title: Synthesis and spectroscopic analysis of chromophoric lipids inducing pH-dependent liposome fusion.
abstract: We design novel chromophoric amphiphiles 6a-c, which lead to pH-dependent membrane fusion of egg phosphatidylcholine (eggPC) liposome containing them. Lipids 6a-c comprise double alkyl chains, a single chain with a 2-nitrophenol group as a pH trigger, and dipeptide (Asp-Asp) between them. The pKa values of 2-nitrophenol groups of 6a-c in liposome are larger than that of hydrophilic compound 9 in an aqueous solution. Absorption spectra indicate that the fields around 2-nitrophenol of 6a-c situated in liposome membranes are more hydrophobic than that of 9 in an aqueous solution, whereas the environments around deprotonated 2-nitrophenolate of 6b and 6c are not so hydrophobic as that of 6a. This means that protonated 2-nitrophenol groups of 6a-c are embedded in bilayer membranes. Deprotonated 2-nitrophenol groups of 6b and 6c must be located in less hydrophobic circumstances, while that of 6a is still embedded in bilayer membranes because of its larger hydrophobicity. Absorption spectra and (1)H NMR spectra respectively suggest that protonated 2-nitrophenol groups of 6a and those of 6c might take face-to-face associations in bilayer membranes.
authors.affiliation: Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan. ttomo@ms.toyama-mpu.ac.jp
authors.forename: Takenori
authors.initials: T
authors.lastname: Tomohiro
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Okuno
authors.forename: Masato
authors.initials: M
authors.lastname: Kodaka
mesh_terms: D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes / Q000138:chemical synthesis / Q000737:chemistry*; D008561:Membrane Fusion; D008563:Membrane Lipids / Q000737:chemistry*; D009596:Nitrophenols / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010713:Phosphatidylcholines / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008081:Liposomes; D008563:Membrane Lipids; D009596:Nitrophenols; D010713:Phosphatidylcholines; C045573:2-nitrophenol