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30 Energetics of Photoinduced Electron...

Publication: Energetics of Photoinduced Electron Transfer in the IndoleO2 Cluster in Gas Phase: Possible Consequences for Photoexcited Tryptophan in Solution


Accession Number

    YG526-0010

Document Delivery
    The Genuine Article Number: YG526

Authors
    Weinkauf R., Schiedt J .

Title
    ENERGETICS OF PHOTOINDUCED ELECTRON TRANSFER IN THE INDOLE-
    CENTER-DOT-O-2 CLUSTER IN GAS PHASE - POSSIBLE CONSEQUENCES FOR
    PHOTOEXCITED TRYPTOPHAN IN SOLUTION

Source
    Photochemistry & Photobiology. 66(5):569-575, 1997 Nov.

ISSN
    0031-8655

KeyWords Plus
   Room-temperature. Aqueous-solution. Amino-acids. Fluorescence. Proteins.
   State. Phosphorescence. Photoionization. Indole. Spectroscopy.

Abstract
    A direct process for an activationless electron transfer from photoexcited
    tryptophan to molecular oxygen is proposed. By photodetachment of
    mass-selected indole . O-2(-) clusters in gas phase a neutral indole(+). O-2(-)
    charge-separated exciplex state is found at 2.25 +/- 0.2 eV above the neutral
    ground state. By theory also, the existence of an excited charge separated
    state at 3.05 +/- 0.2 eV is postulated. In gas phase both charge-separated
    cluster states are energetically below the first singlet states L-1(b) and L-1(a)
    and the lower even below the first triplet state T-1 of indole, In gas-phase
    clusters these energetics imply a very efficient quenching of photoexcited
    indole by fast electron transfer to oxygen. We discuss a similar mechanism for
    tryptophan . O-2 in aqueous environment and find it without activation barrier
    and presumably extremely fast. In the collisional tryptophan*O-2 complex the
    efficiency and the time scale of the charge transfer process should be mostly
    solvent independent, In polar solvent a complete charge separation and free
    superoxide formation are expected. We correlate this model with previous
    fluorescence and phosphorescence quenching data of excited tryptophan by
    O-2 and propose electron transfer to be the relevant process. [References:
    41]

Language
    English

Publication Type
    Article

CC Categories
    Biochemistry & biophysics.

Subset
    Current Contents/Life Sciences

Institution
   Reprint available from:
   Weinkauf R.
   HEINRICH-HEINE-UNIVERSITAET DUESSELDORF
   INST PHYSICAL CHEMISTRY & ELECTROCHEMISTRY I
   40204 DUESSELDORF
   GERMANY

 

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