Li Insertion into Li-Ti-O Spinels: Voltammetric and Electrochemical Impedance Spectroscopy Study

The insertion of Li into nanocrystalline Li-Ti-O spinel electrodes was studied using cyclic voltammetry combined with electrochemical quartz crystal microbalance, open circuit potential measurements, and electrochemical impedance spectroscopy studies. Insertion characteristics of spinel were compared with those of titania polymorphs. The insertion into spinel occurs at potential 300 mV more negative to that of insertion into anatase, and about 40 mV positive to that into rutile. The specific capacity (160 mAh/g) is comparable with that of TiO2 polymorphs. Due to the relatively negative potential of the insertion and significantly lower tendency to self-discharge, Li-Ti-O spinel is more convenient for use in a 2 V lithium-ion battery than are other active phases in the Li-Ti-O system. The behavior of the spinel electrodes in equilibrium can be described by the Frumkin insertion isotherm model. The value of interaction parameter, g, below -4 indicates that the insertion process leads to a first-order phase transition. Diffusion coefficient of Li in spinel ranges between 10-15 and 10-16 cm2 s-1; the charge transfer kinetics depends on the redox composition. Heterogeneous rate constant ranges between 1 × 10-8 and 4 × 10-10 cm s-1 that is ca. two orders of magnitude higher than that reported for anatase. © 2001 The Electrochemical Society. [DOI: 10.1149/1.1392321] All rights reserved

Lithium insertion into titanium dioxide (anatase) electrodes: Microstructure and electrolyte effects

Insertion characteristics of anatase electrodes were studied on single-crystal and polycrystalline electrodes of different microstructures. The lithium incorporation from propylene carbonate solution containing LiClO4 and Li(CF3SO2)2N was studied by means of cyclic voltammetry (CV), the quartz crystal microbalance (QCM) and the galvanostatic intermittent titration technique (GITT). The electrode microstructure affects both the accessible coefficient x and the reversibility of the process. The highest insertion activity was observed for electrodes composed of crystals with characteristic dimensions of ∼10-8 m. The insertion properties deteriorate for higher as well as for smaller crystal sizes. Enhanced insertion was observed in Li(CF3SO2)2N-containing solutions. Lithium insertion is satisfactorily reversible for mesoscopic electrodes; the reversibility in the case of compact polycrystalline and single-crystal electrodes is poor. The reversibility of the insertion improves with increasing electrolyte concentration. The lithium diffusion coefficient decreases with increasing x and ranges between 10-15 and 10-18 cm2 s-1. © Springer-Verlag 2001

Lithium insertion into mesoscopic and single-crystal TiO2 (rutile) electrodes

Electrochemical behavior of single-crystal and mesoscopic TiO2 (rutile) was studied in propylene carbonate solutions at potentials negative to the flatband potential. In electrolytic solutions containing sodium or tetrabutylammonium (Bu4N+), the injected charge is compensated by protonization of the surface and/or by adsorption of cations in the double layer. In electrolytic solutions containing Li+, the insertion into the rutile lattice occurs at potentials below 1.5 V (Li/Li+). At higher potentials, the charge is compensated mainly by a nonfaradaic process. Lithium insertion into rutile proceeds at a potential ca. 0.4 V more negative than the insertion potential into anatase. The maximum insertion capacity of rutile is also lower than that of anatase. The insertion of lithium into rutile is accompanied by an increase of the electrode mass, while the mass/charge relations show hystereses between anodic and cathodic potential sweeps. This behavior is explained in terms of a free convection in the electrode vicinity

Electrochemical oxygenation of diorganyldichlorosilanes: A novel route to generation of diorganylsilanones

Interaction of diorganyldichlorosilanes R2SiCl2 (R = Me, Et, Ph) with superoxide or peroxide anions, produced in situ by electroreduction of molecular oxygen, provides short-living diorganylsilanones R2Si=O. The latter undergo cyclization to give lower perorganylcyclosiloxanes (R2SiO)n, n = 3 or 4 and then insert to the molecules of these primary products to form higher cyclic oligomers. When the process is carried out in the presence of a reagent-trap for silanones (hexamethyldisiloxane, hexamethylcyclotrisiloxane), the products of insertion of diorganylsilanones into the molecule-traps (Me3Si(OSiR2)nOSiMe3 with n ≥ 1, and (Me2SiO)3(R2SiO)m with m ≥ 1, respectively) were obtained. © 2000 Elsevier Science B.V. All rights reserved

Insertion of lithium into mesoscopic anatase electrodes - An electrochemical and in-situ EQCM study

The insertion of Li+ into mesoscopic TiO2 (anatase) electrodes was studied using cyclic voltammetry combined with the in situ gravimetric monitoring of the electrode mass in LiClO4 and Li(CF3SO2)2 N/propylene carbonate (PC)-based solutions. The insertion of Li+ takes place at potentials less than 2.0 V vs Li/Li+. The cathodic process is associated with a mass uptake; the subsequent oxidation process is associated with a mass decrease. The apparent molar mass of the inserted/extracted material is, however, remarkably different from that expected for the simple insertion/extraction of unsolvated Li+ ions. For a more accurate description of the behaviour of the mesoscopic anatase electrodes, we consider them as gold electrodes modified with a porous film. Thus, the mesoscopic anatase electrode behaves similarly to a polymer-modified electrode, i.e. the overall process includes coupled electron/ion transfer (insertion of Li+) and a transfer of neutral species. Analysing the EQCM (electrochemical quartz crystal microbalance) data, one can conclude that the controlling step of the insertion/extraction of Li+ into/from anatase electrodes is a coupled electron/ ion transfer or the transfer of neutral species in solutions containing ClO4 - and (CF3SO2)2N- respectively

