排序方式: 共有29条查询结果,搜索用时 15 毫秒
21.
Kristine Pierloot Birgit Dumez Per-Olof Widmark Björn O. Roos 《Theoretical chemistry accounts》1995,90(2-3):87-114
Summary Generally contracted Basis sets for the atoms H-Kr have been constructed using the atomic natural orbital (ANO) approach, with modifications for allowing symmetry breaking and state averaging. The ANO's are constructed by averaging over the most significant electronic states, the ground state of the cation, the ground state of the anion for some atoms and the homonuclear diatomic molecule at equilibrium distance for some atoms. The contracted basis sets yield excellent results for properties of molecules such as bond-strengths and-lengths, vibrational frequencies, and good results for valence spectra, ionization potentials and electron affinities of the atoms, considering the small size of these sets. The basis sets presented in this article constitute a balanced sequence of basis sets suitable for larger systems, where economy in basis set size is of importance. 相似文献
22.
The design of simulations of free evolution in dipolar-coupled nuclear-spin systems using low-order correlations in Liouville space (LCL) is discussed, and a computational scheme relying on the Suzuki-Trotter algorithm and involving minimal memory requirements is described. The unusual nature of the approximation introduced by Liouville-space reduction in a spinning solid is highlighted by considering the accuracy of LCL simulations at different spinning frequencies, the quasiequilibria achieved by spin systems in LCL simulations, and the growth of high-order coherences in the exact dynamics. In particular, it is shown that accurate LCL simulations of proton spin diffusion occur in a regime where the reduced space excludes the coherences that make the dominant contribution to ∥σ∥(2), the norm-squared of the density matrix. 相似文献
23.
In the framework of relativistic harmonic confinement model for quarks and antiquarks, the masses of S- and P-wave mesons and pseudoscalar decay constants from light flavour to heavy flavour sectors are computed. The residual two-body
Coulomb interaction and the spin-dependent interaction of the confined one gluon exchange effects (COGEP) such as spin-spin
and spin-orbit interactions are perturbatively incorporated with the confinement energy to get the respective vector-pseudoscalar
meson mass differences. Here we employ the same parametrization and model parameters as used in a recent study of low-lying
hadron masses and leptonic decay widths. The results are being compared with the values obtained from other theoretical models
and the experimental values. 相似文献
24.
Dr. Ludmilla Guduff Dr. Patrick Berthault Dr. Carine van Heijenoort Dr. Jean-Nicolas Dumez Dr. Gaspard Huber 《Chemphyschem》2019,20(3):392-398
The analysis of complex mixtures of dissolved molecules is a major challenge, especially for systems that gradually evolve, e. g., in the course of a chemical reaction or in the case of chemical instability. 1D NMR is a fast and non-invasive method suitable for detailed molecular analysis, though of low sensitivity. Moreover, the spectral resolution of proton, the most commonly used and most sensitive stable isotope in NMR, is also quite limited. Spatially encoded (SPEN) experiments aim at creating in one acquisition a 2D data set by simultaneously performing different 1D sub-experiments on different slices of the NMR tube, at the price of an extra loss of sensitivity. Choosing translational diffusion coefficients as the additional dimension (the so-called DOSY approach) helps to recover proton spectra of each molecule in a mixture. The sensitivity limitation of SPEN NMR can, on the other hand, be addressed with hyperpolarization methods. Within hyperpolarization methods, signal amplification by reversible exchange (SABRE), based on parahydrogen, is the cheapest and the easiest one to set up, and allows multi-shot experiments. Here we show that the spectra of a mixture's components at millimolar concentration are resolved in few seconds by combining the SABRE, SPEN and DOSY concepts. 相似文献
25.
Estelle Martineau Jean-Nicolas Dumez Patrick Giraudeau 《Magnetic resonance in chemistry : MRC》2020,58(5):390-403
Nuclear magnetic resonance (NMR) is a well-known analytical technique for the analysis of complex mixtures. Its quantitative capability makes it ideally suited to metabolomics or lipidomics studies involving large sample collections of complex biological samples. To overcome the ubiquitous limitation of spectral overcrowding when recording 1D NMR spectra on such samples, the acquisition of 2D NMR spectra allows a better separation between overlapped resonances while yielding accurate quantitative data when appropriate analytical protocols are implemented. Moreover, the experiment duration can be considerably reduced by applying fast acquisition methods. Here, we describe the general workflow to acquire fast quantitative 2D NMR spectra in the “omics” context. It is illustrated on three representative and complementary experiments: UF COSY, ZF-TOCSY with nonuniform sampling, and HSQC with nonuniform sampling. After giving some details and recommendations on how to apply this protocol, its implementation in the case of targeted and untargeted metabolomics/lipidomics studies is described. 相似文献
26.
Estelle Dumez Dr. Anne‐Catherine Durand Dr. Martial Guillaume Dr. Pierre‐Yves Roger Dr. Robert Faure Dr. Jean‐Marc Pons Dr. Gaëtan Herbette Dr. Jean‐Pierre Dulcère Dr. Damien Bonne Dr. Jean Rodriguez Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(45):12470-12488
The synthesis of various heterocycles and carbocycles (tetrahydrofurans, pyrrolidines, cyclopentanes) has been achieved by using new and efficient ionic addition/cyclization sequences. Nitroolefins play an important role in the Michael addition induced ring‐closing reactions (MIRC) reported in the present article, with various substituted alcohols, amines, Grignard reactants, or malonate derivatives acting as the nucleophile partner. The optimized cascade reactions were high yielding in most cases and highly stereoselective, creating up to three stereogenic centers starting from achiral substrates. 相似文献
27.
Dr. Anna J. Parker Dr. Arnab Dey Mohammad Usman Qureshi Jakob M. Steiner Dr. John W. Blanchard Dr. Jochen Scheuer Nikolas Tomek Dr. Stephan Knecht Felix Josten Dr. Christoph Müller Dr. Patrick Hautle Dr. Ilai Schwartz Prof. Patrick Giraudeau Dr. Tim R. Eichhorn Dr. Jean-Nicolas Dumez 《Angewandte Chemie (International ed. in English)》2023,62(50):e202312302
The HYPNOESYS method (Hyperpolarized NOE System), which relies on the dissolution of optically polarized crystals, has recently emerged as a promising approach to enhance the sensitivity of NMR spectroscopy in the solution state. However, HYPNOESYS is a single-shot method that is not generally compatible with multidimensional NMR. Here we show that 2D NMR spectra can be obtained from HYPNOESYS-polarized samples, using single-scan acquisition methods. The approach is illustrated with a mixture of terpene molecules and a benchtop NMR spectrometer, paving the way to a sensitive, information-rich and affordable analytical method. 相似文献
28.
Achille Marchand Dr. Rituraj Mishra Aurélie Bernard Dr. Jean-Nicolas Dumez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(52):e202201175
Online monitoring by flow NMR spectroscopy is a powerful approach to study chemical reactions and processes, which can provide mechanistic understanding, and drive optimisations. However, some of the most useful methods for mixture analysis and reaction monitoring are not directly applicable in flow conditions. This is the case of classic diffusion-ordered NMR spectroscopy (DOSY) methods, which can be used to separate the spectral information for mixture's components. We describe a fast and flow-compatible diffusion NMR experiment that makes it possible to collect accurate diffusion data for samples flowing at up to 3 mL/min. We use it to monitor the synthesis of a Schiff base with a flow-tube with a time resolution of approximately 2 minutes. The one-shot flow-compatible diffusion NMR described here open many avenues for reaction monitoring applications. 相似文献
29.