Hydrides quantum effects

Quantum effects become important only at veiy low temperatures, i.e. for BIkT 1. The best candidates for observing these effects thus are hydrides. Quantum effects become more pronounced when A and/or B are species with open electronic shells see e.g. the differences between the associations N2 + N2 —> N4 and Q2 + Q2 —> 4 at temperatures below 10 K [10], Before leaving this section, it should be mentioned that alternative approaches such as the ACCS A treatment Irom [18], the perturbed rotational state treatment finm [19] and the semiclassical adiabatic invariance method Irom [20] all represent simplified variants of the here described SACM/CT approach and, like the... 

In a series of experiments on //-containing materials, starting with an experiment on partially deuterated water [Chatzidimitriou-Dreismann 1997 (a)] and later continued with polymers [Chatzidimitriou-Dreismann 2000 (b)], metal hydrides [Chatzidimitriou-Dreismann 2001] etc., it was found that the normalized area ratios Ah /Ad, Ah/A0, and, 4 n/AMetai, did not agree with the expected ratios Ah/Ad = uh/o d, etc., where the an s are the tabulated neutron total scattering CS, but were reduced by up to 30%. This loss of intensity was interpreted as a short-time effect, mainly involving the 77-nuclei (since heavier atoms are observed on a longer time scale and are supposed to be less sensitive to quantum effects). 

We will only present a very brief review of theoretical studies on this system and refer to reader to publications of the groups that have studied it.53 55 Since the catalytic step involves a hydride transfer, a major difficulty is how to treat quantum effects. These works followed different paths. 

Garcia-Viloca, M., Alhambra, C., Truhlar, D.G., Gao, J.L. Hydride transfer catalyzed by xylose iso-merase Mechanism and quantum effects. J. Comput. Chem. 2003, 24(2), 177-90. 

Hydride Transfer Catalyzed by Xylose Isomerase Mechanism and Quantum Effects. 

Experiments have implied that quantum mechanical effects can be involved in the proton and hydride transfer of several biological processes. Specifically, large kinetic isotope effects (KIE) observed for... 

The determination of electron affinities (EAs) is one of the most serious problems in quantum chemistry. While the Hartree-Fock electron affinity can be easily evaluated, most anions turn out to be unbound at this level of theory. Thus, the correlation effects are extremely crucial in evaluating EAs. At this point, lithium hydride and lithium hydride anion make up a very good benchmark system because they are still small enough yet exhibit features of more complicated systems. Four and five electrons, respectively, give rise to higher-order correlation effects that are not possible in H2. 

The enzyme-product complexes of the yeast enzyme dissociate rapidly so that the chemical steps are rate-determining.31 This permits the measurement of kinetic isotope effects on the chemical steps of this reaction from the steady state kinetics. It is found that the oxidation of deuterated alcohols RCD2OH and the reduction of benzaldehydes by deuterated NADH (i.e., NADD) are significantly slower than the reactions with the normal isotope (kn/kD = 3 to 5).21,31 This shows that hydride (or deuteride) transfer occurs in the rate-determining step of the reaction. The rate constants of the hydride transfer steps for the horse liver enzyme have been measured from pre-steady state kinetics and found to give the same isotope effects.32,33 Kinetic and kinetic isotope effect data are reviewed in reference 34 and the effects of quantum mechanical tunneling in reference 35. 

The most effective way for investigation of thermodynamic properties for fullerene hydrides is a combination of the experimental methods, the quantum-chemical calculation of molecular characteristics, the statistical thermodynamic calculation of thermodynamic... 

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