Asymmetric synthesis polymerization of meso oxiranes and thiiranes

The asymmetric synthesis polymerization or “enantiogenic” polymerization of some meso oxiranes, cis-dimethyloxirane (cis-DMO) and cyclohexene oxide (CHO), and thiiranes, cis-dimethylthiirane (cis-DMT) and cyclohexene sulfide (CHS), initiated with different chiral systems was examined. Strong differences in behaviour were observed between oxiranes and thiiranes depending on the initiator used. The initiators based on ZnEt₂ or CdMe₂ and a chiral diol give optically active polymers from meso thiiranes but fail to induce an asymmetric polymer synthesis with meso oxiranes. A new chiral initiator based on ZnEt₂ and (1S,2R)-ephedrine allowed us to prepare optically active poly CHOs, which can be fractionated into fractions exhibiting opposite optical activities. © 1992 Wiley-Liss, Inc.     

Chiral separation of barbiturates and hydantoins by reversed-phase high-performance liquid chromatography using a 25 or 50 mm short ODS cartridge column via β-cyclodextrin inclusion complexes

A high-performance liquid chromatographic method on a 25 or 50 mm short ODS cartridge column has been developed for the resolution of the enantiomers of some optically active barbiturates and hydantoins in human serum. β-Cyclodextrin was used in the mobile phase. This method also seems to be an easy and effective way to test whether β-cyclodextrin would be a useful chiral discriminator for a particular racemate.     

Synthesis of optically active diols using an efficient polymer bound cinchona alkaloid derivative

A new insoluble polymer containing a Cinchona alkaloid derivative has been synthesized and used as chiral ligand in the heterogeneous enantioselective dihydroxylation of olefins. It is shown that the enantioselectivity of the optically active diols obtained from both aliphatic and aromatic substrates is always comparable to that observed in the homogeneous phase under the same reaction conditions. A method for evaluating the enantiomeric excesses of the optically active products is also described. © 1995 Wiley-Liss, Inc.     

Kinetic structures in multi-phase liquid-crystalline composite materials

A mesoscopic kinetic model for phase separation in the presence of liquid crystalline order has been formulated and solved using high performance numerical methods. The thermodynamic phase diagram on temperature–polymer concentration plane indicates the presence of coexistence regions between isotropic and liquid crystalline phases. These regions are partitioned by the phase-separation spinodal and the phase-ordering spinodal. We characterize the morphologies following temperature quenches in the phase diagram. The scenario is completely different from isotropic mixing since the continuous phase exhibits liquid crystalline ordering. Microdomains of the dispersed phase induce long- and short-range forces affecting the kinetics of the phase separation and the emerging structures. Presence of topological defects and elastic distortions around the microdomains formed during the phase separation dominate the morphology. The free energy of the system establishes dynamics and correlations of the morphological structures.     

Synthesis, mesomorphism and luminescence properties of palladium(II) and platinum(II) complexes with dimeric Schiff base liquid crystals

A series of ortho-metallated Pd and Pt complexes containing dimeric liquid crystals Schiff base as cyclometallated ligands and N-benzoyl thiourea derivatives as co-ligands were prepared and investigated for their liquid crystalline properties. Their structures were assigned based on elemental analysis, IR and ¹H NMR spectroscopy while the mesogenic properties were investigated by DSC and polarising optical microscopy. The complexes show either monotropic or enantiotropic transitions with nematic and smectic A phases being displayed, with the mesomorphic behaviour strongly related to the type of N-benzoyl thiourea as well as the metal center used. The structure of a palladium(II) complex has been solved by X-ray diffraction.The platinum(II) complexes show photoluminescence properties both in solution and in solid state at room temperature, with the emission band centered around 600 nm. These are the first examples of metallomesogens based on Schiff base cyclometallated ligands that display luminescence properties.     

