Strong H2 chemisorption on Al2O3 or SiO2 supported group VIII metals

Following hydrogen treatments at high temperature a decrease in hydrogen chemisorption at room temperature is observed in almost all group VIII elements supported on SiO₂ or Al₂O₃. The effect is attributed to self inhibition by strongly chemisorbed hydrogen on the metals.

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VIII , SiO₂ Al₂O₃. .

     

Calorimetric studies of the properties of Pd/Al2O3 with different metal contents

Hydrogen on Pd/Al₂O₃ catalysts (1,2,4% Pd) is sorbed in three forms with a heat of 152.6–2.1 kJ/mol. Metallic surface of the catalysts has been measured by the amount of adsorbed oxygen, whose adsorption heat varies in the range of 313.7–3.4 kJ/mol. Catalytic activity and selectivity of Pd/Al₂O₃ was studied in isoprene hydrogenation.

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Pd/Al₂O₃- 152,6–2,1 /. , 313,7–3,4 /. Pd/Al₂O₃ .

     

Preparation and properties of high dispersity palladium catalysts

Preparation methods for monodisperse sols of palladium with 9, 15, 30 and 75 Å particles are suggested. It has been revealed that with decreasing size of palladium particles (d25 Å), the dissolved hydrogen species disappear. As a result, their behavior in dimethyl ethynyl carbinol hydrogenation is close to the platinum properties.

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9, 15, 30, 75 Å. , (d25 Å) , .

     

A new Ba(OH)2 catalyst for synthesis of diacetone alcohol

The application of new Ba(OH)₂ catalysts for the preparation of diacetone alcohol is described. No loss of activity is observed when they are stored in a dessiccator over NaOH. The same yield as that described in the literature is obtained, but in a much shorter reaction time (9.5 h against 72–120 h)

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Ba(OH)₂ . NaOH . , , (9,5 72–120 ).

     

A bifunctional stopcock-winch device in cells for infrared investigations of solids

A simple glass device is described acting as stopcock and winch at the same time. The device is especially suitable for the dislocation of solid sample holders in IR cells.

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, . .

     

Acidic properties of TiO2?SiO2 catalysts

The acidic properties of a series of TiO₂–SiO₂ catalysts with different Ti/Si mole ratios have been studied. In order to determine the amount of acid centers and the acid strength distribution, the Benesi method of discontinuous titration has been used. Thermogravimetric measurements were also carried out.

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TiO₂–SiO₂ Ti/Si. , - . .

     

Investigation of n-heptane conversion over Pt?Al2O3 catalysts under gradientless reforming conditions

The rates of the total and individual directions of n-heptane conversion in reforming over platinum-on-alumina catalysts were shown to be independent of dilution with hydrogen. They can be described by simple equations following from kinetic concepts in ideal adsorbed layers.

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, - , .

     

4-Aminobicyclo[2.2.2]octanone Derivatives with Antiplasmodial and Antitrypanosomal Activities

4-Aminobicyclo[2.2.2]octanones were converted to their N-oxides and to 4-aminobicyclo[2.2.2]octanes. Furthermore, the 6,7-bis-(4-methoxyphenyl) analogues were synthesized. All products were screened for their activities against Trypanosoma b. rhodesiense and Plasmodium falciparum. The pharmacological results were compared with those of formerly tested bicyclo[2.2.2]octanones and bicyclo[2.2.2]octanols. Structure-activity relationships are discussed.     

Time-resolved fluorescence analysis of the mobile flavin cofactor in p -hydroxybenzoate hydroxylase

Conformational heterogeneity of the FAD cofactor in p-hydroxybenzoate hydroxylase (PHBH) was investigated with time-resolved polarized flavin fluorescence. For binary enzyme/substrate (analogue) complexes of wild-type PHBH and Tyr222 mutants, crystallographic studies have revealed two distinct flavin conformations; the ‘in’ conformation with the isoalloxazine ring located in the active site, and the ‘out’ conformation with the isoalloxazine ring disposed towards the protein surface. Fluorescence-lifetime analysis of these complexes revealed similar lifetime distributions for the ‘in’ and ‘out’ conformations. The reason for this is twofold. First, the active site of PHBH contains various potential fluorescence-quenching sites close to the flavin. Fluorescence analysis of uncomplexed PHBH Y222V and Y222A showed that Tyr222 is responsible for picosecond fluorescence quenching free enzyme. In addition, other potential quenching sites, including a tryptophan and two tyrosines involved in substrate binding, are located nearby. Since the shortest distance between these quenching sites and the isoalloxazine ring differs only little on average, these aromatic residues are likely to contribute to fluorescence quenching. Second, the effect of flavin conformation on the fluorescence lifetime distribution is blurred by binding of the aromatic substrates: saturation with aromatic substrates induces highly efficient fluorescence quenching. The flavin conformation is therefore only reflected in the small relative contributions of the longer lifetimes.     

Effect of metal ions forming bromide complexes on the Belousov-Zhabotinskii reaction

Metal ions forming stable complexes with bromide ions greatly influence both the amplitude and frequency of the Belousov-Zhabotinskii reaction. In case of thallium(I), redox reactions involving the metal ion should also be considered beside complex formation.

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, , , -. (I), , .