Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Chemical Engineering”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43Linked to original sources
PubMed2006

Variable reactivity of an engineered cysteine at position 338 in cystic fibrosis transmembrane conductance regulator reflects different chemical states of the thiol.

In a previous study of T338C CFTR (cystic fibrosis transmembrane conductance regulator) we found that protons and thiol-directed reagents modified channel properties in a manner consistent with the hypothesis that this residue lies within the conduction path, but the observed reactivity was not consistent with the presence of a single thiolate species in the pore. Here we report results consistent with the notion that the thiol moiety can exist in at least three chemical states, the simple thiol, and two altered states. One of the altered states displays reactivity toward thiols like dithiothreitol and 2-mercaptoethanol as well as reagents: mixed disulfides (methanethiosulfonate reagents: MTSET+, MTSES-) and an alkylating agent (iodoacetamide). The other altered state is unreactive. The phenotype associated with the reactive, altered state could be replicated by exposing oocytes expressing T338C CFTR to CuCl2, but not by glutathionylation or nitrosylation of the thiol or by oxidation with hydrogen peroxide. The results are consistent with the hypothesis that substituting a cysteine at 338 can create an adventitious metal binding site. Metal liganding alters thiol reactivity and may, in some cases, catalyze oxidation of the thiol to an unreactive form such as a sulfinic or sulfonic acid.

Alkylating Agents↗
PubMed2026

Design and optimization of a kinase-controlled allosteric switch.

Post-translational control enables rapid and precise regulation of cell behavior. Despite these advantages, general strategies to build phosphorylation-based synthetic circuits are limited. Here we reasoned that engineered allostery, a technique that has been applied to design light- and chemically gated protein switches, could also be used to engineer phosphorylation-controlled protein switches (phospho-switches). Using an allosterically controllable Gal4 transcription factor as a scaffold, we show that a classic kinase Förster resonance energy transfer biosensor architecture can be used as a starting point for phospho-switch design. We optimize all features of the phospho-switch to develop an ERK-controlled transcription factor with a 20-fold phosphorylation-dependent change in transcriptional output. The resulting synthetic ERK-responsive transcription factor responds with comparable sensitivity to the c-fos promoter and reveals spatial ERK signaling patterns in mammalian developmental organoids. We further show that our switch architecture can be generalized to other input kinases and allosterically controlled targets. This work provides a general platform for a new generation of kinase-responsive tools for biosensing and synthetic biology applications.

Allosteric Regulation↗
PubMed2005

Toward in-cylinder absorption tomography in a production engine.

Design requirements for an 8000 frame/s dual-wavelength ratiometric chemical species tomography system, intended for hydrocarbon vapor imaging in one cylinder of a standard automobile engine, are examined. The design process is guided by spectroscopic measurements on iso-octane and by comprehensive results from laboratory phantoms and research engines, including results on temporal resolution performance. Novel image reconstruction techniques, necessary for this application, are presented. Recent progress toward implementation, including details of the optical access arrangement employed and signal-to-noise issues, is described. We present first cross-cylinder IR absorption measurements from a reduced channel-count (nontomographic) system and discuss the prospects for imaging.

Journal Article↗
PubMed2005

Creation of GPCR-based chemical sensors by directed evolution in yeast.

G protein-coupled receptors (GPCRs) form a class of biological chemical sensors with an enormous diversity in ligand binding and sensitivity. To explore structural aspects of ligand recognition, we subjected the human UDP-glucose receptor (P2Y14) functionally expressed in the yeast Saccharomyces to directed evolution. We sought to generate new receptor subtypes with ligand-binding properties that would be useful in the development of practical biosensors. Mutagenesis of the entire UDP-glucose receptor gene yielded receptors with increased activity but similar ligand specificities, while random mutagenesis of residues in the immediate vicinity of the ligand-binding pocket yielded mutants with altered ligand specificity. By first sensitizing the P2Y14 receptor and then redirecting ligand specificity, we were able to create mutant receptors suitable for a simple biosensor. Our results demonstrate the feasibility of altering receptor ligand-binding properties via a directed evolution strategy, using standard yeast genetic techniques. The novel receptor mutants can be used to detect chemical ligands in complex mixtures and to discriminate among chemically or stereochemically related compounds. Specifically, we demonstrate how engineered receptors can be applied in a pairwise manner to differentiate among several chemical analytes that would be indistinguishable with a single receptor. These experiments demonstrate the feasibility of a combinatorial approach to detector design based on the principles of olfaction.

Binding Sites↗
PubMed2005

Combinatorial polyketide biosynthesis by de novo design and rearrangement of modular polyketide synthase genes.