Spontaneous Generation of Chirality in Simple Diaryl Ethers

We studied the spontaneous formation of chiral crystals of four diaryl ethers, 3‐phenoxybenzaldehyde, 1 ; 1,3‐dimethyl‐2‐phenoxybenzene, 2 ; di(4‐aminophenyl) ether, 3 ; and di(p‐tolyl) ether, 4 . Compounds 1 , 3 , and 4 form conformationally chiral molecules in the solid state, while the chirality of 2 arises from the formation of supramolecular helices. Compound 1 is a liquid at ambient temperature, but 2 , 3 , 4 are crystalline, and solid‐state CD‐spectroscopy showed that they could be obtained as optically active bulk samples. It should be noted that the optical activity arise upon crystallization, and no optically active precursors were used. Indeed, even commercial samples of 3 and 4 were found to be optically active, giving evidence for the ease at which total spontaneous resolution may occur in certain systems. Chirality 27:425‐429, 2015. © 2015 Wiley Periodicals, Inc.     

A calorimetry and deuterium NMR study of mixed model membranes of 1-palmitoyl-2-oleylphosphatidylcholine and saturated phosphatidylcholines

Binary phase diagrams have been constructed from differential scanning calorimetry (DSC) data for the systems 1-palmitoyl-2-oleylphosphatidylcholine (POPC)/dimyristoylphosphatidylcholine (DMPC), POPC/dipalmitoylphosphatidylcholine (DPPC) and POPC/distearoylphosphatidylcholine (DSPC). Mixtures of POPC with DMPC exhibit complete miscibility in the gel and liquid crystalline states. Mixtures of POPC with DPPC or with DSPC exhibit gel phase immiscibility over the composition range 0-75% DPPC (or DSPC). These results, when taken together with previous studies of mixtures of phosphatidylcholines, are consistent with the hypothesis that PCs whose order-disorder transition temperatures (Tm values) differ by less than 33 deg. C exhibit gel state miscibility. Those whose Tm values differ by more than 33 deg. C exhibit gel state immiscibility. 2H-NMR spectroscopy has been used to further study mixed model membranes composed of POPC and DPPC, in which either lipid has been labeled with deuterium in the 2-, 10- or 16-position of the palmitoyl chain(s) or in the N-methyls of the choline head group. POPC/DPPC mixtures in the liquid crystalline state are intermediate in order between pure POPC and DPPC at the same temperature. The POPC palmitoyl chain is always more disordered than the palmitoyl chains of DPPC in liquid crystalline POPC/DPPC mixtures. This is attributed to the fact that a POPC palmitoyl chain is constrained by direct bonding to have at least one oleyl chain among its nearest neighbors, while a DPPC palmitoyl chain must have at least one neighboring palmitoyl chain. When liquid crystalline POPC, DPPC and POPC/DPPC mixtures are compared at a reduced temperature (relative to the acyl chain order-disorder transition), POPC/DPPC mixtures are more disordered than predicted from the behavior of the pure components, in agreement with enthalpy data derived from DSC studies. Within the temperature range of the broad phase transition of 1:1 POPC/DPPC, a superposition of gel and liquid crystalline spectra is observed for 1:1 POPC/[2H]DPPC, while 1:1[2H]POPC/DPPC exhibits only a liquid crystalline spectrum. Thus, at temperatures within the phase transition region, the liquid crystalline phase is POPC-rich and the gel phase is DPPC-rich. Comparison of the liquid crystalline quadrupole splittings within the thermal phase transition range suggests that mixing of the residual liquid crystalline POPC and DPPC is highly non-ideal.     

The peculiar thermo-structural behavior of the anionic lipid DMPG

Aqueous dispersions of the anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG), around 100 mM ionic strength, are known to exhibit a thermal behavior similar to that of the largely studied lipid dimyristoyl phosphatidylcholine (DMPC), which undergoes a gel to liquid crystalline phase transition at 23 degrees C, well characterized by differential scanning calorimetry (DSC), and other methods. However, at low ionic strength, DMPG has been shown to present a large gel-fluid transition region, ranging from 18 to 35 degrees C. This intermediate phase is optically transparent and characterized by a continuous change in membrane packing. Structural properties of the DMPG gel-fluid transition region will be discussed, based on results obtained by several techniques: electron spin resonance (ESR) of spin labels at the membrane surface and intercalated at different depths in the bilayer; light scattering; DSC; small angle X-ray scattering (SAXS); and fluorescence spectroscopy of probes in the bilayer.     

Resonance Raman spectra of chlorophylls dissolved in liquid crystal matrices. II. Order parameters of chlorophyll a in an MBBA + EBBA liquid crystalline mixture

The molecular ordering of molecules embedded in a uniaxial liquid crystalline system has been considered. In particular, planar Chl a molecules in an MBBA + EBBA mixture have been studied by using polarized resonance Raman spectroscopy. The second- and fourth-rank order parameters and the orientational distribution function of Chl a in the nematic MBBA + EBBA liquid crystalline phase are discussed.     

