23:2 Diyne PC [DC(8,9)PC]
1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine
Phospholipid containing photo-polymerizable diacetylene fatty acids. These phospholipids produce structures with characteristics of both biomembranes and synthetic polymers.
Notes:
- The UV wavelength for efficient polymerization of diacetylene-containing lipids is 254nm.
- Protect diacetylene phospholipids from light, especially in solution.
- Diacetylene phospholipids will spontaneously polymerize in solution. Store the lipid as a powder for maximum stability.
- Recommend storage at -20° C or less.
The photopolymerization of diacetylenic lipids is topotactic, thus the rate of polymerization depends strongly upon the correct alignment of the acetylenic monomer units. Efficient photopolymerization can only be achieved if the diacetylenic hydrocarbon chains are in a crystal-like lattice that is present at a temperatures well below the lipid transition temperature (40°C). Diacetylenic lipids are photopolymerized using a low pressure mercury arc lamp, where the photoproduct is initially blue in color and then relaxes to form a red polymer.
Experimental Procedures for the Polymerization of Sonicated Vesicles
Always protect diacetylenic lipids from UV light, thus prepare photopolymerizable membranes in yellow or red light. Prepare sonicated vesicles using a probe sonicator, following typical experimental protocols to prepare small unilamellar vesicles. (In the referenced paper, sonicated vesicles were the only photopolymerized structures obtained, presumably large unilamellar vesicles prepared by extrusion are also polymerizable and membrane curvature does not affect the efficiency of photopolymerization). An aliquot of the vesicles is irradiated at 20°C in a 1-mm quartz cell using a low-pressure Hg arc lamp (253.7 nm) 6-13 cm from the sample. Just prior to irradiation the aqueous suspension of vesicles is purged of oxygen by first flushing the photocell with argon and then capping it under an argon atmosphere.
Notes:
- It has been found that the photosensitivity of diacetylenic containing membranes is dependent upon its thermal history. Membranes composed of diacetylenic lipids are light sensitive when prepared below the phase trasition but become insensitive to light after the membranes are heated above the transition temperature (40°C). The membranes remain insensitive to light even after they are cooled to 25°C, and only when they are cooled to near 0°C is light sensitivity regained.
- Photopolymerization of diacetylenic and non-polymerizable lipid (DOPC, DSPC etc.) mixtures depends upon lipid miscibility. High degrees of polymerization cannot be achieved in lipid mixtures where the diacetylenic groups are diluted by other non-polymerizable lipids.