Solid-Effect Dynamic Nuclear Polarization in Viscous Liquids at 9.4 T Using Narrow-Line Polarizing Agents

Dynamic nuclear polarization (DNP) is a hyper polarization method that is widely used for increasing the sensitivity of nuclear magnetic resonance (NMR) experiments. DNP is efficient in solid-state and liquid-state NMR, but its implementation in the intermediate state, namely, viscous media, is still less explored. Here, we show that a 1H DNP enhancement of over 50 can be obtained in viscous liquids at a magnetic field of 9.4 T and a temperature of 315 K. This was accomplished by using narrow-line polarizing agents in glycerol, both the water-soluble alpha,gamma-bisdiphenylen-fi-phenylallyl (BDPA) and triarylmethyl radicals, and a microwave/RF double-resonance probehead. We observed DNP enhancements with a field profile indicative of the solid effect and investigated the influence of microwave power, temperature, and concentration on the 1H NMR results. To demonstrate potential applications of this new DNP approach for chemistry and biology, we show hyperpolarized 1H NMR spectra of tripeptides, triglycine, and glypromate, in glycerol -d8.