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At least 1,009 records · Page 56Linked to original sources
PubMed2004

Development and application of a mobile laboratory for measuring emissions from diesel engines. 2. Sampling for toxics and particulate matter.

Limited data are available on the emission rates of speciated volatile and semivolatile organic compounds, as well as the physical and chemical characteristics of fine particulate matter (PM) from mobile, in-use diesel engines operated on the road. A design for the sampling of these fractions and the first data from in-use diesel sources are presented in this paper. Emission rates for carbonyls, 1,3-butadiene, benzene, toluene, xylene, PM, and elemental and organic carbon (EC and OC) are reported for a vehicle driven while following the California Air Resources Board (ARB) four-mode heavy heavy-duty diesel truck (HHDDT) cycle and while transiting through a major transportation corridor. Results show that distance specific emission rates are substantially greater in congested traffic as compared with highway cruise conditions. Specifically, emissions of toxic compounds are 3-15 times greater, and PM is 7 times greater under these conditions. The dependence of these species on driving mode suggests that health and source apportionment studies will need to account for driving patterns in addition to emission factors. Comparison of the PM/NOx ratios obtained for the above tests provides insight into the presence and importance of "off-cycle" emissions during on-road driving. Measurements from a stationary source (operated and tested at constant engine speed) equipped with an engine similar to that in the HHDDT yielded a greater understanding of the relative dependence of emissions on load versus engine transients. These data are indicative of the type of investigations made possible by the development of this novel laboratory.

Air Pollutants↗
PubMed1999

Occupational risk factors for lung cancer in women: results of a case-control study in Germany.

BACKGROUND: To investigate the association between lung cancer and occupational factors in women. METHODS: Six hundred eighty-six women with lung cancer and 712 controls matched for age and region were interviewed to gather occupational histories and information about other risk factors and confounders. Odds ratios (OR) and 95%-confidence intervals (CI) were calculated. RESULTS: There were 11 cases and 2 controls who reported occupational asbestos exposure. Significantly elevated risks (P < 0.05, smoking-adjusted), were observed in the following industries: chemical, oil (OR 3.7), pottery, glass (OR 2.5), engine, vehicle building (OR 2.2), paper, wood, print (OR 1.9), cleaning service, hairdressing, housekeeping, waste disposal (OR 1.5); and occupations: assemblers, unskilled metal workers (OR 2.5), stock clerks, etc. (OR 1.6), restaurant owners and hoteliers (OR 2.7), as well as waitresses and travel attendants (OR 2.6). CONCLUSIONS: The study provides evidence that both occupations previously observed as hazardous in males, and occupations of particular significance for women only, play a role in the risk of lung cancer in women.

Adult↗
PubMedDate not supplied

Large-scale production of peptides using the solid-phase continuous flow method. Preparative synthesis of the novel tachykinin antagonist MEN 10627.

The large-scale solid-phase continuous flow synthesis of the bicyclic peptide MEN 10627, a new potent Neurokinin A receptor antagonist, is described using the Fmoc-polyamide method on both macrosorb 125 and Macrosorb 250 resin. A new synthesizer designed in-house was realized by assembling Whitey valves and Waters pump in order to allow small-scale (0.0001 mol; 1 x 10 cm Omnifit columns) synthetic studies which were strongly predictive of the conditions required for large-scale (0.01-0.10 mol; 3.6 or 5.9 x 46 cm Büchi columns) production, performed on the same apparatus.

Models, Chemical↗
PubMed2000

Chemico-physical properties of hyaluronan-based sponges.

The aim of this study was to obtain information on the chemico-physical and surface properties of the hyaluronan total benzylic ester sponges to evaluate their stability, surface "cleanliness" and handling for the applications in the tissue engineering. The thermal analysis, the characterization of surface chemical composition and the swelling test were performed on these materials. Moreover, the morphological changes, the rheological behavior, and the molecular weight loss in function of the time were monitored when the sponges were incubated in cell culture medium. The results showed that the sponges were thermally stable up to 220 degrees C and the surface composition was different from that of the bulk for C-O contribution. No contaminants were detected. In culture medium, the samples swelled assuming the rheological properties of biopolymer gel. When the sponges were in contact with the culture medium, their molecular weight remained stable for the first day and a loss of 11% and 31% was recorded for samples removed from culture medium after 3 and 7 days, respectively. With the scanning electron microscopy analysis, the spongy structure appeared with open interconnecting pores. The micrographs related to the samples after incubation in culture medium showed that the degradation was evident on the surface after 1 day. The deterioration of the pore walls and the presence of craters increased with time and, after 3 days, the phenomena were present also in the section.

