EPR Spectroscopic Studies on Inclusion Complexes between Nitroxides and Cyclodextrins

Complexation of 5-doxy-l stearic acid （5-DXSA） with α-，β-，andγ-cyclodextrins， 2，2，6，6-tetramethy-l 4-hydrony-piperdine-1-oxy1（4-hydroxy-T empo） and 2，2，6，6-tetramethy-l 4-palmitoleoy-l piperdine-1-oxyl（4-hydroxy-T empo） with β-CD in aquaous solutions has been studied by electron paramagnet resonance spectroscopy （ EPR） ．T he isotropic nitrogen hyperfine coupling constants a_N and therotational correlation time τ_c of the radicals change regularly after complexing with cyclodextrins. The magnitude of change in τ_c is in the order:5-DXSA·γ-CD＞5-DXSA·α-CD＞5-DXSA·β-CD.This can be explained by different in inclusion site and size of the host/guest molecules. The extent o increase in τ_c values in 4-OH-tempo/β-CD systems is larger than that in 5-DXSA/β-CD or 4-palmitoleoyl-Templ/β-CD systems, this is probably due to the best fit of 4-OH-Tempo to the diameter of inner cavity of β-CD molecule.