Structural and optical characterization of the propolis films

We have performed structural and optical characterizations of the propolis (an organic entity of biological nature) films grown on various non-organic substrates. The films were grown from a propolis melt or a propolis alcohol solution. The crystal structure has been observed in the films precipitated from the solution onto substrates such as an amorphous glass and sapphire or semiconductor indium monoselenide. For any growth method, the propolis film is a semiconductor with the bandgap of 3.07 eV at 300 K that is confirmed by a maximum in photoluminescence spectra at 2.86 eV. We argue that propolis films might be used in various optoelectronic device applications.     

Investigation of MFTIR infrared spectra of peat waxes with sorbed cationic surfactants

Journal of Applied Spectroscopy -     

Altered protein synthesis in rat kidney cells exposed to semiconductor materials

It is thought that the extensive industrial use of arsenic, gallium and indium, which have applications as the materials for III–V semiconductors, will increase human exposure to these compounds in the near future. We have undertaken the development of new biological indicators for assessing exposure to these elements. Element-specific alterations in protein synthesis patterns were expected to occur following exposure to arsenic compounds. We examined alterations in protein synthesis in primary cultures of rat kidney proximal tubule epithelial cells by sodium arsenite, gallium chloride and indium chloride, utilizing two-dimensional gel electrophoresis. After incubation with the chemicals for 20 h, newly synthesized proteins were labeled with [³⁵S]methionine. A protein with a molecular weight (M_r) of 30 000 was markedly induced on exposure to 10 μM arsenite or 300 μM gallium chloride, and synthesis of proteins with M_r values of 85 000, 71 000, 65 000, 51 000, 38 000 and 28 000 were also increased by exposure to arsenite and gallium chloride. No significant changes were observed upon exposure to indium. Some of these increased proteins could be heat-shock proteins.     

Comparison of short range interactions in nematic liquid crystals A 2H-NMR study of 5CB-d19 as a solute

Previous studies using dideuterium as a solute have demonstrated the importance for orientation of the interaction between the solute molecular quadrupole moment and the average electric field gradient present in liquid crystals. With the aim of learning about additional orientational mechanisms, we have studied the temperature dependence of the ²H-NMR spectra of the liquid crystal 5CB-d₁₉ as the solute in three liquid crystal mixtures: 55 wt % 1132/EBBA, 56·5 wt % 1132/EBBA and 70 wt % 5CB/EBBA. In these mixtures, the contribution from the environment to the average electric field gradient at the ²H nucleus of dideuterium is zero. The spectra of 5CB-d₁₉ in the mixtures 55 wt % 1132/EBBA and 56·5 wt % 1132/EBBA are equivalent, but are different from those in 70 wt % 5CB/EBBA. The spectra of 5CB in 55 wt % 1132/EBBA and 70 wt % 5CB/EBBA are analysed using two different models for the short range potential, and param eters of the models are used to compare the potentials in the different mixtures. For a given spectral splitting of the chain C₁ deuteron, the reduced short range potential is the same in all three mixtures studied. The spectral differences observed are a consequence of different nematic-isotropic phase transition temperatures combined with the effect of trans/gauche-isomerization in the hydrocarbon chain.     

Liquid crystalline hexa-amides and side chain polysiloxanes of azacrown [18]-N6

The hexa-4-dodecyloxybenzoyl derivative 1 of azacrown [18]-N₆ was originally reported to have a 'tubular' mesophase on the basis of its large central ring and 6-fold symmetry. Starting in the mesophase, annealing of 1 under a cover slip results in formation of a new crystalline phase that melts directly to an isotropic liquid at the temperature previously observed for the mesophase to isotropic transition. Thus the phase behaviour of 1 is kinetically controlled. The analogous hexa-3,4-bisdodecyloxybenzoyl derivative 2 of azacrown [18]-N₆ has no kinetic limitations to its phase changes and has an enantiotropic columnar liquid crystalline phase. We have synthesized side chain copolysiloxanes with a (CH₂)₁₁ spacer and 75-84 per cent by weight of the same 4-dodecyloxybenzoyl-[18]-N₆ mesogen. The polysiloxanes also display a liquid crystalline phase.     

Manifestation of biquadratic coupling in the smectic C* phase soft mode dielectric response

The soft mode dielectric response of three ferroelectric chiral smectic C* substances is studied in the vicinity of the smectic C*-smectic A* phase transition. For some substances the soft mode dielectric strength exhibits a pronounced anomaly in the C* phase just below the phase transition. We show how this anomaly can be systematically correlated with a corresponding anomaly in the experimentally determined ratio of spontaneous polarization over tilt. By comparing the experimental results with the theoretical predictions of an extended Landau model, we demonstrate how the crossover behaviour of the system can be interpreted as being the consequence of the presence of a biquadratic coupling between tilt and polarization in the Landau free-energy of the system.