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排序方式: 共有2214条查询结果,搜索用时 62 毫秒
981.
982.
Wu CS 《Macromolecular bioscience》2008,8(6):560-567
The use of PLA and PLA-g-AA/starch as materials for the controlled release of encapsulated PSB was evaluated. The results showed that the bacterium degraded both the PLA and the PLA-g-AA/starch composite films, resulting in cell release. Severe disruption of the film structure occurred after incubation for 60-90 d. The PLA-g-AA/starch (20 wt.-%) films were more biodegradable than those made of PLA and also suffered a more pronounced decrease in molecular weight and intrinsic viscosity. Although blending of starch appeared to enhance the biodegradability of the PLA films, the pattern of degradation was quite similar for both types of films. The rate of cell release depends on the biodegradability of the film. 相似文献
983.
A biodegradable GTP composite composed of OPCs crosslinked gelatin with tricalcium phosphate was prepared as a novel bone substitute. The effects of the degree of crosslinking on the swelling ratio, in vitro degradation rate, and morphology of the GTP composite are discussed. Adding OPCs to GP and GTP composites markedly reduced the degradation rate, indicating that OPCs are good crosslinking reagents for gelatin. Cytotoxic tests demonstrated that OPCs, gelatin and tricalcium phosphate released from GTP composite promoted the proliferation of MG-63 cells. Results of this study suggest that the nontoxic GTP composite is suitable for use as a large defect bone substitute. 相似文献
984.
Jun Zhang Jinwu Guo Suqin Li Bangcai Song Kaisheng Yao 《Frontiers of Chemistry in China》2008,3(4):451-453
β-tricalcium phosphate (β-TCP) is a key component of natural bone like hydroxyapatite. Pure and uniformly nanosized β-tricalcium phosphate powders were synthesized using a sol-gel self-propagating combustion method by using citric acid as
a reductant and using fuel and nitrate as the oxidant. The thermal decomposition of nitrate-citrate xero-gel was studied by
thermogravimetric-differential thermal analysis (TG/DTA) and the process mechanism of self-propagating combustion were discussed.
The resulting powders calcined at 1023, 1173 and 1273 K were characterized by Ca/P ratio analysis, X-ray diffraction (XRD),
scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the asprepared powders were
pure β-tricalcium phosphate having regular porous surface very similar to coral. 相似文献
985.
A novel beta-cyclodextrin dimer, 1,10-phenanthroline-2,9-dimethyl-bridged-bis(6-monoammonio-beta-cyclodextrin) (phenBisCD, L), was synthesized. Its zinc complex (ZnL) has been prepared, characterized, and applied as a new catalyst for diester hydrolysis. The formation constant (logK(ML)=9.56+/-0.01) of the complex and deprotonation constant (pK(a)=8.18+/-0.04) of the coordinated water molecule were determined by a potentiometric pH titration at (298+/-0.1) K. Hydrolytic kinetics of carboxylic acid esters were performed with bis(4-nitrophenyl) carbonate (BNPC) and 4-nitrophenyl acetate (NA) as substrates. The obtained hydrolysis rate constants showed that ZnL has a very high rate of catalysis for BNPC hydrolysis, giving a 3.89x10(4)-fold rate enhancement over uncatalyzed hydrolysis at pH 7.01, relative to only a 42-fold rate enhancement for NA hydrolysis. Moreover, the hydrolysis second-order rate constants of both BNPC and NA greatly increases with pH. Hydrolytic kinetics of a phosphate diester catalyzed by ZnL was also investigated by using bis(4-nitrophenyl) phosphate (BNPP) as the substrate. The pH dependence of the BNPP cleavage in aqueous buffer shows a sigmoidal curve with an inflection point around pH 8.11, which was nearly identical to the pK(a) value from the potentiometric titration. The k(cat) of BNPP hydrolysis promoted by ZnL was found to be 9.9x10(-4) M(-1) s(-1), which is comparatively higher than most other reported Zn(II)-based systems. The possible intermediate for the hydrolysis of BNPP, BNPC, and NA catalyzed by ZnL is proposed on the basis of kinetic and thermodynamic analysis. 相似文献
986.
CAO Xue-Gong LINBi-Zhou GENG Feng LI Xiao-Li XIAO Zi-Jing 《结构化学》2008,27(6):743-748
A new reduced molybdenum(V) phosphate (H3dien)2(H2dien)2[NaMo12O24 (OH)6 (HEPO4)(HPO4)5(PO4)2]·nH2O (n= 10.92, dien = diethylenetriamine) has been synthesized under hydrothermal conditions and characterized by elemental analyses, IR and X-ray diffraction. C16H96.84MO12N12NaO72.92P8 (Mr = 3046.73) crystallizes in the monoclinic system, space group P21/c with a = 13.3575(18), b = 21.907(3), c = 15.654(2)A, β= 110.22(2)°, V= 4298.4(10) A^3 Dc = 2.354 g/cm^3, Z = 2,μ(MoKcr) = 1.966 mm^-1, F(000) = 2990.4, the final R = 0.0357 and wR = 0.1086 for 8739 observed reflections with I 〉 2σ(I). It consists of sandwich-shaped cluster anions [Na{Mo6P4}2]^10- held together into a three-dimensional supramolecular framework through intermolecular hydrogen-bonding contacts. A probe reaction of the oxidation of acetaldehyde with H2O2 showed that this compound has high catalytic activity in the reaction. 相似文献
987.
