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 325 records · Page 18Linked to original sources
PubMed2005

Light-switching excimer probes for rapid protein monitoring in complex biological fluids.

Quantitative protein bioanalysis in complex biological fluids presents considerable challenges in biological studies and disease diagnosis. The major obstacles are the background signals from both the probe and the biological fluids where the proteins reside. We have molecularly engineered light-switching excimer aptamer probes for rapid and sensitive detection of a biomarker protein, platelet-derived growth factor (PDGF). Labeled with one pyrene at each end, the aptamer switches its fluorescence emission from approximately 400 nm (pyrene monomer) to 485 nm (pyrene excimer) upon PDGF binding. This fluorescence wavelength change from monomer to excimer emission is a result of aptamer conformation rearrangement induced by target binding. The excimer probe is able to effectively detect picomolar PDGF in homogeneous solutions. Because the excimer has a much longer fluorescence lifetime (approximately 40 ns) than that of the background (approximately 5 ns), time-resolved measurements were used to eliminate the biological background. We thus were able to detect PDGF in a cell sample quantitatively without any sample pretreatment. This molecular engineering strategy can be used to develop other aptamer probes for protein monitoring. Combined with lifetime-based measurements and molecular engineering, light-switching excimer aptamer probes hold great potential in protein analysis for biomedical studies.

Body Fluids↗
PubMed2001

A continuous membrane bioreactor for ester synthesis in organic media: I. Operational characterization and stability.

The feasibility of continuous ester synthesis in a membrane bioreactor (MBR) by a recombinant cutinase from Fusarium solani pisi was investigated, using the optimal conditions previously attained by medium engineering. The objective was to analyze the MBR behavior as a differential or an integral reactor. The main component of the reactor was an anisotropic ceramic membrane with 15,000 NMWCO. The operating variables included the influence of substrates ratio and flow rate on the conversion degree and on the productivity. The highest conversion degree was obtained using 1M of hexanol and 0.1M of butyl acetate as acyl donor. The use of these substrate concentrations led to a conversion degree of 79.3% and a specific productivity of 41 g hexyl acetate/(d x g cutinase), when the permeate flow rate was 0.025 mL/min. The increase of flow rate to 0.4 mL/min decreased the conversion to 35.6%, although the productivity was enhanced to 294 g product/day x g enzyme. The MBR characterization involved the calculations of mass balance, recirculation rate, conversion per pass, number of cycles, and hydraulic residence time. The operational stability was also evaluated in a longterm experiment over 900 hours and the enzyme half-life was estimated to be approximately 2 years.

Acetates↗
PubMed2003

Enhanced degradation of chemical warfare agents through molecular engineering of the phosphotriesterase active site.

The bacterial phosphotriesterase has been utilized as a template for the evolution of improved enzymes for the catalytic decomposition of organophosphate nerve agents. A combinatorial library of active site mutants was constructed by randomizing residues His-254, His-257, and Leu-303. The collection of mutant proteins was screened for the ability to hydrolyze a chromogenic analogue of the most toxic stereoisomer of the chemical warfare agent, soman. The mutant H254G/H257W/L303T catalyzed the hydrolysis of the target substrate nearly 3 orders of magnitude faster than the wild-type enzyme. The X-ray crystal structure was solved in the presence and absence of diisopropyl methyl phosphonate. The mutant enzyme was ligated to an additional divalent cation at the active site that was displaced upon the binding of the substrate analogue inhibitor. These studies demonstrate that substantial changes in substrate specificity can be achieved by relatively minor changes to the primary amino acid sequence.

Binding Sites↗
PubMed2002

Engineered allosteric ribozymes as biosensor components.

RNA and DNA molecules can be engineered to function as molecular switches that trigger catalytic events when a specific target molecule becomes bound. Recent studies on the underlying biochemical properties of these constructs indicate that a significant untapped potential exists for the practical application of allosteric nucleic acids. Engineered molecular switches can be used to report the presence of specific analytes in complex mixtures, making possible the creation of new types of biosensor devices and genetic control elements.

Allosteric Regulation↗
PubMed2000

Advances in enzyme technology--UK contributions.

