6533b82afe1ef96bd128b73f

RESEARCH PRODUCT

Compound Membranes of Linearly Polymerized and Cross-Linked Macrolipids with Phospholipids: Preparation, Microstructure and Applications

subject

description

Methods for the assembly and for studying the structural and dynamic properties of partially polymerized membranes are described. Mixtures of two classes of polymerizable amphiphiles with diacyl phosphatidylcholines are studied: (1) phosphatidylcholines carrying a diacetylene group per chain (abbreviated as (m,n)-DIINPC (where m + n + 6 equals number of C-Atoms per chain) and (2) a phospholipid-like molecule with a polymerizable methacryl ligand connected to the phosphate head group via (CH2CH2O)m spacers which is abbreviated as (m.n)-POMECY (n = number of C-atoms per chain). — Phase diagrams of the lipid mixtures are established by static light scattering in combination with freeze fracture electron microscopy. The latter technique is also used to study the microscopic organization of the components before and after polymerization. Measurements of lateral diffusion by the photobleaching technique allow to determine (1) the fraction of lipid polymerized and (2) the liquidus and solidus lines of individual vesicles. — By suitable choice of the chain lengths of the components, giant vesicles with DIINPC's can be prepared in such a way that they are stable against transitions into the solid state which is a prerequisite for polymerization of this lipid. For that, use is made of the domain-like lateral organization of the lipid components. The cross-linked DIINPC-domains exhibit a structure reminiscent of a two-dimensional sponge with inclusions (microdomains) of monomeric lipid embedded into the network. The mechanical stability of the vesicles against repeated transitions through the phase changes is established by phase contrast microscopy and the tightness by a fluorescence technique. By absorption spectroscopy the existence of a “red” and a “white” species of macrolipid is established. — The mixed vesicles with POMECY exhibit a much mechanical stability against phase changes but are less tight with respect to leakage of small dye molecules. By freeze fracture electron microscopy the degree of polymerization was estimated to N ⌣ 100. These membranes behave as two-dimensional macromolecular solutions up to about 10 mole-% of the polymerizable component. Above this limit lateral decomposition into a dilute solution and a two-dimensional polymer melt occurs.