Lipid hybrid structures

Hybrid structures of dendrimers with other entities have been synthesized for their collective properties. The most common is PEGylation of dendrimers (Kojima et al. 2010) to increase their circulation in the blood and to avoid immune clearance. Lipids have also been attached on the surface of PAMAM dendrimers to reduce toxicity and increase cellular uptake (Jevprasesphant et al. 2003). More interesting architectures have been created such as attachment of C60 fullerene balls (Jensen et al. 2005) on the surface of PAMAM dendrimers that act as nanoreactors by the generation of singlet oxygen species. In another instance, dendrimer-based micelles have also been prepared for anticancer therapy (Jang et al. 2005). Table 85.2 lists some of these hybrid structures. 

All of the above-mentioned examples describe organosiloxane hybrid sheet-like structures. However, cell-mimicry requires spherical structures that can form an inner space as a container. Liposomes and lipid bilayer vesicles are known as models of a spherical cell membrane, which is a direct mimic of a unicellular membrane. However, the limited mechanical stability of conventional lipid vesicles is often disadvantageous for some kinds of practical application. 

Moran, A.P., Zahringer, U., Seydel, U., Scholz, D., Stiitz, P., Rietschel, E.T. Structural analysis of the lipid A component of Campylobacter jejuni CCUG 10936 (serotype 0 2) lipopolysaccharide. Description of a lipid A containing a hybrid backbone of 2-amino-2-deoxy-D-glucose and 2,3-diamino-2,3-dideoxy-D-glucose. Eur J Biochem 198 (1991b) 459-469. 

Because of Its structural similarity to acetate. It is not surprising that cyclopropanecarboxyllc acid (from the mltlclde cycloprate) Is Incorporated readily Into normal fatty acid pathways. Six homologous (i>-cyclopropyl fatty acids were identified from treatment of rats, dogs, and a cow with cycloprate (7-10). Generally, these (it-cyclopropyl fatty acids were not free, but rather were esterified to produce modified hybrid lipids (vide Infra ). 

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