title: Symmetry break of special pair: photochemically induced dynamic nuclear polarization NMR confirms control by nonaromatic substituents.
abstract: Despite the high structural symmetry of cofactor arrangement and protein environment, light-induced electron transfer in photosynthetic reaction centers (RCs) of the purple bacterium Rhodobacter sphaeroides runs selectively over one of the two branches of cofactors. The origin of this functional symmetry break has been debated for several decades. Recently, a crucial role of the substituents has been proposed by theoretical studies [Yamasaki, H.; Takano, Y.; Nakamura, H. J. Phys. Chem. B 2008, 112, 13923-13933]. Photo-CIDNP (photochemically induced dynamic nuclear polarization) MAS (magic angle spinning) NMR demonstrates that indeed the peripheral atoms show opposite electronic effects on both sides of the special pair. While the aromatic system of P(L) receives electron density from its periphery, the electron density of the aromatic ring of P(M) is decreased.
authors.affiliation: Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
authors.forename: Karthick Babu
authors.initials: KB
authors.lastname: Sai Sankar Gupta
authors.forename: A
authors.initials: A
authors.lastname: Alia
authors.forename: Huub J M
authors.initials: HJ
authors.lastname: de Groot
authors.forename: Jörg
authors.initials: J
authors.lastname: Matysik
mesh_terms: D008958:Models, Molecular; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D055668:Photochemical Processes; D012242:Rhodobacter sphaeroides / Q000737:chemistry*