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Water proton and deuterium spin-lattice relaxation in Zeolite ZSM-5 by fast field-cycling NMR relaxometry
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Westlund group)
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The water dynamics in the confined space of the zeolite ZSM-5 has bee ninvestigated by means of the field dependence of 1H- and 2H- spin-lattice relaxation rates using a 1T Stelar FFC2000 fast field-cycling instrument. The NMRD analysis of  the experimental results indicates that the characteristic time dependence ( 50 ns to 1-2.4 μs) is due to water translational diffusion in narrow pores. The temperature dependence of the spin-lattice relaxation rates is weak.Zeolites with different counter ions( H+, NH4+ change the water hydration and the water translational diffusion in the pores drastically. The Zeolite-NH4+ slow down the water motion with a factor of 2.The NMRD profiles show somewhat stretched character and is described by two Lorenzian which indicates that the distribution of pore sizes is broaden.The water 1H and 2H spin lattice relaxation profiles give qualitatively information about water hydration in zeolites with different counter ions and is expected also to indicate structural changes of the zeolites. 

Place, publisher, year, edition, pages
2015.
Keyword [en]
proton, deuterium, spin lattice, relaxation, ZSM-5, zeolite
National Category
Theoretical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-110716OAI: oai:DiVA.org:umu-110716DiVA: diva2:865031
Note

2015, in manuscript

Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2015-11-11
In thesis
1. Analysis of NMR Spin-lattice Relaxation Dispersion on Complex Systems
Open this publication in new window or tab >>Analysis of NMR Spin-lattice Relaxation Dispersion on Complex Systems
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focus on the analysis of spin-lattice NMRD relaxation profilesmeasured in various complex systems such as proteins, zeolites and ionicliquids. Proton, deuterium and fluoride T1-NMRD relaxation profiles wereobtained from a fast-field cycling (FFC) instrument. It is found that alsopossible to obtain NMRD profiles from the molecular dynamics (MD)simulation trajectories. NMRD Profiles were analyzed by using differentrelaxation models, such as the Solomon-Bloembergen-Morgan (SBM) theoryand the Stochastic Liouville (SL) theory.

Paper I described the hydration of protein PrxV obtained from a MDsimulation, and compared with the picture emerges from an analysis byusing a generally accepted relaxation model [appendix C]. The result showsthat the information from NMRD analysis is an averaged picture of watermolecules with similar relaxation times; and the MD simulations containsinformation of all types of interested water molecules with differentresidence times.

In paper II NMRD profiles have been used to characterize the hydration ofthe oxygen-evolving complex in state S1 of photosystem II. NMRDexperiments were performed on both intact protein samples and Mndepletedsamples, and characteristic dispersion difference were foundbetween 0.03 MHz to 1 MHz; approximately. Both the SBM theory and theSL theory have been used to explain this dispersion difference, and it isfound that this is due to a paramagnetic enhancement of 1-2 water moleculesnearby ~10 Å from the spin center of the Mn4CaO5 cluster. The result showsthe reorientation of the molecular cluster is in μs time interval. Whencompare these two theories, the SL theory presented a better interpretationbecause parameters obtained from the SBM theory shows they didn’t fulfilthe presupposed perturbation criterion (the Kubo term).

Paper III deals with the water dynamics in the restricted/confined spaces inthe zeolite samples (H-ZSM-5 and NH4-ZSM-5) and obtained by proton anddeuterium spin-lattice NMRD profiles. The results show that the spin-latticeNMRD can be used to characterize various zeolites. The temperature has aweak effect on the relaxation rate R1, but the change of different counter ionsmay change the hydration and the translational diffusion pores and givedifferent R1.

Proton and fluoride NMRD profiles and MD simulations were both used tostudy the dynamics of BMIM[PF6] in paper IV. Results indicate the reorientation of the molecules are in the ns time regime, and the effectivecorrelation time obtained from 1H and 19F are the same. From the MDsimulation it is found the reorientation of [PF6]- ions is much faster (in ps)compare with BMIM+ ion which moves in the ns time range.

With previous results, the FFC NMRD profiles are indeed very informativetools to study the molecular dynamics of complex systems. The MDsimulation can be used as a complementary method to obtain detailedinformation. By combine these two methods, it provide a more colorfulpicture in the study of protein hydration and liquid molecular dynamics.

Place, publisher, year, edition, pages
Umeå: Umeå university, 2015. 56 p.
Keyword
NMRD, relaxation theory, hydration, MD, FFC, PrxV, OEC complex, ZSM-5, BMIM [PF6, ]
National Category
Theoretical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-110721 (URN)978-91-7601-382-3 (ISBN)
Public defence
2015-11-26, KBC-huset, sal KB3B1, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2015-11-05 Created: 2015-10-26 Last updated: 2015-10-29Bibliographically approved

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