Evaluation of the Performance of a Mediatorless Microbial Fuel Cell by Electrochemical Impedance Spectroscopy

A mediatorless microbial fuel cell was developed using Escherichia coli bacteria and platinised titanium mesh as electrodes, producing a maximum power density of 627 mW m^?2. The performance characteristics of the fuel cell were evaluated using both electrochemical and optical techniques. Cyclic Voltammetry showed that an anaerobically grown cell suspension of E. coli was electrochemically active, and is consistent with a role for E. coli‐secreted mediators in the functioning of the cell, after the formation of a biofilm on the surface of the electrode. Electrochemical impedance spectroscopy (EIS) data show a variation in the internal resistance during bacterial growth. EIS analysis based on an equivalent circuit revealed that the initial internal resistance of the cell (5.6 MΩ) initially reduces by around 50 % over an 8 hour period; more or less the same time where the fuel cell reaches its maximum potential of 860 mV, whereupon the resistance begins to increase resulting in the corresponding fall in potential; this trend was reversible upon the introduction of further nutrients into the cell.     

Azide telechelics chain extended by click reaction: Synthesis,characterization, and cross‐linking

Azide telechelics of poly(dimethylsiloxane) (PDMS), polypropylene oxide (PPO), and polyethylene oxide (PEO) were synthesized from the corresponding epoxy telechelics and characterized. These oligomeric azides were chain extended by reaction with bispropargyl ether of bisphenol A (BPEBA) through a copper‐catalyzed azide‐alkyne cycloaddition (CuAAC) reaction. PDMS manifested a faster reaction in contrast to PPO or PEO. The chain‐extended polymers underwent cross‐linking above 170°C through thermal cleavage of residual (terminal) azide groups. This was manifested in their rheograms and was further substantiated by FTIR and NMR spectroscopic analyses. Dynamic mechanical analyses of the cross‐linked polymers exhibited characteristic transitions of hard and soft segments, implying microphase separation in the system. Microscopic evaluation of the thermally cross‐linked sample revealed a porous morphology with microsized to nanosized pores.     

Statistical method of image analysis of heterogeneities in Ba1 ? xRxF2 + x crystals

A statistical method for image analysis of smooth heterogeneities (with comparatively large luminance grade) is suggested. The method allows one to determine the average dimensions of image heterogeneities and characterize the anisotropy of their dimensions and heterogeneity of image luminance by constructing the corresponding pointer curves. The algorithms suggested for the image analysis are tested on two types of heterogeneities in Ba_{1 − x} R _x F_{2 + x} crystals grown from melts by the Stockbarger method—the cellular substructure and heterogeneity on a nanometer scale. These heterogeneities are characteristic of the whole family of nonstoichiometric fluorite M _{1 − x} R _xF_{2 + x} phases. The analysis of the typical images proves the high efficiency of the method of extraction of quantitative information on heterogeneities in M _{1 − x} R _xF_{2 + x} crystals on various scales. __________ Translated from Kristallografiya, Vol. 48, No. 2, 2003, pp. 376–384. Original Russian Text Copyright ? 2003 by Marychev, Chuprunov, Herrero, Sobolev.     

Ba1−x R x F2 + x Phases (R = Gd-Lu) with distorted fluorite-type structures—products of crystallization of incongruent melts in the BaF2-RF3 Systems (R = Gd-Lu). III. Defect Ba0.75Lu0.25F2.25 structure. A new {Lu8[Ba6F71]} supercluster of defects

The structure of Ba_0.75Lu_0.25F_2.25 crystals grown from melt has been studied by X-ray diffraction analysis (4729 measured reflections, 269 independent reflections with I > σ (I), R = 1.1%, R _w = 0.7%). The crystals are crystallized in the cubic system, sp. gr. Pm $\bar 3$ m, with the lattice parameter a = 5.9870(9) Å. A new complex of defects is singled out—a supercluster of the composition {R ₈[Ba₆F₇₁]}. This supercluster differs from the well-known rare earth octahedral supercluster of the composition {Ba₈[R ₆F_68-69]} because its nucleus is formed not by RE cations but by an alkali earth cation, Ba. The {R ₈[Ba₆F₇₁]} supercluster has a configuration close to that of the [B₁₄F₆₄] fragment of the fluorite structure and can replace the latter isomorphously. The model of the Ba_0.75Lu_0.25F_2.25 crystals consisting of coherently intergrown isostructural microphases having different chemical compositions is characterized by the good agreement of the calculated and experimentally determined occupancies of the F^1? positions. The comparison of the Ba_0.8Yb_0.2F_2.2 (phase studied earlier) and Ba_0.75Lu_0.25F_2.25 structures demonstrates the evolution of the defect structure along the series of rare earths with the corresponding change of the sp. gr. Fm $\bar 3$ m by the sp. gr. Pm $\bar 3$ m.     

Ethanol electrooxidation onto stepped surfaces modified by Ru deposition: electrochemical and spectroscopic studies

Oxidation of ethanol on ruthenium-modified Pt(775) and Pt(332) stepped electrodes has been studied using electrochemical and FTIR techniques. It has been found that the oxidation of ethanol on these electrodes takes place preferentially on the step sites yielding CO(2) as the major final product. The cleavage of the C-C bond, which is the required step to yield CO(2), occurs only on this type of site. The presence of low ruthenium coverages on the step sites promotes the complete oxidation of ethanol since it facilitates the oxidation of CO formed on the step from the cleavage of the C-C bond. However, high ruthenium coverages have an important inhibiting effect since the adatoms block the step sites, which are required for the cleavage of the C-C bond. Under these conditions, the oxidation current diminishes and the major product in the oxidation process is acetic acid, which is the product formed preferentially on the (111) terrace sites.     

