Regulation of saccharide binding with basic poly(ethynylpyridine)s by H+-induced helix formation

A basic host polymer exhibiting pH-regulatable saccharide recognition has been investigated. Poly(m-ethynylpyridine) bearing dialkylamino groups forms helical complexes with saccharides to show induced circular dichroism (ICD). When trifluoroacetic acid was titrated on these complexes, the ICD was gradually enhanced until the amount of the acid reached ca. 0.5 molar equivalence versus the pyridine rings in the polymer, and further addition of the acid suppressed the ICD. The proper addition of the acid also increased the binding constants between the polymer and saccharides. These findings would be due to stabilization of the helical structure consisting of cisoid conformations for each of the adjacent pyridine pairs, which were caused by half-protonation of the pyridine rings. Computational analyses indicated that the pyridinium-pyridine dimeric structure prefers its cisoid conformation to its transoid one.     

Brewster angle microscopic observations of the Langmuir films of amphiphilic spiropyran during compression and under UV illumination

The structure of the Langmuir film of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-l'-octadecyl-8-(docosanoyloxyme thyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP), is investigated using Brewster angle microscopy (BAM). The BAM observations show that the Langmuir film of SP can be roughly categorized into three regimes: a low-temperature regime at 7-13 degrees C; a medium-temperature regime at 23-30 degrees C; a high-temperature regime at 40 degrees C. The low-temperature regime is characterized both by the domains that are formed just after the spreading and by the onset of the surface pressure when the domains are merged together to form continuous trilayers. In the medium-temperature regime, a continuous monolayer film is formed after the solvent evaporation, followed by the growth of "embryos" with compression. Around the phase transition point, the "embryos" serve as the "nucleation sites" of the circular trilayer domains. The characteristic features of the high-temperature regime are similar to the ones of the medium-temperature regime except for the absence of a steep rise in surface pressure after the plateau region and the absence of the circular trilayer domains. UV illumination of the Langmuir films leads to the isomerization of SP into merocyanine (MC). However, J-aggregates of MC are formed only when the circular trilayer domains are present. On the basis of the above results, we present a phase diagram of the Langmuir film of SP. The structure and photoreaction depend strongly on the phase of the Langmuir film, indicating that the area/molecule is not the only decisive parameter.     

Energy Sequence of the Lowest Antibonding Orbitals in Symmetrical Didehydro[n]annulenes with n = 4N+2

A model of a perturbed n-membered perimeter (n = 4N + 2) is used to interpret the ESR.-data for the radical anions of symmetrical tetra-t-butyl-didehydro[n]annulenes with n = 14, 18, 22 and 26 (N = 3, 4, 5 and 6). The singly occupied orbital of such radical anions correlates with one of the doubly degenerate, lowest antibonding perimeter MO's which have been classified as symmetric (Ψ_S) or antisymmetric (Ψ_A) with respect to the mirror plane passing through two opposite centres and perpendicular to the plane of the perimeter. The relevant MO is Ψ_S for n = 14 (N = 3) and 22 (N = 5), but Ψ_A for N = 18 (N = 4) and 26 (N = 6), in accordance with the prediction of the model. It has been shown that the introduction of two symmetrically placed triple bonds into a (4N + 2)-membered perimeter should stabilize Ψ_S and destabilize Ψ_A when N is odd, whereas the reverse should hold when N is even.     

High-Temperature Synchrotron X-Ray Powder Diffraction Study of the Orthorhombic-Tetragonal Phase Transition in La0.63(Ti0.92,Nb0.08)O3

The crystal structure of La_0.63(Ti_0.92,Nb_0.08)O₃ has been refined by the Rietveld analysis of CuKα X-ray powder diffraction data collected at 23°C. This material was confirmed to have an A-site deficient orthorhombic perovskite-type structure with double ideal perovskite ABO₃ units along the c-axis (space group Pmmm, Z=2, a=3.86036(5) Å, b=3.87222(5) Å, c=7.82609(9) Å). Lattice parameters of the same sample have been investigated in situ in the temperature range from 25°C to 496°C by 1.37873(3) Å synchrotron X-ray powder diffraction. The synchrotron X-ray powder diffraction technique was found to be very powerful to determine precise lattice parameters around a phase transition temperature. This compound exhibited a reversible phase transition between the orthorhombic and tetragonal phases at around 370°C. (1) The lattice parameters increased continuously with temperature, while the b/a ratio decreased continuously with temperature and became unity at the orthorhombic-tetragonal transition point. (2) No hysteresis was observed in the lattice parameter values between heating and cooling. These results of (1) and (2) suggest that the orthorhombic-tetragonal phase transition is continuous.     

