MoO3、NiO、ZnO在小表面金红石上的分散行为

Dispersion of MoO3, NiO, ZnO on rutile TiO2 with low specific surface area was studied with Mercury Porosimeter, SEM, XPS and Ammonia Extraction method. The dispersion thresholds of MoO3, NiO, ZnO on three rutile TiO2 carriers were obtained with XPS, and com-pared with those on anatase TiO2 with high specific surf are area. Ammonia Extraction method was used to identify the surface oxide species interarting with support surface in different strength and it was found that the proportions of oxides that can not be extracted by ammonia extraction are different for MoO3, NiO and ZnO which are supported on rutile TiO2.     

Acid-Catalyzed Amine-Borane Reduction of Nitrite

The rate of reduction of nitrite by trimethylamine-borane was followed by observing the decrease in nitrite absorbance under pseudo-first-order conditions. The reaction is acid-catalyzed and exhibits a first-order dependence on both amine-borane and total nitrite concentration. The molar equivalence of NaNO(2) to (CH(3))(3)NBH(3) = 2:1. Equimolar amounts of hydrogen and nitrous oxide are formed, and the molar ratio of nitrite reacted to N(2)O produced is 2:1. In concentrated HCl or H(2)SO(4), a correlation of rate with the Hammett acidity function, h(o), is observed. The reaction is subject to a pronounced inversesolvent isotope effect (k(D)()2(O)/k(H)()2(O) approximately 2.7) and a modest normal substrate effect (k((CH)()3())()3(N.BH)()3/k((CH)()3())()3(N.BD)()3 approximately 1.4). The reaction is first-order in H(3)O(+) in the region pH 0.7-2.7, but a second-order dependence is observed above pH 4 with the transition occurring at pH approximately pK(a) for HNO(2). Results are consistent with a mechanistic model involving preequilibration protonation of molecular nitrous acid followed by rate-limiting hydride attack on H(2)ONO(+) or free NO(+) to produce nitrosyl hydride as a reactive intermediate.     

Water in carbon nanotubes: adsorption isotherms and thermodynamic properties from molecular simulation

Grand canonical Monte Carlo simulations are performed to study the adsorption of water in single-walled (6:6), (8:8), (10:10), (12:12), and (20:20) carbon nanotubes in the 248-548 K temperature range. At room temperature the resulting adsorption isotherms in (10:10) and wider single-walled carbon nanotubes (SWCNs) are characterized by negligible water uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption/desorption hysteresis loops. The width of the hysteresis loops decreases as pore diameter narrows and it becomes negligible for water adsorption in (8:8) and (6:6) SWCNs. Results for the isosteric heat of adsorption, density profiles along the pore axis and across the pore radii, order parameter across the pore radii, and x-ray diffraction patterns are presented. Layered structures are observed when the internal diameter of the nanotubes is commensurate to the establishment of a hydrogen-bonded network. The structure of water in (8:8) and (10:10) SWCNs is ordered when the temperature is 298 and 248 K, respectively. By simulating adsorption isotherms at various temperatures, the hysteresis critical temperature, e.g., the lowest temperature at which no hysteresis can be detected, is determined for water adsorbed in (20:20), (12:12), and (10:10) SWCNs. The hysteresis critical temperature is lower than the vapor-liquid critical temperature for bulk Simple Point Charge-Extended (SPCE) water model.     

Computer simulations of enantioselective ester hydrolyses catalyzed by Pseudomonas cepacia lipase

On the basis of the X-ray crystal structure of the lipase from Pseudomonas cepacia (PcL)-an enzyme representative for a whole family of Pseudomonas lipases (lipase PS, SAM-2, AK 10, and others with a high degree of homology with PcL)-a computational study was performed to rationalize both the enantioselectivity and substrate specificity (tolerance) displayed by this lipase in the enantioselective hydrolysis of racemic esters 1a-12a from various secondary aromatic alcohols. The major goal of this project was the development of a binding model for PcL which is able to rationalize the experimental findings to predict "a priori the enantioselective behavior of PcL toward a wider range of substrates. A two-step modeling procedure, namely, docking experiments followed by construction of tetrahedral intermediates, was used for the simulation of the involved enzyme-substrate recognition/hydrolysis processes. The study of the recognition process (docking experiments) led to unambiguous identification of the binding geometry for the two enantiomeric series of substrates, but did not suggest a definitive interpretation of the behavior of PcL. Taking into consideration the stereoelectronic requirements of the enzymatic hydrolysis reaction, both the enantioselectivity and tolerance of the enzyme were then explained through the study of the tetrahedral intermediates, in turn constructed from the calculated docking geometries of 1a-12a.     

