bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic Behavior of an N‐Metalated β‐Enaminoimine Complex − Preparation of N‐Phosphanylenamine and β‐Enaminoimine Derivatives
Authors: Maraval Alexandrine , Owsianik Krzysztof , Arquier Damien , Igau Alain , Coppel Yannick , Donnadieu Bruno , Zablocka Maria , Majoral Jean‐Pierre 
Published: February 2003

AbstractVariable‐temperature NMR spectroscopy of the β‐enaminoimine complex 2 showed a dynamic process which was attributed to an internal fluxional aldimido N‐zirconated π‐linear/σ‐bent structure. Such an internal rearrangement has been previously proposed to occur in these systems but never observed. We have prepared a variety of (N‐phosphanyl‐β‐enamino)imine ligands using the hydrozirconation/transmetalation reaction of malonodinitrile compounds RCH(CN)2 (R = H, PPh2). In addition to their potential uses in coordination chemistry, these systems are good tools for the study of intramolecular hydrogen bonding. The X‐ray crystal structure of 14 at 180 K shows an unsymmetrical system with the N(H) proton localized on one of the two chelating nitrogen atoms, consistent with the existence in solution of a low barrier proton transfer process with a double‐well potential. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Syntheses and Crystal Structures of Copper and Silver Complexes with New Imine Ligands − Air‐Stable, Photoluminescent CuIN4 Chromophores
Authors: Patra Goutam Kumar , Goldberg Israel 
Published: February 2003

AbstractA series of new imine ligands [1 (C12H12N2S2), 2 (C12H12N2S2), 3 (C24H18N4S2), and 5 (C30H27N7)] have been synthesized (1 and 2 are structural isomers). CuI and AgI complexes of the nonconjugated dithiophene‐diimine ligands 1, 2 and the tripodal imine‐amine ligand 5 have also been prepared and thoroughly characterized by spectroscopic techniques as well as by X‐ray diffraction. In cyclic voltammetry at a glassy carbon milli electrode in anhydrous dichloromethane under dry N2, the corresponding CuI complexes [6 (2C12H12N2S2·CuClO4), 7 (2C12H12N2S2·CuClO4), and 12 (C30H27N7·CuClO4)] show quasi‐reversible CuII/I couples with high redox potentials (1.001 V for 6, 0.958 V for 7, and 0.692 V for 12, vs. Ag/AgCl). This indicates that the π‐acid ligands 1, 2, and 5 preferentially stabilize copper(I) over copper(II). The CuIN4 chromophores in the complexes 6, 7, and 12 display photoluminescence in dichloromethane at room temperature. The related silver complexes of the same three ligands 10 (2C12H12N2S2·AgClO4), 11 (2C12H12N2S2·AgClO4), and 13 [C30H27N7·Ag(CH3CN)ClO4] reveal similar structural features but lack specific photophysical properties. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Reactivity of an Iron(II)/Iron(III) System with Polyamine Ligands in Ethanol: An Electrochemical Study
Authors: Ugalde‐Saldivar Víctor M. , Sosa‐Torres Martha E. , González Ignacio 
Published: February 2003

AbstractThe pentadentate ligand picdien [LA; 1,9‐bis(2′‐pyridyl)‐2,5,8‐triazanonane)] and [Fe(DMSO)6](NO3)3 produce the hexacoordinate coordination compound [FeL′B]2+ after reaction in ethanol. This compound shows a change in the oxidation state of FeIII to FeII as well as an increase in the denticity of the starting ligand LA. The new ligand L′B {1,9‐bis(2′‐pyridyl)‐5‐[(ethoxy‐2′‐pyridyl)methyl]‐2,5,8‐triazanon‐1‐ene} has an imine carbon−nitrogen double bond. This study provides evidence for the nature of the intermediate species during the formation of [FeL′B](BPh4)2. A systematic study was performed based on the evolution of the voltammograms observed after the addition of ligand (LA, LB) or base (LiOEt) to FeIII, FeII solutions or stoichiometric metal‐ligand mixtures (LB is L′B without the imine group). The stability of FeLA3+ and FeLA2+ species in acidic media and under nitrogen atmosphere was confirmed. The reactivity of FeLB3+ and FeLA3+ systems was found to be very similar, and the reduction products were found to be FeII species with simultaneous ligand oxidation, which, in both cases, produces an imine double bond, giving rise to an intramolecular redox reaction. The following disproportionation equation describes the general form of this process: 2 FeL3+ ⇄ FeL2+ + FeL′2+ + 2 H+. The oxidation was verified by the double bond formation in LA and LB giving rise to L′A and L′B as can be seen in the general equation: R1−CH2−NH−R2 ⇄ R1−CH=N−R2 + 2 H+ + 2e−. The disproportionation reaction for FeLA3+ and FeLB3+ species depends on the acidity level of the media: this reaction cannot be verified in acidic media, while neutral and slightly basic media favour formation of the FeII species with L′A and L′B. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis, X‐ray Studies and Magnetic Properties of Dinuclear NiII and CuII Complexes Bridged by the Azo‐2,2′‐bipyridine Ligand
Authors: Campos‐Fernández Cristian S. , Galán‐Mascarós José R. , Smucker Bradley W. , Dunbar Kim R. 
Published: February 2003