Enzyme technology has been a recognised part of bioprocess engineering since its inception in the 1950s and 1960s. In this article the early history of enzyme technology is discussed and the subsequent developments in enzyme isolation, enzyme modification and process technology are described. These creative developments have put enzyme technology in a position of huge potential to contribute to environmentally compatible and cost effective means of industrial chemical synthesis. Recent developments in protein modification to produce designer enzymes are leading a new wave of enzyme application.

Animals↗
PubMed2003

Application of solvent engineering to optimize lipase-catalyzed 1,3-diglyacylcerols by mixture response surface methodology.

1,3-Diacylglycerol (DAG) has been introduced in Japan as a cooking oil under the trade name of Econa to reduce body fat accumulation. Solvent engineering was applied to determine the optimum solvent mixtures for the lipase-catalyzed synthesis of 1,3-DAG by mixture response surface methodology. n-Hexane was required to maintain the lipase activity and the product selectivity could be adjusted by changing the hydrophobicity of reaction medium. The optimum yield (approximately 40%) of 1,3-DAG synthesis was obtained with n-hexane/octane (1:1, v/v).

Catalysis↗
PubMed1995

[Ethical questions about methadone].

The author approaches ethical questions raised by use of methadone in opiates addiction: reduction of drug phenomenon to a strict medical problem, illusion of technical mastery, responsibility of pharmaceutical engineering, medicine under repressive constraint, reduction of damages linked to prohibition. The communication ends on a question about management of drug problems which today encourages a healthy vision of consumption behaviour rather than a "good way of use".

Chemical Engineering↗
PubMedDate not supplied

Engineering surfaces for bioconjugation: developing strategies and quantifying the extent of the reactions.

This study presents two-step and multistep reactions for modifying the surface of plasma-functionalized poly(tetrafluoroethylene) (PTFE) surfaces for subsequent conjugation of biologically relevant molecules. First, PTFE films were treated by a radiofrequency glow discharge (RFGD) ammonia plasma to introduce amino groups on the fluoropolymer surface. This plasma treatment is well optimized and allows the incorporation of a relative surface concentration of approximately 2-3.5% of amino groups, as assessed by chemical derivatization followed by X-ray photoelectron spectroscopy (XPS). In a second step, these amino groups were further reacted with various chemical reagents to provide the surface with chemical functionalities such as maleimides, carboxylic acids, acetals, aldehydes, and thiols, that could be used later on to conjugate a wide variety of biologically relevant molecules such as proteins, DNA, drugs, etc. In the present study, glutaric and cis-aconitic anhydrides were evaluated for their capability to provide carboxylic functions to the PTFE plasma-treated surface. Bromoacetaldehyde diethylacetal was reacted with the aminated PTFE surface, providing a diethylacetal function, which is a latent form of aldehyde functionality. Reactions with cross-linkers such as sulfo-succinimidyl derivatives (sulfo-SMCC, sulfo-SMPB) were evaluated to provide a highly reactive maleimide function suitable for further chemical reactions with thiolated molecules. Traut reagent (2-iminothiolane) was also conjugated to introduce a thiol group onto the fluoropolymer surface. PTFE-modified surfaces were analyzed by XPS with a particular attention to quantify the extent of the reactions that occurred on the polymer. Finally, surface immobilization of fibronectin performed using either glutaric anhydride or sulfo-SMPB activators demonstrated the importance of selecting the appropriate conjugation strategy to retain the protein biological activity.

Biocompatible Materials↗
PubMed1991

Immobilized pH gradients (IPG) simulator--an additional step in pH gradient engineering: II. Nonlinear pH gradients.

