared with regard to their ability in inhibiting hemolysis of rat erythrocytes induced by 2′-2′ azobis (2-amidinopropane) dihydrochloride, lipid peroxidation using the FeSO4-ascorbic acid system, and generation of superoxide radicals using a phenazine methosulfate-nicotinamide adenine dinucleotide system. The effects on the Fe-bleomycin-induced DNA damage reflected pro-oxidant activity. Quercetin and kaempferol were most potent in inhibiting hemolysis, lipid peroxidation and superoxide radical generation. Scopoletin and emodin were similar to quercetin and kaempferol in inhibiting superoxide radical generation and second to them in inhibiting lipid peroxidation. Aurantiamide acetate exhibited some inhibitory activity toward superoxide radical generation. 1,7-dihydroxy-6-methyl-anthraquinone exerted an inhibitory activity only on superoxide radical generation. Shionone and epifriedelinol did not display any antioxidant activity. Quercetin and kaempferol, but not the remaining compounds, exhibited some pro-oxidant activity.

Entrepreneurship education in China

Abstract: China's recent economic success resulted, to a great extent, from the release of the entrepreneurial potential inherent in its business sectors. Yet, entrepreneurship education as a whole remains a relatively new concept and practice, in particular in the higher education sector. This explorative article reviews the recent developments in entrepreneurship education within higher educational institutions in China. The context of these developments and the emerging models in entrepreneurship education are highlighted. The critical factors that will shape the directions of entrepreneurship education are discussed and summarised.

Optimal mixed-level supersaturated design

Abstract: A supersaturated design is essentially a fractional factorial in which the number of potential effects is greater than the number of runs. In this paper, E(f NOD ) criterion is employed for comparing supersaturated designs from the viewpoint of orthogonality and uniformity, and a lower bound of E(f NOD ) which can serve as a benchmark of design optimality is obtained. It is shown that the existing E(s 2) and ave χ2 criteria (for two- and three-level supersaturated designs respectively) are in fact special cases of this criterion. Furthermore, a construction method for mixed-level supersaturated designs is proposed and some properties of the resulting designs are investigated.

Lithium Intercalation in Open‐Ended TiS2 Nanotubes

Abstract: [*] Prof. Dr. J. Chen, Dr. Z.-L. Tao, Dr. S.-L. Li Institute of New Energy Materials Chemistry Nankai University, Tianjin 300071 (P.R.China) Fax: (+86)22-2350-9118 E-mail: chenabc@nankai.edu.cn [**] The authors acknowledge support from the Trans-Century Distinguished Talent Project (Grant No. 200248) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars (Grant No. 2002247; State Education Ministry). We are also thankful to Professors C. X. Cui and X. Q. Zhu, and Drs. Y. T. Shen and Q. Xu for their experimental assistance. Angewandte Chemie

Cosmological Evolution in 1/R-Gravity Theory

Abstract: Recently, corrections of the $L(R)$ type to Einstein-Hilbert action that become important at small curvature are proposed. Those type of models intend to explain the observed cosmic acceleration without dark energy. We derive the full Modified Friedmann equation in the Palatini formulation of those modified gravity model of the $L(R)$ type. Then, we discuss various cosmological predictions of the Modified Friedmann equation.

Preparative separation and determination of matrine from the Chinese medicinal plant Sophora flavescens Ait by molecularly imprinted solid-phase extraction.

Abstract: Molecularly imprinted microspheres (MIMs) were synthesized by micro-suspension polymerization using matrine (MT) as template. The MIMs were employed for solid-phase extraction (SPE) and as chromatographic stationary phase for the determination of MT from the Chinese medicinal plant Sophora flavescens. The effects of the various eluents, their concentrations and volumes on the retention behavior were investigated. The selectivity and capacity of the imprinted microspheres against MT was also discussed. The results showed that the MIMs exhibited stronger specific affinity to MT than to oxymatrine (OMT). Methanol–water (3:7, v/v) was used for washing impurities from the MIMs-SPE cartridge loaded with the herb extracts, while methanol–glacial acetic acid (9:1, v/v) was used for eluting MT. The maximum load of MT and the recovery of MIMs cartridge towards MT were 38.7 μg g–1 and 71.4%, respectively. The method developed might be used to separate and extract effective constituents from Chinese medicinal plants on a large scale.

Some results on ruin probabilities in a two-dimensional risk model

Abstract: Ruin theory under multi-dimensional risk models is very complex. Even in the two-dimensional case, the problem is challenging. In this paper, we consider a bivariate risk model. Three different types of ruin probabilities are defined. Using some results of one-dimensional risk processes, simple bounds for the two-dimensional ruin probabilities are obtained. Numerical examples and simulation experiments are given to illustrate the tightness of the bounds. A partial integral–differential equation satisfied by the two-dimensional ruin probabilities is derived. Although special cases and examples in this paper provide some exciting results, the problem of ruin probability in a multi-dimensional risk model is still far from solved. We hope that this paper stimulates more research by actuaries in this area.

From metallacyclophanes to 1-D coordination polymers: role of anions in self-assembly processes of copper(II) and 2,5-bis(3-pyridyl)-1,3,4-oxadiazole.

