Trigger lipids inducing pH-dependent liposome fusion.

Aspartic acid-derived artificial lipids (ADLs; s indicates the number of the methylene groups, s=2, 4, 6, 8, 10, 12) (Scheme 1) with various carboxyl alkyl chains as head groups are designed and synthesized, which are incorporated into liposome membranes by sonication. Fluorescence resonance energy transfer (FRET) measurements indicate that ADL6, ADL8 and ADL10 have high lipid-mixing ability in the acidic solution. The other ADLs, however, do not induce remarkable liposome fusion at acidic nor neutral pH. The hydrophobicity of the head groups of ADL6, ADL8 and ADL10 is suitable as triggers of membrane fusion.