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1.
The calcium phosphate which corresponds to the formula Ca 3(PO) 4 · nH 2O (2< n<3) was isolated from solutions with Ca/P molar ratio 0.2 and pH 7. The compound was characterised by chemical and thermogravimetric analyses, Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction. The FTIR spectra were compared with spectra of β-tricalcium phosphate (β-TCP) in the atlases for analysis of urinary calculi and other literature data. 相似文献
2.
The paper reports results of a study on the specific adsorption of F −, Cl −, Br −, I −, ClO 3−, BrO 3−, IO 3− and IO 4− on hydrous γ-Al 2O 3. The isotherms of the anion adsorption and the adsorption dependencies on pH and the ionic strength of the solution have been determined under the equilibrium conditions. According to the degree of affinity to γ-Al 2O 3, the anions can be ordered as: I −3− −−3−3−4−−. It has been established that the sorption of IO4− and F− involves the formation of surface complexes in the inner co-ordination sphere, whereas that of Cl−, Br−, I−, ClO3−, BrO3− and IO3− takes place through formation of ion pair complexes in the outer co-ordination sphere. In the dynamic system, the exchange isoplanes and elution curves have been determined for selected anions on columns filled with Al2O3. It has been shown that γ-Al2O3 can be used for isolation and concentration of IO3− from natural waters in order to decrease the limit of the ions determination to 2 μg l−1. Using differential pulse voltammetry (DPV), after isolation and concentration on γ-Al2O3, the content of iodates has been determined in mineral, marine and tap water doped with these ions. 相似文献
3.
在150 ℃下, 仅以高锰酸钾溶液和无水乙醇为原料, 通过水热反应合成前驱体 γ-MnOOH纳米棒. 以 γ-MnOOH纳米棒为自牺牲模板, 分别在350和600 ℃下煅烧90 min, 制备出高纯度的 β-MnO 2和 α-Mn 2O 3纳米棒. 采用X射线粉末衍射(XRD)、 扫描电子显微镜(SEM)及热重分析(TGA)等对所制备的样品进行表征. 结果表明, 前驱物 γ-MnOOH为高纯度的纳米棒状晶体, 直径约100~300 nm, 长度可达数微米, 且终产物 β-MnO 2和 α-Mn 2O 3均具有较高的纯度, 也很好地保持了前驱物的纳米棒状结构. 以二者为锰源, 通过固相反应合成出尖晶石LiMn 2O 4正极材料. 当充放电倍率为0.5 C时, 其首次放电比容量分别可达到120.4和123.9 mA·h/g, 而且表现出良好的循环性能和倍率性能. 相似文献
4.
A series of γ-Al 2O 3 samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al 2O 3 methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO 42−/γ-Al 2O 3 for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO 42−/γ-Al 2O 3 was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO 2. On the other hand, when the calcination temperature of SO 42−/γ-Al 2O 3 increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO 2. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO 42−/γ-Al 2O 3 for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO 42−/γ-Al 2O 3 with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME. 相似文献
5.
采用静电纺丝法制备了PVP/FeC 6H 5O 7复合纳米纤维, 并将复合纤维在500 ℃高温烧结3 h, X射线衍射分析(XRD)表明, 烧结后的产物为正尖晶石结构的γ-Fe 2O 3晶体. 扫描电子显微镜(SEM)观测结果表明, 制得了直径均匀、 连续的复合纳米纤维, 其平均直径约为1000 nm; 烧结后的γ-Fe 2O 3纳米纤维保持了其连续性, 但纤维发生了收缩, 直径较烧结前小, 平均约为600 nm. 比表面积分析表明, γ-Fe 2O 3纳米纤维比表面积为57.18 m 2/g. 气敏性能测试结果表明, 230 ℃为γ-Fe 2O 3纳米纤维检测丙酮气体的最佳工作温度. 在此温度下, γ-Fe 2O 3纳米纤维对丙酮气体表现出高响应度[S=6.9, c(Acetone)=7.88×10 4 mg/m 3]和线性度(7.88×10 2~1.58×10 5 mg/m 3浓度范围内). 同时, γ-Fe 2O 3纳米纤维气体传感器件还表现出良好的长期稳定性. 相似文献
6.
