Condensation of 5-aminobenzimidazoles with β-ketoester

In the present work, we report the condensation of 5-aminobenzimidazoles with β-ketoesters leading to some new imidazo-[4,5-f]-quinoline derivatives. Based on the open chain intermediates obtention, the structure of the obtained imidazo-[4,5-f]-quinoline product has been discussed.     

Synthesis and Crystal Structure of a New Mixed-ligand Nickel（Ⅱ） Coordination Polymer： [Ni（L）（cis-1,4-chdc）]n·1.25nH2O

A new one-dimensional Ni(II) coordination polymer [Ni(L)(cis-1,4- chdc)]n?1.25nH2O has been synthesized under hydrothermal conditions by using 1,4-cyclohexanedicarboxylic acid (1,4-H2chdc) and 2-(3-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (L). Crystallographic data for the compound: triclinic, space group P with a=8.777(2), b=10.662(2), c=13.799(3), α=89.480(4), β=73.933(3), γ=81.980(4)°, V=1228.2(5)3, Z=2, C27H22.50FN4NiO5.25, Mr=568.70, Dc=1.527 g/cm3, F(000)=583, μ(MoKa)=0.846 mm-1, R=0.0634 and wR=0.1465. Neighboring Ni(II) atoms are linked by the cis-1,4-chdc ligands to generate a one-dimensional chain structure. The π-π interactions between the L ligands of neighboring chains led to the formation of a two-dimensional supramolecular layer. The elemental analysis, IR spectrum and TG of the compound have been studied.     

Hydrothermal Reaction,Structure and Magnetic Properties of a Binuclear Cobalt Complex with N-donor Ligand:2-Methyldipyrido[3,2-f:2ˊ3ˊ-h]quinoxaline

One complex [Co1.5(C6H5CHCHCOO)3(Medpq)]·H2O(C6H5CHCHCOO = cinnamic acid, Medpq = 2-methyldipyrido[3,2-f:2,3-h]quinoxaline) 1 has been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectrum, TG, single-crystal X-ray diffraction and magnetic susceptibility measurements. Complex 1 crystallizes in the triclinic system, space group P1, with a = 10.224(5), b = 14.572(5), c = 15.139(5)A, α = 112.704(5), β = 97.168(5), γ = 109.749(5), V = 1871.8(13) 3 and Z = 2(at 293(2) K). In the crystal structure, the Co(1) ion is hexa-coordinated with six atoms from three different cinnamic acid ligands and the symmetric three different cinnamic acid ligands; the Co(2) center adopts a coordination environment with two nitrogen atoms from Medpq ligand and four oxygen atoms from two different cinnamic ligands, assuming a slightly distorted octahedral geometry, respectively. The negative value of the Weiss constant indicates antiferromagnetic exchange interactions between the Co ions.     

Modified Coumarins. I. Synthesis of 5-Phenyl-7H-furo[2, 3-g]chromen-7-ones and 9-Phenyl-7H-furo-[2, 3-f]chromen-7-ones

5-Phenyl-7H-furo[2,3-g]chromen-7-ones and 9-phenyl-7H-furo-[2,3-f]chromen-7-ones, new analogs of psoralen and allopsoralen, are synthesized from 7-hydroxy- and 5-hydroxy-4-phenylcoumarins     

Quinoprotein methanol dehydrogenase: a molecular dynamics study and comparison with crystal structure

One of the mechanisms proposed for methanol oxidation by methanol dehydrogenase (MDH) involves a hydride transfer to the quinone carbonyl carbon C5 of 2,7,9-tricarboxy-1H-pyrrolo[2,3-f]-quinoline-4,5-dione (PQQ), initiated by abstraction of a proton from the substrate methanol by a general base. Molecular dynamics studies are performed on MDH-bound to the C5 reduced intermediate (C5RI) of PQQ, for 3 ns. The structural features of the MD and X-ray structures are compared. An interesting feature observed during simulations is the strong hydrogen bond between oxyanion O5 of C5RI and Asp297-CO₂H in the active site. Asp297-CO₂⁻ is suggested to be the general-base catalyst for removing the hydroxyl proton of methanol in concert with the hydride ion transfer from the putative methoxide to C5 carbonyl of PQQ. The formed Asp297-CO₂H acts as the required proton source for the immediate product. Anticorreleated motions observed in the MD structure are not across the active site to influence the reaction mechanism of MDH.     