Absorption↗
PubMed2004

Powering nanodevices with biomolecular motors.

Biomolecular motors, in particular motor proteins, are ideally suited to introduce chemically powered movement of selected components into devices engineered at the micro- and nanoscale level. The design of such hybrid "bio/nano"-devices requires suitable synthetic environments, and the identification of unique applications. We discuss current approaches to utilize active transport and actuation on a molecular scale, and we give an outlook to the future.

Genetic Engineering↗
PubMed1998

Ligand-induced conformational change in penicillin acylase.

The enzyme penicillin acylase (penicillin amidohydrolase EC 3.5.1. 11) catalyses the cleavage of the amide bond in the benzylpenicillin (penicillin G) side-chain to produce phenylacetic acid and 6-aminopenicillanic acid (6-APA). The enzyme is of great pharmaceutical importance, as the product 6-APA is the starting point for the synthesis of many semi-synthetic penicillin antibiotics. Studies have shown that the enzyme is specific for hydrolysis of phenylacetamide derivatives, but is more tolerant of features in the rest of the substrate. It is this property that has led to many other applications for the enzyme, and greater knowledge of the enzyme's structure and specificity could facilitate engineering of the enzyme, enhancing its potential for chemical and industrial applications. An extensive study of the binding of a series of phenylacetic acid derivatives has been carried out. A measure of the relative degree of inhibition of the enzyme by each of the compounds has been obtained using a competitive inhibition assay, and the structures of a number of these complexes have been determined by X-ray crystallography. The structures reveal a clear rationale for the observed kinetic results, but show also that some of the ligands cause a conformational change within the binding pocket. This change can generally be understood in terms of the size and orientation of the ligand within the active site.The results reveal that ligand binding in penicillin acylase is facilitated by certain amino acid residues that can adopt two distinct, energetically favourable positions in order to accommodate a variety of compounds within the active site. The structures of these complexes provide evidence for conformational changes in the substrate-binding region that may act as a switch in the mechanism of autocatalytic processing of this enzyme.

Catalytic Domain↗
PubMed2001

Generalized dead-end elimination algorithms make large-scale protein side-chain structure prediction tractable: implications for protein design and structural genomics.

The dead-end elimination (DEE) theorems are powerful tools for the combinatorial optimization of protein side-chain placement in protein design and homology modeling. In order to reach their full potential, the theorems must be extended to handle very hard problems. We present a suite of new algorithms within the DEE paradigm that significantly extend its range of convergence and reduce run time. As a demonstration, we show that a total protein design problem of 10(115) combinations, a hydrophobic core design problem of 10(244) combinations, and a side-chain placement problem of 10(1044) combinations are solved in less than two weeks, a day and a half, and an hour of CPU time, respectively. This extends the range of the method by approximately 53, 144 and 851 log-units, respectively, using modest computational resources. Small to average-sized protein domains can now be designed automatically, and side-chain placement calculations can be solved for nearly all sizes of proteins and protein complexes in the growing field of structural genomics.

Algorithms↗
PubMed2002

Bulk chemicals from biotechnology: the case of 1,3-propanediol production and the new trends.

The need for a sustainable resource supply, the rapid advances in plant biotechnology and microbial genetics and the strategic shift of major chemical companies into the area of life sciences are some of the driving forces for renewed interest in producing bulk chemicals from renewable resources by biological processes. The microbial production of 1,3-propanediol as briefly reviewed in this article and compared with the competing chemical processes demonstrates the promise and constraints of bioprocesses for bulk chemicals. The new concept of biorefinery and biocommodity engineering and future research needs in this area are also outlined.

Bacteria↗
PubMed1996

Fluorescence decay of tryptophans in serine proteinases from microorganisms: relation to X-ray models.

Fluorescence decay kinetics of indole groups in five proteinases from microorganisms are reported. The data show differences between the excited state lifetimes of the tryptophans located in identical positions in the polypeptide chains of the closely related proteinases mesentericopeptidase and subtilisin Novo. The lifetime of the single Trp 113 in subtilisins DY and Carlsberg are identical. The microenvironments of this residue in the four subtilisins are identical and probably its fluorescence is quenched in these proteins. The crystallographic models of the enzymes investigated were analysed in the region of the tryptophyl residues and provide an explanation for the observed emission properties.

Bacillus↗
PubMed2005

Engineering the substrate specificity of cytochrome P450 CYP102A2 by directed evolution: production of an efficient enzyme for bioconversion of fine chemicals.