Synthesis and mesomorphic properties of glycosyl dialkyl- and diacyl-glycerols bearing saturated, unsaturated and methyl branched fatty acid and fatty alcohol chains. Part II. Mesomorphic properties

The biophysical properties of a series of glycosyl dialkyl- and diacyl-glycerols bearing unsaturated or chiral methyl branched chains in the tail, and di- and trisaccharide carbohydrate headgroups are described. Thermotropism was investigated by polarising microscopy, the lyotropism was investigated by small angle X-ray diffraction and by the contact preparation method, and the gel to liquid crystalline phase transition by FT-IR-spectroscopy. The compounds displayed thermotropic Smectic A (SmA), cubic and columnar phases, whereas in the lyotropic phase diagram lamellar, hexagonal and cubic phases are found. The introduction of unsaturated or methyl branched chains leads to liquid crystallinity at ambient temperature. The difference between the 1,3-oleyl-glycerol maltoside and the corresponding 1,2-oleoyl-glycerol maltoside is small.     

A model of lipid rearrangements during pore formation in the DPPC lipid bilayer

Context: The molecular bases of pore formation in the lipid bilayer remain unclear, as do the exact characteristics of their sizes and distributions. To understand this process, numerous studies have been performed on model lipid membranes including cell-sized giant unilamellar vesicles (GUV). The effect of an electric field on DPPC GUV depends on the lipid membrane state: in the liquid crystalline phase the created pores have a cylinder-like shape, whereas in the gel phase a crack has been observed.

Objective: The aim of the study was to investigate the geometry of pores created in a lipid bilayer in gel and liquid crystalline phases in reference to literature experimental data.

Methods: A mathematical model of the pore in a DPPC lipid bilayer developed based on the law of conservation of mass and the assumption of constant volume of lipid molecules, independent of their conformation, allows for analysis of pore shape and accompanying molecular rearrangements.

Results: The membrane area occupied by the pore of a cylinder-like shape is greater than the membrane area occupied by lipid molecules creating the pore structure (before pore appearance). Creation of such pores requires more space, which can be achieved by conformational changes of lipid chains toward a more compact state. This process is impossible for a membrane in the most compact, gel phase.

Discussion and conclusions: We show that the geometry of the pores formed in the lipid bilayer in the gel phase must be different from the cylinder shape formed in the lipid bilayer in a liquid crystalline state, confirming experimental studies. Furthermore, we characterize the occurrence of the ‘buffer’ zone surrounding pores in the liquid crystalline phase as a mechanism of separation of neighbouring pores.     

Catalytic diastereoselective sulfimidation of diaryl sulfides and application of chiral sulfimides to asymmetric allylic alkylation

The copper-catalyzed diastereoselective imidation of diaryl sulfides bearing a chiral oxazolinyl moiety at the ortho-position with [N-(p-toluenesulfonyl) imino]phenyliodinane (TsN=IPh) or Chloramine-T trihydrate [TsN(Cl)Na.3H2O] was successfully carried out to give the corresponding optically active N-tosylsulfimides in good yields. For example, the imidation of diphenyl sulfide bearing a methoxymethyl moiety at the 4-position of the oxazoline ring with TsN(Cl)Na.3H2O in acetonitrile in the presence of 10 mol% Cu(OTf)2 at 25 degrees C for 24 h affords the corresponding optically active N-tosylsulfimide in 52% isolated yield with a high diastereoselectivity of 99%. Hydrolysis of the optically active N-p-tosylsulfimides converts them into the corresponding optically active sulfimides in high yields without loss of diastereoselectivity. These novel optically active sulfimides and N-tosylsulfimides work as efficient chiral ligands for palladium(II)-catalyzed allylic alkylation of 1, 3-diphenyl-3-acetoxy-1-propene with dimethyl malonate to give the corresponding alkylation product quantitatively and with a high stereoselectivity (up to 90% ee).     

