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  • Analytical Chemistry and Spectroscopy  (27)
  • Inorganic Chemistry  (14)
  • Atomic, Molecular and Optical Physics  (5)
  • 42.75
  • General Chemistry
  • Surface physics, nanoscale physics, low-dimensional systems
  • 1990-1994  (46)
Collection
Keywords
Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Intermolecular interactions with the direct reaction field method (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 181-189 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct reaction field (DRF) method, developed to incorporate the effects of a (large) semiclassical environment into the Hamiltonian of a quantum mechanical system, is briefly reviewed. It is shown that the DRF method behaves - at least - like a supermolecule SCF calculation. With the water dimer as an example, the similarity with the SCF procedure is demonstrated, and an application to the interaction between the active site of papain and the remaining 3000 or so atoms of this protein shows the inadequacy of dielectric constant models and the necessity of including atomic polarizabilities in model force fields.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380213
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  • 2
    Electronic Resource
    Electronic Resource
    Papain in aqueous solution and the role of Asp-158 in the mechanism: An Ab InitioSCF + DRF + BEM study (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 49-59 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of the solvent on the stability of the zwitterion in the active site of papain is investigated with numerical methods. The solvent is represented by a homogeneous dielectric continuum surrounding a cavity, defined by a fragment of the protein enclosed by a surface obtained following Connolly's method. The discretisized boundary surface is used to solve the Poisson equation in its integral form by means of a numerical approximation based on the boundary element method (BEM), resulting in a set of surface polarization charges. The solvent effect on the proton transfer in papain is studied on the basis of MO-SCF-direct reaction field (DRF) calculations of the energy and charge distribution of the fragment in the field of the surface charges. The role of Asp-158 in the proton transfer in the active site of papain is reevaluated in the presence of the solvent. It is concluded that the effect of the negative charge of Asp-158 is nearly completely screened by the solvent.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400710
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  • 3
    Electronic Resource
    Electronic Resource
    Computation of scanning tunneling microscope images (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 687-702 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article describes the computation of the tunnel current in a scanning tunneling microscope (STM). The calculation accounts for the three-dimensional scattering taking place simultaneously in the first atomic layers of the sample and in the apex of the probing tip. The model is built with the following ingredients: (a) the tip is represented by a cluster of atoms attached to an otherwise planar, free-electron metal surface, and (b) the analyzed sample is a planar free-electron metal with a local potential corrugation induced by an isolated molecule or adatom. The potential barrier includes the strong bending effect due to the image-charge formation occurring as the tunneling electron crosses the gap between the tip and the sample. The specific theoretical approach designed to solve this scattering problem exploits the fast Fourier transform algorithm to construct a transfer matrix in a mixed real- and momentum-spaces representation. The total current is obtained by summing the contributions of all scattered waves traveling in the barrier between the tip and the sample, and it is studied in this article for various positions of the tip relative to the adsorbed atomic cluster. The theory is used here to simulate the scan of a model-aluminum atom on a free-electron metal substrate using electrons focused by a single-atom tungsten tip.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400860
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  • 4
    Electronic Resource
    Electronic Resource
    Determination and distribution of polycyclic aromatic hydrocarbons in native vegetable oils, smoked fish products, mussels and oysters, and bream from the river Elbe (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 104-111 
    Details
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Mass spectrometry ; Food analysis ; Polycyclic aromatic hydrocarbons ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Twenty eight native vegetable oils were analyzed for polycyclic aromatic hydrocarbons. Generally PAH concentrations were low, but olive oils showed significantly higher contamination by light PAH ranging from 53 to 105.6 μg/kg. Muscle and liver samples of bream from the river Elbe contained little or no detectable amounts of PAH, whereas fresh and canned oysters and mussels showed higher contaminations. Highest PAH concentrations have been determined in “smoked oysters in oil” with 75.8 μg/kg benzo[a] pyrene for the oil and 12.2 μg/kg for the oyster meat.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240130206
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  • 5
    Electronic Resource
    Electronic Resource
    Ethyl acetate for the desorption of a liquid chromatographic precolumn on-line into a gas chromatograph (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 157-161 
    Details
    ISSN: 0935-6304
    Keywords: Coupled LC-GC ; Partially concurrent solvent evaporation ; Trace enrichment ; Surface water ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The feasibility of using ethyl acetate for the desorption of trace pollutants from a liquid chromatographic precolumn on-line into a diphenyltetramethyldisilazane-deactivated retention gap and, subsequently analysis by means of capillary gas chromatography has been demonstrated. First 5% of methanol are added to the water sample to prevent sorption of analytes onto parts of the preconcentration system. About 1 ml of this aqueous sample is injected onto a precolumn containing a polymeric stationary phase, using water-methanol (95:5, v/v) for transport and clean-up. The precolumn is desorbed with ethyl acetate and a fraction of 75 μl is injected on-line into the retention gap; separation is then achieved on a capillary CP Sil 19 column. No breakthrough of the test compounds was observed in the preconcentration step. The recovery was quantitative and the response obtained with flame ionization detection was linear in the range 0.1-100 ng/ml. The effect of varying the sorption flow rate on the recovery was studied. The system was applied to the analysis of river water.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240130303
