Equilibrium/nonequilibrium initial configurations in forward/reverse electron transfer within mixed-metal hemoglobin hybrids

Ami D. Patel, Judith M. Nocek, Brian M Hoffman*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


In a protein-protein electron transfer (ET) photocycle, the "forward" ET reaction is initiated with the excited complex, [3DA], in an equilibrium ensemble of configurations, the majority of which exhibit less than the maximal ET matrix element. In contrast, the charge-separated intermediate complex is formed in a nonequilibrium set of configurations with maximal ET matrix elements and would be expected to return to the ground state with the largest rate constant possible unless conformational interconversion first "breaks the connection" and the complex converts to less-reactive substates. According to this analysis, the forward and back ET reactions should show a differential response to viscosity, and the latter could even show an increased rate constant under conditions which suppress departure from the reactive configuration(s). We now report that the viscosity dependences of forward and back ET rate constants for the photocycle within the [α2(Zn),β2(Fe3+N3-)] mixed-metal hemoglobin hybrid at pH 7 show the anticipated behavior: kf decreases as viscosity increases, but, in sharp contrast, kb increases strongly.

Original languageEnglish (US)
Pages (from-to)16766-16767
Number of pages2
JournalJournal of the American Chemical Society
Issue number48
StatePublished - Dec 7 2005

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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