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  • Springer  (200)
  • 2000-2004  (126)
  • 1965-1969  (74)
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  • 1
    Electronic Resource
    Electronic Resource
    Metal substitution in transferrins: specific binding of cerium(IV) revealed by the crystal structure of cerium-substituted human lactoferrin (2000)
    Springer
    JBIC 5 (2000), S. 692-698 
    Details
    ISSN: 1432-1327
    Keywords: Metal substitution Cerium binding Lactoferrin Crystal structure Transferrin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. Proteins of the transferrin family play a key role in iron homeostasis through their extremely strong binding of iron, as Fe3+. They are nevertheless able to bind a surprisingly wide variety of other metal ions. To investigate how metal ions of different size, charge and coordination characteristics are accommodated, we have determined the crystal structure of human lactoferrin (Lf) complexed with Ce4+. The structure, refined at 2.2 Å resolution (R=20.2%, R free=25.7%) shows that the two Ce4+ ions occupy essentially the same positions as do Fe3+, and that the overall protein structure is unchanged; the same closed structure is formed for Ce2Lf as for Fe2Lf. The larger metal ion is accommodated by small shifts in the protein ligands, made possible by the presence of water molecules adjacent to each binding site. The two Ce4+ sites are equally occupied, indicating that the known difference in the pH-dependent release of Ce4+ arises from a specific protonation event, possibly of the His ligand in one of the binding sites. Comparing the effects of binding Ce4+ with those for the binding of other metal ions, we conclude that the ability of transferrins to accommodate metal ions other than Fe3+ depends on an interplay of charge, size, coordination and geometrical preferences of the bound metal ion. However, it is the ability to accept the six-coordinate, approximately octahedral, site provided by the protein that is of greatest importance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750000157
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  • 2
    Electronic Resource
    Electronic Resource
    Technical Opportunities for International Collaborations by the U.S. Fusion Program (2000)
    Springer
    Journal of fusion energy 19 (2000), S. 65-79 
    Details
    ISSN: 1572-9591
    Keywords: Fusion energy ; international collaboration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This report was prepared by a Working Group at the request of the U.S. Department of Energy, Office of Fusion Energy Sciences in 1997. The report addresses technical opportunities for mutually beneficial collaboration between the United States and other international fusion research programs. A number of outstanding opportunities are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012281826821
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  • 3
    Electronic Resource
    Electronic Resource
    Operators with closed range (1967)
    Springer
    Mathematische Annalen 174 (1967), S. 278-284 
    Details
    ISSN: 1432-1807
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01364274
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  • 4
    Electronic Resource
    Electronic Resource
    On a generalised open-mapping theorem (1967)
    Springer
    Mathematische Annalen 172 (1967), S. 217-221 
    Details
    ISSN: 1432-1807
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01351188
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  • 5
    Electronic Resource
    Electronic Resource
    Evolution of Microsatellite Alleles in Four Species of Mice (Genus Apodemus) (2000)
    Springer
    Journal of molecular evolution 51 (2000), S. 166-172 
    Details
    ISSN: 1432-1432
    Keywords: Key words: Homoplasy — Microsatellites — Microsatellite evolution — Allele evolution — Apodemus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Microsatellite length variation was investigated at a highly variable microsatellite locus in four species of Apodemus. Information obtained from microsatellite allele sequences was contrasted with allele sizes, which included 18 electromorphs. Additional analysis of a 400-bp unique sequence in the flanking region identified 26 different haplotype sequences or ``true'' alleles in the sample. Three molecular mechanisms, namely, (1) addition/deletion of repeats, (2) substitutions and indels in the flanking region, and (3) mutations interrupting the repeat, contributed to the generation of allelic variation. Size homoplasy can be inferred for alleles within populations, from different populations of the same species, and from different species. We propose that microsatellite flanking sequences may be informative markers for investigating mutation processes in microsatellite repeats as well as phylogenetic relationships among alleles, populations, and species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002390010077
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  • 6
    Electronic Resource
    Electronic Resource
    The salivary gland chromosomes of Anopheles hectoris (1966)
    Springer
    Chromosoma 19 (1966), S. 126-136 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The salivary gland chromosome map of Anopheles hectoris is described and figured. It is proposed that this map be considered the standard for this species. The hectoris chromosomes show a close relationship to those of Anopheles pseudopunctipennis pseudopunctipennis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00332796
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  • 7
    Electronic Resource
    Electronic Resource
    The structure of the chromosomes in human primordial oocytes (1967)
    Springer
    Chromosoma 22 (1967), S. 358-377 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Primordial oocytes (oocytes in primordial follicles) from human ovaries aged 51/2 months post conception to 11 3/4 years post partum were examined in: (a) squash preparations of fresh and fixed tissue; (b) histological preparations; and (c) thin sections by electron microscopy, in order to study the structure of the chromosomes. — The light microscope shows that the chromosome consists of a thread bearing numerous fine lateral appendages. Cytochemical tests indicate that the thread contains DNA, and is surrounded by material containing RNA and protein. — The electron microscope shows that there are three main structural components in the chromosome: (i) an axis or “core” containing at least two longitudinal strands about 200 Å thick; (ii) a surrounding sheath composed of coiled fibrils which form symmetrically arranged columns and loops, and (iii) clusters of large granules which are associated with the outer parts of the sheath. Small nucleoli and other granular bodies are also present. — These observations indicate the presence of lampbrush chromosomes in the human oocyte. The significance of this type of chromosome in mammals is discussed in relation to the differential radiosensitivity of the oocytes, and to the form of chromosomes at the dictyate stage in rodents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00319880