The first Pd/C-mediated Sonogashira coupling of β-chloroacroleins with terminal alkynes is described here. Pd/C–CuI–PPh 3 was found to be an efficient catalyst system for this coupling reaction. Using this economic and general process a variety of 4-alkynyl-2 H-chromene-3-carbaldehydes and 5-alkynyl-2,3-dihydro benzo[ b]oxepine-4-carbaldehydes were prepared in good yields. 相似文献
7.
It was found that surfactin, an anionic lipopeptide biosurfactant, forms large rod-shaped micelles (micellar weight, 179 000, aggregation number n = 173) having a critical CMC of 9.4 × 10 −6 M and a surface tension at the CMC γCMC of 30 mN m −1 in 0.1 M NaHCO 3 (pH 8.7). This excellent surface-active behaviour was attributed to the ease of piling of surfactin molecules organized by β-sheet formation. Surfactin also showed a possible organization between molecules due to β-sheet structure at the air-water interface under forced experimental conditions. 相似文献
8.
The interaction between vanadium (V) and the carbohydrate β-cyclodextrin (β-CD) has been studied in aqueous solutions (pH ≈ 7.5, 298.15 K) using multinuclear NMR spectroscopy, coupled with measurements of diffusion coefficients and electrical conductivity. The transport properties of vanadate ion solutions are markedly influenced by the presence of β-CD. Data from 51V, 1H and 13C NMR spectroscopy show that these effects are due to strong interactions between this carbohydrate and vanadate due to formation of 2:1 (β-CD:vanadate) complexes. The formation of such 2:1 complexes is also supported by molecular mechanics calculations. Complexation is seen by conductometric and diffusion techniques to lead to a significant decrease in the molar conductivity and diffusion coefficient of vanadate solutions in the presence of β-CD. Using the above stoichiometry, it has been possible to calculate the association constant, leading to the value K = 4.3 × 10 4 M −2 from the analysis of the conductivity data. 相似文献
9.
The methoxycarbonylation of propylene oxide (PO) to methyl β-hydroxybutyrate (MHB) catalyzed by dicobaltoctacarbonyl ([Co 2(CO) 8]) and 3-hydroxypyridine (3-OH-Py) in methanol system has been studied. The effects of different additives, the molar ratio of 3-OH-Py:Co 2(CO) 8, temperature, carbon monoxide (CO) pressure, reaction time on the conversion and selectivity have been investigated. The conversion of propylene oxide is 80.4%, and the yield of methyl β-hydroxybutyrate is 74.9% with selectivity 93.2% when the reaction is carried out for 16 h at 80 °C and 6.0 MPa of CO in methanol, with 0.125 mmol of Co 2(CO) 8, 0.25 mmol of 3-OH-Py. The mechanism of this catalytic reaction has also been proposed. 相似文献
10.
考察了在玫瑰红(RB)存在下 γ-六氯环己烷( γ-HCH)在冰中的光降解. 结果表明, 光敏剂RB通过其激发态[RB] *及其产生的 1加速了 γ-HCH的光降解, RB浓度是影响光降解率最显著的因素; γ-HCH在较低初始浓度下的光敏化降解更快; 无机盐离子的种类和浓度可以改变冰表面上类液层(LLL)的比例从而影响 γ-HCH的光解. 通过分析 γ-HCH光降解产物提出了RB存在时冰中 γ-HCH的光降解作用机理. 相似文献
11.
A novel method for the enantioselective synthesis of β-lactams is described in this study. 2,3-Dihydrobenzooxazin-4-one derived from salicylamide and L-menthone was used as the chiral auxiliary, which reacted with a-bromo-acyl bromides in the presence of pyridine to give carboximides 2. The stereo-controlled Reformatsky-type reactions of carboximides with imines yielded the corresponding trans β-lactams with high enantioselectivities(e.e. 75%-86%) and high chemical yields(63%-85%), meanwhile, the chiral auxiliary dihydrobenzooxazin-4-one was released and recovered. 相似文献
12.
研究了腐植酸(HA)存在下冰相体系中 γ-六氯环己烷( γ-HCH)的光转化规律. 结果表明, HA浓度对 γ-HCH的光转化率呈现低浓度促进而高浓度抑制的现象; 盐离子浓度、 N 及N 对 γ-HCH的光转化率均有促进作用; 低浓度Fe 3+对 γ-HCH的光转化率有促进作用, 当Fe 3+的浓度增大到50 μmol/L时, 呈现抑制效应; γ-HCH在不同pH值条件下光转化速率的大小顺序为碱性>中性>酸性. 冰相中HA通过产生单线态氧( 1O 2)、 羟基自由基(·OH)及三重激发态(HA *)加速 γ-HCH的光转化. HA存在下 γ-HCH的光转化产物主要是五氯环己烯、 邻二氯苯和对二氯苯、 一氯苯, 光转化过程中 1O 2通过消耗中间产物间接加速了 γ-HCH的光转化过程. 相似文献
13.
