Dynamic nuclear polarization (DNP) is often carried out at low temperatures to utilize the high spin polarization of the radical electrons at these temperatures. We have observed that in the absence of microwave irradiation and radical a transient negative polarization is observed for the methyl signals of acetone and DMSO. We suggest that this polarization arises from rotational tunneling levels in this system. For samples dissolved in these solvents, we see a diminished polarization with a microwave frequency of ωe - ωN compared to ωe + ωN, and we relate the two effects due to constructive/destructive interference with proton spin diffusion and spin symmetry diffusion mediating the intermolecular transfer of polarization. Perdeuteration of the solvents acts to nullify this effect. Awareness of this additional factor in the temperature jump DNP experiment allows improved experiment design and polarization of samples which have otherwise proven virtually impossible.
Research Areas and Centers
- Academic Focus: Center for Infection and Inflammation Research (ZIEL)