Rahmat Sadeghi Rahim Hosseini Bahman Jamehbozorg 《The Journal of chemical thermodynamics》2008,40(9):1364-1377
Precise density, sound velocity, water activity, and phase diagram measurements have been carried out on polyethylene oxide (PEO) in aqueous solutions of sodium di-hydrogen phosphate, di-sodium hydrogen phosphate, and tri-sodium phosphate over a range of temperatures at atmospheric pressure. The experimental density and sound velocity data are used to calculate the apparent specific volume and isentropic compressibility as a function of temperature and concentration. It was found that both of the apparent specific volume and isentropic compressibility of PEO in aqueous solutions increase by increasing temperature and charge on the anion of electrolytes. The results show that the slope of constant water activity lines increased with increasing the temperature and charge on the anion of electrolytes and the vapour pressure depression for an aqueous (PEO + sodium phosphate) system is more than the sum of those for the corresponding binary solutions. Furthermore, the effect of temperature and type of anion of salt on the salting-out effect of polyethylene oxide by sodium phosphate salts has been studied. 相似文献
988.
Marina V. Maslova Valeri Naydenov Lidia G. Gerasimova 《Journal of solid state chemistry》2008,181(12):3357-3365
Decomposition of mineral sphene, CaTiOSiO4, by H3PO4 is investigated in detail. During the dissolution process, simultaneous calcium leaching and formation of titanium phosphate (TiP) take place. The main product of decomposition is a solid titanium phosphate-silica composite. The XRD, solid-sate NMR, IR, TGA, SEM and BET data were used to identify and characterize the composite as a mixture of crystalline Ti(HPO4)2·H2O and silica. When 80% phosphoric acid is used the decomposition degree is higher than 98% and calcium is completely transferred into the liquid phase. Formation of Ti(HPO4)2·H2O proceeds via formation of meta-stable titanium phosphate phases, Ti(H2PO4)(PO4)·2H2O and Ti(H2PO4)(PO4).The sorption affinities of TiP composites were examined in relation to caesium and strontium ions. A decrease of H3PO4 concentration leads to formation of composites with greater sorption properties. The maximum sorption capacity of TiP is observed when 60% H3PO4 is used in sphene decomposition.The work demonstrates a valuable option within the Ti(HPO4)2·H2O-SiO2 composite synthesis scheme, to use phosphoric acid flows for isolation of CaHPO4·2H2O fertilizer. 相似文献
989.
We have synthesized a bis(terthiophene)-appended uranyl-salophen complex, comprising N,N′-bis[4-(5,2′:5′,2″-terthiophen-3′-yl)salicylidene]-1,2-ethanediamine-uranyl complexes (TUS), and used it as a monomer for the electrochemical polymerizations (poly-TUS) on glassy carbon surfaces to prepare functionalized conducting polymer (CP) films. The poly-TUS films prepared from propylene carbonate/0.1 M tetrabutyl ammonium perchlorate (TBAP) on a glassy carbon electrode have both the functionality of ion-to-electron transducers (solid contact) and Lewis-acidic binding sites for a monohydrogen phosphate (MHP) ion-selective electrode (ISE). The CP/poly-TUS sensor showed a linear range between 1.0 × 10−1 and 1.0 × 10−4.5 M with a near-Nernstian behavior (−30.4 mV decade−1) at a pH of 8.2. The detection limit of the electrode was 10−5.0 M and the response time was improved (<10 s) compared to that of conventional ISEs (<20 s). For comparison, a conventional ISE (with an internal aqueous solution) based on a TUS monomer/o-nitrophenyl octylether (o-NPOE)/polyvinyl chloride (PVC) liquid membrane with or without tridodecylmethylammonium chloride (TDMACl) as an additive was also constructed and its performance as an MHP-ISE were studied. The superior selectivity and sensitivity of the CP/poly-TUS sensor enabled the direct measurement of MHP in a wide variety of applications. 相似文献
990.
Chloroquine phosphate and promethazine hydrochloride are two main components in compound reserpine tablets. It is difficult to separate the two compounds with capillary electrophoresis (CE). Heuristic evolving latent projections (HELP) is a chemometric algorithm which is suitable for resolving overlapped peaks from CE and HPLC. In this paper, HELP was applied to resolving the completely overlapped peaks of chloroquine phosphate and promethazine hydrochloride from CE. Mathematical separation and satisfactory quantification results can be achieved easily without too much time involved in the procedure. 相似文献