The micro-structural integrity of meso-porous inorganic membranes is of critical importance in their prolonged application. Inspection by transmission electron microscopy of state-of-the-art γ-alumina membrane cross-sections, made by focused ion beam milling, reveals structural defects which adversely affect performance, reproducibility, and lifetime. It is shown that the use of macro-porous supports with a smooth, defect-free deposition surface for membrane dip coating, in combination with purified precursor sols and clean processing, leads to major improvements in micro-structural homogeneity and properties of the membranes. Large particle contaminants/agglomerates can be effectively removed from precursor sols by high-speed centrifugation or ultrasound-assisted screening. While centrifugation is the most practical method for routine use, filter screening provides a more complete removal of agglomerates and larger particles (>80 nm Ø). Application of the purified membrane precursor sols results in membranes in which connected pore defects (pinholes) are no longer detectable for a membrane thickness of >500 nm thick. The almost complete absence of connected pinholes, obtained with improved membrane processing, is demonstrated by near-100% retention of CaCl 2 in aqueous solution by nano-filtration. The γ-alumina processing experience, collected in our group in the years 2002–2006, is accumulated in a 34-step processing protocol for γ-alumina membranes with a >500 nm single layer thickness. 相似文献
14.
A series of Ce xPr 1−xO 2−δ mixed oxides were synthesized by a sol–gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH 3OH and CH 4 on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO 2 was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO 2 crystal lattices. Raman bands at 465 and 1150 cm −1 in Ce xPr 1−xO 2−δ samples are attributed to the Raman active F 2g mode of CeO 2. The broad band at around 570 cm −1 in the region of 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at 195 cm −1 may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The TPR profile of Pr 6O 11 shows two reduction peaks and the reduction process is followed: . The reduction temperature of Ce xPr 1−xO 2−δ mixed oxides is lower than those of Pr 6O 11 or CeO 2. TPR results indicate that Ce xPr 1−xO 2−δ mixed oxides have higher redox properties because of the formation of Ce xPr 1−xO 2−δ solid solutions. The presence of the oxygen vacancies favors CO and CH 3OH oxidation, while the activity of CH 4 oxidation is mostly related to reduction temperatures and redox properties. 相似文献
15.
以 γ-环糊精( γ-CD)为主体, 采用饱和水溶液法对客体二甲戊灵进行包合. 采用紫外光谱以等摩尔连续变化法确定包合物的包合比为1∶1; 红外光谱证明二甲戊灵的部分苯环结构可能进入了 γ-CD的空腔; 热分析结果证明包合作用提升了二甲戊灵的熔点; 粉末X射线衍射谱图中新衍射峰的出现说明形成了新物相; 扫描电镜则直观展现了包合物的外观. 以上结果均表明形成了 γ-CD-二甲戊灵包合物, 其包合平衡常数 K=1123.99 L/mol. 包合作用使二甲戊灵的熔点从54 ℃升至75 ℃, 溶解度提高了约11.5倍, 包合物热贮稳定性达标, 为进一步将其加工成其它水基化农药剂型提供了可能. 相似文献
16.
An enzyme-based microtiter plate assay for γ-aminobutyric acid (GABA) was developed. GABA was quantified using γ-aminobutyrate glutamate aminotransferase and succinic semialdehyde dehydrogenase in the presence of NADP + and -ketoglutarate. The NADPH produced by the series of enzymatic reactions was measured spectrophotometrically at 340 nm. A linear relationship between absorbance and the concentration of GABA was obtained in the ranges from 5.0 × 10 −4 to 1.0 × 10 −2 M. The relative standard deviation for 10 successive measurements was 0.9% at the 10 mM GABA level. This analytical method was applied to the screening of GABA-producing lactic acid bacteria in de Man–Rogosa–Sharpe (MRS) medium. The proposed method enables one to assay 96 samples for an hour without the pre-treatment of samples. The method is by far superior to the traditional HPLC method from the point of view of rapidity and simplicity. 相似文献
17.
