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Investigating the Molecular Order and Orientation of Cholesterol in Mixtures of Polyunsaturated Phospholipids

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Title: Investigating the Molecular Order and Orientation of Cholesterol in Mixtures of Polyunsaturated Phospholipids
Author: Braithwaite, Iain M.
Department: Department of Physics
Program: Physics
Advisor: Davis, James H.
Abstract: Cholesterol is critical to ensure proper functioning of a membrane. Despite this, the movement of cholesterol within the cell is not fully understood. The molecular order of binary and ternary mixtures of polyunsaturated fatty acids with varying degrees of hy- drocarbon chain unsaturation with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and/or cholesterol was studied using 2H NMR. The introduction of cholesterol into sam- ples of 18:1PC, 18:2PC (unsaturated lipid/DMPC-d54/CHOL, 75:5:20mol%) increased the C-2H bond order by ∼30%. Similar bond ordering was found for 20:4PC and 22:6PC samples, however, they were temperature dependent. A two-phase region (lo-ld) was found for 22:6PC:DMPC-d54/CHOL (75:5:20mol%) for temperatures below 286.7 K. The reorientation axis formed an angle of 78±4◦ with respect to the C3-2H bond vector re- gardless of the lipid. The order parameter of cholesterol was temperature independent, and ranged from 0.69±0.04 to 0.78±0.04 depending on the lipid unsaturation. The re- orientation axis of cholesterol was oriented at ∼25◦ to the bilayer normal.
URI: http://hdl.handle.net/10214/2885
Date: 2011-08
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