A Blue-Light-Emitting BODIPY Probe for Lipid Membranes

Abstract

Here we describe a new BODIPY-based membrane probe (1) that provides an alternative to dialkylcarbocyanine dyes, such as DiI-C18, that can be excited in the blue spectral region. Compound 1 has unbranched octadecyl chains at the 3,5-positions and a meso-amino function. In organic solvents, the absorption and emission maxima of 1 are determined mainly by solvent acidity and dipolarity. The fluorescence quantum yield is high and reaches 0.93 in 2-propanol. The fluorescence decays are well fitted with a single-exponential in pure solvents and in small and giant unilamellar vesicles (GUV) with a lifetime of ca. 4 ns. Probe 1 partitions in the same lipid phase as DiI-C18(5) for lipid mixtures containing sphingomyelin and for binary mixtures of dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC). The lipid phase has no effect on the fluorescence lifetime but influences the fluorescence anisotropy. The translational diffusion coefficients of 1 in GUVs and OLN-93 cells are of the same order as those reported for DiI-C18. The directions of the absorption and emission transition dipole moments of 1 are calculated to be parallel. This is reflected in the high steady-state fluorescence anisotropy of 1 in high ordered lipid phases. Molecular dynamic simulations of 1 in a model of the DOPC bilayer indicate that the average angle of the transition moments with respect to membrane normal is ca. 70°, which is comparable with the value reported for DiI-C18.

Atomistic Picture of Fluorescent Probes with Hydrocarbon Tails in Lipid Bilayer Membranes: An Investigation of Selective Affinities and Fluorescent Anisotropies in Different Environmental Phases

“…The fluorescence lifetime (ranging from hundreds of picoseconds to a few nanoseconds) sets a time window over which the rotational motions can be monitored in an experimental context. In line with previous theoretical and experimental analysis [ 34,35 ], a double exponential function is used to describe the rotational correlation function:…”

“…The differences in the preferred position are however less clear than for DiI-C18(5). The markedly small Gibbs free energy differences in these profiles illustrate why within the constraints of the employed theories and simulations a comparison with DiI-C18(5) was needed to identify the lipid phases present in the bright areas which were seen in the confocal microscopy images published in[ 35 ].Based upon our simulations for DiI-C18(5) and the related discussion above, it is subsequently safe to assume that BNP in the employed biological environments can be found in the So phase when a mixture of DOPC (Ld) and DPPC (So) is considered and in the Lo phase when a mixture of DOPC (Ld) and SM/Chol (Lo) is involved. We would like to stress here again the importance of the ratio of the employed mixture, as we employed DOPC:SM:Chol in a 1:2:1 ratio.…”

Exploring the Relationship between BODIPY Structure and Spectroscopic Properties to Design Fluorophores for Bioimaging

“…[5,7] Boron dipyrromethene (BODIPY)d yes are ideal to explore the relationship between structure and spectroscopic properties given their popular use in cellular imaging. BODIPY dyes combine desirable chemical, physical and spectroscopicp roperties [7][8][9][10][11] including chemicals tability,a bsorption maxima (l max ) aroundo ra bove 500 nm, sharp fluorescence emission and good quantum yields for the resulting fluorescence. [5,6,[12][13][14][15] Sharp excitation ande mission peakse nablep recise detection by confocal fluorescencem icroscopy.…”

“…The small aromatic and rigid BOPIDY core, which has both ah igh extinction coefficient and as trong fluorescencee mission, [16] presents ag ood template to synthesise ar ange of analogues with longera bsorption wavelengths. [6,[9][10][11] Reflectingt hese advantages, BODIPY dyes have been employed as molecular probes for bioimaging, molecular detection, photocaging,p hotodynamic therapy and as antimicrobials and laser dyes. [17][18][19][20] However,f or fluorophores containing the BODIPYc ore, the absorption intensity is often compromised in analogues where the absorbance l max has been shifted towards the far-red region.…”

“…[5,7] Previous work has fo-cused on the syntheticc hallenge of generating BODIPY analogues and the independent evaluation of the optical, chemical and physical properties of each individual compound. [5,7,10,11,21] In general, previous attempts to define systematica nd predictivei nformationr egardingp articular substituents or substitution sites [22] have, therefore, focusedo nt he type of modificationm ade to the BODIPYs keleton and rationalising the changes in absorbance and fluorescencet hrough computational and orbitalt reatments of the data involved. [7,11,13,23] Here, we take an alternative approachb yp reparing al ibrary of analogues with substitutions at various positions on the BODIPY skeleton to sample al argec hemical space.B yu sing this information,w eh ave generated ac orrelation table, describing the effect that various substitution patternsh ave.…”