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 721 records · Page 40Linked to original sources
PubMed2002

Chemical design of direct-gap light-emitting silicon.

Quantum confinement effect has been the dominant approach guiding the search for light-emitting silicon. By first-principles total energy calculations of Si delta-doped with oxygen layers, however, we show that this generally accepted mechanism is ineffective. Instead, a different mechanism is proposed based on defect engineering where the oxygen atoms chemically shift the valence band edge of Si away from the zone center, resulting in the desired optical functionality. Our calculation suggests new design principles for light-emitting silicon as well as providing the microscopic origin for the observed strong luminescence and band gap increase in the SiO(001) multi-delta-layers.

Journal Article↗
PubMed1997

Applications of S-layers.

The wealth of information existing on the general principle of S-layers has revealed a broad application potential. The most relevant features exploited in applied S-layer research are: (i) pores passing through S-layers show identical size and morphology and are in the range of ultrafiltration membranes; (ii) functional groups on the surface and in the pores are aligned in well-defined positions and orientations and accessible for binding functional molecules in very precise fashion; (iii) isolated S-layer subunits from many organisms are capable of recrystallizing as closed monolayers onto solid supports at the air-water interface, on lipid monolayers or onto the surface of liposomes. Particularly their repetitive physicochemical properties down to the subnanometer scale make S-layers unique structures for functionalization of surfaces and interfaces down to the ultimate resolution limit. The following review focuses on selected applications in biotechnology, diagnostics, vaccine development, biomimetic membranes, supramolecular engineering and nanotechnology. Despite progress in the characterization of S-layers and the exploitation of S-layers for the applications described in this chapter, it is clear that the field lags behind others (e.g. enzyme engineering) in applying recent advances in protein engineering. Genetic modification and targeted chemical modification would allow several possibilities including the manipulation of pore permeation properties, the introduction of switches to open and close the pores, and the covalent attachment to surfaces or other macromolecules through defined sites on the S-layer protein. The application of protein engineering to S-layers will require the development of straightforward expression systems, the development of simple assays for assembly and function that are suitable for the rapid screening of numerous mutants and the acquisition of structural information at atomic resolution. Attention should be given to these areas in the coming years.

Bacteria↗
PubMed1996

Bypassing the ribosome: peptide synthesis without translation.

Chemical peptide synthesis is well-established but has drawbacks, notably the need to protect side-chain functional groups during reactions. Proteolytic enzymes may be used 'in reverse' to catalyse peptide synthesis without side-chain protection and avoiding the danger of racemization. Enzymic syntheses may use either an equilibrium or a kinetic strategy. Equilibrium synthesis is simply the reversal of hydrolysis, using any type of protease. Kinetic synthesis involves time-dependent acyl transfer using activated substrates and a serine or cysteine protease. Enzymic synthesis often takes place in partially aqueous or non-aqueous reaction media; the medium can often desirably influence the protease's properties. It is possible to tailor a protease to improve its usefulness in peptide synthesis; one can alter the enzyme's properties by means such as chemical modification, PEG-coupling or protein engineering.

Binding Sites↗
PubMed2001

Metabolic engineering as an integrating platform for strain development.

Integration of the analytical framework and experimental tools of metabolic engineering with emerging technologies such as DNA microarrays and directed evolution stands to dramatically improve the approaches by which strain improvement and biocatalyst design are pursued in the future. Progress in genomics and applied molecular biology, together with increasing emphasis on renewable resource utilization for chemical production, has advanced metabolic engineering to the forefront of biotechnological interest.

Industrial Microbiology↗
PubMed1994

Chemical analysis and biological testing of a polar fraction of ambient air, diesel engine, and gasoline engine particulate extracts.

Extracts of gasoline and diesel vehicle exhaust and ambient air particles were fractionated into five fractions according to polarity on a silica gel column. Two medium polar fractions showing high genotoxic activity in the Ames test were further subfractionated, using normal-phase high-performance liquid chromatography. Chemical analyses were performed by means of gas chromatography combined with mass spectrometry and flame ionization and detection. The crude extracts, fractions, and subfractions were assayed with the Ames test, with and without S9, and the most abundant compounds in the subfractions are reported.

Air Pollutants↗
PubMed1996

Technical aspects of water fluoridation in the United States and an overview of fluoridation engineering world-wide.

This paper summaries the technical aspects of water fluoridation in the United States, and gives an overview of the engineering aspects of water fluoridation world-wide. The status of water fluoridation in the USA is summarised. Fluoride chemicals used in the USA are discussed, as well as the equipment used to deliver these chemicals. A brief overview of fluoridation engineering world-wide is also presented.

Asia↗
PubMedDate not supplied

Surface engineering of artificial heart valve disks using nanostructured thin films deposited by chemical vapour deposition and sol-gel methods.

