Constrained stability for biaxial nematic phases

We study the invariance properties of the molecular Hamiltonian interaction put forward by Straley to describe biaxial nematic phases. We show that the reduction to two out of four scalar order parameters, which was accidently remarked upon in the literature, is indeed a rigorous consequence of the Hamiltonian invariance for specific values of the interaction parameters. The stability analysis of the mean-field free energy in the reduction classes for the order parameters reveals a sequence of Landau triple points.     

Optical Storage in Side-Chain Liquid Crystalline Polyesters

Long-term, high resolution holographic storage has been achieved in side-chain liquid crystalline polyesters with high diffraction efficiency. The information can be completely erased by heating the film to about 80°C. The modular architecture of the polyesters permits a varition in the length of the main- and side-chains and the substituents of the azo chromophore. Each of these has a profound influence on the storage properties of the polyesters. In this article, we examine the influence of the length of the side-chains, the probe-beam-polarization dependence of the observed signal on the interface and the crystalline vs. amorphous nature of the films for optical storage.     

Phosphorylated mesoporous carbon as a solid acid catalyst

Mesoporous carbon catalyst supports are attractive due to their wide chemical stability while potentially increasing mass-transport through and providing a path for larger molecules to access catalytic sites. Herein we report the synthesis of a phosphorylated mesoporous carbon solid-acid catalyst characterized by NH(3)-TPD and isopropanol dehydration.     

Synthesis of Anti-Inflammatory α-Arylalkanoic Acids by 1,2-Aryl Shift. New Synthetic Methods (42)

α-Arylalkanoic acids have acquired importance as anti-inflammatory agents and are now in great demand on the pharmaceutical front. Hence, the need has arisen for new and improved, economical synthetic procedures suitable for their preparation and manufacture on an industrial scale. For many years the synthetic approach to this class of compounds was restricted to the Willgerodt and Darzen reactions. More recently, several methods have been developed which are based on the 1,2-aryl shift in acetals of α-functionalized alkyl aryl ketones. This new approach starts from the oxythallation of alkyl aryl ketones first described by Taylor and McKillop in 1971. Asymmetric syntheses of some important arylakanoic acids have also been developed on this basis. The highly toxic thallium salts may be replaced, inter alia, by catalytically effective metal salts.     

On the reaction between coumarins and hydroxylamine

The Posner reaction between coumarin and hydroxylamine was studied and extended to several substituted coumarins. Isolation of some significant reaction intermediates permitted rationalization of a possible reaction pathway.     

Size and shape control in the overgrowth of gold nanorods

We report on a new sustainable approach to manipulate the optical behaviour and geometrical properties of gold nanorods in aqueous solutions by fine control of their overgrowth. In our approach, the overgrowth is realized by modulation of the reduction of the gold ions which are left as Au¹⁺ after the primary step of the synthesis (typically as much as ~80% of the gold ions available in the growth solution). The progress of the reduction requires the gradual addition of ascorbic acid, which transforms the Au¹⁺ into Au⁰ and may be performed in the original growth solution with no need for any further manipulation. By control of the total amount and rate of administration of the ascorbic acid, we prove the possibility to realize a systematic modulation of the average lengths, diameters, shapes (rod or dog-bone like), and light extinction of the nanoparticles. A slow overgrowth leads to a gradual enlargement of the lengths and diameters at almost constant shape. In contrast, a faster overgrowth results into a more complex modification of the overall shape of the gold nanorods.     

Functionalisation of carbon nanohorns

The functionalisation of single wall carbon nanohorns via 1,3-dipolar cycloaddition has been achieved, and the products have been characterised by spectroscopy, microscopy and thermogravimetry.