Specifics of Interaction of Acetone Molecules with Quasi-free Electrons: Analysis of Positron Annihilation Characteristics in Aqueous and Alcoholic Acetone Solutions

The yields of formation of radiolytic hydrogen (H₂) and orthopositronium (o-Ps) in aqueous and alcoholic acetone solutions were experimentally determined. A decrease in the o-Ps yield with an increase in the acetone concentration is much weaker than the decline in the yield of solvated electrons (e^– _s) under picosecond pulse radiolysis conditions. In contrast, the decrease in the o-Ps yield is minimal in higher alcohols where the inhibiting action of acetone e^– _s is most pronounced. These findings seem to contradict the conventional concepts of Ps formation via the intratrack reaction of positron recombination with a track electron (e^–), which competes with the reaction of e^– scavenging by dissolved acetone molecules. This contradiction can be eliminated, assuming that the scavenging of e^– by acetone begins from the formation of the weakly bound transient state (CH₃)₂CO···e^– capable of donating e^– to a positron. This opens up an additional pathway for the formation of the Ps atom.     

Dehydration of tetrafluoropropanol (TFP) by pervaporation via novel PBI/BTDA-TDI/MDI co-polyimide (P84) dual-layer hollow fiber membranes

A novel PBI/P84 co-polyimide dual-layer hollow fiber membrane has been specifically fabricated through the dry-jet wet phase inversion process, for the first time, for the dehydration pervaporation of tetrafluoropropanol (TFP). Polybenzimidazole (PBI) was chosen as the outer selective layer because of its superior hydrophilic nature and excellent solvent-resistance together with robust thermal stability, while P84 co-polyimide was employed as the inner supporting layer because of its good solvent-resistance and thermal stability. The PBI/P84 membrane exhibits superior water selectivity and relatively high permeation flux. At 60 °C, the PBI/P84 dual-layer hollow fiber membrane shows a permeation flux of 332 g/(m² h) and a separation factor of 1990 for a feed solution containing of 85 wt% TFP. The preferential water sorption and the significant diffusivity difference between TFP and water are the main causes of high separation factor. However, an increase in feed temperature will greatly increase the permeation flux but seriously decrease the water selectivity. The activation energy data verify that water can preferentially permeate the PBI membrane due to the strong water affinity of PBI and a much smaller molecular size of water.     

Racemization of chiral amino alcohols III: Effect of Mg or Ca addition on the activity and stability of the Co/γ-Al2O3 catalyst

The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al₂O₃ catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield of over 83% at using the Mg modified Co/γ-Al₂O₃ catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H₂. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous for dispersing and stabilizing the active species of the Co/γ-Al₂O₃ catalyst, protecting from sintering, significantly improving its catalytic activity and stability.     

Interaction between Globular Proteins and Silica Surfaces

The adsorption of bovine serum albumin on silica of three different types, i.e., aerosil, macroporous silica gel, and ground natural quartz, was studied. The IR spectra of this protein adsorbed on aerosil were measured and analyzed. It was shown that the carbonyl groups of albumin macromolecules interact with vicinal hydroxyl groups while imido groups, with individual hydroxyl groups of silica surface. The geminal hydroxyl groups of the surface behaved as single adsorption sites with respect to albumin. The number or such sites on quartz surface was estimated. The IR spectra indicated that the adsorption of albumin macromolecules caused the dehydration of aerosil surface and the appearance of a small amount (to 10%) of unfolded -regions in the secondary structure of the adsorbed protein, while the -helical macromolecular structure remains preserved as a whole. Changes in the tertiary structure of the protein resulted from the adsorption were discussed. Protein macromolecules folded into globules were shown to be tilted with respect to the adsorbent surface.     

Novel acyclic and macrocyclic highly unsaturated silahydrocarbons

Two novel silicon-containing acetylenic synthons, 1-[dimethyl(ethynyl)silyl]-2-[ethynyl(methyl)-(vinyl)silyl]ethyne and bis[(ethynyldimethylsilyl)ethynyl](methyl)vinylsilane, were obtained by the reaction of diethynyl(methyl)vinylsilane with ethylmagnesium bromide and ethynylfluorodimethylsilane. The reaction of magnesium derivatives of the products and diethynyl(methyl)vinylsilane with organylhalosilanes gave macrocyclic polyunsaturated silahydrocarbons containing numerous endo- and exocyclic miltiple bonds.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1612–1616.Original Russian Text Copyright © 2004 by O. Yarosh, Zhilitskaya, N. Yarosh, Istomina, Albanov, Chuvashev, Voronkov.This revised version was published online in April 2005 with a corrected cover date.     

Theoretical studies on vibrational spectra of some halides of Group IIB elements

The vibrational spectra of Group IIB elements halides MX2 and their dimers M2X4 (M=Zn(II), Cd(II) and Hg(II); X=F, Cl, Br and I) have been systematically investigated by ab initio RHF and B3LYP methods with LanL2MB, LanL2DZ and SDD basis sets. The optimized geometries, calculated vibrational frequencies are evaluated via comparison with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, are compared to each other too. The best results can be obtained by RHF/SDD method, with this method, the deviations for MX2 and Hg2X4 are <7%. Some vibrational frequencies of M2X4 that have not been experimentally reported are also predicted.     

EPR study of the nature of active sites and the type of their deactivation in CO hydrogenation on (Ni+Ti)/SiO2 catalysts

As shown by EPR, upon supporting Ni(-C₃H₅)₂ on Ti/SiO₂, the Ni complex is coordinated to Ti³⁺ ions. Deactivation of (Ni+Ti)/SiO₂ catalysts so obtained during CO hydrogenation is due to the oxidation of Ti³⁺ ions and metallic nickel particles by reaction products.

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, Ni(-C₃H₅)₂ Ti/SiO₂ Ni Ti³⁺. , (Ni+Ti)/SiO₂ CO Ti³⁺ .

     

GC–MS analysis of phenolic compounds in fuels after conversion to trifluoroacetate esters

The GC–MS characteristics of trifluoroacetate esters of phenolic compounds are discussed. Linear temperature programmed retention indices and total ion current MS response factors of over 120 phenolic esters are reported. The main GC advantages from analysis of trifluoroacetate esters as compared to plain phenols are enhanced volatility and improved resolution. For example, the elution temperature of a given phenol is typically 50 °C greater than that of the corresponding trifluoroacetate ester. Also, while retention of compounds with two trifluoroacetate groups is only moderately greater than mono esters, underivatized dihydroxy compounds are very difficult to elute from any GC column. Complete resolution of isomeric C₀-, C₁- and C₂-alkylphenol esters is readily achieved on conventional fused silica GC columns; resolution of the corresponding underivatized compounds requires specialized GC columns with low temperature limits. In general, mass spectra of trifluoroacetate esters are more characteristic of a given structure than those of the corresponding phenols and may be more rigorously interpreted towards structural elucidation. A table in the report summarizes some of the more important spectral features used in compound identification. Example applications in analysis of coal-, shale- and petroleum-derived materials are presented. Selected ion monitoring is used to determine individual phenolic components in whole distillates; reconstructed ion chromatograms are used to illustrate distributions of selected species as a function of fuel storage and thermal stress.     

Effect of explosion on the catalytic activity and selectivity of natural fluorite

The effect of various types of shock waves on the catalytic activity of natural fluorite in isopropanol dehydrogenation and dehydration reactions has been studied. Shock treatment is shown to decrease the catalytic reaction temperature and to increase the selective

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