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  • Articles  (40)
  • Chemistry  (32)
  • General Chemistry  (6)
  • Liquid chromatography  (4)
  • Chloroplast reproduction
  • Gonadotrops
  • Seismology
  • Symphytum
  • 2000-2004  (2)
  • 1980-1984  (22)
  • 1955-1959  (10)
  • 1940-1944  (6)
  • 1935-1939
  • 2000  (2)
  • 1983  (8)
  • 1982  (14)
  • 1959  (10)
  • 1943  (6)
Collection
  • Articles  (40)
Publisher
Years
  • 2000-2004  (2)
  • 1980-1984  (22)
  • 1955-1959  (10)
  • 1940-1944  (6)
  • 1935-1939
Year
  • 1
    ISSN: 1615-6110
    Keywords: Angiosperms ; Boraginaceae ; Symphytum ; Phytosterols ; triterpenoids ; chemotaxonomy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract From a comparison of phytosterol and triterpenoid patterns of severalSymphytum officinale cytotypes,S. asperum and their interspecific hybrids,S. ×uplandicum, which were obtained from thin layer chromatography and gaschromatography (also in combination with mass spectrometry), the hybrid character of the latter taxon is clearly shown. The specific value of the triterpenoid isobauerenol as a chemotaxonomical marker within this group is discussed in some detail.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 233 (1983), S. 377-388 
    ISSN: 1432-0878
    Keywords: Gonadotrops ; Gonadotropin secretion ; Steroids ; Brain-pituitary-gonadal axis ; Juvenile teleost
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In a cytophysiological study it was investigated whether in juvenile trout gonadal steroids stimulate the gonadotropic (GTH)-cells directly or indirectly via the brain. Pituitaries of donor animals were transplanted into the caudal musculature of testosterone-treated and non-testosterone-treated host fish. Testosterone treatment caused an increase in GTH-content in the in situ pituitaries and in the grafts. Accordingly, the gonadotrops displayed ultrastructural changes such as the appearance of well-developed Golgi systems and large globules. The stimulation of the morphological development of gonadotrops and of synthesis and storage of GTH in the allografted pituitaries indicates that testosterone affects the GTH-cells directly. In untreated juvenile trout the gonadotropin content of the pituitary and the gonadotropin concentration in the plasma vary with the time of year. This variation and the role of testosterone and gonadotropin-releasing hormone on the release of GTH are discussed.
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  • 3
    ISSN: 0365-9631
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 118 (1983), S. 71-74 
    ISSN: 1615-6102
    Keywords: Chloroplast reproduction ; Guard cells ; Nuclear DNA amount ; Nucleotype ; Regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Chloroplast numbers per guard cell have been determined for plant species for which the specific nuclear DNA amounts have been published by other authors. Regressions of chloroplast number on nuclear DNA amount have been calculated using species, genus, or family means, all adjusted to diploidy. All regressions are positive and significantly different from zero, showing that chloroplast number increases with increasing DNA amount. This result suggests the existence of a nucleotypic effect,i.e., an effect based on DNA amount alone, in addition to other effects.
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  • 5
    ISSN: 1573-5044
    Keywords: callus cultures ; cell suspensions ; regeneration ; pyrrolizidine alkaloids ; polyamines ; Symphytum ; Boraginaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Primary calluses were induced from various organs of Symphytum officinale L. (comfrey) plants on solid MS and B5 medium supplemented with plant growth regulators. The callus was further subcultured on B5 medium. Cell suspension cultures were derived from B5 grown calluses by transfer to liquid B5 medium. Calluses as well as cell suspension cultures could be induced to regenerate whole plants on solid MS medium. Plants regenerated from short term cultures were identical with plants from which cultures were initiated in morphology and chromosome number. Production of pyrrolizidine alkaloids ceased on prolonged subculturing of suspensions although polyamines, which might act as precursors, were still detectable. However, regenerated plants produced the original alkaloids.
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  • 6
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 7
    ISSN: 1612-1112
    Keywords: Liquid chromatography ; Chlorophenols in water ; Preconcentration ; Post-column photochemical dechlorination ; Electrochemical, UV and fluorescence detection ; Column switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A specific HPLC method has been developed for the trace analysis of lower chlorinated aromatic compounds. The method consists of an on-line preconcentration and a post-column reaction step. On-line preconcentration of mono- and dichlorophenols from aqueous samples has been performed using PRP1, a divinylbenzene-styrene copolymeric sorbent as packing material for both pre-and analytical column. Enrichment factors of over 300 were obtained compared to regular (100 μl) loop injections, even for the highly polar monochlorophenols. After reversed-phase separation, post-column photochemical dechlorination is carried out directly in the eluent stream, using a photochemical reactor. Upon dechlorination, fluorescent products are formed, which can be detected selectively. The resulting fluorescence signal shows a linear response to the quantity of solute present over 2 to 3 orders of magnitude (correlation coefficients: 0.990–0.98). For the mono- and dichlorophenols, the detection limit of the photoconversion method is in the lower nanogram range. The method is especially suitable for the analysis of complex matrices such as effluent water samples or biological fluids containing traces of the polar chloroaromatic compounds together with large amounts of other constituents, which interfere when using more general methods of detection like UV absorption. The potential of this technique for automation has been demonstrated by using a microprocessor-controlled column switching unit.
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  • 8
    ISSN: 1612-1112
    Keywords: Liquid chromatography ; Photochemical reaction detection ; Chemical post-column reduction ; Fluorimetric detection ; Air segmented flow systems ; Non-aqueous reversed-phase chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new photochemical reaction method for the on-line fluorimetric detection of natural vitamin K homologs was developed. In addition to its high sensitivity, the method features an interesting selectivity for the determination of these compounds in a complex matrix such as human serum. The formation of different photolysis products as a function of reaction conditions, and the optimalisation of a segmented flow reaction system will be discussed. The results indicate that the method is 4 times more sensitive than UV detection, and at least as selective as fluorescence detection after post-column chemical reduction.
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  • 9
    ISSN: 1612-1112
    Keywords: Liquid chromatography ; Nucleobases ; Nucleosides ; Silica gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention behaviour of nucleobases and nucleosides on unmodified silica with dichloromethane-methanol-water mixtures has been systematically investigated. The degree and order of retention can be varied over a wide range by changing the pH, the type and concentration of the acidic additives and by the methanol and water content of the mobile phase. The retention process cannot be considered as simple adsorption but rather as a very complex mixed distribution process of adsorption and absorption including the involvement of ion-pair formation. Further data on the effect of the type of silica (source of supply) on retention behaviour, column efficiency and column reproducibility are reported. The practical application of unmodified silica for the separation of nucleobases and nucleosides is demonstrated by the analysis of a hydrolysate of calf thymus DNA.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 16 (1982), S. 237-241 
    ISSN: 1612-1112
    Keywords: Liquid chromatography ; Electron capture detection ; Improved interface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An improved interface for the coupling of a liquid chromatograph (LC) and an electron-capture detector (ECD) allows the use of the LC-ECD combination for the determination of various types of chlorinated aromatic compounds. The addition of up to 6% of dioxan to the hexane used as mobile phase can be tolerated without serious deterioration of detector performance. Derivatization of polar compounds such as anilines, phenylurea herbicides, chlorophenols and hydroxylated polychlorobiphenyls with fluorine-and non-fluorine-containing acid anhydrides is a useful tool to extend the application range of LC-ECD. As an example, the analysis of a spiked soil sample is discussed.
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