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Proc Natl Acad Sci U S A. 2007 Oct 2;104(40):15705-10. Epub 2007 Sep 25.

Direct observation of ligand transfer and bond formation in cytochrome c oxidase by using mid-infrared chirped-pulse upconversion.

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  • 1Laboratoire d'Optique et Biosciences, Ecole Polytechnique, Centre National de la Recherche Scientifique and Institut National de la Santé et de la Recherche Médicale U696, 91128 Palaiseau, France.


We have implemented the recently demonstrated technique of chirped-pulse upconversion of midinfrared femtosecond pulses into the visible in a visible pump-midinfrared probe experiment for high-resolution, high-sensitivity measurements over a broad spectral range. We have succeeded in time-resolving the CO ligand transfer process from the heme Fe to the neighboring Cu(B) atom in the bimetallic active site of mammalian cytochrome c oxidase, which was known to proceed in <1 ps, using the full CO vibrational signature of Fe-CO bond breaking and Cu(B)-CO bond formation. Our differential transmission results show a delayed onset of the appearance of the Cu(B)-bound species (200 fs), followed by a 450-fs exponential rise. Trajectories calculated by using molecular-dynamics simulations with a Morse potential for the Cu(B)-C interaction display a similar behavior. Both experimental and calculated data strongly suggest a ballistic contribution to the transfer process.

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