The NMR Chemical Shift: Insight into Structure and Environment

Dios, Angel C. de; Jameson, Cynthia J.

doi:10.1016/s0066-4103(08)60130-1

Cited by 57 publications

(41 citation statements)

References 171 publications

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“…In order to properly compare calculated and experimental results a scaling factor of some type needs to be applied. Even though vibrational averaging, bulk susceptibility, and solvation effects as the underlying reasons for this discrepancy have been studied and discussed at length (29)(30)(31), a consensus set of rules for correction has not been clearly established. In order to correct the chemical shift offset the average systematic deviation between the calculated structures and the experimental was subtracted from the calculated value.…”

Section: Discussionmentioning

confidence: 99%

Calculation of 13C Chemical Shifts in RNA Nucleosides: Structure-13C Chemical Shift Relationships

Rossi

Harbison

2001

Journal of Magnetic Resonance

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Isotropic 13 C chemical shifts of the ribose sugar in model RNA nucleosides are calculated using SCF and DFT-GIAO ab initio methods for different combinations of ribose sugar pucker, exocyclic torsion angle, and glycosidic torsion angle. Idealized conformations were obtained using structures that were fully optimized by ab initio DFT methods starting with averaged parameters from a collection of crystallographic data. Solid-state coordinates of accurate crystal or neutron diffraction structures were also examined directly without optimization. The resulting 13 C chemical shifts for the two sets of calculations are then compared. The GIAO-DFT method overestimates the shifts by an average of 5 ppm while the GIAOSCF underestimates the shifts by the same amount. However, in the majority of cases the errors appear to be systematic, as the slope of a plot of calculated vs experimental shifts is very close to unity, with minimal scatter. The values of the 13 C NMR shifts of the ribose sugar are therefore sufficiently precise to allow for statistical separation of sugar puckering modes and exocyclic torsion angle conformers, based on the canonical equation model formulated in a previous paper.

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Section: Discussionmentioning

confidence: 99%

Calculation of 13C Chemical Shifts in RNA Nucleosides: Structure-13C Chemical Shift Relationships

Rossi

Harbison

2001

Journal of Magnetic Resonance

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“…The sum in Eq. [10] is over all the exited states of the molecule. Before discussing methods for practical evaluation of Eqs.…”

Section: Theory Of Chemical Shieldings Exact Perturbation Theorymentioning

confidence: 99%

“…Before discussing methods for practical evaluation of Eqs. [9] and [10], it is important to understand the behavior of the diamagnetic and paramagnetic terms under coordinate origin translation. Both terms, as shown by Eqs.…”

Section: Theory Of Chemical Shieldings Exact Perturbation Theorymentioning

confidence: 99%

Calculations of chemical shieldings: Theory and applications

Facelli

2004

Concepts Magnetic Resonance

105

127

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ABSTRACT:This article presents a discussion of the origin of the chemical shieldings, which is followed by a rigorous derivation of quantum mechanical formula for their exact calculation and a discussion of the necessary approximations that make these calculations feasible. Comprehensive information on the resources, software and hardware needed for the calculations is given followed by several examples of actual quantum chemical calculations of chemical shieldings. These examples are used to demonstrate how accurate shielding calculations can be used to help the NMR practitioner to solve practical chemical and structural problems.

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“…Temperature can also affect observed chemical shifts through changes in the density of the sample as well as changes in the internal motions of the molecule [25]. For a fair comparison of library and sample spectra, it is important that spectra are taken at the same temperature.…”

Section: Nmr Chemical Shifts and Coupling Constantsmentioning

confidence: 99%

1H and 13C NMR for the Profiling of Natural Product Extracts: Theory and Applications

Dayrit¹,

Dios²

2017

Spectroscopic Analyses - Developments and Applications

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Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) are the principal methods of metabolomics, the branch of '-omics' that deals with small molecules. Although MS is gaining popularity in metabolomics, NMR enjoys a number of key advantages because it is nondestructive, unbiased, quantitative, does not require separation or derivatization, and is amenable to compounds that are difficult to analyze by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). There are two general approaches to the use of NMR for profiling studies: an untargeted approach, which uses chemometric analysis; and a targeted approach, which aims to quantify known compounds in the extract. These approaches, however, are not mutually exclusive and will likely converge in the future. This paper will describe the basic theoretical principles that should be considered to develop NMR into a standard quantitative method. Although 1H NMR is more sensitive, 13C NMR spectra are simpler with less overlapping signals and are less affected by different magnetic field strengths. Various applications of 1H and 13C NMR for the profiling of natural products are described. The use of two-dimensional 1H NMR has been used to overcome problems of spectral overlap. The standardization of the NMR protocol will make it a more useful tool for the profiling of natural products extracts.

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The NMR Chemical Shift: Insight into Structure and Environment

Cited by 57 publications

References 171 publications

Calculation of 13C Chemical Shifts in RNA Nucleosides: Structure-13C Chemical Shift Relationships

Calculation of 13C Chemical Shifts in RNA Nucleosides: Structure-13C Chemical Shift Relationships

Calculations of chemical shieldings: Theory and applications

1H and 13C NMR for the Profiling of Natural Product Extracts: Theory and Applications

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