title: Temperature driven annealing of perforations in bicellar model membranes.
abstract: Bicellar model membranes composed of 1,2-dimyristoylphosphatidylcholine (DMPC) and 1,2-dihexanoylphosphatidylcholine (DHPC), with a DMPC/DHPC molar ratio of 5, and doped with the negatively charged lipid 1,2-dimyristoylphosphatidylglycerol (DMPG), at DMPG/DMPC molar ratios of 0.02 or 0.1, were examined using small angle neutron scattering (SANS), (31)P NMR, and (1)H pulsed field gradient (PFG) diffusion NMR with the goal of understanding temperature effects on the DHPC-dependent perforations in these self-assembled membrane mimetics. Over the temperature range studied via SANS (300-330 K), these bicellar lipid mixtures exhibited a well-ordered lamellar phase. The interlamellar spacing d increased with increasing temperature, in direct contrast to the decrease in d observed upon increasing temperature with otherwise identical lipid mixtures lacking DHPC. (31)P NMR measurements on magnetically aligned bicellar mixtures of identical composition indicated a progressive migration of DHPC from regions of high curvature into planar regions with increasing temperature, and in accord with the "mixed bicelle model" (Triba, M. N.; Warschawski, D. E.; Devaux, P. E. Biophys. J.2005, 88, 1887-1901). Parallel PFG diffusion NMR measurements of transbilayer water diffusion, where the observed diffusion is dependent on the fractional surface area of lamellar perforations, showed that transbilayer water diffusion decreased with increasing temperature. A model is proposed consistent with the SANS, (31)P NMR, and PFG diffusion NMR data, wherein increasing temperature drives the progressive migration of DHPC out of high-curvature regions, consequently decreasing the fractional volume of lamellar perforations, so that water occupying these perforations redistributes into the interlamellar volume, thereby increasing the interlamellar spacing.
authors: Chemical, Materials and Biomolecular Engineering Department, Institute of Material Sciences, University of Connecticut, 97 North Eagleville Road, Storrs, Connecticut 06269-3136, USA.
authors: Mu-Ping
authors: MP
authors: Nieh
authors: V A
authors: VA
authors: Raghunathan
authors: Georg
authors: G
authors: Pabst
authors: Thad
authors: T
authors: Harroun
authors: Kazuomi
authors: K
authors: Nagashima
authors: Hannah
authors: H
authors: Morales
authors: John
authors: J
authors: Katsaras
authors: Peter
authors: P
authors: Macdonald
mesh_terms: D004058:Diffusion; D004134:Dimyristoylphosphatidylcholine; D008051:Lipid Bilayers / Q000737:chemistry*; D008567:Membranes, Artificial; D008954:Models, Biological; D010539:Permeability; D010713:Phosphatidylcholines; D016062:Porosity; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; C032166:1,2-hexanoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine