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

David A. Williamson, Bruce E. Bowler

Research output: Contribution to journalArticlepeer-review


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


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


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