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  • 1
    ISSN: 1435-1536
    Keywords: Circular dichroism ; gelatin ; sodium alkyl sulphates ; aqueousgelatinsolutions ; secondary structure ; pH ; temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The modification of the triple helical structure in aqueous gelatin solutions by changing pH and adding alkyl sulphates at 298 K and after rechilling the solution to 283 K was investigated by CD-measurement. At 298 K the triple helical content at the IEP of the gelatin has its maximum value. It is only weakly affected by adding sodium dodecyl sulphate (SDDS) at concentrations 〈10−4 M/dm3. The unfolding of the triple helix affected by pH and SDDS is reversible by rechilling the solution. The triple helical content of gelatin solutions decreases at SDDS concentrations higher than 10−4 M/dm3. In all cases the decrease of the amount of triple helical structure is connected with an increase of the cis-configuration in single chains and leads to chain reversals. At sufficiently high SDDS concentrationsβ-sheets are formed. These changes are thermally irreversible. Sodium decyl sulphate (SDS) has a more minor influence than SDDS except in the range of the c.m.c. of SDS. At sufficiently high SDS concentrations,β-turns appear.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1435-1536
    Keywords: Gelatin ; hexadecyl- and dodecyl-ammonium bromide ; circular dichroism ; gelatin triple helical structure ; influence of temperature ; pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The interaction between cationic surfactants (hexadecyl and dodecyl trimethyl ammonium bromide) and gelatin was characterized by measuring the circular dichroism. The interaction between the cationic surfactants and gelatin is weak in comparison to that of anionic surfactants. When the concentration of cationic surfactants is sufficiently low, refolding of the gelatin-strands to the triple helical structure by rechilling the solution from 298 K to 283 K is complete. The triple helical content of the solution is affected more strongly by the cationic surfactants in acidic solution than at pHs 7 or 10. The interaction depends on the apolar group of the surfactant and is found to be stronger for DTAB than for CTAB at 298 K. Coagulation of the hydrophobic gelatin-cationic surfactant complexes does not comprise that pan of gelatin which is able to refold the triple helical structure. Therefore, the gelatin-strands of lower molecular weights are thought to react favorably with the surfactant ions.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Limnology 1 (2000), S. 3-9 
    ISSN: 1439-863X
    Keywords: Key words Limnology ; Freshwater ecology ; Fresh water ; Microbial ecology ; Lakes ; Streams ; Biomanipulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The past development and evolution of limnology as a discipline has demonstrated that experimentally controlled disturbances of parts of aquatic ecosystems are essential for quantitative evaluation of causal mechanisms governing their operation. Correlative analyses and modeling only establish hypotheses, not causality, and allow only therapeutic management applications. Rather than constantly searching for differences, commonality must be sought. Among the large diversity of species, communities, and biogeochemical processes controlling growth and reproduction, commonality emerges at the levels of regulation of metabolism. Five areas of current and future limnological research are discussed in relation to greatest needs and promise to yield insights into material and energy flows in freshwater ecosystems and their effective management: (1) coupled metabolic mutualism in the physiological ecology of microbes (viruses, bacteria, fungi, and protists) and their biogeochemical, especially organic, couplings with the environment; (2) biochemical regulation of collective metabolism, recycling, and bioavailability of nutrients and growth regulators; (3) application of genetic and molecular techniques to addressing biogeochemical, evolutionary, and pollution remediation problems; (4) recognition that the metabolism within lakes and streams is dependent upon and regulated to a major extent by organic matter of the drainage basin and especially by the land-water interface biogeochemistry; and (5) recognition that food-web alterations ("biomanipulation") are short-term, expensive therapeutic tools that may minimize effects of eutrophication but will not solve or control eutrophication.
    Type of Medium: Electronic Resource
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