Proton Chemical-Shift Tensors of Methyl Groups; a Multiple-Pulse NMR and LORG/IGLOab InitioStudy

Tesche, B.; Haeberlen, Ulrich

doi:10.1006/jmra.1995.0733

Cited by 8 publications

(8 citation statements)

References 5 publications

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“…For water, the difference between the MP2 and the SCF results is 17.70 ppm in the case of the isotropic shielding of the oxygen atom and 10.05 ppm for the anisotropic shielding of the carbon atom. The previous methanol values [44,48] shown in Table I for the anisotropic case were obtained at the SCF level and, as can be seen, they are in better agreement with our SCF results. A systematic study of NMR parameters for acyclic and isolated alcohols at a lower DFT level has been presented [62].…”

Section: Absolute Chemical Shieldingssupporting

confidence: 90%

Ab initio NMR study of the isomeric hydrogen‐bonded methanol–water complexes

Fileti¹,

Canuto²

2005

Int J of Quantum Chemistry

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Isotropic and anisotropic chemical shifts for all atoms of complexes CH 3 HO . . . H 2 O and CH 3 OH . . . OH 2 have been calculated at the Hartree-Fock, secondorder Møller-Plesset (MP2) and density functional (B3LYP) theoretical levels using the 6-311ϩϩG(2d,2p) basis set. The influence of the hydrogen bond formation on the nuclear magnetic resonance chemical shifts in all atoms is analyzed. The basis set superposition error was taken into account, and its effects were more significant for the anisotropic shieldings on the oxygen atoms of the proton donor CH 3 OH . . . OH 2 and proton acceptor methanol CH 3 HO . . . H 2 O. Using counterpoise correction to the MP2 results, our best estimate for the calculated isotropic and anisotropic shifts of the H atom involved in the hydrogen bond are Ϫ2.98 and 11.95 ppm for CH 3 HO . . . H 2 O and Ϫ2.91 and 11.48 ppm for the CH 3 OH . . . OH 2 isomer, respectively. For the O atom of the OH hydrogen bonded, these calculated shifts are Ϫ5.21 and Ϫ5.35 ppm for CH 3 HO . . . H 2 O and Ϫ6.32 and Ϫ8.75 ppm for CH 3 OH . . . OH 2 . The effect of monomer relaxation was also considered and was found to be appreciable only for the oxygen atom of the proton donor OH due to the distance increase after complex formation.

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Section: Absolute Chemical Shieldingssupporting

confidence: 90%

Ab initio NMR study of the isomeric hydrogen‐bonded methanol–water complexes

Fileti¹,

Canuto²

2005

Int J of Quantum Chemistry

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“…A collection of known chemical shift anisotropies compiled by Duncan in 1990 contains about eighty proton entries, [34] a very modest number when compared with 13 C. Since then only a few single crystals have been measured by proton multiple-pulse techniques. [35–37] Presumably it reflects a number of difficulties when working with single crystals. The sample preparation is challenging and so are accurate sample alignment in the magnet, peak assignment when the unit cell contains many protons, and taking care of peak shifts arising from the magnetic susceptibility of the sample.…”

Section: Introductionmentioning

confidence: 99%

A Magic‐Angle‐Spinning NMR Spectroscopy Method for the Site‐Specific Measurement of Proton Chemical‐Shift Anisotropy in Biological and Organic Solids

Hou

Gupta

Polenova

et al. 2014

Israel Journal of Chemistry

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Proton chemical shifts are a rich probe of structure and hydrogen bonding environments in organic and biological molecules. Until recently, measurements of 1H chemical shift tensors have been restricted to either solid systems with sparse proton sites or were based on the indirect determination of anisotropic tensor components from cross-relaxation and liquid-crystal experiments. We have introduced an MAS approach that permits site-resolved determination of CSA tensors of protons forming chemical bonds with labeled spin-1/2 nuclei in fully protonated solids with multiple sites, including organic molecules and proteins. This approach, originally introduced for the measurements of chemical shift tensors of amide protons, is based on three RN-symmetry based experiments, from which the principal components of the 1H CS tensor can be reliably extracted by simultaneous triple fit of the data. In this article, we expand our approach to a much more challenging system involving aliphatic and aromatic protons. We start with a review of the prior work on experimental-NMR and computational-quantum-chemical approaches for the measurements of 1H chemical shift tensors and for relating these to the electronic structures. We then present our experimental results on U-13C,15N-labeled histdine demonstrating that 1H chemical shift tensors can be reliably determined for the 1H15N and 1H13C spin pairs in cationic and neutral forms of histidine. Finally, we demonstrate that the experimental 1H(C) and 1H(N) chemical shift tensors are in agreement with Density Functional Theory calculations, therefore establishing the usefulness of our method for characterization of structure and hydrogen bonding environment in organic and biological solids.

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“…s = 3 ls and pulse-duration t w = 0.8 ls was used. For further experimental details (e.g., composite preparation pulse, multi-window sampling) see [22].…”

Section: Multiple-pulse Nmrmentioning

confidence: 99%