Studies of Dynamic Nuclear Polarization with Nitroxides in Aqueous Solution
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The dynamic nuclear polarization effect between the nitroxide radical TEMPO and the 1H protons of water solution was investigated at an electron pumping frequency of 9.7 GHz for different experimental conditions. In particular, we compared 14N-4-hydroxy-TEMPO (TEMPOL) with 4-oxo-TEMPO and evaluated the effect of 2H and 15N isotope labelling. Furthermore, we tested the effect of concomitant irradiation on both electron paramagnetic resonance (EPR) lines with the 15N-labelled compound. Our results show that the reduction in the EPR line width given by the 2H and 15N labelling and the collapse in the number of hyperfine lines due to 15N substitution leads to the highest enhancement of ε = −140 ever reported in the literature. Concomitant pumping on two hyperfine lines does not give higher enhancements at our experimental conditions.
KeywordsNitroxides Dynamic Nuclear Polarization TEMPOL Hyperfine Line Dynamic Nuclear Polarization Enhancement
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