Porphyrin to quinone electron transfer across a depsipeptide which forms an α-helical turn

David A. Williamson, Bruce E. Bowler

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17 Scopus citations


A porphyrin linked to a quinone via a three residue depsipeptide, L-proline-L-lactate-L-lactate has been used to investigate the effect of a protein folding interaction on electron transfer rates through a protein medium. Infrared analysis in the amide A (NH stretch region) demonstrates that the major conformation of the compound is an α-helical turn in CH2Cl2. A ROESY NMR experiment corroborates the presence of the α-helical turn through observation of a d(αN) (i,i + 3) through-space contact. Time correlated single photon counting fluorescence lifetime measurements on the porphyrin in the presence and absence of the acceptor quinone indicate that electron transfer is very efficient, k(et) = 5.6 ± 0.3 x 108 s-1, in this compound. Evaluation of the electronic coupling matrix element, H(ab), gives a value of 3.2 ± 0.8 cm-1, approximately 100-fold larger than the expected value of ~0.03 cm-1 for electron transfer along the depsipeptide backbone in the absence of any folding interactions. This result demonstrates that long-range non-covalent protein folding interactions can have profound effects on rates of electron transfer. (C) 2000 Elsevier Science S.A.

Original languageEnglish
Pages (from-to)47-55
Number of pages9
JournalInorganica Chimica Acta
Issue number1-2
StatePublished - 2000


Acknowledgment is made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society for support of this research. We also thank the Howard Hughes Medical Institute (HHMI) for major support to the NMR Center at the University of Colorado Health Sciences Center. We thank Tonny de Beer at the NMR Center for assistance with ROESY experiments. We also thank Mike Machczynski and Jay Winkler at the Beckman Institute’s Laser Resource Center (California Institute of Technology, Pasadena, CA) for their willingness to help with the TCSPC fluorescence lifetime studies. Finally, we thank Julanna Gilbert at the University of Denver for use of FT-IR instrumentation.

FundersFunder number
American Chemical Society


    • Electron transfer rates
    • Infrared analysis
    • Peptide hydrogen bonds
    • Porphyrin
    • Quinone
    • ROESY NMR experiment


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