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  • 1985-1989  (8,271)
  • 1900-1904
  • 1870-1879
  • 1987  (8,271)
  • Chemistry  (8,271)
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  • 1985-1989  (8,271)
  • 1900-1904
  • 1870-1879
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pharmacy world & science 9 (1987), S. 305-314 
    ISSN: 1573-739X
    Keywords: Atrial natriuretic factor ; Blood pressure ; Chemistry ; Diuresis ; Homeostasis ; Kidney ; Muscle, smooth ; Natriuresis ; Receptors, endogenous compounds ; Renin-angiotensin system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is now known that cardiac atria play an important role in blood pressure and volume regulation. Mechanical distension of the atria results in the release of a potent diuretic and natriuretic agent or agents termed the atrial natriuretic factor (ANF). Several structurally related forms of ANF exist in man and it is thought that these represent precursory forms of a single optimally active molecule and/or the presence of more than one form of active ANF. The chemical structure of ANF between different mammalian species is similar. ANF receptors have been identified in kidney, brain, vascular endothelial and smooth muscle cells, tracheal and bronchial smooth muscle and the adrenal glands of many mammalian species, including man. This would suggest that ANF influences blood pressure and volume homoeostasis by affecting any one of a number of biochemical or physiological mechanisms via different target tissues. ANF is now considered a potentially valuable therapeutic agent for the treatment of hypertension and congestive heart failure. Synthesis of potent receptor antagonists could be extremely useful in the treatment of various clinical situations which are produced or complicated by endogenously produced ANF, such as chronic orthostatic hypotension.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 13-19 
    ISSN: 0887-3585
    Keywords: two-dimensional electrophoresis ; ethylnitrosourea ; somatic mutations ; structural variants ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The feasibility of detecting human somatic structural gene mutations by two dimensional electrophoresis has been investigated. A lymphoblastoid cell line was grown as a mass culture in the presence of ethylnitrosourea, after which cells were regrown as single cell clones. A total of 257 polypeptide spots were analyzed in gels derived from 186 clones. Four structural mutations were detected by visual analysis of the gels. Computer analysis of gels corresponding to the mutant clones was also undertaken. At a spot size threshold of 200 spots to be matched using a computer algorithm, all four mutant polypeptides were detected. These results indicate the usefulness of the two-dimensional approach for mutagenesis studies at the protein level.
    Additional Material: 4 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 1-12 
    ISSN: 0887-3585
    Keywords: protein crystallography ; protein refinement ; empirical energy simulations ; error analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The uncertainties in the refined parameters for a 1.5-Å X-ray structure of carbon-monoxy (FeII) myoglobin are estimated by combining energy minimization with least-squares refinement against the X-ray data. The energy minimization, done without reference to the X-ray data, provide perturbed structures which are used to restart conventional X-ray refinement. The resulting refined structures have the same, or better, R-factor and stereochemical parameters as the original X-ray structure, but deviate from it by 0.13 Å rms for the backbone atoms and 0.31 Å rms for the sidechain atoms. Atoms interacting with a disordered sidechain, Arg 45 CD3, are observed to have larger positional uncertainties. The uncertainty in the B-factors, within the isotropic harmonic motion approximation, is estimated to be 15%. The resulting X-ray structures are more consistent with the energy parameters used in simulations.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 20-33 
    ISSN: 0887-3585
    Keywords: calmodulin ; peptide ; calmodulin-binding peptide ; peptide design ; hydrophobic moment ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A basic, amphiphilic α helix is a structural feature common to a variety of inhibitors of calmodulin and to the calmodulin-binding domains of myosin light chain kinases. To aid in recognizing this structural feature in sequences of peptides and proteins we have developed a computer algorithm which searches for sequences of appropriate length, hydrophobicity, helical hydrophobic moment, and charge to be considered as potential calmodulin-binding sequences. Such sequences occurred infrequently in proteins of known crystal structure. This algorithm was used to find the most likely site in the catalytic (γ) subunit of phosphorylase b kinase for interaction with calmodulin (the δ subunit). A peptide corresponding to this site (residues 341-361 of the γ subunit) was synthesized and found to bind calmodulin with approximately an 11 nM dissociation constant. A variant of this peptide in which an aspartic acid at position 7 in its sequence (347 of the γ subunit) was replaced with an asparagin was found to bind calmodulin with approximately a 3 nM dissociation constant.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 0887-3585
    Keywords: proteolytic cleavage ; immunological cross-reaction ; amber fragment ; temperature-sensitive mutant ; stationary growth-phase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Immunological cross-reaction was employed for identification of proteolytic fragments of E. coli RNA polymerase genered both in vitro and in vivo. Several species of partially denatured but assembled RNA polymerase were isolated, which were composed of fragments of the two large subunits, β and β′, and the two small and intact subunits, α and σ. Comparison of the rate and pathway of proteolytic cleavage in vitro of unassembled subunits, subassemblies, and intact enzymes indicated that the susceptibility of RNA polymerase subunits to proteolytic degradation was dependent on the assembly state.Using this method, degradation in vivo was found for some, but not all, of the amber fragments of β subunit in merodiploid cells carrying both wild-type and mutant rpoB genes. Although the RNA polymerase is a metabolically stable component in exponentially growing cells of E. coli, degradation of the full-sized subunits was found in two cases, i.e., several temperature-sensitive E. coli mutants with a defect in the assembly of RNA polymerase and the stationary-phase cells of a wild-type E. coli. The in vivo degradation of RNA polymerase was indicated to be initiated by alteration of the enzyme structure.
    Additional Material: 9 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 54-63 
    ISSN: 0887-3585
    Keywords: domain association ; protein folding ; viscosity dependence ; solvent effects ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The equilibria and kinetics of ureainduced unfolding and refolding of the α subunit of tryptophan synthase of E. coli have been examined for their dependences on viscosity, pH, and temperature in order to investigate the properties of one of the rate-limiting steps, domain association. A viscosity enhancer, 0.58 M sucrose, was found to slow unfolding and accelerate refolding. This apparently anomolous results was shown to be due to the stabilizting effect of sucrose on the folding reaction. After accounting for this stabilization effect by using linear free-energy plots, the unfolding and refolding kinetics were found to have a viscosity dependence. A decrease in pH was found to stabilize the domain association reaction by increasing the refolding rate and decreasing the unfolding rate. This effect was accounted for by protonation of a single residue with a pK value of 8.8 in the native state and 7.1 in the intermediate, in which the two domains are not yet associated. The activation energy of unfolding is 4.8 kcal/mol, close to the diffusion limit. The negative activation entropy of unfolding, -47 cal/deg-mol, which controls this reaction, may result from ordering of solvent about the newly exposed domain interface of the transition state. These results may provide information on the types of noncovalent interactions involved in domain association and improve the ability to interpret the folding of mutants with single amino-acid substitutions at the interface.
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 34-41 
    ISSN: 0887-3585
    Keywords: adrenergic receptors ; affinity chromatography ; electron microscopy ; oligomeric structure ; target size analysis ; HPLC digest mapping ; receptor evolution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have characterized the structure of purified beta-adrenergic receptors by a combination of photoaffinity labeling, high performance liquid chromatography (HPLC)-tryptic mapping, CNBr fragmentation, target size analysis, and electron microscopy of purified receptor molecules. Guinea pig lung beta-adrenergic receptors purified by affinity chromatography, ion exchange chromatography, and HPLC size exclusion chromatography or photoaffinity labeled with [125]-iodocyanopindolol diazirine displayed mobilities on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) that corresponded to Mr = 68,000. Purified, radioiodinated guinea pig lung beta-receptors were subjected to complete trypsin digestion and subsequent reverse-phase HPLC analysis, which revealed nine peptides. Active site labeling and tryptic digestion of partially purified hamster lung beta-receptors produced one peptide, whereas CNBr digestion of the same material produced two labeled fragments, yielding information about the location of the active site within the primary sequence. Purified guinea pig lung receptors were examined with transmission electron microscopy. Electron micrographs revealed slightly asymmetric, rod-shaped structures with an average length of 13 nm and width of 3.4 nm. Many receptors were arranged as apparent dimeric structures. These findings confirm data obtained from target size analysis of guinea pig lung beta-receptors in situ which suggest that receptors may exist as oligomeric arrays in the native membrane. Taken together, these data provide information about putative functional domains of the beta-adrenergic receptor and its quaternary structure.
    Additional Material: 8 Ill.
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  • 9
    ISSN: 0887-3585
    Keywords: intrahelical ion pairs ; frequency of ion pairs in exposed helices ; alpha-helix stabilization ; protein tertiary structure stabilization ; protein-folding pathway ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A survey of 47 globular proteins was made to determine the probability of occurrence of ion pairs separated by 1, 2, 3, … and 8 residues in the alpha helices. As a control, the probability of occurrence of like charged pairs was also determined. The survey showed that ion pairs of the type i, i±3 and i, i±4 are the most predominant. Such a preference was not observed for like charged pairs. The observed frequency of ion pairs is significantly greater than their expected frequency. The normalized frequencies of occurrence of the ion pairs were also found to increase generally with the helix length. These results indicate that the ion pairs may contribute to the stability of solvent-exposed alpha helices. Since the stabilization of protein secondary structure, these results may throw light on the mechanism of protein folding.
