Diesel Electric Locomotive Propulsion Systems?A Look into the Future

The demand for increased productivity in train operation has been the driving force in creating today's energy-efficient high-horsepower diesel electric locomotives. A key in obtaining this productivity improvement has been the evolution of the electric transmission that has allowed the locomotive's effective tractive effort to increase along with its diesel engine horsepower. A means of correlating the relative efficiency, reliability, performance, size, and weight of the available propulsion technologies and control strategies is developed, along with trade-offs in applying these technologies and strategies to locomotives now and in the future. Both dc and the various types of ac propulsion technologies are included. How the basic strategy of individual axle control or total locomotive control (for both dc and ac technologies) relates to locomotive productivity is covered along with variations such as power equipment staging in the overall optimization process.     

Effects of coxsackievirus B3 infection on the acute-phase protein metallothionein and on cytochrome P-4501A1 involved in the detoxification processes of TCDD in the mouse

During acute infections, the synthesis of acute-phase proteins and other proteins participating in the host defence are stimulated in the liver and kidney. In previous studies of coxsackievirus B3 (CB3) infection in mice, we found that cadmium (Cd) accumulates in the kidney, whereas 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) accumulates in the liver. To study if CB3 infection affects the synthesis of the Cd-binding protein metallothionein (MT) and the TCDD-binding/detoxifying cytochrome P-450 (CYP-450) isozyme CYP1A1, the basal and TCDD-induced levels of serum MT and liver CYP1A1 isozyme were determined in healthy and CB3-infected A/J mice. Furthermore, because interferons affect CYP450 activity, the serum levels of the interferons alpha (IFN-alpha) and -beta (IFN-beta) were measured in CB3-infected mice and in mice treated with the interferon-inducer polyinosinic/polycytidylic acid (poly I/C). Virus or poly I/C was administered intraperitoneally (i.p.) on day 0 and 500 ng TCDD/kg bodyweight on day 1. On day 4, CB3 infection had induced MT approximately 10-fold, regardless of TCDD treatment (P < 0.01 in infected mice and P < 0.001 in infected, TCDD-treated mice). TCDD alone induced a 10-fold increase in CYP1A1 activity (P < 0.001), whereas infection alone suppressed the normal CYP1A1 activity by 75% (P < 0.001). Infection also suppressed the TCDD-induced CYP1A1 activity by approximately 30% (n.s.). Poly I/C suppressed CYP1A1 by 20-25% (n.s.) at both basal and TCDD-induced levels. Serum IFN-alpha and IFN-beta levels were undetectable in controls, in TCDD-treated and in the poly I/C-treated groups on day 4, probably because the short IFN peak is detectable only hours after injection. Conversely, on day 4 of the infection, IFN-alpha and IFN-beta were consistently raised in the TCDD-treated infected mice, whereas increased IFNs as a result of infection alone could be detected in only one individual. These results suggest that the normal host responses during acute infections down-regulate detoxifying processes in favour of acute-phase protein synthesis. This may explain the observed changed pattern of accumulation, excretion and toxicity of the environmental pollutants cadmium and TCDD during this common virus infection.     

Understanding nature's strategies for enzyme-catalyzed racemization and epimerization

Epimerases and racemases are enzymes that catalyze the inversion of stereochemistry in biological molecules. In this article, three distinct examples are used to illustrate the wide range of chemical strategies employed during catalysis, and the diverse set of ancestors from which these enzymes have evolved. Glutamate racemase is an example of an enzyme that operates at an "activated" stereocenter (bearing a relatively acidic proton) and employs a nonstereospecific deprotonation/reprotonation mechanism. UDP-N-Acetylglucosamine 2-epimerase acts at an "unactivated" stereocenter and uses a mechanism involving a nonstereospecific elimination/addition of UDP. L-Ribulose phosphate 4-epimerase also acts at an unactivated stereocenter and uses a nonstereospecific retroaldol/aldol mechanism.     