AbstractTwo new paramagnetic transition metal complexes that contain the bridging ligand azo‐2,2′‐bipyridine (abpy) have been prepared and characterized by X‐ray crystallography and magnetic susceptibility measurements. The compound [Ni2(μ‐abpy)(CH3CN)2(NO3)4]·2CH3CN (1·2CH3CN) crystallizes in the triclinic space group P$\bar 1$
with a = 8.290(5) Å, b = 8.343(5) Å, c = 11.180(5) Å, α = 105.36(3)°, β = 94.39(3)°, γ = 107.56(3)°, V = 700.5(7) Å3 and Z = 1. The related salt [Cu2(μ‐abpy)(CH3CN)8][BF4]4 (2) crystallizes in the triclinic space group P$\bar 1$
with a = 10.240(2) Å, b = 10.597(2) Å, c = 10.712(2) Å, α = 64.23(3)°, β = 78.21(3)°, γ = 78.57(3)°, V = 1026.7(3) Å3 and Z = 1. Solutions of 2 eventually produce the polymeric CuI compound {[Cu(μ‐abpy)][BF4]}∞ (3) which was also crystallographically characterized: monoclinic space group P21/n, with a = 9.295(2) Å, b = 9.541(2) Å, c = 13.486(3) Å, β = 91.58(3)°, V = 1195.5(4) Å3 and Z = 4. The magnetic properties of these dinuclear paramagnetic complexes have been studied in detail, and have provided an opportunity for probing the ability of this ligand to mediate magnetic exchange interactions between paramagnetic metal centers. Compound 1 exhibits antiferromagnetic exchange interactions (J = −7.5 cm−1) whereas the magnetic interactions in compound 2 were found to be negligible. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of (η3‐Allyl)bromodicarbonylbis(pyrazole)molybdenum(II) and Reactivity towards [Au(acac)PPh3]: Structure and Dynamic Behavior of the Monometallic Pyrazole and Heterometallic Pyrazolate Complexes
Authors: Paredes Paloma , Miguel Daniel , Villafañe Fernando 
Published: February 2003

AbstractThe reactions of [Mo(η3‐allyl)Br(CO)2(NCMe)2] and two equivalents of Hpz (pyrazole) or Hdmpz (3,5‐dimethylpyrazole) lead to [Mo(η3‐allyl)Br(CO)2(Hpz)2] or [Mo(η3‐allyl)Br(CO)2(Hdmpz)2]. The Hpz and Hdmpz ligands are coordinated cis and trans with respect to the allyl group in the solid state, whereas in their solutions a slow trigonal twist process is detected. These complexes react with Tl(acac) giving [Mo(acac)(η3‐allyl)(CO)2(Hpz)] and [Mo(acac)(η3‐allyl)(CO)2(Hdmpz)], which also undergo a slow trigonal twist process in solution. The latter complex may also be obtained by the reaction of equimolar amounts of [Mo(η3‐allyl)Br(CO)2(Hdmpz)2] and [Au(acac)PPh3], giving [AuBrPPh3] as a by product. The reaction of these molybdenum acac complexes with [Au(acac)PPh3] give rise to the heterobimetallic bridging pyrazolate complexes [Mo(acac)(η3‐allyl)(CO)2(μ‐pz)AuPPh3] and [Mo(acac)(η3‐allyl)(CO)2(μ‐dmpz)AuPPh3]. The solid state structure of the latter, which is also obtained from [Mo(η3‐allyl)Br(CO)2(Hdmpz)2] and two equivalents of [Au(acac)PPh3], with [AuBrPPh3] as a by product, reveals the coordination of the bridging dimethylpyrazolate ligand trans to the allyl group. Two different dynamic processes which are slowed down at low temperatures are detected in solution for each heterobimetallic complex: trigonal twist for the pyrazolate bridging complex, and hindered rotation of the Mo−N bond for the more hindered dimethylpyrazolate complex. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Electro‐oxidation of Carbon Monoxide and Methanol on Carbon‐Supported Pt–Sn Nanoparticles: a DEMS Study
Authors: Manzo‐Robledo A. , Boucher A.‐C. , Pastor E. , Alonso‐Vante N. 
Published: February 2003

