Order electricity reconsidered

We have considered the Landau-de Gennes expansion of the distortion free energy to examine a possible connection between the electric polarization in terms of a gradient of the order parameter and the electric polarization resulting from splay and bend distortions of the director. In addition we have considered the electric polarization connected with the electric quadrupole density, which is not contained in the Landau-de Gennes expansion.     

Photoluminescence study of sexithiophene thin films

To determine the exciton diffusion length of sexithiophene (6T) thin films, quenching of the photoluminescence (PL) of vacuum-deposited 6T films on TiO2 and on quartz has been investigated. For films with a thickness of more than 22 nm and at temperatures below 100 K, additional PL lines appear in luminescence spectra. This feature is related to the structural properties of 6T films. The PL intensity is thermally activated with an activation energy of 18 meV on TiO2 and 6 meV on quartz. When 6T is applied on TiO2, exciton quenching occurs for films up to 120 nm. For 6T on quartz this value is reduced to 60 nm. By comparing the relative luminescence intensities of 6T on quartz and on TiO2 substrates, an exciton diffusion length of 60 +/- 5 nm is derived.     

Accurate determination of lead in wines by inductively coupled plasma mass spectrometry

Summary The capability of inductively coupled plasma mass spectrometry (ICP-MS) for Pb determinations in wine samples is studied. An evaluation is made of the signal behaviour in aqueous ethanolic medium. The effect of preliminary sample preparation on signal suppression or enhancement is investigated in conjunction with the ability of internal standardization to correct for it. As a result, an accurate and precise method of analysis is described in which the sample preparation is limited to a 10-fold dilution and external calibration is applied for quantitation. A detection limit of 0.2 g 1^–1 Pb in wine is achieved. The Pb content of ten different wines was found to range around 40 g 1^–1 with extreme values of 1.63 and 58.8 g 1^–1.     

Do S,S'-coordinated o-dithiobenzosemiquinonate(1-) radicals exist in coordination compounds? the [AuIII(1,2-C6H4S2)2]1 -/0 couple

The square planar, light-green, diamagnetic complex [N(n-Bu)(4)][Au(III)(L(t)()(-)(Bu))(2)] (1) reacts with iodine in acetone affording the neutral paramagnetic species [Au(L(t)()(-)(Bu))(2)] (1a) (S = (1)/(2)) where H(2)[L(t)()(-)(Bu)] represents the ligand 3,5-di-tert-butyl-1,2-benzenedithiol. The corresponding complexes containing the unsubstituted ligand H(2)[L], 1,2-benzenedithiol, namely [N(n-Bu)(3)H][Au(L)(2)] (2) and [Au(L)(2)] (2a), have also been prepared and characterized by X-ray crystallography; the structure of the latter has been reported in ref 10. (197)Au M?ssbauer spectra of 1 and 1a clearly show that the one-electron oxidation is ligand-centered and does not involve the formation of Au(IV) (d(7)). The spectroscopic features of the ligand mixed-valent species 1a were determined by UV-vis, EPR, and IR spectroscopy which allows the detection of S,S-coordinated 1,2-dithiobenzosemiquinonate(1-) radicals in coordination compounds.     

Crystallization kinetics and crystalline morphology of poly(ε-caprolactone) in blends with grafted rubber particles

The crystallization behavior of pure PCL and PCL in blends with crosslinked rubber particles was studied under (non)isothermal crystallization conditions, where the rubber particles were grafted with PCL chains via hydrogen abstraction of the aliphatic moieties in PCL. The crystal growth and the organization of crystals into spherulitic superstructures are significantly influenced by the presence of the grafted rubber particles, which act as an excellent nucleating agent for PCL. The nucleating efficiency shows an exponential dependency on the PCL grafting density and, according to an Avrami analysis, an increased PCL grafting density increases the overall crystallization rate of the PCL matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1438–1448, 2010     

Pressure-tuning of the secondary structures of proteins: Fourier transform infrared studies in the diamond anvil cell

Abstract

A self-deconvolution and fitting procedure is presented that allows the determination of pressure-induced changes in the secondary structure of proteins starting from the infrared spectrum. The method takes into account the elastic as well as the possible conformational shift of the spectral bands. Applications are presented on pressure-induced changes in bovine pancreatic trypsin inhibitor and in gramicidin incorporated into lipid bilayers.     

