Paramagnet induced signal quenching in MAS-DNP experiments in frozen homogeneous solutions.

摘要: Abstract The effects of nuclear signal quenching induced by the presence a paramagnetic polarizing agent are documented for conditions used in magic angle spinning (MAS)–dynamic polarization (DNP) experiments on homogeneous solutions. In particular, we present detailed analysis three time constants: (1) longitudinal build-up constant TB 1H; (2) rotating frame relaxation T1ρ 1H and 13C (3) T2 13C, transverse laboratory frame. These times were measured during microwave irradiation at magnetic field 5 T (140 GHz) as function concentration four agents: TOTAPOL, 4-amino-TEMPO, trityl (OX063), Gd-DOTA compared to those obtained sample lacking doping. We also report EPR constants T1S T2S, DNP enhancements, e, parameter E, defined below, which measures sensitivity enhancement agents electron concentration. observe substantial intensity losses (paramagnetic quenching) with all due broadening mechanisms cross MAS. monoradical biradical TOTAPOL induce ∼40% 50% loss intensity. contrast there is little suppression static samples containing these species. Despite quenching, find that provide gains DNP, particular net optimal biradicals operate effect. discuss possibility much this can be regained development instrumentation methods perform decoupling.