Tetragonal low-temperature structure of LiAl

The cubic face-centered structure of LiAl (, at ) transforms into a tetragonal body-centered structure (I4₁/amd, , at ). This first-order phase transition at about during heating is probably the reason for the so-called “ anomalies” in some physical properties like specific heat, electrical resistivity and nuclear-spin lattice relaxation. This transition seems to be correlated with the composition Li:Al of the alloy and the amount of Li vacancies.     

Chemical and electrochemical polymerisation of pyrrole on polyester textiles in presence of phosphotungstic acid

Polypyrrole (PPy) was chemically synthesised on polyester (PES) textiles to produce conducting textiles. Two different types of counter ion were employed: anthraquinone sulfonic acid (AQSA) and phosphotungstate (). Textiles covered with PPy were characterised by means of FTIR-ATR, SEM, EDX, cyclic voltammetry (CV), surface resistivity measurements and electrochemical impedance spectroscopy (EIS). Additionally, friction and washing assays were done to test the resistance of the layer of conducting polymer (PPy/). Electropolymerisation of PPy/ in acetonitrile medium onto chemically synthesised PES-PPy/ showed the improvement of the coating properties.     

Synthesis of new aromatic perfluorovinyl ether monomers containing phosphonic acid functionality

The synthesis of a new perfluorovinyl ether monomer containing phosphonic acid functionality is reported. It started from 4-[(α,β,β-trifluorovinyl)oxy]bromo benzene prepared in two steps from the nucleophilic substitution of 4-bromophenate to 1,2-dibromotetrafluoroethane. The [(α,β,β-trifluorovinyl)oxy]benzene dialkyl phosphonate was prepared according to various methods of phosphonation like a Michaelis-Arbuzov or a Michaelis-Becker or a palladium catalysed arylation in the presence of various reactants. The influence of the nature of the method and of the reactants onto the yields is discussed. It was shown that reaction involving a palladium triphenyl phosphine catalyst led to the best yield. All different aromatic intermediates and fluoromonomers were characterised by , and NMR, mass spectrometry (EI), and by FTIR.     

Monitoring structural transformations in crystals. Part 4. Monitoring structural changes in crystals of pyridine analogs of chalcone during [2+2]-photodimerization and possibilities of the reaction in hydroxy derivatives

We studied the [2+2]-photodimerization in crystals of pyridine analogs and hydroxy derivatives of chalcone using the X-ray structure analysis. The mutual orientation of adjacent molecules in the crystals was analyzed in a quantitative way and the results were compared with data for known photoactive crystals undergoing the [2+2]-photodimerization. In the case of one pyridine analog, we processed the single-crystal-to-single-crystal photodimerization and determined the structure for the mixed crystal containing both the substrate and the product. We also explained a role of hydrogen bonds in the [2+2]-photodimerization in the case of the hydroxy derivatives of chalcone. C₅H₄N-CO-CHCH-C₆H₅: , , , β=91.318(10)°, monoclinic, . The irradiated crystal of the above analog: , , , β=91.870(10)°, monoclinic, . C₆H₅-CO-CHCH-C₅H₄N: , , , β=110.01(3)°, monoclinic, C2/c,Z=8. C₆H₅-CO-CHCH-C₆H₄(o-OH): , , , β=109.73(5)°, monoclinic, . C₆H₅-CO-CHCH-C₆H₄(p-OH): , , , orthorhombic, .     

Effect of temperature on the volumetric properties of (cyclohexanone + an aromatic hydrocarbon)

The excess molar volume of (cyclohexanone + benzene, or toluene, or ethylbenzene, or styrene) were obtained from the densities measured by means of a vibrating-tube densimeter over the whole composition range at temperatures (293.15, 303.15, 313.15, 323.15, 333.15, 343.15, 353.15) K and atmospheric pressure. The excess molar volume provide the temperature dependence of in the temperature range of (293 to 353) K. The results were correlated using the fourth-order Redlich-Kister equation, with the maximum likelihood principle being applied for the determination of the adjustable parameters. It was found that the in the systems studied increase with rising temperature.     