Conserving quasiparticle calculations for small metal clusters

A novel approach for GW-based calculations of quasiparticle properties for finite systems is presented, in which the screened interaction is obtained directly from a linear response calculation of the density-density correlation function. The conserving nature of our results is shown by explicit evaluation of the f-sum rule. As an application, energy renormalizations and level broadenings are calculated for the closed-shell Na₉ ⁺ and Na₂₁ ⁺ clusters, as well as for Na₄. Pronounced improvements of conserving approximations to RPA-level results are obtained.     

First-Principles Study of Li Doping in a Double-Wall Carbon Nanotube

By performing first-principles calculations, we study Li doping in a double-wall carbon nanotube where a （5,0） tube is confined inside a （14,0） tube. There are three possible sites for Li doping and two of them are energetically favorable. The change of energy band structure is closely related to the doping sites and the charge transfer is investigated. Bader charge analysis indicates that Li prefers to donate its electron to the inner （5,0） tube. Moreover, the Li capacity of the system can reach LIC4.75 which makes it a promising candidate for Li-ion battery materials.     

New implementation of composite fermions in terms of subgroups of a braid group

The new implementation of composite fermions and more generally — of composite anyons is formulated, exploiting one-dimensional unitary representations of appropriately constructed subgroups of the full braid group. The nature of hypothetical fluxes attached to the Jain's composite fermions is explained via additional cyclotron trajectory loops consistently with the braid subgroup structure. It is demonstrated that composite fermions are proper 2D particles (not an auxiliary construction), but associated with braid subgroups instead of the full braid group.     

Proton polarization in the p(e,e′p)π0 reaction and the measurement of quadrupole components in the N to Δ transition

The recoil proton polarization in the π⁰ production off the proton with longitudinally polarized electron beam has been studied as a means to measure quadrupole components in the N to Δ transition. On top of the Δ resonance a high sensitivity to a possible Coulomb quadrupole excitation is found in parallel kinematics. The ratio of S ₁₊/M ₁₊ multipole amplitudes can be determined from the ratio of the two in-scattering-plane recoil proton polarization components. Avoiding the absolute measurement of the polarizations, such a ratio allows small experimental uncertainties. Furthermore, the electron helicity independent proton polarization component enables the characterization of resonant and non-resonant pieces. Received: 3 November 1997     

Frequency measurements of saturated-fluorescence-stabilized CO2 laser lines: comparison with an OsO4-stabilized CO2 laser standard

4 frequency grid, to test the performance of the saturated fluorescence method for CO₂ laser frequency stabilization. The Allan variance for the saturated-fluorescence-stabilized CO₂ laser reached 60 Hz for an integration time of 300 s. We also performed three absolute measurements of CO₂ laser frequencies stabilized by the saturated fluorescence method, with a sub-kHz accuracy. We obtained a 1.7 kHz redshift of the CO₂ saturated fluorescence lines, which we attribute essentially to pressure. This is in contradiction with the previous observation of a blueshift [K.L. SooHoo, C. Freed, J.E. Thomas, H.A. Haus: Phys. Rev. Lett. 53, 1437 (1984)]. Furthermore, significant deviations of the measured frequencies from the data of Maki et al. [A.G. Maki, C.-C. Chou, K. Evenson, L.R. Zink, J.T. Shy: J. Mol. Spec. 167, 211 (1994)] demonstrate the need for a new calibration of the CO₂ frequency grid. Received: 1 December 1997