Phase transition behavior of single phosphatidylcholine bilayers on a solid spherical support studied by DSC, NMR and FT-IR

Abstract

For the first time, the chain melting transition from the gel phase to the liquid crystalline phase of a single DPPC bilayer on a solid, spherical support (silica beads) is observed by differential scanning calorimetry (DSC). This transition is remarkably cooperative, exhibits a transition temperature T(m) which is 2 degrees C lower than usually found for DPPC multilamellar vesicles and its excess enthalpy is about 25% less than in DPPC multilayers. 31P- and 2H-NMR data as well as FT-IR data provide evidence that despite the highly asymmetric characteristic of the model system, the whole single bilayer undergoes the transition at T(m), i.e., there is no decoupling of the two monolayer leaflets at the main phase transition. Furthermore, our results show that the formation of the ripple (P(beta')) phase is inhibited in single bilayers on a solid support. This result confirms a conclusion which we reached previously on the basis of neutron scattering data obtained on planar supported bilayers. The most likely reason for this inhibition as well as for the above mentioned thermodynamic differences between multilamellar vesicles and supported membranes is a significantly higher lateral stress in the latter. Moreover, the exchange of lipids between two populations of spherical supported vesicles (DMPC and chain perdeuterated DMPC) is studied by DSC. It is shown that this exchange process is symmetric and its half-time is a factor of 3-4 higher than observed for small sonicated DMPC vesicles.

Swelling of Phospholipid Floating Bilayers: The Effect of Chain Length

“…This would imply that for the floating bilayer T m is lower than the value reported for multilamellar systems [29,30]. A comparable lowering of the melting temperature has been previously observed on single bilayers on a solid support [32] and was attributed to surface tension effects. Two experimental facts enforce this hypothesis: (i) the swelling temperature T s seems to be always shifted by [4][5] • C from the bulk T m value (figure 3 and 9) independently of the phospholipid chain length; (ii) measurement made on deuterated Di-C 18 -PC in H 2 O in water exhibit also swelling and no literature data were found on a transition to the ripple phase for those deuterated species.…”

Dynamics of supported lipid bilayer deposition from vesicle suspensions

“…The two leaflets exhibit a cooperative main phase transition, indicating that they interact strongly. The lateral stress, which increases with substrate curvature, has a significant effect on phase behavior, resulting in the shift of solidus and liquidus points during the transition [27,41].…”

Supported Bilayers On Silica

“…Some authors report coverage with one lipid bilayer which is separated from the bead surface by a water layer of thickness 1.5-2.0 nm (12,13), whereas others indicate formation of one monolayer at the interface with polar head groups oriented into the aqueous phase (14,15). Deposition of a supported monolayer on quartz with double chains oriented into air was followed by vesicle fusion in water solution to end up with a bilayer (16).…”