Cucurbit[6]uril pseudorotaxanes: distinctive gas-phase dissociation and reactivity

Cucurbit[6]uril forms a doubly charged complex with 1,4-butanediammonium cation that is observed using electrospray ionization Fourier transform mass spectrometry. Such 1:1 complexes are not observed for the smaller cucurbit[5]uril, which forms a 2:1 ammonium:cucurbituril complex instead. The 1:1 complex with cucurbit[6]uril is difficult to fragment via collisional activation; when it does fragment, both breakup of the cucurbituril cage and loss of the amine are observed. Further, the complex reacts with tert-butylamine via slow adduction. In contrast, nonrotaxane analogues (such as doubly charged 2:1 complexes of either protonated 1,4-butanediamine or protonated ethylenediamine with cucurbit[6]uril) fragment via easy loss of the intact amine upon collisional activation and react with tert-butylamine via rapid displacement of the original amine. On the basis of stoichiometry, fragmentation behavior, and reactivity, we conclude that the doubly charged complex of cucurbit[6]uril with 1,4-butanediammonium is a gas-phase pseudorotaxane.     

Molecular characteristics of the inhibition of human neutrophil elastase by nonsteroidal antiinflammatory drugs

Nonsteroidal antiinflammatory drugs(NSAIDs) are known as clinically effective agents for treatment of inflammatory diseases. Inhibition of cyclooxygenase has been thought to be a major facet of the pharmacological mechanism of NSAIDs. However, it is difficult to ascribe the antiinflammatory effects of NSAIDs solely to the inhibition of prostaglandin synthesis. Human neutrophil elastase (HNElastase; HNE, EC 3.4.21.37) has been known as a causative factor in inflammatory diseases. To investigate the specific relationship between HNElastase inhibition and specificity of molecular structure of several NSAIDs, HNElastase was purified by Ultrogel AcA54 gel filtration, CM-Sephadex ion exchange, and HPLC (with TSK 250 column) chromatography. HNElastase was inhibited by aspirin and salicylate in a competitive manner and by naproxen, ketoprofen, phenylbutazone, and oxyphenbutazone in a partial competative manner, but not by ibuprofen and tolmetin. HNElastase-phenylbutazone-complex showed strong Raman shifts at 200, 440, 1124, 1194, 1384, 1506, and 1768 cm(-1). The Raman bands 1194, 1384, and 1768 cm(-1) may represent evidences of the conformational change at -N=N-phi radical, pyrazol ring, and -C=O radical of the elastase-drug complex, respectively. Phenylbutazone might be bound to HNElastase by ionic and hydrophobic interaction, and masked the active site. Inhibition of HNElastase could be another mechanism of action of NSAIDs besides cyclooxygenase inhibition in the treatment of inflammatory diseases. Different inhibition characteristics of HNE-lastase by NSAIDs such as aspirin, phenylbutazone-like drugs and ineffective drugs could be important points for drawing the criteria for appropriate drugs in clinical application.     

Determination of boron in nickel-base alloys by the dianthrimide method

The dianthrimide method for the determination of boron in iron and low-alloy steels may be applied to nickel-base materials. The sample is dissolved, without any loss of boron, by hydrochloric and sulphuric acids and the resulting boric acid determined spectrophotometrically with dianthrimide. Background corrections are necessary to compensate for the absorbance from ions such as nickel and iron.     

Synthesis, characterization, and preliminary intramolecular energy transfer studies of rigid, emissive, rhenium-linked porphyrin dimers

The reaction of pyridyl functionalized porphyrins with Re(CO)(5)Cl in THF results in the formation of porphyrin dimers which, despite incorporation of rhenium into the assemblies, remain fluorescent. The rigid compounds provide an efficient geometry and/or orbital pathway for singlet energy transfer, rendering these compounds suitable, in principle, for the study of both through-bond and through-space energy transfer. Derivatives containing both metallated and freebase porphyrins connected via the metal corners display efficient porphyrin-porphyrin energy transfer. The photophysical properties of the assemblies have been studied by both steady-state and time-resolved fluorescence techniques, yielding approximate rates and efficiencies for porphyrin-porphyrin energy transfer.     

Thick-target PIGE analysis of plant materials preconcentrated by dry ashing

An analytical methodology has been developed for the UV-spectrophotometric determination of carbaryl in waters after its preconcentration onto a polyether type polyurethane foam followed by on-line elution. The aforementioned strategy offers an easy way for in-field sampling and to improve the analytical sensitivity. Several chemical and flow variables (mass of sorbent, sample flow rate, sample volume and carrier flow rate) were studied to ensure the best performance of the system. Recovery studies, carried out on natural water samples spiked with known amounts of carbaryl at concentration levels between 250 and 500 mug l(-1), provided recovery percentages between 94 and 105%. A detection limit of 12 mug l(-1) was achieved and a variation coefficient of 3.4% was obtained at 0.50 mug ml(-1).