Hannover 2013 – scientific programme

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MO: Fachverband Molekülphysik

MO 21: Femtosecond Spectroscopy V

MO 21.6: Talk

Thursday, March 21, 2013, 12:15–12:30, F 102

Transient spin states in the ultrafast relaxation of met-Myoglobin — •Cristina Consani^1,2, Olivier Bräm¹, Gerald Auböck¹, Frank van Mourik¹, and Majed Chergui¹ — ¹Laboratory of Ultrafast Spectroscopy, École Polytechnique Fédérale de Lausanne (EPFL), Switzerland — ²currently at: LS Physikalische Chemie I, IPTC Universität Würzburg, Germany

Myoglobin (Mb) is a small protein consisting of a single polypeptide chain and an iron porphyrin (haem), which is its active site. The central Fe can be found in ferrous (Fe(II)) or ferric (Fe(III)) redox states and bind a variety of small molecules, among them water (met Mb). Despite being one of the most studied proteins, the early haem relaxation pathways following photo-excitation are still subject to controversies. During the last decade, similarities among the ultrafast (UF) transients of different ligated forms of Mb lead to the idea that the haem relaxation is dominated by cooling and is independent of the Fe redox state, of the axial ligand, and of its eventual photo-induced detachment.

Here we present the successful combination of broadband UF fluorescence and transient absorption experiments with a target analysis, which revealed a branching in the ultrafast relaxation of the haem. A significant fraction of the excited state population (about 40%) is found to relax through a cascade pathway involving two transient states, which we assign to electronically excited configurations of the iron characterized by different spin states. The potential of this approach for the study of porphyrin based systems will also be discussed.