title: Coherent infrared emission from myoglobin crystals: an electric field measurement.
abstract: We introduce coherent infrared emission interferometry as a chi(2) vibrational spectroscopy technique and apply it to studying the initial dynamics upon photoactivation of myoglobin (Mb). By impulsive excitation (using 11-fs pulses) of a Mb crystal, vibrations that couple to the optical excitation are set in motion coherently. Because of the order in the crystal lattice the coherent oscillations of the different proteins in the crystal that are associated with charge motions give rise to a macroscopic burst of directional multi-teraHertz radiation. This radiation can be detected in a phase-sensitive way by heterodyning with a broad-band reference field. In this way both amplitude and phase of the different vibrations can be obtained. We detected radiation in the 1,000-1,500 cm(-1) frequency region, which contains modes sensitive to the structure of the heme macrocycle, as well as peripheral protein modes. Both in carbonmonoxy-Mb and aquomet-Mb we observed emission from six modes, which were assigned to heme vibrations. The phase factors of the modes contributing to the protein electric field show a remarkable consistency, taking on values that indicate that the dipoles are created "emitting" at t = 0, as one would expect for impulsively activated modes. The few deviations from this behavior in Mb-CO we propose are the result of these modes being sensitive to the photodissociation process and severely disrupted by it.
authors.affiliation: Laboratory for Optical Biosciences, INSERM U451, Centre National de la Recherche Scientifique Unité Mixte de Recherche 7645, Ecole Polytechnique-Ecole Nationale Supárievre de Techniques Avancáes ENSTA, 91128 Palaiseau Cedex, France.
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Groot
authors.forename: Marten H
authors.initials: MH
authors.lastname: Vos
authors.forename: Ilme
authors.initials: I
authors.lastname: Schlichting
authors.forename: Frank
authors.initials: F
authors.lastname: van Mourik
authors.forename: Manuel
authors.initials: M
authors.lastname: Joffre
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Lambry
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Martin
mesh_terms: D000818:Animals; D004563:Electrochemistry / Q000379:methods; D006736:Horses; D007368:Interferometry; D009206:Myocardium / Q000737:chemistry; D009211:Myoglobin / Q000737:chemistry* / Q000302:isolation & purification; D011487:Protein Conformation; D011489:Protein Denaturation; D013055:Spectrophotometry, Infrared / Q000379:methods
chemical_list: D009211:Myoglobin; C018013:carboxymyoglobin