Crystallographic and conformational analysis of (<Emphasis Type="Italic">E</Emphasis>)-2-isopropyl-4-(<Emphasis Type="Italic">p</Emphasis>-tolyldiazenyl)phenol

The molecular and crystal structures of the title compound, C₁₆H₁₈N₂O, were characterized and determined by single crystal X-ray diffraction method in addition to spectroscopic means such as IR, UV–VIS and ¹H NMR. The compound crystallizes in orthorhombic space group P bca, with a = 9.3350(5) Å, b = 23.4878(13) Å, c = 26.5871(12) Å, Z = 16, D _calc. = 1.1591(1) g/cm³, μ (MoK_α) = 0.073 mm^?1. Monomers of the compound in the crystal structure are linked into C(7) and C(8) chains generated by translation along the [1 0 0] direction with the aid of O–H···N type H-bonds which serve to the stabilization of periodic organization of the molecules beside major and minor component in the disordered azo fragment. In order to describe conformational flexibility and the crystal packing effects on the molecular conformation, potential barriers regarding the rotation along both Ar–N bonds were calculated by varying the related torsional degrees of freedom in every 10° ranging from ?180° to +180° via quantum chemical calculations at DFT/B3LYP level.     

Sensitive sepiolite-carbon nanotubes based disposable electrodes for direct detection of DNA and anticancer drug-DNA interactions

A new surface based on the natural clay mineral sepiolite and a single-walled carbon nanotubes-modified graphite electrode was developed for the electrochemical detection of DNA, and also for anticancer drug-DNA interactions.     

Bias field induced impedance relaxation of TlGaSe2 semiconducting layered crystal at room temperature

Complex Impedance Spectroscopy has been employed for the study of absorption kinetics at TlGaSe₂ layered crystal under Bias voltage at room temperature. Two relaxations mechanisms have been observed. The crystal has “slow” and “fast” relaxation mechanisms in low and high frequency region, respectively. The complex impedance spectra were fitted by the superposition of two Cole‐Cole types of relaxations. The fast relaxation in the higher frequency region may be due to dipolar relaxation and the slow relaxation in the low frequency region may be due to Maxwell‐Wagner type relaxation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Encapsulation of inorganic particles via miniemulsion polymerization. I. Dispersion of titanium dioxide particles in organic media using OLOA 370 as stabilizer

The dispersion of hydrophilic and hydrophobic titanium dioxide (TiO₂) particles in organic media (styrene and cyclohexane) was studied to evaluate the effect of dispersion quality (i.e., size and stability) on the encapsulation efficiencies of subsequent miniemulsion polymerizations. Through screening studies of various block copolymers, OLOA 370 (polybutene–succinimide pentamine) was chosen as the stabilizer for detailed dispersion studies on both types of TiO₂ particles. As a result of strong interactions between the amine end group of the OLOA 370 stabilizer and the hydroxyl groups on the surface of the hydrophilic TiO₂ particles, a good dispersion stability and small particle size (D_v = 39–45 nm) was obtained using 1.0 wt % stabilizer and 20 min of sonification. The dispersions of the hydrophobic TiO₂ particles resulted in a larger average particle size (D_v = 60 nm) and poorer stability. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4419–4430, 2000     

Encapsulation of inorganic particles via miniemulsion polymerization

The encapsulation of TiO₂ particles via miniemulsion polymerization is strongly dependent on the size and stability of the inorganic particles in the monomer medium in which they are initially dispersed. It was found from XPS and FT‐IR studies that both the hydrophilic and hydrophobic TiO₂ particles, which were studied, have hydroxyl groups present on their surfaces, which can strongly interact with the amine end‐groups of the polymeric stabilizer, OLOA370 (polybutene‐succinimide diethyl triamine). It was found from the dispersion and adsorption studies that the amount of OLOA370 retained on the TiO₂ particles is strongly dependent on the area exposed by the sonification that is applied to break up the aggregates in the dispersion process. The TiO₂ dispersions in styrene monomer were themselves dispersed as miniemulsion droplets and subsequently polymerized. It was concluded from the density gradient column (DGC) analysis of the latexes obtained from the encapsulation polymerizations, that the stability of the inorganic particles in the monomer, as well as their particle size, significantly influence the encapsulation efficiencies. The use of the hydrophilic titanium dioxide particles in combination with the stabilizer, OLOA370, resulted in a good dispersibility, dispersion stability, and small TiO₂ particle size. This lead to better encapsulation efficiencies compared to the hydrophobic particles. The poorer results obtained with the hydrophobic TiO₂ particles were attributed to their larger particle size, which resulted from the reduced adsorption of the OLOA370. Fewer hydroxyls and the presence of the trimethoxy octyl silane (TMOS) groups, which themselves are unable to provide sufficient steric stability, are proposed to explain these findings.     

The photocopy method: measuring living chain distributions in radical polymerization

We have developed a method to measure living chain molecular weight distributions (MWDs) in free radical polymerization (FRP). By laser photolysis of photoinhibitor molecules included in the polymerizing mixture, the living chains are instantaneously flooded with small molecule radicals carrying fluorescent labels. These radicals react with living chain radical end groups, kinetically freezing growth of living chains and simultaneously end -labelling them: the living chain population has been photocopied. The living MWD is obtained from subsequent analysis by GPC equipped with fluorescence detection. We have measured low conversion thermally initiated PMMA living MWDs, Exponential behaviour is found for large chain length N, in accord with classical Flory-Schultz theory, but at smaller N we establish strong deviations, consistent with the stretched exponential predicted by modern FRP theory incorporating first principles chain length dependencies of termination rate constants. However, this behaviour may derive at least partially from distortions produced by the photocopying technique which can generate power law or logarithmic forms at small N.