jp5b10085_si_001.pdf (1.97 MB)
Factor Analysis of Conformations and NMR Signals of Rotaxanes: AIMD and Polarizable MD Simulations
journal contribution
posted on 2016-02-04, 15:00 authored by Pingying Liu, Wei Li, Zigui Kan, Hui Sun, Jing MaThe
interlocked ⟨rod | ring⟩ structures of pseudorotaxanes
and [2]rotaxanes are usually maintained by the complex hydrogen-bonding
(H-bonding) network between the rod and ring. Ab initio molecular
dynamics (AIMD) using generalized energy-based fragmentation approach
and polarizable force field (polar FF)-based molecular dynamics (MD)
simulations were performed to investigate the conformational changes
of mechanically interlocked systems and to obtain the ensemble-averaged
NMR chemical shifts. Factor analysis (FA) demonstrates that the ring
H-donor (2,6 pyridinedicarboxamide group) plays an important role
in the ring–rod recognition. In comparison to the conventional
fixed-charge force field, the polarization effect is crucial to account
for the H-bonding interactions in supramolecular systems. In the hybrid
scheme, the polar FF-based MD simulations are used to generate different
initial states for the AIMD simulations, which are able to give better
prediction of ensemble-averaged NMR signals for chemically equivalent
amide protons. The magnitude of the deshielding shift of NMR signal
is correlated with the length of hydrogen bond. The polar FF model
with variable charges shows that the dipole–dipole interactions
between the flexible diethylene glycol chain of ring and polar solvents
induce the upfield shifts of NMR signals of rod H-donors and the directional
distribution of the neighboring CH3CN solvents.