Temperature Driven Annealing of Perforations in Bicellar Model Membranes

Journal Article · Sat Jan 01 00:00:00 EST 2011 · Langmuir

DOI:https://doi.org/10.1021/la104750x· OSTI ID:1024327

Nieh, Mu-Ping ^[1]; Raghunathan, V. A. ^[2]; Pabst, Georg ^[3]; Harroun, Thad ^[4]; Nagashima, K ^[5]; Morales, H ^[5]; Katsaras, John ^[6]; Macdonald, P ^[5]

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1. University of Connecticut, Storrs
2. Raman Research Institute, India
3. Austrian Academy of Sciences, Graz
4. Brock University, Canada
5. University of Toronto, Canada
6. ORNL

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), {sup 31}P NMR, and {sup 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. {sup 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, {sup 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.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Laboratory Directed Research and Development (LDRD) Program
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1024327
• Journal Information: Langmuir, Vol. 27, Issue 8; ISSN 0743-7463
• Country of Publication: United States
• Language: English