title: Photochemically Induced Dynamic Nuclear Polarization Observed by Solid-State NMR in a Uniformly (13)C-Isotope-Labeled Photosynthetic Reaction Center.
abstract: A sample of solubilized and quinone-depleted reaction centers from the purple bacterium Rhodobacter (R.) sphaeroides wild type has been prepared entirely (13)C and (15)N isotope labeled at all positions of the protein as well as of the cofactors. In this sample, the occurrence of the solid-state photo-CIDNP (photochemically induced dynamic nuclear polarization) effect has been probed by (13)C solid-state magic-angle spinning NMR under illumination. Under continuous illumination, signal intensities are modified by the three-spin mixing (TSM) mechanism. Time-resolved illumination experiments reveal the occurrence of light-induced nuclear polarization on the time scale of hundreds of microseconds, initially dominated by the transient polarization of the singlet branch of the radical-pair mechanism. A first kinetic analysis shows that the lifetime of the polarization from the singlet branch, indicated by the enhanced absorptive intensities of the signals from aliphatic carbons, is significantly extended. Upon arrival of the polarization from the triplet decay branch, emissive polarization caused by the TSM mechanism is observed. Also, this arrival is significantly delayed. The decay of TSM polarization occurs in two steps, assigned to intra- and intermolecular spin diffusion.
authors.affiliation: Universität Leipzig , Institut für Analytische Chemie, Linnéstr. 3, D-04103 Leipzig, Germany.
authors.forename: Shubhajit
authors.initials: S
authors.lastname: Paul
authors.affiliation: EaStCHEM School of Chemistry, Biomedical Sciences Research Complex and Centre of Magnetic Resonance, University of St Andrews , St Andrews KY16 9ST, Scotland.
authors.forename: Bela E
authors.initials: BE
authors.lastname: Bode
authors.affiliation: Universität Leipzig , Institut für Analytische Chemie, Linnéstr. 3, D-04103 Leipzig, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Matysik
authors.affiliation: Universität Leipzig , Institut für Medizinische Physik und Biophysik, Härtelstr. 16, D-04107 Leipzig, Germany.|Gorlaeus Laboratoria, Leiden Institute of Chemistry , Einsteinweg 55, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Alia
mesh_terms: D066241:Carbon-13 Magnetic Resonance Spectroscopy; D055668:Photochemical Processes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000201:enzymology*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins