Lyotropic mesophase of imogolite, 2. Microscopic observation of imogolite mesophase

Imogolite, though achiral, forms cholesteric spherulites in the anisotropic phase as shown by the regular striations arranged in a swirl-like or fingerprint pattern observed through a polarizing microscope. Electron microscopy revealed the raft-like imogolite sheet floating in the anisotropic phase. The structure of the imogolite sheet was deduced from periodicities observed by an electron microscope using various imaging conditions. The origin of the twisting force to maintain the cholesteric ordering is also discussed.     

Lyotropic mesophase of imogolite, 3 observation of liquid crystal structure by scanning electron and noval polarized optical microscopy

The mesophase (lyotropic liquid crystal) of the inorganic rod-like polymer, imogolite, displays a typical fingerprint texture under a polarized optical microscope (POM), although the mesophase reveals no circular dichroism. The scanning electron microscope revealed a honeycomb structure of thin sheets having pleats in the freeze-dried sample prepared from the mesophase solution, and POM shows also a fingerprint texture from the same sample. A novel polarized optical microscopic observation procedure was introduced to eliminate the contrast variation and extinction due to the zero amplitude effect which depends on the orientational variation of anisotropic bodies with respect to a polarizer direction under the crossed Nicols. Various textures of lyotropic imogolite liquid crystals were observed with the procedure, and the results were accounted for by a honey-comb structure of curled thin sheats having pleats. The honey-comb model is consistent with the observation by scanning electron microscopy on the freeze-dried sample.     

Studies on the phase separation of polyetherimide-modified epoxy resin, 1. Effect of curing rate on the phase structure

The effect of the curing rate on the phase structure of a new polyetherimide-modified epoxy systems was studied. Through changing cure agents and cure temperature, selecting different molecular weights and end groups of the polyetherimide (PEI) polymers, the curing rates, the phase separation processes and the morphology of the cured blends were observed employing differential scanning calorimetry, time-resolved light scattering and scanning electron microscopy. The highly active cure agent 4,4′-oxydianiline leads to phase separation in the early stage of spinodal decomposition and to a co-continuous phase structure. As to the 4,4′-diaminodiphenyl sulfone cured systems, not only the curing rate, but the mobility of the PEI molecule also affected the final morphology of the PEI-modified epoxy resin.     

Lyotropic and thermotropic liquid-crystalline phase formation from fractions of a semiflexible cellulosic polymer

The benzoic acid ester of (2-hydroxypropyl)cellulose (BzPC) was prepared and fractionated from acetone solution by precipitation with methanol-water (85:15, by volume). The fractions were characterized by low-angle laser light scattering in tetrahydrofuran, and by size exclusion chromatography with a low-angle laser light scattering detector. Dilute solution viscosities were measured in acetone and benzene, and the results were interpreted on the basis of a worm-like chain model for BzPC. The critical concentrations of polymer necessary to form lyotropic cholesteric phases in acetone and benzene were found to decrease as the molar mass of the polymer increased, reaching a limiting volume fraction of ≈ 0,35 for high molar mass fractions. The experimental results were compared with the prediction of recent theories for the formation of liquid crystalline phases from semiflexible polymers; the chain parameters required by the theories were estimated from dilute solution viscosities. The fractions of BzPC also showed a thermotropic transition from liquid crystalline phase to isotropic melt. The transition temperature increased sharply with increasing molar mass to reach a limiting value of 176°C.     

Acrylonitrile-sodium methallylsulfonate copolymer in dimethyl sulfoxide. NMR approach to the phase diagram

The temperature and concentration dependences of the physical state of solutions of an acrylonitrile-sodium methallylsulfonate copolymer in dimethyl sulfoxide (DMSO) are investigated from calorimetric and NMR measurements within the temperature range where the solvent crystallization and/or polymer ordering in solution can occur. (i) For solutions of global monomeric molar fraction higher than 0.45, ordering of a fraction (<0.15) of the polymer can occur. Temperatures of polymer melting and polymer ordering are reported. The composition of the liquid phase coexisting with ordered polymer is found to depend on the global concentration of the solution. At low temperatures, i.e., at temperatures for which DMSO crystallizes, three phases are found to coexist: ordered polymer, crystalline DMSO and disordered solution. (ii) For solutions of global monomeric molar fractions smaller than 0.45, the polymer is disordered at all temperatures. Crystallization of pure DMSO is observed and the melting/crystallization curve of DMSO is determined by NMR and described with simple thermodynamic considerations.     

Effect of molecular weight and polydispersity on kinetics of dissolution and release from ph/temperature-sensitive polymers

N-isopropylacrylamide (NIPAAm) polymers exhibit a lower critical solution temperature (LCST). Aqueous solutions of these polymers are soluble below their LCST and precipitate above their LCST. The LCST is dependent on pH for polymers with ionizable groups because of a change in hydrophilicity with ionization and electrostatic repulsion that cause a shift in the LCST. We have designed a novel polymeric delivery system that utilizes linear, pH/temperature-sensitive terpolymers of NIPAAm, butyl methacrylate (BMA) and acrylic acid (AA). This system allows the aqueous loading of drugs in polymeric beads with high loading efficiency while preserving the bioactivity of the protein drug. Furthermore, the unique properties of the pH/temperature-sensitive polymeric bead make it a potential system for oral drug delivery of peptide and protein drugs to different regions of the intestinal tract. This study aims at investigating the effect of polydispersity and molecular weight (MW) of terpolymers of poly(NIPAAm-co-BMA-co-AA) with feed mol ratio of NIPAAm/BMA/AA 85/5/10 on the polymer dissolution rate and on the release kinetics of a model protein, namely insulin. Varying the weight average MW (Mw) and polydispersity of the polymer modulated the polymer dissolution rate and the release rate of insulin from pH/temperature-sensitive polymeric beads. An increase in the polydispersity of the polymer through the addition of high MW polymer chains caused a decrease in the release rate of insulin and in the polymer dissolution rate. High MW polymer chains impose a certain degree of interaction between polymer chains due to chain entanglement. There is a limiting value of MW above which chain entanglement has no effect on drug release rate.     

Effect of molecular weight and polydispersity on kinetics of dissolution and release from pH/temperature-sensitive polymers

N-isopropylacrylamide (NIPAAm) polymers exhibit a lower critical solution temperature (LCST). Aqueous solutions of these polymers are soluble below their LCST and precipitate above their LCST. The LCST is dependent on pH for polymers with ionizable groups because of a change in hydrophilicity with ionization and electrostatic repulsion that cause a shift in the LCST. We have designed a novel polymeric delivery system that utilizes linear, pH/temperature-sensitive terpolymers of NIPAAm, butyl methacrylate (BMA) and acrylic acid (AA). This system allows the aqueous loading of drugs in polymeric beads with high loading efficiency while preserving the bioactivity of the protein drug. Furthermore, the unique properties of the pH/temperature-sensitive polymeric bead make it a potential system for oral drug delivery of peptide and protein drugs to different regions of the intestinal tract. This study aims at investigating the effect of polydispersity and molecular weight (MW) of terpolymers of poly(NIPAAm-co-BMA-co-AA) with feed mol ratio of NIPAAm/BMA/AA 85/5/ 10 on the polymer dissolution rate and on the release kinetics of a model protein, namely insulin. Varying the weight average MW (M_w) and polydispersity of the polymer modulated the polymer dissolution rate and the release rate of insulin from pH/temperature-sensitive polymeric beads. An increase in the polydispersity of the polymer through the addition of high MW polymer chains caused a decrease in the release rate of insulin and in the polymer dissolution rate. High MW polymer chains impose a certain degree of interaction between polymer chains due to chain entanglement. There is a limiting value of MW above which chain entanglement has no effect on drug release rate.     

Morphology,phase transitions and viscoelastic properties of poly(oxybisdimethylsilylene). A mesophase in a silicon analogue of a polyether

Poly(oxybisdimethylsilylene) (POBDMS)

1 System. name: poly[oxy(tetramethyldisilane-1,2-diyl)].

has been studied by differential scanning calorimetry, polarizing microscopy, wide-angle X-ray scattering and dynamic mechanical measurements. The polymer shows a weakly marked glass transition near 154 K and three first-order transitions: a crystal-to-crystal transition at 256 K, a crystal-to-mesophase transition at 294 K and a transition to the isotropic melt at 325 K. These transitions are correlated with the mechanical relaxations measured as a function of temperature. The rheological behaviour of the polymer in the isotropic liquid state and in the mesophase has been studied, as well. The properties of POBDMS are discussed in comparison with liquid-crystalline polymers with mesogenic groups.     