Biosynthesis of novel thermoplastic polythioesters by engineered Escherichia coli

The development of non-petrochemical sources for the plastics industry continues to progress as large multinationals focus on renewable resources to replace fossil carbon. Many bacteria are known to accumulate polyoxoesters as water-insoluble granules in the cytoplasm. The thermoplastic and/or elastomeric behaviour of these biodegradable polymers holds promise for the development of various technological applications. Here, we report the synthesis and characterization of microbial polythioesters (PTEs), a novel class of biopolymers of general technological relevance. Biosynthesis of PTE homopolymers was achieved using a recombinant strain of Escherichia coli that expressed a non-natural pathway consisting of a butyrate kinase, a phosphotransbutyrylase, and a PHA synthase. Different homopolymers were produced, consisting of either 3-mercaptopropionate, 3-mercaptobutyrate, or 3-mercaptovalerate repeating units, if the respective mercaptoalkanoic acids were provided as precursor substrates to the fermentative process. The PTEs contributed up to 30% (w/w) of the cellular dry weight and were identified as hydrophobic inclusions in the cytoplasm. The chemical and stereochemical homogeneity of the purified PTEs were identified by different methods, and the estimated physical properties were compared to the oxypolyester equivalents, revealing low crystalline order and, for the poly(3-mercaptopropionate) improved thermal stability. The ability to produce PTEs through a biosynthetic route opens up new avenues in the field of biomaterials.     

Stereoselective release behaviors of imprinted bead matrices

In this work, the stereoselective release behaviors of “low”-swelling molecularly imprinted polymer (MIP) bead matrices in pressed-coat tablet type were studied. Either R-propranolol selective MIP or S-propranolol selective MIP was combined with excipients and racemic propranolol and fabricated into the matrix. Subsequently, the release of different propranolol enantiomers from the matrices was examined. Also, the microscopic structure of the hydrated “low”-swelling MIP matrix was determined using a cryogenic scanning electron microscope in order to compare with that of the hydrated “high”-swelling MIP matrix. In vitro release profiles of the “low”-swelling matrices showed a difference in the release of enantiomers, in that the non-template isomer was released faster than the template isomer. However, in the last phase of dissolution this difference reduced and later reversed, resulting at last in the type of specificity being similar to that obtained previously with “high”-swelling MIP matrices.

n summary, MIP beads can be fashioned into matrices and incorporated into different formulations to regulate the resultant stereoselectivity. From the behaviors of stereoselective release observed in MIP matrices, we can conclude that the enantioselective-controlled delivery mechanism of MIPs via formulations depends on the relative affinity of the enantiomer for the template sites, as well as the nature of the polymer, such as hydrophobicity and swellability.     

Ion channel mimetic micropore and nanotube membrane sensors

This paper describes synthetic micropore and nanotube membranes that mimic the function of a ligand-gated ion channel; that is, these membranes can be switched from an "off" state (no or low ion current through the membrane) to an "on" state (higher ion current) in response to the presence of a chemical stimulus. Ion channel mimics based on both microporous alumina and Au nanotube membranes were investigated. The off state was obtained by making the membranes hydrophobic by chemisorbing either a C18 silane (alumina membrane) or a C18 thiol (Au nanotube membrane). Water and electrolyte are forbidden from entering these very hydrophobic pores/nanotubes. The transition to the on state was induced by the partitioning of a hydrophobic ionic species (e.g., a drug or a surfactant) into the membrane. The membrane switches to the on state because at a sufficiently high concentration of this ionic analyte species, the pores/nanotubes flood with water and electrolyte. A pH-responsive membrane was also prepared by attaching a hydrophobic alkyl carboxylic acid silane to the alumina membrane.     

Correction for particle-wall interactions in the separation of colloids by flow field-flow fractionation

