Chiral liquid crystalline polymers: Recent issues and perspectives

The syntheses and structures of chiral liquid crystalline polymers (LCPs) are briefly reviewed with emphasis on the established structure-property correlations. The most recent advances and future trends in their potential applications in optics and electrooptics are also outlined, with particular reference to the ferroelectric, electroclinic, piezoelectric, and nonlinear optical properties of chiral LCPs.     

Efficient Chemoselective Oxidation of Phenylmethanols to Aldehydes with Iodosobenzene

Primary phenylmethanols are selectively and efficiently oxidized to the corresponding aldehydes by the system C₆H₅IO/(C₆H₅)₄PBr/CH₂Cl₂, T = 298 K under aerobic conditions. The use of the relatively stable iodosobenzene, an iodine(III) compound, in place of the usually employed and potentially explosive iodine(V) reagents, the easy work-up procedure, and the facile recycling of solvent and oxidant provides a convenient and environmentally benign oxidation method.     

Polyelectrolytes Multilayers to Modulate Cell Adhesion: A Study of the Influence of Film Composition and Polyelectrolyte Interdigitation on the Adhesion of the A549 Cell Line

Polyelectrolyte multilayers (PEMs) with different polycation/polyanion pairs are fabricated by the layer‐by‐layer technique employing synthetic, natural, and both types of polyelectrolytes. The impact of the chemical composition of PEMs on cell adhesion is assessed by studying cell shape, spreading area, focal contacts, and cell proliferation for the A549 cell line. Cells exhibit good adhesion on PEMs containing natural polycations and poly(sodium 4‐styrenesulfonate) (PSS) as polyanion, but limited adhesion is observed on PEMs fabricated from both natural polyelectrolytes. PEMs are then assembled, depositing a block of natural polyelectrolytes on top of a stiffer block with PSS as polyanion. Cell adhesion is enhanced on top of the diblock PEMs compared to purely natural PEMs. This fact could be explained by the interdigitation between polyelectrolytes from the two blocks. Diblock PEM assembly provides a simple means to tune cell adhesion on biocompatible PEMs.

     

Structure and dynamics of dextran in binary mixtures of a good and a bad solvent

The structure and dynamics of the common polysaccharide dextran have been investigated in mixed solvents at two different temperatures using small-angle X-ray scattering (SAXS) and viscosity measurements. More specifically, binary mixtures of a good solvent (water, formamide, dimethylsulfoxide, ethanolamine) and the bad solvent ethanol as the minority component have been considered. The experimentally observed effects on the polymer conformation (intrinsic viscosity, coil radius, and radius of gyration) of the bad solvent addition are discussed in terms of hydrogen bonding density and are correlated with the Hansen solubility parameters and the surface tension of the solvent mixtures. Hydrogen bonding appears to be an important contributor to the solubility of dextran but is not sufficient to capture the dextran coil contraction in the mixtures of good+bad solvents.     

Determination of butamyrate citrate in cough preparations by derivative UV spectrophotometry and high performance liquid chromatography.

Derivative spectrophotometric procedures and an isocratic high performance liquid chromatographic method for the determination of butamyrate citrate (Sinecod, Safarol) in cough syrups have been developed. In the spectrophotometric method, direct measurement of the drug at its absorption maxima is impossible because of interference from different absorbing excipients. Extraction of butamyrate citrate was performed with n-pentane/isopropyl alcohol. Quantification was carried out through the use of 1D derivative at a trough depth of 253.6 nm where interferences from other coextracted compounds are negligible. The extraction efficiency expressed as a % recovery and precision were assessed by fortifying placebo syrup(s) with known amounts of the compound. Also, a reversed phase high performance liquid chromatographic method was used with a mobile phase containing 0.015 M aqueous tetraethylammonium hydrogen sulfate, methanol and acetonitrile 40:30:30 adjusted to pH 3.50 with ammonium hydroxide. The retention behavior of butamyrate citrate as a function of both pH and salt concentration in the aqueous portion of the mobile phase was investigated. Quantification was achieved with UV detection at 258 nm based on peak area. The HPLC method clearly separates the analyte from its degradation products derived after storage of samples under different stress conditions such as acid, alkaline, temperature, oxygen and light. The described methods were successfully applied to the determination of butamyrate citrate in commercial pharmaceutical products and in placebo syrups prepared in the laboratory with good accuracy and precision. The results of the present study show that the use of the derivatives and the HPLC procedure provide precise and sensitive methods for the determination of the compound in pharmaceutical formulations.