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General
Information:
The UV wavelength for efficient polymerization of diacetylene-containing
lipids is 254nm.
Protect diacetylene phospholipids from light, especially in solution.
Recommend storage at -20° C or less.
Diacetylene phospholipids will spontaneously polymerize in solution thus store the lipid as a neat powder.
Preparation
Lipids that polymerize have been the subject of a number of
recent research efforts. These lipids originated from the
work of Chapman in 1980. The diacetylenic lipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine
is patented and Avanti has obtained worldwide rights
to manufacture and distribute this molecule. Multi-kilogram
quantities are available.
References
Regen, S.L., (1991), "Polymerized Liposomes as Drug
Carriers", Polymer- Controlled Drug Delivery,
83-97.
Johnston, D.S., Sanghera, S., Pons, M. Chapman, D., (1980),
"Phospholipid Polymers-Synthesis and Spectral Charac-teristics",
Biochimica et Biophysica Acta, 602, 57-69.
Freeman F.J. & Chapman, D., (1988), "Polymerizable
Liposomes: Applications in Biology and Medicine", in
Liposomes as Drug Carriers, (Gregoriadis, G., Ed.)
21-839.
Hayward, J.A. & Chapman, D., (1984), "Biomembrane
surfaces as models for polymer design: the potential for
haemocompatibility," Biomaterials, 5, 135-142
Georger, J.H., et al, (1987), "Helical and tubular
micro-structures formed by polymerisable phosphatidylcholines.
Journal of the American Chemical Society, 109, 6169-6175.
Notes on the Polymerization of the Diacetylenic Lipid
1,2-Bis(10,12-Tricosadiynoyl)-sn-
Glycero-3-Phosphocholine
Much of the information given in this brief experimental description of the ultraviolet-light initiated
photopolymerization of diacetylene-containing lipids was obtained from research as described by
Warunee Srisiri, Youn-Sik Lee, Thomas M. Sisson, Bruce Bondurant and David F. O'Brien Polymerization of supramolecular assemblies: Comparison of lamellar and inverted hexagonal phases
Department of Chemistry, C. S. Marvel Research Laboratories, University of Arizona, Tucson, Arizona 85721, USA [Science Direct]
Lee YS, O'Brien DF. Chain substituted polymerizable ether lipids: synthesis of sorbyl and diacetylenic ether glycerophosphocholine.
C.S. Marvel Laboratories, Department of Chemistry, University of Arizona, Tucson
85721. [PubMed]
Neumann R, Ringsdorf H, Patton EV, O'Brien DF. Preparation and characterization of long chain amino acid and peptide vesicle membranes. Biochim Biophys Acta. 1987 Apr 23;898(3):338-48. [PubMed]
Sonicated vesicles composed of pure 10,12-tricosadiynoyl containing lipids, as well as mixtures of
the polymerizable lipid with non-polymerizble lipids such as dioleoylphosphocholine (DOPC) and
distearoylphosphocholine (DSPC) are polymerizable but to different degrees. 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.