    Additional Material: 5 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 79-80 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 12
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 72-77 
    ISSN: 0887-3585
    Keywords: CO equilibrium constants ; des-(Arg 141α)HbA ; heme proteins ; high-affinity state ; kinetics ; ligand binding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A few years ago we reported that histidine (HC3) 146β plays a major role in the pH-dependent propeties of the R-state of human hemoglobin, accounting for close to 50% of the R-state Bohr effect. We have extended these studies by examining the role of arginine 141α, another group known to affect the overall Bohr effect. We have compared the pH dependencies of the rate constants for the dissociation and combination of the fourth carbon monoxide molecule, I4 and I′4, respectively, for native hemoglobin A (HbA) and a control reconstututed HbA, and des-(Arg 141α) HbA, the hemoglobin molecule resulting from the enzymatic removal of the C-terminal arginine of the α-chain of human Hb. From these kinetic contants the pH dependence of L4, by about 80% between pH 6 and 8, where the aldkaline Bohr effect normally occurs, The sum of the effects of the removal of His 146β and of Arg 141α is grater than 100%. This suggests that at least one of these modifications altrs the contrubutions of other residues of this Bohr effect.
    Additional Material: 4 Ill.
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  • 13
    ISSN: 0887-3585
    Keywords: hybrid immunologlobulin ; compatible plasmids ; transfection ; mouse IgG1 ; mouse IgG2a ; dansyl ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have produced a series of hybrid IgG1-IgG2a mouse immunoglobulins with identical light chains (L) and variable regions to facilitate the identification of structural features associated with functional differnces between immunoglobulin isotypes. Hybrid heavy chain (H) constant region gene segments were generated by genetic recombination in Escherichia coli between plasmids carrying mouse γ1 and γ2a gene segments. Crossovers occured through out these segments although the frequency was highest in regions of high nucleotide sequence homology. Eleven variant immunoglobulins produced by transfected hybridoma cell lines are assembled into H2L2 tetramers and properly glycosylated. In addition, all 11 immunoglbulins have identical antigen combining sites specific for the fluorescent hapten ε-dansyll-L-lysine. Protein A binding was used as probe of the structural integrity of the Fc portion of the variant antibodies. Differeneces in protein A binding between IgG1 and IgG2a appear to be due to amino acid differances at postions 252 (Thr→Met) and 254 (Thr→Ser) of the heavy chain (EU numbering).
    Additional Material: 8 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 111-117 
    ISSN: 0887-3585
    Keywords: crystallography ; antigen ; glycoprotein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Neuraminidases from different subtypes of influenza virus are characterized by the absence of serlogical cross-reactivity and an amino acid sequence homology of approximately 50%. The three-dimensional structure of the neuraminidase antigen of subtype N9 from an avian influenza virus (A/tern/Australia/G70c/75) has been determined by X-ray crystallography and shown to be folded similarly to neuraminidase of subtype N2 isolated from a human influenza virus. This result demontrates that absence of immunological cross-reactivity is no measure of dissimilarity of polypeptide chain folding. Small differences in the way in which the subunits are organized around the molecular fourfold axis are observed. Insertions and deletions with respect to subtype N2 neuraminidase occur in four regions, only one of which is located within the major antigenic determinants around the enzyme active site.
    Additional Material: 4 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 90-110 
    ISSN: 0887-3585
    Keywords: compact units ; coefficient of compactness ; folding intermediates ; protein structural hierarchy ; primitive units ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The coefficient of compactness was recently introduced and used to locate domains in lysozyme and ribonuclease (Zehfus and Rose: Bio-chemistry 25:5759-5765, 1986). Nineteen additional proteins now have been analyzed by using this measure. Complete listings of compact units and plots showing their hierarchic organization are presented for all twenty-one proteins. Large compact units correspond well to protein domains; however, many smaller compact structures of equal or better compactness are also found. Since small compact units could represent subdomains or protein-folding intermediates, their structural composition is further examined.
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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 118-129 
    ISSN: 0887-3585
    Keywords: homologous proteins ; hydropathy index ; chain flexibility ; α/β barrels ; tryptophan ; synthase aplha subunit ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The amino acid sequences of the α subunits of tryptophan synthase form ten different microorganisms were alingned by standard procedures. The α helics, β strands and turns of each sequence were predicted separately by two standard prediction algorithms and averaged at homologous sequence positions. Additional evidence for conserved secondary structure was derived form profiles of average hydropathy and chain flexibility values, leading to a joint prediction. There is good agreement between (1) predicted β strands, maximal hydropathy and minimal flexibility, and (2) predicted loops, great chain flexibility, and protein segments that accept insertions of various lengths in individual sequences. The α subunit is predicted to have eight repeated β-loop-α-loop motifs with an extra N-terminal α helix and an intercalated segment of highly conserved residues. This pattern suggests that the teritiary structure of the α subunit is an eightfold α/β barrel. The distribution of conserved amino acid residues and publilshed data on limited proteolysis, chemical modification, and mutagenesis are consistent with the α/β barrel structure. Both the active site of the α subunit and the combining site for the β2 subunit are at the end of the barrel formed by the carboxyl-termini of the β strands.
    Additional Material: 6 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 153-161 
    ISSN: 0887-3585
    Keywords: accessbility ; hydrophobic effect ; protein conformation ; Boltzmann statistics ; maximum likelihood ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Globular proteins fold into compact particles with interior amino acid residues shielded from the surounding aqueous environment. An early hypothesis holds that entropic hydophobic forces dirve this phenomenon. However, previous analyses based on a binary description of the accesible surfaces of amino acid residues in proteins did not support theis hypothesis. This report shows that a complete description of accessible surface areas is given by parametric distribution fuctions with three modes. The modes are formed by partitioning the available accessible surface area of the amino acids into three segments; the data for each segment are characterized by a mode-specific model. In the “repulsive” mode, probabilities of accessibility decrease exponentially with exposed surface area, as predicted by the hydrophobic hypothesis. A distinct “buried” mode is needed to account for an excess of residues at or near zero accessibility for most amino acids, consistent with the use of binary descriptions of accessibility. A third mode exists which is termed “near neutral” because it is described by a nearly uniform distribution of accessibility for the hydrophiliic amino acids. Empirical energies calculated for the repulsive mode correlate well with measured free energies of transfer of amino acids from water to organic solvents, while those from the buried mode correlate well with measured free energies of hydration of the side chains. Poor cross correlations between these energies give an explanation for the previous conflict in interpreting these data.
    Additional Material: 2 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 162-166 
    ISSN: 0887-3585
    Keywords: protein folding ; secondary structure prediction ; tertiary structure prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In recent years, the protein-folding problem has attracted the attention of molecular biologists. Efforts have focused on developing heuristic and energy-based algorithms to predict the three-dimensional structure of a protein from its amino acid sequence. We have applied a series of heuristic algorithms to the sequence of human growth hormone. A family of five structures which are generically right-handed fourfold α-helical bundles are found from an investigaion of ∼108 structures. A plausible receptor binding site is suggested. Independent crystallographic analysis confirms some aspects of these predictions. These methods only deal with the “core” structure, and conformations of many residues are not defined. Further work is required to identify a unique set of coordinates and to clarify the topological alternatives available to α-helical proteins.
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  • 19
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 130-152 
    ISSN: 0887-3585
    Keywords: amino acid hydophobicity scale ; QSAR ; amino acids ; peptide side chains ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The fragment method of calculation partition coefficients (P) has been extended to include the common amino acids (AAs). The results indicate that polar and charged side chains influence the hydrophobicity of atoms in the side chain in a predictable manner. Feild effects, as evidenced through polar proximity factors and bond factors, need to be considered for accurate estimation of transfer phenomena. The calculated log P and ΔG°′ values of the 20 AAs agree well with the observed values. Pro calculates to be more hydrophilic than the observed log P. Hydrophobicity scales for peptide side chain residues are compared and evaluated in terms of suitability. Calculated π values for nonpolar side chain residures agree well with the observed values; calculated values for uncharged polar side chain residues deviate by about 0.6 log units except for Gln and Cys; and polar side chain residues with charged side chains calculate as too hydorphilic. Reasons for the differences are explored. We also suggest that tightly bound water to polar moieties in amino acids and peptides may be transferred into the octanol phase during partitioning experiments. A quantitative methodology is persented which characterizes the thermodynamic partitioning of groups and individual atoms in amino acids and proteins.
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 21
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 177-187 
    ISSN: 0887-3585
    Keywords: evolution ; protein structure ; nucleotide binding domain ; gene sequence ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The intron/exon organization of the human gene for glycogen phosphorylase has been determined. The segments of the polypeptide chain that corresponds to the 19 exons of the gene are examined for relationships between the three-dimensional structure to the protein and gene structure. Only weak correlations are observed between domains of phosphorylase and exons. The nucleotide binding domains that are found in phosphorylase and other glycolytic enzymes are examined for relationships between exons of the genes and structures of the domains. When mapped to the three-dimensional structures, the intron/exon boundaries are shown to be widely distributed in this family of protein domains.
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  • 22
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 188-201 
    ISSN: 0887-3585
    Keywords: NMR ; NOE ; protein conformation ; structure data base ; structure fragments ; modelling ; distance matrices ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A method to build a three-dimensional protein model from nuclear magnetic resonance (NMR) data using fragments from a data base of crystallographically determined protein structures is presented. The interproton distances derived from the nuclear Overhauser effect (NOE) data are compared to the precalculated distances in the known protein structures. An efficient search algorithm is used, which arranges the distancs in matrices akin to a Cα diagonal distance plot, and compares the NOE distance matrices for short sequential zones of the protein to the data base matrices. After cluster analysis of the fragments found in this way, the structure is built by aligning fragments in overlapping zones. The sequentially long-range NOEs cannot be used in the initial fragments search but are vital to discriminate between several possible combinations of different groups of fragments. The method has been tested on one simulated NOE data set derived from a crystal structure and one experimental NMR data set. The method produces models that have good local structure, but may contain larger global errors. These models can be used as the starting point for further refinement, e.g., by restrained molecular dynamics or interactive graphics.
