Fig. 8.

Spin–lattice relaxation in the intermediate exchange regime. a Model of 130R1 in T4L based on the crystal structure [29]. b EPR spectrum of T4L 130R1 in 25% w/w Ficoll 70 at 298 K (black trace), along with a two-component MOMD spectral simulation (dashed trace). The spectra of the individual components α and β, determined by the simulation, are also given below with intensities scaled by the relative populations. Rotational correlation times and order parameters determined from the simulation are given below each spectrum as {τ_R,S}. c A representative saturation recovery curve for T4L 130R1 in a nitrogen atmosphere under the same conditions as for the CW spectrum (black trace), with a double-exponential fit (white trace) and the tenfold-magnified (10×) residuals to single- and double-exponential fits below. The inset shows the dependence of the spin–lattice relaxation rate (W_α and W_β) on [NiEDDA] for the fast and slow SR components of 130R1 (open diamonds and solid squares, respectively, plotted on separate axes). The lines here are from a fit of Eqs. (1)–(8) with a nonzero average exchange rate, k. Dashed lines on each trace are placed to emphasize the nonlinearity of the fits