Synthesis and characterization of liquid crystalline polyacrylates and polymethacrylates containing benzyl ether and diphenyl ethane based mesogens

The synthesis and radical polymerization of a novel series of acrylates and methacrylates containing p-cyanophenyl-p-hydroxybenzyl ether, p-methoxyphenyl-p-hydroxybenzyl ether, and 1-(p-cyanophenyl)-2-(p-hydroxyphenyl) ethane groups attached to the polymerizable group through aliphatic spacers containing 11 and 6 methylenic units is described. The resulting polymers were characterized by differential scanning calorimetry and optical polarization microscopy. All polymers exhibited enantiotropic mesomorphism. Low molar mass compounds based on benzyl ether or diphenyl ethane units exhibit only monotropic or virtual transitions. This demonstrates that the “polymer effect” stabilizes mesophases obtained from “mesogenic units” which do not contain rigid interconnecting groups.     

Isomorphism within the hexagonal columnar mesophase of molecular and macromolecular self- and co-assembled columns containing tapered groups

The phase behaviour of binary mixtures of self-assembled tapering molecules based on monoesters of oligooxyethylene glycol and 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoic acid, their corresponding polymethacrylates, and of 4'-methyl (benzo-15-crown-5)-3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate within their hexagonal columnar mesophase (Φ_h) is described. The binary blends between molecular tapers co-assemble into a single supramolecular column resulting in isomorphism within their Φ_h mesophase over the entire range of composition. The binary blends between polymethacrylates containing tapered side groups co-assemble into a single Φ_h phase only when the columns of the parent polymers are of similar diameters. This results in binary mixtures which are isomorphic within the Φ_h mesophase over the entire composition range. When the diameters of the columns formed by the parent polymers are dissimilar, isomorphic mixtures are obtained only over a narrow range of composition. Binary mixtures between molecular tapers and macromolecular systems containing tapered side groups co-assemble into a single column to the extent that intercalation of the molecular taper, within the column formed by the macromolecular system containing tapered side groups, is permissible. In all systems increased intracolumnar interactions can be induced by complexation of CF₃SO₃Li by the oligooxyethylenic receptors leading to isomorphism in otherwise non-isomorphic mixtures. Ternary mixtures between molecular tapers with non-specific oligooxyethylenic receptors and specific crown ether receptors and CF₃SO₃ Na as the third component are non-isomorphic within their Φ_h phase due to preferential complexation of the alkali metal cation by the column of the crown ether containing the molecular taper. This results in two columns of dissimilar diameters, which are isomorphic in the Φ_h phase only within a limited range of composition.     

The amino terminus of cGMP-dependent protein kinase Iβ increases the dynamics of the protein's cGMP-binding pockets

The type I cGMP-dependent protein kinases play critical roles in regulating vascular tone, platelet activation and synaptic plasticity. PKG I α and PKG Iβ differ in their first ~100 amino acids giving each isoform unique dimerization and autoinhibitory domains with identical cGMP-binding pockets and catalytic domains. The N-terminal leucine zipper and autoinhibitory domains have been shown to mediate isoform specific affinity for cGMP. PKG Iα has a >10 fold higher affinity for cGMP than PKG Iβ, and PKG Iβ that is missing its leucine zipper has a three-fold decreased affinity for cGMP. The exact mechanism through which the N-terminus of PKG alters cGMP-affinity is unknown. In the present study, we have used deuterium exchange mass spectrometry to study how PKG Iβ's N-terminus affects the conformation and dynamics of its cGMP-binding pockets. We found that the N-terminus increases the rate of deuterium exchange throughout the cGMP-binding domain. Our results suggest that the N-terminus shifts the conformational dynamics of the binding pockets, leading to an "open" conformation that has an increased affinity for cGMP.     

Synthesis and Characterization of Polymethacrylates,Polyacrylates, and Poly(Methylsiloxane)S Containing 4-[S(-)-2-Methyl-1-Butoxy]-4′-(ω-Alkanyl-1-OXY)-α-Methylstilbene Side Groups

Abstract

The synthesis and characterization of polymethacrylates, polyacrylates, and poly(methylsiloxane)s containing 4-[S(-)-2-methyl-1-butoxy]-4′-(ω-alkanyl-1-oxy)-α-methylstilbene side groups with ω-alkanyl from 11-undecanyl to 2-ethyl are presented. According to both differential scanning calorimetry and thermal optical polarized microscopy analyses, the poly(methylsiloxane)s containing 1-octyl and 1-hexyl as ω-alkanyl groups exhibit enantiotropic S _A and S _C* mesophases. All other polymers display only an enantiotropic S _A mesophase.     

Molecular Engineering of Liquid Crystal Polymers by Living Polymerization. VIII. Influence of Molecular Weight on the Phase Behavior of Poly {ω-[(4-Cyano-4′-biphenyl)-oxy]alkyl Vinyl Ether}s with Ethyl,Propyl, and Butyl Alkyl Groups

The synthesis and living cationic polymerization of 2-[4-cyano-4′-biphenyl)oxy]ethyl vinyl ether (6–2), 3-[4-cyano-4′-biphenyl)oxy]-propyl vinyl ether (6-3), and 4-[4-cyano-4′-biphenyl)oxy]butyl vinyl ether (6-4) are described. The mesomorphic behaviors of poly(6–2), poly(6-3), and poly(6-4) with different degrees of polymerization and narrow molecular weight distributions were compared to those of 6–2, 6–3, and 6–4 and of 2-[(4-cyano-4′-biphenyl)oxy]ethyl ethyl ether (8–2), 3-[(4-cyano-4′-biphenyl)oxy]propyl ethyl ether (8–3), and 4-[4-cyano-4′-biphenyl)oxy]butyl ethyl ether (8–4) which are model compounds of the monomeric structural units of poly(6–2), poly(6–3), and poly(6–4). In the first heating scan, all three polymers exhibit an x (unidentified) mesophase which overlaps the glass transition temperature, and an enantiotropic nematic mesophase. In the second and subsequent heating and cooling scans, poly(6–3) and poly(6–4) display only the enantiotropic nematic mesophase. Both in the first and subsequent scans, only poly(6–2) with degrees of polymerization lower than 4 exhibits an enantiotropic nematic mesophase.     

Enantioselective decarboxylative alkylation reactions: catalyst development, substrate scope, and mechanistic studies

α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.     

Crystallization study of sol-gel un-doped and Pd-doped TiO2 materials

Sol-gel nanostructured titania materials have been reported to have applications in areas ranging from optics via solar energy to gas sensors. In order to enhance the photocatalytic activity, there are many studies regarding the doping of titanium dioxide (TiO₂) material with either non-metals (S, C, N, P) or metals (Ag, Pt, Nd, Fe). The present work has studied some un-doped and Pd-doped sol-gel TiO₂ materials (films and gels), with various surface morphologies and structures, obtained by simultaneous gelation of both precursors Ti(OEt)₄ and Pd(acac)₂. Their structural evaluation and crystallization behavior with thermal treatment were followed by DTA/TG analysis, infrared (IR) spectroscopy, Fourier transform infrared (FTIR), spectroellipsometry (SE), X-ray diffraction (XRD) and atomic force microscope (AFM). The influence of Pd on TiO₂ crystallization for both supported and un-supported materials was studied (lattice parameters, crystallite sizes, internal microstrains). The changes in the optical properties of the TiO₂-based vitreous materials were correlated with the changes of the structure. The hydrophilic properties of the films were also connected with their structure, composition and surface morphology.