Absence of curie relaxation in paramagnetic solids yields long 1H coherence lifetimes

NMR of paramagnetic systems in solution is hampered by relaxation enhancement (PRE). Here we present a method to access paramagnetic line widths in microcrystalline samples under magic angle spinning. We demonstrate that a CPMG technique may advantageously be combined with fast MAS of paramagnetic solids and suitable adiabatic pulses both to provide increased sensitivity and to allow experimental determination of the homogeneous coherence lifetimes T (2)'. In this way, we show that the Curie contribution to PRE is absent in solids and, therefore, that the lifetimes of nuclear coherences may be longer than in liquids for paramagnetic systems, even for protons.