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51.
We formulate and solve the analog of the universal Conformal Ward Identity for the stress-energy tensor on a compact Riemann
surface of genus g > 1, and present a rigorous invariant formulation of the chiral sector in the induced two-dimensional gravity on higher genus
Riemann surfaces. Our construction of the action functional uses various double complexes naturally associated with a Riemann
surface, with computations that are quite similar to descent calculations in BRST cohomology theory. We also provide an interpretation
of the action functional in terms of the geometry of different fiber spaces over the Teichmüller space of compact Riemann
surfaces of genus g > 1.
Received: 12 September 1996 / Accepted: 6 January 1997 相似文献
52.
Mariateresa Giustiniano Sveva Pelliccia Ettore Novellino Gian Cesare Tron 《Tetrahedron letters》2018,59(13):1196-1199
N-Substituted α-amino acid amides can be easily obtained in two steps using the four-component Ugi reaction followed by chemoselective cleavage of the resulting tertiary amide. The use of the sacrificial acid, 2-hydroxymethylbenzoic acid is associated to shorter reaction times, higher yields, and safer and greener reaction conditions compared to strategies based on trifluoroacetic acid, a toxic and environmental hazardous reagent. The optimized procedure was easily scaled up to gram amounts. 相似文献
53.
Antonello Santini Ettore Benedetti Carlo Pedone Giuseppe Caliendo Vincenzo Santagada Paolo Grieco Elisa Perissutti 《Structural chemistry》1996,7(3):173-181
The solid-state molecular conformations and crystal structures of three analogues of the CP-96,345 molecule, an important nonpeptidic SP antagonist, namely the (±)-2-(3-phenylbenzilidene)-3-(2-benzylamino) quinuclidine, theo-chloro- and theo-methoxy-derivatives, have been determined by X-ray diffusion analyses and refined to finalR values of 0.055, 0.045, and 0.056, respectively. All three molecules in the solid state show the same disposition of the substituents of the double bond and differences in the conformation mainly caused by the need of releasing intramolecular strains and/or nonbonded interactions. The observed molecular structures are compared to the reported solid-state structure of the CP-96,345 and correlated to the biological activity as NK antagonists. 相似文献
54.
55.
A practical and efficient conversion of 4-bromomethyl-5-methyl-1, 3-dioxol-2-one 1 into the corresponding carbinol 2, a useful building block for the preparation of prodrugs, is reported. 相似文献
56.
A classical result in Lorentzian geometry states that a strongly causal spacetime is globally hyperbolic if and only if the Lorentzian distance is finite valued for every metric choice in the conformal class. It is proved here that a non-total imprisoning spacetime is globally hyperbolic if and only if for every metric choice in the conformal class the Lorentzian distance is continuous. Moreover, it is proved that a non-total imprisoning spacetime is causally simple if and only if for every metric choice in the conformal class the Lorentzian distance is continuous wherever it vanishes. Finally, a strongly causal spacetime is causally continuous if and only if there is at least one metric in the conformal class such that the Lorentzian distance is continuous wherever it vanishes. 相似文献
57.
Non-equilibrium vibrational kinetics as recently developed for adlayers is applied to experimental data on H-atom recombination and abstraction at solid surfaces. This model allows one to fit vibrational and translational energy distribution functions of the excited diatoms leaving the surface. Eley–Rideal and Langmuir–Hinshelwood mechanisms involving vibrationally excited adatoms are presented together with a criterion for establishing their relative contribution to the total reaction rate. Analogies of this multilevel ‘hot atom' (HA) model with recently employed two and three levels HA kinetic schemes are presented and discussed. 相似文献
58.
59.
van Well RM Marinelli L Altona C Erkelens K Siegal G van Raaij M Llamas-Saiz AL Kessler H Novellino E Lavecchia A van Boom JH Overhand M 《Journal of the American Chemical Society》2003,125(36):10822-10829
Sugar amino acids (SAAs) are useful building blocks for the design of peptidomimetics and peptide scaffolds. The three-dimensional structures of cyclic hybrid molecules containing the furanoid epsilon-SAA III and several amino acids were elucidated to study the preferred conformation of such an epsilon-SAA and its conformational influence on the backbone of cyclic peptides. NMR-based molecular dynamics simulations and empirical calculations of the cyclic tetramer 1, consisting of two copies of the SAA residue and two amino acids, revealed that it is conformationally restrained. The two SAA residues adopt different conformations. One of them forms an unusual turn, stabilized by an intraresidue nine-member hydrogen bond. The methylene functionalities of the other SAA residue are positioned in such a way that an intraresidue H bond is not possible. The X-ray crystal structure of 1 strongly resembles the solution conformation. Molecular dynamics calculations in combination with NMR analysis were also performed for compounds 2 and 3, which contain the RGD (Arg-Gly-Asp) consensus sequence and were previously shown to inhibit alpha(IIb)beta(3)-receptor-mediated platelet aggregation. The biologically most active compound 2 adopts a preferred conformation with the single SAA residue folded into the nine-member H bond-containing turn. Compound 3, containing an additional valine residue, as compared with compound 2, is conformational flexible. Our studies demonstrate that the furanoid epsilon-SAA III is able to introduce an unusual intraresidue hydrogen bond-stabilized beta-turn-like conformation in two of the three cyclic structures. 相似文献
60.