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  • 23
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 236-259 
    ISSN: 0887-3585
    Keywords: atomic probability distributions of proteins ; anisotropy and anharmonicity of motions in proteins ; multiple occupancy of atomic positions in proteins ; molecular dynamics simulation ; lysozyme ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Positional probability density functions (pdf) for the atomic fluctuations are determined from a molecular dynamics simulation for hen egg-white lysozyme. Most atoms are found to have motions that are highly anisotropic but only slightly anharmonic. The largest deviations from harmonic motion are in the direction of the largest rms fluctuations in the local principal axis frame. Backbone atoms tend to be more nearly harmonic than sidechain atoms. The atoms with the largest anharmonicities tend to have pdfs with multiple peaks, each of which is close to harmonic. Several model pdfs are evaluated on the basis of how well they fit probability densities from the dynamics simulations when parameterized in terms of the moments of the distribution. Gram-Charlier and Edgeworth perturbation expansions, which have been successful in describing the motions of small molecules in crystals, are shown to be inadequate for the distributions found in the dynamics of proteins. Multipeaked distribution functions are found to be more appropriate.
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  • 24
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    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 260-261 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 25
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987) 
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
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  • 26
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    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 298-307 
    ISSN: 0887-3585
    Keywords: α-bungarotoxin ; neurotropism ; rhabdo-virus ; α-subunit ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Peptides corresponding to portions of loop 2 of snake venom curare-mimetic neurotoxins and to a structually similar region of rabies virus glycoprotein were synthesized. Interaction of these peptides with purified Torpedo electric organ acetylcholine receptor was tested by measuring their ability to block the binding of 125I-labeled α-bungarotoxin to the receptor. In addition, inhibition of α-bungarotoxin binding to a 32-residue synthetic peptide corresponding to positions 173-204 of the α-subunit was determined. Neurotoxin and glycoprotein peptides corresponding to toxin loop 2 inhibited labeled toxin binding to the receptor with IC50 values comparable to those of nicotine and the competitive antagonist d-tubocurarine and to the α-subunit peptides with apparent affinities between those of d-tubocurarine and α-cobratoxin. Substitution of neurotoxin residue Arg37, the proposed counterpart of the quatenary ammonium of acetylcholine, with a negatively charged Glu residue reduced the apparent affinity about 10-fold. Peptides containg the neutotoxin invarint residue Trp29 had 10- to 100-fold higher affinites than peptides lacking this residue. These results demonstrate that relatively short synthetic peptides retain some of binding ability of the native protein from which they are derived, indicating that such peptides are useful in the study of proetin interactions. The ability of the peptides to compete α-bungarotoxin binding to the receptor with apparent affinites comparable to those of other cholinergic ligands indicates that loop 2 of the neurotoxins and the strucually similar segment of the rabies virus glycoprotein act as recognition sites for the acetylcholine receptor. Invarient toxin residues Arg37 and Trp29 and their viral homologs play important, although not essential, roles in binding, possibly by interaction with complementary anionic and hydrophobic subsites on the acetylcholine receptor. The α-subunit peptide most likely contains all of the determinants for binding of the toxin and glycoprotein peptides present on the α-subunit, because these peptides bind to the 32-residue α-subunit peptides with the same or greater affinity as to the intact subunit.
    Additional Material: 9 Ill.
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  • 27
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    Proteins: Structure, Function, and Genetics 2 (1987), S. 308-329 
    ISSN: 0887-3585
    Keywords: conformational dynamics ; normal mode analysis ; Young's modulus ; rigid structural elements ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The normal mode analysis of conformational fluctuation is carried out for a small globular protein, bovine pancreatic trypsin inhabitor. Results are analyzed mainly to reveal the mechanical construction of the protein molecule. We take dihedral angles, including peptide ω angles, as independent variables for the normal mode analysis. There are 306 such angles in this molecule. Motions in modes with frequencies lower than 120 cm-1 are showned to involve atoms in the whole protein molecule, and spatial change of displacement vectors is continues, i.e., those of atoms near in space are similar. To quantitate the observation of the continuity, a correlation function of direction vectors of atomic displacement is calculated. From this function we define a Quantity that is interpreted as the wave length of an equivalent elastic plane wave. From this Quantity we deduce eefective young's modulus for each mode. For the mode with the lowest frequency 4.4 cm-1, it terned out to be 0.8 × 109 dyn cm-2, the value two orders magnitude softer than, for instance, α-helices. Prompted by this observation, the four lowest frequency modes and also the harmonic motions in the thermal equilibrium are analyzed further mainly to detect relatively rigid structural elements in the molecule. From this analysis emerges a mechanical picture of the protein molecule that is made up of relatively rigid elements held together by very soft parts.
    Additional Material: 15 Ill.
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  • 28
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    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 2 (1987), S. 330-339 
    ISSN: 0887-3585
    Keywords: van der Waals radii ; conformation ; amino acid residue ; dipeptide approximation ; molecular modeling ; systematic conformationl search ; N-alkyl amino acid ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Effective van der Waals radii were celebrated in such a way that molecular models built from standard bond lengths and bond angels reproduced the amino acid conformations observed by crystallography in proteins and peptides. The celebrations were based on the comparision of the Ramachandbran plots prepared from high-resolution X-ray data of protins and peptides with the allowed φ,ψ torsional angel space for the depeptide molecular models. The celebrated radii are useful as criteria with which to filter energetically improbable conformations in molecular modeling studies of proteins and peptides.
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  • 29
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    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 14 (1987) 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 30
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    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 14 (1987), S. i 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 31
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Amino acids can be identified unambiguously in form of their dansylated methyl esters by combination of thin-layer chromatography on polyamide and subsequent mass spectrometry without prior substance elution from the chromatographic polyamide carrier. The evaporation intensity of the amino acid derivatives is sufficient to get excellent mass spectra with significant structural information also with very small amounts of starting material (picomole level), which guarantee a high separation power in the TLC step. Besides the methylester derivatives, in part, products additionally methyl substituted at the sulfonamide nitrogen could be separated.
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  • 32
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The simple combination of thin-layer chromatography on polyamide with subsequent mass spectrometry of the separated compounds together with the carrier material has been employed for unambiguous identification of individual dipeptides in a mixture. The dipeptides were analysed in the form of their dansyl methyl ester derivatives. The appearance of molecular ions in the electron impact mass spectra simultaneously with the ions dans-NH=CHR⌝+ indicating the corresponding N-terminal amino acid residue enables a rapid and sensitive structure elucidation of the dipeptides. The chromatography and mass spectrometry can be performed with 0.2-0.3 nmol dipeptide.
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  • 33
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    Biological Mass Spectrometry 14 (1987), S. 357-362 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several classes of environmentally significant compounds were introduced into an ion trap detector (ITD) by capillary column gas chromatography, and the performance of the device as a gas chromatography/mass spectrometry (GC/MS) system was studied. The experiments conducted included studies of the precision of selected ion monitoring (SIM) measurements, the precision of relative ion abundance measurements in full mass range scans, the sensitivity and instrument detection limits in SIM and full mass range data acquisition, and the linear range of concentration calibration. It was observed that resolution may be lost and saturation may occur under certain conditions, and that the data system can report artifact ions under these conditions.
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  • 34
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Brominated dioxins and dibenzofurans (PBDDs and PBDFs) are known contaminants in commercial fire retardant preparations. Further, they are formed in incineration processes involving polybrominated biphenyl and diphenylether fire retardants. This report presents the characterization of polybrominated dioxins and dibenzofurans. In particular, environmental monitoring methodology for PBDDs and PBDFs has been developed, and confirmation criteria for GC/MS analyses are presented.
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  • 35
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    Biological Mass Spectrometry 14 (1987), S. 473-477 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analysis of reports in the world's literature suggests that average sperm densities for groups of unselected males were relatively constant at about 108 million cells per ml prior to 1950. Subsequent to that time mean sperm densities appear to have declined. Regression analysis indicates the existence of significant negative correlations between mean sperm densities and production of synthetic organic chemicals among other parameters. Phthalate esters are one class of large volume organic chemicals that are known to disturb testicular function in laboratory animals. These compounds are also the most abundant man-made chemicals in the environment. Plots of the concentration of dibutylphthalate in the cellular fraction of ejaculates against either the sperm density or the total number of sperm for the same ejaculates gave two clusters of points. These clusters suggest the existence of two or more populations vis à vis phthalate metabolism; both of which show a negative correlation between phthalate concentration and sperm production.
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  • 36
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    Biological Mass Spectrometry 14 (1987), S. 481-485 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report a case of n-nonacosane storage disease, which went undiagnosed until the death of a 55-year-old farmer. Clinical, histological, and biochemical features are discussed. n-Nonacosane storage was identified by gas chromato-graphic-mass spectrometric analysis of different tissue extracts, n-nonacosane concentration reaching 1.2 mg g-1 of lung tissue and 0.32 mg g-1 of liver tissue. It was possible to rule out a work-induced intoxication, and n-nonacosane storage appeared to be accounted for by a lifelong, heavy consumption of unpeeled apples and Brussels sprouts.
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  • 37
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new technique known as thermally-assisted fast atom bombardment (TA-FAB) has been applied to the analysis of a series of cyclic tetrapeptide mycotoxins in order to demonstrate the usefulness of the method for structural elucidation. TA-FAB uses saturated aqueous solutions of highly hydroxylated compounds, such as fructose, as alternatives to the usual viscous liquid matrices employed in conventional FAB. During the TA-FAB analysis, the probe tip is resistively heated causing diffeiences to occur in the desorption profiles for the analyte and the matrix ions enabling an optimization for analyte desorption as a function of temperature. In this study, direct comparisons are made between TA-FAB, conventional FAB, and electron impact ionization for the analysis of the Helminthosporium carbonum mycotoxins at the 1.5 μg level. The results demonstrate the superior capacity of TA-FAB to provide both molecular weight confirmation and significant fragmentation to aid in the structural elucidation of these important biomolecules.
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  • 38
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    Biological Mass Spectrometry 14 (1987), S. 517-521 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three glutathione conjugates of acetaminophen were characterized by fast atom bombardment/mass spectrometry (FAB/MS) and fast atom bombardment/mass spectrometry/mass spectrometry (FAB/MS/MS). The conjugates, 3-(glutathion-S-yl)acetaminophen, 3-(glutathion-S-yl)diacetaminophen and 3-(diglutathion-S-yl)diacetaminophen showed intense [MH]+ ions at m/z 457, 606 and 911, respectively. Only 3-(glutathion-S-yl)acetaminophen showed any fragmentation by FAB/MS. Structurally characteristic fragmentation was observed with all three conjugates when the [MH]+ ions were collisionally activated. The loss of the glycine (GLY) and glutamic acid (GLU) moieties indicated the presence of at least one glutathione (GSH) group. Multiple losses, some of which could only occur via cleavages in both GSH moieties, were observed with the diglutathione conjugate.
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  • 39
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    Biological Mass Spectrometry 14 (1987), S. 549-553 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A GC-MS procedure has been developed for the quantitation in plasma and urine of rimantadine, an antiviral drug effective against type A influenza. The assay utilizes selective ion monitoring, methane negative ion chemical ionization (NCI) and stable isotope dilution. Sensitivity to NCI is effected by derivation of rimantadine with pentafluorobenzoyl chloride. The method has been used to quantitate plasma concentrations of rimantadine over a range from 4.2 ng/ml to 416 ng/ml, and urinary concentrations of rimantadine over a range of 21 ng/ml to 2077 ng/ml.
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  • 40
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    Biological Mass Spectrometry 14 (1987), S. 127-129 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described to assign the positional series of methylene interrupted polyenoic acids, in complex mixtures, isolated from hydrolysed lipid extracts. It entails a simple comparison of the intensities of three ions of m/z 108, 150 and 192.
    Additional Material: 2 Ill.
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  • 41
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The behaviour of 1,1·,1″-phosphinothioylidinetrisaziridine (thiotepa) in water and aqueous salt solution of various acidity was studied by field ionization mass spectrometry (FI-MS), TLC and potentiometric titration. The rate of thiotepa hydrolysis increased with increasing thiotepa, or sodium chloride concentration, and with decreasing pH. As hydrolysis products of thiotepa, mono- and dichloro derivatives formed in neutral, salt-containing and acidic solution, tepa, and products formed by P—N bond cleavage and release of aziridine have been identified.
    Additional Material: 6 Ill.
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  • 42
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methodology for the qualitative and quantitative analysis of the anthelmintic fenbendazole and its metabolites in goat feces using electron impact (EI)/direct exposure probe (DEP)/mass spectrometric (MS) and tandem mass spectrometric (MS/MS) techniques is presented. Analyses were conducted on extracts from spiked feces and feces from animals treated per os with 5 mg fenbendazole/kg, with samples being collected at zero time and at twelve hour intervals for 144 h. The results of the EI/DEP/MS quantitation of these samples are compared to those for the same samples analysed by high pressure liquid chromatography (HPLC). Mass spectral data for fenbendazole and its metabolites are presented and the advantages of the use of EI/DEP/MS and/or DEP/MS/MS over HPLC are discussed. This methodology may be used as a confirmatory method for the HPLC analysis of fenbendazole and its metabolites or may be used as a method in its own right for the rapid qualitative and quantitative analysis of these compounds.
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  • 43
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Known and possible phenolic and primary and secondary amine metabolites of lidocaine were added to urine from drug-naive rats. These metabolites were derivatized in this aqueous medium by acetylation with acetic anhydride or by pentafluorobenzoylation with pentafluorobenzoyl chloride. The derivatives were simultaneously extracted into an organic solvent. The products were separated by gas chromatography (flame ionization detection for acetates and electron-capture detection for pentafluorobenzoates) and identified by combined gas chromatography/mass spectrometry. Mass spectral fragmentation pathways were readily deduced; diagnostic fragment ions were identified and were valuable for characterization purposes. Structural isomers could be distinguished on the basis of their GC retention times.Extractive derivatization using pentafluorobenzoyl chloride is an attractive analytical procedure for the identification of phenolic and dealkylated metabolites of lidocaine.
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  • 44
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 45
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    Biological Mass Spectrometry 14 (1987), S. 213-220 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermospray HPLC/MS analysis of the metabolites of arachidonic acid proved to be sensitive and specific. The compounds included were hydroxy-fatty acids (5-HETE, 12-HETE, and 15-HETE) and prostaglandins PGD2, PGE2, PGF2α, PGA2, PGA1, TXB2, and 6-Keto-PGF1α. Thermospray HPLC/MS analysis allows for simultaneous monitoring of each compound without the need for additional sample preparation or derivatization. The thermospray spectra for the metabolites exhibited [M + NH4]+ ions and fragment ions because of sequential loss of equivalents of H2O. HPLC/MS showed detection limits in the 0.5 to 5 ng range when using multiple ion detection for most of the metabolites. Post-column derivatization of these metabolites using trimethylanilinium hydroxide (TMAH) to form the methyl esters is also presented. This derivatization resulted in a gain in ion current by a factor of 3-6 for most compounds while adding potential specificity to the analysis. The thermospray spectra of the derivatives were nearly identical to the spectra of the free acid except the peaks were incremented by 14 daltons due to the methyl ester formation. The derivatization of the carboxylic acid group proved to be complete under thermospray conditions producing the maximum ion current and causing no compromise in operation of the interface.
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  • 46
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    Biological Mass Spectrometry 14 (1987), S. 649-651 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The identified urinary metabolites of male rats exposed to indan are: 1- and 2-indanone; 1-, 2- and 5-indanol; 2-and 3-hydroxyl-1-indanone; and cis- and trans-indan-1,2-diol. Indan causes kidney damage in male rats in a manner similar to the cyclic hydrocarbons cis- and trans-decalin and JP-10. Lesions produced by indan occur only in male rats and not in female or control rats.
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  • 47
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dinucleoside monophosphates bearing usual protecting groups at the exocyclic amino functions of the heterocyclic bases, the 5′-hydroxy group, the phosphate moiety and the O-6-position of the guanine ring have been analysed by FAB mass specrometry in the negative ion mode. These non-charged key intermediates for oligodeoxynucleotide synthesis exhibit very simple spectra in the mass range of m/z 400-1500 using tetra-ethylene glycol as matrix. Most of the observed ions could easily be assigned. Apart from deprotonated molecular ions sequence specific ions arising from C-O-P bond cleavage and ions derived from loss of protecting groups were observed. The simplicity of spectra interpretation makes FAB mass spectrometry to a rapid and valuable tool for unambiguous identification of dimeric synthons for oligonucleotide synthesis.
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  • 48
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    Biological Mass Spectrometry 14 (1987), S. 141-142 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 49
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    Biological Mass Spectrometry 14 (1987), S. 131-140 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixtures of both synthetic and naturally occurring (human plasma) cholesteryl esters have been examined by capillary gas chromatography/mass spectrometry (GC/MS). A magnetic sector mass spectrometer was used and a variety of ionization modes were assessed with a view to obtaining structural information on intact cholesteryl esters. By employing ammonia as reagent gas, with negative ion scanning, spectra were produced from which the nature of steryl and fatty acyl moieties could be readily deduced. Analyses were performed at an ion source temperature of 300°C in order to maintain the integrity of the gas chromatographic profile. The technique described is of general use for the GC/MS analysis of steryl esters, particularly in conjunction with magnetic sector instruments.
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  • 50
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermospray spectra on a magnetic sector mass spectrometer, by definition measured at high accelerating voltages, are seen to be highly fragmented. This is rationalised in terms of the necessity to accelerate ions through a region of high pressure in the vicinity of the ion-collecting orifice at the spray volume, where ions may be energized by ion molecule collisions. In this region, a high percentage of the parent ion current is lost through the dispersion of the ion beam and by the collisional activation of molecular ions resulting in extensive fragmentation. The investigation of means by which these effects may be minimized has led to the construction of an improved sector thermospray source. Comparative results for gramicidin S demonstrate that its fragmentation is reduced and that the intensity of the protonated molecular ion is greatly enhanced.
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  • 51
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    Biological Mass Spectrometry 14 (1987), S. 183-185 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetates of 12 positionally isomeric tetradecenols (Δ2-Δ13) have been prepared and their mass spectra measured without any prior chemical modification. Comparison of spectra of all the isomers has shown the variation in intensities of some predominant fragments with the position of the double bond on the 14 carbons chain. The mass spectra were interpreted in terms of the relative intensity ratio of the fragment ion peaks to locate the double bond positions. A procedure for elucidation of the positional isomerism of tetradecenyl acetates is given.