Abstract: The reaction of various CuII salts with 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L) in CH3CN−H2O medium affords different complexes, the solid structures of which are controlled only by the choice of the counteranions. Reaction of Cu(ClO4)2·6H2O or Cu(NO3)2·3H2O and L yields the novel bimetallic macrocyclic complex [Cu2L2(H2O)6](ClO4)4(H2O)4 (1) [monoclinic, space group P21/m, a = 8.745(5) A, b = 16.179(10) A, c = 14.930(8) A, β = 93.253(10)°, Z = 2] or [CuL(NO3)2]2(CH3CN)2 (2) [triclinic, space group P1, a = 7.863(3) A, b = 8.679(3) A, c = 13.375(5) A, α = 74.121(5)°, β = 78.407(6)°, γ = 86.307(6)°, Z = 1]. However, with the replacement of CuII perchlorate or nitrate salts with CuSO4·5H2O or Cu(OAc)2·H2O in the above reaction, two different one-dimensional (1-D) coordination polymers {[Cu2L2(H2O)6(SO4)2](H2O)6}n (3) [triclinic, space group P1, a = 7.078(3) A, b = 11.565(4) A, c = 12.561(5) A, α = 109.511(6)°, β = 105.265(6)°, γ = 94.042(6)°, Z = 1] or {[Cu2L(μ-OAc)4]}n (4) [monoclinic, space group C2/c, a ...

The First Azide(μ1,1)-Bridged Binuclear Cobalt(II)−Imino Nitroxide Complex with Ferromagnetic Behavior

Abstract: The first azide(μ1,1)-bridged binuclear cobalt(II) complex with a chelated imino nitroxide radical, [Co2(immepy)2(N3)4]·2EtOH, was structurally and magnetically characterized, where immepy = 4,4,5,5-tetramethyl-2-(6‘-methyl-2‘-pyridyl) imidazoline-1-oxyl. Five nitrogen atoms complete the coordination sphere of the Co(II) ion, showing a distorted trigonal bipyramid geometry. Two N3- anions act as bridges between cobalt ions in the μ1,1 coordination mode, resulting in a binuclear structure with an inversion center. Magnetic studies show that ferromagnetic couplings occurred between the adjacent cobalt(II) ions through N3-(μ1,1) bridges, and antiferromagnetic couplings between the cobalt(II) ions and organic radicals.

Structural transformation mediated by o-, m-, and p-phthalates from two to three dimensions for manganese/phthalate/4,4 '-bpy complexes (4,4 '-bpy=4,4 '-bipyridine)

Abstract: Three isomers of o-, m-, and p-phthalate are used to link together Mn centres, resulting in [Mn(phth)(H2O)x]n moieties (phth = phthalate dianion) with single-chain, double-chain and sheet structures, respectively, which predetermine the extended structures derived from the crosslinkage of 4,4′-bipyridine, and show the influence of isomerism of the phthalate on topological changes of the final polymers from two dimensional (2D) single-layer, double-layer to 3D network architectures. These structural changes in topology are correlated with the differences in the magnetic and optical properties of the polymers.

Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to enones using chiral spiro phosphoramidites as ligands.

Abstract: Novel monodentate chiral spiro phosphoramidite ligands have been readily synthesized in good yields from enantiomerically pure 1,1‘-spirobiindane-7,7‘-diol. The new ligands were highly efficient in the copper-catalyzed conjugate addition of Et2Zn to enones with up to 98% enantiomeric excess.

Total quality management principles and practices in China

Abstract: Considers the role and practices of total quality management in China. After a brief overview, considers the evolution of quality practices and the links to economic reform in China. From the quality literature, develops a measuring instrument to assess the extent and pervasion of quality practices in China. Then applies this instrument to 428 Northern Chinese companies representing different forms of ownership. Finds that the implementation of quality was highly variable. In general, joint venture companies scored highly in quality practices, in contrast, state owned enterprises scored poorly. Privately owned companies also scored well in some aspects of quality implementation. Concludes that the poor quality performance of state owned companies can be attributed to the attitudes and structures created during the period of the command economy.

Culture of primary rat hepatocytes within porous chitosan scaffolds

Abstract: Chitosan is considered to be a very promising biopolymer for various biomedical and pharmaceutical uses because of its nontoxic and biocompatible natures (Chandy T, Shama P. Biomater Artif Cells Artif Org 1990;18:1-24). In this study, we prepared porous chitosan scaffolds by lyophilization of chitosan solution. The scaffolds were modified with water-soluble polyanionic species such as alginate and heparin. The pore structures of these scaffolds were viewed via light and scanning electron microscopy. The scaffolds prepared have a high porosity of approximately 90% with mean pore sizes from 50 to 200 microm. They were used as substrates for hepatocytes culture. The cell attachment ratio was much higher than on monolayer membrane and hepatocytes exhibited a round cellular morphology with many microvilli evident on the surface of the cells. Metabolic activities of the cells were evaluated in terms of albumin secretion and urea synthesis. It was found that hepatocytes cultured on the modified scaffolds showed an increase in albumin secretion during the first 4 days and were more stable than those on monolayer membrane and nonmodified scaffolds. Therefore, primary rat hepatocytes cultured on modified scaffolds would be beneficial to liver assist device.

Gravitational potential in Palatini formulation of modified gravity

Abstract: General Relativity has so far passed almost all the ground-based and solar-system experiments. Any reasonable extended gravity models should consistently reduce to it at least in the weak field approximation. In this work we derive the gravitational potential for the Palatini formulation of the modified gravity of the L(R) type which admits a de Sitter vacuum solution. We conclude that the Newtonian limit is always obtained in those class of models and the deviations from General Relativity is very small for a slowly moving source.