While in the companion paper (Tonani, C. & Righetti, P. G., Electrophoresis 1991, 12, 1011-1021) we gave the general outline of our new computer program, immobilized pH gradients (IPG) simulator, able to simulate and optimize linear pH gradients for isoelectric focusing in immobilized pH gradients, in the present report we extend the application of such a program to: (i) convex exponential gradients, (ii) logarithmic and (iii) polynomial gradients. Such gradients are meant to give equal space to protein spots in complex protein mixtures (e.g., cell lysates, biological fluids) and follow the statistical distribution of protein pI values along the pH axis. They will prove of fundamental importance in two-dimensional maps, both because they optimize the spreading of spots in the two-dimensional plane and because of the excellent reproducibility of immobilized pH gradients. The following concave exponential recipes are given: pH 3-8, pH 3-9, pH 3-10, pH 3-11, pH 4-7, pH 4-8, pH 4-9, pH 4-10, pH 4-11, pH 5-8, pH 5-9, and pH 5-10, as well as the most extended pH 2.5-11 interval. Two interesting logarithmic gradients are described: pH 3-6 and pH 3-7 and one sigmoidal (derived with a polynomial of 5th degree): pH 3-11.

Chemical Engineering↗
PubMed1991

Immobilized pH gradients (IPG) simulator--an additional step in pH gradient engineering: I. Linear pH gradients.

A new computer program, called immobilized pH gradients (IPG) simulator, is proposed for calculating and optimizing any recipe for use in isoelectric focusing in immobilized pH gradients. Unlike our previous monoprotic electrolyte gradient simulation (MGS) and polyelectrolyte gradient simulation (PGS) programs, based on minimizing CV(beta), the present program has a target function the minimization of the quadratic moment around zero of the residuals (mu 2). With this algorithm it is possible to formulate IPG recipes which have deviations from linearity well below 1% of the given pH interval (a limit set with the previous MGS and PGS programs), in fact, as small as 0.1-0.2% (in pH units). The new simulator performs 2-3 times better than the previous ones in the pH 4-10 range, and is absolutely necessary when working outside this range, at extreme pH values, where CV(beta) cannot work against the buffering power of bulk water, thus generating pH recipes with huge deviations from linearity. In the latter cases, mu 2 performs 10 times better than CV(beta). When utilizing strong titrants for extended pH intervals, the "all or none" rule has been discovered: such titrants should always be used in tandem, since omission of one of the two at either the acidic or basic extremes produces strongly distorted pH profiles. Our new, most powerful simulator also contains equations for creating nonlinear gradients, notably: concave and convex exponentials and sigmoidal (see the companion paper: Righetti, P. G. and Tonani, C., Electrophoresis 1991, 12, 1021-1027).

Algorithms↗
PubMed1998

Metabolic delivery of ketone groups to sialic acid residues. Application To cell surface glycoform engineering.

The development of chemical strategies for decorating cells with defined carbohydrate epitopes would greatly facilitate studies of carbohydrate-mediated cell surface interactions. This report describes a general strategy for engineering the display of chemically defined oligosaccharides on cell surfaces that combines the concepts of metabolic engineering and selective chemical reactivity. Using a recently described method (Mahal, L. K., Yarema, K. J., and Bertozzi, C. R. (1997) Science 276, 1125-1128), we delivered a uniquely reactive ketone group to endogenous cell surface sialic acid residues by treating cells with the ketone-bearing metabolic precursor N-levulinoylmannosamine (ManLev). The ketone undergoes highly selective condensation reactions with complementary nucleophiles such as aminooxy and hydrazide groups. The detailed quantitative parameters of ManLev metabolism in human and nonhuman-derived cell lines were determined to establish a foundation for the modification of cell surfaces with novel epitopes at defined cell-surface densities. Ketones within the glycoconjugates on ManLev-treated cells were then reacted with synthetic aminooxy and hydrazide-functionalized carbohydrates. The remodeled cells were endowed with novel lectin binding profiles as determined by flow cytometry analysis. The simplicity and generality of this method make it well suited for use in the study of carbohydrate-mediated cell surface interactions.

Animals↗
PubMed1997

Ceramics transformed: manipulating crystal structures to toughen bioceramics.

Ceramics have tremendous potential as engineering materials for the construction of medical devices but are inhibited by their inherent brittleness. This article discusses how this problem has been addressed by the development of the process of transformation toughening and places this in the broader context of the new generation of "smart" materials.

Biocompatible Materials↗
PubMed2004

Folate biofortification in tomatoes by engineering the pteridine branch of folate synthesis.