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  • 52
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    Biological Mass Spectrometry 14 (1987) 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 53
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    Biological Mass Spectrometry 14 (1987), S. 207-211 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eight normal subjects ingested 125 mg of p-tyramine-β,β-2H2 hydrochloride and the 3 h and following 21 h urine collections were analysed by mass spectrometry with selected ion monitoring for the deuterated metabolites: free and conjugated p-tyramine-β,β-2H2, free p-octopamine-β-2H1, free and conjugated p-hydroxyphenylacetic acid-α-2H1 and -α,α-2H2, and free p-hydroxymandelic acid-α-2H1. These metabolites accounted for 72% of the ingested label, of which conjugated p-tyramine and free p-hydroxyphenylacetic acid constituted 90%. Approximately 50% of the total deuterated tyramine and 70% of the total deuterated p-hydroxyphenylacetic acid were excreted in the first three hours, although there was considerable variation between individuals. The presence of a small amount of p-hydroxyphenylacetic acid-α-2H1 suggests that some exchange of deuterium occurred at the intermediate p-hydrophenylacetaldehyde stage.These results, based as they are on metabolites labelled with the stable isotope deuterium, ought to be more reliable than earlier studies in which unlabelled tyramine was ingested with the resultant metabolites, indistinguishable from their endogenous metabolic counterparts, being measured by fluorimetry or gas chromatography.
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  • 54
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    Biological Mass Spectrometry 14 (1987), S. 221-227 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Human exposure to aromatic amines may be monitored by measuring the amount of sulfinamide adduct bound to hemoglobin. In order to develop a sensitive and selective method for measuring aromatic amines present in low concentrations the mass spectra of the pentafluoropropionamide derivatives of a series of aromatic amines were determined under various ionization conditions. With electron ionization the aromatic amine derivatives typically yield intense molecular ions with fragmentation leading to elimination of C2F5 and COC2F5. Higher molecular weight polycyclic aromatic amines, e.g., 6-aminochrysene, give prominent molecular ions as well as intense ions corresponding to M-174 (loss of CNHCOC2F5). With positive chemical ionization using methane as reagent gas the derivatives give protonated molecular ions as the base peaks, as well as the associated ions at M + 29 and M + 41. Negative ion chemical ionization yields, primarily, peaks corresponding to the loss of HF from the molecular anions. Negative ion chemical ionization with selected ion monitoring is generally more suitable than positive chemical ionization or electron ionization for the quantitative analysis of aromatic amines present in biological samples in the mid femtomolar range. Exposure of human subjects to aromatic amines was determined via basic hydrolysis of the isolated sulfinic acid amide hemoglobin adducts. Analysis of the derivatized extracts by gas chromatography/negative ion chemical ionization/mass spectrometry demonstrated the presence of aniline, ortho-, meta-, and para-toluidine, 2-naphthylamine, and 4-aminobiphenyl. The hemoglobin adduct levels of these amines in both cigarette smokers and nonsmokers were determined. The mean values of the adduct levels of ortho- and para-toluidine, 2-naphthylamine, and 4-aminobiphenyl were higher in smokers than in nonsmokers, while the mean adduct values of aniline and meta-toluidine were similar in both groups. Adducts of 2-, 3-, 4-ethylaniline, 2,3-, 2,4-, 2,5-, 2,6-dimethylaniline, and 3-aminobiphenyl have been detected in smokers' blood. 1-Aminoanthracene, 9-aminophenanthrene, and 6-aminochrysene have not been detected. GC/MS procedures were also used to determine the extent of binding of aniline-2,3,4,5,6-d5 to hemoglobin in rats administered aniline-d5.
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  • 55
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    Biological Mass Spectrometry 14 (1987), S. 479-479 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 56
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The single dose pharmacokinetics of deuterium-labelled cannabinol (2H2-CBN) were evaluated in six male cannabis users with different degree of abuse after smoking an average dose of 19 mg and after intravenous administration of 20 mg CBN. Plasma levels were measured for up to 72 h with selected ion monitoring by GC/MS using 2H7-CBN as internal standard. The systemic availability of smoked CBN was found to be 39 ± 26% (min-max 6-65%). The mean plasma clearance was 19.1 ± 2.6 ml min-1 kg-1 and the volume of distribution was determined to 50 ± 23 1 kg-1. The apparent terminal half lives for CBN were 32 ± 17 h and 43 ± 29 h after intravenous administration and smoking, respectively.
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  • 57
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    Biological Mass Spectrometry 14 (1987), S. 533-534 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 58
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    Biological Mass Spectrometry 14 (1987), S. 523-531 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Derivatization of prostaglandins and thromboxane B2 using diethyl amino ethyl chloride and diethyl amino ethyl bromide improved thermospray HPLC/MS sensitivity. The derivatization was evaluated for prostaglandin A1, A2, D2, E2, F1α, F2α, and thromboxane B2. The derivatization reaction, thermospray operating conditions, and mode of detection were optimized to produce the most intense [M + H]+ or [M - H]- ions for the derivative. Derivatization was better than 99% complete in 1 hour at 75°C. No thermal degradation of the prostaglandins was observed. Positive thermospray ionization proved the mode most sensitive, enabling detection from 10 to 300 pg of each prostaglandin under multiple ion detection. The thermospray spectra exhibited intense [M + H]+ ions for the derivative with a few fragment ions from sequential losses of water from the [M + H]+ ion. Detection of a prostaglandin metabolite in plasma over the concentration range from 3 ppm to 30 ppb was possible using this derivatization.
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  • 59
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas chromatographic and mass spectrometric properties of leukotriene B4, 20-hydroxy-leukotriene B4 and 20-carboxy-leukotriene-B4 were investigated as their methyl ester trimethylsilyl, methyl ester allyldimethylsilyl and methyl ester tert-butyldimethylsilyl ethers. The gas chromatographic properties of the trimethylsilyl and tert-butyldimethylsilyl ether derivatives were good with respect to peak shape and sensitivity, whereas the allyldimethylsilyl ether derivative gave a lower sensitivity. The sensitivity defined as the quantity that could be passed through the gas chromatographic column.The three derivatives showed a mass spectrometric fragmentation pattern with cleavage of the C12—C13 bond as an important feature. Particularly, the allyldimethylsilyl ether derivative of the three compounds studied exhibited a high tendency for C12—C13 bond cleavage resulting in a fairly intense ion at m/z 435. However, the mass spectra indicated multiple fragmentation pathways due to the presence of double bonds, leading to decreased intensities of the high mass ions. A quantitative analysis by selected ion monitoring of the most intense high mass ions in the respective mass spectrum demonstrated that neither derivative would allow measurements in the low picogram range. Catalytic hydrogenation of the double bonds was performed and the methyl ester trimethylsiyl, methyl ester allyldimethylsilyl and methyl ester tert-butyldimethylsilyl ether derivatives of the reduced compounds were prepared. Saturation of the double bonds increased the gas chromatographic sensitivity for the three derivatives as well as the intensities of the high mass ions in their mass spectra. The high sensitivity that can be obtained by measurement of such high mass ions was demonstrated by quantification of leukotriene B4 in lung tissue samples by selected ion monitoring.
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  • 60
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    Biological Mass Spectrometry 14 (1987), S. 355-355 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 61
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    Biological Mass Spectrometry 14 (1987), S. 363-367 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The indoor air quality of the offices of smokers and nonsmokers was surveyed for volatile organic compound identities and concentrations. These results were examined to determine whether environmental tobacco smoke contamination could be distinguished from airborne pollutants outgassing from other sources. It was not possible to positively attribute volatile organic contaminants to environmental tobacco smoke. It was possible to distinguish between smokers' and nonsmokers' offices by determining airborne nicotine levels.
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  • 62
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxygen-enhanced negative chemical ionization MS is sensitive and specific for the detection of polychlorinated biphenyls (PCBs) without isobaric interferences (qualitative or quantitative) from congeners of higher levels of chlorination. The collision-induced dissociation (CID) spectra of the [M - Cl + O]- ion of 40 PCB congeners have been acquired on a triple quadrupole mass spectrometer.Qualitative relationships between structure of the congener and its CID spectrum suggest that reliable identification of PCB congeners is possible even where capillary column gas chromatographic separation is incomplete. Congeners with hydrogen atoms located para and meta to the biphenyl linkage show most abundant collision-induced loss of HCl, whereas congeners with a penta-chloro phenyl ring show least CID loss of HCl. Congeners IUPAC 105 and 121 have CID spectra suggesting a pathway for sequential loss of HCl and CO neutrals during the collision-induced dissociation of the [M - Cl + O]- ion of these molecules. Unambiguous identification of PCB congeners in natural materials will require a complete set of pure, synthetic PCB congeners: identification problems are illustrated using an extract of Northern Shark (dogfish) liver oil.
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  • 63
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    Biological Mass Spectrometry 14 (1987), S. 535-541 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A moving belt interface was used to identify budesonide metabolites, obtained from rat and mouse liver incubations, by liquid chromatography/mass spectrometry (LC/MS). The metabolites were separated on a small-bore C18 column with an ethanol/water gradient as mobile phase at a flow rate of 0.2 ml min-1. A spray device was used for deposition of the aqueous solvent on to the belt. Chemical ionization mass spectra were obtained with methane as the reagent gas. Deuterium-labelled budesonide, which was used to facilitate metabolite identification by the isotope cluster technqiue, was found to be slightly separated from the unlabelled analogue on the LC column. Incubations were also performed under 18O2 to elucidate the mechanism of a new metabolic pathway (16α, 17α-acetal splitting) and to confirm the oxidative nature of reactions leading to hydroxylated metabolites. The moving belt LC/MS technique afforded higher sensitivity, and gave more abundant MH+ ions of the compounds studied, than previously found by direct probe mass spectrometry. Phthalate ester background, partly from the polymide belt, complicated the identification of minor metabolites.
