Polarizing Agents and Mechanisms for High-Field Dynamic Nuclear Polarization of Frozen Dielectric Solids

摘要: This article provides an overview of polarizing mechanisms involved in high-frequency dynamic nuclear polarization (DNP) frozen biological samples at temperatures maintained using liquid nitrogen, compatible with contemporary magic-angle spinning (MAS) magnetic resonance (NMR). Typical DNP experiments require unpaired electrons that are usually exogenous via paramagnetic doping agents. Thus, the resulting mechanism depends on electron and spin interactions induced by species. The Overhauser Effect (OE) DNP, which relies time-dependent spin-spin interactions, is excluded from our discussion due lack conducting aqueous solutions containing entities. particular interest to us primarily time-independent, for significant electron-nucleus transfer through such as Solid (SE), Cross (CE) or Thermal Mixing (TM), involving one, two multiple spins, respectively. Derived monomeric radicals initially used high-field experiments, bi- multiple-radical agents facilitate CE/TM generate NMR signal enhancements dielectric solids low (<100 K). For example, large (∼300 times 5 T) a biologically biradical, 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL), have enabled high-resolution MAS sample systems existing submicron domains embedded larger biomolecular complexes. scope this review focused recently developed applications leads up future developments per CE mechanism. Because feasible solid-state microwave source when performed <20K, lower power mW) possible forcing high proportion biradicals fulfill frequency matching condition (two EPR frequencies separated frequency) strategies hetero-radical moieties and/or molecular alignment. In addition, combination excited triplet stable radical might provide alternative without requirement.