Plants are the main source of folate in human diets, but many fruits, tubers, and seeds are poor in this vitamin, and folate deficiency is a worldwide problem. Plants synthesize folate from pteridine, p-aminobenzoate (PABA), and glutamate moieties. Pteridine synthesis capacity is known to drop in ripening tomato fruit; therefore, we countered this decline by fruit-specific overexpression of GTP cyclohydrolase I, the first enzyme of pteridine synthesis. We used a synthetic gene based on mammalian GTP cyclohydrolase I, because this enzyme is predicted to escape feedback control in planta. This engineering maneuver raised fruit pteridine content by 3- to 140-fold and fruit folate content by an average of 2-fold among 12 independent transformants, relative to vector-alone controls. Most of the folate increase was contributed by 5-methyltetrahydrofolate polyglutamates and 5,10-methenyltetrahydrofolate polyglutamates, which were also major forms of folate in control fruit. The accumulated pteridines included neopterin, monapterin, and hydroxymethylpterin; their reduced forms, which are folate biosynthesis intermediates; and pteridine glycosides not previously found in plants. Engineered fruit with intermediate levels of pteridine overproduction attained the highest folate levels. PABA pools were severely depleted in engineered fruit that were high in folate, and supplying such fruit with PABA by means of the fruit stalk increased their folate content by up to 10-fold. These results demonstrate that engineering a moderate increase in pteridine production can significantly enhance the folate content in food plants and that boosting the PABA supply can produce further gains.

Aldehyde-Lyases↗
PubMed1993

Parameters influencing the productivity of recombinant E. coli cultivations.

In the past 10 to 15 years, many of the promises of microbial genetic engineering have been realized: the use of recombinant Escherichia coli has moved from the laboratory to the production facility, and the manufacture of therapeutic recombinant proteins such as human growth hormone and interleukins is a rapidly growing industry. Along with this progress, however, have come new problems to solve: bioreactor operators have discovered that large-scale cultivations of plasmid-containing bacteria do not behave in exactly the same way as those of plasmid-free cells, plasmid stability has been recognized as a major hurdle, and the protein product might not be present in a soluble form but rather as intracellular granules that resist solubilization. These and other difficulties represent a new generation of challenges for genetic engineering. However, genetic engineering can do more than solve these problems. Molecular biological techniques also have the ability to create new opportunities: to produce new compounds, to use cheaper substrates, to facilitate downstream processing, and to optimize production in new ways. The productivity of a cultivation can generally be expressed as the product of the cell density and the specific biological activity. Both of these parameters are influenced by a variety of factors. For recombinant cultivations, though, the level of biological activity, a reflection of the plasmid copy number and expression efficiency, is the more interesting and important consideration and will therefore be given more attention in our review. In this contribution, our general goal is to discuss the factors that influence the productivity of recombinant E. coli cultivations, covering parameters relating to DNA; parameters relating to protein synthesis; parameters relating to proteins; and parameters relating to downstream processing. The object is not to tell the reader how to choose the perfect plasmid, host, and cultivation conditions, but to make known the many variables involved in designing a recombinant process and to point out recent and potential advances made possible by genetic engineering. The discussion focuses on the production of a protein, but many of the same concepts apply to other cultivations of recombinant E. coli, including cases in which the desired product is not a protein or the cells have been designed for a special metabolic capability such as pollutant biodegradation.

Bacterial Proteins↗
PubMed2001

Engineering the prion protein using chemical synthesis.

