Structural Properties of Inverted Hexagonal Phase:
A Hybrid Computational and Experimental Approach
Posted on 2020-06-12 - 14:05
Inverted/reverse
hexagonal (HII) phases are of special
interest in several fields of research, including nanomedicine. We
used molecular dynamics (MD) simulation to study HII systems
composed of dioleoylphosphatidylethanolamine (DOPE) and
palmitoyloleoylphosphatidylethanolamine (POPE) at
several hydration levels and temperatures. The effect of the hydration
level on several HII structural parameters, including deuterium
order parameters, was investigated. We further used MD simulations
to estimate the maximum hydrations of DOPE and POPE HII lattices at several given temperatures. Finally, the effect of acyl
chain unsaturation degree on the HII structure was studied
via comparing the DOPE with POPE HII systems. In addition
to MD simulations, we used deuterium nuclear magnetic resonance (2H NMR) and small-angle X-ray scattering (SAXS) experiments
to measure the DOPE acyl chain order parameters, lattice plane distances,
and the water core radius in HII phase DOPE samples at
several temperatures in the presence of excess water. Structural parameters
calculated from MD simulations are in excellent agreement with the
experimental data. Dehydration decreases the radius of the water core.
An increase in hydration level slightly increased the deuterium order
parameter of lipids acyl chains, whereas an increase in temperature
decreased it. Lipid cylinders undulated along the cylinder axis as
a function of hydration level. The maximum hydration levels of PE
HII phases at different temperatures were successfully
predicted by MD simulations based on a single experimental measurement
for the lattice plane distance in the presence of excess water. An
increase in temperature decreases the maximum hydration and consequently
the radius of the water core and lattice plane distances. Finally,
DOPE formed HII structures with a higher curvature compared
to POPE, as expected. We propose a general protocol for constructing
computational HII systems that correspond to the experimental
systems. This protocol could be used to study HII systems
composed of molecules other than the PE systems used here and to improve
and validate force field parameters by using the target data in the
HII phase.
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Ramezanpour, M.; Schmidt, M. L.; Bashe, B. Y. M.; Pruim, J. R.; Link, M. L.; Cullis, P. R.; et al. (2020). Structural Properties of Inverted Hexagonal Phase:
A Hybrid Computational and Experimental Approach. ACS Publications. Collection. https://doi.org/10.1021/acs.langmuir.0c00600