Macromolecular synthesis from saccharic lactones. Polyaddition of D-glucaro- and D-mannaro- 1,4:6, 3-dilactones with diisocyanates and hydrolyzability of the resulting polyurethanes having dilactone rings in the main chains

Polyaddition of saccharic acid dilactones prepared from D-glucose and D-mannitol, D-glu-caro-, and D-mannaro-1,4:6,3-dilactones ( 1 and 2 , respectively), with hexamethylene di-isocyanate ( 3a ) and methyl (S)-2,6-diisocyanatocaproate ( 3b ) was carried out by using dibutyltin dilaurate as a catalyst at 50, 25, and 0°C to give polyurethanes ( 4 and 5 ) having dilactone moieties in the main chains. The resulting polymers were found to decompose easily in phosphate buffers under neutral or slightly basic conditions (pH 7 or 8). Therefore, the polyurethanes may be used as novel degradable polymeric materials. © 1995 John Wiley & Sons, Inc.     

Determination of lead at the ng ml-1 level by reduction to plumbane and measurement by inductively-coupled plasma emission spectrometry

A detection limit of 1 ng ml^-1 for lead is obtained by the reported method. Samples are prepared in 0.5 M hydrochloric acid—0.8 M hydrogen peroxide. Plumbane is produced (with 64% efficiency) by the addition of 5% sodium tetrahydroborate in 0.5% NaOH, and is transported by the argon feed directly to an inductively-coupled argon plasma for emission spectrometry. Decreased hydrogen generation and greater stability of the plasma also contribute to the improved detection limit. The method is shown to be generally applicable to As, Sb, Bi, Sn, Te and Se, with detection limits at the ng ml^-1 level.     

Preparation and biological activities of a bivalent poly(ethylene glycol) hybrid containing an active site and its synergistic site of fibronectin

A bivalent poly(ethylene glycol) or PEG hybrid of fibronectin-related peptides was prepared. An active site peptide (RGD) and its synergistic site peptide (PHSRN) of fibronectin were conjugated with an amino acid-type PEG (aaPEG) to form PHSRN-aaPEG-RGD. A moderate spatial array between RGD and PHSRN in fibronectin may be required for synergic activity. The bivalent hybrid exhibited potent cell spreading activity and exhibited potent anti-metastatic activity in a model of experimental metastasis with B16-BL6 cells in mice. PEG may serve as a spacer for maintaining the desired spatial array.     

Characteristics of a zirconia composite membrane fabricated by a laser firing method

By a method of laser firing, a high zirconia containing (70%) composite membrane on porous ceramic tubing was successfully fabricated. The laser sintered composite membrane was characterized by gas separation/permeation experiments. In the separation experiment of a CO₂---CH₄ gaseous mixture, it was found that the separation factor of CH₄ over CO₂ was 1.15. In the pure gases permeation experiment, it was found that Knudsen diffusion is considered to be predominant in the permeation mechanism for pure gases H₂, He, CH₄, N₂, O₂, and CO₂, and the permeation mechanism of H₂O at lower temperature depends mainly on surface diffusion and on Knudsen diffusion at higher temperature.     

Close-packed colloidal crystalline arrays composed of polystyrene latex coated with titania nanosheets

We have demonstrated that polystyrene latex coated with titania nanosheets can be fabricated into a close-packed colloidal crystalline array, and that these coated colloidal spheres can be used to control the peak position of optical stop bands through the coating. The titania-nanosheets-coated polystyrene latex was prepared by the layer-by-layer (LBL) assembly coating process, involving alternating lamination of cationic polyelectrolytes and anionic titania nanosheets on monodisperse polystyrene latex particles. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with the coating of titania nanosheets. This red shift was caused by an increase in refractive index upon coating, as revealed by angle-resolved reflection spectra measurements. The current work suggests new possibilities for the creation of advanced colloidal crystals having tunable optical properties from tailored colloidal spheres.     

Studies on pyridonecarboxylic acids . 2. Synthesis and antibacterial activity of 8-substituted-7-fluoro-5-oxo-5H-thiazolo[3,2-a]quinoline-4-carboxylic acids

A series of 8-substituted-7-fluoro-5-oxo-5H-thiazolo[3,2-a]quinoline-4-carboxylic acids was prepared and evaluated for antibacterial activity. These compounds were synthesized from ethyl 2-mercaptoquinoline-3-carboxylates 17 which were obtained from anilines 11 by a route involving an intramolecular cyclization reaction.