Indirect Coupling: Theory and Applications in Organic Chemistry

Barfield, Michael

doi:10.1002/9780470034590.emrstm0236

Cited by 2 publications

(3 citation statements)

References 154 publications

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“…Distortions in the field also arise due to the magnetic moments of nearby nuclei, and result in a splitting of the signal known as coupling. Coupling may occur either through-space (direct spin-spin coupling) or through-bond (indirect spin-spin coupling) [ 120 ]. In solution-state NMR experiments, through-bond coupling is observed, while the through-space interactions are removed due to random reorientations of the molecule [ 121 ].…”

Section: Methods To Study Structurementioning

confidence: 99%

“…In solution-state NMR experiments, through-bond coupling is observed, while the through-space interactions are removed due to random reorientations of the molecule [ 121 ]. The strength of the coupling interaction, known as the coupling constant, J, is a function of the electron density between the nuclei in question; therefore, the coupling is highly indicative of the intervening structure [ 120 ]. Scalar coupling is typically observed for nuclei which are 2 (geminal) or 3 (vicinal) bonds apart from each other; however, longer range coupling may be observed for rigid or π-bonded systems [ 122 ].…”

Section: Methods To Study Structurementioning

confidence: 99%

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Current and Future Experimental Strategies for Structural Analysis of Trichothecene Mycotoxins—A Prospectus

Shank

Foroud

Hazendonk

et al. 2011

Toxins

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Fungal toxins, such as those produced by members of the order Hypocreales, have widespread effects on cereal crops, resulting in yield losses and the potential for severe disease and mortality in humans and livestock. Among the most toxic are the trichothecenes. Trichothecenes have various detrimental effects on eukaryotic cells including an interference with protein production and the disruption of nucleic acid synthesis. However, these toxins can have a wide range of toxicity depending on the system. Major differences in the phytotoxicity and cytotoxicity of these mycotoxins are observed for individual members of the class, and variations in toxicity are observed among different species for each individual compound. Furthermore, while diverse toxicological effects are observed throughout the whole cellular system upon trichothecene exposure, the mechanism of toxicity is not well understood. In order to comprehend how these toxins interact with the cell, we must first have an advanced understanding of their structure and dynamics. The structural analysis of trichothecenes was a subject of major interest in the 1980s, and primarily focused on crystallographic and solution-state Nuclear Magnetic Resonance (NMR) spectroscopic studies. Recent advances in structural determination through solution- and solid-state NMR, as well as computation based molecular modeling is leading to a resurgent interest in the structure of these and other mycotoxins, with the focus shifting in the direction of structural dynamics. The purpose of this work is to first provide a brief overview of the structural data available on trichothecenes and a characterization of the methods commonly employed to obtain such information. A summary of the current understanding of the relationship between structure and known function of these compounds is also presented. Finally, a prospectus on the application of new emerging structural methods on these and other related systems is discussed.

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Section: Methods To Study Structurementioning

confidence: 99%

Section: Methods To Study Structurementioning

confidence: 99%

Current and Future Experimental Strategies for Structural Analysis of Trichothecene Mycotoxins—A Prospectus

Shank

Foroud

Hazendonk

et al. 2011

Toxins

View full text Add to dashboard Cite

show abstract

“…The transmission of spin−spin coupling information from the perturbing to the responding nucleus depends as indicated by the Ramsey mechanism strongly on the electronic structure of a given molecule and in this way also on its geometry and conformation. There are numerous review articles that describe the dependence of the SSCC on geometrical and conformational parameters ,− of which the work on the Karplus relationship is best known. − There is also extensive work on the relationship between charge distribution, orbital hybridization, and contact densities to explain the FC term. − These approaches proved successful in reproducing qualitatively many trends observed for SSCCs. Noteworthy in this connection areinvestigations carried out by Contreras and co-workers 11-13 who carefully studied the transmission mechanism of many different SSCCs and who provided simple explanations for observed SSCCs.…”

Section: Introductionmentioning

confidence: 99%

Elucidation of the Electronic Structure of Molecules with the Help of NMR Spin−Spin Coupling Constants: The FH Molecule

2005

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It is demonstrated how the one-bond NMR spin-spin coupling constant (SSCC) (1)J(FH) can be used as a source of information on the electronic structure of the FH molecule. For this purpose, the best possible agreement between measured and calculated SSCC is achieved by large basis set coupled perturbed density functional theory calculations. Then, the calculated value is dissected into its four Ramsey terms: Fermi contact, the paramagnetic spin-orbit term, the diamagnetic spin-orbit term, and the spin dipole term, which in turn are decomposed into orbital contributions and then described by their spin densities and orbital current densities. In this way, the SSCC gives detailed information about the electronegativity of F, the bond polarity, the bond polarizability, the volume and the polarizability of sigma and pi lone pair orbitals, the s- or p-character of the bond orbital, the nature of the LUMO, and the density distribution around F.

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Indirect Coupling: Theory and Applications in Organic Chemistry

Cited by 2 publications

References 154 publications

Current and Future Experimental Strategies for Structural Analysis of Trichothecene Mycotoxins—A Prospectus

Current and Future Experimental Strategies for Structural Analysis of Trichothecene Mycotoxins—A Prospectus

Elucidation of the Electronic Structure of Molecules with the Help of NMR Spin−Spin Coupling Constants: The FH Molecule

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