Cooperativity and kinetics of phase transitions in nanopore-confined bilayers studied by differential scanning calorimetry.

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 approximately 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.