Water molecular reorientation in ice and tetrahydrofuran clathrate hydrate from lineshape analysis of ¹⁷O spin-echo NMR spectra

Abstract

Lineshape analysis of 17 O spin-echo NMR spectra has been used to study water molecular reorientations in ice-Ih and THF Structure II clathrate hydrate. The kinetics was determined by the changes of the lineshapes of the 17 O central transitions at different temperatures. A model involving 12 orientations and 4-step jumps of water molecular orientations was proposed. Semi-classical exchange formalism was employed to simulate the lineshape of the central transitions of the 17 O nuclei. Lineshape analysis gave the quadrupolar coupling constant C Q = 6.43 MHz and the asymmetry parameter h = 0.935, for both ice-Ih and THF gas hydrate. The theoretical lineshape simulations resulted in activation energies of water molecular reorientations E a = 55.2 ± 2.1 kJ mol -1 and E a = 30.5 ± 0.8 kJ mol -1 for ice-Ih and THF hydrate, respectively. The range of dynamic rates in THF clathrate hydrate is such that before melting, a pseudo-isotropic lineshape is observed that retains a second-order quadrupolar shift. The water reorientation process is discussed in light of recent results on Bjerrum defect injection obtained from molecular dynamics simulation and structural studies.Key words: Ice-Ih, THF clathrate hydrate, 17 O NMR, molecular reorientations of solid water, Kinetics, residual second order quadrupolar shift, dynamics of non-integer quadrupolar nuclei.Résumé : On a fait appel à l'analyse de la forme des raies des spectres RMN du 17 O avec écho de spin pour étudier les réo-rientations moléculaires de l'eau dans la glace-Ih et dans l'hydrate du clathrate du THF de structure II. On a déterminé les cinétiques par les changements dans les formes des raies des transitions centrales du 17 O, à diverses températures. On propose un modèle impliquant 12 orientations et des transitions en quatre étapes des orientations moléculaires de l'eau. On a utilisé un formalisme d'échange semi-classique pour simuler la forme des raies des transitions centrales du noyau 17 O. Une analyse de la forme des raies permet de déterminer la constante de couplage quadripolaire CQ = 6,43 Mhz et le paramètre d'asymétrie h = 0 935 pour la glace-Ih et l'hydrate du THF gazeux. Les simulations des formes des raies théoriques ont permis d'évaluer les énergies d'activation des réorientations moléculaires de l'eau Ea = 55,4 ± 2,1 kJ mol -1 et Ea = 30,4 ± 0,8 kJ mol -1 , respectivement pour la glace-Ih et l'hydrate du THF. La plage des vitesses dynamiques pour l'hydrate du clathrate du THF est telle que, avant la fusion, il et possible d'observer une forme de raie pseudo-isotrope qui conserve un déplacement quadripolaire du deuxième ordre. On discute du processus de réorientation de l'eau à la lumière de résultats récents sur l'injection du défaut de Bjerrum obtenu à partir de simulations de la dynamique moléculaire et d'étu-des structurales.Mots-clés : glace-Ih, hydrate du clathrate du THF, RMN du 17 O, réorientations moléculaires de l'eau solide, cinétique, dé-placement quadripolaire résiduel du second ordre, dynamique des noyaux quadripolaires non ...

Solid-State 17O NMR of Oxygen–Nitrogen Singly Bonded Compounds: Hydroxylammonium Chloride and Sodium Trioxodinitrate (Angeli’s Salt)

“…In addition, information about the 17 O NMR tensor orientation in the molecular frame is critical in the analysis of solid-state 17 O NMR spectra obtained for systems where molecular motion is significant. 43,44 The CASTEP results for the 17 Figure 4, if one looks only at the individual tensor components, the only feature is that all three components for O3 of the Angeli's salt are shifted toward the higher frequency end, leading to an increase in δ iso , as previously noted. Now if one links the tensor components between the two compounds according to their orientations within the respective molecular frame of reference one immediately sees that the tensor component perpendicular to the molecular plane changes very little.…”

Communication: Heterogeneous water dynamics on a clathrate hydrate lattice detected by multidimensional oxygen nuclear magnetic resonance

“…The guest-detected line broadening vanishes for temperatures near and above 200 K. 8 Furthermore, in this temperature regime exponential relaxation prevails as suggested by 17 O line shape analyses carried out for THF clathrate hydrate at T ≥ 180 K. 37 To summarize, our novel oxygen-17 four-time NMR experiment revealed clear evidence for heterogeneous water dynamics in THF clathrate hydrate on the millisecond scale. Thus, our study resolves an important question regarding the dynamics in an ice-like crystal.…”

Dynamic Nuclear Polarization of 17O: Direct Polarization

“…The asymmetry parameter and isotropic chemical shift were 0.95 and 0 ppm, respectively, agree well with literature studies of frozen water. 135, 136 An ordered ice crystal structure 117 , which apparently occurs at cryogenic temperatures, was calculated using GIPAW in order to evaluate the calculated oxygen NMR properties, crystal structure, and DNP NMR experimental data. The two crystallographic oxygen sites contained quadrupolar coupling constants of −6.632 and −7.034 MHz with asymmetry parameters of 0.91 and 0.88.…”

“… i - Ba et al 136 ; ii - Spiess et al 135 ; iii - Dong et al 106 ; iv - 17 O MAS NMR data acquired at 17.4 T (see Figure S4); * -Where multiple crystallographic oxygen sites existed the averages of these are presented within the table (please refer to supporting information Tables S1 to S3). Experimental uncertainties are given in parenthesis.…”