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  • PACS. 71.45.Lr Charge-density-wave systems - 72.15.Gd Galvanomagnetic and other magnetotransport effects  (2)
  • pH  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    The modification of the triple helical structure of gelatin in aqueous solution 3. The influence of cationic surfactants (1989)
    Springer
    Colloid & polymer science 267 (1989), S. 429-433 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01410188
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  • 2
    Electronic Resource
    Electronic Resource
    Charge-density-wave instabilities and quantum transport in the monophosphate tungsten bronzes with m = 5 alternate structure (2000)
    Springer
    The European physical journal 17 (2000), S. 215-226 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 71.45.Lr Charge-density-wave systems - 72.15.Gd Galvanomagnetic and other magnetotransport effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Resistivity, thermoelectric power and magnetotransport measurements have been performed on single crystals of the quasi two-dimensional monophosphate tungsten bronzes (PO2)4(WO3)2m for m =5 with alternate structure, between 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density instability (CDW) at 160 K and a possible second one at 30 K. Large positive magnetoresistance in the CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen oscillations detected at low temperatures are attributed to the existence of small electron and hole pockets left by the CDW gap openings. Angular dependent magnetoresistance oscillations (AMRO) have been found at temperatures below 30 K. The results are discussed in terms of a weakly corrugated cylindrical Fermi surface. They are shown to be consistent with a change of the Fermi surface below 30 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070135
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic instabilities in the quasi-two-dimensional conducting monophosphate tungsten bronzes K P W O ( ) (2000)
    Springer
    The European physical journal 16 (2000), S. 593-600 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 71.45.Lr Charge-density-wave systems - 72.15.Gd Galvanomagnetic and other magnetotransport effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The monophosphate tungsten bronzes KxP4W8O32 are quasi-two-dimensional conductors. The parent compound P4W8O32 shows two charge density wave instabilities (CDW). The layered structure of the doped compounds contains pseudo hexagonal tunnels stabilised by the insertion of potassium for 0.75〈 x 〈2. In order to study the role of the band filling in the CDW instabilities, we have performed resistivity, magnetoresistance, Hall effect, thermopower and specific heat measurements on the doped compounds with 0.8〈 x 〈1.94. Anomalies at a temperature depending on x appear on all the transport properties. From transport data, we have obtained a phase diagram which shows surprisingly a maximum at 170 K for x =1.3. In the whole range of temperature studied (4.2 K-300 K), the transport properties of KxP4W8O32 show a change for . The diagram is discussed in term of non-monotonous behaviour for the density of states versus the energy and in relation to previous X-ray studies. The transitions in KxP4W8O32 do not seem to be conventional Peierls instabilities in contrast with those observed in pure P4W8O32.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070177
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  • 4
    Electronic Resource
    Electronic Resource
    The modification of the triple helical structure of gelatin in aqueous solution I. The influence of anionic surfactants, pH-value, and temperature (1988)
    Springer
    Colloid & polymer science 266 (1988), S. 1061-1067 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01428818
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