AbstractA comparative study between carbon supported Platinum–Tin (Pt–Snsyn), synthesized via the carbonyl route, and the commercial (Pt3Sn) from E–TEK is reported. The electro‐oxidation of methanol and adsorbed CO, in sulphuric acid medium, were used as probes to evaluate the performance of these electrocatalysts. In‐line differential mass spectrometry (DEMS) was used for this purpose. Both nanoparticulate materials had a mean particle size of <d> = 1.68 ± 0.72 nm, and <d> = 3.58 ± 1.94 nm, respectively. It is demonstrated that, under the same experimental conditions, our homemade Pt–Snsynis less sensitive to poisoning by CO. This observation was again verified during the oxidation of methanol. These results are discussed in terms of the local disorder of the particles surface atoms, favourably induced by size effect and the preparation route employed.
Fuel Cell Operation with Oxygen Enrichment
Authors: Fournier M. , Hamelin J. , Agbossou K. , Bose T.K. 
Published: February 2003

AbstractExperimental results on the performance of a Ballard 5 kW proton exchange membrane fuel cell stack for different oxygen contents in the oxidant are presented. A description of the experimental setup is given. Polarization, power, and efficiency curves as a function of the current density, for different oxygen concentrations are presented. This detailed characterization of the fuel cell stack behavior is required in order to evaluate the effects of oxygen enrichment on the net power output of the stack. This investigation is done in the framework of a project on stand‐alone power generation systems using renewable energy sources, and based on hydrogen production and storage. An electrolyzer, powered by the excess electrical energy from renewable energy sources, produces hydrogen. The stored hydrogen could then be used to feed an energy conversion device, such as a fuel cell stack, which acts as a secondary power source in periods of high demand. Therefore, a second objective is to evaluate the possibility of using the oxygen produced by the electrolyzer for the enrichment. Other oxygen enrichment techniques such as membrane gas separation and pressure swing adsorption are also discussed. Net available power and system efficiency are used as comparison factors.
Mathematical Modelling and Simulation of Polymer Electrolyte Membrane Fuel Cells. Part I: Model Structures and Solving an Isothermal One‐Cell Model
Authors: Hertwig K. , Martens L. , Karwoth R. 
Published: February 2003

AbstractAmongst the various types of fuel cells, the polymer electrolyte membrane fuel cell (PEM‐FC) can be used favourably in vehicles and for in house energy supply. The focus of the development of these cells is not only to provide cost‐effective membranes and electrodes, but also to optimise the process engineering for single cells and to design multi‐cell systems (cell stacks). This is a field in which we have successfully applied the methods of mathematical modelling and simulation. Initially, in this work, a partial model of a single membrane‐electrode unit was developed in which the normal reaction technology fields (concentration, temperature, and flow‐speed distributions) were calculated, but also the electrical potential and current density distribution in order to develop model structures for technically interesting PEM‐FC. This allows the simulation of the effects that the geometric parameters (electrode and membrane data and the dimensions of the material feed and outlet channels) and the educt and coolant intake data have on the electrical and thermal output data of the cell. When complete, cell stacks consisting of a number of single cells, most of which have bipolar switching, are modelled the distribution of the gas flows over the single cells and the specific conditions of heat dissipation must also be taken into consideration. In addition to the distributions mentioned above, this simulation also produces characteristic current‐voltage and power‐voltage curves for each application that can be compared with the individual process variations and cell types, thus making it possible to evaluate them both technically and economically. The results of the simulation of characteristic process conditions of a PEM‐FC operated on a semi‐technical scale are presented, which have been determined by means of a three‐dimensional model. The distributions of the electrical current density and all component voltage drops that are important for optimising the conditions of the process are determined and also the water concentration in the membrane as an important factor that influences the cell’s momentary output and the PEM‐FC’s long‐term stability.
Empirical Model Equations for the Direct Methanol Fuel Cell DMFCs
Authors: Argyropoulos P. , Scott K. , Shukla A.K. , Jackson C. 
Published: February 2003