The P450 cytochromes constitute a large family of hemoproteins that catalyze the monooxygenation of a diversity of hydrophobic substrates. CYP102A2 is a catalytically self-sufficient cytoplasmic enzyme from Bacillus subtilis, containing both a monooxygenase domain and a reductase domain on a single polypeptide chain. CYP102A2 was subjected to error-prone PCR to generate mutants with enhanced activity with fatty acids and other aromatic substrates. The library of CYP102A2 mutants was expressed in BL21(DE3) Escherichia coli cells and screened for their ability to oxidize different substrates by means of an activity assay. After a single round of error-prone PCR, the variant Pro15Ser exhibiting modified substrate specificity was generated. This variant showed approximately 6- to 9-fold increased activity with SDS, lauric acid and 1,4-naphthoquinone, and enhanced activity for other substrates such as ethacrynic acid and epsilon-amino-n-caproic acid. Molecular modeling of the CYP102A2 monooxygenase domain suggested that Pro15 is located in a short helical segment and is involved in extensive interactions between the N-terminal domain and the beta2 sheet, which contribute to the formation of the substrate binding site. Thus, Pro15 appears to affect substrate binding and catalysis indirectly. These results clearly demonstrate the importance of remote residues, not readily predicted by rational design, for the determination of substrate specificity. In addition, we report here that the Pro15Ser variant of CYP102A2 can be efficiently immobilized on epoxy-activated Sepharose at pH 8.5 and 4 degrees C. The immobilized variant of CYP102A2 retains most of its activity (81%) and shows improved stability at 37 degrees C. The approach offers the possibility of designing a P450 bioreactor that can be operated over a long period of time with high efficiency and which can be used in fine chemical synthesis.

Amino Acid Sequence↗
PubMed2005

An organic-inorganic hybrid scaffold for the culture of HepG2 cells in a bioreactor.

Much interest has recently been shown in the potential utility of bioartificial liver (BAL) as a bridge support for patients and as a module for experimental purposes. A radial-flow bioreactor (RFB), one of the perfused bed/scaffold-type bioreactors, enables a highly functional three-dimensional culture as BAL. The functional capacity of bioreactors depends not only on their mechanistic structures but also on scaffolds packed in them. In the present study, we examined the possible utility of a new porous organic-inorganic-hybrid scaffold in an RFB. The scaffold was made from tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS) by a sol-gel method using sieved sucrose particles as a porogen. In the porous TEOS-PDMS hybrid scaffold, human hepatocellular carcinoma cells (HepG2) proliferated actively and formed cell clusters more efficiently than they did in a polyvinyl-alcohol scaffold. When cultivated in PDMS-TEOS, HepG2 cells secreted a approximately three-fold greater amount of albumin than that secreted in a monolayer culture. For potential application of BAL to pharmacological studies and future clinical use, it is essential to develop a method to propagate liver cells that maintain highly specific functions. The present results indicate that PDMS-TEOS may be a promising scaffold for developing such functional culture methods.

Albumins↗
PubMed2003

Metabolic oligosaccharide engineering as a tool for glycobiology.

Oligosaccharides transact information exchange at the cell surface and modulate the activities and distribution of proteins within cells. Recently, the ability to modify monosaccharide structures within cellular glycans through metabolic processes has offered a new avenue for biological studies. The technique of metabolic oligosaccharide engineering has been used to disrupt glycan biosynthesis, chemically modify cell surfaces, probe metabolic flux inside cells, and to identify specific glycoprotein subtypes from the proteome.

Animals↗
PubMed2005

A Gly/Ala switch contributes to high affinity binding of benzoxazinone-based non-peptide oxytocin receptor antagonists.

Non-peptide antagonists of the oxytocin receptor (OTR) have been developed to prevent pre-term labour. The benzoxazinone-based antagonists L-371,257 and L-372,662 display pronounced species-dependent pharmacology with respect to selectivity for the OTR over the V(1a) vasopressin receptor. Examination of receptor sequences from different species identified Ala(318) in helix 7 of the human OTR as a candidate discriminator required for high affinity binding. The mutant receptor [A318G]OTR was engineered and characterised using ligands representing many different chemical classes. Of all the ligands investigated, only the benzoxazinone-based antagonists had decreased affinity for [A318G]OTR. Molecular modelling revealed that Ala(318) provides a direct hydrophobic contact with a methoxy group of L-371,257 and L-372,662.

Alanine↗
PubMed2006

Modeling and simulation of deformation of hydrogels responding to electric stimulus.

