No abstract available

No abstract available

No abstract available

[en] Study of drawn fibres prepared from an isostatic polypropylene modified by an ethylene aminoalkylacrylate copolymer has been done using the broad line of ¹H NMR. NMR spectra were measured on the set of fibres prepared with a draw ratio λ from 1 to 5.5 at two temperatures, one of them corresponding to the onset of segmental motion and the other one is the minddle of the temperature interval as determined by decrease of the second moment M₂. Decomposition of the spectra into elementary components related to the amorphous, intermediate and crystalline regions of partially crystalline polymers has been made. The drawing of the fibres was found to enhance the chain mobility in the amorphous region and to restrain the molecular motion in the intermediate region. Such behaviour well supports conclusions predicted in the earlier study based on the spin-lattice relaxation time T₁ and dynamic mechanical data treated using the WLF theory. (Authors)

[en] Trisubstituted borohydrides such as trialkylborohydrides, trialkoxyborohydrides and mixed alkoxyalkylborohydrides constitute a highly attractive class of reducing agents in organic synthesis. Trialkylborohydrides have proven to be powerful selective reducing agents. On the other hand, trialkoxyborohydrides proved to be very mild reducing agents, whereas mixed alkoxyalkylborohydrides showed their unique reducing characteristics.

[en] Proton magnetic resonance spectroscopy (MRS) has become an important tool to study in vivo certain biochemical aspects of brain disorders. In the last decade this technique has been applied to the in vivo investigation of pathophysiological aspects of psychiatric disorders, extending knowledge of the related brain alterations. This review will focus on providing some background to clarify technical and biochemical issues and it will describe the studies that have been performed in schizophrenia. The results will be framed in a more general context to highlight what we have learned and what remains to be understood from the application of this technique to schizophrenia

[en] In deuterium NMR spectra of phosphatidylethanolamine bilayers with an extremely high content of saturated fatty acids, each C1 deuteron of the glycerol backbone gave rise to a doublet.¹ This suggests the presence of two backbone conformations, the exchange between which is slow on an NMR time scale. The origin of the two conformations has been investigated in this work using saturated 1,2-diacyl-sη-glycero-3-phosphoethanolamine specifically deuterated in the glycerol backbone. The results showed that the two conformations originate from different domains, which have different fatty acid compositions. The differential scanning calorimetry of the bilayers suggested that the size of the domain is not large enough to show an independent phase transition. Thus, the formation of microdomains in the phosphatidylethanolamine bilayers has been concluded. Conformational difference in different domains was shown to be restricted to the C1 position of the glycerol backbone. The microdomains of phosphatidylethanolamine were retained even in the presence of other phospholipids

[en] To study the origin of semimetal-metal and metal-insulator transformations, localization effects and C-E bonding in fluorine-intercalated graphite C_xF, ¹³C and ¹⁹F NMR investigations have been carried out for a wide range of fluorine content, 3.8 < x < 12.7. Fluorine spectra for small fluorine content, x > 8, are attributed to mobile fluorine acceptor species which are responsible for the increase of electric conductivity in the dilute compound. When increasing the fluorine content to x ∼ 8 corresponding to the maximum electric conductivity, covalent C-P bonds start to oc- cur. The number of these bonds grows with fluorine content resulting in the decrease in conductivity which is caused by a percolation mechanism rather than by a change in bond length. A difference in ¹⁹F chemical shift for fluorine-intercalated graphite C_xF and covalent graphite fluoride (CF)_n has been observed and is attributed to different C-P bonding in these compounds

[en] Hepatitis C virus (HCV) has been known to be an enveloped virus with a positive strand RNA genome and the major agent of the vast majority of transfusion associated cases of hepatitis. For viral replication, HCV structural proteins are first processed by host cell signal peptidases and NS2/NS3 site of the nonstructural protein is cleaved by a zinc-dependent protease NS2 with N-terminal NS3. The four remaining junctions are cleaved by a separate NS3 protease. The solution conformations of NS4B/5A, NS5A/5B substrates and NS5A/5B inhibitor have been determined by two-dimensional nuclear magnetic resonance (NMR) spectroscopy. NMR data suggested that the both NS5A/5B substrate and inhibitor appeared to have a folded turn-like conformation not only between P1 and P6 position but also C-terminal region, whereas the NS4B/5A substrate exhibited mostly extended conformation. In addition, we have found that the conformation of the NS5A/5B inhibitor slightly differs from that of NS5A/5B substrate peptide, suggesting different binding mode for NS3 protease. These findings will be of importance for designing efficient inhibitor to suppress HCV processing

[en] In recent years, there has been considerable interest in the study of liquid crystalline materials not only because of their many industrial applications from high strength polymer fibres to liquid crystal electrooptic displays but also there is much interest in their fundamental behaviour. Until relatively recently, molecules which were known to exhibit liquid crystalline phases consisted of a fairly rigid core to which are attached either one or two flexible alkyl chains. However, polymeric systems exhibiting mesophases have also been discovered, the molecules of which usually consist of the same rigid units linked via flexible spacers. Since the discovery of these semi-flexible main group liquid crystal polymers, many compounds have been synthesised which consist of just two mesogenic groups attached via a flexible spacer. These systems are known as liquid crystalline dimers and reflect the properties of polymeric systems since their structures are so similar. However, because of their simplicity are far easier to model theoretically and due to their intriguing physical properties, are very widely studied. This work is concerned with the synthesis and study of the physical properties of certain liquid crystalline monomers and dimers by ESR and NMR spectroscopy. The study involves measurement of the orientational order, using ESR and ²H NMR spectroscopy, measurement of the symmetry of certain mesophases using ²H NMR spectroscopy and also an investigation of the elastic behaviour of certain monomers and dimers by ESR spectroscopy. Liquid crystal molecules are non-rigid and possess very little symmetry which greatly complicates their study. To overcome their study, probe molecules have been used which possess some symmetry and so provides a more detailed study of these materials and their properties. We describe, where necessary, a synthesis of these materials and details of the probe molecules used. (author)