Analytical characterization of mannosylerythritol lipid biosurfactants produced by biosynthesis based on feedstock sources from the agrofood industry

Mannosylerythritol lipids (MELs) are currently one of the most promising biosurfactants because of their multifunctional applications and good biodegradability. Depending on the yeast strain and the feedstock used for the fermentation process, structural variations in the MELs obtained occur. Therefore, MELs produced by Pseudozyma aphidis DSMZ 70725 with a soybean oil feedstock were characterized by chromatography and mass spectrometry (MS). Column chromatography with silica provided fractionation of the different types of MEL. High-performance liquid chromatography combined with MS was employed for the analysis of the MEL fractions and crude mixtures. A characteristic MS pattern for the MELs was obtained and indications of the presence of new MEL homologues, showing the incorporation of longer and more unsaturated fatty acid chains than previously reported, were given. Gas chromatography?CMS analysis confirmed the presence of such unsaturated fatty acid chains in the MELs, demonstrating the incorporation of fatty acids with lengths ranging from C₈ to C₁₄ and with up to two unsaturations per chain. The incorporation of C₁₆ and C₁₈ fatty acid chains requires further investigation. MS/MS data allowed the unambiguous identification of the fatty acids present in the MELs. The product ion spectra also revealed the presence of a new isomeric class of MELs, bearing an acetyl group on the erythritol moiety.     

Sub-micrometer thermoplastic vulcanizates obtained by reaction-induced phase separation of miscible mixtures of poly(ethylene) and alkyl methacrylates

Sub-micrometer (μm) thermoplastic vulcanizates (TPVs) with cross-linked rubber particles with sizes ranging from 70 to 400 nm were prepared by reaction-induced phase separation (RIPS) of initially miscible blends of poly(ethylene) (PE), lauryl methacrylate (LMA) and divinylbenzene (DVB). Cross-linking under static conditions led to (partial) connectivity of the rubber particles via chemical bridging of grafted PE chains. Dynamic preparation conditions caused the connected structure to break-up, which led to a significant enhancement of the mechanical properties and the melt processability. The addition of 25-80 wt% extender oil resulted in a reduced complex viscosity and yield stress in the melt, without deteriorating the mechanical properties. The relatively good elastic recovery and excellent ultimate properties of these high hardness TPVs may be explained by the sub-μm rubber dispersions.     

High Resolution Tip Enhanced Raman Mapping on Polymer Thin Films

Advanced tip enhanced Raman mapping (TERM) was applied to high resolution chemical identification on nanoscale. Thin poly(methyl methacrylate)/poly(styrene acrylonitrile) (SAN28/PMMA) blend films were measured at different stages of phase separation. New insights into the phase evolution behavior of the thin films were obtained, when the TERM images were compared. An unexpected morphology transition was observed after a few minutes annealing at 250 °C. No surface enrichment of PMMA was observed, differing from the previous reports on a similar well-studied system of SAN33/PMMA. The glass transition temperature, the surface and interfacial tension were found to be the main factors responsible for the phase evolution behavior of SAN28/PMMA films.     

Synthesis of 8‐substituted tetrahydro‐γ‐carbolines

The Fischer reaction is applied to the synthesis of 8‐substituted tetrahydro‐γ‐carbolines with electron‐donating or electron‐withdrawing groups, using catalytic or thermal methods. The reaction conditions must be varied according to the nature of the N 1 substituent of the piperidone. The best results are observed when a releasing group is present on the arylhydrazine and a benzyl substituent on the nitrogen of piperidone. Formation of carbolines with a withdrawing substituent is observed in soft acidic conditions; in others, reaction ended at the hydrazone level or did not evolve.