An integrated approach to NMR spin relaxation in flexible biomolecules: Application to Β-D-glucopyranosyl-(1→6)-α-D -mannopyranosyl-OMe

Mirco Zerbetto, Antonino Polimeno, Dmytro Kotsyubynskyy, Leila Ghalebani, Jozef Kowalewski, Eva Meirovitch, Ulrika Olsson, Göran Widmalm

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The description of the reorientational dynamics of flexible molecules is a challenging task, in particular when the rates of internal and global motions are comparable. The commonly used simple mode-decoupling models are based on the assumption of statistical independence between these motions. This assumption is not valid when the time scale separation between their rates is small, a situation that was found to arise in oligosaccharides in the context of certain internal motions. To make possible the interpretation of NMR spin relaxation data from such molecules, we developed a comprehensive approach generally applicable to flexible rotators with one internal degree of freedom. This approach integrates a stochastic description of coupled global tumbling and internal torsional motion, quantum chemical calculations of the local potential and the local geometry at the site of the restricted torsion, and hydrodynamics-based calculations of the diffusive properties. The method is applied to the disaccharide Β-D-Glcp-(1→6)-α-D-[6- 13C]-Manp-OMe dissolved in a DMSO-d6/D2O cryosolvent. The experimental NMR relaxation parameters, associated with the 13CH2 probe residing at the glycosidic linkage, include 13CT1 and T2 and 13C-{1H} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253-293 K. These data are predicted successfully by the new theory with only the H-C-H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed.

Original languageEnglish
Article number234501
JournalJournal of Chemical Physics
Issue number23
StatePublished - 2009

Bibliographical note

Funding Information:
M.Z. and A.P. acknowledge support provided by the Italian Ministero dell’Istruzione, Università e Ricerca (MIUR) [Grant No. PRIN2006 (2006033728)], by the University of Padova Grant “Progetto Strategico” HELIOS 2009, and by the Consorzio Interuniversitario per la Scienza e la Tecnologia dei Materiali (INSTM), Grant PROMO 2008. J.K., D.K., and G.W. acknowledge the support from the Swedish Research Council, the Carl Trygger Foundation, and the Magn. Bergvalls Foundation. We are indebted to the CERM infrastructure access program (EUNMR, Contract No. RII3-026145) for the generous grant of the instrument time on the 21.1 T spectrometer as well as for invaluable technical support. E.M. acknowledges support from the Israel Science Foundation, Grant No. 347/07; the Israel–U.S. Binational Science Foundation, Grant No. 2006050; the German-Israeli Science Foundation for Scientific Research and Development, Grant No. 928-190.0/2006; and the Damadian Center for Magnetic Resonance Research at Bar-Ilan University.


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