Transfer of H-1 and C-13 Dynamic Nuclear Polarization from Immobilized Nitroxide Radicals to Flowing Liquids

In this study, H-1 and C-13 dynamic nuclear polarization (DNP) was generated at a magnetic field strength of 0.33 T utilizing silica phase immobilized nitroxide (SPIN) samples. The polarization was subsequently transferred to flowing liquids and monitored at a magnetic field strength of 4.7 T. These solid/liquid intermolecular transfer (SLIT) experiments provide efficient polarization transfer without the necessity of the free radical system present in the monitoring fluid. Specifically, ultimate H-1 SLIT DNP Overhauser enhancements of -5 6 and -110 have been observed for benzene and chloroform in the presence of SPIN system 2, respectively. The C-13 SLIT DNP enhancement for benzene is dominated by three-spin effects and poor leakage factors (f(c)). However, a particularly favorable case is the chloroform/SPIN 2 system which exhibits a scalar dominated enhancement. For this case, positive enhancements 40--60 times the C-13 thermal Boltzmann magnetization at 4.7 T have been observed. The large scalar dominated 13C DNP enhancement for this system represents one of the largest experimental enhancements reported to date. The 13C DNP spectra for other samples which exhibit favorable scalar 13C dominated enhancements (e.g., Freon 113) are also presented. Three different SPIN systems were also prepared and characterized in the present study.