Formation of heterogeneous polymer structures during photoinduced crosslinking of oligo(ester acrylates) in the presence of a nonpolymerizable component

The morphology of polymers prepared through the photoinduced polymerization of oligo(carbonate dimethacrylate) in the presence of different nonpolymerizable additives (methanol, dinonyl phthalate, hexane, toluene, benzene, and carbon tetrachloride) is studied via the method of atomic force microscopy. Depending on the nature and concentration of an additive, the photoinduced polymerization of the above composite systems is shown to be accompanied by microphase separation and formation of a porous polymeric material. In the case of methanol, homogeneous porous structures with characteristic pore sizes of several hundred nanometers are formed. In the case of dinonyl phthalate, the characteristic pore sizes lie below 100 nm. The synthesized porous polymers can sorb both polar and nonpolar solvents. The photoinduced polymerization of an oligomer in the medium of toluene, benzene, or carbon tetrachloride leads to the formation of polymer nanoparticles whose dimensions are controlled by the nature of a solvent.     

Fluorescence assay of tyrosine in blood plasma

A more simple and sensitive assay for the quantitative determination of tyrosine in blood plasma is developed on the basis of a modification of the method of S. Udenfriend (1962). A volume of 0.2 ml of plasma is used in the analysis; after its deproteinization with trichloroacetic acid, it is reacted with sodium nitride, nitrous acid, and 1-nitroso-2-naphthol at 65°C, and the content of the reaction product is measured by the fluorescence at λ_ex/λ_em=460/570 nm. The consumption of plasma and reagents is reduced by a factor of 5–10 compared to the original method; in addition, the stage of extraction with an organic solvent is excluded. The linear dependence of the fluorescence signal on the tyrosine concentration within the range of 2–60 μg/ml, high specificity, accuracy, and reproducibility of the assay are shown. The importance of tyrosine determination in monitoring of glucocorticoid therapy and protein catabolism is discussed. Institute of Photobiology, National Academy of Sciences of Belarus, 27, Akademicheskaya St., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 366–371, May–June, 1998.     

An efficient approach to azirino and pyrrolo-fused dibenzazepines. Conformations of substituted dibenzo[c,f]pyrrolo[1,2-a]azepines

An effective approach to azepino-fused heterocycles is described. trans-1-Aryl-7,11b-dihydro-1H-azirino[1,2-a]dibenzo[c,f]azepines were synthesised via a domino sequence: isomerization of gem-dichloroaziridine-intramolecular Friedel-Crafts acylation of the tethered benzene ring catalysed by SnCl(4) and subsequent hydride induced intramolecular cyclization. Cycloaddition of dibenzazepinium ylides, generated by heating these aziridines, to activated C[double bond]C, C[triple bond]C dipolarophiles and fullerene C(60), leads to derivatives of dibenzo[c,f]pyrrolo[1,2-a]azepine. The reaction proceeds with complete stereoselectivity via cycloaddition of only W-ylide, which due to the high barrier does not undergo E,Z-isomerization under the reaction conditions. It was found that 2,3,9,13b-tetrahydro-1H-dibenzo[c,f]pyrrolo[1,2-a]azepine systems can exist in conformations of two types depending on the substituents at the pyrrolidine carbons in β-position with respect to nitrogen. Details of cycloaddition reactions and the conformational behavior of cycloadducts were studied by DFT calculations at the B3LYP/6-31G(d) level.     

A simple route to side-chain fluorinated β-lactams from ring-fluorinated aziridines

β-Lactams bearing a Ph₂CF substituent at the C(4)-atom were synthesized from N-alkyl-2-fluoro-3,3-diphenylaziridines. The transformation was realized using SbF₃-mediated isomerization of the monofluoroaziridines to fluorinated aldimines, followed by Staudinger reaction with ketenes. It was shown that this reaction sequence can be performed as a one-pot procedure.     

Photoelectron emission from semiconductors with low valence band dispersion

In application to the group of compounds under consideration, a simple analytical expression is obtained for the quantum yield. Electron scattering processes of both elastic and inelastic nature are taken into account. The influence of such scattering processes on the structure of the spectral dependence of the quantum yield is discussed. It is shown that they can be responsible for the appearance of a number of features in this spectral dependence.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 68–72, April, 1982.     

Solution lifting method for handling meta-variables in TH∃OREM∀

We approach the problem of finding witnessing terms in proofs by the method of meta-variables. We describe an efficient method for handling meta-variables in natural style proofs and its implementation in the THOREM system. The method is based on a special technique for finding meta-substitutions when the proof search is performed in an AND-OR deduction tree. The implementation does not depend on the search strategy and allows easy integration with various special provers as well as with special unification/solving engines. We demonstrate the use of this method in the context of a special forward/backward inference strategy for producing proofs in elementary analysis. Bibliography: 28 titles.Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 293, 2002, pp. 94–117.     

Preparation of Poly(methyl methacrylate) Nanoparticles 15–50 nm in Diameter from Submicrometer-Sized Latex Particles

Russian Journal of Applied Chemistry - A procedure was developed for preparing poly(methyl methacrylate) nanoparticles of 15–50 nm size from coarser (200–300 nm) polymer latex particles...     

Efficiency of Pyrrole Electropolymerization under Various Conditions

The electrooxidative polymerization of pyrrole on the surface of a glassy carbon electrode was studied, while varying the solvent, the type and concentration of supporting electrolyte, redox mediator addition to the polymerization medium, and hydrodynamic conditions. The efficiency of polymerization was determined as the ratio of the charge of the redox response of the polymer film under the standard conditions to the total charge of film formation in the monomer solution. The above factors were varied to determine the conditions that allow minimization of the ratio in order to obtain the highest yield of the polymer product. This was achieved by using a combination of a redox mediator addition with active stirring of solution.