title: Direct observation of subpicosecond vibrational dynamics in photoexcited myoglobin.
abstract: Determining the initial pathway for ultrafast energy redistribution within biomolecules is a challenge, and haem proteins, for which energy can be deposited locally in the haem moiety using short light pulses, are suitable model systems to address this issue. However, data acquired using existing experimental techniques that fail to combine sufficient structural sensitivity with adequate time resolution have resulted in alternative hypotheses concerning the interplay between energy flow among highly excited vibrational levels and potential concomitant electronic processes. By developing a femtosecond-stimulated Raman set-up, endowed with the necessary tunability to take advantage of different resonance conditions, here we visualize the temporal evolution of energy redistribution over different vibrational modes in myoglobin. We establish that the vibrational energy initially stored in the highly excited Franck-Condon manifold is transferred with different timescales into low- and high-frequency modes, prior to slow dissipation through the protein. These findings demonstrate that a newly proposed mechanism involving the population dynamics of specific vibrational modes settles the controversy on the existence of transient electronic intermediates.
authors.affiliation: Dipartimento di Fisica, Università di Roma, La Sapienza, I-00185 Roma, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Ferrante
authors.affiliation: Dipartimento di Fisica, Università di Roma, La Sapienza, I-00185 Roma, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Pontecorvo
authors.affiliation: Istituto di Fotonica e Nanotecnologie (IFN-CNR), Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milano, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Cerullo
authors.affiliation: LOB, Ecole Polytechnique, CNRS, INSERM, Université Paris-Saclay, 91128 Palaiseau Cedex, France.
authors.forename: M H
authors.initials: MH
authors.lastname: Vos
authors.affiliation: Dipartimento di Fisica, Università di Roma, La Sapienza, I-00185 Roma, Italy.|Center for Life Nano Science@Sapienza, Istituto Italiano di Tecnologia, Viale Regina Elena 291, 00161 Rome, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Scopigno
mesh_terms: D006418:Heme / Q000737:chemistry / Q000378:metabolism; D008027:Light; D009211:Myoglobin / Q000737:chemistry*; D010782:Photolysis; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D013997:Time Factors; D014732:Vibration
chemical_list: D009211:Myoglobin; C018013:carboxymyoglobin; C055547:deoxymyoglobin; D006418:Heme