Tuning mesomorphic properties and handedness of chiral calamitic liquid crystals by minimal modification of the effective core

Two pairs of calamitic liquid crystalline molecules, (+)-2-[4'-(S)-sec-butoxyphenyl]-5-(4'-hexoxyphenyl)toluene ((+)-S-1) and (+)-2-(4'-hexoxyphenyl)-5-[4'-(S)-sec-butoxyphenyl]toluene ((+)-S-2), (-)-2-[4'-(R)-sec-butoxyphenyl]-5-(4'-hexoxyphenyl)toluene ((-)-R-1) and (-)-2-(4'-hexoxyphenyl)-5-[4'-(R)-sec-butoxyphenyl]toluene ((-)-R-2), have been designed and synthesized. Each of the molecules consists of a p-terphenyl core substituted with a methyl group on the middle ring, a chiral sec-butoxy tail, and an achiral n-hexoxy tail. The geometrical difference between (+)-S-1 ((-)-R-1) and (+)-S-2 ((-)-R-2) lies only in the location of the methyl group on the effective mesogenic core. Yet, such a small change in the structure gives rise to remarkable differences in mesogenic properties and handedness. Both (+)-S-1 and (-)-R-1 have an enantiotropic cholesteric phase (N*) and a monotropic twist grain boundary C* phase (TGBC*), whereas (+)-S-2 and (-)-R-2 exhibit only a monotropic N* phase. Moreover, (+)-S-1 ((-)-R-1) and (+)-S-2 ((-)-R-2) have opposite handedness in the N* phase, and (+)-S-1 and (-)-R-1 even have a helical inversion from N* to TGBC* phase through a non-helical chiral mesophase.     

Chemo-enzymatic functionalisation of lignocellulose materials using oxiranes

A new non-selective chemo-enzymatic process using oxiranes for functionalisation of lignocellulose materials has been developed. Using a lipase and hydrogen peroxide, soybean oil and linoleic acid were epoxidised resulting in a 52.7% and 92.4% relative conversion to oxirane, respectively. A commercial oxirane, 1,2-epoxyoctane and oxiranes generated from epoxidation of oils (using lipase and hydrogen peroxide) were successfully coupled onto long chain alkylamines while the oxiranes were in turn readily coupled onto phenolic lignin model compounds. Treatment of beech veneers with dodecylamine using this process resulted in a reduction in surface O/C ratio and a 90% increase in hydrophobicity. Since oxiranes react directly with hydroxyl groups and other functional groups this method may provide a new enzymatic non-targeted approach for the functionalisation of various polymeric materials.     

The phase behavior of hydrated cholesterol.

The thermotropic phase behavior of cholesterol monohydrate in water was investigated by differential scanning calorimetry, polarizing light microscopy, and x-ray diffraction. In contrast to anhydrous cholesterol which undergoes a polymorphic crystalline transition at 39 degrees C and a crystalline to liquid transition at 151 degrees C, the closed system of cholesterol monohydrate and water exhibited three reversible endothermic transitions at 86, 123, and 157 degrees C. At 86 degrees C, cholesterol monohydrate loses its water of hydration, forming the high temperature polymorph of anhydrous cholesterol. At least 24 hours were required for re-hydration of cholesterol and the rate of hydration was dependent on the polymorphic crystalline form of anhydrous cholesterol. At 123 degrees C, anhydrous crystalline cholesterol in the presence of excess water undergoes a sharp transition to a birefringent liquid crystalline phase of smectic texture. The x-ray diffraction pattern obtained from this phase contained two sharp low-angle reflections at 37.4 and 18.7 A and a diffuse wide-angle reflection centered at 5.7 A, indicating a layered smectic type of liquid crystalline structure with each layer being two cholesterol molecules thick. The liquid crystalline phase is stable over the temperature range of 123 to 157 degrees C before melting to a liquid dispersed in water. The observation of a smectic liquid crystalline phase for hydrated cholesterol correlates with its high surface activity and helps to explain its ability to exist in high concentrations in biological membranes.     

Synthesis of L-arabinitol and xylitol monomers for the preparation of polyamides. Preparation of an L-arabinitol-based polyamide.

