نتایج جستجو برای: nmr shielding tensor

تعداد نتایج: 110240  

Density functional theory methods(DFT) and natural bond orbital (NBO) analysis were used to investigate the effects of isomerism and side chain mutation at a microscopic level on the stability, binding energy and NMR/NQR tensors of structural isomers, L- methionylasparagine (Met-Asn) and L- asparagylmethionine (Asn-Met) in the gas phase. The results represented that the isomerism and side chain...

2011
Teemu Pennanen Juha Vaara

Paramagnetic, or open-shell, systems are often encountered in the context of metalloproteins, and they are also an essential part of molecular magnets. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for chemical structure elucidation, but for paramagnetic molecules it is substantially more complicated than in the diamagnetic case. Before the present work, the theory of NMR of ...

2001
R. F. Campbell E. Meirovitch J. H. Freed

The model of Mason, Polnaszek, and Freed for ESR-slow-tumbling spectra is extended to the case of NMR line shapes for arbitrary tilt of the internal axis of relatively rapid rotation with respect to the principal axes of the chemical shielding tensor for a decoupled I = 1 / 2 nucleus. The theory is applied to an analysis of 31P NMR spectra from partially hydrated dipalmitoylphosphatidylcholine ...

2002
Jean-Christophe Hus Rafael Brüschweiler

A general method is presented for the reconstruction of interatomic vector orientations from nuclear magnetic resonance ~NMR! spectroscopic data of tensor interactions of rank 2, such as dipolar coupling and chemical shielding anisotropy interactions, in solids and partially aligned liquid-state systems. The method, called PRIMA, is based on a principal component analysis of the covariance matr...

1988
Ned H. Martin

The long-held “shielding cone” model of the through-space NMR shielding effect of a carbon-carbon double bond predicts only the effect of the magnetic anisotropy of the double bond; it ignores other important contributors to the overall shielding. GIAO-SCF and GIAO-MP2 calculations have been performed on a simple model system, methane moved sequentially above ethene or 2-methylpropene. These ca...

2011
Matti Hanni

This thesis presents computational studies of both the static and dynamic parameters of the nuclear magnetic resonance (NMR) spectroscopy of gaseous xenon. First, state-of-the-art static magnetic resonance parameters are computed in small xenon clusters by using methods of quantum chemistry, and second, time-dependent relaxation phenomena are investigated via molecular dynamics simulations at d...

Journal: :Physical chemistry chemical physics : PCCP 2016
Bożena Adrjan Włodzimierz Makulski Karol Jackowski Taye B Demissie Kenneth Ruud Andrej Antušek Michał Jaszuński

An absolute shielding scale is proposed for (207)Pb nuclear magnetic resonance (NMR) spectroscopy. It is based on ab initio calculations performed on an isolated tetramethyllead Pb(CH3)4 molecule and the assignment of the experimental resonance frequency from the gas-phase NMR spectra of Pb(CH3)4, extrapolated to zero density of the buffer gas to obtain the result for an isolated molecule. The ...

Journal: :Journal of the American Chemical Society 2001
R H Havlin D D Laws H M Bitter L K Sanders H Sun J S Grimley D E Wemmer A Pines E Oldfield

We have carried out a solid-state magic-angle sample-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic investigation of the (13)C(alpha) chemical shielding tensors of alanine, valine, and leucine residues in a series of crystalline peptides of known structure. For alanine and leucine, which are not branched at the beta-carbon, the experimental chemical shift anisotropy (CSA) spans (...

Journal: :Physical chemistry chemical physics : PCCP 2013
Jan Vícha Michael Patzschke Radek Marek

A methodology for optimizing the geometry and calculating the NMR shielding constants is calibrated for octahedral complexes of Pt(IV) and Ir(III) with modified nucleic acid bases. The performance of seven different functionals (BLYP, B3LYP, BHLYP, BP86, TPSS, PBE, and PBE0) in optimizing the geometry of transition-metal complexes is evaluated using supramolecular clusters derived from X-ray da...

2002
R. G. Griffin Francis Bitter A. Pines S. Waugh

13C chemical shielding tensors in three oxalates were investigated in order to determine the effe~ts of protonation and conformation changes on the tensor elements and their orientations. The expenmental results. together with those in the accompanying paper [R. G. Griffin and D. J. Ruben, J. Chern. ~hys. 63, 1272 (1975)], indicate that, while neither of these factors seems to seriously effect ...

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