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排序方式: 共有209条查询结果,搜索用时 15 毫秒
61.
Forryan CL Klymenko OV Wilkins SJ Brennan CM Compton RG 《The journal of physical chemistry. B》2005,109(44):20786-20793
In this paper we present a mathematical model for the surface-controlled dissolution of cylindrical solid particles. This is employed to interpret experimental data published previously for the dissolution of potassium bicarbonate in dimethylformamide at elevated temperatures. Significant kinetic differences in assuming cylindrical rather than spherical shapes are reported with the former representing a closer approximation to the true shape of the particles as revealed by scanning electron microscopy. From the fits of experimental data to the cylindrical model for the surface-controlled dissolution, the dissolution rate constant, k, for the dissolution of KHCO(3) in DMF was found to be (9.6 +/- 1.6) x 10(-9) mol cm(-2) s(-1) at 100 degrees C, and the activation energy for the dissolution was 34.5 kJ mol(-1) over the temperature range of 60-100 degrees C. Comparison between cylindrical and spherical dissolution theory highlights the importance of considering the particle shapes for realistic modeling of surface-controlled dissolution kinetics. 相似文献
62.
Woods KK Maehigashi T Howerton SB Sines CC Tannenbaum S Williams LD 《Journal of the American Chemical Society》2004,126(47):15330-15331
The crystal structure of [d(CGCAAATTTGCG)]2 has been determined to 1.5 A resolution, representing the first high-resolution structure of this DNA fragment. The ion interactions are novel. A spermine molecule replaces a Mg2+ observed in analogous structures. Unlike lower-resolution structures, the minor groove is narrow and the major groove lacks extra Watson-Crick hydrogen bonds. In addition, a monolayer of solvent sites, including a "spine of hydration", is visible in the minor groove. The crystal of [d(CGCAAATTTGCG)]2 was grown from a solution containing spermine, magnesium, and lithium. The conformation recapitulates that of "monovalent-minus" DNA. 相似文献
63.
Michael Hyde Andrew J. Saterlay Shelley J. Wilkins John S. Foord Richard G. Compton Frank Marken 《Journal of Solid State Electrochemistry》2002,6(3):183-187
Nanofilm deposits of a porous Sn(IV) oxide are formed by anodic electrodeposition on a polished boron-doped diamond electrode
immersed in an aqueous Sn2+ solution. Mechanically and electrochemically stable deposits of 10–15 nm thickness are formed irrespective of the Sn2+ concentration and mass-transport enhancement by power ultrasound. Atomic force microscopy images indicate the presence of
a smooth and noncrystalline film, which is stable under ambient conditions. n-type semiconducting characteristics are observed
for the aqueous solution redox couples Fe(CN)6
3–/4– and Ru(NH3)6
3+/2+. However, preliminary results from voltammetric experiments indicate that the small and neutral organic molecule N,N,N′,N′-tetramethylphenylenediamine is able to diffuse through the porous film to undergo oxidation directly at the surface of the
boron-doped diamond electrode.
Electronic Publication 相似文献
64.
An algorithm (ASSEMBLE) to construct all structures consistent with the structural implications of the chemical and spectroscopic properties of an unknown molecule is described. The design of ASSEMBLE takes cognizance of the need to supply some nonoverlapping substructure information in addition to the molecular formula, and the use of structural constraints that cannot be directly expressed as non-overlapping fragments. ASSEMBLE employs several heuristics (rules) intended to avoid the assembly of identical (isomorphic) graphs. To provide a non-redundant list of structures, duplicate structures are recognized and removed by a naming algorithm. ASSEMBLE also perceives different π-resonance forms as identical structures even when they are topologically non-equivalent. 相似文献
65.
