Studies on polypyrrole film in room temperature melt

A bluish-black shining free standing polypyrrole film (PPy) of electronic conductivity 130 S cm-1 has been prepared by electrochemical oxidative polymerization of pyrrole on Pt/transparent glass conducting electrode resistance 15 O cm-1, using a room temperature melt as an electrolyte, composed of 1:3 stoichiometric ratio of cetyl pyridinium chloride and anhydrous aluminum chloride at 0.58 V versus Al wire as a reference electrode. The film possessed a charge transfer resistance of 132 O, and showed two absorption peaks at 457 and 1264 nm in the UV-vis–NIR diffused reflectance spectra. The morphology of the film was hexagonal. The potential step technique suggested a layered structure. This thin film can easily be peeled off from the electrode surface after three cycles and can be used for various applications like dissipation of electrostatic charge, battery electrode materials, solid electrolytic capacitor, electrochromic windows and displays, microactuators etc. It was also characterized by IR, thermal and SEM studies.

Insight into the key aspects of the regeneration process in the NOx storage reduction (NSR) reaction probed using fast transient kinetics coupled with isotopically labelled (NO)-N-15 over Pt and Rh-containing Ba/Al2O3 catalysts

For the first time, the coupling of fast transient kinetic switching and the use of an isotopically labelled reactant (15NO) has allowed detailed analysis of the evolution of all the products and reactants involved in the regeneration of a NOx storage reduction (NSR) material. Using realistic regeneration times (ca. 1 s) for Pt, Rh and Pt/Rh-containing Ba/Al2O3 catalysts we have revealed an unexpected double peak in the evolution of nitrogen. The first peak occurred immediately on switching from lean to rich conditions, while the second peak started at the point at which the gases switched from rich to lean. The first evolution of nitrogen occurs as a result of the fast reaction between H2 and/or CO and NO on reduced Rh and/or Pt sites. The second N2 peak which occurs upon removal of the rich phase can be explained by reaction of stored ammonia with stored NOx, gas phase NOx or O2. The ammonia can be formed either by hydrolysis of isocyanates or by direct reaction of NO and H2.

The study highlights the importance of the relative rates of regeneration and storage in determining the overall performance of the catalysts. The performance of the monometallic 1.1%Rh/Ba/Al2O3 catalyst at 250 and 350 °C was found to be dependent on the rate of NOx storage, since the rate of regeneration was sufficient to remove the NOx stored in the lean phase. In contrast, for the monometallic 1.6%Pt/Ba/Al2O3 catalyst at 250 °C, the rate of regeneration was the determining factor with the result that the amount of NOx stored on the catalyst deteriorated from cycle to cycle until the amount of NOx stored in the lean phase matched the NOx reduced in the rich phase. On the basis of the ratio of exposed metal surface atoms to total Ba content, the monometallic 1.6%Pt/Ba/Al2O3 catalyst outperformed the Rh-containing catalysts at 250 and 350 °C even when CO was used as a reductant.

Insight into association reactions on metal surfaces: Density-functional theory studies of hydrogenation reactions on Rh(111)

Hydrogenation reaction, as one of the simplest association reactions on surfaces, is of great importance both scientifically and technologically. They are essential steps in many industrial processes in heterogeneous catalysis, such as ammonia synthesis (N-2+3H(2)-->2NH(3)). Many issues in hydrogenation reactions remain largely elusive. In this work, the NHx (x=0,1,2) hydrogenation reactions (N+H-->NH, NH+H-->NH2 and NH2+H-->NH3) on Rh(111) are used as a model system to study the hydrogenation reactions on metal surfaces in general using density-functional theory. In addition, C and O hydrogenation (C+H-->CH and O+H-->OH) and several oxygenation reactions, i.e., C+O, N+O, O+O reactions, are also calculated in order to provide a further understanding of the barrier of association reactions. The reaction pathways and the barriers of all these reactions are determined and reported. For the C, N, NH, and O hydrogenation reactions, it is found that there is a linear relationship between the barrier and the valency of R (R=C, N, NH, and O). Detailed analyses are carried out to rationalize the barriers of the reactions, which shows that: (i) The interaction energy between two reactants in the transition state plays an important role in determining the trend in the barriers; (ii) there are two major components in the interaction energy: The bonding competition and the direct Pauli repulsion; and (iii) the Pauli repulsion effect is responsible for the linear valency-barrier trend in the C, N, NH, and O hydrogenation reactions. For the NH2+H reaction, which is different from other hydrogenation reactions studied, the energy cost of the NH2 activation from the IS to the TS is the main part of the barrier. The potential energy surface of the NH2 on metal surfaces is thus crucial to the barrier of NH2+H reaction. Three important factors that can affect the barrier of association reactions are generalized: (i) The bonding competition effect; (ii) the local charge densities of the reactants along the reaction direction; and (iii) the potential energy surface of the reactants on the surface. The lowest energy pathway for a surface association reaction should correspond to the one with the best compromise of these three factors. (C) 2003 American Institute of Physics.

