Cholesterol-based dimeric liquid crystals: synthesis,mesomorphic behaviour of frustrated phases and DFT study

Chiral unsymmetrical dimeric liquid crystals consisting of a cholesterol moiety as chiral entity and a substituted salicylidene imine core (with the substituent being butyl or fluoro or chloro group) interconnected through an even methylene spacer have been synthesised and their mesomorphic properties are characterised. All the dimers exhibit enantiotropic mesophases. The butyl homologue exhibited N* phase only, the fluoro- and chloro-substituted compound exhibited frustrated blue phases (BPs), N* phase and SmC* or twisted grain boundary (TGB) phases. The occurrence of a fluid frustrated phase, the BP, in particular, observed in compounds with a polar moiety and bent optimised conformation by density functional theory (DFT) study, indicates the importance of polar structures and bent shape of the compounds. Theoretical calculation was performed in order to study the optimised conformation, polarity and electron density distribution of the synthesised cholesterol derivatives using DFT. Time-dependent density functional theory (TD-DFT) calculation also had been carried out to investigate the absorption spectra and HOMO–LUMO energies. The experimental and theoretical absorption spectra are also presented.     

Nematic Phase of Polar Unsymmetrical Bent-Core Molecules

In liquid crystalline systems, the presence of polar groups at lateral or terminal positions is fundamentally and technologically important. Bent-core nematics composed of polar molecules with short rigid cores usually exhibit highly disordered mesomorphism with some ordered clusters that favourably nucleate within. Herein, we have systematically designed and synthesized two new series of highly polar bent-core compounds comprised of two unsymmetrical wings, highly electronegative −CN and −NO₂ groups at one end, and flexible alkyl chains at the other end. All the compounds showed a wide range of nematic phases composed of cybotactic clusters of smectic-type (N_cyb). The birefringent microscopic textures of the nematic phase were accompanied by dark regions. Further, the cybotactic clustering in the nematic phase was characterized via temperature-dependent XRD studies and dielectric spectroscopy. Besides, the birefringence measurements demonstrated the ordering of the molecules in the cybotactic clusters upon lowering the temperature. DFT calculations illustrated the favourable antiparallel arrangement of these polar bent-core molecules as it minimizes the large net dipole moment of the system.     

Chemical and structural characterization of α-N-acetylgalactosaminidase I and II from starfish, <Emphasis Type="Italic">asterina amurensis</Emphasis>

Background

The marine invertebrate starfish was found to contain a novel α-N-acetylgalactosaminidase, α-GalNAcase II, which catalyzes removal of terminal α-N-acetylgalactosamine (α-GalNAc), in addition to a typical α-N-acetylgalactosaminidase, α-GalNAcase I, which catalyzes removal of terminal α-N-acetylgalactosamine (α-GalNAc) and, to a lesser extent, galactose. The interrelationship between α-GalNAcase I and α-GalNAcase II and the molecular basis of their differences in substrate specificity remain unknown.

Results

Chemical and structural comparisons between α-GalNAcase I and II using immunostaining, N-terminal amino acid sequencing and peptide analysis showed high homology to each other and also to other glycoside hydrolase family (GHF) 27 members. The amino acid sequence of peptides showed conserved residues at the active site as seen in typical α-GalNAcase. Some substitutions of conserved amino acid residues were found in α-GalNAcase II that were located near catalytic site. Among them G171 and A173, in place of C171 and W173, respectively in α-GalNAcase were identified to be responsible for lacking intrinsic α-galactosidase activity of α-GalNAcase II. Chemical modifications supported the presence of serine, aspartate and tryptophan as active site residues. Two tryptophan residues (W16 and W173) were involved in α-galactosidase activity, and one (W16) of them was involved in α-GalNAcase activity.

Conclusions

The results suggested that α-GalNAcase I and II are closely related with respect to primary and higher order structure and that their structural differences are responsible for difference in substrate specificities.

     

TTF-TCNQ complex based printed biosensor for long-term operation

A printed amperometric glucose sensor based on glucose oxidase adsorbed on crystals of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) is described. The sensitivity and the stability of the sensor are affected by the binder and solvent used for the preparation of the GOD.TTF-TCNQ paste. The sensors are continuously used in a flow injection analysis (FIA) system under continuous polarization at 0.15 V (vs Ag/AgCl) at 37°C. The developed sensors exhibit a large response current, an extended linear range and oxygen independence. The sensors can be used for more than 3 months. The GOD.TTF-TCNQ paste is suitable for the preparation of planar sensor by screen printing method.     

Layer-layer assembly for extremely stable glucose sensors

A novel fabrication of an amperometric glucose sensor by layer after layer approach is described. The sensor electrode is fabricated by arranging a layer of Pt black, a layer of glucose oxidase (GOD) and a layer of stabilizer gelatin on a shapable electro-conductive (SEC) film surface. Finally, the dried layered-assembly is cross-linked by exposing to a diluted glutaraldehyde solution. The performance of the developed sensor is evaluated by a FIA system at 37°C and under a continuous polarization at 0.4 V (vs. Ag/AgCl). The sensitivity of the sensor was dependent on the amount of GOD loaded. The highest sensitivity (3.6 μA/mM cm⁻²) of the sensor was obtained at a GOD loading of 160 μg/cm², and the linear dynamic range was extended to 80 mM level when the sensor was covered with a polycarbonate membrane. The sensor shows an extremely stable response for several weeks and a storage stability of over 2 years.     

ChemInform Abstract: Onium Ions. Part 55. Calculational Study of the Protonation of BXH2 and BX2H (X: F and Cl). Structures of BXH3+ and BX2H2+ and Their Dihydrogen Complexes BXH5+ and BX2H4+.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Onium Ions. Part 54. N2+6 and N2+4 Dications and Their N12 and N10 Azido Derivatives. DFT/GIAO‐MP2 Theoretical Studies.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Chemistry in Superacids. Part 40. Protonated Borane—Lewis Base Complexes BH4X+ (X: NH3, PH3, H2O,H2S,CO).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Chemistry in Superacids. Part 48. B—H Bond Protonation in Mono‐ and Diprotonated Borane Complexes H3BX (X: N2H4, NH2OH,and H2O2) Involving Hypercoordinate Boron

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.