Quantum-chemical studies

Eurther quantum chemical studies involving uracil derivatives concern the conformations and properties of uridines [98CEJ621,98JA5488,98JOC1033, OOJCS (P2)677], the nucleophilic attack in pseudouridine synthases [99JA9928], and the aza analogs of uracil [99JST349]. 

Most studies concerning pyrimidines originate from biochemical questions. Since these systems are dominated by hydrogen-bonding and/or dispersion contributions, methods beyond the Hartree-Fock level are mandatory. The success of quantum chemical studies in this field is impressive and many effects could be explained on the basis of these theoretical investigations. 

G. Pacchioni, F. Illas, S. Neophytides, and C.G. Vayenas, Quantum-Chemical Study of Electrochemical Promotion in Catalysis, J. Phys. Chem. 100, 16653-16661 (1996). 

Fournier JM, (1985) Actinide Solids. 5f Dependence of Physical Properties. 59160 1-56 Fournier JM, Manes L (1985) Magnetic Properties of Actinide Solids. 59160 127-196 Fraga S, Valdemoro C (1968) Quantum Chemical Studies on the Submolecular Structure of the Nucleic Acids. 4 1-62 Frasinski LJ, see Codling K (1996) 85 1-26... 

Quantum-chemical studies have indeed shown that the presence ofa surrounding cavity lowers the barriers of charge separation that occur when a molecule is activated by zeoHtic protons [9] as shown in Figure 1.10. 

On the basis of the quantum-chemical studies, it has been established that it is the so called oxyanion hole of the enzyme that binds the carbonyl oxygen or nitrile nitrogen, enhancing the attack of a nucleophile, which is, in turn, activated by histidine (Scheme 5.22) [110]. 

Refiy, B., Kolonits, M., Schulz, A., Klapotke, T.M. and Hargittai, M. (2000) Intriguing Gold Trifluorides — Molecular Structure of Monomers and Dimers An Electron Diffraction and Quantum Chemical Study. Journal of the American Chemical Society, 122, 3127—3134. 

Fraga, S., Valdemoro, C. Quantum Chemical Studies on the Submolecular Structure of the Nucleic Acids. Vol. 4, pp. 1-62. 

Besides these generalities, little is known about proton transfer towards an electrode surface. Based on classical molecular dynamics, it has been suggested that the ratedetermining step is the orientation of the HsO with one proton towards the surface [Pecina and Schmickler, 1998] this would be in line with proton transport in bulk water, where the proton transfer itself occurs without a barrier, once the participating molecules have a suitable orientation. This is also supported by a recent quantum chemical study of hydrogen evolution on a Pt(lll) surface [Skulason et al., 2007], in which the barrier for proton transfer to the surface was found to be lower than 0.15 eV. This extensive study used a highly idealized model for the solution—a bilayer of water with a few protons added—and it is not clear how this simplification affects the result. However, a fully quantum chemical model must necessarily limit the number of particles, and this study is probably among the best that one can do at present. 

Da Silva, G. Chen, C.-C. Bozzelli, J. W. Quantum chemical study of the thermal decomposition of o-quinone methide (6-methylene-2,4-cyclohexadien-l-one). J. Phys. Chem. A 2007, 111, 7987-7994. 

E. Broclawik, J. Haber, Quantum chemical study of the reaction of ammonia with transient oxygen species, J. Mol. Catal., 1993, 82, 353. 

The quantum chemical studies of Pd and Pt molecular systems carried out since 1990 are reviewed7 with 482 references to complement earlier comprehensive reviews. Topics covered... 

Higher Oxidation States of Cd and Hg Quantum-chemical Studies 1257... 

Experimental methods used for studies of Cd and Hg complexes in solution and in the solid state are reviewed briefly, with examples for the application of the method under discussion in recent work. In a separate section quantum-chemical studies, including consideration of relativistic effects, on existing and not-yet-existing species with Cd and/or Hg, are also surveyed. 

Several quantum-chemical studies have been performed on Hg(CN)2 and related species, applying different approaches with consideration of relativistic effects in order to get MO schemes and energies as a basis for discussion of bonding, valence XPS,105 UPS,106 XANES and EXAFS spectra.41 The latter study also showed Hg(CN)2 to be dissolved in H20 in molecular form (/-(Hg—C) 202, r(C—N) 114 pm), and obviously not to be hydrated, a remarkable finding insofar as solvates of Hg(CN)2 with various donor molecules are well known.2 However, in contrast to Cd(CN)2 (see above), Hg(CN)2 as such does not form clathrates. 

Consider, for example, the well-studied reaction between C+ and NH3, for which one set of products consists of the ion CH2N+ + H. But what is the structure of the product ion Based on detailed quantum chemical studies of the very complex potential surface, it is likely that two isomers are produced initially—the linear HCNH+ ion and the T-shaped H2NC+form89—although it is also possible that the latter form can subsequently isomerize via a unimolecular path into the more stable... 

Voityuk AA, MichelBeyerle ME, Rosch N (1997) Protonation effects on the chromophore of green fluorescent protein. Quantum chemical study of the absorption spectrum. Chem Phys... 

Altoe P, Bemardi F, Garavelli M, Orlandi G, Negri F (2005) Solvent effects on the vibrational activity and photodynamics of the green fluorescent protein chromophore a quantum-chemical study. J Am Chem Soc 127 3952-3963... 

Hobza, P., H. L. Selzle, and E. W. Schlag. 1993. New Structure for the Most Stable Isomer of the Benzene Dimer A Quantum Chemical Study. J. Phys. Chem. 97, 3937. 

Loew, G., and D. S. Berkowitz. 1975. Quantum Chemical Studies of Morphinelike Opiate Narcotic Analgesics I. Effect of N-substituent Variations. J. Med. Chem. 18, 656. 

Martin, M., F. Sanz, M. Campillo, L. Pardo, J. Perez, and J. Turmo. 1983a. Quantum Chemical Study of the Molecular Patterns of MAO Inhibitors and Substrates. Int. J. Quant. Chem. 23, 1627. 

Weinstein, H., R. Osman, S. Topiol, and J. R Green. 1981b. A Quantum Chemical Studies on Molecular Determinants for Drug Action. Ann. N. Y. Acad. Sci. 367, 434. 

Vollmer J. M., Curtiss L. A., Vissers D. R., Amine K., Reduction mechanisms of ethylene, propylene, and vinylethylene carbonates - A quantum chemical study, J Electrochem. Soc., (2004) 151 (1), A178-A183. 

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