title: Ultrafast dynamics of the photo-excited hemes b and cnin the cytochrome b6f complex.
abstract: The dynamics of hemes b and cnwithin the cytochrome b6f complex are investigated by means of ultrafast broad-band transient absorption spectroscopy. On the one hand, the data reveal that, subsequent to visible light excitation, part of the b hemes undergoes pulse-limited photo-oxidation, with the liberated electron supposedly being transferred to one of the adjacent aromatic amino acids. Photo-oxidation is followed by charge recombination in about 8.2 ps. Subsequent to charge recombination, heme b is promoted to a vibrationally excited ground state that relaxes in about 4.6 ps. On the other hand, heme cnundergoes ultrafast ground state recovery in about 140 fs. Interestingly, the data also show that, in contrast to previous beliefs, Chl a is involved in the photochemistry of hemes. Indeed, subsequent to heme excitation, Chl a bleaches and recovers to its ground state in 90 fs and 650 fs, respectively. Chl a bleaching allegedly corresponds to the formation of a short lived Chl a anion. Beyond the previously suggested structural role, this study provides unique evidence that Chl a is directly involved in the photochemistry of the hemes.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA and Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
authors.forename: Rachna
authors.initials: R
authors.lastname: Agarwal
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Spectroscopie Ultrarapide (LSU), ISIC, Faculté des Sciences de Base and Lausanne Centre for Ultrafast Science (LACUS), Station 6, 1015 Lausanne, Switzerland. a.chauvet@sheffield.ac.uk and The University of Sheffield, Department of Chemistry, Dainton Building, Brook Hill, Sheffield S3 7HF, UK.
authors.forename: Adrien A P
authors.identifier: http://orcid.org/0000-0002-1649-0898
authors.initials: AA
authors.lastname: Chauvet
mesh_terms: D024322:Amino Acids, Aromatic / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D045346:Cytochrome b6f Complex / Q000737:chemistry*; D004583:Electrons; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry*; D008027:Light; D010084:Oxidation-Reduction; D010777:Photochemistry
chemical_list: D024322:Amino Acids, Aromatic; D002734:Chlorophyll; C031690:heme C; D006418:Heme; D045346:Cytochrome b6f Complex; D000077194:Chlorophyll A