title: Low-frequency cooperative dynamics in L-, D-, and DL-alanine crystals: a 13C and 15N cross-polarization magic-angle-spinning NMR study.
abstract: Knowledge of the dynamical changes in molecular configurations in various amino acid structures over a wide range of time scales is important since such changes may influence the structural transformations and the diverse biological functionalities of proteins. Using the temperature dependence of the rotating-frame NMR spin-lattice relaxation times T(1rho) of protons as a probe, we have investigated the low-frequency (approximately 60-100 kHz) dynamics in the crystal structures of L-, D-, and DL- alanine (C(12)H(28)O(8)N(4)) polymorphs. The proton relaxation times T(1rho) were obtained from (13)C <-- (1)H and (15)N <-- (1)H cross-polarization magic-angle-spinning NMR experiments over a temperature range of 192-342 K. The data reveal that the time scales of these low-frequency dynamical processes are distinctly different from the localized, high-frequency rotational motion of methyl and amine groups. The strongly asymmetric T(1rho) versus temperature curves and the subtle dynamical differences between the DL-alanine and the L- and d-enantiomorphs indicate that these low-frequency processes are cooperative in nature and are sensitive to molecular packing.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California 95616, USA. sbsen@ucdavis.edu
authors.forename: Sabyasachi
authors.initials: S
authors.lastname: Sen
authors.forename: Ping
authors.initials: P
authors.lastname: Yu
authors.forename: Subhash H
authors.initials: SH
authors.lastname: Risbud
authors.forename: Reay
authors.initials: R
authors.lastname: Dick
authors.forename: David
authors.initials: D
authors.lastname: Deamer
mesh_terms: D000409:Alanine / Q000737:chemistry*; D002247:Carbon Isotopes; D003460:Crystallization; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008968:Molecular Conformation; D009038:Motion; D009587:Nitrogen Isotopes; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D000409:Alanine