This paper reports the first detailed study on meso-unsubstituted azuliporphyrins, an important family of porphyrin-like molecules where one of the usual pyrrole rings has been replaced by an azulene subunit. Although the azulene moiety introduces an element of cross-conjugation, zwitterionic resonance contributors with tropylium and carbaporphyrin substructures give azuliporphyrins diatropic character that falls midway between true carbaporphyrins and nonaromatic benziporphyrins. Protonation affords an aromatic dication where this type of resonance interaction is favored due to the associated charge delocalization. Two different "3 + 1" syntheses of meso-unsubstituted azuliporphyrins have been developed. Acid-catalyzed reaction of readily available tripyrrane dicarboxylic acids with 1,3-azulenedicarbaldehyde, followed by oxidation with DDQ or FeCl(3), affords good yields of azuliporphyrins. Alternatively, azulene reacted with acetoxymethylpyrroles (2 equiv) in refluxing acetic acid/2-propanol to give tripyrrane analogues, and following a deprotection step, condensation with a pyrrole dialdehyde in TFA-CH(2)Cl(2) gave the azuliporphyrin system. The latter approach was also used to prepare 23-thia- and 23-selenaazuliporphyrins. However, reaction of the azulitripyrrane with 2,5-furandicarbaldehyde produced a mixture of three oxacarbaporphyrins in moderate yield. The free base forms of thia- and selenaazuliporphyrins both showed intermediary aromatic character that was considerably enhanced upon protonation. The UV-vis spectra for azuliporphyrins and their heteroanalogues showed four bands between 350 and 500 nm and broad absorptions at higher wavelengths. Addition of TFA gave dications that showed porphyrin-like spectra with Soret bands between 460 and 500 nm. In the presence of pyrrolidine, azuliporphyrins and their heteroanalogues undergo nucleophilic attack on the seven-membered ring to give carbaporphyrin adducts. These systems also undergo oxidative rearrangements under basic conditions with t-BuOOH to give benzocarbaporphyrins. The selenaazuliporphyrin afforded two benzoselenacarbaporphyrins, a previously unknown core-modified carbaporphyrin system. The proton NMR spectra for these compounds showed strong diatropic ring currents with the internal CH resonance upfield above -5 ppm, while the meso-protons resonated downfield near 10 ppm. The UV-vis spectra were also porphyrin-like and gave strong Soret bands at ca. 440 nm. 相似文献
66.
Converting a non-unique connection table to a unique (canonical) name can be accomplished by assigning unique sequence numbers on the basis of topological (constitutional) properties. An algorithm is reported which performs this task by perceiving the topological symmetry of the molecule. A convention for assigning a single name to topologically unique structures which vary only in the position of π-electrons (resonance forms) is also presented. 相似文献
67.
Christopher J. Burns Robert D. Groneberg Joseph M. Salvino Gerard McGeehan Stephen M. Condon Robert Morris Matthew Morrissette Rose Mathew Shelley Darnbrough Kent Neuenschwander Anthony Scotese Stevan W. Djuric John Ullrich Richard Labaudiniere 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》1998,110(20):3044-3047
68.
69.
Andrew J. Saterlay Shelley J. Wilkins Christiaan H. Goeting John S. Foord Richard G. Compton Frank Marken 《Journal of Solid State Electrochemistry》2000,4(7):383-389
The use of boron-doped diamond has a considerable impact in electrochemistry owing to the wide potential range accessible,
low background currents, extreme hardness, and the ease of chemical modification of diamond surfaces. It is shown here that,
although the electrodeposition of silver metal is known to yield very poorly adhering films with a poor electrical contact,
a silver oxysalt deposit formed on anodically pre-treated diamond surfaces adheres strongly with good electrical contact.
The deposit is stable even in the presence of ultrasound. Voltammetric and XPS studies reveal that the silver oxide deposit,
in contrast to the silver metal deposit, is efficiently stripped from the diamond surface by applying a sufficiently negative
potential. The silver oxysalt Ag7O8NO3, deposited onto two types of boron-doped diamond electrodes, a 50 μm thick polycrystalline thin film deposited on a tungsten
substrate and a polished free standing diamond plate, is shown to act as an electrocatalyst for oxygen evolution and for the
oxidation of toluene. This development opens up the possibility of boron-doped diamond being applied as an inert and conducting
substrate material for a wide range of oxidic materials, which can then be utilised as active electrocatalysts at high applied
potentials.
Received: 17 March 2000 / Accepted: 10 April 2000 相似文献
70.
M. Manickam Alun Smith Maura Belloni Elwyn J. Shelley Peter R. Ashton Neil Spencer 《Liquid crystals》2013,40(4):497-504
The synthesis and characterization of four C 60 Bingel cyclopropanation adducts incorporating bis-biphenylene (three adducts) and bis-triphenylene (one adduct) moieties are described. The thermal analysis (POM and DSC) of these materials reveals that they are not liquid crystalline. However, two of the precursor bis-biphenylene malonate esters possess monotropic mesophases. Furthermore, each of the corresponding C60adducts is miscible in the melts of the precursor malonate ester, and at low dopings, retains the liquid crystalline monotropic mesophases of the precursor. 相似文献