Diffusion of a singly charged nitroxide in solution

Includes bibliographical references (leaves 37-39)EPR spectra of aqueous solutions of the singly charge nitroxide 4-trimethylammonium-2, 2, 6, 6-tetramethylpiperidine-1-oxyl iodine (CAT 1) are studied as functions of the molar concentration, c = 0.1 - 100 mM, and the temperature from 260 - 353 K. Additionally, spectra of 60 and 70 wt% glycerol solutions of CAT 1 were also studies as functions of the molar concentration, c = 0.1 - 40 mM, and the temperature from 260 - 353 K. Spinspin broadening of the EPR lines averaged over the three lines is separated into contributions due to spin exchange, (Bex), and dipolar, (Bdip), interactions yielding values of the fractional broadening by spin exchange, D.(T), that vary from near unity at !.. = 500 to approximately 50% at!..= 30, where 1J represents the shear viscosity of the 7] 7] solution. 0.(1) is a continuous function of both!.. and the inverse rotational correlation 7] time of CAT -1. Values of d{Bex> are very close to a prediction using the Stokes-Einstein de equation modified to take the charge of the spin probe into account