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  • Key words Paradigm  (1)
  • Photochemical reactions of biomolecules biochemical reaction mechanisms and kinetics, model reactions  (1)
  • Polymer and Materials Science  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Vectorial photoinduced electron transfer in phospholipid vesicles and LB bilayers (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 1471-1477 
    Details
    ISSN: 0392-6737
    Keywords: Photochemical reactions of biomolecules biochemical reaction mechanisms and kinetics, model reactions ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Photoinduced electron transfer (PET) was studied in phospholipid vesicles and in Langmuir-Blodgett bilayers in the attempt to produce a model for electron transfer processes in biological media. Spatial organization of the reaction centers in lipid membranes needs to be controlled in order to provide high efficiency of light-to-chemical energy conversion. We designed a phospholipid system where the donor is localized in the inner bilayer whereas the acceptor is at the polar groups-water interface. We used dipalmitoylphosphatidic acid vesicles containing low molar fractions of dipalmitoylphosphatidylcholine with pyrene (donor) bound to one of the alkyl chains. Methylviologen (acceptor) was added to the external aqueous phase; upon photoexcitation of the donor we observed the electron transfer to take place in a unidirectional manner from the inside of the bilayer to the interface. Information about the location of the donor was obtained studying the photophysical properties of the pyrene chromophore in vesicles and in LB layers. The photoinduced electron transfer reaction was evidenced by quenching of pyrene fluorescence in the presence of increasing concentrations of acceptor, the process was studied both with steady-state and time-resolved fluorescence emission. Fluorescence intensity was found to decrease with increasing concentration of methylviologen, similar results were obtained for vesicles and LB layers of analog composition immersed in a methylviologen solution. Lifetimes of the excited species were found to be of the same order of magnitude in vesicle and LB-layer systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02462031
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  • 2
    Electronic Resource
    Electronic Resource
    Paradigms, supermolecules, electron transfer and chemistry at a distance. What's the problem? The science or the paradigm? (1998)
    Springer
    JBIC 3 (1998), S. 201-209 
    Details
    ISSN: 1432-1327
    Keywords: Key words Paradigm ; Deoxyribonucleic acid ; Electron transfer ; Chemistry at a distance ; Molecular wire
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: It is typical of the present time, that two practically unknown chemists, one from a veterinary college and the other from an agricultural institute, pass judgement on the loftiest problems of Chemistry, those which will probably never be solved, particularly the question of the position of atoms in space, and they undertake such a paradigm with an impudence and assurance that absolutely astonish the true scientist H. Kolbe [1] New paradigms and new truths in science are not usually adopted because opponents are eventually convinced of their persuasive character, but, more often, because opponents gradually die; the new paradigms are readily adopted by the new generation of students as the laws of nature, just as the dead opponents accepted the old paradigm M. Planck [2]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050222
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  • 3
    Electronic Resource
    Electronic Resource
    Polyelectrolyte effects on the quenching of pyrene fluorescence in solutions of a pyrene substituted poly(acrylic acid) (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 259-269 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quenching of pyrene fluorescence by nitromethane, Tl+, Cu2+, I-, and 4-dimethylaminopyridine (DMAP) in aqueous solutions of a pyrene substituted poly(acrylic acid) (1) was influenced by the “polyelectrolyte effect” of 1. The efficiency of quenching in solutions of 1 was measured in terms of the Stern-Volmer constants for dynamic and static quenching which were obtained from comparison of the intensity and lifetime of pyrene fluorescence in solutions of 1 and a monomer model compound. The efficiency of quenching in solutions of 1 was always greater at high pH (9) in comparison to that at low pH (4). The ionization of carboxylic groups in 1 caused an expansion of the polymer mainchain and concomitant exposure of the pyrene molecules to the aqueous phase and quencher. The polyanion domain of 1 favored the condensation of cationic quenchers and could account for very efficient quenching in case of Cu2+ and Tl+. A very efficient quenching of pyrene fluorescence in solutions of 1 by DMAP at high pH was attributed to the hydrophobic interactions of DMAP and pyrene moiety. The iodide ions were less efficient quenchers of pyrene fluorescence due to electrostatic repulsion from the polyanion. The efficiency of quenching by nitromethane was not significantly affected by ionization of the carboxylic groups in 1.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080250123
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