Carbon-deuterium interaction

Membranes and model membranes exhibit liquid crystalline behavior and this has been exploited in a number of studies to obtain valuable information on the structure and dynamics of membrane associated peptides and proteins as well as on the interaction of the peptides with the membranes themselves. NMR spectroscopy of nuclei such as proton, carbon, deuterium, nitrogen and phosphorus has been utilized for such purposes. Structure elucidation of membrane-associated peptides and proteins in oriented bilayers by solid-state NMR spectroscopy has been reviewed. A survey on the use of static uniaxially oriented samples for structural and topological analysis of membrane-associated polypeptides is available. The theoretical background has been dealt with and a number of examples of applications provided. In addition, ongoing developments combining this method with information from solution NMR spectroscopy and molecular modelling as well as exploratory studies using dynamic nuclear polarization solid-state NMR have been presented. The use of N chemical shift anisotropy, dipolar interactions and the deuterium quadrupolar split-... 

In all non-bonded interactions which we shall discuss below, at least one of the atoms belongs to the element of hydrogen, and it is always hydrogen linked to carbon which is isotopic and consists of either protium or deuterium. It is frequently stated that protium requires more space than deuterium, but it is worth while examining this statement in detail. 

ESEEM measurements of perdeuterated all-trany-p-carotene imbedded in activated Cu-substituted MCM-41 molecular sieve revealed (Gao et al. 2005) that two deuterons of the carotenoid interact with the Cu2+ at a distance of 3.3 A. Possible double bonds of P-carotene with one deuterium at each carbon that could interact with Cu are C7=C8, CH-C12, 05=05, 02 - C1T, and C8 =C7. 

Support for such an interaction of the H—C bonds with the carbon atom carrying the positive charge is provided by substituting H by D in the original halide, the rate of formation of the ion pair is then found to be slowed down by 10% per deuterium atom incorporated a result compatible only with the H—C bonds being involved in the ionisation. This is known as a secondary kinetic isotope effect, secondary... 

This corresponds to an isotope effect of approximately 3.5% per deuterium. In comparison, the secondary /3-deuterium KIEs in SN1 reactions are all normal and range from 5% to 15% per deuterium. Because the normal KIEs in SN1 reactions result from the weakening of the C,—L bond by a hyperconjugative interaction with the incipient carbocation in the transition state, the authors concluded that hyperconjugative interactions are present also in the transition state for the insertion reaction. The normal secondary /3-deuterium KIE observed for the insertion reaction is consistent with the dipolar three-centre transition state structure [15] proposed by Seyferth et al. (1970a,b) because the partial positive charge on the a-carbon is stabilized by hyperconjugation. 

The finding that thiamine, and even simple thiazolium ring derivatives, can perform many reactions in the absence of the host apoenzyme has allowed detailed analyses of its chemistry [33, 34]. In 1958 Breslow first proposed a mechanism for thiamine catalysis to this day, this mechanism remains as the generally accepted model [35]. NMR deuterium exchange experiments were enlisted to show that the thiazolium C2-proton of thiamine was exchangeable, suggesting that a carbanion zwitterion could be formed at that center. This nucleophilic carbanion was proposed to interact with sites in the substrates. The thiazolium thus acts as an electron sink to stabilize a carbonyl carbanion generated by deprotonation of an aldehydic carbon or decarboxylation of an a-keto acid. The nucleophilic carbonyl equivalent could then react with other electro-... 

The 2,3,4,5-tetra-0-acetyI-a(deht/do-pentoses are hydrated to the extent of — 90% in 7 3 oxolane -deuterium oxide.80 On the other hand, the 2,3,4,5-tetra-O-methylaldohexoses are hydrated74 to a lesser extent in aqueous solution at 37 °. When the carbon chain is in the planar, zigzag form, hydration is favored, and the ratio of aldehydrol to free aldehyde is — 2 1 (mannose and galactose) but when the chain is in a sickle form, hydration is impeded by 1,3-parallel interactions, and the ratio is —1 2 (glucose and allose). 

Other theoretical studies discussed above include investigations of the potential energy profiles of 18 gas-phase identity S 2 reactions of methyl substrates using G2 quantum-chemical calculations," the transition structures, and secondary a-deuterium and solvent KIEs for the S 2 reaction between microsolvated fluoride ion and methyl halides,66 the S 2 reaction between ethylene oxide and guanine,37 the complexes formed between BF3 and MeOH, HOAc, dimethyl ether, diethyl ether, and ethylene oxide,38 the testing of a new nucleophilicity scale,98 the potential energy surfaces for the Sn2 reactions at carbon, silicon, and phosphorus,74 and a natural bond orbital-based CI/MP through-space/bond interaction analysis of the S 2 reaction between allyl bromide and ammonia.17... 

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