Formation of NH4[Hg-3(NH)(2)](NO3)(3) and transformation to [Hg2N](NO3)

NH4[Hg-3(NH)(2)](NO3)(3) (1) and [Hg2N](NO3) (2) are obtained from cone. aqueous ammonia solutions of Hg(NO3)(2) at ambient temperature and under hydrothermal conditions at 180 degreesC, respectively, as colourless and dark yellow to light brown single crystals. The crystal structures {NH4[Hg-3(NH)(2)](NO3)(3): cubic, P4(I)32, a = 1030.4(2) pm, Z = 4, R-all = 0.028; [Hg2N](NO3): tetragonal, P4(3)2(1)2, a = 1540.4(1), c = 909.8(1) pm, Z = 4, R-all = 0.054} have been determined from single crystal data. Both exhibit network type structures in which [HNHg3] and [NHg4] tetrahedra of the partial structures of 1 and 2 are connected via three and four vertices, respectively. 1 transforms at about 270 degreesC in a straightforward reaction to 2 whereby the decomposition products of NH4NO3 are set free. 2 decomposes at about 380 degreesC forming yellow HgO. Most certainly, I is identical with a mineral previously analyzed as

[Ag(NH3)(2)]ClO4: Crystal structures, phase transition, and vibrational spectra

[Ag(NH3)(2)](ClO4) is obtained from a solution of AgClO4 in cone. ammonia as colourless single crystals (orthorhombic, Pnmn, Z = 4, a = 795.2(1) pm, b 617.7(1) pm, c = 1298.2(2) pm, R-all = 0.0494). The structure consists of linearly coordinated cations, [Ag(NH3)(2)](+), stacked in a staggered conformation and of tetrahedral (ClO4)(-) anions. A first order phase transition was observed between 210 and 200 K and the crystal structure of the low-temperature modification (monoclinic. P2/m, Z = 4, a = 789.9(5) pm, b = 604.1(5) pm, c = 1290.4(5) pm, beta = 97.436(5)degrees, at 170 K, R-all = 0.0636) has also been solved. Spectroscopic investigations (IR/Raman) have been carried out and the assignment of the spectra is discussed.

Self-potential signatures associated with an injection experiment at an in situ biological permeable reactive barrier

Strategies available to evaluate the performance of in situ permeable reactive barriers are currently not well developed and often rely on fluid and media sampling directly from the permeable reactive barrier (PRB). Here, we investigate the utility of the self-potential (SP) method as a technique to monitor in situ PRB performance. Our field study was conducted at in situ biological PRB in Portadown, Northern Ireland, UK, which was emplaced to assist in the remediation of groundwater contamination (e.g., hydrocarbons, ammonia) that resulted from the operations and waste disposal practices of a former gasworks. Borehole SP measurements were collected during the injection of contaminant groundwater slugs in an attempt to monitor/detect the response of the microbial activity associated with the breakdown of the added contaminants into the PRB. In addition, an uncontaminated groundwater slug was injected into a different portion of the PRB as a ‘control’ and SP measurements were collected for comparison to the SP response of the contaminant slugs. The results of the SP signals due to the contaminant injections show that the magnitude of the response was relatively small (<10 mV) yet showed a consistent decrease during both contaminant injections. The net decrease in SP recorded during the contaminant injections slowly rebounded to near background values through ~44 hours post-injection. The SP response during the uncontaminated injection showed a slight, albeit negligible (within the margin of error), 1 mV increase in the measured SP signals, in contrast to the contaminant injections. The results of the SP signals recorded from the uncontaminated groundwater injection also persisted through a period of ~47 hours after injection but show a net increase in SP relative to pre-injection values. Based on the difference in SP response between the contaminated and uncontaminated injections, we suggest that the responses are likely to be the result of differences in the chemistry of the injection types (contaminated versus uncontaminated) and in situ groundwater. We argue that the SP signals associated with the contaminated injections are dominated by diffusion (electrochemical) potential, possibly enhanced by a microbial effect. While the results of our investigation show a consistent SP response associated with the contaminant injections that is dominated by diffusional effects, further studies are required in order to better understand the effect of microbial activity on SP signals and the potential utility for the SP method to detect/monitor changes that may be indicative of biological PRB performance.

