How to use deshielding in a sentence? Find typical usage patterns (collocations)/phrases/context for "deshielding" and check conjugation/comparative form for "deshielding". Mastering all the usages of "deshielding" from sentence examples published by news publications.
Since this is a tertiary amide, it exists in a cis/trans mixture, which underlies the two conformations of kalkitoxin. Structure (c) is a string of two methylene groups, then a methine group bearing a high-field methyl group. The next two groups identified (d,e) are identical and opposing strings of CH2-CH-CH3, however the left grouping's methylene protons experience greater deshielding, due to their proximity to the adjacent imine. Deshielding is an effect of a nearby electronegative atom withdrawing electron density from a given atom nucleus, eliciting an increased chemical shift as measured by NMR.
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It might appear from the above that all nuclei of the same nuclide (and hence the same γ) would resonate at exactly the same frequency. This is not the case. The most important perturbation of the NMR frequency for applications of NMR is the "shielding" effect of the surrounding shells of electrons.Principle of Shielding and Deshielding . NMRCentral.
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The structure of kalkitoxin was first determined by characterizing six partial structures which were subsequently connected to yield the total structure. This investigation was largely carried out through various NMR experiments. Structure (a) is a sec-butyl group, indicated by characteristic deshielding of its central methine group due to the adjacent carbonyl. Structure (b) contains this carbonyl group, and an adjacent tertiary methylated nitrogen atom, constituting a tertiary amide group.
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Gomes, J. A. N. F.; Mallion, R. B. Chem. Rev.; (Review); 2001; 101(5); 1349-1384. The effect helps distinguish these nuclear environments and is therefore of great use in molecular structure determination. In benzene, the ring protons experience deshielding because the induced magnetic field has the same direction outside the ring as the external field and their chemical shift is 7.3 ppm compared to 5.6 for the vinylic proton in cyclohexene.
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Interaction of triethylphosphine oxide with a Lewis acidThe 31P chemical shift (δ) of Et3PO is sensitive to chemical environment but can usually be found between +40 and +100 ppm. The O atom in Et3PO is a Lewis base, and its interaction with Lewis acid sites causes deshielding of the adjacent P atom. Gutmann described an Acceptor Number (AN) scale for solvent Lewis acidity V. Gutmann, "Solvent effects on reactivities of organometallic compounds", Coord. Chem. Rev., 1976, 18, 225–255. doi: 10.1016/S0010-8545(00)82045-7 with two reference points relating to the 31P NMR chemical shift of Et3PO in the weakly Lewis acidic solvent hexane (δ = 41.0 ppm, AN 0) and in the strongly Lewis acidic solvent SbCl5 (δ = 86.1 ppm, AN 100).
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The application of secondary chemical shifts to characterize protein flexibility is based on an assumption that the proximity of chemical shifts to random coil values is a manifestation of increased protein mobility, while significant differences from random coil values are an indication of a relatively rigid structure. Even though chemical shifts of rigid residues may adopt random coil values as a result of comparable contributions of shielding and deshielding effects (e.g. from torsion angles, hydrogen bonds, ring currents, etc.), combining the chemical shifts from multiple nuclei into a single parameter allows one to decrease the influence of these flexibility false positives. The improved performance originates from the different probabilities of random coil chemical shifts from different nuclei being found among amino acid residues in flexible regions versus rigid regions.
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