title: Strategy for Enhancement of (13)C-Photo-CIDNP NMR Spectra by Exploiting Fractional (13)C-Labeling of Tryptophan.
abstract: The photo-CIDNP effect has proven to be useful to strongly enhance NMR signals of photochemically active proteins simply by irradiation with light. The evolving characteristic patterns of enhanced absorptive and emissive NMR lines can be exploited to elucidate the photochemistry and photophysics of light-driven protein reactions. In particular, by the assignment of (13)C NMR resonances, redox-active amino acids may be identified and thereby electron-transfer pathways unraveled, in favorable cases, even with (13)C at natural abundance. If signal enhancement is weak, uniform (13)C isotope labeling is traditionally applied to increase the signal strength of protein (13)C NMR. However, this typically leads to cross relaxation, which transfers light-induced nuclear-spin polarization to adjacent (13)C nuclei, thereby preventing an unambiguous analysis of the photo-CIDNP effect. In this contribution, two isotope labeling strategies are presented; one leads to specific but ubiquitous (13)C labeling in tryptophan, and the other is based on fractional isotope labeling affording sets of isotopologs with low probability of next-neighbor isotope accumulation within individual tryptophan molecules. Consequently, cross relaxation is largely avoided while the signal enhancement by (13)C enrichment is preserved. This results in significantly simplified polarization patterns that are easier to analyze with respect to the generation of light-generated nuclear-spin polarization.
authors.affiliation: Technische Universität München , Lehrstuhl für Biochemie, Lichtenbergstr. 4, 85748 Garching, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eisenreich
authors.affiliation: Technische Universität München , Lehrstuhl für Biochemie, Lichtenbergstr. 4, 85748 Garching, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Joshi
authors.affiliation: Universität Hamburg , Institut für Lebensmittelchemie, Bundesstr. 45, 20146 Hamburg, Germany.
authors.forename: Boris
authors.initials: B
authors.lastname: Illarionov
authors.affiliation: Albert-Ludwigs-Universität Freiburg , Institut für Physikalische Chemie, Albertstr. 21, 79104 Freiburg, Germany.
authors.forename: Sylwia
authors.initials: S
authors.lastname: Kacprzak
authors.affiliation: Albert-Ludwigs-Universität Freiburg , Institut für Physikalische Chemie, Albertstr. 21, 79104 Freiburg, Germany.
authors.forename: Michail
authors.initials: M
authors.lastname: Lukaschek
authors.affiliation: Albert-Ludwigs-Universität Freiburg , Institut für Physikalische Chemie, Albertstr. 21, 79104 Freiburg, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Kothe
authors.affiliation: Technische Universität Berlin , Institut für Chemie, Müller-Breslau-Str. 10, 10623 Berlin, Germany.
authors.forename: Nediljko
authors.initials: N
authors.lastname: Budisa
authors.affiliation: Universität Hamburg , Institut für Lebensmittelchemie, Bundesstr. 45, 20146 Hamburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Fischer
authors.affiliation: Technische Universität München , Lehrstuhl für Biochemie, Lichtenbergstr. 4, 85748 Garching, Germany.
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.affiliation: Albert-Ludwigs-Universität Freiburg , Institut für Physikalische Chemie, Albertstr. 21, 79104 Freiburg, Germany.|Freiburg Institute for Advanced Studies (FRIAS) , Albertstr. 19, 79104 Freiburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
mesh_terms: D018554:Avena / Q000166:cytology; D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D055668:Photochemical Processes; D017785:Photons; D011789:Quantum Theory; D014364:Tryptophan / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D002247:Carbon Isotopes; D014364:Tryptophan