Interactions between DPPC lipid bilayers and lignin G-G dimers (coniferyl alcohol) and their derivatives were studied using molecular dynamics (MD) simulations. Commercial G-G derivatives (CGds) and benzene modified G-G dimers (BMGds) show a higher affinity for the bilayer interior than natural dimers. In this study we compare MD results for the gel to liquid-crystalline transition temperature (Tm) with differential scanning calorimetry (DSC) experiment results. Specifically, the MD simulation systems studied consist of fully hydrated DPPC lipid bilayers in the presence of different concentrations of lignin dimers. After initial equilibration of the systems a cooling followed by a heating procedure is used to take the lipid bilayer from a liquid-like state to a gel-like state and then back. We captured the transition from gel to liquid phase by defining and analyzing of a normalized deuterium order parameter (NScd) averaged over all carbon atoms located in the middle of the lipid tails. Typically, with varying temperature the NScd exhibits, well defined, slightly different slopes at the beginning and at the end of the temperature interval and a relatively large slope change in the intermediate range, around the transition temperature Tm. The MD results show a very sharp and clear drop for a pure DPPC bilayer with Tm of 316.5 K which is very close to the experimental value of 314 K. However, once lignols are added to the system, the signal becomes nosier and wider. For 20 mol % lignols/lipids of CGds and BMGds, Tm shifts by -7.1K and -6.7K, respectively. This is qualitatively consistent with experimental values of -1.5K and -6 K. For 40 mol% lignols/lipids of CGds and BMGds, Tm shifts by -25K and -24.3K, respectively. While the trend for 40% is still correct, the MD shifts are much larger than from DSC. We further analyze the MD trajectories and study the location of the lignols and their effects on bilayer structure to explain the observed trends.

Molecular dynamics simulation study of the effect of lignin dimers on the gel to liquid-crystalline transition temperature in DPPC bilayers

2019 Spring National Meeting

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