Influence of the composition of the polymer matrix on the electrooptical properties of films with a dispersed liquid crystal

Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined.     

Use of Organohydridodisilanes for Controlling the Molecular-Weight Distribution of High-Conversion Polymers

The polymerization of methyl methacrylate to high conversion in the presence of a series of disilanes as chain-transfer agents was studied, and the chain-transfer constants at low and high conversions were determined. The molecular-weight characteristics of the polymers were estimated by gel permeation chromatography.     

Methyl transfer in glycine N-methyltransferase. A theoretical study

Density functional theory calculations using the hybrid functional B3LYP have been performed to study the methyl transfer step in glycine N-methyltransferase (GNMT). This enzyme catalyzes the S-adenosyl-L-methionine (SAM)-dependent methylation of glycine to form sarcosine. The starting point for the calculations is the recent X-ray crystal structure of GNMT complexed with SAM and acetate. Several quantum chemical models with different sizes, employing up to 98 atoms, were used. The calculations demonstrate that the suggested mechanism, where the methyl group is transferred in a single S(N)2 step, is thermodynamically plausible. By adding or eliminating various groups at the active site, it was furthermore demonstrated that hydrogen bonds to the amino group of the glycine substrate lower the reaction barrier, while hydrogen bonds to the carboxylate group raise the barrier.     

Photochromic dihetarylethenes. 18. New approach to the synthesis of dithienothiophene and preparation of its photochromic derivative

A new approach to the synthesis of dithienothiophene was developed, and 1,2-bis(2,6-dimethyldithieno[3,2-b;2",3"-d]thiophen-3-yl)hexafluorocyclopent-1-ene was prepared. The latter compound is the first representative of photochromic dihetarylethenes with the fused tricyclic fragments linked through the perfluorocyclene bridge.     

Investigation of radiochemical conversions in extraction systems based on tributyl phosphate

The use of halogenated organic compounds under the effect of ionizing radiation requires a comprehensive knowledge of their radiation stability. There is little experimental evidence on the radiolysis of fluorine-containing organic compounds in the literature, while a theoretical generalization enabling one to predict the main radiolysis pathways is completely lacking. This paper is concerned with the identification of stable radiolysis products of trichloromethyl-1,1,2-trifluoro-2,2-dichloroethyl ether (C₃F₃Cl₅ O), γ-irradiated separately and the extraction system based on tributyl phosphate. Practically all the C₃F₃Cl₅O radiolysis products were identified with the aid of gas-liquid chromatography, GC-MS, IR, UV and NMR spectroscopy and elemental analysis. Upon C₃F₃Cl₅O radiolysis, the formation of CCl₄, Cl₂, COCl₂, C₂ Cl₆, freons of various composition and long-chained ethers like CFCl₂−CF₂−O−CCl₂−CCl₃ takes place. The identification of radiolysis products allows to draw well-founded conclusions on the mechanism of C₃F₃Cl₅O radiolysis, representing a wide class of chlorine- and fluorine-containing organic compounds.     

An efficient approach towards the convergent synthesis of "fully-carbohydrate" mannodendrimers

Glycosylation of sugar trityl ethers with sugar 1,2-O-(1-cyano)ethylidene derivatives (the trityl-cyanoethylidene condensation) has been applied to the synthesis of highly branched (dendritic) mannooligosaccharides incorporating a Manalpha1-->3(Manalpha1-->6)Man structural motif. The convergent synthetic strategy used to assemble these oligosaccharides was based on the use of glycosyl acceptors and/or a glycosyl donor already bearing this structural motif. The former were represented by mono- and ditrityl ethers of ManalphaOMe, Manalpha1-->3ManalphaOMe, and Manalpha1-->3(Manalpha1-->6)ManalphaX, where X=OMe or SEt. The pivotal glycosyl donor was the peracetylated 1,2-O-(1-cyano)ethylidene-3,6-di-O-(alpha-D-mannopyranosyl)-beta-D-mannopyranose (1), prepared by orthogonal Helferich glycosylation of the known 1,2-O-(1-cyano)ethylidene-beta-D-mannopyranose with tetra-O-acetyl-alpha-D-mannopyranosyl bromide followed by O-acetylation. Glycosylation of acetates of methyl 6-O-trityl-alpha-D-mannopyranoside and methyl 3,6-di-O-trityl-alpha-D-mannopyranoside with one equivalent of the donor 1 gave rise to the isomeric tetrasaccharide derivatives, Manalpha1-->3(Manalpha1-->6)Manalpha1-->6ManalphaOMe and Manalpha1-->3(Manalpha1-->6)Manalpha1-->3ManalphaOMe, respectively. The latter derivative was further mannosylated at the remaining 6-O-trityl acceptor site to give the protected pentasaccharide Manalpha1-->3(Manalpha1-->6)Manalpha1-->3(Manalpha1-->6)ManalphaOMe. The isomeric pentasaccharide, Manalpha1-->3(Manalpha1-->6)Manalpha1-->6(Manalpha1-->3)ManalphaOMe, was prepared by reaction of 1 with the 6-O-trityl derivative of (Manalpha1-->3)ManalphaOMe. In a similar fashion, 6'- and 6"-O-trityl derivatives of the branched trisaccharide Manalpha1-->3(Manalpha1-->6)ManalphaOMe served as precursors for two isomeric mannohexaosides. The 3,6-di-O-trityl ether of ManalphaOMe and the 6',6"-di-O-trityl ether of Manalpha1-->3(Manalpha1-->6)ManalphaX (X=OMe or SEt) were efficiently bis-glycosylated with the donor 1 to give the corresponding protected mannoheptaoside and mannononaoside. The yields of these glycosylations with the donor 1 ranged from 50 to 66 %. Final deprotection of all the oligosaccharides was straightforward and afforded the target products in high yields. Both the acylated and deprotected products were characterized, and the intersaccharide connectivities were elucidated by extensive one- and two-dimensional NMR spectroscopy. The described blockwise convergent approach allows assembly of a variety of 3,6-branched mannooligosaccharides.