title: Overhauser DNP with 15N labelled Frémy's salt at 0.35 Tesla.
abstract: The effectiveness of dynamic nuclear polarization (DNP) as a tool to enhance the sensitivity of liquid state NMR critically depends on the choice of the optimal polarizer molecule. In this study the performance of (15)N labelled Frémy's salt as a polarizing agent in Overhauser DNP is investigated in detail at X-band (0.35 T, 9.7 GHz EPR, 15 MHz (1)H NMR) and compared to that of TEMPONE-D,(15)N employed in previous studies. Both radicals provide similar maximum enhancements of the solvent water protons under similar conditions but a different saturation behaviour. The factors determining the enhancement and effective saturation were measured independently by EPR, ELDOR and NMRD and are shown to fulfil the Overhauser equation. In particular, following the theory of EPR saturation we provide analytical solutions for the dependence of the enhancement on the microwave field strength in terms of saturation transfer between two coupled hyperfine lines undergoing spin exchange. The negative charge of the radical in Frémy's salt solutions can explain the peculiar properties of this polarizing agent and indicates different suitable application areas for the two types of nitroxide radicals.
authors: Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors: Maria-Teresa
authors: MT
authors: Türke
authors: Giacomo
authors: G
authors: Parigi
authors: Claudio
authors: C
authors: Luchinat
authors: Marina
authors: M
authors: Bennati
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D008962:Models, Theoretical; D009587:Nitrogen Isotopes / Q000737:chemistry; D009603:Nitroso Compounds / Q000737:chemistry*; D011522:Protons; D014867:Water / Q000737:chemistry
chemical_list: D009587:Nitrogen Isotopes; D009603:Nitroso Compounds; D011522:Protons; D014867:Water; C001259:Fremy's salt