Pyrolytic carbon (PyC) is widely used in manufacturing commercial artificial heart valve disks (HVD). Although PyC is commonly used in HVD, it is not the best material for this application since its blood compatibility is not ideal for prolonged clinical use. As a result thrombosis often occurs and the patients are required to take anti-coagulation drugs on a regular basis in order to minimize the formation of thrombosis. However, anti-coagulation therapy gives rise to some detrimental side effects in patients. Therefore, it is extremely urgent that newer and more technically advanced materials with better surface and bulk properties are developed. In this paper, we report the mechanical properties of PyC-HVD, i.e. strength, wear resistance and coefficient of friction. The strength of the material was assessed using Brinell indentation tests. Furthermore, wear resistance and coefficient of friction values were obtained from pin-on-disk testing. The micro-structural properties of PyC were characterized using XRD, Raman spectroscopy and SEM analysis. Also in this paper we report the preparation of freestanding nanocrystalline diamond films (FSND) using the time-modulated chemical vapour deposition (TMCVD) process. Furthermore, the sol-gel technique was used to uniformly coat PyC-HVD with dense, nanocrystalline-titanium oxide (nc-TiO2) coatings. The as-grown nc-TiO2 coatings were characterized for microstructure using SEM and XRD analysis.

Biomedical Engineering↗
PubMed1999

Determination of the effect of exposure to gasoline components on a high density polyethylene geomembrane using the comprehensive test system.

The comprehensive testing system (CTS) for geomembranes was used to test the compatibility of high-density polyethylene (HDPE) geomembrane landfill liner material with chemicals typically found in motor vehicle fuel. The CTS is a testing apparatus specifically designed to test the effects of simultaneously applying mechanical load, fluid head, and chemical exposure on the geomembrane. A combination of these factors is present on the geomembrane material in service, and the CTS provides a laboratory reproduction of actual field conditions. The article provides a description of gasoline based upon the desirable qualities of gasoline and provides background on testing of rubbers used in gasoline-powered engine parts. The test's chemicals were gasoline, motor oil, benzene, ethylbenzene, toluene, xylenes, and iso-octane (2,2,4 trimethyl pentane). This work found that gasoline had an effect on the geomembrane greater than the effect of any of the pure chemicals except ethylbenzene. Benzene, and the other aromatic compounds (ethylbenzene, toluene, and xylenes) are typically the primary regulatory concerns at fuel contaminated sites. The fact that gasoline had a greater effect on the performance of the HDPE geomembrane indicated that chemicals are present in gasoline which can decrease the performance of the containment structures used to hold gasoline, while not having a significant health risk. The clear implication is that risk assessments conducted on facilities must not only include the health risks of chemicals placed in a facility, but must also consider the effect of the chemical on a containment structure. The fact that low-health-risk chemicals may have a great impact on the effectiveness of containment structures leads to a possible synergistic mechanism where the low-health-risk chemicals enable a pathway for greater-health-risk chemicals to enter the environment.

Gasoline↗
PubMed2003

Tissue engineering in dentistry.

Advances in tissue engineering provide an increased level of understanding of the mechanical and chemical stimuli that regulate tissue responses. Oral tissue engineering can be applied to recreate missing osseous or dental structures or correct orofacial deformities, changing the patient's smile, midfacial height, and the soft tissue drape. Biomechanical principles can also be applied to tissue engineering to enhance the bone/tooth or bone/implant functionality and long-term stability. Advancements are also being achieved in the area of biomimetics that will allow the creation of new biologic replacements for missing oral structures. The opportunity for bioengineering to charter the course of tooth regeneration is an exciting prospect and will improve the quality of life for patients for decades to come.

Biomechanical Phenomena↗
PubMed1993

Designer enzyme and cell applications in industry and in environmental monitoring.

Renewed world interest in enzyme biotechnological industries now derives from the expectation that many new biocatalysts will be created by genetic engineering associated with protein engineering designer techniques, or by chemical modification of existing enzymes by use of protein tailoring methods. The biocatalysts produced are mainly enzymes, abzymes (catalytic antibodies) and synzymes (synthetic analogues or mimics), and these will be used in industry, synthesis, therapy: and in bioanalysis of components of foodstuffs, and the environment including water, air and soil. The biocatalysts, including whole cells, are firstly incorporated into a particular bioreactor form by use of enzyme engineering techniques such as immobilization, and are then used, as appropriate, to modify their substrates. Improved processing or enhanced products are thereby achieved in the case of manufacturing industry: or monitoring signals are generated, often in the form of a measurable change in current flow, in the case of environmental biosensors. Designer enzymes and cells can be made now for identified applications where the presently available biocatalysts are inadequate, incompatible or uncompetitive.