Synthesis of the alkaloids hopromine, hoprominol and hopromalinol, using transamidation methods.

Synthesis of the unsym. Homalium alkaloids hopromine (I, R = H, R1 = pentyl), hoprominol (I, R = OH, R1 = pentyl) and hopramalinol (I, R = OH, R1 = Ph), in diastereoisomeric mixt. form, is reported. The component eight-membered azalactams are first prepd. N-(3-halogenopropyl)-4-pentyl- and 4-heptylazetidin-2-ones are aminated and ring expanded in liq. ammonia to give, after reductive methylation, the corresponding 4-alkyl-5-methyl-1,5-diazacyclooctan-2-ones. Synthesis of the 4-(2-hydroxyheptyl)-5-methyl-1,5-diazacyclooctan-2-one required for hoprominol and hopromalinol is carried out via 4-allyl ?-lactam ring expansion to the eight-membered 4-allylazalactam, followed by methylation, epoxidn. and epoxide opening with lithium dibutylcuprate. A similar epoxidn.-cuprate sequence was carried out on the epoxypropyl ?-lactam, as its N-tert-butyldimethylsilyl deriv., and led to a convenient copper-catalyzed N- to O-migration of the protection; this migration is examd. Alkylation gave O-tert-butyldimethylsilyl-protected N-(3-chloropropyl)-4-(2-hydroxyheptyl)azetidin-2-one which could be aminated and transamidated in excellent yield, to give, after methylation, a superior sequence to the required eight-membered hydroxy azalactam. Although satisfactory for attachment of the first azalactam unit, a dibromobutane coupling system proved unreactive for the second. Couplings with unmethylated, methylated, and benzyloxycabronyl-protected azalactams were examd. using (E)-1,4-dibromobutene and (Z)-1,4-dichlorobutene as the bridging unit. Employing the latter, coupling the first N-methylated azalactam with potassium bis(trimethylsilyl)amide as the base, and then the second with bis(trimethylsilyl)amide-sodium hydride as the base system, provided a satisfactory synthetic outcome. Hydrogenation under acidic conditions gave the unsym. structures hopromine, hoprominol and hopromalinol, as well as the more simple and sym. alkaloid, homaline.

Helix pomatia agglutinin lectin-binding oligosaccharides of aggressive breast cancer

Predicting long-term outcome after breast-cancer diagnosis remains problematic, particularly for patients with clinically small, axillary lymph node- negative tumours, Evidence suggests that the lectin Helix pomatia agglutinin (HPA) identifies oligosaccharides associated with poor-prognosis cancer. Our aim was to identify oligosaccharides that bind HPA in aggressive breast cancers. Breast-cancer cell lines (MCF-7, BT-549 and BT-20) and a cell line From human milk (HBL-100), which showed a range of HPA-binding intensities, were used to extract HPA-binding glycoproteins, Oligosaccharides were released using anhydrous hydrazine and separated on a range of HPLC matrices. We investigated whether HPA-binding oligosaccharides from cell lines were present in human breast-cancer tissues, using 69 breast-cancer specimens from patients with between 5 and 10 years' follow-up. A monosialylated oligosaccharide was over-expressed in the cell line that bound HPA strongly. Further analysis by normal-phase HPLC showed that the 2-aminobenzamide-conjugated oligosaccharide had a hydrodynamic volume of 4.58 glucose units (HPAgly 1), Increased expression of HPAgly 1 was associated with HPA staining of breast-cancer specimens (Student's t-test p = 0.025). Analysis of oligosaccharide levels and disease-free survival after treatment for breast cancer indicated a shorter disease-free interval for patients with elevated levels of HPAgly 1, This is the first time that histochemical lectin staining has been correlated with biochemical mapping of oligosaccharides, Using this approach, we have identified a monosialylated HPA lectin-binding oligosaccharide present in breast-cancer cells grown in vitro which is elevated in breast-cancer specimens that bind the lectin, (C) 2001 Wiley-Liss, Inc.

