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Cooperativity and Kinetics of Phase Transitions in Nanopore-Confined Bilayers Studied by Differential Scanning Calorimetry

Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204

Correspondence: Address reprint requests and inquiries to Alex Smirnov, Tel.: 919-513-4377; Fax: 919-513-7353; E-mail: alex_smirnov{at}ncsu.edu.

The first-order nature of the gel-to-liquid crystal phase transition of phospholipid bilayers requires very slow temperature rates in differential scanning calorimetry (DSC) experiments to minimize any rate-dependent distortions. Proportionality of the DSC signal to the rate poses a problem for studies of substrate-supported bilayers that contain very small volumes of the lipid phase. Recently, we described lipid bilayers self-assembled inside nanoporous substrates. The high density of the nanochannels in these structures provides at least a 500-fold increase in the bilayer surface area for the same size of the planar substrate chips. The increased surface area enables the DSC studies. The rate-dependent DSC curves were modeled as a convolution of a conventional van't Hoff shape and a first-order decay curve of the lipid rearrangement. This analysis shows that although confinement of bilayers to the nanopores of 177 nm in diameter results in a more than threefold longer characteristic time of the lipid rearrangement and a decrease in the cooperative unit number, the phase transition temperature is unaffected.

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