Headspace-programmed temperature vaporizer-fast gas chromatography-mass spectrometry coupling for the determination of trihalomethanes in water

A new method based on the use of a headspace autosampler in combination with a GC equipped with a programmable temperature vaporizer (PTV) and an MS detector has been developed for the screening and quantitative determination of trihalomethanes (THMs) in different aqueous matrices. The use of headspace generation to introduce the sample has the advantage that no prior sample treatment is required, thus minimizing the creation of analytical artifacts and the errors associated with this step of the analytical process. The PTV inlet used was packed with Tenax-TA. The injection mode was solvent vent, in which the analytes are retained in the hydrophobic insert packing by cold trapping, while the water vapour is eliminated through the split line. This allows rapid injection of the sample in splitless mode, very low detection limits being achieved without the critical problem of initial sample bandwidth. The capillary column used allowed rapid separations with half-height widths ranging from 1.68 s (chloroform) to 0.66 s (bromoform). The GC run time was 7.3 min. The use of mass spectrometry allows the identification and quantification of the analytes at the low ppt level. The S/N ratio was at least 10-fold higher when the SIM mode was used in data acquisition as compared to the scan mode. The proposed method is extremely sensitive, with detection limits ranging from 0.4 to 2.6 ppt.     

Carbonyl and nitrosyl diruthenium compounds: Crystal structure of [Ru2(O2CMe)(DPhF)3(CO)]BF4 · CH2Cl2 and its isomorphous nitrosyl analogue

The reaction of [Ru₂(O₂CMe)(DPhF)₃(H₂O)]BF₄ (DPhF = N,N′-diphenylformamidinate) with CO gas leads to [Ru₂(O₂CMe)(DPhF)₃(CO)]BF₄ (1), that is the first isolated carbonyl complex containing the Ru₂⁵⁺ unit. The nitrosyl analogue [Ru₂(O₂CMe)(DPhF)₃(NO)]BF₄ (2) is prepared by reaction of Ru₂Cl(O₂CMe)(DPhF)₃ with NOBF₄. However, the attempts to obtain the cyanide derivative by reaction of Ru₂Cl(O₂CMe)(DPhF)₃ or [Ru₂(O₂CMe)(DPhF)₃(H₂O)]BF₄ with NaCN were unsuccessful. The structure of compounds 1 · CH₂Cl₂ and 2 · CH₂Cl₂ are described. Both compounds are isomorphous. The magnetic measurements at variable temperature demonstrate that 1 is paramagnetic with one unpaired electron in all range of temperature, in contrast to the three unpaired electrons usually present in Ru₂⁵⁺ complexes. The analogous nitrosyl compound 2 is diamagnetic.     

Cumulative reaction probabilities and transition state properties: a study of the F + H2 reaction and its deuterated isotopic variants

A comparative quantum mechanical (QM) and quasiclassical trajectory (QCT) study of the cumulative reaction probabilities (CRPs) is presented in this work for the F + H(2) reaction and its isotopic variants for low values of the total angular momentum J. The agreement between the two sets of calculations is very good with the exception of some features whose origin is genuinely QM. The agreement also extends to the CRP resolved in the helicity quantum number k. The most remarkable feature is the steplike structure, which becomes clearly distinct when the CRPs are resolved in odd and even rotational states j. The analysis of these steps shows that each successive increment is due to the opening of the consecutive rovibrational states of the H(2) or D(2) molecule, which, in this case, nearly coincide with those of the transition state. Moreover, the height of each step reflects the number of helicity states compatible with a given J and j values, thus indicating that the various helicity states for a specific j have basically the same contribution to the CRPs at a given total energy. As a consequence, the dependence with k of the reactivity is practically negligible, suggesting very small steric restrictions for any possible orientation of the reactants. This behavior is in marked contrast to that found in the D + H(2) reaction, wherein a strong k dependence was found in the threshold and magnitude of the CRP. The advantages of a combined QCT and QM approaches to the study of CRPs are emphasized in this work.     

A new multiresponse optimization approach in combination with a D-Optimal experimental design for the determination of biogenic amines in fish by HPLC-FLD

A new strategy to approach multiresponse optimization in conjunction to a D-optimal design for simultaneously optimizing a large number of experimental factors is proposed. The procedure is applied to the determination of biogenic amines (histamine, putrescine, cadaverine, tyramine, tryptamine, 2-phenylethylamine, spermine and spermidine) in swordfish by HPLC-FLD after extraction with an acid and subsequent derivatization with dansyl chloride. Firstly, the extraction from a solid matrix and the derivatization of the extract are optimized. Ten experimental factors involved in both stages are studied, seven of them at two levels and the remaining at three levels; the use of a D-optimal design leads to optimize the ten experimental variables, significantly reducing by a factor of 67 the experimental effort needed but guaranteeing the quality of the estimates. A model with 19 coefficients, which includes those corresponding to the main effects and two possible interactions, is fitted to the peak area of each amine. Then, the validated models are used to predict the response (peak area) of the 3456 experiments of the complete factorial design. The variability among peak areas ranges from 13.5 for 2-phenylethylamine to 122.5 for spermine, which shows, to a certain extent, the high and different effect of the pretreatment on the responses. Then the percentiles are calculated from the peak areas of each amine. As the experimental conditions are in conflict, the optimal solution for the multiresponse optimization is chosen from among those which have all the responses greater than a certain percentile for all the amines. The developed procedure reaches decision limits down to 2.5 μg L⁻¹ for cadaverine or 497 μg L⁻¹ for histamine in solvent and 0.07 mg kg⁻¹ and 14.81 mg kg⁻¹ in fish (probability of false positive equal to 0.05), respectively.