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891.
Reforming of dimethyl ether with carbon dioxide into synthesis gas has been carried out over a mixed catalyst containing Cu-based methanol decomposition catalyst and alumina. The catalyst is found to show a high activity and selectivity. Catalyst stability and deactivation mechanism was also examined. 相似文献
892.
Kunio Kimura Kazufumi Kobashi Hitoshi Maeda Yuhiko Yamashita 《Macromolecular rapid communications》2003,24(2):190-193
The dual self‐assembling polycondensation of p‐acetoxybenzoic acid (ABA) and p‐acetamidobenzoic acid in Therm S 800 was examined at 300 °C. Needle‐like crystals and lath‐like crystals were formed simultaneously through reaction‐induced crystallization of oligomers at a molar ratio of 30–50 mol‐% ABA in the feed. The needle‐like crystals comprised more p‐oxybenzoyl units, whereas the lath‐like ones contained higher amounts of p‐benzamide moieties.
893.
Norikazu Ueyama Kazuyuki Takahashi Akira Onoda Takaaki Okamura Hitoshi Yamamoto 《Macromolecular Symposia》2003,204(1):287-294
Biologically important Ca-proteins and Ca-biominerals as metal-polymer complexes are often regulated by the complexation and demetalation with the biopolymers. Metal-oxygen bond is supported by NH···O hydrogen bonds between coordinating oxyanion and neighboring amide NH and by the successive hydrogen bonding networks. Carboxylate anion under hydrophobic conditions has a high basicity that leads to a covalent Ca-O bond character that is significantly affected by the NH···O hydrogen bond. The hydrogen bonds in Asp-containing tripeptide fragments in Ca-proteins presumably control coordination/dissociation of metal-oxygen bonds. Our systematic studies of carboxylate, sulfonate and phosphate Ca(II) complexes demonstrate a relationship between the basicity of oxyanion in carboxylate and hydrogen bonds as cooperating with the oligopeptide conformation in Asp-containing Ca(II) complexes. Hydrogen bonds between carboxylate oxyanion and amide NH, controlled by a conformational switching of oligopeptide fragments, seem to be one of essential factors for the regulatory formation of Ca-proteins and nano-architectures in connection with the interface structure of inorganic and organic phases in biominerals. 相似文献
894.
de Boer I Matysik J Amakawa M Yagai S Tamiaki H Holzwarth AR de Groot HJ 《Journal of the American Chemical Society》2003,125(44):13374-13375
Solid-state NMR is an emerging method to obtain structural information in molecular biology and nanotechnology for systems that are inaccessible to solution NMR or diffraction methods. While solution NMR generally converges upon families of structures in a bottom-up approach, solid NMR structure determination will have to take into account the top-down constraints that follow from the additional requirement that the entire 3D space must be packed in an orderly fashion. We used MAS NMR together with molecular modeling calculations in steps to establish a detailed model of the local crystal structure of an aggregate of uniformly 13C- and 15N-labeled Cd-chlorophyllide d, a model for the chlorosomal antennae. In this way we converge upon a space group P21 with a = 14.3 A, b = 27.3 A, c = 6.4 A, beta = 147.2 degrees and Z = 2. 相似文献
895.
The fluorescence spectra of 6-propionyl-2-(dimethylamino)naphthalene (Prodan) were observed as a function of pressure for the bilayer membrane systems of dilauroylphosphatidylcholine (DLPC), dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and distearoylphosphatidylcholine (DSPC). The wavelength of the emission maximum, lambdamax, was found to be 480, 430, and 500 nm for the liquid crystalline (Lalpha), ripple gel (P'beta), and pressure-induced interdigitated gel (LbetaI) phase, respectively. Since the lambdamax reflects the solvent property around the probe molecules, we could speculate on the location of the Prodan molecules in the bilayer membranes; in the Lalpha phase of the lipid bilayer, the Prodan molecules distribute around the phosphate of the lipids (i.e. the polar region). The Lalpha/P'beta phase transition caused the Prodan molecules to move into the less polar region near the glycerol backbone. The fluorescence intensity of the Prodan in the P'beta phase was dependent on the chain length of the lipids and on pressure; the shorter the chain length of the lipid, the stronger the fluorescence intensity of the Prodan. Moreover, for the DLPC bilayer membrane system, the fluorescence intensity at 430 nm increased with increasing pressure, indicating that the partition of Prodan into the DLPC bilayer membrane is promoted by applying pressure. In the case of the DPPC and DSPC bilayers, as the pressure increased further, the pressure-induced interdigitation caused the Prodan molecules to squeeze out of the glycerol backbone region and to move the hydrophilic region near the bilayer surface. The ratio of fluorescence intensity at 480 nm to that at 430 nm, F480/F430, showed a sharp change at the phase-transition pressure. In the case of the DPPC and DSPC bilayers, the values of F480/F430 showed an abrupt increase above a certain pressure higher than the Lalpha/P'beta transition pressure, which corresponds to the interdigitation from the P'beta to the LbetaI phase. The plot of F480/F430 versus pressure is available for recognition of the bilayer phase transitions, especially the bilayer interdigitation. 相似文献
896.
Mohammed Lahcini Hicham Qayouh Takao Yashiro Peter Simon Hans R. Kricheldorf 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):503-509
The usefulness of bismuth, calcium, magnesium and zinc salts for the preparation of poly(butylene succinate), PBSu, was studied. Two different approaches were compared. Firstly, 1,4-butanediol (or in a few experiments ethanediol) dimethyl succinate were condensed at temperatures up to 240°C in the presence of Bi2O3. Regardless of the feed ratio, only low molar mass polyesters having two diol endgroups were obtained. Secondly, 1,4-butanediol and succinic anhydride were polycondensed in refluxing decalin with azeotropic removal of water. BiCL3, BiBr3, BiI3, and Bi-triflate were used as catalyst and the monomer/catalyst ratio was varied. The highest molar masses were achieved with BiCl3. Analogous polycondensations catalysed with ZnCl2, Zn-triflate, MgCl2, Mg-triflate and CaCl2 were unsuccessful. Yet the BiCl3, decalin method was also successfully applied to the combination of succinic anhydride and 1,5-pentanediol. 相似文献
897.
Nakabayashi K Nishio M Kubo K Kosaka W Miyasaka H 《Dalton transactions (Cambridge, England : 2003)》2012,41(20):6072-6074
A diagram of energies between the HOMO of donor (D) and LUMO of acceptor (A) vs.ΔE(1/2)(DA) (= E(1/2)(D) - E(1/2)(A): E(1/2) = first-redox potential) clearly demonstrates the ionicity in the series of D/A assemblies, [{Ru(2)(CF(3)CO(2))(4)}(2)(TCNQR(x))]·n(solv) (TCNQR(x) = 2,5- or 2,3,5,6-R-substituted 7,7,8,8-tetracyano-p-quinodimethane; R(x) = H(4), F(2), Cl(2), Br(2), F(4), Me(2), (OMe)(2)). 相似文献
898.
M Goto A Wilk K Kataoka S Chodankar N Tamai M Fukui J Kohlbrecher HO Ito H Matsuki 《Langmuir : the ACS journal of surfaces and colloids》2012,28(33):12191-12198
The myristoylpalmitoylphosphatidylcholine (MPPC) bilayer membrane shows a complicated temperature-pressure phase diagram. The large portion of the lamellar gel (L(β)'), ripple gel (P(β)'), and pressure-induced gel (L(β)I) phases exist as metastable phases due to the extremely stable subgel (L(c)) phase. The stable L(c) phase enables us to examine the properties of the L(c) phase. The phases of the MPPC bilayers under atmospheric and high pressures were studied by small-angle neutron scattering (SANS) and fluorescence spectroscopy using a polarity-sensitive fluorescent probe Prodan. The SANS measurements clearly demonstrated the existence of the metastable L(β)I phase with the smallest lamellar repeat distance. From a second-derivative analysis of the fluorescence data, the line shape for the L(c) phase under high pressure was characterized by a broad peak with a minimum of ca. 460 nm. The line shapes and the minimum intensity wavelength (λ″(min)) values changed with pressure, indicating that the L(c) phase has highly pressure-sensible structure. The λ″(min) values of the L(c) phase spectra were split into ca. 430 and 500 nm in the L(β)I phase region, which corresponds to the formation of a interdigitated subgel L(c) (L(c)I) phase. Moreover, the phase transitions related to the L(c) phase were reversible transitions under high pressure. Taking into account the fluorescence behavior of Prodan for the L(c) phase, we concluded that the structure of the L(c) phase is highly probably a staggered structure, which can transform into the L(c)I phase easily. 相似文献
899.
Ayumi Yoshida Aranya Manosroi Jiradej Manosroi Hitoshi Yamauchi Masahiko Abe 《Colloids and surfaces. B, Biointerfaces》1995,4(6):423-432
Molecular interactions between phospholipids and mangostin in a lipid bilayer have been investigated in terms of the maximum additive concentration (MAC) of mangostin in liposomes, the surface potential, particle size, microscopic-viscosity and microscopic-polarity of liposomes, and the permeability of glucose. The mangostin used is a natural product extract: 1,3,6-trihydroxy-7-methoxy-2,8-bis(3-methyl-2-butenyl)-9-xanthenenone.
The MAC of mangostin was fairly dependent upon the nature of the liposomes (uncharged, negatively charged or positively charged). Solubilization of mangostin in the liposomal bilayer resulted in both an increase in the negative charge on the liposomal surface, strenghthening the state of the bilayer membrane, and a depression in the release of the glucose involved. Mangostin was found to temporarily stabilize the liposomal bilayer, although the bilayer membrane is still unstable in the long run. 相似文献
900.
The treatment of enantiopure aryl dichloromethyl sulfoxides in THF with strong bases such as LDA, LiHMDS, NaHMDS, and KHMDS resulted in racemization of the sulfur stereogenic center of the sulfoxides even at ?78 °C. The rate of the racemization was found to be dependent on the alkali metal of the bases used. This is the first example of the racemization of the sulfur stereogenic center of α-sulfinyl carbanions at low temperatures. 相似文献