title: A coupled proton-transfer and twisting-motion fluorescence probe for lipid bilayers.
abstract: A new and sensitive molecular probe, 2-(2'-hydroxyphenyl)imidazo[1, 2-a]pyridine (HPIP), for monitoring structural changes in lipid bilayers is presented. Migration of HPIP from water into vesicles involves rupture of hydrogen (H) bonds with water and formation of an internal H bond once the probe is inside the vesicle. These structural changes of the dye allow the occurrence of a photoinduced intramolecular proton-transfer reaction and a subsequent twisting/rotational process upon electronic excitation of the probe. The resulting large Stokes-shifted fluorescence band depends on the twisting motion of the zwitterionic phototautomer and is characterized in vesicles of dimyristoyl-phosphatidylcholine and in dipalmitoyl-phosphatidylcholine at the temperature range of interest and in the presence of cholesterol. Because the fluorescence of aqueous HPIP does not interfere in the emission of the probe within the vesicles, HPIP proton-transfer/twisting motion fluorescence directly allows us to monitor and quantify structural changes within bilayers. The static and dynamic fluorescence parameters are sensitive enough to such changes to suggest this photostable dye as a potential molecular probe of the physical properties of lipid bilayers.
authors.affiliation: Instituto de Química-Física, CSIC, Serrano 119, 28006 Madrid, Spain.
authors.forename: C R
authors.initials: CR
authors.lastname: Mateo
authors.forename: A
authors.initials: A
authors.lastname: Douhal
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D008051:Lipid Bilayers / Q000737:chemistry*; D008956:Models, Chemical; D013050:Spectrometry, Fluorescence; D013054:Spectrophotometry, Atomic; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D008051:Lipid Bilayers; D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine