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The longitudinal relaxivities of seven water-soluble nitroxide derivatives of low-molecular weight have been measured at 5 degrees C and 37 degrees C in water and in serum between 0.01 and 200 MHz. The nuclear magnetic relaxation dispersion (NMRD) profiles show a clear relationship between the relaxivity observed in serum and the relative balance of the hydrophobic/hydrophilic character of the paramagnetic molecules. From the data analysis, contributions arising from a population of nitroxides characterized by reduced mobility can be extracted. The values of the correlation times are consistent with a system involving nitroxides adsorbed at the surface of albumin and magnetically interacting with the protons of hydrogen bonded water molecules.
Vallet et al. (Fri,) studied this question.