Use of microtechnologies for intensifying industrial processes

The use of new technologies based on microstructured reactors in industrial processes, including the obtainment of hydrogen peroxide, the catalytic oxidation of ammonia, the utilization of rocket fuels, fine organic synthesis, polymerization, and phase transfer catalysis, were considered. The transition to microtechnologies considerably increases the performance of the process; at the same time, the product yield increases as compared with periodically operating reactors, which allows for a reduction of costs at the separation stage of the reaction mixture and the extraction of the reaction products.

Effect of activated carbon xerogel pore size on the capacitance performance of ionic liquid electrolytes

The use of ionic liquid (IL) electrolytes promises to improve the energy density of electrochemical capacitors (ECs) by allowing for operation at higher voltages. Several studies have also shown that the pore size distribution of materials used to produce electrodes is an important factor in determining EC performance. In this research the capacitative, energy and power performance of ILs 1-ethyl-3- methylimidazolium tetrafluoroborate (EMImBF4), 1-ethyl-3-methylimidazolium dicyanamide (EMImN(CN)2), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (DMPImTFSI), and 1-butyl-3-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (BMPyT(F5Et)PF3) were studied and compared with the commercially utilised organic electrolyte 1M tetraethylammonium tetrafluoroborate solution in anhydrous propylene carbonate (Et4NBF4–PC 1 M). To assess the effect of pore size on IL performance, controlled porosity carbons were produced from phenolic resins activated in CO2. The carbon samples were characterised by nitrogen adsorption– desorption at 77 K and the relevant electrochemical behaviour was characterised by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The best capacitance performance was obtained for the activated carbon xerogel with average pore diameter 3.5 nm, whereas the optimum rate performance was obtained for the activated carbon xerogel with average pore diameter 6 nm. When combined in an EC with IL electrolyte EMImBF4 a specific capacitance of 210 F g1 was obtained for activated carbon sample with average pore diameter 3.5 nm at an operating voltage of 3 V. The activated carbon sample with average pore diameter 6 nm allowed for maximum capacitance retention of approximately 70% at 64 mA cm2.

A survey of molecular line emission towards ultracompact HII regions

We have used the JCMT to survey molecular line emission towards 14 ultracompact HII regions (G5.89, G9.62, G10.30, G10.47, G12.21, G13.87, G29.96, G31.41, G34.26, G43.89, G45.12, G45.45, G45.47, and G75.78). For each source, we observed up to ten 1 GHz bands between 200 and 350 GHz, covering lines of more than 30 species including multiple transitions of CO isotopes, CH3OH, CH3CCH, CH3CN and HCOOCH3, and sulphuretted molecules. The number of transitions detected varied by a factor of 20 between sources; which were chosen following observations of high-excitation ammonia (Cesaroni et al. 1994a) and methyl cyanide (Olmi et al. 1993). In half our sample (the line-poor sources), only (CO)-O-17: (CO)-O-18, SO, (CS)-S-34 and CH3OH were detected. In the line-rich sources, we detected over 150 lines, including high excitation lines of CH3CN, HCOOCH3; C2H5CN, CH3OH, and CH3CCH. We have calculated the physical conditions of the molecular gas. To reproduce the emission from the line-rich sources requires both a hot, dense compact core and an ambient cloud consisting of less dense, cooler gas. The hot cores, which are less than 0.1 pc in size; reach densities of at least 10(8) cm(-3) and temperatures of more than 80 K. The line-poor sources can be modelled without a hot core by a 20-30 K, 10(5) cm(-3) cloud. We find no correlation between the size of the HII region and the current physical conditions in the molecular environment. A comparison with chemical models (Millar et al. 1997) confirms that grain surface chemistry is important in hot cores.

Miniaturization of heterogeneous catalytic reactors: Prospects for new developments in catalysis and process engineering

This paper gives an overview of the research done since 1999 at Eindhoven University of Technology in the Netherlands in the field of miniaturization of heterogeneous catalytic reactors. It is described that different incentives exist for the development of these microstructured reaction systems. These include the need for efficient research instruments in catalyst development and screening, the need for small-scale reactor devices for hydrogen production for low-power electricity generation with fuel cells, and the recent quest for intensified processing equipment and novel process architectures (as in the fine chemicals sector). It is demonstrated that also in microreaction engineering, catalytic engineering and reactor design go hand-in-hand. This is illustrated by the design of an integrated microreactor and heat-exchanger for optimum performance of a highly exothermic catalytic reaction, viz. ammonia oxidation. It is argued that future developments in catalytic microreaction technology will depend on the availability of very active catalysts (and catalyst coating techniques) for which microreactors may become the natural housing.

