Cholesterol-containing non-ionic amphiphilic polymers

Abstract

Cholesterol-containing amphiphilic monomers, 1-ethenyl-3-(8-(cholest-5-en-3$\beta$-yloxy)-3,6-dioxaoctyl)-2-pyrrolidone (ECDP) and 1-ethenyl-3-(6-(cholest-5-en-3$\beta$-yloxy)hexyl)-2-pyrrolidone (ECHP), and cholesterol-containing amphiphilic polymers, poly(ECDP-co-N-vinylpyrrolidone) and poly(ECHP-co-N-vinylpyrrolidone), were synthesised, and their properties and suprastructures were investigated. ECDP formed vesicles in water by sonication, whereas ECHP did not. The polymerization of preformed vesicles derived from ECDP in water by water-soluble initiator resulted in the formation of polymeric vesicles of ECDP which were more stable to the addition of ethanol and tannic acid than the monomeric vesicles exhibiting higher long-term stability. The solution behaviors and the suprastructures of the cholesterol-containing amphiphilic polymers were influenced by copolymer composition and molecular weight. The polymers with low N-vinylpyrrolidone (NVP) content, apparently insoluble in water, were dispersed by sonication or by injection of organic solution into water to form vesicles. The more water-soluble polymers with high NVP content formed hydrophobic microdomains in water into which cholesterol was efficiently incorporated. The polymers underwent morphological change as cholesterol was solubilized and discrete lamellar bilayers were observed by electron microscope. Thus formed bilayers were considered to be responsible for the efficient cholesterol solubilization of the amphiphilic polymers. Some resemblances to certain biological membrane systems were found in the present solubilization systems.