H isotope effect

Itou, T., Teramoto, A., Matsuo, T., and Suga, H., Isotope effect on the order-disorder transition in aqueous schizophyllan, Carbohydr. Res., 160, 243, 1987. 

Table 2.1 Adiabatic corrections (cm ) for H-D and Mu-H isotope effects (Bardo,R. D., Kleinman, L. I., Raczkowski, A. W. and Wolfsberg, M., J. Chem. Phys. 69, 1106, 1978) ...

Ishida, T., Lujii, Y. 2006 Enrichment of Isotopes in Kohen, A., Limbach, H. H. Isotope effects in Chemistry and Biology (Boca Raton, FL, CRC Press, Taylor Francis)... 

In contrast to the isotope effects observed in d° olefin polymerization catalysts, Brookhart and coworkers [134] have detected an inverse H/ H isotope effect of 0.59 in the Co(iii)-catalyzed polymerization of ethylene. This inverse effect was ascribed to a P-agostic CH bond which is stronger in the ground state than the free C-H bond during or just prior to the insertion step (see Scheme 1.6). 

Ab initio calculations at the MP2/6-31+ G level have been performed for gas-phase El elimination reactions of CH3CH2X (X = NH3"1", Br, Cl, F, SH) promoted by NH . OH-, F-, PH2. SH-, and Cl- in order to determine how changes in transition-state geometry, from reactant-like to product-like, influence kinetic isotope effects.9 Secondary isotope effects (a-H) on leaving group departure are correlated with the hybridization at C7 in the transition state, whereas there is no such correlation between secondary (/5-H) isotope effects and the transition state hybridization at C/ . The primary deuterium isotope effect is influenced markedly by the nucleophilic atom concerned but approach to a broad maximum for a symmetric transition structure can be discerned when due allowance is made for the element effect. 

Two new lines of evidence suggest that proton abstraction comes first. A careful study of both and H isotope effects supports the carbanion intermediate, as does the strong inhibition by anions of 3-nitropropionate and 3-nitro-2-hydroxypropionate. To provide a good electron sink the carboxylate group adjacent to the proton that is removed by fumarate hydratase must either be actually protonated in the enzyme-substrate (ES) complex or paired with and hydrogen bonded to a positively charged group. 

Before the structure of the enzyme was determined, chemical modification experiments (using proteolysis and mass spectrometry to identify the modified residue) and site-directed mutagenesis were used to identify Arg 21, Tyr 28, and a His as catalytically important side chains.Substrate and solvent H isotope effects, proton inventory studies, and the pH-dependence of the kinetic parameters and were used to identify the enzyme mechanismas an E]CB elimination reaction proceeding via an enolate intermediate, with the initial proton abstraction as the rate-limiting step. The unusual sharp increase in and above pH 9 was interpreted as the effect of an active-site Arg side chain on the basicity of a His. " ... 

The value for the Si—H isotope effect is near that to be expected for a transition state with considerable H—H bonding. This has been used as an argument for a transition state resembling product, but this would not seem to stand the scrutiny of more recent interpretations of isotope effects (225). 

Krauledat, H. Brintzinger, H. H. Isotope effect on olefin insertion in catalytic polymerization by zirconocene. Evidence for an a-agostic interaction in the transition state. Angew. Chem., Int. Ed. Engl. 1990, 29,1412-1413. 

A review entitled New phosphorus-tellurium heterocycles in the quasi-binary system RP/Te , which contains and Te NMR data, has appeared. H/ H isotope effect on the translational and rotational motion of liquid water and ammonia has been assessed by NMR measurements.The diffusion of ammonia in binary mixtures has been investigated using the pulsed-field gradient technique. A quantitative structure-property relationship of the P NMR chemical shifts has been developed for a large set of phosphines.The NMR spectrum of [P(CF3)2] has been analysed as X3MAY3 and determined.An iterative lineshape analysis of N NMR spectra of [N3] has been described. and P NMR studies of a liquid-crystalline cyclotriphos-... 

The D/H isotope effect for the self diffusion coefficient of the water in solutions of CsCl in D O and H O was according to Sacco et al. [16] in agreement with the structure-breaking properties of both ions of this salt and with the more extensive ( stronger ) hydrogen bonded network of the D O relative to H O, see Table 3.8. 

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