An amperometric monoamine oxidase biosensor for determining some antidepressants

An amperometric biosensor based on a platinum screen-printed electrode and immobilized monoamine oxidase is developed to determine antidepressants of different classes. Petylyl, pyrazidol, and flu-oxetine can be determined with determination limits of 8 × 10-9, 8 × 10-7, and 8 × 10-10 M, respectively. A procedure is proposed for determining fluoxetine in tablets. It is shown that petylyl can be selectively determined by an immunochemical technique using the developed biosensor and immobilized antibodies in the concentration range from 1 × 10-4 to 1 × 10-8 M. © 2007 MAIK Nauka

Estimation of several antidepressants using an amperometric biosensor based on immobilized monoamine oxidase

An amperometric biosensor was developed on the basis of a printed platinum electrode and immobilized monoamine oxidase for detecting antidepressants of various classes. The analytical potential of the electrode was assessed: Petylyl (desipramine) and pyrazidol could be estimated from lower detection limits of 8 × 109 M for Petylyl and 8 × 107 M for pyrazidol. A method for estimating pyrazidol in tablets is described. © 2007 Springer Science+Business Media, Inc

Theoretical conformational analysis of cyclic organophosphorus and organosilicon compounds

The structure of some six- and eight-membered phosphorus and silicon heterocycles was established by the method of dipole moments and density functional theory calculations. There are two necessary conditions for the feasibility of the transannular interaction in these heterocycles: (1) the favorable disposition of the donor and acceptor centers in a molecule and (2) the presence of the substituents with the considerable polarizing effect at the heteroatom. Copyright © Taylor & Francis Group, LLC

Magnetic properties of different-aged chernozemic soil profiles

© 2006-2016 Asian Research Publishing Network (ARPN).In order to estimate the rate of magnetic susceptibility enhancement in automorphic temperate soils, magnetic properties and mineral weathering degree of different-aged chernozemic soils derived from a uniform parent material have been studied. In this work, layer samples of mature virgin leached chernozem and young chernozemic soils formed on the embankment of an earthy archaeological monument were used. Magnetic, physical and chemical and mineralogical analysis show that magnetic susceptibility enhancement in organogenic soils is associated with increase in loss on ignition, cation exchange capacity, degree of dispersion, as well as with decrease in amphiboles/zircon, amphibole/rutile and amphibole/ilmenite ratios. Magnetic susceptibility enhancement in different-aged chernozemic soils results from maghemite (or maghemite associations) formation. After 750-800 years, magnetic susceptibility in organogenic soils reached only about half of its value in a mature chernozem. These results indicate that the formation of mature magnetic profile in automorphic temperate soils is a very long process. The newly formed chernozemic soils are now at the stage of active formation of secondary magnetic minerals, but the resource of primary ferrous silicates (which are less resistant to weathering) is not exhausted in mature virgin chernozem yet

Effect of β-alanine on humoral immune response in low-dose allergy model

At the present time, the efforts of many research groups around the world are aimed at finding new factors triggering the allergic sensitization process linked with IgE synthesis to harmless allergens. According to the recent data, production of tissue cytokines is induced in tissue cells by alarmins, thus, in turn, eliciting pro-allergic immune response. Previously we have shown that β-alanine could be a potential alarmin capable to stimulate production of tissue cytokines. The aim of this work was to determine the impact of β-alanine on humoral immune response in low-dose allergy model. BALB/c mice were immunized by recombinant Asp f 2 protein or commercial ovalbumin (OVA) in the withers 3 times a week with or without β-alanine supplementation. To determine the mechanism of β-alanine effect, α-L-alanine, an isomer which is not MrgD receptor ligand, and β-aminoisobutyrate with β-alanine-like affinity to MrgD ligand, were compared. According to our data, β-alanine stimulated specific IgE and IgG1 production in a short-term course (7 immunizations) and enhanced antibody affinity after long-term (14 immunizations) protocol in the case of low-immunogenic protein Asp f 2. In the case of high-immunogenic OVA protein, the impact of β-alanine was significant only upon antibody affinity. Hence, β-alanine accelerates specific IgE production in the case of low-immunogenic protein. The impact of β-alanine on specific IgE production was not linked to specific MrgD receptor activation, because β-aminoisobutyrate, which is the other ligand of this receptor, did not have a similar effect upon humoral immune response. The effect of β-alanine on IgG1 production seems also independent of MrgD receptor, since the common proteinogenic amino acid α-L-alanine also enhanced specific IgG1 production. The effect of β-alanine on humoral immune response could be linked to its non-specific action, e.g., due to its ability to induce oxidative stress through blocking taurine transporter, or due to its ability to stimulate cellular metabolism