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211.
The stability of OH on Pt(111) has been investigated to determine the role of hydrogen bonding in stabilizing the overlayer. We find that the optimal structure is a mixed (OH+H2O) phase, confirming recent density-functional theory predictions. The reaction O+3H(2)O forms a hexagonal (sqrt[3]xsqrt[3])R30 degrees -(OH+H2O) lattice with a weak (3x3) superstructure, caused by ordering of the hydrogen bonds. The mixed overlayer can accommodate a range of H(2)O/OH compositions but becomes less stable as the H2O content is reduced, causing defects in the hydrogen-bonding network that lift the (3 x 3) superstructure and destabilize the overlayer. 相似文献
212.
Chemisorbed O and water react on Pd(1 1 1) at low temperatures to form a mixed OH/H2O layer with a (√3 × √3)R30° registry. Reaction requires at least two water molecules to each O before the (2 × 2)O islands are consumed, the most stable OH/water structure being a (OH + H2O) layer containing 0.67 ML of oxygen, formed by the reaction 3H2O + O → 2(H2O + OH). This structure is stabilised compared to pure water structures, decomposing at 190 K as OH recombines and water desorbs. The (√3 × √3)R30° − (OH + H2O) phase cannot be formed by O/H reaction and is distinct from the (√3 × √3)R30° structure formed by O/H coadsorption below 200 K. Mixed OH/water structures do not react with coadsorbed H below 190 K on Pd(1 1 1), preventing this phase catalyzing the low temperature H2/O2 reaction which only occurs at higher temperatures. 相似文献
213.
Hodgson James Johansen Adam M. Pollock Murray 《Methodology and Computing in Applied Probability》2022,24(3):2123-2148
Methodology and Computing in Applied Probability - For rare events described in terms of Markov processes, truly unbiased estimation of the rare event probability generally requires the avoidance... 相似文献
214.
Atmospheric pressure chemical ionisation liquid chromatography/multistage mass spectrometry (APCI-LC/MSn) provides a rapid, on-line method for the assignment of individual bacteriophaeophorbide c and d methyl esters (BPMEs) in complex mixtures. The MS2 spectrum for each component is diagnostic of the type of BPME (c or d), and characteristic losses in MS5 and MS6 permit assignment of the alkyl substituents at positions C-8 and C-12 of the macrocycle. MS5 mass chromatograms permit the deconvolution of coeluting isobaric BPMEs, revealing the true profiles of the individual components. The distributions are different in lake sediments from la Salada de Chiprana (Spain) and Kirisjes Pond (Antarctica), and a novel BPME c with a neo-pentyl substituent has been observed in the Kirisjes Pond sediment. 相似文献
215.
Hodgson DM Le Strat F Avery TD Donohue AC Brückl T 《The Journal of organic chemistry》2004,69(25):8796-8803
Levulinic acid-derived 6-diazoheptane-2,5-dione (9) serves as a common precursor in a formal synthesis of frontalin 19, and in syntheses of cis-nemorensic acid 1, 4-hydroxy-cis-nemorensic acid 2, 3-hydroxy-cis-nemorensic acid 3, and nemorensic acid 4. The key step in these syntheses is the Rh(2)(OAc)(4)-catalyzed tandem carbonyl ylide formation-intermolecular 1,3-dipolar cycloadditions of diazodione 9 with formaldehyde, alkynes or allene, which occur with high regioselectivity. Subsequent oxidative cleavage of the ring originally derived from the cyclic carbonyl ylide intermediate provides a straightforward access to polysubstituted tetrahydrofurans, and in particular an efficient entry to the nemorensic acids. Enantioselective cycloadditions with diazodione 9, using chiral rhodium catalysts, gave cycloadducts in up to 51% ee. 相似文献
216.
Enhancing the Electrochemical Performance of the LiMn2O4 Hollow Microsphere Cathode with a LiNi0.5Mn1.5O4 Coated Layer 下载免费PDF全文
Wei Liu Dr. Jun Liu Kunfeng Chen Dr. Shaomin Ji Yanling Wan Prof. Dr. Yichun Zhou Prof. Dr. Dongfeng Xue Prof. Dr. Peter Hodgson Dr. Yuncang Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(3):824-830
Spinel cathode materials consisting of LiMn2O4@LiNi0.5Mn1.5O4 hollow microspheres have been synthesized by a facile solution‐phase coating and subsequent solid‐phase lithiation route in an atmosphere of air. When used as the cathode of lithium‐ion batteries, the double‐shell LiMn2O4@LiNi0.5Mn1.5O4 hollow microspheres thus obtained show a high specific capacity of 120 mA h g?1 at 1 C rate, and excellent rate capability (90 mAhg?1 at 10 C) over the range of 3.5–5 V versus Li/Li+ with a retention of 95 % over 500 cycles. 相似文献
217.
Dielectromagnetics made from organic–inorganic hybrid silica-coated iron powders were characterised by determination of their physical, mechanical and magnetic properties. The influence of three main factors, dielectric composition, addition level and heat treatment conditions were investigated. Results showed that these factors have significant effects on the performance of the dielectromagnetics. Increase in the organic phase content in these dielectric coatings tends to increase both the electrical resistivity and magnetic permeability of dielectromagnetics, although the strength and density are slightly impaired. Increasing the coating thickness leads to improvements in resistivity and thus reduced eddy current losses, but these are offset by reductions in density, strength and particularly magnetic permeability. A hybrid organic–inorganic coating formulation based on 40 mol% MTMS and 60 mol% TEOS precursors was found to be the optimum composition investigated. Addition levels between 0.1% and 0.3% were found to offer a good compromise between maximum permeability (μmax>400) and minimum loss (typically <8 W/kg) for operation at 50 Hz/1 T, and the system can be optimised within this range for the desired performance. 相似文献
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220.
Kwan IC Delley RJ Hodgson DR Wu G 《Chemical communications (Cambridge, England)》2011,47(13):3882-3884
We report that the ability of disodium 5'-deoxy-5'-thioguanosine-5'-monophosphate, Na(2)(5'-GSMP), to self-associate into a helical G-quadruplex structure in aqueous solution at pH 8 is significantly higher than that of disodium guanosine-5'-monophosphate, Na(2)(5'-GMP), which supports our earlier hypothesis regarding the importance of cation bridging. 相似文献