Effect of the introduction of certain additives to the CO + H2 mixture and the scheme for the formation of alcohols higher than C1

The effect of additions of certain alcohols (methanol, ethanol, 2-propanol, and 2-butanol) to the synthesis gas on the distribution of the products during the hydrogenation of CO to alcohols at zinc-chromium oxide catalysts, promoted by various amounts of K₂O, was studied. The results demonstrate the fundamental applicability of the principal theories of chain growth proposed by other authors for copper-containing catalysts. However, it was shown that the probability of -addition is lower while that of -addition is higher at the zinc-chromium-potassium catalysts than at copper-containing catalysts, and the calculated amounts of isobutanol obtained from the data for ethanol and propanols do not agree with the experimental data. It was found that there is an isomeric transition from the secondary alcohols (2-propanol, 2-butanol) to the primary alcohols at the surface of the catalyst, and this can evidently change the normal course of chain growth in the alcohols. It can be concluded that the activity of the alcohol added to synthesis gas in reaction with other C-fragments present on the surface of the catalyst increases with increase in the number of carbon atoms in the alcohol.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 501–505, July–August, 1990.     

Guidelines for the analysis of free energy calculations

Journal of Computer-Aided Molecular Design - Free energy calculations based on molecular dynamics simulations show considerable promise for applications ranging from drug discovery to prediction of...     

Variable charges at govalent bonds and phonon dispersion in silicon

A model of variable charges at covalent bonds is proposed to describe the effective atomic interaction in a crystal lattice. It is shown that, in the region of elastic deformations, it is sufficient to take account only of the linear term in the expansion of the charge with respect to the relative deformation of the bond. Expressions are obtained for the dynamic matrix on the basis of the pseudopotential model and the model of variable charges at the bonds. The results of calculating the phonon spectrum of silicon are in good agreement with experimental data and reflect the characteristic features of the spectrum.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 95–98, July, 1988.     

Optimal vorticity regime in the flow tract of a hydroturbine

A study is made of the problem of maximizing the power taken from the shaft of the working rotor of a hydroturbine for a fixed available energy difference in the framework of a two-dimensional axisymmetric flow model. Necessary conditions of optimality of first and second order are derived and used to set up an algorithm for numerical solution of the problem. The results of calculations are given, and a comparison is made with optimal solutions obtained using two- and one-dimensional models of axisymmetric flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 68–73, May–June, 1984.     

Clarification of coal-clay disperse systems with modified polyacrylamide flocculant

Modification of polyacrylamide under mild conditions was studied.     

Predicting hydration free energies using all-atom molecular dynamics simulations and multiple starting conformations

Molecular dynamics simulations in explicit solvent were applied to predict the hydration free energies for 23 small organic molecules in blind SAMPL2 test. We found good agreement with experimental results, with an RMS error of 2.82 kcal/mol over the whole set and 1.86 kcal/mol over all the molecules except several hydroxyl-rich compounds where we find evidence for a systematic error in the force field. We tested two different solvent models, TIP3P and TIP4P-Ew, and obtained very similar hydration free energies for these two models; the RMS difference was 0.64 kcal/mol. We found that preferred conformation of the carboxylic acids in water differs from that in vacuum. Surprisingly, this conformational change is not adequately sampled on simulation timescales, so we apply an umbrella sampling technique to include free energies associated with the conformational change. Overall, the results of this test reveal that the force field parameters for some groups of molecules (such as hydroxyl-rich compounds) still need to be improved, but for most compounds, accuracy was consistent with that seen in our previous tests.