title: Dynamics of the Special Pair of Chlorophylls of Photosystem II.
abstract: Cholophylls are at the basis of the photosynthetic energy conversion mechanisms in algae, plants, and cyanobacteria. In photosystem II, the photoproduced electrons leave a special pair of chlorophylls (namely, P(D1) and P(D2)) that becomes cationic. This oxidizing pair [P(D1),P(D2)](+), in turn, triggers a cascade of oxidative events, eventually leading to water splitting and oxygen evolution. In the present work, using quantum mechanics/molecular mechanics calculations, we investigate the electronic structure and the dynamics of the P(D1)P(D2) special pair in both its oxidized and reduced states. In agreement with previously reported static calculations, the symmetry between the two chlorophylls was found to be broken, the positive charge being preferentially located on P(D1). Nevertheless, this study reveals for the first time that large charge fluctuations occur along dynamics, temporarily inverting the charge preference for the two branches. Finally, a vibrational analysis pinpointed that such charge fluctuations are strongly coupled to specific modes of the special pair.
authors.affiliation: University of L'Aquila , 67100 L'Aquila, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Narzi
authors.affiliation: University of L'Aquila , 67100 L'Aquila, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Bovi
authors.affiliation: La Sapienza - University of Rome , 00185 Roma, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: De Gaetano
authors.affiliation: University of L'Aquila , 67100 L'Aquila, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Guidoni
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry*
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll