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排序方式: 共有537条查询结果,搜索用时 15 毫秒
111.
Electrospray ionization mass spectrometry (ESI-MS) and subsequent MS/MS analyses were used to directly detect palladium-containing cationic reaction intermediates in a ligand controlled palladium(II)-catalyzed oxidative Heck arylation. All potential intermediates were observed as dmphen-ligated palladium(II) species, suggesting that the dmphen bidentate ligand is attached to the metal center during the entire catalytic cycle. The study supports previous mechanistic propositions and provides new information regarding the composition of aryl-containing Pd(II) complexes in an ongoing oxidative Heck reaction. In addition, sodium acetate was found to be a useful base alternative to previously used tertiary amines. 相似文献
112.
Stereoselective synthesis of 3-aminoindan-1-ones and subsequent incorporation into HIV-1 protease inhibitors 总被引:1,自引:0,他引:1
A new method for the stereoselective synthesis of 3-aminoindan-1-ones from triflates of salicylic sulfinyl imines and ethylene glycol vinyl ether has been developed. The reaction sequence starts with a regioselective Heck reaction followed by stereoselective Lewis acid mediated annulation. Acidic cleavage of the sulfinamides produced pure (R)- and (S)-3-aminoindan-1-ones, which were successfully isolated and incorporated into active HIV-1 protease inhibitors. 相似文献
113.
Yang LM Ravindran P Vajeeston P Tilset M 《Physical chemistry chemical physics : PCCP》2012,14(14):4713-4723
The chemical bonding, electronic structure, and optical properties of the experimentally available metal-organic framework IRMOF-14 and its metal-substituted analogues M-IRMOF-14 (M = Zn, Cd, Be, Mg, Ca, Sr, Ba), which contain a pyrene-2,7-dicarboxylate linker group, have been systematically investigated using DFT calculations. The unit cell volume and atomic positions were optimized with the Perdew-Burke-Ernzerhof (PBE) functional and showed good agreement between experimental and theoretical equilibrium structural parameters for Zn-IRMOF-14. The calculated bulk moduli indicate that the whole M-IRMOF-14 series are soft materials. The estimated band gap from DOS calculations for the M-IRMOF-14 series is ca. 2.5 eV, essentially independent of the metal ion and indicative of nonmetallic character. The band gap value is distinctly different from those calculated previously for the M-IRMOF-1 (benzene-1,4-dicarboxylate linker; ca. 3.5 eV) and M-IRMOF-10 (biphenyl-4,4'-dicarboxylate linker; ca. 3.0 eV) series and this confirms that the identity of the linker is a key parameter to control band gaps in an isoreticular series of main-group MOFs. In view of potential uses of MOFs in organic semiconducting devices such as field-effect transistors, solar cells, and organic light-emitting devices, the linear optical properties of these materials were also investigated. Comparisons are made with the M-IRMOF-1 and M-IRMOF-10 series. 相似文献
114.
Ponseca CS Yartsev A Wang E Andersson MR Vithanage D Sundström V 《Journal of the American Chemical Society》2012,134(29):11836-11839
The few-picosecond (ps) decay of terahertz (THz) photoconductivity typically observed for conjugated polymer:fullerene blends (at excitation fluencies ~10(15) photons/cm(2) per pulse) is shown to be a result of charge pair annihilation for two polymer:PCBM blends. At a factor of 100 lower excitation density, the THz decay is in the hundreds of ps time scale, implying that very high carrier mobility (~0.1 cm(2) V(-1) s(-1)) prevails for long time after charge formation, of importance for free charge formation in organic solar cells. 相似文献
115.
Recently, the scaling result z=d for the dynamic critical exponent at the Bose glass to superfluid quantum phase transition has been questioned both on theoretical and numerical grounds. This motivates a careful evaluation of the critical exponents in order to determine the actual value of z. We study a model of quantum bosons at T=0 with disorder in 2D using highly effective worm Monte?Carlo simulations. Our data analysis is based on a finite-size scaling approach to determine the scaling of the quantum correlation time from simulation data for boson world lines. The resulting critical exponents are z=1.8±0.05, ν=1.15±0.03, and η=-0.3±0.1, hence suggesting that z=2 is not satisfied. 相似文献
116.
Mats Linder Adam Johannes Johansson Tjelvar S. G. Olsson John Liebeschuetz Tore Brinck 《Journal of computer-aided molecular design》2012,26(9):1079-1095
A novel computational Diels–Alderase design, based on a relatively rare form of carboxylesterase from Geobacillus stearothermophilus, is presented and theoretically evaluated. The structure was found by mining the PDB for a suitable oxyanion hole-containing structure, followed by a combinatorial approach to find suitable substrates and rational mutations. Four lead designs were selected and thoroughly modeled to obtain realistic estimates of substrate binding and prearrangement. Molecular dynamics simulations and DFT calculations were used to optimize and estimate binding affinity and activation energies. A large quantum chemical model was used to capture the salient interactions in the crucial transition state (TS). Our quantitative estimation of kinetic parameters was validated against four experimentally characterized Diels–Alderases with good results. The final designs in this work are predicted to have rate enhancements of ≈103–106 and high predicted proficiencies. This work emphasizes the importance of considering protein dynamics in the design approach, and provides a quantitative estimate of the how the TS stabilization observed in most de novo and redesigned enzymes is decreased compared to a minimal, ‘ideal’ model. The presented design is highly interesting for further optimization and applications since it is based on a thermophilic enzyme (T opt ?=?70?°C). 相似文献
117.
Mats Aigner 《Communications in Mathematical Physics》2001,216(1):17-22
The existence of the Ginzburg–Landau vortex number is established for any configuration with finite action. As a consequence,
Bogomol'nyi's formula for the critical action is valid for any finite action configuration.
Received: 16 November 1999 / Accepted: 7 July 2000 相似文献
118.
Ulf Ryde Mats H. M. Olsson Björn O. Roos Antonio Carlos Borin 《Theoretical chemistry accounts》2001,105(6):452-462
The accuracy of theoretical calculations on models of the blue copper proteins is investigated using density functional theory
(DFT) Becke's three-parameter hybrid method with the Lee–Yang–Parr correlation functional (B3LYP) and medium-sized basis sets.
Increasing the basis set to triple-zeta quality with f-type functions on all heavy atoms and enlarging the model [up to Cu(imidazole-CH3)2(SC2H5) (CH3SC2H5)0/+] has only a limited influence on geometries and relative energies. Comparative calculations with more accurate wave-function–based
methods (second-order M?ller–Plesset perturbation theory, complete-active-space second-order perturbation theory, coupled-cluster
method, including single and double replacement amplitudes and in addition triple replacement perturbatively) and a variety
of basis sets on smaller models indicate that the DFT/B3LYP approach gives reliable results with only a small basis set dependence,
whereas the former methods strongly depend on the size of the basis sets. The effect of performing the geometry optimizations
in a continuum solvent is quite small, except for the flexible Cu-SMet bond. The results of this study confirm the earlier results that neither the oxidized nor the reduced copper site in the
blue proteins is strained to any significant degree (in energy terms) by the protein surrounding.
Received: 7 July 2000 / Accepted: 17 November 2000 / Published online: 21 March 2001 相似文献
119.
Mats Andersson 《Bulletin des Sciences Mathématiques》2004,128(6):481-512
We define a residue current of a holomorphic mapping, or more generally of a holomorphic section of a holomorphic vector bundle, by means of Cauchy-Fantappie-Leray type formulas, and prove that a holomorphic function that annihilates this current belongs to the corresponding ideal locally. We also prove that the residue current coincides with the Coleff-Herrera current in the case of a complete intersection. The residue current is globally defined and this is used in some geometric applications. By means of the residue current we also construct, for an arbitrary ideal, an integral formula for interpolation and division. 相似文献
120.