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Abstract:
We have investigated the reorientational mobility of n-hexane and n-pentanol guest molecules in Dianin's compound and in zeolite 5A by molecular mechanics/dynamics calculations (MM/MD) and temperature-dependent solid-state 2H NMR. To choose the proper motional models for the different host-guest systems, MM calculations were first performed and minimum-energy structures for the compounds were established. The calculations were performed on a crystallographic unit cell, with periodic boundary conditions to minimize edge effects. MD methods were then applied to the minimized structures and provided an insight into the different dynamic modes experienced by the guest molecules in their host cages. Several structural parameters of the host-guest systems were monitored for a total simulation period of up to 100 ps both at low temperature (77 K) and high temperature (300 K). 2H NMR spectra of perdeuterated and specifically deuterated guest molecules in their inclusion compounds were acquired as a function of temperature. After detection the observed line shapes were analyzed in terms of motional models, taking into account experimental parameters and the results of the MD calculations. The solid-state 2H NMR showed a very high degree of agreement with the results of the molecular modeling calculations.
