Lipids with polymerizable group

The components can be chosen so that the material is biocompatible, opening up possibilities for use in controlled-release drug-delivery and other medical and biological applications that call for nontoxicity. It is known that many biological lipids form bicontinuous cubic phases, and many of these have modifications with polymerizable groups, such as the monolinolein case discussed above. 

K. Dorn 105 > polymerized dialkylammonium lipids with the polymerizable methacryloyl moiety either in the head group (29) or at the end of one of the hydrophobic chains (5). GPC revealed Mw 1.9 x 106, Mn 3.5 x 105, Mw/Mn 5.4 for (29) and Mw 1.9 xl06,Mn 3.9 x 105, Mw/Mn 2.4 for (5). It was also found that Mw varies inversely with the time of sonication, i.e. in smaller liposomes lower-molecular-weight polymers are formed. In a following paper, K. Dorn 108 present data for the permeability of monomeric and polymeric vesicles from (29). 

The final class of important synthetic lipids are those with a polymerizable substituent. A significant concept present is the introduction of a hydrophilic spacer group between the hydrophobic core and the polymerizable group. Only in polymers made of spacer lipids does the polymer chain remain flexible enough to decouple its movements from those of the membrane in order to... 

Figure 10.9. Structures of the polymerizable diacetylene containing lipid with lanthanide chelating head groups (EDTA or chelimadic add) used by Roy and co-workers for Tb sensitization are shown.

For some time, there has been interest in the controlled release properties of stabilized liposomes.(i-3) A number of methods for stabilizing liposomes have been developed. Liposomes have been prepared from lipids which contain polymerizable groups such as methacrylate, butadiyne, or diacetylene and subsequently polymerized.(4-6) Another strategy is to n e liposomes from lipids with amino add headgroups and then potymerize the liposome Ity potycondensatioiL(7) Alternatively, stabilized liposomes have been prepared from prepolymerized amphiphiles.(8) Recently, the design and preparation of... 

Since the fatty acid chains in each lipid were 18 carbons and 16 carbons, respectively, it is reasonable that they could form a mixed lipid phase. Furthermore the bis-dienoyl substitution of 15 favors the formation of crosslinked polymer networks. Ohno et al. showed that the dienoyl group associated with the sn-1 chain could be polymerized by lipid soluble initiators, e.g. AIBN, whereas the dienoyl in the sn-2 chain was unaffected by AIBN generated radicals. Conversely, radicals from a water-soluble initiator, e.g. azo-bis(2-amidinopropane) dihydrochloride (AAPD), caused the polymerization of the sn-2 chain dienoyl group, but not the sn-1 chain. These data provide clear evidence for the hypothesis of Lopez et al. that the same reactive group located in similar positions in the sn-1 and sn-2 chains of polymerizable 1,2-diacyl phospholipids are positionally inequivalent [23]. 

All four types of polymerizable lipids shown in Fig. 4 have been realized synthetically. In this context, one need not attempt to reproduce mother nature slavishly (Fendler 8)). Kunitake 9) was able to show that simple molecules like dialkyldimethyl-ammonium salts also form bilayer assemblies. Fuhrhop 10) and Kunitake U) could accomplish the formation of monolayer liposomes with molecules containing only one alkyl chain and two hydrophilic head groups. Acryloylic and methacryloylic groups (type a and d, Table 1), as well as diacetylenic, butadienic, vinylic and maleic acid groups (type b and c), have been used as polymerizable moieties. A compilation of amphiphilic, photopolymerizable molecules is given in Table 1. 

Natural lipids used for fusion experiments were mainly phospholipids with different chain lengths and their mixtures with cholesterol. As polymerizable lipids, butadienic derivatives with a phosphatidylcholine (19) and a dimethylammonium head group (26) were used in the fusion experiments. 

Figure 10.4. Polymerizable lipids used for the detection of oligosaccharides (with primary amine as the head groups) are shown.

---