The evaluation of crown ether based niosomes as cation containing and cation sensitive drug delivery systems

A novel crown ether amphiphile N-hexadecanoyl-2-aminomethyl-15-crown-5 (PCE) has been synthesised from hexadecanoic acid N-hydroxysuccinimide ester and 2-aminomethyl-15-crown-5, with the aim of developing a cation containing or cation sensitive controlled release system. Niosomes were prepared with a 1:1 molar ratio of PCE and cholesterol (CHOL) with and without the addition of 10 mol% Solulan C24 (poly-24-oxyethylene cholesteryl ether). A water-soluble fluorescent marker, rhodamine B was encapsulated within these niosomes. Rhodamine B containing PCE/CHOL niosomes of approximately 6.3 mu m diameter were visualised by optical microscopy and sonicated PCE/CHOL niosomes of approximately 134 nm in size were visualised by transmission electron microscopy. The release of the fluorescent marker rhodamine B from PCE/CHOL niosomes was slightly increased by the addition of calcium ions but remained unaffected by the addition of sodium ions. This is thought to be due to a slightly greater ease of divalent cation chelation by the crown ether head groups when compared to the monovalent cation, the latter of which are more highly solvated in aqueous solution. This is the first study on the effect of ions on the release properties of crown ether based niosomes. These systems may be developed as cation containing or cation sensitive release systems for drug delivery and other industrial uses. (C) 1997 Elsevier Science B.V.