Henry Lamparski

Polymerization and domain formation in lipid assemblies

Lipid assemblies are arrays of noncovalently associated amphiphiles, i.e. supramolecular assemblies. They may be classified as supported or self-supported assmeblies. The advent of methods to polymerize these supramolecular assemblies has opened up opportunities for the creation of new materials. This review emphasizes the interaction of polymerization and lipid domain formation within supramolecular assemblies. The polymerization of amphiphilic assemblies can “lock in” preexisting lipid domains or create lipid domains from random mixtures depending on the nature of the polymerizable amphiphile. Lipid diacetylenes or fluorinated lipids provide a convenient means to form an unpolymerized immiscible mixture of reactive and nonreactive lipids in monolayers or bilayers. In contrast the polymerization of dienoyl-, sorbyl-, or acryloyl-substituted lipids can effectively induce the phase separation of unreactive lipids from the growing polymeric domains. Polymerization-induced lipid domains can endow bilayer vesicles with latent instability sites or can be used to concentrate membrane-associated electron or energy transfer cofactors. These polymeric materials suggest new approaches to the delivery of reagents as well as the transduction of light energy.

Two-dimensional polymerization of lipid bilayers : Effect of lipid lateral diffusion on the rate and degree of polymerization

Hydrated amphiphiles can yield quite complex lyotropic liquid crystals such as the lamellar (bilayer) and nonlamellar phases. Lamellar structures can be solidlike or liquid crystalline. An important characteristic of these lamellar phases is the lateral diffusion of the lipids which increases by ca. 102 at the main phase transition, Tm. The rate (Rp) and degree (Xn) of polymerization were determined for polymerizable lipids in these two phases. A determination of the effect of temperature between 25 and 45 °C on the Rp of redox-initiated polymerization of mono-SorbPC bilayers showed a discontinuity near the Tm. The calculated activation energy, Ea, and frequency factor, A, for the polymerization at temperatures below Tm are 10 kcal/mol and 107, respectively. A similar calculation for the polymerization at temperatures above the Tm gave an Ea = 24 kcal/mol and A = 1016. The degree of polymerization, relative to poly(methyl methacrylate) standards, for bilayers of mono-SorbPC at temperatures above and below...