Syntheses of [F]5-fluoro-3-nitro-l-tyrosine

The detection of 3-nitro-l-tyrosine has been used as a biomarker of “reactive nitrogen species” in biological matrices and has been an ongoing challenge in analytical chemistry. In this work, fluorine-18 labelled 5-fluoro-3-nitro-l-tyrosine (FNT) was synthesized as a potential radiotracer to probe the biological fate of 3-nitro-l-tyrosine. The synthesis of []FNT was carried out by reaction of []3-fluoro-l-tyrosine with NaNO₃ in TFA solvent for 5 min at 4 °C. The radiochemical yield (RCY) of []FNT was 96±2% and []3-fluoro-l-tyrosine, was 29±1%, relative to []3-fluoro-l-tyrosine and []F₂, respectively. The syntheses of []FNT were also accomplished by direct fluorination of 3-nitro-l-tyrosine with []F₂ and by nitration of l-tyrosine with NaNO₃, followed by fluorination, in TFA (4 °C) or anhydrous HF (−65 °C) solvent. The latter two synthetic routes produced []FNT in 13.5±1.5% RCY, within 1 h. Products were characterized by use of , and NMR spectroscopy and mass spectrometry.     

A selective and sensitive ‘naked eye’ anion detector based on an imine-π-TCNQ assembly

A colorimetric heterocyclic imine based chemosensor is designed for detection of and under physiological pH conditions. The charge-transfer (CT) sensor is highly coloured with and recognition giving rise to a purple-to-yellow colour change that is visible to the naked eye and is reversible upon removal of anion.     

Temperature-dependent diffraction studies on the phase evolution of tetraindium heptabromide

The mixed-valent compound In₄Br₇ undergoes a higher-order phase transition below which leads to a decrease in symmetry from the trigonal to the monoclinic (C2/c) system via . The phase transition has been monitored by X-ray powder diffraction using a linear position-sensitive detector between 15 and , and the crystal structures at room temperature and at 90 K have been refined by means of time-of-flight neutron powder-diffraction data; at , the lattice parameters are , , , and β=98.20(1)°; the new unit cell contains 88 atoms (Z=8) of which 12 are symmetry-independent. Due to their electronic instability because of a second-order Jahn-Teller effect, two of the three crystallographically independent monovalent indium cations are severely affected by the phase transition with respect to their coordination spheres; bond-valence calculations reveal significant strengthening of In⁺-Br⁻ bonding upon symmetry reduction. Structural changes and group-subgroup relationships as well as possible intermediate phases are discussed.     

Effect of initial monomer concentration on the equilibrium swelling and elasticity of hydrogels

The linear swelling ratio α and the effective network chain length N of a series of poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels were investigated as a function of the gel preparation concentration . PDMAAm hydrogels were prepared at a fixed cross-linker ratio but at various initial monomer concentrations. It was found that α is not a monotonic function of . As is increased, α first decreases up to about and remains constant in a narrow range of , but then it increases continuously. The -dependence of α is due to the variation of the network chain length N depending on the gel preparation concentration. In the range of below 0.1, N follows the scaling relationship , while at higher concentrations, N varies only slightly with . The increase of α with N obeys the relation , as predicted by the Flory-Rehner theory.     

Structural characterization and ferroelectric ordering in (C3N2H5)5Sb2Br11

A ferroelectric crystal (C₃N₂H₅)₅Sb₂Br₁₁ has been synthesized. The single crystal X-ray diffraction studies (at 300, 155, 138 and 121 K) show that it is built up of discrete corner-sharing bioctahedra and highly disordered imidazolium cations. The room temperature crystal structure has been determined as monoclinic, space group, P2₁/n with: , and and β=96.19^°. The crystal undergoes three solid-solid phase transitions: ) discontinuous, continuous and discontinuous. The dielectric and pyroelectric measurements allow us to characterize the low temperature phases III and IV as ferroelectric with the Curie point at 145 K and the saturated spontaneous polarization value of the order of along the a-axis (135 K). The ferroelectric phase transition mechanism at 145 K is due to the dynamics of imidazolium cations.