| Abstract
| - Spin trapping using a nitrone and electron paramagnetic resonance (EPR) spectroscopy is commonly employed in the identification of transient radicals in chemical and biological systems. There has also been a growing interest in the pharmacological activity of nitrones, and there is, therefore, a pressing need to develop nitrones with improved spin trapping properties and controlled delivery in cellular systems. The β-cyclodextrin (β-CD)−cyclic nitrone conjugate, 5-N-β-cyclodextrin-carboxamide-5-methyl-1-pyrroline N-oxide (CDNMPO) was synthesized and characterized. 1-D and 2-D NMR show two stereoisomeric forms (i.e., 5S- and 5R-) for CDNMPO. Spin trapping using CDNMPO shows distinctive EPR spectra for superoxide radical anion (O2•−) compared to other biologically relevant free radicals. Kinetic analysis of O2•− adduct formation and decay using singular value decomposition and pseudoinverse deconvolution methods gave an average bimolecular rate constant of k = 58 ± 1 M−1 s−1 and a maximum half-life of t1/2 = 27.5 min at pH 7.0. Molecular modeling was used to rationalize the long-range coupling between the nitrone and the β-CD, as well as the stability of the O2•− adducts. This study demonstrates how a computational approach can aid in the design of spin traps with a relatively high rate of reactivity to O2•−, and how β-CD can improve adduct stability via intramolecular interaction with the O2•− adduct.
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