Time-resolved Raman spectroscopy with subpicosecond resolution: vibrational cooling and delocalization of strain energy in photodissociated (carbonmonoxy)hemoglobin |
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Authors: | J W Petrich J L Martin D Houde C Poyart A Orszag |
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Affiliation: | Laboratoire d'Optique Appliquée, Ecole Polytechnique, ENSTA, INSERM U275, Palaiseau, France. |
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Abstract: | A Raman spectrometer that provides both subpicosecond resolution and independent, tunable pump and probe pulses is described. The spectrometer is employed to obtain time-resolved spectra of (carbonmonoxy)hemoglobin (HbCO) at times from 0.2 to 95 ps subsequent to ligand photodissociation. The spectra are interpreted in terms of a vibrationally hot heme that cools substantially in 10 ps. Concomitant with the proposed vibrational cooling is a slower relaxation, which we suggest results from a protein response to heme doming induced by ligand detachment. Results and interpretations are discussed in the context of current models of the heme photophysics and of hemoglobin reactivity. |
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