Thermoplastic liquid crystalline triblock elastomers, 1. Synthesis and phase behaviour

Side-chain liquid crystalline ABA triblock copolymers with a backbone of polystyrene-block-1,2-polybutadiene-block-polystyrene and 5-[(4′-cyano-4-biphenylyl)oxy]pentanoic acid as side chains were synthesized. The block copolymers possess narrow molecular weight distributions. The liquid crystalline (LC) phase behaviour was characterized by means of differential scanning calorimetry (DSC) and X-ray scattering. Nematic and smectic polymers are accessible by variation of the spacer length.     

Characterization of Shigella type 1 fimbriae: expression, FimA sequence, and phase variation.

This study documents the presence of type 1 fimbriae on Shigella and confirms these mannose-sensitive adherence structures to be bona fide components of the Shigella surface. While laboratory-passaged Shigella strains and lyophilized clinical isolates failed to express type 1 fimbriae, 6 of 20 recent clinical isolates, including 4 Shigella flexneri strains, 1 Shigella boydii strain, and 1 Shigella dysenteriae strain, produced type 1 fimbriae as detected by mannose-sensitive hemagglutination (MSHA) and electron microscopy. Optimal production of a predominantly Fim+ population required serial passage every 48 to 72 h in unshaken brain heart infusion broth at 37 degrees C. Fim+ Shigella cultures were capable of reversibly switching to a non-MSHA, afimbriated phase during serial aerobic cultivation on tryptic soy agar plates. The amino acid sequence of S. flexneri type 1 FimA contained 18 substitutions compared to that of Escherichia coli fimbrillin. Indirect immunoelectron microscopy suggested the presence of both shared and unique epitopes on E. coli and S. flexneri type 1 fimbriae. Random phase variation between fimbriated and afimbriated states in Shigella was accompanied by the genomic rearrangement associated with phase variation in E. coli.     

The phase diagram of the monoolein/water system: metastability and equilibrium aspects

Interest in the liquid crystal structure, transport and membrane protein crystallizing properties of the monoolein/water system has grown in the recent past. Monoolein is also an important homolog in a series of monoacylglycerols used to decipher how lipid molecular structure relates to liquid crystal phase behavior--information needed for rational design applications and for understanding the origin of membrane lipid diversity. To make intelligent use of the monoolein/water system, a reliable and detailed temperature-composition phase diagram is needed. The phase diagram of Briggs et al. (J Phys II France 1996;6:723-51) was constructed for this purpose. However, we have established that the liquid crystal phases in the latter below ca. 20 degrees C are metastable. By implementing a sub-zero degree (degrees C) sample incubation prior to data collection in the heating direction, we can reset the system into the lamellar crystal phase which we assume represents equilibrium behavior. We have re-examined the low-temperature part of the phase diagram and characterized structurally the new 'equilibrium' phases by static and time-resolved low- and wide-angle X-ray diffraction and by differential scanning calorimetry. A more complete phase diagram that incorporates the new equilibrium behavior at low temperatures is reported.     

Effect of cytokines on HLA-DR and IL-1 production by a monocytic tumour, THP-1.

The monocytic tumour, THP-1, expresses many of the properties of monocytes, both by cell surface staining and its capacity to produce monokines. It was used as a source of homogenous monocytic cells as a model to determine whether a variety of highly purified or recombinant cytokines could induce HLA-DR expression and the production of interleukin-1 (IL-1). Interferon-gamma (IFN-gamma) alone induced HLA-DR. Tumour necrosis factor (TNF), lymphotoxin (LT) and granulocyte-macrophage colony-stimulating factor (GM-CSF) alone were able to induce IL-1 but not HLA-DR. When IFN-gamma was combined with TNF, induction of HLA-DR and IL-1 was enhanced in a synergistic manner. These effects were detectable at a pretranslational level as synergistic effects were observed on DR alpha mRNA and IL-1 beta mRNA levels. The results demonstrate the specificity of IFN-gamma as the inductive stimulus for HLA-DR expression by THP-1 cells. As IFN-gamma and TNF are products of activated T cells, the synergistic role for these molecules in macrophage activation is discussed.     

