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M Solution (m + solution)
Selected AbstractsMesoporous Hydrous Manganese Dioxide Nanowall Arrays with Large Lithium Ion Energy Storage CapacitiesADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Dawei Liu Abstract Novel nanowall arrays of hydrous manganese dioxide MnO2,·,0.5H2O are deposited onto cathodic substrates by the potentiostatic method from a mixed aqueous solution of manganese acetate and sodium sulfate. The deposition is induced by a change of local pH resulting from electrolysis of H2O, and hierarchical mesoporous nanowall arrays are formed as a result of simultaneous precipitation of manganese hydroxide and release of hydrogen gas bubbles from the cathode. The morphology and lithium ion intercalation properties are found to change appreciably with the concentration of the precursor electrolyte, with a significant reduction in specific surface area with an increased precursor concentration. For example, mesoporous nanowall arrays deposited from 0.1,M solution possess a surface area of ,96,m2 g,1 and exhibit a stable high intercalation capacity of 256,mA hg,1 with a film of 0.5,µm in thickness, far exceeding the theoretical limit of 150,mA hg,1 for manganese dioxide bulk film. Such mesoporous nanowall arrays offer much greater energy storage capacity (e.g., ,230,mA hg,1 for films of ,2.5,µm) than that of anodic deposited films of the same thickness (,80,mA hg,1). Such high lithium ion intercalation capacity and excellent cyclic stability of the mesoporous nanowall arrays, especially for thicker films, are ascribed to the hierarchically structured macro- and mesoporosity of the MnO2,·,0.5H2O nanowall arrays, which offer large surface to volume ratio favoring interface Faradaic reactions, short solid-state diffusion paths, and freedom to permit volume change during lithium ion intercalation and de-intercalation. [source] Hydrogen bonding in benzenesulfonic and 4-toluenesulfonic acids dissolved in N,N,-dimethylformamide: an FT-Raman studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2004Jose M. Alía Abstract Solutions of benzenesulfonic acid (BSA) and monohydrated 4-toluenesulfonic acid (PTSA) in dimethylformamide (DMF) were studied by FT-Raman spectroscopy in the concentration range 1.0,5.0 mol dm,3. Spectra in the region of the acid S,OH and benzenesulfonate anion SO3, stretching bands were analysed using band-fitting procedures in order to ascertain the degree of acid dissociation. In BSA solutions, this parameter changes from 0.34 (1.02 M solution) to 0.11 (5.01 M solution) despite the strong character of the acid. Interaction of DMF with undissociated BSA produces a new band in the ,(C,,N,C,) Raman spectral region near 866 cm,1, displaced ,11.0 cm,1 and assigned to DMF molecules hydrogen-bonded to BSA. In PTSA solutions, hydrogen bonds are formed with the oxonium ion (H3O+) dissociated from the acid. In this case, the displacement observed is only ,7.0 cm,1, indicating a weaker interaction. From the concentration of hydrogen-bonded DMF, the mean number of hydrogen-bonds participating in bonding with each solvent molecule can be calculated. This number changes, in BSA solutions, from ca. 0.5 in the less concentrated solutions up to ca. 1.0 in the most concentrated. This result supports the conclusion that BSA,DMF complexes of fixed stoichiometry are not present in the range of concentrations studied here. On the contrary, the oxonium ions form a stable complex of stoichiometry (DMF)2·H3O+ which does not change with the acid concentration. Copyright © 2004 John Wiley & Sons, Ltd. [source] Reversible Double-Helix,Random-Coil Transition Process of Bis{hexa(ethynylhelicene)}sCHEMISTRY - AN ASIAN JOURNAL, Issue 2 2008Hiroki Sugiura Dr. Abstract Two compounds with two hexa(ethynylhelicene) parts connected by a flexible haxadecamethylene and a rigid butadiyne linker were synthesized. The 1H,NMR spectroscopic and CD analyses and vapor-pressure osmometry (VPO) of these two compounds revealed intramolecular double-helix formation. Upon heating a 5-,M solution in toluene, the double-helix structure unfolded to form a random coil, and on cooling it folded again into a double helix. The thermodynamic stabilities of both structures were dependent on temperature, and the structural change in both compounds is due to the large enthalpies and entropies under equilibrium. The rate constants of their unfolding were obtained by assuming a pseudo-first-order reaction; the compound with a rigid linker unfolded slower than that with a flexible linker. The former has a larger activation energy, and its double-helix and random-coil conformers were separated by chromatography. The rate of folding was also faster for the flexible-linker compound with larger activation energy. The rate constants for the folding of both compounds slightly decreased with increasing temperature, which was ascribed to the presence of exothermic pre-equilibrium and rate-determining steps. The folding was markedly accelerated with increasing random-coil concentration, which suggests the involvement of self-catalysis. A mechanism of folding was proposed. The involvement of different mechanisms of folding and unfolding was suggested by the kinetic studies, and it was confirmed by the presence of hysteresis in the melting profiles. The difference in linker structure also affected the thermal-switching profiles of the double-helix,random-coil structural changes. [source] Spectrophotometric determination of the transition system for interactions involving model hydrogen bonds in acetonitrileJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2002Józef Mago Abstract The bonds formed by interactions of picric acid (HA) with each of 12 (un)substituted pyridines (B) in acetonitrile (AN) were studied by UV,vis spectrophotometry to determine the corresponding to the transition system. The choice of both model system and experimental technique enabled the effect of heteroconjugation to be observed and the effects of formation of two theoretically possible homoconjugates (AHA, and BHB+) to be eliminated. The relationship between the wavelength at the absorbance maximum (,max) for 10,4,M solutions of complexes of picric acid with (un)substituted pyridines in acetonitrile and was found to have a sigmoidal shape with an inflection point at of ca ,0.3. On the basis of this relationship and UV,vis spectra, the picric acid,3-acetylpyridine system was recognized as that being the nearest to the transition system. The fact that the transition was lower than zero has been explained by the remarkable effect of species having the average structures A,···+HB on the established ,max values. The general results of this work and our previous results based on IR and 1H NMR studies, and also the lack of any experimental counterexamples, indicate that the zero value of constitutes a fundamental basis for predicting which one, among the given family of protonic hetero systems, is the most likely to show transitional properties in acetonitrile. Finally, it is postulated that the protonic hetero systems which are the most likely to show transitional properties in a given solvent S are those for which is close to zero, the eventual shift arising from peculiarity of the technique applied. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effects of tributyltin(IV) chloride on the gametes and fertilization of Ascidia malaca (Ascidiacea: Tunicata)APPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2003L. Villa Abstract Ascidia malaca gametes before fertilization incubated in 10,5 or 10,7,M solutions of tributyltin(IV) chloride, TBTCl, for 3,h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||