Bay‐Annulated Perylene Tetraesters: A New Class of Discotic Liquid Crystals

Selenium‐annulated perylene tetraesters that stabilize the hexagonal columnar phase have been synthesized and characterized, and their thermal and photophysical behavior has been determined. The mesophase range decreased with an increase in chain length. A comparative account of the structure–property relationships of this series of compounds with respect to parent perylene tetraesters, N‐ and S‐annulated perylene tetraesters, in terms of their thermal, photophysical and electrochemical behavior is provided. The bay‐annulation of perylene tetraesters is a good option to modify the thermal and photophysical properties of perylene derivatives and it can provide a new avenue for the synthesis of several technologically important self‐assembling perylene derivatives.     

Effect of core group substituents on the monomer mesophase,photocuring, and film viscoelastic properties of mesogenic diacrylates

In this paper, the influence of molecular structure variations on the mesophase behavior, photocurability, and film properties of polymerizable mesogenic diacrylates is reported. The effect of methoxy or chloro substituent on the mesophase behavior of the monomers, present at the 2‐position of the phenylene core, in comparison to the unsubstituted core, has been studied using thermal and photo‐DSC techniques. These monomers were used in combination with a chiral dopant to form cholesteric mesophases, which was subsequently crosslinked through photopolymerization. Optical microscopy and polarized optical microscopy (POM) were used to study the morphology of monomers as well as the photopolymerized films. Optical images show the influence of chiral dopant on the texture present in the films, both before and after the crosslinking. POM images show the mesophase present in the monomers and the free films. Evaluation of viscoelastic properties of the photocured films demonstrates the influence of mesogenic core substituents on the network transition temperature, modulus, and damping characteristics. Copyright © 2008 John Wiley & Sons, Ltd.     

Multivalent Sialosides: A Tool to Explore the Role of Sialic Acids in Biological Processes

Sialic acids (Sias) are fascinating nine‐carbon monosaccharides that are primarily found on the terminus of the oligosaccharide chains of glycoproteins and glycolipids on cell surfaces. These Sias undergo a variety of structural modifications at their hydroxy and amine positions, thereby resulting in structural diversity and, hence, coordinating a variety of biological processes. However, deciphering the structural functions of such interactions is highly challenging, because the monovalent binding of Sias is extremely weak. Over the last decade, several multivalent Sia ligands have been synthesized to modulate their binding affinity with proteins/lectins. In this Minireview, we highlight recent developments in the synthesis of multivalent Sia probes and their potential applications. We will discuss four key multivalent families, that is, polymers, dendrimers, liposomes, and nanoparticles, and will emphasize the major parameters that are essential for the specific interactions of these molecules with proteins in biological systems.     

Versatile Aerogel Fabrication by Freezing and Subsequent Freeze‐Drying of Colloidal Nanoparticle Solutions

A versatile method to fabricate self‐supported aerogels of nanoparticle (NP) building blocks is presented. This approach is based on freezing colloidal NPs and subsequent freeze drying. This means that the colloidal NPs are directly transferred into dry aerogel‐like monolithic superstructures without previous lyogelation as would be the case for conventional aerogel and cryogel fabrication methods. The assembly process, based on a physical concept, is highly versatile: cryogelation is applicable for noble metal, metal oxide, and semiconductor NPs, and no impact of the surface chemistry or NP shape on the resulting morphology is observed. Under optimized conditions the shape and volume of the liquid equal those of the resulting aerogels. Also, we show that thin and homogeneous films of the material can be obtained. Furthermore, the physical properties of the aerogels are discussed.     

Polystyrene-Supported Aminocatalyst Derived from Diarylprolinol for Asymmetric α-Amination of Aldehydes

A new class of polystyrene-supported aminocatalysts with a triazole linker from diphenyl prolinol were developed. Their catalytic activity was tested in the asymmetric α-amination of aldehydes. The substrate scope of this catalysis was studied under the optimized reaction conditions. The reusability of the polystyrene-supported aminocatalyst was demonstrated up to four cycles. Based on the reaction results, a reaction mechanism was proposed for the asymmetric α-amination of aldehydes.     

Formation and characterization of microemulsions containing polymeric silicone

We have prepared microemulsions consisting of water/[40 wt % polyoxyethylene (20 mol) glycerin isostearate (abbreviated as POE-GIS) + 60 wt % random copolymer of polyoxyethylene (POE, 38 mol)/polyoxypropylene (POP, 10 mol) pentaerythritol tetramethyl ether {abbreviated as PEPTME (38/10)}]/[polyoxyethylene (POE, 19 mol)/polyoxypropylene (POP, 19 mol) polydimethylsiloxane copolymer (abbreviated as POE/POP-PDMS)] and water/[40 wt % POE-GIS + 60 wt % PEPTME (38/10)]/[95 wt % POE/POP-PDMS + 5 wt % oleic acid (abbreviated as OA)] systems and characterized them with optical observation, rheometry, and freeze-fracture transmission electron microscopy (FF-TEM) images. Bicontinuous and droplet-type O/W (oil-in-water) microemulsions are formed depending on the volume fraction of water. The bicontinuous structure observed in the oil-rich region, upon successive dilution with water, is transformed into a droplet-type microemulsion without phase separation.The prepared droplet-type microemulsion containing polymeric silicone and random copolymer PEPTME (38/10) as a cosurfactant in the water-rich region has potential applications in cosmetics.