Steady-state fluorometric studies have been performed on 2-(2′-hydroxy-5′-methylbenzoyl)-1,5-diphenylpyrrole (HMBDPP) in aqueous and aqueous β-cyclodextrin (β-CD) environments at ambient temperature. The fluorophore mostly shows a single emission in aqueous solution. Addition of β-CD to the aqueous solution of the fluorophore results in the development of another emission band at higher energy. The difference in the fluorometric behaviour is assigned to a remarkable change in the polarity of the microenvironment within the supramolecular structural environment compared to that of the bulk aqueous phase. Semi-empirical calculation (AM1-SCI) rules out the possibility of intramolecular proton transfer reaction in any of the S 0, S 1 and T 1 states of the fluorophore. It is proposed that HMBDPP exists mostly in the intermolecularly hydrogen-bonded form (open conformer) in aqueous solution while within β-CD environment, it is the intramolecularly hydrogen-bonded form (closed conformer) that predominates. 相似文献
18.
This work aims to identify of non-reversible structural changes induced in β-lactoglobulin by permeation through porous ultrafiltration membranes. The evaluation of these structural changes is performed using a fluorescence methodology, which combines the use of three different, complementary, fluorescence techniques: steady-state fluorescence, picosecond time-resolved fluorescence and steady-state fluorescence anisotropy. The identification of the nature of the structural changes induced upon permeation is possible through comparison of the fluorescence responses obtained for β-lactoglobulin solutions collected after permeation (permeates and retentates) with those induced by chemical (addition of Guanidine hydrochloride, GndHCl) and thermal denaturation of β-lactoglobulin. The fluorescence approach used allowed to identify irreversible losses of structural integrity of β-lactoglobulin in the permeates, while β-lactoglobulin retentates seemed to be unaffected by the ultrafiltration process. The mechanisms that regulate the structural alterations of β-lactoglobulin and the magnitude of these alterations depend on the protein to membrane pore size ratio, λ, being more substantial at higher λ (severe pore constriction). Under these conditions (permeation with a 10 kDa membrane) the structural changes induced in the proteins are dictated by the high shear stress at the membrane pore walls. The increase of the membrane cut-off (30 kDa membrane) induces a decrease in the magnitude of the shear stress and the effect of protein–membrane chemical interactions becomes noticeable. 相似文献
19.
The β-diketiminato fluoride complex (LTiF 3) (1) (L = HC(CMeN(2,6- iPr 2C 6H 3)) 2, “NacNac”) has been obtained using two synthetic routes, interaction of TiF 4 and NacNacK·2THF in toluene and interaction of LTiCl 3 and 3 equiv. of Me 3SnF in toluene. The trifluoro complex (LTiF 3) (1) is soluble in the non-polar solvents toluene and hexane and moderately active in polymerization of ethylene; the activity is higher than that of LTiMe 3 and comparable with that of the oxo-bridged complexes LTiCl(μ-O) 2TiClL and LTiMe(μ-O) 2TiMeL·toluene. Compound 1 was characterized by single crystal X-ray structural analysis, elemental analysis, NMR spectroscopy, and mass spectrometry. Complex 1 in the solid state is a centrosymmetric dimer containing two LTiF 2 moieties connected by two bridging fluorines, whereas C 6D 6 and CD 3CN solutions of 1 contain the monomeric complex at room temperature. 相似文献
20.
We report herein the interaction of three kinds of ionic liquids, i.e., 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF 6), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF 4) and 1-butyl-3-methylimidazolium chloride (bmimCl) with β-cyclodextrin (β-CD) using 2-( p-aminophenyl)-3,3-dimethyl-5-carboethyoxy-3 H-indole (1) as a fluorescent probe through a competitive method. The formation of the 1:1 (guest:host) inclusion complex was suggested and the association constants at different temperatures were estimated, from which the thermodynamic parameters Δ GΘ, Δ HΘ and Δ SΘ were also obtained. The negative entropy and enthalpy changes indicated that the formation of above inclusion complexes was entropically unfavorable and enthalpy-driven. Conductivity measurements were also employed to study above systems. The results showed agreement with those based on the competitive method. Furthermore, through NMR, the location of anions in the system of ILs and β-CD was investigated. We suggested that the anion was accommodated to a great extent by the cavity forming ion pair with imidazolium cation which was totally in the cavity of β-CD. The above work demonstrated that molecule 1 is a very sensitive fluorescence probe for studying the interaction of a non-fluorescent guest with cyclodextrins. 相似文献
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