A low field proton–electron double resonance study for paramagnetic solutions

Abstract

Dynamic nuclear polarization has been observed in solutions of a series of aromatic hydrocarbons with Galvinoxyl and α,γ-Bisdiphenylene-β-phenyl allyl complex with benzene (1 : 1) free radicals in a low magnetic field of 1.44 mT. The measurements were performed at three different temperatures to test the dipolar and the scalar part of the coupling between the hydrogen nucleus (¹H) and the unpaired electron. At all temperatures and concentrations, negative Overhauser enhancements were measured, indicating that the proton–electron interaction is predominantly dipolar. The observed enhancements vary from −36 to −325 for the samples with BDPA, whereas it varies from −47 to −282 for the samples with GALV. Overhauser enhancement was not observed in the samples prepared with Ethylbenzene, Tetralin and Quinoline for only GALV free radical at all concentrations and temperatures. These solvents may have scavenging effects on the GALV radical due to their behaviour. The high and low frequency relaxation components were calculated for all samples and the relation between them is compared with theory. It was observed that dissolved molecular oxygen in the o-Xylene solvent medium with BDPA and GALV causes the ¹H NMR signal enhancement to decrease dramatically. These findings will be discussed in detail.

Keywords:

• dynamic nuclear polarization
• proton–electron double resonance
• oximetry
• free radical
• free radical scavenger

PACS:

• 33.25.+k
• 33.35.+r
• 33.40.+f

Acknowledgements

This work was partly supported by the Research Fund of the Uludag Universtiy Project number: F-2009/44. The authors would like to thank the Uludag University for financial support. The authors would like to thank Professor Dr Aytac Yalciner, for kind suggestions and discussions, Dr Huseyin Ovalioglu for experimental assistance and Yunus Kaya for viscosity measurements.