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91.
Hideaki Takahashi Hajime Ohno Ryohei Kishi Masayoshi Nakano Nobuyuki Matubayasi 《Chemical physics letters》2008,456(4-6):176-180
In a recent development we proposed a quantum chemical approach to compute free energy change for chemical reactions in condensed phases by combining the QM/MM method with the theory of energy representation (QM/MM-ER). We extend in this Letter the novel approach to compute reduction free energy of isoalloxazine ring of FAD (flavin adenine dinucleotide) immersed in water within the framework of the QM/MM-ER method. The characteristic feature of our approach is that the excess electron to be attached on the FAD is identified as a solute. The reduction free energy has been obtained as −80.1 kcal/mol in the aqueous solution. 相似文献
92.
Magnetically Alignable Bicelles with Unprecedented Stability Using Tunable Surfactants Derived from Cholic Acid 下载免费PDF全文
Ryoichi Matsui Dr. Noriyuki Uchida Dr. Masataka Ohtani Kuniyo Yamada Arisu Shigeta Prof. Dr. Izuru Kawamura Prof. Dr. Takuzo Aida Dr. Yasuhiro Ishida 《Chemphyschem》2016,17(23):3916-3922
Five novel surfactants were prepared by modifying the three hydroxy groups of sodium cholate with triethylene glycol chains endcapped with an amide ( SC‐C1 , SC‐ n C4 , and SC‐ n C5 ) or a carbamoyl group ( SC‐O n C4 and SC‐O t C4 ). The phase behavior of aqueous mixtures of these surfactants with 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphatidylcholine (DMPC) was systematically studied by 31P NMR spectroscopy. The surfactants endcapped with carbamate groups ( SC‐O n C4 and SC‐O t C4 ) formed magnetically alignable bicelles over unprecedentedly wide ranges of conditions, in terms of temperature (from 21–23 to >90 °C), lipid/surfactant ratio (from 5 to 8), total lipid content (5–20 wt %), and lipid type [DMPC, 1,2‐dilauroyl‐sn‐glycero‐3‐phosphatidylcholine (DLPC), or 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphatidylcholine (POPC)]. In conjunction with appropriate phospholipids, the carbamate‐endcapped surfactants afforded unique bicelles, characterized by exceptional thermal stabilities (from 0 to >90 °C), biomimetic lipid compositions (DMPC/POPC=25:75 to 50:50), and extremely large 2H quadrupole splittings (up to 71 Hz). 相似文献
93.
Yuki Kanazawa Prof. Hayato Tsuji Prof. Masahiro Ehara Prof. Ryoichi Fukuda Dr. Deborah L. Casher Prof. Kohei Tamao Prof. Hiroshi Nakatsuji Prof. Josef Michl 《Chemphyschem》2016,17(19):3010-3022
The photophysical properties of oligosilanes show unique conformational dependence due to σ‐electron delocalization. The excited states of the SAS, AAS, and AEA conformations of peralkylated n‐hexasilanes, in which the SiSiSiSi dihedral angles are controlled into a syn (S), anti (A), or eclipsed (E) conformation, were investigated by using UV absorption, magnetic circular dichroism (MCD), and linear dichroism spectroscopy. Simultaneous Gaussian fitting of all three spectra identified a minimal set of transitions and the wavenumbers, oscillator strengths, and MCD B terms in all three compounds. The results compare well with those obtained by using the symmetry‐adapted‐cluster configuration interaction method and almost as well with those obtained by time‐dependent density functional theory with the PBE0 functional. The conformational dependence of the transition energies and other properties of free‐chain permethylated n‐hexasilane, n‐Si6Me14, was also examined as a function of dihedral angles, and the striking effects found were attributed to avoided crossings between configurations of σσ* and σπ* character. 相似文献
94.
The disintegratability of tablets prepared from two types of solid dispersions containing the water-soluble polymer TC-5 and the enteric polymer HP-55 as an excipient were compared. The disintegratability was better in the tablets of solid dispersions containing non-water-soluble HP-55 than those containing TC-5. In consideration of the dissolubility of solid dispersions containing HP-55, the mean diameter of the solid dispersion (coating powder) must be controlled to 120 microm or less, but as this markedly increases the adhesion/aggregation tendency of the particles (angle of repose: 47 degrees ), control of the adhesion/aggregation tendency emerged as another problem. Therefore, surface-modification was performed in a high-speed agitating granulator using 0.1% light anhydrous silicic acid as a surface modifier, and marked improvement in the flowability was observed. This made continuous tableting using a rotary tablet machine possible even with the poorly flowable solid dispersions. Also, in tableting of the solid dispersions, no recrystallization of amorphous itraconazole by the tableting pressure was observed, and the tablets maintained satisfactory dissolubility. Moreover, it was possible to obtain the rapidly disintegrating tablets with very satisfactory properties, i.e., a tablet hardness of 30 N or higher and a disintegration time of 30 s or less, by the addition of croscarmellose as a disintegrant at 2% to the surface-modified solid dispersion and selection of the tableting pressure at 4.5 kN. 相似文献
95.
With the hope of mimicking the chemical and biological properties of natural 6-O-methyl-D-glucose-containing polysaccharides (MGPs), synthetic 6-O-methyl-D-glucose-containing polysaccharides (sMGPs) were designed and synthesized from alpha-, beta-, and gamma-cyclodextrins (CDs). The synthetic route proved to be flexible and general, to furnish a series of sMGPs ranging from 6-mer to 20-mer. A practical and scalable method was discovered selectively to cleave the CD derivatives and furnish the linear precursors to the glycosyl donors and acceptors. The Mukaiyama glycosidation was adopted to couple the glycosyl donors with the glycosyl acceptors. Unlike in the 3-O-methyl-D-mannose-containing polysaccharide (sMMP) series, the amount of the Mukaiyama acid required in the sMGP series increased with an increase of substrate size; that is, for large oligomers, more than one equivalent of the acid was required. 相似文献
96.
Ishimatsu R Shigematsu F Hakuto T Nishi N Kakiuchi T 《Langmuir : the ACS journal of surfaces and colloids》2007,23(2):925-929
The structure of the electrical double layer on the aqueous solution side has been studied by measuring electrocapillary curves at the polarized interface between a room-temperature ionic liquid (RTIL), tetrahexylammonium bis(trifluoromethylsulfonyl)imide, and water (W) at different concentrations of LiCl. Thermodynamic analysis of the electrocapillary curves indicates that Li+ ions negatively adsorb at the point of zero charge. The adsorption of Li+ and Cl- ions in the polarized potential window of about 200 mV can be explained by the Gouy's double layer model, and the specific adsorption of Li+ and Cl- ions at the RTIL|W interface is negligible within the polarized potential window. 相似文献
97.
Yoshimoto M Miyazaki Y Umemoto A Walde P Kuboi R Nakao K 《Langmuir : the ACS journal of surfaces and colloids》2007,23(18):9416-9422
The decomposition of hydrogen peroxide (H2O2) was examined in aqueous solution (50 mM Tris-HCl buffer, pH 7.4, containing 100 mM NaCl) at 25 degrees C in pure buffer or in the presence of either vesicles or micelles formed from various phosphatidylcholines (PCs). In the absence of PCs, more than 90% of the initially added H2O2 (1.0 mM) remained intact after incubation for 120 h. The effect of the PCs on the decomposition of H2O2 was studied by using different PCs that varied in terms of number of carbon atoms in the two acyl chains n as well as in terms of the degree of unsaturation. PCs with short hydrocarbon chains (n = 4, 6-8) were dissolved in the buffer solution in the form of nonassociated monomers or as micelles in equilibrium with monomers at a fixed PC concentration of 10 mM. The presence of these short-chain PCs slightly enhanced the H2O2 decomposition rate. Micelles formed by non-lipid detergents (sodium cholate, Triton X-100, and sodium dodecylsulfate) had a similar effect. In marked contrast, PCs with long hydrocarbon chains (n > or = 10) dispersed in buffer solution as vesicles (liposomes) significantly enhanced the rate of H2O2 decomposition, with the most effective PC being 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at 25 degrees C. This indicates that the packing density of the PC molecules influences the reactivity, presumably through the direct interaction of the PC assemblies with H2O2 molecules. Furthermore, in the case of vesicles formed from PCs with unsaturated acyl chains (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC; 1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC), carbon-carbon double bond oxidation did not occur extensively under the conditions used. This indicates that the observed effect of PCs on the decomposition of H2O2 is indeed related to the assembly structure (vesicle vs micelles vs monomers) and is clearly not related to the presence of unsaturated hydrocarbon chains. Fluorescence polarization measurements of two fluorescent probes embedded either in the acyl chain region of the vesicles (DPH, 1,6-diphenyl-1,3,5-hexatriene) or on the surface of the vesicles (TMA-DPH, 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide) show that the presence of H2O2 leads to a decrease in the fluidity of the lipid-water surface and not to a change in the fluidity of the hydrophobic region of the vesicle bilayer. This indicates that the decomposition of H2O2 is triggered through interactions between H2O2 and the polar head group area of PC vesicles. 相似文献
98.
Shuhei Fukawa Masahiko Hada Ryoichi Fukuda Shinji Tanaka Hiroshi Nakatsuji 《Journal of computational chemistry》2001,22(5):528-536
Linear and nonlinear halogen dependencies of the 13C magnetic shielding constants of CH4−nIn, CH4−nBrn, CCl4−nIn, and CBr4−nIn were fairly reproduced by the ab initio generalized unrestricted Hartree–Fock (GUHF)/finite perturbation (FP) method including spin‐orbit (SO) interaction and spin‐free relativistic (SFR) terms. As seen from the experimental trends, the calculated 13C chemical shifts in CCl4−nIn and CBr4−nIn depend linearly on n=0–4, while those in CH4−nIn and CH4−nBrn depend nonlinearly. We found that both the linear and nonlinear dependencies are due to the relativistic effects, and especially due to the Fermi–Contact (FC) term originating from the SO interaction. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 528–536, 2001 相似文献
99.
100.
Akihiro Hiroki Masaru Yoshida Junko Yamashita Masaharu Asano Nicole Reber Reimar Spohr Minoru Kumakura Ryoichi Katakai 《Journal of polymer science. Part A, Polymer chemistry》1998,36(10):1495-1500
Thermoresponsive porous gel membranes were synthesized by a simultaneously occurring process consisting of radiation-induced polymerization and crosslinking in aqueous solutions at various concentrations of acryloyl-L -proline methyl ester(A-ProOMe) without a crosslinker. Permeation of p-nitrophenol (PNP) through a thermoresponsive porous gel membrane obtained at a monomer concentration of 80% (w/w) drastically reduced around 14°C, the lower critical solution temperature (LCST) of linear poly(A-ProOMe) in water, from 0.60 × 10−3 cm/min at 10°C to no permeation at 18°C, accompanied by changes in both size and shape of pores associated with gel shrinkage. Moreover, it was found that porous gel membranes with a porosity of approximately 60% had a greater PNP permeability constant through porous gel membranes with mutually connected pores obtained at a monomer concentration of 50% (w/w) than individually supported pores obtained at a monomer concentration of 70% (w/w). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1495–1500, 1998 相似文献