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161.
Elia Tfouni Fabio Gorzoni Doro Anderson Jesus Gomes Roberto Santana da Silva Gustavo Metzker Patricia Graça Zanichelli Benini Douglas Wagner Franco 《Coordination chemistry reviews》2010,254(3-4):355-371
Methodologies for the immobilization and characterization of ruthenium complexes into/onto functionalized silica gel, zeolites, polymers, dendrimers, sol–gel, nano and microparticles are described. The corresponding spectroscopic, electrochemical, and photochemical properties as well as chemical reactivities are used for their characterization and study. Comparison between the reactivities of immobilized and in solution species is presented. Some biological applications are also described. 相似文献
162.
Andrei Jitianu John Doyle Glenn Amatucci Lisa C. Klein 《Journal of Sol-Gel Science and Technology》2010,53(2):272-279
Hybrid melting gels were prepared by a sol–gel process, starting with a mono-substituted siloxane and a di-substituted siloxane.
Methyl-modified melting gels were prepared using (a) methyltriethoxysilane (MTES) with dimethyldiethoxysilane (DMDES) and
(b) methyltrimethoxysilane (MTMS) together with dimethyldimethoxysilane (DMDMS). The gels with MTES–DMDES were prepared with
concentrations between 50–50 and 75–25 mol%. The gels with MTMS–DMDMS were prepared with concentrations between 50–50 and
70–30 mol%. For both systems, the consolidation temperature, after which the melting gel no longer softens, increased with
an increase in the amount of the mono-substituted siloxane, increasing from 135 to 160 °C for MTES–DMDES and increasing from
145 to 170 °C for MTMS–DMDMS. Coatings formed on mica substrates were about 1 mm thick, and showed no visible cracks. The
surfaces of the coatings were profiled using micro-Raman spectroscopy, which revealed that methyl groups were concentrated
at the surfaces of the films. All contact angles measured with water were greater than 90°. 相似文献
163.
Kshitish Patankar David A. Dillard Scott W. Case Michael W. Ellis Yongqiang Li Yeh‐Hung Lai Michael K. Budinski Craig S. Gittleman 《Journal of Polymer Science.Polymer Physics》2010,48(3):333-343
Pinhole formation in proton exchange membranes (PEM) may be caused by a process of flaw formation and crack propagation within membranes exposed to cyclic hygrothermal loading. Fracture mechanics can be used to characterize the propagation process, which is thought to occur in a slow, time‐dependent manner under cyclic loading conditions, and believed to be associated with limited plasticity. The intrinsic fracture energy has been used to characterize the fracture resistance of polymeric material with limited viscoelastic and plastic dissipation, and has been found to be associated with long‐term durability of polymeric materials. Insight into this limiting value of fracture energy may be useful in characterizing the durability of proton exchange membranes, including the formation of pinhole defects. In an effort to collect fracture data with limited plasticity, a knife slit test was adapted to measure fracture energies of PEMs, resulting in fracture energies that were two orders of magnitude smaller than those obtained with other fracture test methods. The presence of a sharp knife blade reduces crack tip plasticity, providing fracture energies that may be more representative of the intrinsic fracture energies of the thin membranes. Three commercial PEMs were tested to evaluate their fracture energies (Gc) at temperatures ranging from 40 to 90 °C and humidity levels varying from dry to 90% relative humidity (RH). Experiments were also conducted with membrane specimens immersed in water at various temperatures. The time temperature moisture superposition principle was applied to generate fracture energy master curves plotted as a function of reduced cutting rate based on the humidity and temperature conditions of the tests. The shift with respect to temperature and humidity suggests that the slitting process is viscoelastic in nature. Also such shifts were found to be consistent with those obtained from constitutive tests such as stress relaxation. The fracture energy is more sensitive to temperature than on humidity. The master curves converge at the lowest reduced cutting rates, suggesting similar intrinsic fracture energies; but diverge at higher reduced cutting rates to significantly different fracture energies. Although the relationship between Gc and ultimate mechanical durability has not been established, the test method may hold promise for investigating and comparing membrane resistance to failure in fuel cell environments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 333–343, 2010 相似文献
164.
The present work is a continuation of an earlier investigation of the effect of severe thermal pretreatment on the redox
properties of platinum electrodes in aqueous media. The most interesting observation was that raising the solution temperature
to ca. 75 °C resulted in a dramatic anodic response in the positive sweep at ca. 0.25 V (RHE). Such behaviour was noted earlier
at room temperature but only when the thermally pretreated sample was further activated by cathodic polarization. This transition
at 0.25 V was partially reversed on the negative sweep, but the cathodic process involved was subject to severe inhibition.
There is independent evidence for similar behaviour for gold in aqueous acid solution. The relevance of the present results
to the operation of fuel cell anodes is outlined.
Received: 2 December 1999 / Accepted: 24 February 2000 相似文献
165.
Elin S. Karlsson Caroline H. Johnson Sunil Sarda Lisa Iddon Mazhar Iqbal Xiaoli Meng John R. Harding Andrew V. Stachulski Jeremy K. Nicholson Ian D. Wilson John C. Lindon 《Rapid communications in mass spectrometry : RCM》2010,24(20):3043-3051
The use of high‐performance liquid chromatography/mass spectrometry (HPLC/MS) and proton nuclear magnetic resonance (1H NMR) spectroscopy for the kinetic analysis of acyl glucuronide (AG) isomerisation and hydrolysis of the 1‐β‐O‐acyl glucuronides (1‐β‐O‐AG) of phenylacetic acid, (R)‐ and (S)‐α‐methylphenylacetic acid and α,α‐dimethylphenylacetic acid is described and compared. Each AG was incubated in both aqueous buffer, at pH 7.4, and control human plasma at 37°C. Aliquots of these incubations, taken throughout the reaction time‐course, were analysed by HPLC/MS and 1H NMR spectroscopy. In buffer, transacylation reactions predominated, with relatively little hydrolysis to the free aglycone observed. In human plasma incubations the calculated rates of reaction were much faster than for buffer and, in contrast to the observations in buffer, hydrolysis to the free aglycone was a significant contributor to the overall reaction. A diagnostic analytical methodology based on differential mass spectrometric fragmentation of 1‐β‐O‐AGs compared to the 2‐, 3‐ and 4‐positional isomers, which enables selective determination of the former, was confirmed and applied. These findings show that HPLC/MS offers a viable alternative to the more commonly used NMR spectroscopic approach for the determination of the transacylation and hydrolysis reactions of these AGs, with the major advantage of having the capability to do so in a complex biological matrix such as plasma. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
166.
167.
Kelly Chibale Nicholas Greeves Lisa Lyford J. Elizabeth Pease 《Tetrahedron: Asymmetry》1993,4(12):2407-2410
Optically active secondary alcohols were obtained in high chemical yield and optical purity (up to 85% ee) from the lanthanide-mediated enantioselective addition of alkyl nucleophiles to aromatic aldehydes. 相似文献
168.
Richard F. Smith Lisa A. Dennis William J. Ryan George Rodriguez Keith A. Brophy 《Journal of heterocyclic chemistry》1992,29(1):181-183
Three mechanistic pathways are considered for the hydroxide-promoted conversion of 1,1-disubstituted-3-amino-4,5-dihydro-1H-pyrazolium halides 1 to 1,1-disubstituted hydrazines, ammonia and sodium 3-hydroxypropanoate. Evidence presented in this paper supports a hydrolysis mechanism c that is initiated by hydroxide ion addition to the 3-position of 1 to form a tetrahedral intermediate 7 . 相似文献
169.
170.
In the Fall of 1999, Illinois State University (ISU) piloted a new General Chemistry I course. This course now includes cooperative learning exercises that were developed and implemented in biweekly discussion sections over the past four semesters. We now have discussion exercises all taught by six different tenured and tenure-track faculty members. This study focuses on the effect on student behaviors and learning in General Chemistry I. Data were obtained from student surveys, student interviews, instructor feedback, and examination results. The results obtained in this study show that student interest in chemistry can be maintained or increased by the incorporation of cooperative learning into the general chemistry curriculum. In addition, this cooperative learning approach promoted attendance, was enjoyable for many students, and seemed to have some positive effect on achievement. 相似文献