Type I polyketide synthase (PKS) genes consist of modules approximately 3-6 kb long, which encode the structures of 2-carbon units in polyketide products. Alteration or replacement of individual PKS modules can lead to the biosynthesis of 'unnatural' natural products but existing techniques for this are time consuming. Here we describe a generic approach to the design of synthetic PKS genes where facile cassette assembly and interchange of modules and domains are facilitated by a repeated set of flanking restriction sites. To test the feasibility of this approach, we synthesized 14 modules from eight PKS clusters and associated them in 154 bimodular combinations spanning over 1.5-million bp of novel PKS gene sequences. Nearly half the combinations successfully mediated the biosynthesis of a polyketide in Escherichia coli, and all individual modules participated in productive bimodular combinations. This work provides a truly combinatorial approach for the production of polyketides.

Amino Acid Sequence↗
PubMed2003

The first semi-synthetic serine protease made by native chemical ligation.

Selective incorporation of non-natural amino acid residues into proteins is a powerful approach to delineate structure-function relationships. Although many methodologies are available for chemistry-based protein engineering, more facile methods are needed to make this approach suitable for routine laboratory practice. Here, we describe a new strategy and provide a proof of concept for engineering semi-synthetic proteins. We chose a serine protease Streptomyces griseus trypsin (SGT) for this study to show that it is possible to efficiently couple a synthetic peptide containing a catalytically critical residue to a recombinant fragment containing the other active site residues. The 223-residue hybrid SGT molecule was prepared by fusing a chemically synthesized N-terminal peptide to a large C-terminal fragment of recombinant origin using native chemical ligation. This C-terminal polypeptide was produced from full-length SGT by cyanogen bromide cleavage at a genetically engineered Met57 position. This semi-synthetic hybrid trypsin is fully active, showing kinetics identical to the wild-type enzyme. Thus, we believe that it is an ideal model enzyme for studying the catalytic mechanisms of serine proteases by providing a straightforward approach to incorporate non-natural amino acids in the N-terminal region of the protein. In particular, this strategy will allow for replacement of the catalytic His57 residue and the buried N-terminus, which is thought to help align the active site, with synthetic analogs. Our approach relies on readily available recombinant proteins and small synthetic peptides, thus having general applications in chemical engineering of large proteins where the N-terminal region is the focal interest.

Amino Acid Sequence↗
PubMed1964

A general review of chemical sterilization in space research.

The unsolved problems in the biology and the chemistry of chemical sterilization are legion. This discussion of them emphasizes some interesting areas for useful research. Studies in molecular biology and cancer chemotherapy have produced information which has important implications in chemical sterilization, particularly with the alkylating and the oxidizing agents. Many of these problems must be solved soon if chemical sterilization is to play the role it should in space research by providing means for effectively controlling the rate and extent of mingling of the forms of terrestrial life with those of extraterrestrial life. In space research in the United States, recent work on chemical sterilization has laid heavy emphasis on the identification and exploration of principles of engineering sciences which control sterilization effectiveness. These principles are reviewed and their significance in chemical sterilization is discussed in terms of the engineering factors involved. Among these factors are: consequence of sterilant polymerization or reaction with the object to be sterilized; criteria for chemical sterilization process effectiveness; depletion of the concentration of the sterilant by evaporation or chemical reaction, including polymerization; obstacles to the diffusion or convection of the sterilizing chemical to the immediate vicinity of the microorganisms to be destroyed; protection of the microorganisms from direct contact with the sterilant; phase behavior of the sterilant in the environment of the sterilization process; presence of water or water vapor; the nature, sources and numbers of microorganisms which survive standard chemical sterilization processes; and the length of exposure required to sterilize at each temperature. The significance of chemical sterilization to space science has been well reviewed at the previous COSPAR symposia. Because several thorough reviews of the empirical knowledge concerning the effects of chemical agents on microorganisms have been published recently, this information is not discussed again for chemical sterilants other than the alkylating agents and several of the oxidizing agents. This lack of emphasis indicates only that these other chemicals have not been applied to a large extent in space research to date and that discussions of their sterilizing properties are readily available in other recent reviews. In the future, interest in many of these other chemical sterilants will increase as the variety of devices to be sterilized and the variety of functions which sterilized devices are expected to perform increase.

Alkylating Agents↗
PubMedDate not supplied

Metabolic engineering of propanediol pathways.

