A computer simulation study of the influence of a liquid crystal medium on polymerization

We present a simple molecular level model based on Gay-Berne monomers linked by finitely extendable nonlinear elastic potential bonds for describing main chain polymerization in liquid crystals. We apply the model to study the influence that the order of the medium has on the characteristics of the chains obtained. We find that the chains prepared from the nematic are actually straighter than those obtained from a polymerization in the isotropic phase and that they are characterized by a small number of hairpins as experimentally observed.     

The conformations of alkyl chains in fluids. A maximum entropy approach

We present a maximum entropy internal order method for analyzing chain conformations in liquid crystalline solutions. We show how prior knowledge of the conformational distribution can be taken into account and apply the method to the determination of the conformation of n-alkanes in liquid crystals without invoking molecular field or other approximate theoretical models.     

Temperature-Dependent Dynamical Evolution in Coum/SBE-β-CD Inclusion Complexes Revealed by Two-Dimensional FTIR Correlation Spectroscopy (2D-COS)

A combination of Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR) and 2D correlation analysis (2D-COS) was applied here for the first time in order to investigate the temperature-dependent dynamical evolution occurring in a particular type of inclusion complex, based on sulfobutylether-β-cyclodextrin (SBE-β-CD) as hosting agent and Coumestrol (7,12-dihydorxcoumestane, Coum), a poorly-soluble active compound known for its anti-viral and anti-oxidant activity. For this purpose, synchronous and asynchronous 2D spectra were calculated in three different wavenumber regions (960–1320 cm⁻¹, 1580–1760 cm⁻¹ and 2780–3750 cm⁻¹) and over a temperature range between 250 K and 340 K. The resolution enhancement provided by the 2D-COS offers the possibility to extract the sequential order of events tracked by specific functional groups of the system, and allows, at the same time, the overcoming of some of the limits associated with conventional 1D FTIR-ATR analysis. Acquired information could be used, in principle, for the definition of an optimized procedure capable to provide high-performance T-sensitive drug carrier systems for different applications.     

Analysis of human histone H4 by capillary electrophoresis in a pullulan-coated capillary,LC-ESI-MS and MALDI-TOF-MS

The object of the present study was the analysis of the human histone H4 (a core histone) in order to evaluate the state of its acetylation. Capillary electrophoresis (CE) using a pullulan-coated capillary provides a rapid and efficient approach to the separation of monoacetylated, diacetylated and triacetylated H4 isoforms from human cells. By using a simple running buffer of 100 mM triethanolamine-phosphate solution at pH 2.5 and exploiting the effectiveness of pullulan-based coverage in preventing adsorptive phenomena, the separation of the differently acetylated isoforms was achieved in less than 15 min with high efficiency and reproducibility. The proposed method was for the first time applied in the analysis of histone H4 fractions obtained from cell lines treated with different histone deacetylase (HDAC) inhibitors, used as potential anticancer drugs. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) analysis demonstrated that the acetylation occurred in the histone H4 tail, whereas the CE separation allowed for a fast determination of the percentages of H4 acetylated isoforms in real samples; the results were in agreement with those obtained from liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS) analysis. Therefore, the proposed CE method is a useful complementary support to the hyphenated techniques for the rapid monitoring of the activity of HDAC inhibitors.     

Electrical Properties of Single Walled Carbon Nanotube Reinforced Polystyrene Composites

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research communities due to their good electrical conductivity, high stiffness and high strength at relatively low CNT contents. Effective utilization of CNT in composites depends primarily on the ability to disperse them homogeneously throughout the polymer matrix, avoiding the formation of bundles due to van der Waals interactions existing between the nanotubes. In this work composites of polystyrene at various percentages of SWNT were fabricated using Latex Technology technique, a polymer type-independent method based on using a surfactant as a dispersing agent. An electrical characterization of SWNT composites was performed both in DC and AC modes. From the analysis of DC data a percolative behavior was found for the conductivity as function of SWNT content. The innovative contribution of this work consists in the modeling of the composite material upon its electrical properties. AC measurements and the analysis of impedance as function of angular frequency lead to the formulation of an equivalent circuit able to model the composite material in correspondence of the percolative threshold.     

A note on 3-blocked designs

A blocking set of a design different from a 2-(λ + 2, λ + 1, λ) design has at least 3 points. The aim of this note is to establish which 2-(v, k, λ) designs D with r ≥ 2λ may contain a blocking 3-set. The main results are the following. If D contains a blocking 3-set, then D is one of the following designs: a 2-(2λ + 3, λ + 1, λ), a 2-(2λ + 1), λ + 1, λ), a 2-(2λ - 1, λ, λ), a 2-(4λ + 3, 2λ + 1, λ) Hadamard design with λ odd, or a 2-(4λ - 1, 2λ, λ) Hadamard design. Moreover a blocking 3-set in a 2-(4λ + 3, 2λ + 1, λ) Hadamard design exists if and only if there is a line with three points. In the case of 2- (4λ - 1, 2λ, λ) Hadamard design with λ odd, we give necessary and sufficient conditions for the existence of a blocking 3-set, while in the case λ even, a necessary condition is given. © 1997 John Wiley & Sons, Inc.     

Seebeck Effect in Silicon Semiconductors

An extended hydrodynamic model will be used for the coupled system of electrons and phonons. This system is formed by a set of balance equations derived from the Bloch-Boltzmann-Peierls (BBP) kinetic equations applying the moment method and solving the problem of the closure by means of the Maximum Entropy Principle of Extended Thermodynamics. By using this model with a suitable limit, thermoelectric effects in bulk silicon are investigated.     

Photocatalytic Water Oxidation by a Mixed‐Valent MnIII3MnIVO3 Manganese Oxo Core that Mimics the Natural Oxygen‐Evolving Center

The functional core of oxygenic photosynthesis is in charge of catalytic water oxidation by a multi‐redox Mn^III/Mn^IV manifold that evolves through five electronic states (S_i , where i=0–4). The synthetic model system of this catalytic cycle and of its S₀→S₄ intermediates is the expected turning point for artificial photosynthesis. The tetramanganese‐substituted tungstosilicate [Mn^III₃Mn^IVO₃(CH₃COO)₃(A‐α‐SiW₉O₃₄)]^6? (Mn₄POM) offers an unprecedented mimicry of the natural system in its reduced S₀ state; it features a hybrid organic–inorganic coordination sphere and is anchored on a polyoxotungstate. Evidence for its photosynthetic properties when combined with [Ru(bpy)₃]²⁺ and S₂O₈^2? is obtained by nanosecond laser flash photolysis; its S₀→S₁ transition within milliseconds and multiple‐hole‐accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH 5) with a quantum efficiency of 1.7 %.     

Surface plasmon resonance, fluorescence, and circular dichroism studies for the characterization of the binding of BACE-1 inhibitors

The mechanism of action underlying β-secretase 1 (BACE-1) inhibition was characterized by a surface plasmon resonance (SPR) method using primary amino groups to immobilize OM99-2, a well-known highly potent peptidic BACE-1 inhibitor, on the carboxyl groups of the dextran layer of a sensor chip. The diluted BACE-1 was mixed with buffer or the test compound and the mixture was flushed through the chip. BACE-1 binding to the immobilized peptide inhibitor was quantified. This SPR method was used to identify BACE-1 inhibitor binding sites and the mechanism of action (competitive/noncompetitive) and to validate findings of fluorescence resonance energy transfer (FRET) inhibition studies. To support this, a multimethodological approach (circular dichroism and fluorescence spectroscopy) was applied in parallel to FRET inhibition studies to characterize the binding modes of peptidic and nonpeptidic BACE-1 inhibitors. Circular dichroism spectroscopy served to correlate the conformation of BACE-1 with enzymatic activity and to monitor secondary structure changes upon ligand binding. In a complementary approach, direct fluorescence spectroscopy was used to characterize different BACE-1 inhibitor binding sites. The influence of pH and inhibitors on BACE-1 secondary structure was also elucidated. This multimethodological approach was applied to identify binding modes of bis(7)-tacrine and myricetin in comparison with well-known peptidic inhibitors.