The use of skin environment-sensitive liposomes for transdermal penetration is beneficial for improving cosmetic efficacy.

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A combination of 2,2,6,6-tetramethyl-1-piperidinyloxyl and tetraalkylammonium tribromides (R4NBr3), which are available from the corresponding tetraalkylammonium bromides via electrooxidation with potassium bromide, has proved to be useful for oxidations of primary and secondary alcohols to the corresponding aldehydes and ketones, respectively. The oxidation reaction proceeds smoothly even with a 0.5–1.0 mol% of N-oxyl compounds and 1.5–2.0 equivalents of tetraalkylammonium tribromides in an aqueous-organic two-phase solution buffered at pH 8.0–8.6. This recyclable oxidant/co-oxidant combination system may involve the formation of N-oxoammonium salts, actual oxidizing agents of alcohols, by the action of hypobromite species generated from R4NBr3 in the binary solution. Utility of the method is highlighted by the selective oxidation of benzylic alcohols bearing electron-releasing groups on the aromatic nucleus to the corresponding aldehydes or ketones without any bromination and overoxidation.

Dual-signal-sensitive copolymers were synthesized by copolymerization of methoxy diethylene glycol methacrylate, methacrylic acid, and lauroxy tetraethylene glycol methacrylate, which respectively provide temperature sensitivity, pH sensitivity, and anchoring to liposome surfaces. These novel copolymers, with water solubility that differs depending on temperature and pH, are soluble in water under neutral pH and low-temperature conditions, but they become water-insoluble and form aggregates under acidic pH and high-temperature conditions. Liposomes modified with these copolymers exhibited enhanced content release at weakly acidic pH with increasing temperature, although no temperature-dependent content release was observed in neutral conditions. Interaction between the copolymers and the lipid monolayer at the air-water interface revealed that the copolymer chains penetrate more deeply into the monolayer with increasing temperature at acidic pH than at neutral pH, where the penetration of copolymer chains was moderate and temperature-independent at neutral pH. Interaction of the copolymer-modified liposomes with HeLa cells demonstrated that the copolymer-modified liposomes were adsorbed quickly and efficiently onto the cell surface and that they were internalized more gradually than the unmodified liposomes through endocytosis. Furthermore, the copolymer-modified liposomes enhanced the content release in endosomes with increasing temperature, but no such temperature-dependent enhancement of content release was observed for unmodified liposomes.