库仑加线性位基态解析解

应用新发展的单一轨迹积分方法求解库仑加线性位的基态量子波函数,得到基态能量和波函数的一般解析表达式,并讨论了解的收敛性.应用此方法讨论了重夸克偶素系统.     

Polyethylene imine derivatives ('synzymes') accelerate phosphate transfer in the absence of metal

The efficient integration of binding, catalysis, and multiple turnovers remains a challenge in building enzyme models. We report that systematic derivatization of polyethylene imine (PEI) with alkyl (C(2)-C(12)), benzyl, and guanidinium groups gives rise to catalysts ('synzymes') with rate accelerations (k(cat)/k(uncat)) of up to 10(4) for the intramolecular transesterification of 2-hydroxypropyl-p-nitrophenyl phosphate, HPNP, in the absence of metal. The synzymes exhibit saturation kinetics (K(M) approximately 250 microM, k(cat) approximately 0.5 min(-1)) and up to 2340 turnovers per polymer molecule. Catalysis can be specifically and competitively inhibited by anionic and hydrophobic small molecules. The efficacy of catalysis is determined by the PEI derivatization pattern. The derivatization reagents exert a synergistic effect, i.e., their combinations increase catalysis by more than the sum of each single modification. The pH-rate profile for k(cat)/K(M) is bell shaped with a maximum at pH 7.85 and can be explained as a combination of two effects that both have to be operative for optimal activity: K(M) increases at high pH due to deprotonation of PEI amines that bind the anionic substrate and kcat decreases as the availability of hydroxide decreases at low pH. Thus, catalysis is based on substrate binding by positively charged amine groups and the presence of hydroxide ion in active sites in an environment that is tuned for efficient catalysis. Inhibition studies suggest that the basis of catalysis and multiple turnovers is differential molecular recognition of the doubly negatively charged transition state (over singly charged ground state and product): this contributes a factor of at least 5-10-fold to catalysis and product release.     

Simple solvent-free preparation of dispersed composites and their application as catalysts in oxidation and hydrocarboxylation of cyclohexane

A simple and clean mechanochemical synthesis at room temperature was employed to prepare CuO-Fe₂O₃-CoCl₂ (100 nm scale), MoO₃-V₂O₅, CuO-CoCl₂, Fe₂O₃-CoCl₂, CuO-V₂O₅, Cu(CH₃COO)₂-V₂O₅, Cu(CH₃COO)₂-MoO₃ (1–100 μm scale) 3d metal based dispersed composites with different ratios of components using simple metal salts/oxides and multiwalled carbon nanotubes (CNT) or graphene oxide (GO) additives (CoCl₂-CNT, CoCl₂-GO). The thus prepared composite materials were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energy-dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). XPS analysis revealed no metal redox change upon ball milling treatment, which however promotes metal hydroxylation.The catalytic activity of the prepared composites in the heterogeneous low power microwave-assisted oxidation of cyclohexane with aq. H₂O₂ at 30 °C was notorious with yields up to 31% and selectivity up to 94% towards cyclohexanol (upon treatment with PPh₃) for the CuO-CoCl₂-based material. The hydrocarboxylation of cyclohexane with CO, water and K₂S₂O₈ to produce cyclohexanecarboxylic acid bearing one more carbon atom at 60 °C is achieved with yields up to 17% for the reaction performed in the presence of the CuO-CoCl₂ catalyst. The clean CuO-CoCl₂ (1:2) catalyst preparation and the catalytic reaction (oxidation of cyclohexane) can be achieved in one-pot at low temperature, without any added organic solvent, and by using exclusively the mechanochemical energy input, with a marked 23% yield at 30 °C.     

A note on Thomassen?s conjecture

In 1983 C. Thomassen [8] conjectured that for every k,g∈N there exists d such that any graph with average degree at least d contains a subgraph with average degree at least k and girth at least g. A result of Pyber, Szemerédi, and the second author implies that the conjecture is true for every graph G with average .We strengthen this and show that the conjecture holds for every graph G with average for some constants α, β depending on k and g.     

On a conjecture of Thomassen concerning subgraphs of large girth

In 1983 C. Thomassen conjectured that for every k, g∈? there exists d such that any graph with average degree at least d contains a subgraph with average degree at least k and girth at least g. Kühn and Osthus [2004] proved the case g = 6. We give another proof for the case g = 6 which is based on a result of Füredi [1983] about hypergraphs. We also show that the analogous conjecture for directed graphs is true. © 2010 Wiley Periodicals, Inc. J Graph Theory 67:316‐331,2011     

Development of catalytically active silver colloid nanoparticles stabilized by dextran

Colloidal silver nanoparticles (Ag-NPs) with a mean diameter of 6.1 nm and a narrow size distribution were prepared by reduction of the correspondent metal salt with injection of NaBH(4), in the presence of dextran, and characterized by UV-vis, TEM, and DLS. The concentration of all reactants involved in the formation of the nanoparticles was optimized with the use of a new multivariate method, which revealed a significant reduction in the number of experiments when compared with the vast majority of univariate methods described in the literature. The Ag-NPs-dextran composite was able to efficiently catalyze the p-nitrophenol reduction in water by NaBH(4) with a rate constant normalized to the surface area of the nanoparticles per unit volume (k(1)) of 1.41 s(-1) m(-2) L, which is higher than values ever reported for Ag-NPs catalytic systems.     

Spectra of graphs obtained by a generalization of the join graph operation

Taking a Fiedler’s result on the spectrum of a matrix formed from two symmetric matrices as a motivation, a more general result is deduced and applied to the determination of adjacency and Laplacian spectra of graphs obtained by a generalized join graph operation on families of graphs (regular in the case of adjacency spectra and arbitrary in the case of Laplacian spectra). Some additional consequences are explored, namely regarding the largest eigenvalue and algebraic connectivity.     

Collective phase-like mode and the role of lattice distortions at TN ~TC in RMn2O5 (R= Pr, Sm, Gd, Tb, Bi)

We report on electronic collective excitations in RMn(2)O(5) (R =Pr, Sm, Gd, Tb) showing condensation starting at and below ~T(N) ~T(C)~ 40-50 K. Their origin is understood as partial delocalized e(g) electron orbitals in the Jahn-Teller distortion of the pyramid dimer with strong hybridized Mn(3+)-O bonds. Our local probes, Raman, infrared, and x-ray absorption, back the conclusion that there is no structural phase transition at T(N)~T(C). Ferroelectricity is magnetically assisted by electron localization triggering lattice polarizability by unscreening. We have also found phonon hardening as the rare earth is sequentially replaced. This is understood as a consequence of lanthanide contraction. It is suggested that partially f-electron screened rare earth nuclei might be introducing a perturbation to e(g) electrons prone to delocalize as the superexchange interaction takes place.