A high saturation factor in Overhauser DNP with nitroxide derivatives: the role of 14N nuclear spin relaxationElectronic supplementary information (ESI) available: Synthesis of FN derivatives, the experimental setup for DNP, CW EPR spectra and power dependence of the central line, ELDOR saturation spectra and time evolution PR-EPR, PR-ELDOR curves for all samples, the relaxation model of the 14N nitroxide radical, comparison of the experimental and calculated saturation factors, and dependence o

• Main Authors: Enkin, Nikolay, Liu, Guoquan, Gimenez-Lopez, Maria del Carmen, Porfyrakis, Kyriakos, Tkach, Igor, Bennati, Marina
• Format: Journal Article
• Language: English
• Published: 21.04.2015
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp00935a

Overhauser DNP enhancements of toluene were measured at a magnetic field of 0.35 Tesla in a series of chemically functionalized nitroxide radicals. We observe that the enhancements increase systematically with polarizer size and rotational correlation time. Examination of the saturation factor of 14 N nitroxides by pulsed ELDOR spectroscopy led to a quantitative interpretation of the enhancements, for which the saturation factor increases up to almost unity due to enhanced nuclear ( 14 N) relaxation in the nitroxide radical. The observation has a direct impact on the choice of optimum DNP polarizers in liquids. Functionalization of nitroxide radicals leads to an increase of the saturation factor and of the Overhauser DNP enhancement.