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  • 64
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    Biological Mass Spectrometry 14 (1987), S. 587-588 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 65
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    Biological Mass Spectrometry 14 (1987), S. 599-602 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the quantification in plasma of CP-55,940, a new non-opiate oral analgetic agent, using capillary gas chromatography/mass spectrometry. After extraction, derivation of the drug and a structural analog internal standard is carried out with trifluoracetyl imidazole. The derivative exhibited excellent gas chrornatographic properties. Electron impact yielded an abundant high mass ion whose monitoring permitted the sensitive and specific determination of CP-55,940 down to 0.5 ng ml-1.
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  • 66
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    Biological Mass Spectrometry 14 (1987), S. 613-616 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for the quantification of tulobuterol in human plasma, based upon selective extraction and high resolution capillary gas chromatography-mass spectrometry. The mass spectrometric determination is based on selected ion monitoring of two fragment ions derived from the N,O-heptafluorobutyryl derivatives of tulobuterol and its internal standard, deschlorotulobuterol. The plasma work-up procedure consists of extraction of 1.0 ml alkalinised plasma with dichloromethane, back-extraction into an acidified aqueous phase, followed by a final extraction with dichloromethane after realkalinisation. The method gave interference-free and linear results. The between-assay variability is 4.7% CV at the 3.0 μg l-1 plasma concentration level. The assay permitted quantitative measurements down to 170 ng tulobuterol per litre of plasma and hence provided sufficient sensitivity for quantification of plasma levels after therapeutic doses.
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  • 67
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    Biological Mass Spectrometry 14 (1987), S. 627-632 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In phytochemical and chemotaxonomic research work mass spectrometry plays an outstandingly important role. Using gas chromatography/mass spectrometry (GC/MS) we established the chemotaxa of Tanacetum vulgare L. Chemotypes with essential oils countaining 60-90% of artemisia ketone, carveol, dihydrocarvone, myrtenol, umbellulone, terpinen-4-ol, davanone, and Tagetes species containing various essential oils can be clearly distinguished by their spectra; we examined many variations of Tagetes erecta, T. lucida, T. minuta, T. patula and T. tenuifolia. We have identified α-β-pinene-, 1,8-cineol-, linalool-, camphor-, nerol-, geraniol- and γ-gurjonene as components of Achillea distans L. Injecting the essential oil direct from the oil-secreting organs of T. minuta plants we identified using GC/MS 6-10 and 16% eugenol from the involucral bract and hypsophyll, respectively, as well as β-ocimene, dihydrotagetone, tagetone, Z- and E-ocimenones. In the course of studies on essential fatty acids Borago officinalis and Lappula squarrosa were selected from 70 species of the family Boraginaceae to obtain seed oil as a source of γ-linolenic acid, and for the PG synthesis we isolated several grams of γ-linolenic acid, as well as C18:4, i e. octadecatetraenic acid, from L. squarrosa on the basis of the mass spectra. From the seed oil of Aquilegia vulgaris C18:3 (5) from the oil of Limnanthes dougloasii C20:1 (5) and from the seed oils of Delphinium consolida and of Tropaeolum species (T. majus, T. minus, T. peregrinum) C20:1 (11) fatty acids were identified on the basis of spectra.
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  • 68
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bile from rats treated with acetaminophen was analyzed by direct injection onto a thermospray liquid chromatography/mass spectrometry (LC/MS) system. Two conjugated metabolites of acetaminophen were separated by the high-pressure liquid chromatographic system and analyzed by mass spectrometry. The conjugates were identified as the glutathione-acetaminophen conjugate and the glucuronide-acetaminophen conjugate by comparison of the chromatographic retention times and the mass spectra to that of the synthetic standards. No evidence of acetaminophen metabolites was observed when bile samples were subjected to direct analysis by fast atom bombardment mass spectrometry.
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  • 69
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    Biological Mass Spectrometry 14 (1987), S. 733-736 
    ISSN: 0887-6134
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
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  • 70
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct analysis of unpurified urine from patients with β-ketothiolase deficiency and glutaryl-coenzyme A dehydrogenase deficiency was carried out by methylation and fast atom bombardment mass spectrometry. Previously unidentified signals consistent with unusual acylcarnitines were detected. In the former disease, thermospray liquid chromatography/mass spectrometry analysis confirmed the identification of tiglylcarnitine and differentiated it from a biological isomer, 3-methylcrotonylcarnitine. In glutaric aciduria, glutarylcarnitine was confirmed by detection of glutaric acid liberated upon base hydrolysis of a purified acylcarnitine fraction. The discovery of these metabolites suggests that L-carnitine therapy might be beneficial for the enhanced excretion of toxic metabolites that accumulate in patients with these disorders.
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  • 71
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 111-125 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have prepared a number of high molecular weight, soluble, symmetrical dialkyl substituted germanium homopolymers and germanium-silicon copolymers. In solution, the absorption of the homopolymers was ∼ 20 nm red shifted from the crossponding silicon derivatives. This was somewhat unexpected based on theoretical predictions and has been rationalized on the basis of conformational arguments. In the solid state, samples of poly(di-n-hexylgermane) and poly(di-n-octylgermane) are strongly thermochromic. The effect is attributed to the conformational locking of the backbone which is caused by the crystallization of the side groups. In this regard, the germanium derivatives behave similarly to the corresponding silicon polymers, and the convergence of the long wavelength absorptions for both types of polymers is consistent with theoretical predictions. The germanium-silicon copolymers are also strongly thermochromic, but the long wavelength absorption is somewhat blue shifted (8 nm) from the respective homopolymers. As expected, the new germanium homo and copolymers are quite sensitive to light and readily undergo chain scission to produce lower molecular weight materials.
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  • 72
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 181-189 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vinyl acetate-vinyl alcohol copolymers were fractionated in order to obtain their degree of hydrolysis distributions. In the method employed for fractionation, the differences in molecular weight of copolymer did not affect the fractional separation. Degree of hydrolysis distributions was found to be broad, with a pronounced maximum at a low degree of hydrolysis. Viscosity measurements were performed both for the precipitated fractions and unfractionated polymer. The Huggins constant was found to increase with a decrease in the degree of hydrolysis of polyvinyl acetate. These results were interpreted in terms of a polymer molecular association. From values of Huggins constants, comparative information about copolymer “blockiness” is also established.
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  • 73
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 271-284 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copolyesters containing ethylene terephthalate and p-oxybenzoate units in mole ratios of ca. 80:20, 70:30, 40:60, and 20:80, respectively, were examined by direct pyrolysis-mass spectrometry to obtain information about the thermal stabilities and the sequences distributions of the two types of units as a function of composition. Thermal stability as measured by rate of volatilization increased with increasing oxybenzoate content, as did the amount of char residue formed. The electron impact mass spectrum of the volatile fragments showed the formation of predominantly linear fragments with carboxyl and vinyl end groups. Dimer, trimer, and tetramer fragments containing either or both types of units could be identified and their relative amounts could be estimated from peak intensities. The results were consistent with those expected for random distributions of the two units, i.e., for statistical copolymers.
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  • 74
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 23-30 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Poly[styrene (ST)-tetrahydrofuran (THF)-2-methyl-2-oxazoline(MeOz)] triblock and graft copolymers were prepared by ionic polymerizations. Poly(ST-THF) graft copolymers were synthesized by coupling of ST-4-vinylpyridine (4VP) copolymer with a large excess of PTHF dication. The ion coupling of PST dianion with PTHF dication was accompanied by the side reaction (abstraction of α proton of oxonium ion). After tosylation of terminal hydroxyl groups of PTHF blocks, cationic copolymerizations of MeOz with poly(ST-THF) block and graft copolymers were carried out, and characteristics of produced copolymers were investigated in some detail.
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  • 75
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 77-86 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acetylation of linalool with acetic anhydride was carried out in the presence of polystyrene-bound aminopyridines and triethylamine. The catalytic activity of the immobilized aminopyridines increased with decreasing percentage of ring substitution and with increasing spacer-chain length. The increased activity is attributed to an increase in the amount of aminopyridine units complexed with acetic anhydride. The acetylation could be successfully conducted by use of a mixture of the immobilized aminopyridines and polymer-supported benzyldiethylamine, which effectively trapped acetic acid formed in the reaction system.
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  • 76
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 127-136 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radicals formed in poly(methyl methacrylate) (PMMA) under vacuum by UV irradiation at room temperature were carefully examined from 77 K to 300 K by electron spin resonance (ESR). The conventional nine-line spectrum was observed with significant overall intensity changes in contrast to previous reports. The intensity decreases greatly as the temperature increases from 77 K to 100 K. The intensity of the ESR spectrum increases as the temperature increases gradually from 100 K to 260 K. The spectral changes were reversible at all temperatures. Three different models are considered to interpret the temperature dependence of the intensity of the ESR spectrum. The results indicate that the ESR spectrum depends on (1) the steady-state concentration of the propagating radical in the polymer, (2) the conformational distributions of the radicals, and (3) the environmental structures of the polymer matrix.
