Lipid Nanotube Arrays: Exploring Nanoscale Phenomena on Lipid-Substrate Interfaces.

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Title: Lipid Nanotube Arrays: Exploring Nanoscale Phenomena on Lipid-Substrate Interfaces.
Author: Alaouie, Ali Mustafa
Advisors: Professor Alex I. Smirnov, Committee Chair
Abstract: Substrate-supported-phospholipids bilayers (SSPB) could be utilized to stabilize functional membrane proteins on solid surfaces while providing an ideal medium to mimic the many properties of biological membranes. Our approach to the fabrication of SSPB relies on the property of phospholipids to self-assemble inside Anodic Aluminum Oxide (AAO) nanoporous substrates into cylindrical structures, which we call 'lipid nanotubes'. In our design, the phospholipids are adequately protected from any surface perturbations or contamination and yet accessible to solute molecules. Furthermore, when compared with planar supported membrane designs, our substrate would have a larger surface area covered with lipids for an identical outside dimensions. This improvement would allow for accommodating more functional proteins. An additional advantage is that our porous biochip should be able to retain more water and for a longer time duration through capillary action. Since water is known to be essential for the phospholipids to maintain their bilayer assembly, our design will be more robust in handling and applications than the fragile planar surface assemblies. The purpose of this research was to investigate the presence and formation of ordered lipid nanotubes as well as studying the effects of nano-scale confinement on the structure and dynamics of self-assembled phospholipid membranes. These lipid nanotubes were found to behave very much similar to unsupported phospholipid bilayers. The existence of ordered lipid nanotube assemblies was confirmed by spin-labeling electron paramagnetic resonance (sl-EPR). Differential scanning calorimetry and spin-labeling experiments demonstrated that the main phase transition temperatures for AAO-confined and unsupported DMPC bilayers were essentially the same; however, the van't Hoff enthalpy was lower for AAO-confined bilayers. Additionally, it was observed that the main effect of nanopore confinement is in longer time constants associated with lipid rearrangement during the phase transition and/or motional restrictions but not in the thermodynamics as previously thought. This research also examined the inclusion of a model gramicidin A (gA) ion channel into lipid nanotube arrays and demonstrated using sl-EPR that ordered assemblies are present in addition to confirming that the active dimer form of gA was being formed.
Date: 2006-08-28
Degree: PhD
Discipline: Chemistry

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