1 research outputs found
Molecular Simulations of Hydrogen Bond Cluster Size and Reorientation Dynamics in Liquid and Glassy Azole Systems
We
simulated the dynamics of azole groups (pyrazole, imidazole,
1,2,3-triazole, 1,2,4-triazole, and tetrazole) as neat liquids and
tethered via linkers to aliphatic backbones to determine how tethering
and varying functional groups affect hydrogen bond networks and reorientation
dynamics, both factors which are thought to influence proton conduction.
We used the DL_Poly_2 molecular dynamics code with the GAFF force
field to simulate tethered systems over the temperature range 200β900
K and the corresponding neat liquids under liquid state temperatures
at standard pressure. We computed hydrogen bond cluster sizes; orientational
order parameters; orientational correlation functions associated with
functional groups, linkers, and backbones; time scales; and activation
energies associated with orientational randomization. All tethered
systems exhibit a liquid to glassy-solid transition upon cooling from
600 to 500 K, as evidenced by orientational order parameters and correlation
functions. Tethering the azoles was generally found to produce hydrogen
bond cluster sizes similar to those in untethered liquids and hydrogen
bond lifetimes longer than those in liquids. The simulated rates of
functional group reorientation decreased dramatically upon tethering.
The activation energies associated with orientational randomization
agree well with NMR data for tethered imidazole systems at lower temperatures
and for tethered 1,2,3-triazole systems at both low- and high-temperature
ranges. Overall, our simulations corroborate the notion that tethering
functional groups dramatically slows the process of reorientation.
We found a linear correlation between gas-phase hydrogen bond energies
and tethered functional group reorientation barriers for all azoles
except for imidazole, which acts as an outlier because of both atomic
charges and molecular structure