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 171-180 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based on dynamic thermogravimetric analysis (TGA) of fluorinated aromatic polyamides, we found that substituting terephthaloyl units for isophthaloyl units usually increased the thermal stability of the polymers. In contrast, the first steps of thermal degradation of poly(5,5′-sulfonyl-2,2′-difluoro-diphenyl terephthalamide) (2,2′-DIF-PSDPT) and poly(5,5′-sulfonyl-2,2′-difluorodphenyl isophthalamide)(2,2′-DIF-PSDPI) followed almost the same curve. This was attributed to the relative flexibility of the —SO2— group, and also to the activating effect on the dehydrofluorination reaction, which was believed to be the first step of the degradation of the ortho-fluorinated aromatic polyamides, , resulting in the formation of benzoxazole groups, , on the polymer backbone. With fluorinated aromatic polyamides having ortho fluorine to the amide nitrogen, the electron releasing —CH2— group deactivated the nucleophilic substitution of the dehydrofluorination reaction and the electron withdrawing group —SO2— activated the reaction, so that the onset degradation temperatures of the fluorinated aromatic units R in followed the order:
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 231-239 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New bicyclic and tricyclic compounds have been synthesized by the Lewis acid-catalyzed condensation of epoxides with cyclic acid anhydrides or cyclic bislactones. These materials take part in the anionic addition polymerization of amine-functional polyamides with diepoxides, and modify the shrinkage that is characteristic of the reaction. It is possible to control the extent of shrinkage by choosing an appropriate comonomer and by adjusting the concentration of this material in the reaction mixture.
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 653-667 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three types of wholly aromatic block copolymers were synthesized using the phosphorylation reactions of Yamazaki and Higashi. Each copolymer contained blocks of rigid and flexible units. The first copolymer, PBA/PABH-T, contains blocks of poly(p-benzamide) and the polyterephthalamide of p-aminobenzhydrazide. The second copolymer, PBA/MPD-I, contains blocks of poly(p-benzamide) and poly(p-phenylene isophthalamide), whereas the third, PPD T/MPD-I, contains blocks of poly(p-phenylene terephthalamide) and poly(m-phenylene isophthalamide). Three synthetic routes were used for the preparation of the block copolymers. In the two-step polycondensation (A), monomers of the flexible block are added to the rigid prepolymer. The multistep method (B) differs in that the rigid prepolymer is carboxy-terminated prior to addition of the monomers of the flexible block. Carboxy-terminated prepolymer of the rigid block is reacted with amine-terminated prepolymer of the flexible block in the two-pot condensation (C). The presence of a considerable amount of the flexible homopolymer is indicated by viscosity, extraction, and NMR studies, particularly when methods A and C were used. The flexible homopolymer can be extracted by using a nonsolvent for the rigid blocks. Extraction of the rigid homopolymer (which may also be presumed to be produced) entails a more elaborate procedure. In principle, one can use these methods to obtain pure block copolymer for study of mixtures with the rigid and flexible homopolymers. Phase studies of some of these systems will be reported in a following paper.
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 711-717 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some regularities of radical alternating copolymerization of maleic anhydride with allyl chloroacetate are studied. The formation of donor-acceptor complexes between comonomers with complexing constant Kc = 0.052 L/mol is found using 1H NMR spectroscopy. The kinetic parameters for this copolymerization reaction are found and the quantitative contribution of monomer complexes to chain-growth radical reactions is calculated. It is shown that either a “free-monomer” mechanism (dilute solutions) or a “mixed” mechanism (concentrated solutions) prevails for chain growth during radical copolymerization depending on total monomer concentration. It is found that inhibition of degradative chain transfer in the course of the reaction studied takes place owing to the presence of α-chlorine atom in the allyl chloracetate molecule and formation of charge transfer complex.
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 433-436 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 451-465 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A group of block copolymers containing diacetylenes as chain extenders in their hard segments was prepared, based on urethanes, esters, ureas, and amides as hard segments and polybutadienes, polyethers, polyesters, and polysiloxanes as soft segments. Almost all block copolymers were photoreactive, but there was a wide range of sensitivities. The photoreactivity of the copolymers was found to depend on the reactivity of the monomer unit, on the width of the diacetylene stacks in the hard segments, and on the degree of phase separation in the solid films.To explore the range of monomer reactivities we prepared 15 crystalline monomers. Urethanes were in general the most reactive, and this was attributed in part to the specific effect of hydrogen bonding which brings about a shortening of the C1 to C4 distance between diacetylenes tend to reduce the photoreactivity.The behavior of identical diacetylene units in the monomer crystal, in the homopolymer, and in the block copolymer is discussed in this paper.
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  • 83
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 551-563 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three copolyimides containing crosslinkable alkyne groups either in the main chain backbone or as endgroups, have been synthesized and characterized in regard to their structure, molecular weight, solubility, film-forming properties, crystallinity, crosslinking behavior, and thermal stability. A good correlation between the structure of the polymers and their properties has been established.
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  • 84
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 581-593 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The H-abstraction by ĊH3 and ĊD3 radicals from PMMA molecules is investigated at 77 and 120 K. The film samples are prepared from the mixture of normal and deuterated PMMA. The reaction is of the first order with respect to radical concentration. Its rate is retarded in time as compared to the exponential law. An analysis of the molecular product ratio for the reaction allows the primary isotopic effect to be estimated. The initial reaction rate depends nonmonotonously on the proportion of the deuterated polymer in the matrix. Namely, there exists a range of isotopic compositions, with the reaction rate increasing with the portion of a deuteropolymer in the mixture. At 77 K the reaction rate of ĊD3 is lower than that of ĊH3 in PMMA of a mixed isotopic composition. This results from the proximity of ĊD3 with unreactive parental macromolecules, which reduces the local H concentrations around ĊD3 as compared to the mean concentration. At 120 K the radical decay rates do not differ. This fact cannot be explained by unfrozen mobilities of radicals at high temperatures or by their migration from parental macromolecules. The phenomenon is interpreted in terms of thermal fluctuations involving a great area around a radical and ensuring its migration within this area. The electron spin echo method is used to estimate the distance between a radical and its parental macromolecule, a ≥ 9.6 Å. This is the lower limit of the reaction accessibility.
    Additional Material: 8 Ill.
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  • 85
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 637-652 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization of di-n-butyl itaconate (DBI) intiated with AIBN was kinetically investigated in benezene. The polymerization rate (Rp) was expressed by: Rp = k[AIBN]0.5[DBI]1.7. The polymerization showed a considerably low overall activation energy of 15.3 kcal/mol. The initiator efficiency of AIBN in this system decreased with increasing DBI concentration, ranging from 0.34 to 0.55°C, which is ascribable to viscosity effect due to the monomer. From an ESR study, the polymerization system was found to involve two kinds of persistent radicals, namely, primary propagating (III) and propagating (I) radicals. The relative concentration of III to I increased with decreasing monomer concentration. Azo-nitrile initiators such as AVN and ACN similarly produced two persistent radicals, while MAIB, DBPO, and PBO yielded only propagating radical I as persistent. The MAIB-initiated polymerization of DBI was also performed in benzene. Similar kinetic features were observed, that is, a higher dependence of Rp on the DBI concentration and a low overall activation energy (14.4 kcal/mol). The following rate equation was obtained at 50°C:Rp = k[MAIB]0.5[DBI]1.6. The initiator efficiency of MAIB decreased with increasing DBI concentration, ranging from 0.32 to 0.53 at 50°C. The concentration of propagating radical I was determined by ESR at 50 and 61°C, from which kp and kt were estimated. The kp value increased with increasing monomer concentration, while the kt one decreased with the DBI concentration. These values are much lower compared with those of MMA.
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  • 86
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 685-702 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modified polyimide films containing cobalt have been prepared by the addition of cobalt(II) chloride to a solution containing one of the diamines 4,4′-oxydianiline (ODA) or 4,4′-diaminodiphenylsulfide (DDS) and one of the dianhydrides 3.3′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA) or 4,4′-bis(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride (BDSDA) and characterized by thermal methods, UV-visible spectra, room-temperature direct-current electrical resistivity measurements, and X-ray photoelectron and Auger electron spectroscopy. A principal goal of this work was to establish if there was coordination of the potential donor atoms of the polymide to cobalt. UV-visible spectra of the modified polyamic acid solutions and polyimide films and a titration study of a model system do not show any appreciable coordination with either the polyamic acid or the polyimide; rather, the cobalt(II) appears to be coordinated to the solvent, N,N-dimethylacetamide (DMAc), as [Co(DMAc)4]2+, until the temperature is raised above 200°C. X-ray photoelectron spectra of films cured only to 200°C also do not show significant shifts in the binding energies of the potential donor atoms from those binding energies of the undoped polymers, confirming little direct coordination of the cobalt to atoms of the polyimide. Heating the films to 300°C in a forced-air oven causes the formation of a cobalt oxide layer on the air side of the polymer. Direct-current electrical resistivity measurements on this surface show a 104-106 reduction in resistivity due to this layer.
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  • 87
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 743-743 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 88
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 215-221 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The laser Raman phonon spectroscopic technique has been used to study the photopolymerization reaction of 1,4 bis[β-pyridyl(2)vinyl] benzene (P2VB). Raman and infrared spectroscopy have been used to study the intramolecular vibrations of the reactant and the product and to characterize them. Absence of any large Stokes' shift between absorption and emission bands of the monomer crystal shows that exciton-phonon coupling is weak, and the reaction is not likely to be phonon mediated. Phonon spectroscopy shows that the reaction proceeds by a heterogeneous mechanism. Sharp phonon bands of the product, however, suggests that the photopoly P2VB lattice is highly ordered.
