Nitroxide exchange experiments

Scheme 10.8 Measuring the alkoxyamine (R—T) dissociation rate using a nitroxide-exchange experiment where the scavenger S is TMIO.

The quantitative ESR measurements reported later by Bon et al. [135] proved to be a rather straightforward and accurate means to determine the rate coefficients for the homolytic alkoxyamine C-O bond cleavage over a range of temperatures for 2-tert-butoxy-l-phenyl-l-(l-oxy-2,2,6,6-tetramethylpiperidinyl)ethane and a polystyrene-TEMPO. The acquired kinetic data for alkoxyamines were compared by the authors with data obtained via nitroxide-exchange experiments using HPLC and with literature data [137]. 

Pulse Measurements. Comparison of 3-pulse PELDOR data for nitroxide biradicals with interspin distances of 15.4 to 24.0 A at X-band and S-band demonstrated the separation of nuclear hyperfine and dipolar interactions and the separation of contributions from dipolar and exchange interactions.20 However, the deeper nuclear modulation at S-band limits the options for interpulse spacings. The inability to observe dipolar modulation in a PELDOR experiment... 

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