23 Highly Efficient Charge Transfer in...

Accession Number
    VU825-0040

Document Delivery
    The Genuine Article Number: VU825

Authors
    Weinkauf R., Schanen P., Metsala A., Schlag EW., Burgle M., Kessler H .

Title
    HIGHLY EFFICIENT CHARGE TRANSFER IN PEPTIDE CATIONS IN THE GAS
    PHASE-THRESHOLD EFFECTS AND MECHANISM

Source
    Journal of Physical Chemistry. 100(47):18567-18585, 1996 Nov 21.

ISSN
    0022-3654

KeyWords Plus
    Range electron-transfer. Multiphoton dissociation spectra. Molecular ion
    spectroscopy. Long-range. Energy-transfer. Supersonic jet. Benzene cation.
    Radiationless transitions. Photoelectron-spectra. Exciplex formation.

Abstract
    We present new experimental data demonstrating specific, photoactivated
    positive charge migration in isolated peptide radical cations. The effect
    exhibits a threshold behavior, which we can directly correlate with energetics
    of local electronic states. A new very efficient mechanism for charge transfer
    in cations is proposed that involves an extended coulomb state (EC) of
    shakeup character. Our investigations are performed on laser-desorbed,
    cooled, neutral peptides in the gas phase. Charge localization in the peptide
    is achieved by resonant UV two-photon ionization at an aromatic
    chromophore. Charge flow in the cations can be activated by absorption of a
    first visible (VIS) photon. Presence of charge in the aromatic chromophore is
    probed by resonant absorption of a second VIS photon and monitored by
    dissociation. While this charge detection is found to work in isolated,
    positively charged chromophores or amino acids, it is efficiently quenched in
    some peptides. We explain this by photoactivated charge transfer and charge
    storage in nonaromatic groups of the peptides. At threshold this process is
    found to be strongly dependent on amino acid substitution even far away
    from the site of photoactivation. For analysis we first set up a local molecular
    orbital model for peptide cations and subsequently obtain a landscape of
    local electronic cation states formed by local hole and low-lying extended
    coulomb states. Charge transfer is found to be a through-bond mechanism
    involving energetically accessible electronic states along the path of charge
    flow. Charge transfer between hole states is mediated with very high
    efficiency through saturated carbon bridges by extended coulomb states. This
    new mechanism seems to be generally applicable to large extended
    molecular radical cations. Only barriers of the size of a full length of a certain
    defined
    amino acid are found to block charge transfer. The model qualitatively
    accounts for the order of the rates of the processes involved. [References:
    99]

Language
    English

Publication Type
    Article

CC Categories
    Physical chemistry/chemical physics.

Subset
    Current Contents/Physical, Chemical & Earth Sciences

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