Phase and Dynamic Behavior of Binary Lipid Bilayer on Solid Surface
Date Issued
2015
Date
2015
Author(s)
Wei, Yuan-De
Abstract
Cell membranes are composed of different types of lipids, protein, cholesterol and other different substances. A phospholipid comprises a hydrophilic head group and two hydrophobic tails, so it can form a bilayer in aqueous environment. A supported lipid bilayer (SLB) is a lipid membrane fixed on a hydrophilic solid surface, so the lipid membrane is quite stable in an aqueous solution, allowing the use of some characterization tools. Therefore, SLB is a popular model for studying cell membranes. In this work, we employed dissipative particle dynamics (DPD) method to investigate the transition temperatures and phase behavior of supported binary lipid mixtures. Depending on temperature, a lipid bilayer can exist in different phases, and the phase separation of lipid can be observed in two-component supported lipid bilayers. The morphology of binary mixtures are strongly dependent on the structure and the molar composition of the two constituents. For most phospholipids, the tails of lipid are highly ordered and the membrane thickness is larger at low temperature, which is called the gel phase. When the bilayer at high temperature, the gel phase undergoes a transition to liquid phase where the tails are disordered and the membrane thickness is smaller. The main transition temperature is the temperature where the phase transition occurred. We also found that phase transition in mixed lipid bilayers is different from single component lipid bilayers, there is no longer a single transition from gel phase to liquid phase. A gel and liquid coexistence region separated from gel and liquid phase. As increasing the difference between two lipid tails length, the coexistence region is more distinctly. In our previous work, we have confirmed the validity of the pure lipid bilayer in simulation. Confirming the validity of our binary system with thermodynamics is our next step. In order to measure the main transition temperature, we used to use DSC to measure the heat capacity in experiment, and use statistical thermodynamics relation in simulation. In this work, we tried to use different methods to measure the main transition temperature, likes order parameter and diffusivity. And then, we studied the morphology of binary lipid bilayer with two different tails length by thickness, standard deviation of thickness, thickness distribution and order parameter.
Subjects
Dissipative particle dynamics
Supported lipid bilayer
phase separation
Type
thesis
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