Simulation of NMR Spectra from MD trajectories. Application to Solid State 2H NMR of Deuterated ImTPA Host Guest Crystals

Cook, Dennis (2020) Simulation of NMR Spectra from MD trajectories. Application to Solid State 2H NMR of Deuterated ImTPA Host Guest Crystals. Masters thesis, University of East Anglia.

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This work predicts the effects of molecular motions on NMR measurements, namely 2H NMR line shapes arising from quadrupolar coupling (Pake pattern) and T1 relaxation times directly and completely from the results of all-atom MD simulations. Simulations were performed on a host guest system of ImTPA crystals at two characteristic temperatures. The resulting trajectories have been used for the first time to predict 2H NMR line shapes based on the theoretical and computational methodology originally developed by Oganesyan for the prediction of EPR spectral line shapes from atomistic MD trajectories [1] adapted for predicting NMR spectra.
DFT methods have been employed to optimise the structures of host and guest molecules, generating parameters for the force fields in MD runs using GROMACS and calculated the quadrupolar coupling tensor components of 2H sites in Imadazolium Ions.
2H NMR spectra were predicted using two approaches; i) direct propagation of the density matrix (DP) for the spin system using the Stochastic Liouville Equation (SEL) [2] and time dependent Liouville superoperator and ii) applying fast motional limit (FML) approximation which employs the motionally averaged quadrupolar coupling tensor. The results are compared to the experimental measurements available from the literature.
It is concluded that the NMR predictions based on the FML approach provide an adequate representation of the two-states jump motions of the Imidazolium Ions in ImTPA capturing accurately their impact on the NMR line shapes at different temperatures. Predictions by DP method are broadly in agreement with the FML but, in comparison with EPR, require longer trajectories for an adequate spectral simulation.
Predictions of T1 relaxation times arising from the dynamical modulation of the quadrupolar coupling term in the spin-Hamiltonian are reported at both temperatures for a range of magnetic field strengths using the same MD trajectories.

Item Type: Thesis (Masters)
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Nicola Veasy
Date Deposited: 18 Mar 2021 10:57
Last Modified: 18 Mar 2021 10:57


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