ROTATIONAL-DYNAMICS OF DI-TERT-BUTYL-NITROXIDE IN NORMAL AND SUPERCOOLED WATER - AN ELECTRON-PARAMAGNETIC-RESONANCE STUDY

In order to obtain dynamical information on the water solvent, which i s characterized by a strong anomalous behavior in its structural and t ransport properties especially in the supercooled region, low concentr ation di-tert-butyl-nitroxide (DTBN) aqueous solutions were studied by Electron Paramagnetic Resonance spectroscopy in the temperature range from 28 down to -17-degrees-C. The accurate spectra reconstruction, a chieved by a multi-parameters Monte Carlo fitting algorithm, allowed u s to reliably extract some relevant spectral parameters of the spin pr obe, which were connected to the probe dynamics in the framework of th e motional narrowing magnetic relaxation theory. The observed trend wi th the temperature showed however a significant deviation from what ex pected from the magnetic relaxation model. This anomalous behavior is discussed in terms of the influence upon the probe motion of solvent-i nduced local fluctuating structures which, very likely, are connected to the water hydrogen bond network dynamics.