Water quantum

D. Marx, M. E. Tuckerman, and M. Parrinello (2000) Solvated excess protons in water quantum effects on the hydration structure. J. Phvs. Condens. Matter A 12, p. 153... 

Direct photoreaction is the only photoreaction pathway in distilled water. Quantum yields observed in air-saturated, distilled water have generally been... 

The rate is relatively high in water (quantum yield around 5.0 x 10 ) and one order of magnitude lower in other solvents tested, but scarcely dependent on their apolar, protic or aprotic nature. Large variations in the product composition are found and using a triplet quencher on the one hand, and benzo-phenone as sensitiser on the other hand, Morrison et al. could isolate two different processes, through singlet and triplet excited states, respectively. The composition of the product of both processes is solvent-dependent,... 

Yang S, Cho M (2009) Direct calculations of vibrational absorption and circular dichroism spectra of alanine dipeptide analog in water quantum mechanical/molecular mechanical molecular dynamics simulations. J Chem Phys 131 135102-1-135102-8... 

Positively Charged Ions in Water Quantum Calculatimis. 253... 

Marx D, Tuckerman ME, Parrinello M (2000) Solvated excess protons in water quantum effeets on the hydration stracture. J Phys Condens Matter A 12 153-159... 

A study of photosubstitution in six (substituted) pyridine and pyrazine pen-tacyanocobaltate(III) complexes [Co(CN)5L]" complements an earlier study of similar pentacyanoferrate(II) complexes. Irradiation in ligand field bands results in 100% replacement of L by water quantum yields range from 0.12 to 0.40. The results are similar to those for the iron(II) complexes, with such differences as are observed assignable to the large difference in importance of tt back bonding to cobalt(III) and to iron(II). ... 

Pugliano N and Saykally R J 1992 Measurement of quantum tunnelling between ohiral isomers of the oyolio water trimer Science 257 1936-40... 

The ability to act as a lone pair acceptor is not confined to Group III, and can occur wherever a quantum level is incomplete. This ability to accept electrons explains why covalent chlorides, with the exception of carbon tetrachloride, are readily hydrolysed, the apparently anomalous behaviour of carbon tetrachloride being readily explained by the fact that the carbon has a completed quantum level and is unable to form an intermediate complex with water. 

When carbon forms four covalent bonds with halogen atoms the second quantum level on the carbon is completely filled with electrons. Most of the reactions of the Group IV tetrahalides require initial donation by a Lewis base (p. 91) (e.g. water, ammonia) which attaches initially to the tetrahalide by donation of its electron pair. Hence, although the calculated free energy of a reaction may indicate that the reaction is energetically favourable, the reaction may still not proceed. Thus we find that the tetrahalides of carbon... 

Behrens, P.H., Mackay, D.H.J., White, G.M., Wilson, K.R. Thermodynamics and quantum corrections from molecular dynamics for liquid water. J. Chem. Phys. 79 (1983) 2375-2389. 

Drukker, K., Hammes-Schiffer, S. An analytical derivation of MC-SCF vibrational wave functions for the quantum dynamical simulation of multiple proton transfer reactions Initial application to protonated water chains. J. Chem. Phys. 107 (1997) 363-374. 

TIte NCC water model. (After Corongiu G 1992. Molecular Dynamics Simulation fir Liquid Water Using risable and Flexible Potential. International Journal of Quantum Chemistry 42 1209-1235.)... 

Fig. 7.12 Experimental and calculated infrared spectra for liquid water. The black dots are the experimental values. The thick curve is the classical profile produced by the molecular dynamics simulation. The thin curve is obtained by applying quantum corrections. (Figure redrawn from Guilbt B 1991. A Molecular Dynamics Study of the Infrared Spectrum of Water. Journal of Chemical Physics 95 1543-1551.)...

In aqueous solution, riboflavin has absorption at ca 220—225, 226, 371, 444 and 475 nm. Neutral aqueous solutions of riboflavin have a greenish yellow color and an intense yellowish green fluorescence with a maximum at ca 530 nm and a quantum yield of = 0.25 at pH 2.6 (10). Fluorescence disappears upon the addition of acid or alkah. The fluorescence is used in quantitative deterrninations. The optical activity of riboflavin in neutral and acid solutions is [a]=+56.5-59.5° (0.5%, dil HCl). In an alkaline solution, it depends upon the concentration, eg, [a] J =—112-122° (50 mg in 2 mL 0.1 Ai alcohohc NaOH diluted to 10 mL with water). Borate-containing solutions are strongly dextrorotatory, because borate complexes with the ribityl side chain of riboflavin = +340° (pH 12). 

The use of QM-MD as opposed to QM-MM minimization techniques is computationally intensive and thus precluded the use of an ab initio or density functional method for the quantum region. This study was performed with an AMi Hamiltonian, and the first step of the dephosphorylation reaction was studied (see Fig. 4). Because of the important role that phosphorus has in biological systems [62], phosphatase reactions have been studied extensively [63]. From experimental data it is believed that Cys-i2 and Asp-i29 residues are involved in the first step of the dephosphorylation reaction of BPTP [64,65]. Alaliambra et al. [30] included the side chains of the phosphorylated tyrosine, Cys-i2, and Asp-i 29 in the quantum region, with link atoms used at the quantum/classical boundaries. In this study the protein was not truncated and was surrounded with a 24 A radius sphere of water molecules. Stochastic boundary methods were applied [66]. 

JB Koerner, T Ichiye. Interactions of the rubredoxm redox site analogue [Fe(SCH3)4] with water An ah initio quantum chemistry study. J Phys Chem B 104 2424-2431, 2000. 

However, theories that are based on a basis set expansion do have a serious limitation with respect to the number of electrons. Even if one considers the rapid development of computer technology, it will be virtually impossible to treat by the MO method a small system of a size typical of classical molecular simulation, say 1000 water molecules. A logical solution to such a problem would be to employ a hybrid approach in which a chemical species of interest is handled by quantum chemistry while the solvent is treated classically. 

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