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At least 253 records · Page 14Linked to original sources
PubMed2001

Chemical analysis of diesel engine nanoparticles using a nano-DMA/thermal desorption particle beam mass spectrometer.

Diesel engines are known to emit high number concentrations of nanoparticles (diameter < 50 nm), but the physical and chemical mechanisms by which they form are not understood. Information on chemical composition is lacking because the small size, low mass concentration, and potential for contamination of samples obtained by standard techniques make nanoparticles difficult to analyze. A nano-differential mobility analyzer was used to size-select nanoparticles (mass median diameter approximately 25-60 nm) from diesel engine exhaust for subsequent chemical analysis by thermal desorption particle beam mass spectrometry. Mass spectra were used to identify and quantify nanoparticle components, and compound molecular weights and vapor pressures were estimated from calibrated desorption temperatures. Branched alkanes and alkyl-substituted cycloalkanes from unburned fuel and/or lubricating oil appear to contribute most of the diesel nanoparticle mass. The volatility of the organic fraction of the aerosol increases as the engine load decreases and as particle size increases. Sulfuric acid was also detected at estimated concentrations of a few percent of the total nanoparticle mass. The results are consistent with a mechanism of nanoparticle formation involving nucleation of sulfuric acid and water, followed by particle growth by condensation of organic species.

Aerosols↗
PubMed1979

[Concepts for the synthesis of new biologically active substances].

Three concepts for the synthesis of biologically active compounds are discussed and illustrated by examples. In addition to the accidental finding of biologically active compounds, synthesized purely for chemical reasons, analogy models can serve as guidelines for synthesis. In the latter, naturally occurring or synthetic biologically active molecules are modified to optimize or alter the biological properties. A third approach for the synthesis of active substances is oriented according to the side of action. Models from biochemistry and molecular biology serve as a basis for synthesis planning.

Biochemical Phenomena↗
PubMed1994

Determination of oxygen permeability and volumetric oxygen transfer rate of shaken flasks.

The oxygen permeability passing through the gauze layer and the actual and apparent volumetric oxygen transfer rate, KLa and (KLa)app, respectively, were determined in specially designed Erlenmeyer flasks, which have an oxygen electrode inserted in the middle part of flasks. The oxygen transfer rate was determined by sulfite oxidation. As a result, the oxygen permeability passing through 8 layers of gauze at 37 degrees C, 220 rpm, with 50 ml sulfite solution in a 500-ml flask was 43.7 mol/m.h atm; as the oxygen partial pressure decreased by 6.1%, the value of KLa increased by 100%; the relationship between rotational speed of shaker, n(rpm); volume of flask, V(ml); liquid content in flask, VL(ml); temperature of shaker, t(degrees C) and KLa, as well as (KLa)app (1/h) were: [formula: see text]

Chemical Engineering↗
PubMed2006

Chemical compound navigator: a web-based chem-BLAST, chemical taxonomy-based search engine for browsing compounds.

A novel technique to annotate, query, and analyze chemical compounds has been developed and is illustrated by using the inhibitor data on HIV protease-inhibitor complexes. In this method, all chemical compounds are annotated in terms of standard chemical structural fragments. These standard fragments are defined by using criteria, such as chemical classification; structural, chemical, or functional groups; and commercial, scientific or common names or synonyms. These fragments are then organized into a data tree based on their chemical substructures. Search engines have been developed to use this data tree to enable query on inhibitors of HIV protease (http://xpdb.nist.gov/hivsdb/hivsdb.html). These search engines use a new novel technique, Chemical Block Layered Alignment of Substructure Technique (Chem-BLAST) to search on the fragments of an inhibitor to look for its chemical structural neighbors. This novel technique to annotate and query compounds lays the foundation for the use of the Semantic Web concept on chemical compounds to allow end users to group, sort, and search structural neighbors accurately and efficiently. During annotation, it enables the attachment of "meaning" (i.e., semantics) to data in a manner that far exceeds the current practice of associating "metadata" with data by creating a knowledge base (or ontology) associated with compounds. Intended users of the technique are the research community and pharmaceutical industry, for which it will provide a new tool to better identify novel chemical structural neighbors to aid drug discovery.

Computational Biology↗
PubMed1989

Chemical synthesis in protein engineering: total synthesis, purification and covalent structural characterization of a mitogenic protein, human transforming growth factor-alpha.

Successful approaches to protein engineering required that the desired analogs be easily and rapidly obtained in sufficient quantities and purities for unambiguous structural and functional characterizations. Chemical synthesis is the method of choice for engineering small peptides. We now demonstrate that with improved methodologies and instrumentation, total chemical synthesis can be used to produce a small protein in a form suitable for engineering studies. Active human transforming growth factor-alpha (TGF-alpha), a 50 amino acid long protein with three disulfide bonds, has been synthesized and purified in multiple tens of mg amounts in less than 7 days. The purified human TGF-alpha migrated as a single band on SDS-polyacrylamide gels, ran as a single sharp major band at pI = 6.2 on isoelectric focusing gels, displayed an MW = 5546.2 (Th.5546.3) by mass spectrometry, contained three disulfide bonds and had EGF receptor binding, mitogenic and soft agar colony formation activities. The locations of disulfide bonds were found to be analogous to those found in epidermal growth factor (EGF) and in human TGF-alpha expressed in bacteria.

Amino Acid Sequence↗
PubMed1985

Chemical modifications and genetic engineering of food proteins.

