Unusual mesomorphic behaviour of new bent‐core mesogens derived from 4‐cyanoresorcinol

New five‐ring bent‐core mesogens derived from 4‐cyanoresorcinol as the central core have been synthesized. The mesophases were assigned by polarizing microscopy, X‐ray diffraction and electro‐optical measurements. It was found that the mesophase behaviour clearly depends on the direction of the carboxyl linking groups between the aromatic rings. If the outer and inner ester linking groups of a wing are in the same direction then nematic phases and, for long chain members, SmC and SmCP_A phases are observed. If the outer and inner linking groups are in opposing directions a dimorphism, SmA–SmAP_A, is observed and the clearing temperatures are increased by about 55?K. It is remarkable that in the SmCP_A phases of the first series, polar switching preferably takes place through a collective rotation of the molecules around their long axes which is accompanied by the inversion of the chirality of the smectic layers.     

Combination of molecular rods and half-discs: transition from lamellar to columnar order in multichain mononuclear ortho-palladated metallomesogens

Novel ortho-palladated phenylpyrimidine-1,3-diketonato organyls with successively increasing numbers of alkyl chains were synthesized and investigated by polarizing optical microscopy and X-ray diffraction. A discontinuous transition from a lamellar to a columnar organization is observed, dependent on the number of chains: molecules with four or five chains from smectic phases (SmA, SmC), the related compound with six chains in the molecule is nonmesomorphic, whereas molecules with seven or eight chains form hexagonal columnar mesophases.     

Poly(L-lactide) (PLLA)/multiwalled carbon nanotube (MWCNT) composite: characterization and biocompatibility evaluation

Much effort has been directed at the fabrication of carbon nanotubes (CNTs)/polymer composites and the characterization of their physical properties. Among them, composites comprising CNTs and the biocompatible polymers are of special interest due to their potential for specific biomedical applications. we report the preparation of the MWCNT/poly(L-lactide) composite and the corresponding spectroscopic (Raman) and the microscopic (SEM, TEM) characterization. The electronic transport, thermal properties, and biocompatibility of this composite have also been investigated. The Raman spectroscopic analysis suggests the interaction between PLLA and MWCNT occurs mainly through the hydrophobic C-CH3 functional groups. The DC conductivity of the composite increases as the MWCNT loading is increased. Such behavior can be described by a percolation mechanism in which a percolation threshold at about 14 wt % MWCNT loading is observed with the maximum end conductivity of 0.1 S x cm(-1). The DSC study of the PLLA/MWCNT composite reveals that the MWCNTs in the composite have the effect of inducing crystallization and plasticizing the polymer matrix. The results from the cell culture test suggest that the presence of MWCNT in the composite inhibits the growth of the fibroblast cells.     

DFT and MD studies on the influence of the orientation of ester linkage groups in banana-shaped mesogens

The influence of the direction of ester linkage groups on the structural and electronic properties of five-ring banana-shaped molecules with a central 1,3-phenylene unit has been investigated including hexyloxy and dodecyloxy terminal chains. DFT studies on the B3LYP/6-31G(d) level were performed on the conformational behaviour of the ten isomers in a systematic way. The one- and two-fold potential energy scans show that the flexibility of the wings significantly depends on the orientation of the carboxyl linkage groups. Moreover, the different directions of the carboxyl groups between the aromatic rings cause remarkable changes on the dipole moment and its components of the molecules. These findings are supported by investigations on the global charge pattern of the molecules calculated from electrostatic potential group charges. The bending angle alpha obtained from a simple model for the five-ring bent-core molecules is a characteristic structural parameter which can be correlated with experimental findings. Calculations on the bent-core molecules in an external electric dipole field related to the direction of their polar axis show remarkable effects with respect to the flexibility and polarity of the isomers. First molecular dynamics simulations on the banana-shaped molecules were carried out within the AMBER 7 package. The trajectories of relevant structural parameters support the findings of the DFT studies. The results concerning the structure and polarity revealed from the DFT and MD calculations of the ten isomers can be correlated with data from dielectric measurements and mesophase properties.     

Analysis of alkyl polyglucosides in industrial products by capillary electrophoresis with pulsed amperometric detection

Pulsed amperometric detection following micellar electrokinetic chromatography has been applied successfully to the direct detection of alkyl polyglucosides (APGs) in shampoos and other industrial products without prior conversion to highly absorbing or fluorescing derivatives. For electrochemical detection, it is necessary to dissociate the hydroxyl groups of the APGs. Thus, we used 0.1 M NaOH in the outlet vial to dissociate the APGs. The main problems associated with the combination of electrochemical detection and capillary electrophoresis are the need to isolate the detector from the electric field used in the capillary electrophoresis separation and the difficulty of aligning the working electrode with the end of the capillary. To overcome these problems, a simple capillary-electrode holder was constructed. This holder automatically aligns the capillary and the electrode in a wall-jet configuration without the aid of micropositioners and facilitates the replacement of electrodes and capillaries without reconstruction of the entire capillary/electrode setup. Special microcylindrical gold electrodes have been produced by sealing 300-μm-diameter gold wire into borosilicate-glass capillaries.     

Large-scale synthesis of high purity “Phos reagent” useful for oligonucleotide therapeutics

A large-scale, cost-effective, and environmentally clean synthesis of high purity 2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite (Phos reagent) has been accomplished on a commercial scale. Treatment of PCl₃ with diisopropylamine followed by 3-hydroxylpropionitrile furnished the Phos reagent in excellent yield. The ³¹P NMR of the Phos reagent prepared at large-scale show consistent purities >99% when several key factors are controlled. These controlling factors include sourcing high purity key raw materials, identification and elimination of critical impurities, stability and storage of Phos reagent.     

SmA-SmC-B2 polymorphism in an achiral cyano substituted banana-shaped mesogen

A new achiral five-ring banana-shaped mesogen is presented which has a cyano substituent in the 4-position of the central core. Microscopical, X-ray, dielectric and electro-optical investigations give evidence for the unusual phase sequence B₂, SmC, SmA. The B₂ phase shows an antiferroelectric switching behaviour; the spontaneous polarization was found to be 330 nCcm^-2.