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991.
Dana Kubies Jaroslav Š?udla Rudolf Puffr Antonín Sikora Josef Baldrian Jana Ková?ová Miroslav Šlouf František Rypá?ek 《European Polymer Journal》2006,42(4):888-899
Poly(ε-caprolactone) (PCL) masterbatches with the intercalated and the exfoliated morphology were prepared by ring opening polymerization of ε-caprolactone in the presence of organomodified montmorillonite (MMT) Cloisite 30B. Poly(l-lactide) (PLLA) nanocomposites with Cloisite 30B or PCL masterbatches were prepared by melt blending. The effects of the silicate type, MMT content and the nanocomposite morphology on thermal and mechanical properties of PLLA nanocomposites were examined. The montmorillonite particles in PLLA/Cloisite 30B and PLLA/intercalated masterbatch nanocomposites were intercalated. In contrary to expectations, the exfoliated silicate layers of exfoliated masterbatch were not transferred into the PLLA matrix. Due to a low miscibility of PCL and PLLA, MMT remained in the phase-separated masterbatch domains. The stress-strain characteristics of PLLA nanocomposites, Young modulus E, yield stress σy and yield strain εy, decreased with increasing MMT concentration, which is associated with the increase in PCL content. The expected stiffening effect of MMT was low due to a low aspect ratio of its particles and was obscured by both plastifying effects of PCL and low PLLA crystallinity. Interestingly, in contrast to the neat PLLA, ductility was enhanced in all PLLA/Cloisite 30B materials and in PLLA/masterbatch nanocomposites with low MMT concentrations. 相似文献
992.
Mark E. Snow 《Journal of computational chemistry》1992,13(5):579-584
Protein-folding potentials, designed with the explicit goal that the global energy minimum correspond to crystallographically observed conformations of protein molecules, may offer great promise toward calculating native protein structures. Achieving this promise, however, depends on finding an effective means of dealing with the multiple-minimum problem inherent in such potentials. In this study, a protein-folding-potential test system has been developed that exhibits the properties of general protein-folding potentials yet has a unique well-defined global energy minimum corresponding to the crystallographically determined conformation of the test molecule. A simulated-annealing algorithm is developed that locates the global minimum of this potential in four of eight test runs from random starting conformations. Exploration of the energy-conformation surface of the potential indicates that it contains the numerous local minima typical of protein-folding potentials and that the global minimum is not easily located by conventional minimization procedures. When the annealing algorithm is applied to a previously developed actual folding potential to analyze the conformation of avian pancreatic polypeptide, a new conformer is located that is lower in energy than any conformer located in previous studies using a variety of minimization techniques. 相似文献
993.
P. Berastegui S. HullF.J. Garc? Garc? J. Grins 《Journal of solid state chemistry》2002,168(1):294-305
The structures of the oxyorthogermanate La2(GeO4)O and the apatite-structured La9.33(GeO4)6O2 have been refined from powder neutron diffraction data. La2(GeO4)O crystallizes in a monoclinic unit cell (P21/c) and is cation stoichiometric in contrast to previous reports. La9.33(GeO4)6O2 crystallizes in a hexagonal unit cell (P63/m) and the powder diffraction data show anisotropic peak broadening that is observed in electron diffraction patterns as incommensurate diffuse spots at hkq reciprocal planes (with q=1.6-1.7) and can be attributed to a correlated disorder in the “apatite channels”. This compound was doped up to a nominal composition close to M2La8(GeO4)6O2 with M=Ca, Sr, Ba. The dopant ions preferentially occupy the 4f sites as the number of La vacancies decreases. The measured ionic conductivity of La9.33(GeO4)6O2 is about 3 orders of magnitude larger than for La2(GeO4)O at high temperatures and decreases with increasing dopant content from the highest value of about 0.16 S cm−1 at 1160 K. 相似文献
994.
A modified thiocyanate method without extraction by using rhodamine 6G as a secondary ligand was developed. Molybdenum in 1.0×10−2 M HCl, after the addition of ascorbic acid, was heated for 10 min in a 90 °C water bath for reduction. Suitable amounts of glycerine, Triton X-100, rhodamine 6G solutions and 2+1 (v/v) 9 M H2SO4+3 M KHSO4 were added in this order. This solution was allowed to cool to room temperature and the absorbance at 570 nm was measured against a reagent blank 45 min after the addition of thiocyanate solution and the second aliquot of Triton X-100 solution. The complex was stable for at least 4 h, the order of reagent addition was important, and thiocyanate should be in large excess. Beer’s law was obeyed over the range 0.9×10−6 to 1.1×10−5 M Mo with the molar absorptivity being 1.1×105 l mol−1 cm−1. The R.S.D. for the determination of 0.7 mg Mo l−1 was 1.83% (n=8). Possible interferences of various cations and anions on molybdenum determination were studied. The proposed method was applied to the determination of molybdenum in a dental alloy, Wiron 99. 相似文献
995.
5-Hydroxytryptamino-induced calcium sparks in cultured rat stomach fundus smooth muscle cells 总被引:1,自引:0,他引:1
With the imaging fluorescence probe of Ca2+ (fluo-3) and a laser scanning confocal micro-scope, the spontaneous localized calcium release event was first discovered in resting rat cardiac myocytes by Cheng[1] in 1993. A mathematical simulation is developed with computer in order to reveal the effect, which is immediately suggested that these events are likely to reflect the local-ized release of Ca2+ from a small cluster of ryanodine-sensitive Ca2+ release channels in sar-coplasmic reticulum … 相似文献
996.
