Search results for "ionic"
showing 10 items of 2016 documents
Structural disorder and electronic hybridization in NicMg1−cO solid solutions probed by XANES at the oxygen K edge
2007
A series of NicMg1−cO solid solutions has been studied for the first time looking at the structural disorder by means of x-ray absorption near-edge-structure (XANES) spectroscopy at the oxygen K edge. The experimental XANES signals were analysed within the full multiple scattering formalism and were interpreted taking into account clusters of up to 15 coordination shells around an absorbing oxygen atom. The substitution of nickel atoms by magnesium atoms results in a dramatic decrease of the empty density of states in the conduction band close to the Fermi level due to an exchange of the 3d(Ni)–2p(O) interaction with 3p(Mg)–2p(O). Besides, a simultaneous small decrease of the 3d(Ni)–2p(O) h…
Dopant-Host oxide interactions and proton mobility in Gd:BaCeO3
2009
The local structure of Gd:BaCeO3 at different dopant concentrations (2-20%) was studied by X-ray absorption spectroscopy. The EXAFS analysis shows that the environment of the regular Ba2+ and Ce4+ cations is to a limited extent affected by doping. The local structure of gadolinium shows an expansion of the first coordination shell of oxygens, consistent with the ionic radius of Gd3+, but a contraction of the next neighboring shells of cations. In particular, the Ba2+ second neighbors get closer to the dopant, which can be originated by the effective negative charge sharply localized on the dopant. Comparison between EXAFS data of dry and hydrated compounds confirms this interpretation, show…
Classical ionic fluids in the mean spherical approximation
1980
The recently obtained analytical solution of the mean spherical approximation has been used to calculate thermodynamic and structural properties of aqueous solutions of asymmetric electrolytes. The same approximation has also been used to calculate structure functions of pure and mixed molten salts. The agreement between experimental or “quasi-experimental” structure functions and those obtained within the framework of the MSA is quite good especially when the ionic radii are obtained by fitting the long wavelength limit of the structure functions to the isothermal compressibility of the system, under the condition that the diameter ratio is the same as in the crystal.
Mössbauer effect study of the electronic ground state of iron(II) in [57FexM1−x(bipy)3](ClO4)2 (M = Mn, Ni, Zn) and [57FexM1−x(phen)3](ClO4)2 (M = Ni…
1980
Earlier work in our laboratory on the effect of metal dilution on the 5T2(Oh ⇌ 1A1(Oh) equilibrium in polycrystalline spin crossover systems of iron(II) has shown that the relative stability of the high spin state, 5T2(Oh), at a given temperature, increases markedly with decreasing iron concentration. These results have initiated the present work. Using 57Fe Mossbauer spectroscopy, we have investigated the electronic ground state of iron(II) in the highly diluted solid solutions [FexM1−xL3] with L = bipy, M = Mn, Ni, Zn, x ≲ 0.005 and L = phen, M = Ni, Zn, x ≲ 0.005. Although the critical field potential (Vc) of the pure iron complexes, which are known to be low spin, is reported to be not …
Luminescent Ionic Transition-Metal Complexes for Light-Emitting Electrochemical Cells
2012
Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of Ir(III) are by far the most util…
Impact of Surface Charge Directionality on Membrane Potential in Multi-ionic Systems
2020
The membrane potential (Vmem), defined as the electric potential difference across a membrane flanked by two different salt solutions, is central to electrochemical energy harvesting and conversion. Also, Vmem and the ionic concentrations that establish it are important to biophysical chemistry because they regulate crucial cell processes. We study experimentally and theoretically the salt dependence of Vmem in single conical nanopores for the case of multi-ionic systems of different ionic charge numbers. The major advances of this work are (i) to measure Vmem using a series of ions (Na+, K+, Ca2+, Cl-, and SO42-) that are of interest to both energy conversion and cell biochemistry, (ii) to…
Do zwitterionic species exist in the non-enzymatic peptide bond formation?
2012
The use of proper computational methods and models has allowed answering the controversial question of whether zwitterionic species exist in the mechanism of peptide bond synthesis in aqueous solution. In fact, the different conformations of zwitterionic species open the door to different mechanistic paths.
Molecular “Pincer” from a Diimidazolium Salt: A Study of Binding Ability
2013
The anion recognition ability of the dicationic imidazolium salt 3,3′-di-n-octyl-1,1′- (1,3-phenylenedimethylene)diimidazolium 1,5-naphthalenedisulfonate ([m-Xyl-(oim)2][1,5-NDS]) was investigated in acetonitrile solution by means of proton NMR titrations. A wide range of anions, comprising simple inorganic ions, halides, and mono- and dicarboxylates was taken into account. The study showed that this receptor binds carboxylate anions more strongly than halides. Moreover [m- Xyl-(oim)2][1,5-NDS] displays selectivity for di- over monocarboxylate anions. The complex stability was mainly affected by the anion basicity in the presence of monocarboxylates, whereas the flexibility of the alkyl cha…
In vitro pulsatile and continuous transdermal delivery of buserelin by iontophoresis
1993
Abstract Transdermal delivery of buserelin, a nonapeptide, from hydroxyethylcellulose hydrogel through isolated human stratum comeum was studied. In vitro studies were carried out in a drug release apparatus (DAB 10/USP XII) using self designed rotary disk cells equipped with platinum electrodes. Different forms of current were examined. A pulsatile application of continuous current resulted in a step-like permeation profile. Different on/off ratios (5 min/55 min; 10 min/50 min; 15 min/45 min)) were studied. When continuous non-interrupted current with different current densities (0.1–0.3 mA·cm −2 ) was applied, linear dependence of the final cumulative amount of buserelin on current durati…
Bright Blue Phosphorescence from Cationic Bis-Cyclometalated Iridium(III) Isocyanide Complexes
2012
We report new bis-cyclometalated cationic indium(III) complexes [((CN)-N-boolean AND)(2)Ir(CN-tert-Bu)(2)](CF3SO3) that have tert-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4'-fluoropheny1)-R-pyridines (where R is 4-methoxy, 4-tert-butyl, or 5-trifluoromethyl) as (CN)-N-boolean AND ligands. The complexes are white or pale yellow solids that show irreversible reduction and oxidation processes and have a large electrochemical gap of 3.58-3.83 V. They emit blue or bluegreen phosphorescence in liquid/solid solutions from a cyclometalating-ligand-centered excited state. Their emission spectra show vibronic structure with the highest-energy luminescence peak at 440-…