ABSTRACT
Paramagnetic systems are materials with positive magnetic susceptibility, associated with unpaired electrons. Paramagnetic solutions of interest to chemists usually contain free radicals or transition metal complexes, including metalloproteins. The paramagnetic species influence nuclear magnetic resonance spectra of liquids in several ways and a general account of the various phenomena can be found in the book by Bertini and co-workers. The effect of greatest interest for the present book is the fact that the nuclear spin-relaxation rates are enhanced. The paramagnetic relaxation enhancement is caused by a random variation of the electron spin–nuclear spin interactions, which open new pathways for longitudinal as well as transverse relaxation. A theory of the electron spin-relaxation in hydrated first transition metal series ions was formulated by Bloembergen and Morgan in the early 1960s. Determinations of the paramagnetic transverse relaxation are less common, since both the measurements and their interpretation are somewhat more complicated.