In recent years, the technology of solid-phase peptide synthesis (SPPS) has improved to the extent that chemical synthesis of small proteins may be a viable complementary strategy to recombinant expression. We have prepared several modified and wild-type prion protein (PrP) polypeptides, of up to 112 residues, that demonstrate the flexibility of a chemical approach to protein synthesis. The principal event in prion disease is the conformational change of the normal, alpha-helical cellular protein (PrPc) into a beta-sheet-rich pathogenic isoform (PrP(Sc)). The ability to form PrP(Sc) in transgenic mice is retained by a 106 residue 'mini-prion' (PrP106), with the deletions 23-88 and 141-176. Synthetic PrP106 (sPrP106) and a His-tagged analog (sPrP106HT) have been prepared successfully using a highly optimized Fmoc chemical methodology involving DCC/HOBt activation and an efficient capping procedure with N-(2-chlorobenzyloxycarbonyloxy) succinimide. A single reversed-phase purification step gave homogeneous protein, in excellent yield. With respect to its conformational and aggregational properties and its response to proteinase digestion, sPrP106 was indistinguishable from its recombinant analog (rPrP106). Certain sequences that proved to be more difficult to synthesize using the Fmoc approach, such as bovine (Bo) PrP(90-200), were successfully prepared using a combination of the highly activated coupling reagent HATU and t-Boc chemistry. To mimic the glycosylphosphatidyl inositol (GPI) anchor and target sPrP to cholesterol-rich domains on the cell surface, where the conversion of PrPc is believed to occur, a lipophilic group or biotin, was added to an orthogonally side-chain-protected Lys residue at the C-terminus of sPrP sequences. These groups enabled sPrP to be immobilized on either the cell surface or a streptavidin-coated ELISA plate, respectively, in an orientation analogous to that of membrane-bound, GPI-anchored PrPc. The chemical manipulation of such biologically relevant forms of PrP by the introduction of point mutations or groups that mimic post-translational modifications should enhance our understanding of the processes that cause prion diseases and may lead to the chemical synthesis of an infectious agent.

Amino Acid Sequence↗
PubMed1989

Fimbriae of Bacteroides nodosus: protein engineering of the structural subunit for the production of an exogenous peptide.

The pattern of sequence variation between Bacteroides nodosus fimbrial subunits of different serotypes suggests a degree of flexibility, which might be exploited for protein engineering approaches for the expression of other peptides. We have tested this using the well-characterized peptide epitope from VP1 of foot-and-mouth disease virus (FMDV), residues 144-159: LRGDLQVLAQKVARTL (strain 01-BFS). Using bacterial codon usage, several oligonucleotides were designed for the substitution of this sequence internally at hypervariable regions of the fimbrial subunit (aligned for maximum homology), and for its addition at the carboxyterminus with a diglycine spacer as a flexible hinge. Following site-directed mutagenesis in phage M13, the modified genes were placed under PL promoter control and placed in a broad host range vector. Analysis of the variant proteins expressed in E. coli showed that these substitutions affected, to varying extents, recognition by both anti-fimbrial and anti-FMDV antibodies, indicating that hypervariable region 2 is a major antigenic determinant of the fimbrial subunit and that local stereochemical effects can influence antibody binding to the FMDV peptide antigenic determinant. In Pseudomonas aeruginosa, viable transformants could only be obtained with the mutant gene encoding the carboxy-terminal graft. These cells provided fimbrial preparations comprised of the modified subunit. This then constitutes the prototype for the development of a general expression system for the production of vaccine epitopes and other bioactive peptides. Furthermore, there is considerable scope for further modification of the system, for example by engineering specific chemical or protease cleavage sites for release of the grafted peptide. Alternatively, the fimbriae themselves may serve as a useful supramolecular carrier or adjuvant for immune provocation.

Amino Acid Sequence↗
PubMed2005

Band gap engineering of CdTe nanocrystals through chemical surface modification.

We demonstrate band gap control of CdTe nanocrystals by selective surface modification using alkanethiol molecules. Both absorption and emission wavelengths can be tuned simply by mixing a dispersion of the nanocrystals with alkanethiol at room temperature, resulting in blue shifts in the optical spectra during reaction. The degree of blue shift depends on both the concentration of alkanethiols and the reaction time, thereby providing kinetic control over the emission peak wavelength of the nanocrystals in mild conditions. The observed spectral changes are suggested to be caused by a decrease in the size of the CdTe core through formation of CdTe1-x(SC10)x shells because of specific exchange of Te with alkanethiolates. The results reported herein provide a new band gap engineering scheme for semiconductor nanocrystals and offer opportunities for the design of ligand-stabilized semiconductor nanocrystals with tunable composition and optical properties.

Journal Article↗