Biotechnology↗
PubMed2004

Engineering strontium binding affinity in an EF-hand motif: a quantum chemical and molecular dynamics study.

Proteins with the ability to specifically bind strontium would potentially be of great use in the field of nuclear waste management. Unfortunately, no such peptides or proteins are known -- indeed, it is uncertain whether they exist under natural conditions due to low environmental concentrations of strontium. To investigate the possibility of devising such molecules, one of us (CV), in a previous experimental study, proposed starting from an EF-hand motif of the protein calmodulin and mutating some residues to change the motif's specificity for calcium into one for strontium. In this paper, which represents a theoretical complement to the experimental work, we analyzed small-molecule crystallographic structures and performed quantum chemical calculations to identify possible mutations. We then constructed seven mutant sequences of the EF-hand motif and analyzed their dynamical and binding behaviors using molecular dynamics simulations and free-energy calculations (using the MM/PBSA method). As a result of these analyzes we were able to isolate some characteristics that could lead to mutant peptides with enhanced strontium affinity.

Amino Acid Motifs↗
PubMed2004

Second-generation biopharmaceuticals.

The majority of first generation biopharmaceuticals are unengineered murine monoclonal antibodies or simple replacement proteins displaying an identical amino acid sequence to a native human protein. While some such products continue to be approved, an increasing number of modern biopharmaceuticals are engineered, second-generation products. Engineering can entail alteration of amino acid sequence, alteration of the glycocomponent of a glycosylated protein, or the covalent attachment of chemical moieties such as polyethylene glycol. Engineering has been applied in order to alter a protein's immunological or pharmacokinetic profile, or in order to generate novel fusion products. Better understanding of the links between protein structure and function will underpin the development of an increasing number of engineered biopharmaceuticals in the future.

Animals↗
PubMed2004

LEAPT: lectin-directed enzyme-activated prodrug therapy.

Targeted drug delivery to selected sites allows reduced toxicity, enhanced efficiency and interchangeable target potential [Langer, R. (2001) Science 293, 58-59 and Molema, G. & Meijer, D. K. F., eds. (2001) Drug Targeting (Wiley-VCH, Weinheim, Germany)]. We describe a bipartite drug-delivery system that exploits (I) endogenous carbohydrate-to-lectin binding to localize glycosylated enzyme conjugates to specific, predetermined cell types followed by (II) administration of a prodrug activated by that predelivered enzyme at the desired site. The carbohydrate structure of an alpha-L-rhamnopyranosidase enzyme was specifically engineered through enzymatic deglycosylation and chemical reglycosylation. Combined in vivo and in vitro techniques (gamma scintigraphy, microautoradiography and confocal microscopy) determined organ and cellular localization and demonstrated successful activation of alpha-L-rhamnopyranoside prodrug. Ligand competition experiments revealed enhanced, specific localization by endocytosis and a strongly carbohydrate-dependent, 60-fold increase in selectivity toward target cell hepatocytes that generated a >30-fold increase (from 0.02 to 0.66 mg) in protein delivered. Furthermore, glycosylation engineering enhanced the serum-uptake rate and enzyme stability. This created enzyme activity (0.2 units in hepatocytes) for prodrug therapy, the target of which was switched simply by sugar-type alteration. The therapeutic effectiveness of lectin-directed enzyme-activated prodrug therapy was shown through the construction of the prodrug of doxorubicin, Rha-DOX, and its application to reduce tumor burden in a hepatocellular carcinoma (HepG2) disease model.

Animals↗
PubMed2005

Response of primary fibroblasts and osteoblasts to plasma treated polyetheretherketone (PEEK) surfaces.

Polyetheretherketone (PEEK) is a synthetic polymer with suitable biomechanical and stable chemical properties, which make it attractive for use as an endoprothetic material and for ligamentous replacement. However, chemical surface inertness does not account for a good interfacial biocompatibility, and PEEK requires a surface modification prior to its application in vivo. In the course of this experimental study we analyzed the influence of plasma treatment of PEEK surfaces on the cell proliferation and differentiation of primary fibroblasts and osteoblasts. Further we examined the possibility of inducing microstructured cell growth on a surface with plasma-induced chemical micropatterning. We were able to demonstrate that the surface treatment of PEEK with a low-temperature plasma has significant effects on the proliferation of fibroblasts. Depending on the surface treatment, the proliferation rate can either be stimulated or suppressed. The behavior of the osteoblasts was examined by evaluating differentiation parameters. By detection of alkaline phosphatase, collagen I, and mineralized extracellular matrix as parameters for osteoblastic differentiation, the examined materials showed results comparable to commercially available polymer cell culture materials such as tissue culture polystyrene (TCPS). Further microstructured cell growth was produced successfully on micropatterned PEEK foils, which could be a future tool for bioartificial systems applying the methods of tissue engineering. These results show that chemically inert materials such as PEEK may be modified specifically through the methods of plasma technology in order to improve biocompatibility.

