An integrated approach to NMR spin relaxation in flexible biomolecules: Application to beta-D-glucopyranosyl-(1 -> 6)-alpha-D-mannopyranosyl-OMe

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 \u3b2-D-Glcp-(1\u21926)-\u3b1-D-[6-math]-Manp-OMe dissolved in a DMSO-d6/D2O cryosolvent. The experimental NMR relaxation parameters, associated with the mathH2 probe residing at the glycosidic linkage, include math T1 and T2 and math-{math} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253\u2013293 K. These data are predicted successfully by the new theory with only the H\u2013C\u2013H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed

NMR investigation of guest-host complex between chloroform and cryptophane C

International audienceGuest–host complex between cryptophane C, possessing two non-equivalent caps, and chloroform is investigated by NMR spectroscopy. The kinetics of the chloroform exchange between the bound and free sites is determined by 1H exchange spectroscopy. Moreover, the preferential orientation of chloroform molecule with respect to the cryptophane C frame is examined by the NOESY and ROESY experiments. The experimental findings are compared to the results of quantum chemical calculations. Copyright © 2010 John Wiley & Sons, Ltd

Measuring Molecular Dynamics and Activation Energies for Quaternary Acyclic Ammonium and Cyclic Pyrrolidinium Ionic Liquids Using14N NMR Spectroscopy

The N-14 NMR spin-lattice (R-1) and spin-spin (R-2) relaxation rates were determined as a function of temperature for a series of tetra-alkyl acyclic ammonium and cyclic pyrrolidinium ionic liquids (ILs). Through the use of the R-2/R-1, ratio method, it was shown that for the majority of these ILs, the reorientational dynamics are not in the extreme narrowing regime, but instead are in the dispersive relaxation regime, thus allowing a unique solution for the correlation time to be determined. The temperature variation of the R-2 relaxation rate, along with the temperature variation of the calculated correlation times, allowed activation energies for the reorientational dynamics to be measured and compared. In addition, these NMR relaxation experiments enabled the N-14 quadrupolar coupling product to be extracted, which revealed surprising temperature dependence. Collectively, the N-14 NMR results allow the impact of cation and anion identity on the local reorientational dynamics of these ILs to be delineated