Phase Behavior of Mixed Lipid Bilayers Adsorbed on a Surface
Date Issued
2014
Date
2014
Author(s)
Sie, Bing-Yan
Abstract
Biological membranes are composed of different types of lipids. Lipids comprise a hydrophilic head and two hydrophobic tails. A lipid bilayer anchored to a hydrophilic solid surface is called a supported lipid bilayer (SLB). A SLB can exist stably within a solution for more than several weeks or months. As a consequence, a SLB is an ideal model for studying biological membrane.
Lipid bilayers can exhibit different phases depending on temperature. Generally, a lipid bilayer can be in either a liquid or a solid (gel) phase at a given temperature. The bilayer can take on a solid-ordered phase state at low temperatures but exhibit a liquid-disordered state at high temperatures. That is, the lipid tails are highly ordered in the gel phase and become disordered in the liquid phase. For some lipids, there exists a rippled phase between the gel and liquid phases. The temperature at which a transition from the gel phase to the rippled phase takes place is called the pre-transition temperature (Tp) and it is linked to the formation of periodic membrane ripples. Subsequently the melting of the bilayer from the rippled phase to the liquid phase occurs at the main transition temperature (Tm).
In this work, we use dissipative particle dynamics to investigate the phase
behaviors of supported mixed lipid bilayers. It is found that certain physical properties, such as membrane thickness, membrane area, lipid order parameter are a function of temperature. Tmcan be accurately determined from the inflection point of the property versus temperature curves. Our results reveal that Tms of lipids with unsaturated bonds are greatly reduced and Tm of a mixed lipid bilayer situates between Tms of constituent pure lipids depending on the mixing ratio. Phase separation becomes more significant as difference in lipid tail length increases or number of unsaturated bonds grows. Moreover, the mechanical properties, such as bending and stretching modulus, dip to a minimum value as temperature reaches Tm indicating the membrane becomes most soft and stretchable at the main transition temperature.
Subjects
生物膜
脂質
轉移溫度
Type
thesis
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