Molecular motion in solid odd‐numbered paraffin C19H40: Proton spin relaxation spectroscopy from 5.8 kHz to 86 MHz

Dynamics of solid alanine by means of nuclear magnetic resonance relaxometry

¹H nuclear magnetic resonance relaxometry was applied to investigate the dynamics of l-alanine in the solid phase (powder). The experimental studies were carried out in a very broad frequency range, covering four orders of magnitude-from 4 kHz to 40 MHz (referring to the ¹H resonance frequency) in order to probe motional processes of much different time scales by a single experiment. To get access to the dynamics of different proton groups of alanine, the ¹H spin-lattice relaxation measurements were performed for non-deuterated and partially deuterated alanine. The experiments were carried out in the temperature range of 293 K-370 K (non-deuterated alanine) and 318 K-370 K (partially deuterated alanine). As a result of a thorough theoretical analysis of the extensive set of experimental results, three motional processes occurring on different time scales are identified and quantitatively described. The slowest process occurs on a time scale of μs and it is attributed to the collective dynamics of a 3D hydrogen bond network of alanine, while the intermediate, attributed to the dynamics of the NH₃ group, corresponds to the range of tenths of ns. The fast process describes the rotation of the CH₃ group.

Spectroscopy of the conformational disorder in molecular films: Tetracosane and squalane on Pt(111)

The spectroscopic investigation of the molecular vibrations of adsorbed branched and unbranched alkane molecules using helium atom scattering (HAS) provides evidence for the thermal formation of gauche defects in tetracosane (C24H50) monolayers above 200 K. HAS results for the vibration of tetracosane molecules perpendicular to the Pt(111) surface reveal a strong frequency decrease and peak broadening above the transition temperature which can be related to a reduction of the force holding the molecules to the surface. This reduction of the force is interpreted as being due to the thermal formation of gauche defects within the tetracosane molecules.

Solid state molecular motion in sucrose octapalmitate as studied by deuterium NMR spectroscopy

Sucrose octapalmitate-d11, d24 and d248 have been synthesized. Using 2H NMR T1 and analyses of the temperature dependence of the lineshapes, a detailed description of the solid state molecular motional modes is presented. Activation energies for methyl and methylene group rotation in the fatty acyl chains have been determined. The sucrose moiety is found to be static on the solid state deuterium NMR timescale.