A general diagram of the human genome.

A general diagram of the whole structure of the human genome is drafted on a logarithmic metric scale located in the radius of a circle showing a full haploid set of chromosomes. A base pair scale of DNA is displayed in circumferences at different orders of magnitude from one metre down to one picometre (10(-12) m).     

Oligosaccharide-based thermotropic liquid crystals, 4. Synthesis of cellobiose-based twin and triplet derivatives and their mesophase properties

Previous work from this laboratory has shown that cellobiose octaalkanoate (COA) functions as a thermotropic discotic mesogen, forming a hexagonal ordered columnar phase (D_ho). In this work, we prepared the COA-based discotic twin and triplet derivatives and examined the mesomorphic properties of the derivatives by DSC, polarization microscopy and X-ray diffraction. In the former derivative, two cellobiose heptadecanoate (CHD) molecules (monomers) are combined through an alkyl spacer of varying length by ether and ester linkages at the C-1 position of the reducing end units of the monomers. Three CHD molecules having an alkyl spacer are connected with a coupling agent for the latter derivative. The results revealed that (i) all the twin derivatives form a distinct discotic columnar phase, (ii) the thermal stability of the mesophases of the twins is enhanced, compared with that of the monomer, when the length of the flexible spacer is appropriate, (iii) the twins with a relatively short spacer form a discotic rectangular ordered (D_ro) phase, while those with a longer spacer form a pseudo-D_ho phase, (iv) the triplets also form a discotic columnar mesophase, but not a hexagonal ordered columnar (D_ho) phase, (v) the thermal stability of the mesophases of the triplets strongly depends on the chemical nature of coupling cores, and (vi) the packing structures of the cellobiose cores within the columns of both derivatives are markedly different from that of the monomer.     

Effect of surface-functionalized nanoparticles on the elongation phase of beta-amyloid (1-40) fibrillogenesis

The influence of nanoparticles of various sizes and surface functionalities on the self-assembling fibrillogenesis of beta-amyloid (1-40) peptide was investigated. Functionalized nanoparticles including quantum dots and gold nanoparticles were co-incubated with monomeric Aβ(1-40) peptides under seed-mediated growth method to study their influences on the elongation phase of the fibrillogenesis. It is observed that charge-to-surface area ratio of the nanoparticles and the functional moiety and electrostatic charges of the conjugated ligands on the particle surfaces took crucial regulatory role in the Aβ(1-40) fibrillogenesis.     

Effect of sintering on porosity, phase, and surface morphology of spray dried hydroxyapatite microspheres

This article deals with the effect of sintering temperature on the physical and chemical characteristics of hydroxyapatite microspheres (HAMs) obtained by spray drying method. A set of specimens were sintered in a conventional furnace at 500-1100 degrees C. The surface morphology, phase composition, size distribution, specific surface area, and porosity were characterized by scanning electron microscope, X-ray diffractometer, laser diffraction particle size analyzer, and specific surface area analyzer, respectively. The results indicated that at 800 degrees C, hydroxyapatite crystals began to grow and were sintered together, which caused a drastic decrease in both the specific surface area and the pore volume. Great changes took place on the surfaces of HAMs during sintering. When the samples were sintered at the temperature of 500 and 600 degrees C, no obvious changes can be found on the surfaces of the samples, but at 800 degrees C, open-micropore surfaces came forth. Besides, the dispersibility of the samples decreased at high temperature (1100 degrees C) because small particles tended to aggregate together.     

Studies on the phase separation of polyetherimide-modified epoxy resin, 2. Effect of molecular weight of PEI on the structure formation

The effect of molecular weight on the structure formation of polyetherimide modified epoxy system was studied. Using time-resolved light scattering (TRLS) and scanning electron microscopy (SEM), the process of phase separation and the morphology of the blends were investigated. As the curing reaction proceeds, the phase separation occurs first in the large molecular weight polyetherimide (PEI) modified epoxy resin and the time of occurrence of phase separation is increased with the decrease of the inherent viscosity of PEI. Because of the different viscosity of the blends, the blends display varied morphologies from a PEI particle dispersion to co-continuous phases. Changing of the PEI molecular weight may be another possible route to control the morphology of the PEI modified epoxy resins.