Transport in ceria electrolytes modified with sintering aids: effects on oxygen reduction kinetics

Small (2 mol%) cobalt oxide additions to ceria-gadolinia (CGO) materials considerably improve sinterability, making it possible to obtain ceramics with 95–99% density and sub-micrometre grain sizes at 1,170–1,370 K. The addition of Co causes a significant shift of the electrolytic domain to lower pO₂. This modification to the minor electronic conductivity of the electrolyte material has influence on the cathodic oxygen reduction reaction. The impedance technique is shown to provide information not only about polarisation resistance, but also about the active electrode area from analysis of the current constriction resistance. It is demonstrated that this current constriction resistance can be related to the minor electronic contributions to total conductivity in these materials. A simple imbedded grid approach gives control of the contact area allowing the properties of the electrolyte materials to be studied. A much lower polarisation resistance for the Co-containing CGO electrolyte is observed, which can be clearly attributed to an increased three-phase reaction area in the Co-containing material, as a consequence of elevated p-type conductivity.     

NADH Electrooxidation Using Bis(1,10-phenanthroline-5,6-dione) (2,2'-bipyridine)ruthenium(II)-Exchanged Zirconium Phosphate Modified Carbon Paste Electrodes

We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10‐phenanthroline‐5,6‐dione)(2,2′‐bipyridine)ruthenium(II) ([Ru(phend)₂bpy]²⁺) exchanged into the inorganic layered material zirconium phosphate (ZrP). X‐Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)₂bpy]²⁺ intercalation from 10.3 Å to 14.2 Å. The UV‐vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)₂bpy]²⁺. The UV‐vis spectrophotometric results indicate that the [Ru(phend)₂bpy]²⁺ concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)₂bpy]²⁺ exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°′=–38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis–Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented.     

Spectroscopic and photochemical properties of the lichen compound lobaric acid

Lichens synthesize and accumulate photoprotective compounds against possible damage induced by UV radiation in the photobiont. A biological model has been recently formulated that allows the use of lichens to evaluate changes at different UV radiation levels. The thermodynamics, photophysical and photochemical properties of lobaric acid were studied in acetonitrile, ethanol and Brij 35(3%) micelles at different pH values. Also the sun protector factor (SPF) was determined by in vitro methods. Lobaric acid was extracted from Stereoculon alpinum Laur. and characterized by means of standard procedures. Solutions were irradiated in oxygen and under nitrogen conditions with a UV medium pressure lamp. Lobaric acid absorbs at 287, 303 nm, and no fluorescence emission was observed. The maximum value of the molar extinction coefficient (5479.6 M(-1) cm(-1)) was obtained in Brij 35 at pH 12. Solubility is pH dependant and is highest in Brij 35 at pH 12 (4.45 x 10(-4) M). Photoconsumption quantum yields ranged between 10(-4) and 10(-5) in aerobic and anaerobic experimental conditions. Lobaric acid SPF was very low (0.5) compared with homosalate (4.0), (reference solar filter). Two pKa values, 5.05 (carboxylic acid group deprotonation) and 9.75 (phenolic OH deprotonation), were determined.     

Certain graphs with exactly one irreducible T-module with endpoint 1, which is thin

Journal of Algebraic Combinatorics - Let $$\Gamma $$ denote a finite, simple and connected graph. Fix a vertex x of $$\Gamma $$ and let $$T=T(x)$$ denote the Terwilliger algebra of $$\Gamma $$ with...     

Comparative voltammetric study of 2,4-dinitrophenol (DNP), albumin and DNP-albumin as an analytical approach to the use of DNP as a universal label in immunoelectrochemical assays

A comparative electrochemical study of 2,4-dinitrophenol (DNP), albumin and DNP-albumin has been carried out at a hanging mercury drop electrode, in order to use DNP as a universal label in immunoelectrical assays. Several electrochemical techniques have been used. Differential pulse voltammetry has proved to be the most suitable. Wide dynamic linear ranges (more than three orders of magnitude for DNP-albumin) and low detection limits have been achieved (5 x 10(-10)M, 2 x 10(-10)M, 3 x 10(-12)M for DNP, albumin and DNP-albumin, respectively). Good reproducibility has been obtained in all cases (R.S.D. < 2.2%).     