A model for simulation of pH-sensitive hydrogels is refined in this paper to extend its application to electric-sensitive hydrogels, termed the refined multi-effect-coupling electric-stimulus (rMECe) model. By reformulation of the fixed-charge density and consideration of finite deformation, the rMECe model is able to predict the responsive deformations of the hydrogels when they are immersed in a bath solution subject to externally applied electric field. The rMECe model consists of nonlinear partial differential governing equations with chemo-electro-mechanical coupling effects and the fixed-charge density with electric-field effect. By comparison between simulation and experiment extracted from literature, the model is verified to be accurate and stable. The rMECe model performs quantitatively for deformation analysis of the electric-sensitive hydrogels. The influences of several physical parameters, including the externally applied electric voltage, initial fixed-charge density, hydrogel strip thickness, ionic strength and valence of surrounding solution, are discussed in detail on the displacement and average curvature of the hydrogels.

Computer Simulation↗
PubMed2004

Directed evolution governed by controlling the molecular recognition between an abzyme and its haptenic transition-state analog.

The catalytic antibody, 6D9, was subjected to directed evolution in the phage-display system using two structurally related transition-state analogs (TSAs) for panning. One analog, TSA 3, was originally used for immunization, and the other, TSA 4, a derivative of TSA 3, was designed to optimize the differential affinity for the transition state relative to the ground state so as to provide variants with improved reaction rates. We previously reported that by panning with TSA 4, we could obtain variants with highly improved catalytic rate enhancement (k(cat)/k(uncat)), and Tyr (L27e) seemed to play a key role in stabilizing the transition-state structure [Nat. Biotechnol. 19 (2001) 563]. Here, we examined in detail a large number of the variants selected by these haptens, in order to elucidate the mechanism of the directed evolution driven by them. ELISA with 3- and 4-bovine serum albumin (BSA) showed that variants selected by these TSAs exhibited distinct binding patterns. All the variants whose rate enhancement was greater than five-fold of that of 6D9 had Tyr (L27e) and were obtained from the library panned with TSA 4, but not from the library panned with TSA 3. Kinetic studies showed that TSA 4 could efficiently select variants with increased differential binding affinity for the transition state relative to the ground state, and these variants exhibited improved rate enhancements. This study verified the difference of in vitro evolution driven by the two structurally related TSAs and stresses the importance of designing an appropriate hapten for panning.

Animals↗
PubMed2006

Control of SBR switching by fuzzy pattern recognition.

The sequencing batch reactor (SBR) is a widely used process for biological removal of nutrients (nitrogen and phosphorus) from wastewater. It is based on the metabolism of specialised bacteria, which under alternate anaerobic/aerobic conditions uptake phosphorus and perform denitrification. Intermittent operation is normally operated on a fixed switching schedule with ample margin for possible inaccuracies, with the result that the process operation is highly inefficient. This paper proposes a switching strategy based on the indirect observation of process state through simple physico-chemical measurements and the use of an inferential engine to determine the most appropriate switching schedule. In this way the duration of each phase is limited to the time strictly necessary for the actual loading conditions. Experimental results show that the treatment cycle can be significantly shortened, with the results that more wastewater can be treated. The switching strategy is based on innovative data-processing techniques applied to simple process signals including pH, oxido-reduction potential (ORP) and dissolved oxygen (DO). They include wavelet filtering for signal denoising and fuzzy clustering for features extraction and decision-making. The formation of a knowledge-base and its adaptation during the operation are also discussed.

Aerobiosis↗
PubMed2002

The decay of chlorine associated with the pipe wall in water distribution systems.

Free chlorine decay rates in water distribution systems for bulk and wall demands should be modelled separately as they have different functional dependencies. Few good quality determinations of in situ wall demand have been made due to the difficulty of monitoring live systems and due to their complexity. Wall demands have been calculated from field measurements at 11 locations in a distribution system fed from a single source. A methodology for the laboratory determination has been evolved and shown to give results that are similar to the in situ results. Pipe materials were classified as either having high reactivity (unlined iron mains) or low reactivity (PVC, MDPE and cement-lined ductile iron). The results indicate that wall decay rates for the former are limited by chlorine transport and for the latter by pipe material characteristics. The wall decay rate is inversely related to initial chlorine concentration for low reactivity pipes. In general, water velocity increases wall decay rates though the statistical confidence is low for low reactivity pipes. A moderate biofilm coating did not influence the wall decay rate for low reactivity pipes.

Biofilms↗