New, stable β-phosphorus-labelled pyrrolidine nitroxides from nitrones for magnetometry: an ESR investigation
✍ Scribed by D. Lawrence Haire; Edward G. Janzen; Guoman Chen; Valerie J. Robinson; Ivan Hrvoic
- Book ID
- 101251770
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 207 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
The present study was devoted to the design and synthesis of new, prototypical nitroxides for use in dynamic nuclear polarization (DNP) magnetometers. SpeciÐcally, eight b-phosphorylated pyrrolidine nitroxides were synthesized. Their large (ca. 5.0 mT) b-31P hyperÐne splittings render them desirable for magnetometry applications. Seven of these free radicals are 2-dialkylphosphityl-2,5,5-trialkyl-or 2-diarylphosphityl-2,5,5-trialkylpyrrolidine nitroxides. Structural and solvent e †ects on the ESR spectra of these nitroxides were explored. Hydrolysis of a phosphityl group creates a remarkable eighth nitroxide. It exhibits an extremely pH-dependent ESR spectrum. Other nitroxides (e.g. b-aminyls) are known to show pH-dependent ESR spectra (*aN B 0.15 mT), and these have been proposed by Keana et al. as novel, sensitive pH indicators. Whereas they operate by changes in the nitroxide nitrogen hyperÐne splitting, the present special nitroxide displays little change in the nitroxide nitrogen splitting (*aN B 0.03 mT). A very robust variation in the b-31P hyperÐne splitting (*aN B 0.35 mT), however, is observed. Hence it may be a much more sensitive pH probe molecule than Keana et al.Ïs. It is proposed that this ESR variation for the present nitroxide is due to conformational changes that are pH dependent. Copyright