In the characterization of materials by field-flow fractionation (FFF), the experienced analyst understands the importance of incorporating additives in the carrier liquid that minimize or eliminate interactions between the analyte and accumulation wall, particularly in aqueous systems. However, as FFF is applied to more difficult samples, such as those with high surface energies, it is increasingly difficult to find additives that completely eliminate particle-wall interactions. Furthermore, the analyst may wish to use specific conditions that preserve the high surface energy of particles, to study their interaction with other materials through their behavior in the FFF channel. With this in mind, Williams and co-workers developed a model that quantifies the effect of particle-wall interactions in FFF using an empirically determined interaction parameter. In this work, the model is evaluated for the application of flow FFF in carrier liquids of low ionic strength, where particle-wall interactions are magnified. The retention of particles ranging in size from 64 to 1000 nm is measured using a wide range of field strengths and retention levels. The model is found to be generally valid over the entire range, except for minor discrepancies at lower levels of retention. Although retention levels are dramatically affected by particle-wall interactions, the point of steric inversion (500 nm), where the size-based elution order reverses, is not affected. When particle-wall interactions are not accounted for, they lead to a bias in particle sizes calculated from standard retention theory of up to 70%. The model can also be used to refine the measurement of channel thickness, which is important for the accurate conversion of retention parameters to particle sizes. In this work, for example, errors in channel thickness led to systematic errors on the order of 10% in particle diameter.     

In-channel electrochemical detection for microchip capillary electrophoresis using an electrically isolated potentiostat

A new electrode configuration for microchip capillary electrophoresis (CE) with electrochemical (EC) detection is described. This approach makes it possible to place the working electrode directly in the separation channel. The "in-channel" EC detection was accomplished without the use of a decoupler through the utilization of a specially designed, electrically isolated potentiostat. The effect of the working electrode position on the separation performance (in terms of plate height and peak skew) of poly(dimethylsiloxane)-based microchip CEEC devices was evaluated by comparing the more commonly used end-channel configuration with this new in-channel approach. Using catechol as the test analyte, it was found that in-channel EC detection decreased the total plate height by a factor of 4.6 and lowered the peak skew by a factor of 1.3. A similar trend was observed for the small, inorganic ion nitrite. Furthermore, a fluorescent and electrochemically active amino acid derivative was used to directly compare the separation performance of in-channel EC detection to that of a widely used laser-induced fluorescence (LIF) detection scheme. In this case, it was found that the plate height and peak skew for both detection schemes were essentially equal, and the separation performance of in-channel EC detection is comparable to LIF detection.     

Aspartame optical biosensor with bienzyme-immobilized eggshell membrane and oxygen-sensitive optode membrane

An aspartame optical biosensor has been fabricated by employing a bienzyme system composed of alpha-chymotrypsin and alcohol oxidase immobilized onto an eggshell membrane and an oxygen-sensitive optode membrane as the transducer. The detection schemes involve the enzymatic reactions of aspartame leading to the depletion of the oxygen level of the medium with a concomitant enhancement of the fluorescence intensity of the oxygen-sensitive membrane. The scanning electron and transmission electron micrographs show the microstructure of the eggshell membrane which is successfully immobilized with bienzyme. Using this novel immobilization technique, the aspartame biosensor shows extremely good stability with a shelf life of at least 8 months. The rate change of the fluorescence intensity in 4 min is found to be linearly related to the concentration of aspartame. The useful analytical working range of the biosensor is from 0.056 to 3.07 mM aspartame. The effects of temperature, pH, and ionic strength on the response of the aspartame biosensor are investigated in detail. Citric acid, cyclamic acid, D-fructose, D-galactose, D-glucose, hydrogen peroxide, DL-malic acid, L-phenylalanine, saccharin, sodium benzoate, and sucrose show no interferences but ethanol interferes strongly. The aspartame biosensor has been applied to determine aspartame contents in some commercial products.     

Measurements of chemical warfare agent degradation products using an electrophoresis microchip with contactless conductivity detector

This paper reports on a microfluidic device for the screening of organophosphonate nerve agent degradation products. The miniaturized system relies on an efficient chip-based separation of alkyl methylphosphonic acids (breakdown products of Sarin, Soman, and VX nerve agents) followed by their sensitive contactless conductivity detection. Experimental parameters relevant to the separation and detection processes have been optimized to yield high sensitivity (with 48-86 microg L(-1) detection limits), fast response (50 s for a three alkyl methylphosphonic acid mixture), high precision (RSD = 3.8-5.0%), and good linearity (over the 0.3-100 mg L(-1) range). Applicability to natural (river) water samples is demonstrated. The new microsystem offers promise for monitoring degradation products of chemical warfare agents, with advantages of speed/warning, efficiency, portability, sample size, and cost compared to conventional ion chromatography or capillary electrophoresis systems.