AbstractEmpirical model equations, proposed for polymer electrolyte fuel cells, are used to predict the cell voltage vs. current density response of a liquid feed direct methanol fuel cell. The model equations are validated against experimental data for a small‐scale fuel cell over a wide range of methanol concentration and temperatures. A new empirical equation is presented which is able to predict the voltage response of liquid feed direct methanol fuel cells over a wide range of operating conditions and even in the case of very low current densities caused by, for example, the use of dilute methanol solutions or low cell temperatures.
Reliable Fuel Cell Simulation Using an Experimentally Driven Numerical Model
Authors: Lunghi Piero , Bove Roberto 
Published: February 2003

AbstractThe necessity of a simulation tool for integrated power plant with MCFCs has led to the development of a numerical model by which it is possible to evaluate the performances of the cell and the plant the cell is embedded in. Many mathematic models can be found in the literature that evaluate electrochemical fuel cell performance [1–9]; however the model must be developed according to a specific target. In other words, if the main purpose of the study is, for example, shape optimization, the model must be very accurate concerning internal conditions, such as current density, temperature distribution, etc. The models found in the literature [1–3, 5, 9] seem to produce excellent results. However, the aim here is to create a mathematical model for fuel cell stacks, which can be integrated into a simulation modular code for the Balance of the Plant (BoP) optimization. Plant modelling can be performed using commercially available software. Often, since fuel cells are innovative devices, numerical codes that simulate their behaviour must be implemented by using a proprietary code. Previous papers can be found in the literature [4, 10, 11], where fuel cell stacks are inserted in an entire power plant, but very often the fuel cell block is zero‐dimensional and it is not affected by the variation in input parameters. The authors, for this purpose, have developed a module to be integrated into commercial software for plants simulation, Aspen Plus. The model adopted is simple, but at the same time, it calculates with good accuracy fuel cell performance under any conditions. Another important element taken into account during the code development is the validation through experimental data. In the present work, the authors have adopted an analytic model for evaluating the electrochemical performance [6] of a fuel cell and results obtained are compared with those found out during the tests on a Molten Carbonate Fuel Cell. Some phenomena not described in the original model are considered and an enhanced model for the cell performance is developed. The model obtained is therefore used to analyse fuel cell behaviour under several operating conditions. These results seem to fit very well with experimental analyses conducted in the test rig of the University of Perugia.
In Situ Investigation of Two‐Phase Flow Patterns in Flow Fields of PEFC’s Using Neutron Radiography
Authors: Geiger A.B. , Tsukada A. , Lehmann E. , Vontobel P. , Wokaun A. , Scherer G.G. 
Published: February 2003

AbstractA novel in situ method for the investigation of the two‐phase flow patterns occurring in the flow fields of polymer electrolyte fuel cells (PEFC’s) has been developed. In these experiments, the gas / liquid two‐phase flow in hydrogen fuel cells as well as in direct methanol fuel cells (DMFC’s) has been studied. Unique results and the promising use of neutron radiography for PEFC research are shown. Its current limitations but also future developments and opportunities are discussed.
Kinetics of Methanol Oxidation on Supported and Unsupported Pt/Ru Catalysts Bonded to PEM
Authors: Khazova O.A. , Mikhailova A.A. , Skundin A.M. , Tuseeva E.K. , Havránek A. , Wippermann K. 
Published: February 2003

AbstractThe kinetics and mechanism of methanol adsorption and oxidation on real Pt/Ru (1:1) electrodes were investigated. In model electrode systems, the addition of supporting proton‐conducting electrolyte is necessary. Therefore, the influence of sulphuric acid on the kinetics of methanol adsorption and oxidation was also investigated. It turns out that the steady state adsorption is not significantly affected by the addition of sulphuric acid. However, if sulphuric acid is used as an additional electrolyte, the rate of methanol adsorption and steady state oxidation decreases, whereas the active surface of the catalyst increases. The mechanism of methanol oxidation is not affected by the addition of sulphuric acid. At low potentials, the adsorption of methanol is found to be much faster than its oxidation. Hence, the oxidation of the methanol intermediate species is believed to be the rate‐determining step under these conditions. This result is confirmed by apparent orders of reaction of about 0.5. At potentials in the range of 0.3–0.5 V, a mixed activation‐adsorption control is supposed, whereas at potentials more positive than 0.5 V, the adsorption of methanol is probably the rds. This is supported by the apparent reaction orders and apparent activation energies of methanol oxidation.
Genotypic and phenotypic characteristics of antibiotic‐producing soil Streptomyces investigated by RAPD‐PCR
Authors: Gharaibeh Raad , Saadoun Ismail , Mahasneh Amjad 
Published: February 2003