Microbial fermentation is an important technology for the conversion of renewable resources to chemicals. In this paper, we describe the application of metabolic engineering for the development of two new fermentation processes: the microbial conversion of sugars to 1,3-propanediol (1,3-PD) and 1,2-propanediol (1,2-PD). A variety of naturally occurring organisms ferment glycerol to 1,3-PD, but no natural organisms ferment sugars directly to 1,3-PD. We first describe the fed-batch fermentation of glycerol to 1,3-PD by Klebsiella pneumoniae. We then present various approaches for the conversion of sugars to 1,3-PD, including mixed-culture fermentation, cofermentation of glycerol and glucose, and metabolic engineering of a "sugars to 1,3-PD" pathway in a single organism. Initial results are reported for the expression of genes from the K. pneumoniae 1,3-PD pathway in Saccharomyces cerevisiae. The best naturally occurring organism for the fermentation of sugars to 1,2-PD is Thermoanaerobacterium thermosaccharolyticum. We describe the fermentation of several different sugars to 1,2-PD by this organism in batch and continuous culture. We report that Escherichia coli strains engineered to express either aldose reductase or glycerol dehydrogenase convert glucose to (R)-1,2-PD. We then analyze the ultimate potential of fermentation processes for the production of propanediols. Linear optimization studies indicate that, under aerobic conditions, propanediol yields that approach the theoretical maximum are possible and CO2 is the primary coproduct. Without the need to produce acetate, final product titers in the range of 100 g/L should be possible; the high titers and low coproduct levels should make product recovery and purification straightforward. The examples given in this paper illustrate the importance of metabolic engineering for fermentation process development in general.

Biotechnology↗
PubMed2003

Biodegradable synthetic polymers for tissue engineering.

This paper reviews biodegradable synthetic polymers focusing on their potential in tissue engineering applications. The major classes of polymers are briefly discussed with regard to synthesis, properties and biodegradability, and known degradation modes and products are indicated based on studies reported in the literature. A vast majority of biodegradable polymers studied belongs to the polyester family, which includes polyglycolides and polylactides. Some disadvantages of these polymers in tissue engineering applications are their poor biocompatibility, release of acidic degradation products, poor processability and loss of mechanical properties very early during degradation. Other degradable polymers such as polyorthoesters, polyanhydrides, polyphosphazenes, and polyurethanes are also discussed and their advantages and disadvantages summarised. With advancements in tissue engineering it has become necessary to develop polymers that meet more demanding requirements. Recent work has focused on developing injectable polymer compositions based on poly (propylene fumarate) and poly (anhydrides) to meet these requirements in orthopaedic tissue engineering. Polyurethanes have received recent attention for development of degradable polymers because of their great potential in tailoring polymer structure to achieve mechanical properties and biodegradability to suit a variety of applications.

Biocompatible Materials↗
PubMed1989

Current biotechnological developments in Belgium.

In recent years, actions have been undertaken by the Belgian government to promote process innovation and technical diversification. Research programs are initiated and coordinated by the study committee for biotechnology setup within the Institute for Scientific Research in Industry and Agriculture (IRSIA). As a result of this action, the main areas where biotechnological processes are developed or commercially exploited include plant genetics, protein engineering, hybridoma technology, biopesticides, production by genetic engineering of vaccines and drugs, monoclonal detection of human and animal deseases, process reactors for aerobic and anaerobic wastewater treatment, and genetic modification of yeast and bacteria as a base for biomass and energy. Development research also includes new fermentation technologies principally based on immobilization of microorganisms, reactor design, and optimization of unit operations involved in downstream processing. Food, pharmaceutical, and chemical industries are involved in genetic engineering and biotechnology and each of these sectors is overviewed in this paper.

Agriculture↗
PubMed2001

Flux estimation using isotopic tracers: common ground for metabolic physiology and metabolic engineering.

Metabolic physiologists and metabolic engineers share the need to estimate flux. However, the physiologist often works with systems that do not maintain steady state for long. Many sites cannot be sampled, and calculating mass and isotopic balance for the entire system may not be feasible. To deal with these constraints, metabolic physiologists have developed specialized isotopic techniques that may be unfamiliar to metabolic engineers. A selection of these techniques is presented here, not because it is anticipated that they would be used by engineers exactly as in the physiologist's setting, but because they illustrate novel applications of tracer methodology. Creative engineers may find new adaptations of these tools in metabolic engineering and opportunities to increase redundancy. Physiologists, entering into a dialog with engineers, may see more clearly the potential of comprehensive models and revisit the impediments to a more complete analysis of human metabolic systems.

Animals↗
PubMed2004

The influence of oxygen and hydrostatic pressure on articular chondrocytes and adherent bone marrow cells in vitro.

Tissue engineering of articular cartilage from chondrocytes or stem cells is considered to be a potential aspect in the treatment of cartilage defects. In order to optimize culture conditions the influence of low oxygen tension (5%) - single or in combination with intermittent hydrostatic pressure (HP: 30/2 min on/off loading; 0.2 MPa) - on the biosynthetic activity (sulfate and proline incorporation) of human osteoarthritic chondrocytes cultured on collagen I/III membranes was investigated. Additionally, chondrogenesis from high density or monolayer cultures of bovine adherent bone marrow cells (aBMC) with and without chondrogenic medium supplements (CM) was analyzed by RT-PCR (mRNA expression of aggrecan and collagen type II). We could show that low oxygen tension increases significantly the biosynthesis of collagen I/III membrane-associated chondrocytes and even higher under co-stimulation with HP. While there is no chondrogenesis in monolayer cultures, CM induces expression of cartilage matrix molecules in high density cultures of aBMC which is even increased under the influence of low oxygen tension. Both, low oxygen tension and HP without CM are alone not sufficient stimuli for chondrogenesis. It can be concluded that low oxygen tension and HP might be useful tools in cartilage tissue engineering and that these physico-chemical factors promote but do not induce chondrogenesis under the given conditions.

Animals↗
PubMed1993

The low prevalence of occupational asthma and antibody-dependent sensitization to diphenylmethane diisocyanate in a plant engineered for minimal exposure to diisocyanates.

BACKGROUND: Diisocyanate chemicals are leading causes of occupational asthma (OA). METHODS: We conducted a cross-sectional study of 243 workers exposed to diphenylmethane diisocyanate (MDI) in a urethane mold plant that had been designed to minimize MDI exposure (levels were maintained below 0.005 ppm and were continuously monitored). All participants were screened by questionnaire and tests for serum antibodies to MDI-human serum albumin (HSA). On the basis of questionnaire responses, diagnoses were derived that included OA; non-OA; work-related and non-work-related rhinitis; and lower respiratory irritant responses. Serial peak expiratory flow rate studies were performed for 2 weeks in 43 workers with and in 23 workers without lower respiratory symptoms. RESULTS: Results of serial peak expiratory flow rate studies were abnormal in 3 (33%) of 9 workers with OA, in 2 (50%) of 4 with non-OA, and in 2 (9%) of 23 case control subjects. A significant association was found between peak flow rate variability and a questionnaire asthma diagnosis (chi 2 p < 0.002). Physicians confirmed three cases of OA, one of which occurred in a control worker who was free of symptoms. In all three cases asthma symptoms remitted after the worker left the workplace. Serum specific IgE and IgG levels were elevated in 2 of 243 workers, one of whom was prick test positive to MDI-HSA and had had cutaneous anaphylaxis after MDI exposure. CONCLUSIONS: On the basis of these cases, specific work activities associated with exposure to MDI were identified and corrective measures were instituted. Strict control and monitoring of ambient MDI exposure was associated with a low prevalence of specific sensitization to MDI and a lower than expected prevalence of OA.

Air Pollutants, Occupational↗
PubMed2000

The formation of reactive oxygen species catalyzed by neutral, aqueous extracts of NIST ambient particulate matter and diesel engine particles.

It is important to characterize the chemical properties of particulate matter in order to understand how low doses, inhaled by a susceptible population, might cause human health effects. The formation of reactive oxygen species catalyzed by neutral, aqueous extracts of two ambient particulate samples, National Institute of Standards & Technology (NIST) Standard Reference Materials (SRM) 1648 and 1649, and two diesel particulate samples, NIST SRM 1650 and SRM 2975, were measured. The formation of reactive oxygen species was estimated by measuring the formation of malondialdehyde from 2-deoxyribose in the presence of ascorbic acid; H2O2 was not added to this assay. SRM 1649, ambient particulate matter collected from Washington, DC, generated the most malondialdehyde, while SRM 2975, diesel particulate matter collected from a forklift, yielded the least amount. Desferrioxamine inhibited the formation of malondialdehyde from the particulate samples providing additional data to support the observation that transition metals were involved in the generation of reactive oxygen species. Six transition metal sulfates (iron sulfate, copper sulfate, vanadyl sulfate, cobalt sulfate, nickel sulfate, and zinc sulfate) were assayed for their ability to generate reactive oxygen species under the same conditions used for the particulate samples in order to facilitate comparisons between particles and these transition metals. The concentration of transition metals was measured in aqueous extracts of these particulate samples using ion-coupled plasma mass spectrometry (ICP-MS) analysis. There was qualitative agreement between the concentrations of Fe, Cu, and V and the amount of malondialdehyde produced from extracts of these particulate samples. These data suggest that transition metals can be dissolved from particles in neutral, aqueous solutions and that these metals are capable of catalyzing the formation of reactive oxygen species.

Air Pollutants, Occupational↗
PubMed2004

Formula for a new foam.

As the 2010 phaseout date for chlorofluorocarbons draws nearer, materials engineers are working to find replacements for these ozone-depleting chemicals in the production of plastics and other products. One team of engineers is focusing on a combination of two low-cost and environmentally benign substances--supercritical carbon dioxide and clay nanoparticles--to meet these needs. The result is a strong yet lightweight alternative that retains all the beneficial qualities of solid plastic.

Aluminum Silicates↗