title: Can metal ion complexes be used as polarizing agents for solution DNP? A theoretical discussion.
abstract: Dynamic nuclear polarization (DNP) can be used to dramatically increase the NMR signal intensities in solutions and solids. DNP is usually performed using nitroxide radicals as polarizing agents, characterized by sharp EPR lines, fast rotation, fast diffusion, and favorable distribution of the unpaired electron. These features make the nitroxide radicals ideally suited for solution DNP. Here, we report some theoretical considerations on the different behavior of some inorganic compounds with respect to nitroxide radicals. The relaxation profiles of slow relaxing paramagnetic metal aqua ions [copper(II), manganese(II), gadolinium(III) and oxovanadium(IV)] and complexes have been re-analyzed according to the standard theory for dipolar and contact relaxation, in order to estimate the coupling factor responsible for the maximum DNP enhancement that can be achieved in solution and its dependence on field, temperature and relative importance of outer-sphere versus inner-sphere relaxation.
authors.affiliation: CERM, University of Florence, Via Luigi Sacconi 6, 50019, Sesto Fiorentino, Italy, luchinat@cerm.unifi.it.
authors.forename: Claudio
authors.initials: C
authors.lastname: Luchinat
authors.forename: Giacomo
authors.initials: G
authors.lastname: Parigi
authors.forename: Enrico
authors.initials: E
authors.lastname: Ravera
mesh_terms: D000465:Algorithms; D056831:Coordination Complexes / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D008962:Models, Theoretical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D012996:Solutions; D013816:Thermodynamics
chemical_list: D056831:Coordination Complexes; D007477:Ions; D008670:Metals; D012996:Solutions