Liya?Wang Zhiliang?Liu Chenxi?Zhang Zhanquan?Liu Daizheng?Liao Zonghui?JiangEmail author Shiping?Yan 《中国科学B辑(英文版)》2003,46(6):533-541
A novel one-dimensional manganese(II) complex containing nitronyl nitroxide radical [Mn2(IM2-py)2(Ac)2(μ1,1-N3)(μ1,3-N3) · EtOH]
n
was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group p21/n. Each Mn(II) ion is six-coordinated in a distorted octahedral environment. The two N atoms of the nitronyl nitroxide radical
and the two O atoms of acetate ligands are in the equatorial plane, whereas the two different azido bridging ligands are in
trans axial position. Mn(II) ions are linked by nitrogen atom of μ1,1-azido and oxygen atoms of two carboxy groups to form a Mn-Mn unit. Mn-Mn units are linked by azido ligands through μ1,3 bridging style to form a one-dimensional chain. The compound is connected by the coordination bonds, π-π interactions and
hydrogen bonds as a three-dimensional structure. Magnetic susceptibility data support that there are stronger antiferromagnetic
interactions between the radical and Mn(II) ion, weak antiferromagnetic interactions between the Mn-R units, and very weak
antiferromagnetic interactions between the R-Mn-Mn-R units. 相似文献
997.
Several criteria are known for determining which connectionsA are determined uniquely by their curvatureF, or byF and its covariant derivatives. On a principal bundle with semi-simple gauge groupG over a 4-manifoldM, a sufficient condition forF to determineA uniquely is that the linear mapB [F B] from Lie algebra-valued 1-forms to 3-forms (pulled back toM via a local gauge) be invertible on an open dense set inM. Recently F. A. Doria has claimed that this condition is also necessary. We present counterexamples to this claim, and also to his assertion thatF determinesA uniquely if the restriction of the bundle to every open subset ofM has holonomy group equal toG andF is not degenerate as a 2-form over spacetime.This research was supported in part by N. S. F. grant MCS80-03419 (first author) and by an NSERCC operating grant (second author) 相似文献
998.
The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows obvious electrocatalytic activity for the oxidation of epinephrine (EP). In phosphate buffer (pH 7.73), a sensitive oxidation peak was observed at 0.190V with the PCA modified Au electrode. The peak current is proportional to the concentration of EP in the range of 2.0×10–56.0×10–4molL–1 and 5.0×10–6 2.0×10–4molL–1 for cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with the detection limits of 1.8×10–7 and 1.3×10–7molL–1, respectively. The possible reaction mechanism is also discussed. The PCA self-assembled monolayer modified gold electrode is highly stable and can be applied to the determination of EP in practical injection samples. Application is simple, rapid and produces accurate results. 相似文献
999.
Jenny?ZevallosEmail author Alejandro?Toro-Labbé Otilia?Mó Manuel?Yá?ez 《Structural chemistry》2005,16(3):295-303
High level ab initio and density functional theory calculations have been carried out to investigate the relative stability of the different conformers of hyponitrous acid and its mono- and dithio-derivatives. Geometries and vibrational frequencies were obtained at the B3LYP/6-311+G(d,p) level and final energies through B3LYP/6-311++G(3df,2pd) single point calculations. The reliability of this theoretical scheme has been assessed by comparing these DFT results with those obtained at the G3 level of theory, for some suitable cases. The cis conformers of hyponitrous acid and its mono- and dithio-derivatives are systematically more stable than the
trans ones because in the cis conformation a dative interaction between the nitrogen-lone pairs and the σNX^* antibonding orbital is significantly favored. Quite interestingly, in general, the conformers presenting an intramolecular hydrogen bond (IHB) are not the global minima of the corresponding potential energy surfaces and only for hyponitrous acid the conformer with a OH ⋅s O IHB is slightly more stable than the cis conformer without IHB. The low stability of the tautomers with IHB is closely related with another weak intramolecular interaction which involves the lone-pairs of the chalcogen atoms and the πNN* antibondig orbital, and which is significantly perturbed when the IHB is formed. 相似文献
1000.
Javier Revilla Abdelhamid Ela?&#x;ssari Pascal Carriere Christian Pichot 《Journal of colloid and interface science》1996,180(2):405
The adsorption of bovine serum albumin (BSA) onto polystyrene latexes bearing various amounts of sugar moieties has been investigated as a function of pH and ionic strength and the results were compared to those for bare polystyrene latexes having negative surface charges. The functionalized latexes were produced by seeded copolymerization of (0.3 μm) liposaccharidic monomer onto polystyrene particles obtained by soap-free emulsion polymerization of styrene using potassium persulfate as initiator. At first, the electrophoretic mobility behavior of the various latexes was examined as a function of pH: a significant decrease was observed in the case of saccharide-containing latex particles compared to the bare particles. The adsorption of BSA onto these latexes exhibited a reduced amount of adsorbed BSA for those latex particles bearing saccharide groups. This adsorbed amount depends on the yield of saccharidic monomer incorporated onto the surfaces of the latex particles. 相似文献