title: Spectral editing through laser-flash excitation in two-dimensional photo-CIDNP MAS NMR experiments.
abstract: In solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) MAS NMR experiments, strong signal enhancement is observed from molecules forming a spin-correlated radical pair in a rigid matrix. Two-dimensional (13)C-(13)C dipolar-assisted rotational resonance (DARR) photo-CIDNP MAS NMR experiments have been applied to obtain exact chemical shift assignments from those cofactors. Under continuous illumination, the signals are enhanced via three-spin mixing (TSM) and differential decay (DD) and their intensity corresponds to the electron spin density in pz orbitals. In multiple-(13)C labelled samples, spin diffusion leads to propagation of signal enhancement to all (13)C spins. Under steady-state conditions, direct signal assignment is possible due to the uniform signal intensity. The original intensities, however, are inaccessible and the information of the local electron spin density is lost. Upon laser-flash illumination, the signal is enhanced via the classical radical pair mechanism (RPM). The obtained intensities are related to isotropic hyperfine interactions aiso and both enhanced absorptive and emissive lines can be observed due to differences in the sign of the local isotropic hyperfine interaction. Exploiting the mechanism of the polarization, selectivity can be increased by the novel time-resolved two-dimensional dipolar-assisted rotational resonance (DARR) MAS NMR experiment which simplifies the signal assignment compared to complex spectra of the same RCs obtained by continuous illumination. Here we present two-dimensional time-resolved photo-CIDNP MAS NMR experiments providing both directly: signal assignment and spectral editing by sign and strength of aiso. Hence, this experiment provides a direct key to the electronic structure of the correlated radical pair.
authors: Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
authors: Karthick Babu
authors: KB
authors: Sai Sankar Gupta
authors: Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands; Francis Bitter Magnet Laboratory, Albany Street 150, NW14, Cambridge, MA 02139, USA.
authors: Eugenio
authors: E
authors: Daviso
authors: ETH Zürich, Physical Chemistry, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
authors: Gunnar
authors: G
authors: Jeschke
authors: Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands; Institut für Analytische Chemie, Universität Leipzig, Linnéstr. 3, 04103 Leipzig, Germany.
authors: A
authors: A
authors: Alia
authors: ETH Zürich, Physical Chemistry, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
authors: Matthias
authors: M
authors: Ernst
authors: Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands; Institut für Analytische Chemie, Universität Leipzig, Linnéstr. 3, 04103 Leipzig, Germany. Electronic address: joerg.matysik@uni-leipzig.de.
authors: Jörg
authors: J
authors: Matysik
mesh_terms: D000465:Algorithms; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010777:Photochemistry / Q000379:methods*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000528:radiation effects; D011829:Radiation Dosage; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins
keywords: DARR; Hyperfine interaction; MAS NMR; Photo-CIDNP; Spectral editing; laser excitation