Asymmetric polymerization of the mixture of TrMA and MMA initiated by chiral complexes

A mixture of triphenylmethyl methacrylate (TrMA) and methyl methacrylate (MMA) was polymerized with chiral anionic initiator, such as fluorenyl lithium-(-)-sparteine [FlLi-(-)-Sp] and fluorenyl lithium-(+)-2S,3S-dimethoxy-1,4-bis(dimethylamino) butane [FlLi-(+)-DDB] in toluene at -78 degrees C. The results show that after the stable helix formed, when FlLi-(+)-DDB was used as the initiator, TrMA and MMA could be copolymerized, whereas when FlLi-(-)-Sp was used, the two monomers tended to be selectively polymerized into two polymers. This phenomenon has been explained by the existence of helix-selective polymerization. (C) 1997 John Wiley & Sons, Inc.

Synthesis of a series of chiral copolymers with azo groups and investigations of reversible liquid crystalline alignment induced by the LB films of these materials

A series of liquid crystalline copolymers, poly{2-hydroxyethyl methacrylate}-co-{6-[4-(S-2-methyl-1-butyloxycarbonylphenylazo)phenoxy]hexyl methacrylate} with an azobenzene moiety as photoreactive mesogenic unit, was prepared and investigated by using DSC, polarized optical microscopy and X-ray diffraction. The results show that these polymers exhibit smectic phases. Z-type Langmuir-Blodgett films of these copolymers were successfully deposited onto calcium fluoride and quartz. Reversible homeotropic and planar liquid crystal alignments were induced by using the photochromism of the LB films of one of the copolymers containing 20.6 mol % of the azo unit.

Study on computer perception of topological symmetry

A new algorithm for computer perception of topological symmetry is proposed. A node library containing various kinds of nodes is built, and the index number of the library is used as initial atom class identifier (CI) to discriminate the different types of non-hydrogen atoms. The path index (PI) and ringindex (RI) are calculated from the CI, and the global topological enviroment is defined as the sum of PIs and RIs. The topological symmetry can be detected by the iterative calculation of the global topological enviroment.

Synthesis of a new series of chiral Schiff's bases and their copper complexes

A new series of chiral Schiff's bases containing 2-hydroxybenzilideneaniline moieties and their copper complexes were synthesized and studied by differential scanning calorimetry, polarized optical microscopy, X-ray diffraction and EPR measurement. The results show that most of the Schiff's bases and only two of the copper complexes exhibited chiral smectic liquid crystal phases.

SYNTHESIS AND VARIABLE-TEMPERATURE FTIR STUDY OF 5 CHIRAL LIQUID-CRYSTALS INDUCED BY INTERMOLECULAR HYDROGEN-BONDING

Five new chiral liquid crystal systems induced by intermolecular hydrogen bonding between 4-[(S)-2-chloro-3-methyl]butyroyloxy-4'-stilbazole (MBSB, proton acceptor) and 4-alkoxybenzoic acids (nBA, proton donors) were prepared. Their liquid crystalline properties were investigated by DSC and polarized optical microscopy. Chiral nematic and chiral smectic phases were observed, and the thermal stability of one complex was studied through temperature dependent infrared spectroscopy.

SYNTHESIS AND PHASE-BEHAVIOR STUDIES OF 2 NEW CHIRAL LIQUID-CRYSTALS OF SCHIFF-BASE - THE INFLUENCE OF INTRAMOLECULAR HYDROGEN-BOND ON THE PHASE-BEHAVIOR

Two new chiral liquid crystals of schiff-base type have been synthesized. This series of compounds contain a-chloro acidic ester chain prepared from commercially available L-valine. Both of the compounds exhibit tilted smectic phases; their phase transitions were studied using DSC and polarized optical microscopy; the influence of intramolecular hydrogen bonds on the phase behavior was studied as well.

SYNTHESIS OF SOME CHIRAL LIQUID-CRYSTALS AND STUDY OF THE EFFECT OF INTRAMOLECULAR HYDROGEN-BONDING ON THE PHASE-BEHAVIOR

The synthesis of three new series of chiral Schiffs bases containing benzilideneaniline and 2-hydroxybenzilideneaniline moieties as mesogenic cores is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements were used to study the phase transition temperatures and behaviour. The results reveal that most of these materials show chiral smectic mesomorphism.

