Date of Award

2016

Degree Type

Thesis

Degree Name

Master of Science in Chemical Engineering (MSChE)

Department

Chemical Engineering

First Advisor

Hongyan Yuan

Abstract

In the following work, the effect of shock impulses (2.5–10.0 mPa * s) on lipid bilayer membranes consisting of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phoshocholine) and varying amounts of cholesterol (10% and 50%) has been studied using molecular dynamics. Both models were equilibrated for 7 nanoseconds in an NPT ensemble at 310 K and 1 atm. After equilibration, the 50% cholesterol model showed a larger average membrane thickness and an increased average deuterium order parameter (SCD) of carbons in lipid tails when compared to the 10% model. In addition, values such as the total area per lipid and area per POPC were reduced in the 50% model when compared to the 10% cholesterol model.

After application of similar shock impulses to the 50% and 10% cholesterol models, the structural effects on each respective bilayer model were compared. The change in bilayer thickness due to shock impulse was measured for both models at all impulses tested. These values were used to calculate the percent decrease in bilayer thickness of both models. On average, the 50% cholesterol model showed a 1-2 % lesser reduction in bilayer thickness then the 10% cholesterol model at the shock impulses tested. After application of shock impulses to both models, the temporal change of the instantaneous averaged order parameter SCDi of the upper and lower monolayers of both models was calculated at shock impulses of 7.5 mPa * s and 10. mPa. * s. In both models, regardless of shock impulse, the SCDi value of the upper monolayer decreased followed by a decrease in the SCDi. parameter of the lower monolayer. These effects can be linked to the collapse phase of the lipid bilayer due to shockwave. Once the shockwave has fully traveled through the lipid bilayer, the SCDi parameter of the lower monolayer begins to increase which indicates beginning of the rebound phase. Finally, the increased fluidity of the lipid bilayer models was examined through calculation of the lateral displacement of the lipids in both models during the shockwave impulse ranges tested. The 50% model showed a slightly higher later displacement at the shock impulse ranges tested but not significantly higher to make any conclusions.

In addition, the efficiency of the shock impulse based on the distance of the shock water slab from the lipid bilayer was analyzed. The right boundary of the shock slab was placed 1 Ǻ and 10 Ǻ away from the lipid bilayer and similar shock impulses of 2.5, 5.0, 7.5 and 10 mPa * s were applied. It was shown that placement of the shock slab 10 Ǻ away from the lipid bilayer causes a greater decrease in average bilayer thickness and slight increases in kinetic energy, temperature and pressure of the system. This could be owed to better momentum transfer among molecules achieved when the water slab is placed 10 Ǻ away rather than 1 Ǻ away.

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