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  • 6
    Electronic Resource
    Electronic Resource
    Investigations into the use of capillary GC with atomic emission detection. The influence of the molecular structure on the element response (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 447-450 
    Details
    ISSN: 0935-6304
    Keywords: Capillary GC ; Atomic emission ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240130617
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of planar chlorobiphenyls in animal fat (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 797-802 
    Details
    ISSN: 0935-6304
    Keywords: Capillary GC ; GPC and HPLC sample preparation ; Automation ; Planar chlorobiphenyls ; Horse fat ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The occurrence of the highly toxic non-ortho substituted (planar) chlorobiphenyls (CBs) at low levels in wildlife, (human) fat, and fish generates the need for a routine analytical procedure. The use of a fully automated system for the separation of planar and non-planar CBs, consisting of a gel permeation chromatography system, a sample preparation system employing extraction columns, and a porous graphitic carbon HPLC column is described, and tested with horse fat. Gas chromatography on capillary columns, with electron-capture or high resolution mass spectrometric detection, is used for quantitation of the CBs.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240131202
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  • 8
    Electronic Resource
    Electronic Resource
    A continuous two-phase reaction system coupled on-line with capillary chromatography for the determination of polar solutes in water (1992)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 15 (1992), S. 242-248 
    Details
    ISSN: 0935-6304
    Keywords: Capillary GC ; On-line extractive alkylation ; On-line acylation ; Carboxylic acids ; Amines ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gas chromatographic procedures are described for the determination of carboxylic acids and chlorinated anilines in water samples.Propionic acid and 2,6-difluorobenzoic acid in aqueous solution have been simultaneously alkylated and extracted by means of a continuous two-phase reaction system, and then quantitated by on-line coupled capillary gas chromatography; tetrahexyl-ammonium hydrogen sulfate was used as phase transfer catalyst and pentafluorobenzyl bromide as reagent.A factorial design approach was used to optimize on-line derivatization of aqueous propionic acid with regard to pH and concentration of phase transfer catalyst. Alkylation and extraction, under optimized conditions, followed by quantitation of the pentafluorobenzyl ester by flame ionization detection furnished a linear calibration for concentrations between 0.1 and 10 μg/ml. The relative standard deviation was 9-15 %.The continuous two-phase reaction system was also used to determine (chlorinated) anilines present in water at concentrations of 0.1-1 μg/ml; pentafluorobenzoyl chloride was used as reagent and analysis was performed by capillary gas chromatography with flame ionization or electron capture detection. The on-line acylation of p-chloroaniline was optimized with regard to pH, reagent concentration, and reaction time.The on-line reaction system worked satisfactorily for both applications, although excess reagent caused some problems with the chromatography.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240150408
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  • 9
    Electronic Resource
    Electronic Resource
    Selective and sensitive detection of organic contaminants in water samples by on-line trace enrichment-gas chromatography-mass spectrometry (1993)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 397-403 
    Details
    ISSN: 0935-6304
    Keywords: Coupled LC-GC-MS ; Aqueous sample ; s-Triazine Herbicides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Liquid chromatographic (LC) type trace enrichment is coupled online with capillary gas chromatography (GC) with mass spectrometric (MS) detection for the analysis of aqueous samples. A volume of 1-10 ml of an aqueous sample is preconcentrated on a trace-enrichment column packed with a polymeric stationary phase. After cleanup with HPLC-grade water the precolumn is dried with nitrogen and subsequently desorbed with ethyl acetate. A fraction of 60 μl is introduced on-line into a diphenyltetramethyldisilazane-deactivated retention gap under partially concurrent solvent evaporation conditions and using an early solvent vapor exit. The analytes are separated and detected by means of GC-MS. The potential of the LC-GC-MS system for monitoring organic pollutants in river and drinking water is studied. Target analysis is carried out with atrazine and simazine as model compounds; the detection limits achieved under full-scan and multiple ion detection conditions are 30 pg and 5 pg, respectively. Identification of unknown compounds (non-target analysis), is demonstrated using a river water sample spiked with 168 pollutants varying in polarity and volatility.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240160703
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  • 10
    Electronic Resource
    Electronic Resource
    Microcolumn liquid chromatography with thermionic detection of the enantiomers of O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX) (1994)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 95-97 
    Details
    ISSN: 0935-6304
    Keywords: Chemical warfare agents ; Microcolumn liquid chromatography ; Enantiomeric separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved interface for the on-line coupling of microcolumn liquid chromatography (micro-LC) with thermionic detection (TID) is described. Modifications have been made to enable separate adjustment of the eluent introduction and the detector flame temperature in order to improve the sensitivity and ease of use of the system.The micro-LC-TID was used for the chiral separation of the nerve agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX). Baseline separation for the enantiomers of VX was obtained on Chiralcel OD using 1% isopropanol in hexane as the eluent. The detection limit of VX using 60 nl injections is ca. 5 μg/ml (ppm range). However, when using large-volume injections (10 μl) the detection limit is ca. 25 ng/ml (ppb range).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240170210
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