Dihydrochlorides of 1,5-diamino-1,5-dideoxy-2,3,4-tri-O-methyl-L-arabinitol (and xylitol) and pentachlorophenyl esters of 2,3,4-tri-O-methyl-L-arabinaric (and xylaric) acids have been prepared as suitable bifunctional monomers for linear polycondensations. A new aregic AABB-type L-arabinitol-based polyamide is also described from the corresponding monomers. It was crystalline with T(m) 250 degrees C, optically active, and soluble in the usual organic solvents, including chloroform, and in water. Its M(w) obtained by GPC was 27,500 with a polydispersity of 1.4.     

Lipid organization and dynamics of the monostearoylglycerol-water system. A 2H NMR study

Deuterium labeled monostearoylglycerols with fully ([2H(35)]-MSG) and selectively ([11-(2)H(2)]-MSG) deuterated chains have been synthesized and used as a probe for 2H NMR. At low temperature monoglyceride-water systems form the coagel or crystalline phase, which transforms with increasing temperature subsequently into the gel, liquid crystalline and cubic phase. The 2H NMR spectra exhibit characteristic features representative of these phases. The gel phase is metastable and gradually transforms into the coagel at temperatures below 40 degrees C. The undercooled cubic phase transforms into the liquid crystalline phase during days. In the liquid crystalline phase, the chain order profile indicates an increase of the chain flexibility towards the methyl group. In the liquid crystalline phase, bilayers spontaneously align in a magnetic field with their normal perpendicular to the field. The results demonstrate that 2H NMR can serve as a convenient tool to study both structure and dynamics of different monoglyceride-water phases.     

Beneficial Effects of Liquid Crystalline Phases in Solid‐State Dye‐Sensitized Solar Cells

Two novel double‐alkyl functionalized imidazolium ionic liquid crystals have successfully been utilized to demonstrate the benefits of the liquid crystalline phase on the ssDSSC performance. In particular, a good balance between dye regeneration and hole transport is only realized in the liquid crystalline phase. Devices that employ a single component ionic liquid based electrolyte show a remarkably stable efficiency during 1000 h under outdoor operation temperature conditions and 1 sun illumination.     

Invited review liquid crystal models of biological materials and silk spinning

A review of thermodynamic, materials science, and rheological liquid crystal models is presented and applied to a wide range of biological liquid crystals, including helicoidal plywoods, biopolymer solutions, and in vivo liquid crystals. The distinguishing characteristics of liquid crystals (self-assembly, packing, defects, functionalities, processability) are discussed in relation to biological materials and the strong correspondence between different synthetic and biological materials is established. Biological polymer processing based on liquid crystalline precursors includes viscoelastic flow to form and shape fibers. Viscoelastic models for nematic and chiral nematics are reviewed and discussed in terms of key parameters that facilitate understanding and quantitative information from optical textures and rheometers. It is shown that viscoelastic modeling the silk spinning process using liquid crystal theories sheds light on textural transitions in the duct of spiders and silk worms as well as on tactoidal drops and interfacial structures. The range and consistency of the predictions demonstrates that the use of mesoscopic liquid crystal models is another tool to develop the science and biomimetic applications of mesogenic biological soft matter.     

Action of cobra venom phospholipase A2 on the gel and liquid crystalline states of dimyristoyl and dipalmitoyl phosphatidylcholine vesicles

The activity of phospholipase A2 from cobra venom toward phospholipid in single-walled, sonicated vesicles was analyzed, particularly with respect to its activity toward the saturated phosphatidylcholines in the gel and liquid crystalline states. When egg phosphatidylcholine vesicles are used as substrate, the phospholipase has an apparent Km of 4.4 mM, an apparent Vmax of 100 mumol min-1 mg-1 of protein, and a pH optimum of 5.0 at 40 degrees C. The phospholipase hydrolyzed the gel state of dimyristoyl phosphatidylcholine vesicles and dipalmitoyl phosphatidylcholine vesicles at a rate 2 to 3 times greater than the liquid crystalline state, taking into account temperature effects on the enzymatic reaction itself. The results suggest that, toward sonicated vesicles, there is no specific enhancement of the rate when the both liquid crystalline and gel states are present together, as has been suggested to occur for multibilayers studied with other phospholipases. An apparent stimulation of activity as the reaction proceeded was observed above the phase transition temperature. This might be attributed to an increase in the phase transition temperature caused by free fatty acids so that, in the presence of reaction products, the enzyme is actually hydrolyzing gel state phospholipid which was found to be the preferred lipid state for phospholipase activity.