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  • 1985-1989  (5,436)
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  • 1
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in International Journal of Environmental Research and Public Health 15 (2018): 723, doi:10.3390/ijerph15040723.
    Description: There has been a massive increase in recent years of the use of lead (Pb) isotopes in attempts to better understand sources and pathways of Pb in the environment and in man or experimental animals. Unfortunately, there have been many cases where the quality of the isotopic data, especially that obtained by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS), are questionable, resulting in questionable identification of potential sources, which, in turn, impacts study interpretation and conclusions. We present several cases where the isotopic data have compromised interpretation because of the use of only the major isotopes 208Pb/206Pb and 207Pb/206Pb, or their graphing in other combinations. We also present some examples comparing high precision data from thermal ionization (TIMS) or multi-collector plasma mass spectrometry (MC-ICP-MS) to illustrate the deficiency in the Q-ICP-MS data. In addition, we present cases where Pb isotopic ratios measured on Q-ICP-MS are virtually impossible for terrestrial samples. We also evaluate the Pb isotopic data for rat studies, which had concluded that Pb isotopic fractionation occurs between different organs and suggest that this notion of biological fractionation of Pb as an explanation for isotopic differences is not valid. Overall, the brief review of these case studies shows that Q-ICP-MS as commonly practiced is not a suitable technique for precise and accurate Pb isotopic analysis in the environment and health fields
    Keywords: Lead isotopes ; ICP-MS ; TIMS ; MC-ICP-MS ; Environment ; Humans ; Rats ; Fractionation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 27 (1988), S. 311-320 
    ISSN: 1432-1432
    Keywords: Genome composition ; Coding sequences ; Isochores ; Humans ; Murids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The compositional distributions of coding sequences and DNA molecules (in the 50-100-kb range) are remarkably narrower in murids (rat and mouse) compared to humans (as well as to all other mammals explored so far). In murids, both distributions begin at higher and end at lower GC values. A comparison of homologous coding sequences from murids and humans revealed that their different compositional distributions are due to differences in GC levels in all three codon positions, particularly of genes located at both ends of the distribution. In turn, these differences are responsible for differences in both codon usage and amino acids. When GC levels at first+second codon positions and third codon positions, respectively, of murid genes are plotted against corresponding GC levels of homologous human genes, linear relationships (with very high correlation coefficients and slopes of about 0.78 and 0.60, respectively) are found. This indicates a conservation of the order of GC levels in homologous genes from humans and murids. (The same comparison for mouse and rat genes indicates a conservation of GC levels of homologous genes.) A similar linear relationship was observed when plotting GC levels of corresponding DNA fractions (as obtained by density gradient centrifugation in the presence of a sequence-specific ligand) from mouse and human. These findings indicate that orderly compositional changes affecting not only coding sequences but also noncoding sequences took place since the divergence of murids. Such directional fixations of mutations point to the existence of selective pressures affecting the genome as a whole.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 74 (1988), S. 137-150 
    ISSN: 1432-2234
    Keywords: MINDO/SR ; Nickel ; Hydrogen ; Surface ; Coverage ; Work function ; Magnetism ; Heat of adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The MINDO/SR method is used to study surface properties such as the work function, heat of adsorption and magnetic moment as a function of hydrogen coverage. A good correlation between theory and experiment is found. Furthermore, a qualitative analysis of surface geometry changes due to hydrogen chemisorption is presented.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0878