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  • 89
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 285-297 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electronic paramagnetic resonance (EPR) and conductivity of pristine and iodine-doped PPMQ were studied. The pristine polymer EPR signal exhibited a Lorentzian line shape. Unpaired spin density measurements indicated that the spin concentrations of the undoped polymer lie in the range of one spin per 150-190 repeat units at room temperature. The peak-to-peak width doubled, the line shape became asymmetric and the spin concentration in the polymer increased slightly after doping with iodine. EPR saturation experiments show that the spin lattice relaxation time T1 is sensitive to trace impurity. Considerable reduction of T1 after doping with iodine shows strong coupling between the spin system and N-iodonium nucleus. Conductivity increases up to 5 orders of magnitude by iodine doping; at room temperature, the best value found was 0.017 S/cm. The activation energy for conductance after doping is about half that of pristine polymer.
    Additional Material: 9 Ill.
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  • 90
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 327-335 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alternating copolymers of β-methylstyrene and maleic anhydride were prepared by free-radical-initiated polymerization in bulk and in toluene as a solvent. The reactivity ratios k1c/k12 and k2c/k21 were calculated from the change of copolymerization rate with a monomer feed at a constant total monomer concentration according to the generalized model of Shirota and coworkers. From the equation Rp = Rp(f) + Rp(CT) were calculated Rp(f) and Rp(CT), and it was found that in toluene the copolymerization proceeds predominantly by the addition of CT-complex monomers. Termination occurs predominantly by homotermination of β-methyl-styrene macro free radicals, kt22, but the cross termination kt21 is also operative.
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  • 91
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 343-351 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymerization of vinyl chloride in the presence of systems containing a transition metal compound/Lewis base and an organoaluminum compound of a different length of carbon chain have been carried out. The influence of the structure and the concentrations of particular components on the polymerization yield and molecular weight of the products has been determined. The polymerization of vinyl chloride proceeds according to the free radical mechanism, and the effectiveness of such types of initiators decreases with an increase in the length of the substituent chain in the organoaluminum chain. When using ethyl derivatives, the maximum degree of vinyl chloride conversion is about 75%, and for polystyryl or polyisoprenylaluminum of an average polymerization degree of 50-100, the conversion did not exceed 0.5%. The maximum polymerization degree of vinyl chloride in block copolymers containing polyisoprenyl or polystyryl units was 90-300.
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  • 92
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 437-441 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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  • 93
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1553-1562 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of organometallic cocatalysts on the polymerization of disubstituted acetylenes were investigated. Diphenylacetylene did not polymerize with TaCl5 alone, while it produced a polymer quantitatively in the presence of appropriate cocatalysts (Me4Sn, Et3SiH, etc.). The poly(diphenylacetylene) formed was an insoluble yellow solid. 1-Phenyl-1-alkynes (1-Phenyl-1-butyne and -1-octyne) polymerized with TaCl5 and NbCl5 alone to yield polymers whose weight-average molecular weights (Mw's) were ca. 5 × 105. Use of cocatalysts (nBu4Sn etc.) to the polymerization of these monomers accelerated the reaction, and increased the polymer molecular weights up to ca. 1.5 × 106. The poly(1-phenyl-1-alkynes) were soluble white solids. Internal octynes (2-, 3-, and 4-octynes) gave mixtures of a polymer and cyclotrimers with TaCl5 alone. In contrast, cyclotrimers formed virtually selectively by addition of cocatalysts. Thus, various effects of organometallic cocatalysts were observed depending on the kind of monomer.
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  • 94
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1619-1631 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total absorption spectrum of the UV absorber sodium 2-(2′-hydroxy-5′-methylphenyl) benzotriazole sulfonate (TINS) has been resolved into contributions by two ground-state forms in acetonitrile-water solvent mixtures and hydrogen bonding polymer and protein substrates. These two ground-state species can be assigned to (i) a planar intramolecularly hydrogen bonded form which can undergo the efficient nonradiative energy dissipation process of excited-state intramolecular proton transfer (ESIPT), and (ii) a fluorescent nonplanar species in which ESIPT is effectively prevented. The mole fractions of each contributing conformer in the polymeric substrates have been estimated. In all the polymer systems studied, a significant proportion of the TINS molecules exist in the nonplanar form and thus may not contribute to photostabilization of the substrate. The proportion of nonplanar molecules varied from 11 to 86% in synthetic polymers and 20 to 41% in protein substrates.
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  • 95
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    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1653-1662 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MS and GPC analyses are used to identify the cyclic oligomers formed in the polycondensation reactions of aromatic dithiols and dibromoalkanes leading to aromatic-aliphatic polysulfides. A correlation exists between the two sets of data obtained by these techniques. Mass spectra of the cyclic oligomers formed in the polymerization reactions are reported.
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  • 96
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1709-1712 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 97
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1697-1708 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal degradation of vinylidene chloride/methyl acrylate/phenylacetylene (VDC/MA/PA) terpolymers containing a constant 9 wt % methyl acrylate and small but varying amounts of phenylacetylene has been examined in the solid phase and in bibenzyl solution. Thermally promoted degradative dehydrochlorination, largely uncomplicated by methyl chloride formation, readily occurs at temperatures approaching 200°C. Incorporation of phenylacetylene into the polymer structure greatly facilitates degradative dehydrochlorination. Indeed, the presence of phenylacetylene induces the formation of polyene segments during the polymerization so that all the terpolymers, even at very low phenylacetylene loading, are tan in color. The decreased stability of polymers containing internal unsaturation arises from an increased rate of initiation for the degradation reaction. The propagation rate is largely unaffected by the level of unsaturation initially present in the polymer. Thus random double bonds have been identified as the principal defect sites responsible for the facile degradation of Saran copolymers. Species which promote the degradation of Saran polymers probably do so by facilitating the introduction of double bonds into the structure. The ratio of hydrogen chloride to stilbene formed for degradation of the terpolymers in bibenzyl solution is ca. 35:1. This is strongly reminiscent of PVDC degradation and suggests that for degradation of either the homopolymer or Saran copolymers the chain-carrying allylic radical pair does not dissociate to any appreciable extent as dehydrochlorination occurs.
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  • 98
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1717-1728 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bulk polymerization and copolymerization of N-(1,1′-dimethyl-3-oxobutyl) acrylamide oxime have been studied. Polymerization of diacetone acrylamide oxime was carried out with different initiating systems. The rate of polymerization of diacetone acrylamide oxime with azoisobutyronitrile as the initiating system was much higher than with peroxides. However, in the case of perester initiating systems (t-butyl perbenzoate and t-butyl per ethyl-2-hexanoate), cobalt salt promoted the polymerization rate markedly. Diacetone acrylamide oxime readily formed copolymers with a variety of comonomers (crosslinking agents and reactive diluents). Gel permeation chromatography has shown a higher reactivity of diacetone acrylamide oxime with trimethylol propane trimethacrylate as crosslinking agent and N-vinyl-pyrrolidone as reactive diluent. Therefore, the dynamic mechanical analyses presented an increase in Tg with trimethylolpropane trimethacrylate and N-vinyl-pyrrolidone as comonomers. The terpolymer formed with diacetone acrylamide oxime, trinethylolpropane trimethacrylate, and N-vinyl-pyrrolidone exhibited interesting mechanical properties and high temperature behavior.
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  • 99
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1681-1695 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal degradation of vinylidene chloride/phenylacetylene copolymers containing small but varying amounts of phenylacetylene has been examined in both the solid phase and in bibenzyl solution. Incorporation of phenylacetylene into the poly(vinylidene chloride) structure greatly facilitates degradative dehydrochlorination. Indeed, the presence of phenylacetylene promotes the formation of polyene segments during the polymerization process so that all the copolymers, even at very low phenylacetylene loading, are tan in color. The decreased stability of polymers containing interal unsaturation arises from an increased rate of initiation for degradative dehydrochlorination. The propagation rate is largely unaffected by the level of unsaturation initially present in the polymer. The ratio of hydrogen chloride to stilbene formed for degradation of these copolymers in bibenzyl solution is approximately 35:1. This suggests that the chlorine atom of the initially-formed radical pair preferentially abstracts an adjacent hydrogen atom rather than interacting with solvent, i.e., the chain-carrying radical pair does not dissociate appreciably as the unzipping dehydrochlorination occurs. Thus random double bonds introduced in a variety of ways may be identified as principal defect sites responsible for the initiation of the degradative dehydrochlorination of poly(vinylidene chloride). Species which promote the degradation of poly(vinylidene chloride) probably do so by facilitating the introduction of random double bonds into the structure.
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  • 100
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    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1745-1753 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solid polymer electrolytes with different stoichiometries were prepared from molten poly(ethylene oxide) (PEO) containing various amounts of potassium thiocyanate (KSCN). X-ray diffraction and conductivity measurements revealed that both morphology and conductivity were dependent on their stoichiometries, and that the highest conductivity at ambient temperature corresponded to 3.98 × 10-6 S cm-1 for the amorphous complex with the composition of X = 0.15 (X = [KSCN]/[EOunit]). The temperature dependence of the conductivity showed a WLF-type behavior for the amorphous complex, whereas it showed an Arrhenius-type behavior for a crystalline complex with the composition of X = 0.2. It was also found that the ionic mobility at 60°C of the amorphous complex was approximately 2.25 times greater than that of the crystalline complex. Furthermore, results of the infrared reflection spectroscopy measurements suggested that the mobility of potassium ion (K+) was correlated to the degree of the interaction between K+ and ether oxygens.
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