The preparation of highly ordered single layer ZSM-5 coating on prefabricated stainless steel microchannels

An elegant way to prepare catalytically active microreactors is by applying a coating of zeolite crystals onto a metal microchannel structure. In this study the hydrothermal formation of ZSM-5 zeolitic coatings on AISI 316 stainless steel plates with a microchannel structure has been investigated at different synthesis mixture compositions. The procedures of coating and thermal treatment have also been optimized. Obtaining a uniform thickness of the coating within 0.5 mm wide microchannels requires a careful control of various synthesis variables. The role of these factors and the problems in the synthesis of these zeolitic coatings are discussed. In general, the synthesis is most sensitive to the H2O/Si ratio as well as to the orientation of the plates with respect to the gravity vector. Ratios of H2O/Si=130 and Si/template=13 were found to be optimal for the formation of a zeolitic film with a thickness of one crystal at a temperature of 130 degreesC and a synthesis time of about 35 h. At such conditions, ZSM-5 crystals were formed with a typical size of 1.5 mu mx1.5 mu mx1.0 mum and a very narrow (within 0.2 mum) crystal size distribution. The prepared samples proved to be active in the selective catalytic reduction (SCR) of NO with ammonia. The activity tests have been carried out in a plate-type microreactor. The microreactor shows no mass transfer limitations and a larger SCR reaction rate is observed in comparison with pelletized Ce-ZSM-5 catalysts; (C) 2001 Elsevier Science B.V. All rights reserved.

Non-genetic mechanisms communicating antibiotic resistance:rethinking strategies for antimicrobial drug design

Introduction: Infections by multidrug-resistant bacteria are of great concern worldwide. In many cases, resistance is not due to the presence of specific antibiotic-modifying enzymes, but rather associated with a general impermeability of the bacterial cell envelope. The molecular bases of this intrinsic resistance are not completely understood. Moreover, horizontal gene transfers cannot solely explain the spread of intrinsic resistance among bacterial strains. Areas covered: This review focuses on the increased intrinsic antibiotic resistance mediated by small molecules. These small molecules can either be secreted from bacterial cells of the same or different species (e.g., indole, polyamines, ammonia, and the Pseudomonas quinolone signal) or be present in the bacterial cell milieu, whether in the environment, such as indole acetic acid and other plant hormones, or in human tissues and body fluids, such as polyamines. These molecules are metabolic byproducts that act as infochemicals and modulate bacterial responses toward antibiotics leading to increasing or decreasing resistance levels. Expert opinion: The non-genetic mechanisms of antibiotic response modulation and communication discussed in this review should reorient our thinking of the mechanisms of intrinsic resistance to antibiotics and its spread across bacterial cell populations. The identification of chemical signals mediating increased intrinsic antibiotic resistance will expose novel critical targets for the development of new antimicrobial strategies.

Adsorption of metal ions on nitrogen surface functional groups in activated carbons

A commercially available coconut-shell-derived active carbon was oxidized with nitric acid, and both the original and oxidized active carbons were treated with ammonia at 1073 K to incorporate nitrogen functional groups into the carbon. An active carbon with very high nitrogen content (similar to9.4 wt % daf) was also prepared from a nitrogen-rich precursor, polyacrylonitrile (PAN). These nitrogen-rich carbons had points of zero charge (pH(pzc)) similar to H-type active carbons. X-ray absorption near-edge structure (XANES) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and temperature-programmed desorption (TPD) were used to characterize the nitrogen functional groups in the carbons. The nitrogen functional groups present on the carbon surface were pyridinic, pyrrolic (or indolic), and pyridonic structures. The adsorption of transition metal cations Cd2+, Ni2+, and Cu2+ from aqueous solution on the suite of active carbons showed that adsorption was markedly higher for carbons with nitrogen functional groups present on the surface than for carbons with similar pH(pzc) values. In contrast, the adsorption characteristics of Ca2+ from aqueous solution were similar for all the carbons studied. Flow microcalorimetry (FMC) studies showed that the enthalpies of adsorption of Cd2+(aq) on the active carbons with high nitrogen contents were much higher than for nitric acid oxidized carbons studied previously, which also had enhanced adsorption characteristics for metal ion species. The enthalpies of adsorption of Cu2+ were similar to those obtained for Cd2+ for specific active carbons. The nitrogen functional groups in the carbons act as surface coordination sites for the adsorption of transition metal ions from aqueous solution. The adsorption characteristics of these carbons are compared with those of oxidized carbons.