Donor-donor energy migration (DDEM) as a tool for studying aggregation in lipid phases.
A BODIPY-labelled sulfatide (N-(BODIPY-FL-pentanoyl)-galactosylcerebroside-sulfate, hereafter abbreviated as BD-Sulfatide) was solubilised at different concentrations in lipid vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Time-correlated single photon counting experiments show that the fluorescence relaxation is mono-exponential (with a lifetime of 6.5 ns) at molar ratios of BD-Sulfatide: DOPC that are less than 1:100. The fluorescence steady-state anisotropy decreases monotonously at molar ratios smaller than 1:1000, which is compatible with donor-donor energy migration (DDEM) among the BODIPY groups. A model that assumes DDEM across the lipid bilayers, as well as in their planes, was used to analyse the time-resolved fluorescence anisotropy. Only two parameters appear in the model namely: the bilayer thickness (d) and the average number density (C2) distribution of BD-Sulfatide in the lipid bilayers. The extracted d-values vary between 35 and 40 A, which is about the reported thickness of a bilayer of DOPC (38 A). Hence, the BODIPY groups are preferentially located in the water-lipid interface. At low concentration the experimental C2-values and those independently calculated are in good agreement, while the experimental values gradually become lower with increasing BD-Sulfatide concentration. These results are compatible with an aggregation of the sulfatides and self-quenching of BODIPY, which is clearly established at higher concentrations of the BD-Sulfatide.
Mikhalyov
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Department of Chemistry: Biophysical Chemistry, Umeå University, Sweden.
Bogen
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Johansson
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D001896:Boron Compounds / Q000737:chemistry*; D004735:Energy Transfer; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008433:Mathematics; D015394:Molecular Structure; D010713:Phosphatidylcholines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; C017251:1,2-oleoylphosphatidylcholine