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of Processing Temperature on the Oxygen Quenching Behavior of Tris(4,7′-diphenyl-1,10′-phenanthroline) Ruthenium (II) Sequestered Within Sol-Gel-Derived Xerogel Films (2000)
    Springer
    Journal of sol gel science and technology 17 (2000), S. 71-82 
    Details
    ISSN: 1573-4846
    Keywords: fluorescence ; multidomain xerogels ; high-temperature processing ; fluorophore accessibility ; lifetimes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel processing methods offer novel pathways for tailoring glasses. Amongst the issues that have received the least attention are the effects of the curing temperature on the behavior and photophysics of a dopant molecule sequestered within a sol-gel-derived xerogel. Of particular interest to our group are the effects of processing variables on the ability of a dopant molecule, that is sequestered within a xerogel glass, to be accessed by an analyte and the distribution of the dopant sites within the xerogel. The thermal stability of the luminophore tris(4,7′-diphenyl-1,10′-phenanthroline) ruthenium (II) ([Ru(dpp)3]2+) provides a convenient way to address these issues and develop an understanding of how one might best exploit curing temperature to construct improved chemical sensors. This paper focuses on quantifying how the film curing temperature affects the spectroscopy and O2 quenching of ([Ru(dpp)3]2+) sequestered within sol-gel-derived xerogel thin films. Our quenching data on films once they have been cured demonstrate that there is a dramatic increase in the sensitivity of the ([Ru(dpp)3]2+) molecules to O2 quenching when the films have been cured at elevated temperatures. This arises primarily because there are two main types of ([Ru(dpp)3]2+) microenvironments within the glass and higher temperature curing leads to an increase in the bimolecular quenching rate between O2 and ([Ru(dpp)3]2+). This is accomplished as follows. Below a curing temperature of 100–150°C, ∼15% of the xerogel-doped ([Ru(dpp)3]2+) molecules are not accessed to any detectable degree by the O2 molecules during the ([Ru(dpp)3]2+) excited-state luminescence lifetime. However, as the xerogel is cured at or above 150°C, residual silanol-bound waters (or other impurities) dissociate from the xerogel and those ([Ru(dpp)3]2+) molecules that were initially inaccessible become accessible to O2. The dissociation of these water molecules, plus other events, also causes the originally inaccessible ([Ru(dpp)3]2+) population to ultimately exhibit a quenching rate that is greater than the fraction of initially accessible ([Ru(dpp)3]2+) molecules that were formed under ambient curing conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008765106291
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  • 9
    Electronic Resource
    Electronic Resource
    On the Origin of the Heterogeneous Emission from Pyrene Sequestered Within Tetramethylorthosilicate-Based Xerogels: A Decay-Associated Spectra and O2 Quenching Study (2000)
    Springer
    Journal of sol gel science and technology 17 (2000), S. 83-90 
    Details
    ISSN: 1573-4846
    Keywords: xerogels ; pyrene ; decay associated spectra ; oxygen quenching ; multiple domain types
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Steady-state and time-resolved fluorescence spectroscopy are used to determine the local microheterogeneity surrounding pyrene molecules sequestered within tetramethylorthosilicate-derived xerogels. After compensation for the intrinsic background emission from the xerogel, we find that the pyrene intensity decay kinetics are best described by a two-term rate law. This is consistent with the pyrene molecules distributing primarily into two microenvironments. Under ambient conditions, the individual pyrene microenvironments exhibit excited-state fluorescence lifetimes that differ by ∼100 ns. However, the pyrene I1 to I3 band ratios that are associated with each microenvironment are statistically equivalent to one another. These results show that the local dipolarity surrounding these pyrene microenvironments are similar, but the decay rates associated with each microenvironment are very different. The longer-lived pyrene species (Environment #1) constitutes ∼1/2 of the total fluorescence and it exhibits an O2 quenching sensitivity (Ksv1) of (5.19 ± 0.52 × 10−3 %O2 −1 and a bimolecular quenching constant (kq1) of (2.30 ± 0.23) × 104 %O2 −1 s−1. Environment #2, associated with the shorter-lived pyrene species, exhibits an O2 quenching sensitivity (Ksv2) of (2.31 ± 0.16) × 10−2 %O2 −1 and a bimolecular quenching constant (kq2) of (2.11 ± 0.23) × 105 %O2 −1 s−1. These results are interpreted as follows: Environment #1 consists of pyrene molecules sequestered within a relatively rigid siloxane network wherein non-radiative decay pathways are lessened, but these pyrene molecules are not quenched readily by O2. Environment #2 consists of pyrene molecules adsorbed onto surface silanols within the xerogel. These pyrene molecules are quenched by the silanols and they are simultaneously more accessible to O2 compared to Environment #1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008717207199
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  • 10
    Electronic Resource
    Electronic Resource
    Thermal decomposition and electrical conductivity of oxide cathode emission materials (2000)
    Springer
    Journal of materials science 11 (2000), S. 489-495 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Thermal decomposition and electrical conductivity of oxide cathode emission materials used for cathode ray tubes (CRTs) have been studied under different heat treatment conditions for commercial sprayed cathode systems based on barium-strontium carbonate precursors. Conversion of the carbonate precursor commenced at temperatures above approximately 700 K in vacuum, evidenced by increases in conductivity, however, the rate of the conversion reaction increased dramatically as the temperature was increased. The corresponding chemical and microstructural changes have also been investigated by thermo-gravimetric analysis (TGA) and scanning electron microscopy (SEM), with multiple decomposition stages identified corresponding to the conversion of the carbonate precursor and separate activation steps associated with the reaction of barium oxide with the Mg and Al activating agents in the nickel cathode substrate. © 2000 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008916501674
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