Relationships of structure to function of proteins can be studied using chemical modifications of amino-acid side chains and, more recently, recombinant deoxyribonucleic acid techniques to alter primary sequences. A wide array of chemical modifications are available to the food chemist for manipulating the functionality of food proteins. The esterification of side-chain carboxyl groups in proteins to yield polycationic polymers is emphasized in this review as an example of changing the functionality of a protein via chemical derivatization. However, chemical modifications of proteins generally suffer from a lack of control in the extent of derivatization attainable, oftentimes yielding polydisperse products. Recent advances in recombinant deoxyribonucleic acid technology offer the opportunity to relate systematically well-defined alterations in the primary sequence to changes in protein functionality. Using oligonucleotide-directed mutagenesis, one can now use synthetic oligodeoxynucleotides to prepare semisynthetic genes coding for specific changes in the primary sequence of proteins. Incorporation of the altered genes into an appropriate host can lead to the production of the modified protein for structure-function relationship studies. These recombinant deoxyribonucleic acid techniques may eventually provide the means to engineer proteins and enzymes.

Circular Dichroism↗
PubMed2001

Recovering antibody secretion using a hapten ligand as a chemical chaperone.

Engineered antibodies have come to the forefront as research reagents and clinical therapeutics. However, reduced stability or expression levels pose a major problem with many engineered antibodies. As a model for understanding functional consequences of variable region mutation, we have studied the assembly and trafficking of anti-phenylphosphocholine antibodies. Previously, we identified severe secretion defects because of mutations in the heavy chain second complementarity determining region, which is involved in antigen binding. Here we demonstrate that immunoglobulin secretion is increased up to 27-fold by incubating stably transfected PCG1-1 cells with cognate hapten p-nitrophenylphosphocholine. Secretion was unaffected by nonbinding analogs. Radiotracer and metabolic labeling experiments demonstrated specific cellular uptake of p-nitrophenylphosphocholine and increased intracellular heavy and light chain assembly. Brefeldin A inhibited hapten-mediated immunoglobulin secretion but not assembly, indicating that assembly occurs early within the biosynthetic pathway. Recovery of secretion correlated with antigen binding capacity, suggesting that the rescue mechanism involves stabilization of heavy and light chain variable domains. This model system provides the first demonstration that cognate ligands can increase intracellular assembly of functional anti-hapten antibody within mammalian cells and suggests that small molecules of appropriate specificity and affinity acting as chemical chaperones may find application for increasing or regulating immunoglobulin expression.

Arginine↗
PubMed2001

Properties, modifications and applications of biopolyesters.

Poly(hydroxyalkanoates) (PHAs), of which poly(hydroxybutyrate) (PHB) is the most common, can be accumulated by a large number of bacteria as energy and carbon reserve. Due to their biodegradability and biocompatibility these optically active biopolyesters may find industrial applications. A general overview of the physical and material properties of PHAs, alongside with accomplished applications and new developments in this field is presented in this chapter. The properties of PHAs are dependent on their monomer composition and therefore it is of great interest that recent research has revealed that, in addition to PHB, a large variety of PHAs can be synthesized microbially. The monomer composition of PHAs depends on the nature of the carbon source and microorganism used. PHB is a typical highly crystalline thermoplastic whereas medium chain length PHAs are elastomers with low melting points and a relatively lower degree of crystallinity. By (chemical) modification of the PHAs, the ultimate properties of the materials can be adjusted even further, when necessary. Applications that have been developed from PHB and related materials (e.g. Biopol) can be found in very different application areas and cover packaging, hygienic, agricultural and biomedical products. Recent application developments based on medium chain length PHAs range from high solid alkyd-like paints to pressure sensitive adhesives, biodegradable cheese coatings and biodegradable rubbers. Technically, the prospects for PHAs are very promising. When the price of these materials can be further reduced, application of biopolyesters will also become economically very attractive.

Bacteria↗
PubMed2006

Universal scaling for polymer chain scission in turbulence.

We report that previous polymer chain scission experiments in strong flows, long analyzed according to accepted laminar flow scission theories, were in fact affected by turbulence. We reconcile existing anomalies between theory and experiment with the hypothesis that the local stress at the Kolmogorov scale generates the molecular tension leading to polymer covalent bond breakage. The hypothesis yields a universal scaling for polymer scission in turbulent flows. This surprising reassessment of over 40 years of experimental data simplifies the theoretical picture of polymer dynamics leading to scission and allows control of scission in commercial polymers and genomic DNA.

Biophysical Phenomena↗
PubMed2001

On the need for engineering models of integrated chemical and biological oxidation of wastewaters.

Experimental examples of sequential chemical and biological oxidation treatment have been previously reviewed by Scott and Ollis, and economic estimates proposed by Esplugas and Ollis. Despite the prevalence of examples evident in these reviews and in recent conferences, very little use of kinetic models to codify and rationalize results on complex or simulated wastewaters has appeared. In consequence, models are not widely available nor have they yet received widespread acceptance as a method of analysis and reporting. To ameliorate this situation we here report a summary of important kinetic behaviors characteristic of individual chemical and biological kinetics, and provide experimental examples from recent works which illustrate the utility of such simple kinetic forms to construct two step treatment engineering models for complex wastewater and waters.

Biodegradation, Environmental↗
PubMed2006

Chemical kinetic modeling study of the effects of oxygenated hydrocarbons on soot emissions from diesel engines.

A detailed chemical kinetic modeling approach is used to examine the phenomenon of suppression of sooting in diesel engines by the addition of oxygenated hydrocarbon species to the fuel. This suppression, which has been observed experimentally for a few years, is explained kinetically as a reduction in concentrations of soot precursors present in the hot products of a fuel-rich diesel ignition zone when oxygenates are included. The kinetic model is also used to show how different oxygenates, ester structures in particular, can have different soot-suppression efficiencies due to differences in the molecular structure of the oxygenated species.

Journal Article↗