Freezing of Molecular Motions Probed by Cryogenic Magic Angle Spinning NMR.
Cryogenic magic angle spinning makes it possible to obtain the NMR spectra of solids at temperatures low enough to freeze out most molecular motions. We have applied cryogenic magic angle spinning NMR to a crystalline small-molecule solid (ibuprofen sodium salt), which displays a variety of molecular dynamics. Magic angle (13)C NMR spectra are shown for a wide range of temperatures, including in the cryogenic regime down to 20 K. The hydrophobic and hydrophilic regions of the molecular structure display different behavior in the cryogenic regime, with the hydrophilic region remaining well-structured, while the hydrophobic region exhibits a broad frozen conformational distribution.
†School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
Maria
M
Concistrè
‡Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy.
Elisa
E
Carignani
‡Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy.
Silvia
S
Borsacchi
†School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
Ole G
OG
Johannessen
‡Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy.
Benedetta
B
Mennucci
§School of Engineering Science, University of Southampton, Southampton, United Kingdom.
Yifeng
Y
Yang
‡Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy.
Marco
M
Geppi
†School of Chemistry, University of Southampton, SO17 1BJ Southampton, United Kingdom.
Malcolm H
MH
Levitt
conformational exchange; ibuprofen; methyl rotation; solid-state MAS NMR; static and dynamic structural disorder