Structure and Dynamics in Amphiphilic Bilayers: NMR and MD simulation Studies

Abstract

Solid-state nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations were employed to study molecular structure and dynamics in amphiphilic bilayers. This thesis reports on method development and practical applications to two types of bilayer systems: simple cell membrane models composed of phosphatidylcholine lipids and cholesterol; and liquid crystals composed of ethyleneoxide-based surfactants often used in technological applications and in fundamental studies of amphiphile self-assembly.



Structural analysis of the systems is done by means of C-H bond order parameters. Complete profiles of C-H bond order parameters are determined by using advanced solid-state 13C-1H NMR recoupling techniques. The profiles are obtained from samples with natural abundance of isotopes by combining polarization transfer methods with different sensitivities. The analysis of the order parameters measured is based on a combination of NMR experiments and MD simulations.



With respect to the dynamics in bilayer systems, an NMR protocol for measurement of rotational diffusion is presented and applied to a lipid bilayer system. The method enables quantification of the effective correlation time of C-H bond reorientation motions at time-scales between nanoseconds and microseconds.

Abstract (Swedish)

Popular Abstract in English

Drizzle a thin stream of olive oil into water. The oil splashes into tiny little drops first, and in a fraction of a second, they emerge from bulk to the surface, and then coalesce to form a thin layer. This phenomenon relates to the molecular properties of the liquids. Olive oil is composed, in a large extent, of molecules with a fierce name, triglycerides, which are built by a glycerol group and three fatty acid chains attached to it. Although glycerol alone dissolves in water, the fatty acid chains are insoluble which renders the olive oil immiscible in water.



Lecithins are natural molecules very similar to triglycerides, except for one of the fatty acid groups that is replaced by a water-soluble chain. Thus, when lecithins are mixed with water, a part of the molecules wants to be hydrated but their fatty acid chains will force their way to avoid any occasional contact with the water molecules (scientific studies indicate that rather water wants to avoid fat but that's another story). This love/hate duality makes lecithin molecules to adopt a position that pleases both parties: they self-assemble into a two molecule thick bilayer film, with the insoluble parts forming an inner core of fat, and the water soluble parts directing outwards to the aqueous medium.



This thesis concerns how lecithins and other molecules with a similar love/hate duality towards water, behave within a fluid bilayer. Focus is put on applying and developing methods to find out how they displace themselves and how fast they move. The studies were carried out by combining two types of techniques. One uses an intrinsic property of particles called spin which can be accessed in a truly ingenious way by nuclear magnetic resonance (NMR) spectroscopy. The second method dismisses the real molecules, and instead calculates, through the single use of computers, how the molecules should move, in order to ultimately generate an atomic-detail computer animation of the bilayer.



If one can already watch the molecules in the computer why to worry with performing experiments then? This thesis delves around this and other related questions, and represents a little contribution as part of a wide effort to make the movies better.

• author: Ferreira, Tiago
• supervisor: Daniel Topgaard
• opponent: Dr. Gawrisch, Klaus, Laboratory of Membrane Biochemistry and Biophysics, NIH
• organization: Physical Chemistry
• publishing date: 2013
• type: Thesis
• publication status: published
• subject: Physical Chemistry
• defense location: Lecture hall B, Center for Chemistry and Chemical Engineering, Lund
• defense date: 2013-06-05 13:15:00
• ISBN: 978-91-7422-322-4
• language: English
• LU publication?: yes
• id: e7ad4ba3-24da-4d9a-a992-b5f8fbb967a4 (old id 3878850)
• date added to LUP: 2016-04-04 10:56:26
• date last changed: 2018-11-21 21:01:41