Proton NMR study of molecular motion in solid cortisone

Area of Science:

• Solid-state chemistry
• Molecular dynamics
• Nuclear Magnetic Resonance (NMR) spectroscopy

Background:

• Cortisone is a corticosteroid hormone with anti-inflammatory properties.
• Understanding the molecular dynamics of crystalline pharmaceuticals is crucial for drug stability and efficacy.

Purpose of the Study:

• To investigate the molecular dynamics of polycrystalline cortisone using proton NMR.
• To determine the reorientation behavior of methyl groups within the cortisone molecule.

Main Methods:

• Proton Nuclear Magnetic Resonance (NMR) spectroscopy was employed.
• Measurements were conducted over a temperature range of 56 K to 400 K at 14 and 25 MHz.
• Data analysis utilized the Kubo-Tomita dipolar relaxation theory.

Main Results:

• Observed reductions in the second moment and distinct minima in spin-lattice relaxation time.
• These changes were attributed to the reorientation of methyl groups at carbons 18 and 19.
• The experimental data were well-fitted by the Kubo-Tomita theory across the entire temperature range.

Conclusions:

• The study successfully characterized the reorientational dynamics of methyl groups in polycrystalline cortisone.
• Identified unusually large differences in activation energies (5.9 and 15.5 kJ/mol) for the two methyl groups.
• Provided specific relaxation constants (6.4 and 7.9 x 10(8) s-2) for these reorientations.