THERMODYNAMICS OF SOME LONG-CHAIN BIRADICALS STUDIED BY EPR SPECTROSCOPY

Four biradicals of differing chain lengths have been prepared by spin- labelling the sulphhydryl groups of dithiothreitol. Temperature-depend ent EPR spectra of these biradicals indicate that the dynamics of bira dicals is associated with both fast and slow exchanges of conformation s. The three-conformational model incorporating cage configuration is found to be more appropriate. Certain thermodynamic parameters of conf ormational changes have been calculated from the experimental EPR para meters, obtained by the use of simulation procedures developed recentl y.