22 Elementary Processes in Peptides

Accession Number
    RK018-0029

Document Delivery
    The Genuine Article Number: RK018

Authors
    Weinkauf R., Schanen P., Yang D., Sonkara S., Schlag EW .

Title
    ELEMENTARY PROCESSES IN PEPTIDES - ELECTRON MOBILITY AND 
    DISSOCIATIONS IN PEPTIDE CATIONS IN    THE GAS PHASE

Source
    Journal of Physical Chemistry. 99(28):11255-11265, 1995 Jul 13.

ISSN
    0022-3654

KeyWords Plus
    Pulsed laser desorption. Ionization mass-spectrometry. Resonant 2-photon
    ionization. Supersonic molecular-beams. Charge-transfer. Exciplex formation.
    Bichromophoric molecules. Solvent polarity. Jet. Spectroscopy.

Abstract
    Neutral peptides of natural amino acids of the type (X)(n)-Y (n = 1,2,3) are
    prepared in the gas phase by laser desorption and supersonic cooling. Local
    ionization is performed by resonant laser excitation in aromatic amino acids
    (Y) located at the C-terminal end. In a one-color experiment, subsequent UV
    photofragmentation of the cation is shown to directly reflect the prior charge
    migration in these large molecules. Peptides are engineered, which show
    either fragment ions originating from the chromophore or from the opposite
    N-terminal side (X). The results show that by changing local ionization
    energies and thus absolute positions of ionic dissociation energies, one has
    complete control over different paths of chemical reactivity. The length
    dependence of the process shows, that charge mobility seems to be not the
    bottleneck for dissociation pathways at high internal energies: charge
    transfer over more than 10 sigma-bonds is shown. When we apply a local
    picture and estimate local ionization potentials, we find, for the peptides used
    here, that after localized ionization, positive charge is statically localized at
    the initial prepared site. In a two-color experiment (UV + VIS) we observe
    indications that in the photoexcited tripeptide cation Leu-Leu-Tyr charge
    transfer can occur at internal energies of about 2.2 eV, an energy at which no
    dissociation occurs. We interpret the process in terms of direct
    photoexcitation into a charge transfer (CT) band or by a photoexcitation to a
    localized state followed by nonradiative relaxation to a CT state. For the
    charge-transfer process we propose a through bond HOMO electron transfer
    (hole transfer) as the relevant mechanim. Consequences of our findings for
    charge migration and fragmentation processes in peptides are discussed.
    [References: 68]

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