Molecular motions in solid estradiol studied by nuclear magnetic resonance spectroscopy.

The temperature dependence of the proton nuclear magnetic resonance (NMR) relaxation time T1 and second moment M2 of polycrystalline beta-estradiol hemihydrate (1,3,5-estratriene-3,17 beta-diol) is measured at frequencies of 14 and 25 MHz. Below 260 K relaxation is found to be dominated by C3 reorientation of the single methyl group in each molecule, characterized by an activation energy of 9.4 +/- 0.1 kJ/mol. Above 260 K another relaxation mechanism becomes evident, characterized by an activation energy of 22 +/- 2 kJ/mol and ascribed to motion of the water molecules in the solid.