STRUCTURE AND SITE-SYMMETRY INVESTIGATION ON THE HEXAGONAL KCAY(PO4)(2)

A new double phosphate, KCaY(PO4)(2), isostructural with hexagonal LaPO4, is reported. It crystallizes in the hexagonal system with a = 0.6903 nm and c = 0.6331 nm. Its vibrational spectra, IR and Raman spectra showed that the site symmetry of the PO4 anion slightly deviated from D-2 toward C-2.

SYNTHESIS OF A NEW CHIRAL LIQUID-CRYSTAL WITH SCHIFF-BASE GROUP AND INVESTIGATION OF TEMPERATURE-DEPENDING FTIR SPECTRA

A new chiral liquid crystal with Schiff base group has been prepared, The structure of liquid crystal was confirmed by elementary analyses and H-1 NMR. Its phase transition was investigated by polarized optical microscope, DSC and temperature-depending FTIR spectra. The results showed that the chiral Schiff base showed monotropic phases behavior in certain temperature range, the phase sequence is I-N-*-S-B-S-G-K on the cooling sequence.

ALGORITHM FOR COMPUTER PERCEPTION OF TOPOLOGICAL SYMMETRY

For the exhaustive and irredundant generation of candidate structures in ESESOC (Expert System for the Elucidation of the Structures of Organic Compounds), a new algorithm for computer perception of topological equivalence classes of the nodes (non-hydrog

ASYMMETRIC ALKYLATION MEDIATED BY CHIRAL PHASE-TRANSFER CATALYSTS

Seven chiral phase-transfer catalysts, among which three have not been reported so far, have been prepared and applied to the asymmetric alkylation of alpha-isopropyl benzyl cyanide and alpha-isopropyl-p-chlorobenzyl cyanide. The result showed that short reaction time, low temperature, high catalyst concentration and non-polar solvent would improve the optical yield. The influence of structure of the catalyst on the asymmetric reaction was preliminarily studied. The optical purity of the products were evaluated by gas chromatography with a chiral column.

Breaking seasonal limitation: year-round sporogenesis in the brown alga Laminaria saccharina by blocking the transport of putative sporulation inhibitors

Year-round induction of sporogenesis of Laminaria saccharina was performed by mechanically blocking the transport of the putative sporulation inhibitors produced by the blade meristem and culturing the plants in constant short days. Sporogenesis was successfully induced by removal of the blade meristem, either by cultivating distal blade fragments or by performing a transverse cut in the frond. The earliest sorus formation after artificial induction was 10 days. The age of the sporophytes used for induction was 6-11 months or 2 years in tank-grown or field-collected sporophytes, respectively. Zoospores were successfully released in all cases. Thus, by year-round artificial induction of sporogenesis, (1) sporeling production of L. saccharina and thereafter sporophyte cultivation could be achieved without seasonal limitation, and (2) the life cycle of L. saccharina (from spore to spore) could be completed within 8 months under controlled conditions. (C) 2004 Elsevier B.V. All rights reserved.

Simulation of the ocean surface mixed layer under the wave breaking

A one-dimensional mixed-layer model, including a Mellor-Yamada level 2.5 turbulence closure scheme, was implemented to investigate the dynamical and thermal structures of the ocean surface mixed layer in the northern South China Sea. The turbulent kinetic energy released through wave breaking was incorporated into the model as a source of energy at the ocean surface, and the influence of the breaking waves on the mixed layer was studied. The numerical simulations show that the simulated SST is overestimated in summer without the breaking waves. However, the cooler SST is simulated when the effect of the breaking waves is considered, the corresponding discrepancy with the observed data decreases up to 20% and the MLD calculated averagely deepens 3.8 m. Owing to the wave-enhanced turbulence mixing in the summertime, the stratification at the bottom of the mixed layer was modified and the temperature gradient spread throughout the whole thermocline compared with the concentrated distribution without wave breaking.

A microwave emissivity model of sea surface under wave breaking

With the effective medium approximation theory of composites, a remedial model is proposed for estimating the microwave emissivity of sea surface under wave breaking driven by strong wind on the basis of an empirical model given by Pandey and Kakar. In our model, the effects of the shapes of seawater droplets and the thickness of whitecap layer (i.e. a composite layer of air and sea water droplets) over the sea surface on the microwave emissivity are investigated by calculating the effective dielectric constant of whitecaps layer. The wind speed is included in our model, and the responses of water droplets shapes, such as sphere and ellipsoid, to the emissivity are also discussed at different microwave frequencies. The model is in good agreement with the experimental data of microwave emissivity of sea surface at microwave frequencies of 6.6, 10.7 and 37GHz.