Animals↗
PubMed1994

A new genetically engineered vaccine for animal growth promotion.

The chemically synthesized somatostatin (ss) gene was fused in phase with the 3'-end of hepatitis B virus surface antigen (HBsAg) gene. The fusion gene HBs/ss was then recombined into the genome of vaccinia virus. This recombinant virus (vv-HBs/ss) can express hybrid HBsAg/ss particles which present as determinants on their surfaces, thereby bearing a good immunogenicity. This new strategical vaccine of ss can elicit the production of antibody capable of neutralizing ss in the plasma, and consequently enhance the growth of animals.

Animals↗
PubMed2006

The chemical nature of the 2'-substituent in the pentose-sugar dictates the pseudoaromatic character of the nucleobase (pKa) in DNA/RNA.

We here show that the pKa (error limit: 0.01 to 0.03 pKa unit) of a nucleobase in a nucleotide can be modulated by the chemical nature of the 2'-substituent at the sugar moiety. This has been evidenced by the measurement of nucleobase pKa in 47 different model nucleoside 3',5'-bis- and 3'-mono-ethylphosphates. The fact that the electronic character of each of the 2'-substituents (Fig. 1) alters the chemical shift of the H2' sugar proton, and also alters the pKa of the nucleobase in the nucleotides has been evidenced by a correlation plot of pKa of N3 of pyrimidine (T/C/U) or pKa of N7 of 9-guaninyl with the corresponding deltaH2' chemical shifts at the neutral pH, which shows linear correlation with high Pearson's correlation coefficients (R = 0.85-0.97). That this modulation of the pKa of the nucleobase by a 2'-substituent is a through-bond as well as through-space effect has been proven by ab initio determined pKa estimation. Interestingly, experimental pKas of nucleobases from NMR titration and the calculated pKas (by ab initio calculations utilizing closed shell HF 6-31G** basis set) are linearly correlated with R = 0.98. It has also been observed that the difference of ground and protonated/de-protonated HOMO orbital energies (DeltaHOMO, a.u.) for the nucleobases (A/G/C/T/U) are well correlated with their pK(a)s in different 2'-substituted 3',5'-bis-ethylphosphate analogs suggesting that only the orbital energy of HOMO can be successfully used to predict the modulation of the chemical reactivity of the nucleobase by the 2'-substituent. It has also been demonstrated that pKa values of nucleobases in 3',5'-bis-ethylphosphates (Table 1) are well correlated with the change in dipole moment for the respective nucleobases after protonation or de-protonation. This work thus unambiguously shows that alteration of the thermodynamic stability (Tm) of the donor-acceptor complexes [ref. 20], as found with various 2'-modified duplexes in the antisense, siRNA or in triplexes by many workers in the field, is a result of alteration of the pseudoaromatic character of the nucleobases engineered by alteration of the chemical nature of the 2'-substitution.

DNA↗
PubMed1981

Restrictions on permissible paths for changing efficiencies of operation of flow reactors.

Sometimes a continuous flow stirred tank reactor can exhibit two or more different states of chemical reaction for the same flow rate. If such a situation is possible, a state of low reactive efficiency can be converted to one of higher efficiency by first decreasing the flow rate and then increasing it to the original value. This transition can never be accomplished by first increasing and then decreasing the flow rate. Similarly, a state of high reactive efficiency can be converted to one of lower efficiency only by first increasing and then decreasing the flow rate. These restrictions on permissible order of operations seem to differ from restrictions on efficiencies of cyclic heat engines and on directions of chemical change in closed systems as derived previously from thermodynamics.

Journal Article↗
PubMed2006

Structure and in vitro cytocompatibility of the gastropod shell of Helix pomatia.

Distinguishing features of biological constructions are high stability and adaptation to their environment. Beside biocompatibility, nontoxicity and degradability these characteristics are demanded for new biomaterials in the field of tissue engineering. This study investigated the chemical composition, the organization and the in vitro osteoconductive potential of the terrestrial gastropod shell (Helix pomatia) on CAL72 and human osteoblast-like cells. Chemical composition of the biomaterial was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) was performed to analyze the architecture of the snail shell and the morphology of the seeded cells. A double staining procedure (FDA/PI) and a proliferation test (EZ4U) assessed the viability of the cells. Microscopical images showed the multilayered architecture of the aragonite shell with hexagonal crystals on the inner side. The cells spread well on the biomaterial and the highest proliferation rate could be measured with CAL72 cells on the inner shell surface. The osteoconductive effects of this natural biomaterial could encourage further experiments in the field of tissue engineering.

Animals↗