B Peplinska | PubMed Health

PubMed1998

Molecular dynamics in solid L-adrenaline by proton NMR.

Proton NMR measurements of the spectrum, second moment, spin-lattice relaxation time T1 and dipolar relaxation time T1D were carried out on polycrystalline L-adrenaline at 14 and 25 MHz between 55 and 400 K. Between 70 K and 250 K relaxation is dominated by C3 reorientation of the single methyl group in each molecule, characterized by an activation energy 8.3+/-0.3 kJ/mole. Below 70 K tunnelling assisted relaxation is significant, characterized by an excitation energy of 1.9+/-0.2 kJ/mole. Above 250 K an additional molecular motion becomes significant, with activation energy above 28 kJ/mole, attributed to conformational motion of the methylene group in the ethylamine side chain.

Epinephrine↗

PubMed1998

Molecular motion in solid all-trans retinoic acid (vitamin A acid) by proton NMR.

An investigation of the molecular dynamics of all-trans retinoic acid (vitamin A) has been carried out in the solid state by proton NMR. Measurements were made of T1 at 14 and 25 MHz and of second moment at 25 MHz in the temperature range 55 to 420 K for both monoclinic and triclinic forms. In the monoclinic state relaxation was attributed to methyl group reorientation below 250 K and to conformational motion of the cyclohexene ring above this temperature. Activation energies and time constants were derived for the motions. In the triclinic state the same motions were active, but the cyclohexene ring motion was less restricted and some of the methyl group motions were more restricted indicating that hindrances to the motions were at least partly determined by the intermolecular packing arrangements.

Magnetic Resonance Spectroscopy↗