AbstractRandom amplified polymorphic DNA (RAPD) analysis has been used to determine the relatedness of 73 antibiotic‐producing soil Streptomyces isolates that were recovered from different soil habitats in Jordan based on their RAPD‐PCR fingerprints. Genetic polymorphisms between these isolates showed three common bands of 2777, 800 and 250 bp shared by approximately (95%) of them. Some specific bands were also observed. Further analysis of RAPD patterns with the UPGMA resulted in clustering the tested isolates into two main super clusters. Super cluster I was more homogenous than super cluster II and contained all the reference strains. However, super cluster II consists of unrelated isolates within five small groups. As RAPD fingerprints of the tested isolates linked to their phenotypes, differentiation between isolates with different cultural properties was observed.
A novel membrane glycoprotein of Escherichia coli
Authors: Kumar Manoj , Mishra Nivedita , Upreti R. K. 
Published: February 2003

AbstractA novel glycoprotein (Gp45) has been isolated and purified from Escherichia coli. To our knowledge, Gp45 is the third glycoprotein isolated from E. coli membrane and it is the second in the non‐pathogenic strain of the organism. For the isolation of Gp45, cell extract or membrane fraction was treated with sodium deoxycholate for 4 h and precipitated with trichloroacetic acid (TCA). The supernatant fraction of TCA containing the Gp45 was further purified on DEAE‐Sephadex A‐25. SDS‐PAGE showed a single band at 45 kDa position that stained with periodic‐Schiff reagent. It contained 60% carbohydrate and 40% protein content. The monosaccharide composition also substantiated the characteristics of the glycoprotein. The E. coli grown in presence of 14C‐glucosamine further confirmed the localization and biosynthesis of this glycoprotein on the membrane during the growth phase. Bacitracin, a general inhibitor of the glycosylation, inhibited its biosynthesis.
Identification of a major protein upon phosphate starvation of Pseudomonas aeruginosa PAO1
Authors: Madhusudhan Kunapuli T. , McLaughlin Robert , Komori Naoka , Matsumoto Hiroyuki 
Published: February 2003

AbstractTo understand the physiology of non‐differentiating bacteria exposed to nutrient deprivation and stress, various approaches have been employed in combination with detailed analysis of protein synthesis pattern. In this study, separation of proteins from clarified cell extracts of Pseudomonas aeruginosa PAO1 grown under phosphorus limiting conditions was achieved by high resolution two‐dimensional gel electrophoresis (2‐DE). Limitation of phosphate in the growth medium revealed significant differences in the 2‐DE pattern of proteins between phosphate starved cells and an unstarved control. A major protein identified as PstS, a phosphate binding protein of the pts operon was exclusively found on 2‐DE gels of phosphate starved bacteria. The identity of protein was established based on the results of Edman degradation, amino acid analysis and mass spectrometry. PstS was also found in other pseudomonads, and therefore, it can be used as a landmark protein in proteomic studies. Additionally, we propose utilizing pstS of pseudomonads for testing bioavailable phosphate from soils and water streams.
Entomopathogenic effect of Aspergillus giganteus and Penicillium corylophilum on two triatomine vectors of Chagas disease
Authors: da Costa Gisela Lara , de Moraes Aurea Maria Lage , Galvão Cleber 
Published: February 2003

AbstractTwo strains, Penicillium corylophilum and Aspergillus giganteus, of the most frequent species found in a survey of triatomines, were used for bioassays in the second and fourth nymphs stage of Triatoma infestans and Panstrongylus megistus. Two procedures, bite and pulverization, were used and compared. A. giganteus was most effective, causing mortality in at least 50% of the nymphs of the two species tested with exception of the nymphs of the fourth stage of P. megistus. Variation in entomopathogenic capacity of the fungal species were observed in the experiments. The two procedures used proved effective.