Viscosity effects on the thermal decomposition of bis(perfluoro-2-N-propoxypropionyl) peroxide in dense carbon dioxide and fluorinated solvents

The thermal decomposition of the free-radical initiator bis(perfluoro-2-N-propoxyprionyl) peroxide (BPPP) was studied in dense carbon dioxide and a series of fluorinated solvents. For the fluorinated solvents, the observed first-order decomposition rate constants, k(obs), increased with decreasing solvent viscosity, suggesting a single-bond decomposition mechanism. The k(obs) values are comparatively larger in dense carbon dioxide and similar to the "zero-viscosity" rate constants extrapolated from the decomposition kinetics in the fluorinated solvents. The decomposition activation parameters demonstrate a compensation behavior of the activation enthalpy with the activation entropy upon change in solvent viscosity. Comparison of the change in activation parameter values upon change in solvent viscosity for BPPP with two additional initiators, acetyl peroxide (AP) and trifluoroacetyl peroxide (TFAP), further suggests that carbon dioxide exerts a very minimal influence on the decomposition mechanism of these initiators through solvent-cage effects.     

Automated protein design and sequence optimisation: scoring functions and the search problem

Advances in molecular biology may mean that almost any protein sequence can be synthesised, but perhaps this has served to highlight the inadequacy of theoretical work. For a given protein fold, it is probably not possible to reliably predict an "ideal" sequence. We identify and survey several aspects of the problem. Firstly, it is not clear what is the best way to score a sequence-structure pair. Secondly, there is no consensus as to what the score function should represent (free energy or some abstract measure of sequence-structure compatibility). Finally, the number of possible sequences is astronomical and searching this space poses a daunting optimisation problem. These problems are discussed in the light of recent experimental successes.     

Heterometallic nickel(II) samarium(III) diethylenetriaminepentaacetate, a starting material for the preparation of samarium nickelate films

A reaction of samarium oxide, nickel oxocarbonate, and diethylenetriaminepentaacetic acid (H₅DTPA) taken in stoichiometric proportions in water gave SmNiDTPA · 10H₂O as a glassy solid. The formation of this heterometallic complex was confirmed by data from elemental analysis, IR spectroscopy, thermal analysis, and X-ray fluorescence analysis. An aqueous solution of the complex was used to deposit SmNiO₃ films onto a single-crystal SrTiO₃(001) substrate. The SmNiO₃ phase in films obtained upon 3-h annealing at 500°C was identified by powder X-ray diffraction. Films deposited from a solution of an equimolar mixture of monometallic samarium and nickel diethylenetriaminepentaacetates contained no samarium nickelate.     

Detection and separation of two forms of cotton-plant pyrophosphatase

Two pyrophosphatase isoenzymes with identical molecular weights but differing in the pH optima of their action and also in their senstivity to some bivalent metal ions have been isolated from extracts of the cotyledons of three-day cotton-plant shoots by gel filtration and ion-exchange chromatography.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 375–378, May–June, 1985.     

Pheromones of insects and their analogs. XXVII. Synthesis of 10-hydroxy-4,8-dimethyldeca-4E,8E-dienoic acid and of racemic 4,8-dimethyldecanal from geranyl acetate

10-Hvdroxy-4,8-dimethyldeca-4E,8E-dienoic acid and racemic 4,8-dimethyldecanal (components of beetle pheromones) have been synthesized from geranyl acetate.Institute of Chemistry, Bashkir Scientific Center, Urals Branch, Academy of Sciences of the USSR, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 272–276, March–April, 1991.     

The preparation of chloroplatinic acid labelled with platinum radioisotopes

A procedure has been worked out for the preparation of chloroplatinic acid from natural metallic platinum irradiated in a nuclear reactor and purified from¹⁹⁹Au impurities by extraction from acidic solutions with ethyl acetate. It was shown that the effective K X-ray activity of natural platinum on irradiation with moderate neutron fluxes /3×10¹³/ was comparable with that of^195mPt obtained from 100%¹⁹⁴Pt/with identical neutron fluxes/. Contaminations from¹⁹³Pt /50 years/ is insignificant and do not produce noticeable radiation loads on the organism on medical tests in vivo.     

Air-gap sulfide sensor with super-nernstian response in the low concentration range

An air-gap sulfide sensor is presented which operates on the basis of selective extraction of H₂S from an acidified sample into a small alkaline electrolyte film containing the dicyanoargentate (I) complex. This complex is partly decomposed during the measurement by the absorbed sulfide, and the potential of a silver sulfide-based indicator electrode which is in direct contact only with the electrolyte, then depends on the sulfide concentration of the sample. Because of the extraction and dissociation equilibria, the sensor responds in the low sulfide concentration range with a slope four times larger than that of a normal sulfide electrode. The lower limit of linearity is 10^?8 mol l^?1, because sulfide accumulates in the electrolyte film.     

Nitrobenzene oxidation of fractions of cotton-plant dioxane lignin

Summary Analysis of the products of alkaline nitrobenzene oxidation of lignin fractions has confirmed their chemical inhomogeneity and has shown that in the various fractions the amounts of condensed syringly and guaiacyl structures differed markedly.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii No. 1, pp. 82–84, January–February, 1979.