Temperature dependence of the Mössbauer spectra of amorphous and nanocrystallized Fe86Zr7Cu1B6

Mössbauer measurements have been performed on amorphous and nanocrystalline alloy ribbons of nominal composition Fe₈₆Zr₇Cu₁B₆. The nanocrystalline samples were obtained by annealing the as-quenched alloy at different temperatures in the range between 650 and 870 K. Mössbauer spectra of the as-quenched amorphous sample have been recorded at 77 K, room temperature and above the Curie temperature (330 K) at 360 K. We have also performed Mössbauer measurements at room temperature in the nanocrystalline alloys to characterize the phases that appear after the annealing and their relative concentration. The as-quenched sample spectra reveal the existence of two inequivalent sites for Fe. Such a feature is also observed in the remaining amorphous phase of the annealed samples. In the first steps of crystallization, -Fe precipitates and its concentration increases with the annealing temperature. The experimental results suggest that the composition of the whole amorphous phase does not suffer large changes during crystallization.     

Diffusion in a one-dimensional gas of hard point particles

We simulate the classical diffusion of a particle of massM in an infinite one-dimensional system of hard point particles of massm in equilibrium. Each computer run corresponds to about 10⁸ collisions of the diffusive particle. We find that (t) 1/t fort large enough, and a crossover from an M m regime where=2 to=3 forM=m. The diffusion constant has a sharp maximum atM=m. We study moments x(t)² and x(t)⁴, and examine the behavior ofq ² (t)=x(t)⁴/3x(t)²². We find thatq(t)1 (consistent with a normal distribution) in theM limit (for all timest) and in the t limit for allM. On sabbatical leave from IVIC-Instituto Venezolano de Investigaciones Cientificas.     

Synthesis and acid-base properties of (1H-benzimidazol-2-yl-methyl)phosphonate (Bimp2-). Evidence for intramolecular hydrogen-bond formation in aqueous solution between (N-1)H and the phosphonate group

The synthesis of (1H-benzimidazol-2-yl-methyl)phosphonic acid, H2(Bimp)+/-, is described: 2-chloromethylbenzimidazole was reacted with ethylchloroformate to give 1-carboethoxy-2-chloromethylbenzimidazole which was treated with trimethyl phosphite and after hydrolysis with aqueous HBr H2(Bimp)+/- was obtained. In H2(Bimp)+/- one proton is at the N-3 site and the other at the phosphonate group; both acidity constants were determined in aqueous solution by potentiometric pH titrations (25 degrees C; I = 0.1 M, NaNO3) and this furnished the pKa values of 5.37 +/- 0.02 and 7.41 +/- 0.02, respectively. The acidity constant for the release of the primary proton from the P(O)(OH)2 group of H3(Bimp)+ was estimated: pKa = 1.5 +/- 0.2. Moreover, Bimp2- can be further deprotonated at its neutral (N-1/N-3)H site to give the benzimidazolate residue, but this reaction occurs only in strongly alkaline solution (KOH); application of the H_ scale developed by G. Yagil (J. Phys. Chem., 1967, 71, 1034) together with UV spectrophotometric measurements gave pKa = 14.65 +/- 0.12. Comparisons with acidity constants taken from the literature show that this latter pKa value is far too large and this allows the conclusion that an intramolecular hydrogen bond is formed between the (N-1/N-3)H site and the phosphonate group of Bimp2-; the formation degree of this hydrogen-bonded isomer is estimated to be 98 +/- 2%. The general relevance of this and the other results are shortly discussed and the species distribution for the Bimp system in dependence on pH is provided.     

Ab initio molecular dynamics simulation of a room temperature ionic liquid

Ab initio molecular dynamics simulations have been performed for the first time on the room-temperature organic ionic liquid dimethyl imidazolium chloride [DMIM][Cl] using density functional theory. The aim is to compare the local liquid structure with both that obtained from two different classical force fields and from neutron scattering experiments. The local structure around the cation shows significant differences compared to both the classical calculations and the neutron results. In particular, and unlike in the gas-phase ion pair, chloride ions tend to be located near a ring C-H proton in a position suggesting hydrogen bonding. The results are used to suggest ways in which the classical potentials may be improved.