    Keywords: Skeletal muscles ; Ultrastructure ; Exercise ; Glycogen ; Humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Distribution of glycogen particles in semithin and ultrathin sections of biopsy samples from human muscles subjected to either short- or long-term running were investigated using PAS and Periodic Acid-ThioSemiCarbazide-Silver Proteinate (PA-TSC-SP) staining methods. Glycogen particles were predominantly found immediately under the sarcolemma or aligned along the myofibrillar Iband. After long-term exhaustive exercise type-1 fibers with a few or no glycogen particles in the core of the fibers were frequently observed. The subsarcolemmal glycogen stores of these “depleted” type-1 fibers were about three times as large as after exhaustive short-time exercise. Another indication of utilization of subsarcolemmal glycogen stores during anaerobic exercise was that many particles displayed a pale, rudimentary shape. This observation suggests fragmental metabolization of glycogen. Thus, depending on type of exercise and type of fiber differential and sequential glycogen utilization patterns can be observed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985) 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The σ-orbital manifold of cubane 1, as suggested by its PE spectrum, is divided into two sets separated by a 3 eV gap extending from ∼ -10.5 eV to ∼ -13.5 eV. Halogen substituents with np AO basis energies falling into this gap (e.g. Cl or Br) will, therefore, hyperconjugate appreciably with both sets. Interaction with the lower-lying set will lead to the usual destabilization (‘normal’ hyperconjugation), whereas interaction with the set above will necessarily lead to a ‘stabilization’ (‘inverted’ hyperconjugation). As a result the lone-pair ionization energies of Cl or Br substituted cubanes (derived from PE spectra) are much larger than naively expected for an alkyl halide containing as much as 8 C-atoms. In particular no significant shift of the eg-1 lone-pair bands in the PE spectra of 1,4-dichloro- and 1,4-dibromocubane can be detected with respect to the first ionization energies of the free atoms Cl and Br, or of HCl and HBr.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title sponge is shown to contain eight new sesquiterpenoids for which a common, unusual biogenetic origin is postulated. The compounds are shown to be: (-)-(1R*,4R*)-3-(3′-furyl)methyl-2-p-menthen-7-yl acetate ((-)-8b); two diols separated as the monoacetates (-)-(1S*,4R*)-3-(3′-furyl)methyl-l-hydroxy-2-p-menthen-7-yl acetate ((-)-13a) and the (-)-(1R*,4R*)-epimer (-)-13b, the two C(4)-epimeric 4-ethoxy-3-(1′(7′),2′-p-menthadien-3′-yl)methyl-2-buten-4-olides ((+)-14a and (-)-14b), (-)-3-(3′-furyl)methyl-7-nor-2-p-menthen-l-one ((-)-11), (-)-(3Z)-1-(3′-furyl)-4,8-dimethylnona-3, 7-dien-2-yl acetate ((-)-17), and (+)-3-(5′,7′-seco-2′(10′)-pinen-7′-yl)methylfuran ((+)-15).
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical synthesis and biological activities of a new α-melanotropin derivative are described. Nα-(5-Bromovaleryl)-Nα-deacetyl-α-melanotropin contains the 5-bromopentanoyl group as a chemical ‘handle’ in place of the acetyl group of the natural hormone. The synthesis involved a new protected intermediate which allowed the selective deprotection of either the Nα or Nα amino group. The title compound reacted with sodium thiosulfate to give Nα-deacetyl-Nα-(5-(sulfothio)valeryl)-α-melanotropin, a key intermediate for the preparation of tobaccomosaic virus/α-melanotropin disulfide conjugates. As a basis for the study of the conjugates, biological activities of the title compound on Cloudman S-91 mouse melanoma cell cultures (tyrosinase stimulation, binding, and cyclic AMP accumulation) were determined. They proved to be quite similar to the corresponding α-melanotropin activities. Differences in bindings may be explained by stronger hydrophobic interaction of the new derivative with the lipid phase of the target cell membranes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 76-82 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The carbonyl group in lactones and, to a lesser extent, in lactams tends to show a C—C=O angle that is larger than the O—C=O or N—C=O angle, the difference increasing in magnitude as the ring size decreases. The observed trend provides information on ratios of force constants characterising the flexibility of the s-cis-ester group and may be interpreted in terms of incipient chemical reaction to -O—(CH2)n—C≡O+. Molecular orbital calculations (MINDO/3, MNDO, EH) for model compounds provide an electronic interpretation of this angle difference in terms of an anomeric interaction between the p-type lone pair on the carbonyl O-atom and the antibonding C-O or C-N orbital.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 110-118 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclic octa- and decapeptides have been prepared, and their ion selectivity in solvent polymeric membranes was studied. Cyclo(-LPro-DLeu-)5 behaves as an ionophore which selects Mg2+ over Ca2+ by a factor of 100. Cyclo(LPro-LLeu)5 induces selectivity in membranes for Mg2+ over Li+, Na+ and K+ by a factor of 400, 200 and 10, respectively, while selectivity of Mg2+ over Ca2+ is poor. Some evidence is presented which indicates that certain ionophores exhibit high selectivity for monovalent magnesium complexes.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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