Temperature dependence of the configurational free energy of a branched polymer

We consider a lattice model of branched polymers in dilute solution in which the polymer is modelled as an animal, weakly embeddable in the (simple cubic) lattice. In order to model the effect on the thermodynamic properties of changing the temperature or the quality of the solvent, we include an energy associated with the number of nearneighbour contacts between pairs of vertices of the animals. We show that the configurational free energy of the animal is a continuous function of the temperature and derive rigorous upper and lower bounds on the temperature dependence of the free energy. Finally, we comment on similarities between these results and corresponding ones for a model in which the energy is associated with the cyclomatic index of the animal.     

The prism algorithm for two-electron integrals

A new approach to the evaluation of two-electron repulsion integrals over contracted Gaussian basis functions is developed. The new scheme encompasses 20 distinct, but interrelated, paths from simple shell-quartet parameters to the target integrals, and, for any given integral class, the path requiring the fewest floating-point operations (FLOPS ) is that used. Both theoretical (FLOP counting) and practical (CPU timing) measures indicate that the method represents a substantial improvement over the HGP algorithm.     

Methyltriazolocoumarins: New furocoumarin isosters as potential photochemotherapeutic agents

A number of new methyltriazolocoumarins with a linear psoralen-like structure or an angular angelicin-like structure were synthetized. The syntheses were performed starting from the appropriate methylated 7-aminocoumarins which were nitrated, reduced and successively diazotized with concomitant cyclization to form the condensed triazolo ring. The new methyltriazolocoumarins show promising spectroscopic properties which are potentially predictive of their photochemical and photobiological behaviour.     

Highly polarized enamines. 2. Synthesis and investigation of the further amination of derivatives of α,α-DIAMINO-β-cyano-β-nitroethylene

Highly polarized enediamines of the a, -diamino--cyano--nitroethylene type have been obtained by the hydrolysis of 4-chloro-5-nitropyrimidines. Several chemical conversions of the enamines obtained have been studied, particularly leading to derivatives of 2-(cyanonitromethylene)imidazoline and -hexahydropyrimidine, and also to derivatives of N, N-bisvinylpiperazine and 7 methylene-1, 4-diazabicyclo(2.2. 1 ]heptane.Center for Drug Chemistry, All-Russian Chemical and Pharmaceutical Research Institute, Moscow 119815. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 811–820, June, 1996. Original article submitted February 6, 1996.For Part 1, see [1].     

Role of tetraethoxysilane hydrolysis and polycondensation catalysts in synthesis of wide-pore silica gels

A study has been made of the effect of combining tetraethoxysilane hydrolysis and polycondensation catalysts operating by different mechanisms on the texture parameters of synthesized silica gels. The effect of hydrothermal treatment of a fluorine-containing silica hydrogel on the thermal stability of the xerogel texture was demonstrated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 2, pp. 95–98, March–April, 1994.     

Photosensitivity of holographic recording media based on films of polymer compositions with cadmium sulfide nanoparticles

The effect of doping with CdS nanoparticles of recording medium films for the thermoplastic holographic recording process, which are based on photosemiconductors (oligomers and cooligomers of glycidylcarbazole) and a dielectric (a styrene copolymer with octyl methacrylate) containing a photoconductivity sensitizer, on their photosensitivity was studied. The enhancement of photosensitivity of films by doping with nanoparticles is associated with the appearance of an additional channel for transport of electrons generated from sensitizer molecules. A difference in informational properties between the oligomer and the polymer films was revealed.     

Quick Determination of the Total Content of Aromatic Hydrocarbons in Reformer Naphthas by <Superscript>1</Superscript>H NMR Spectroscopy

A procedure for fast determination of the total content of arenes in reformer naphthas by ¹H NMR spectroscopy was developed and tested. Their content is determined from the ratio of the integral intensities of the signals of aromatic protons and alkane methyl protons, using a calibration plot constructed on the basis of GLC data.     

X-ray crystallographic investigation of the adduct of 1-demethylamino-2-(4-bromophenyl-2H-isoindole with N-phenylmalemide

An unusual path for the reaction of 2-aryl-1-dimethylamino-2H-isoindoles with N-R-maleimides, leading to the imides of l,2-dihydronaphthalene-2,3-dicarboxylic adds, was established by x-ray crystallographic analysis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 614–618, May, 1992     

Mechanism of the Reaction of Xenon Tetraoxide with Hydrogen: A Photochemical Reaction

The dependence of the rate of a photochemical reaction of XeO₄with H₂on the concentrations of H₂and the diluent gases He and CO₂is studied at room temperature. The results are compared with the data for the dark reaction. A mechanism with the elementary energetic branched-chain reaction OH (v) + XeO₄OH + O + XeO₃is proposed to explain the results of the study.