Inclusion Complexes of Spin Adducts by ß Cyclodextrin

Spulber, Mariana, and Shulamith Schlick

Spin trapping electron spin resonance (ESR) techniques have been used in our laboratory to study oxygen and carbon-centered free radicals generated during fragmentation of polymeric membranes used in fuel cells.1-4 We have explored the potential of cyclodextrins (CDs) to encapsulate the spin adducts of 5,5-dimethyl-1-pyroline (DMPO), N-tert-Butyl-α-phenylnitrone (PBN) and 2-methyl-2-nitrosopropane (MNP) and to increase their stability through the formation of inclusion complexes. Here we describe the effect of ßCD on DMPO/OH and PBN/OH adducts, and on MNP adducts derived from attack of hydroxyl radicals on acetic acid (AA) and difluoroacetic acid (DFAA) in aqueous solutions at 300 K.5 The complexation with ßCD led to significant stabilization of the DMPO and PBN adducts but only slight changes of the hyperfine splittings and line widths were detected, possibly due to location of the nitroxide radical fragment outside the hydrophobic inner cavity of the cyclodextrin molecule. For MNP as a spin trap, however, the interaction with ßCD is stronger; the di-tert-butyl nitroxide radical (DTBN) and the MNP adducts were detected outside the CD as well as inclusion complexes, and were studied as a function of temperature and CD concentration.

1. Kadirov, M.K.; Bosnjakovic, A.; Schlick, S.; J. Phys. Chem. B 2005, 109, 7664-7670.

2. Bosnjakovic, A.; Schlick, S.; J. Phys. Chem. B 2006, 111, 10720-10728.

3. Lund, A.; Macomber, L.; Danilczuk, M.; Stevens, J.; Schlick, S. J. Phys. Chem. B 2007, 111, 9484-9491.

4. Danilczuk, M.; Coms, F.D.; Schlick, S. Fuel Cells 2008, 8(6), 436-452. 5. Spulber, M.; Schlick, S., manuscript in preparation.