11 research outputs found
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Water dynamics in glycosphingolipid aggregates studied by LAURDAN fluorescence.
We have characterized the fluorescence properties of 6-dodecanoyl-2-dimethylamine-naphthalene (LAURDAN) in pure interfaces formed by sphingomyelin and 10 chemically related glycosphingolipids (GSLs).1 The GSLs contain neutral and anionic carbohydrate residues in their oligosaccharide chain. These systems were studied at temperatures below, at, or above the main phase transition temperature of the pure lipid aggregates. The extent of solvent dipolar relaxation around the excited fluorescence probe in the GSLs series increases with the magnitude of the glycosphingolipid polar headgroup below the transition temperature. This conclusion is based on LAURDAN's excitation generalized polarization (GPex) and fluorescence lifetime values found in the different interfaces. A linear dependence between the LAURDAN GPex and the intermolecular spacing among the lipid molecules was found for both neutral and anionic lipids in the GSLs series. This relationship was also followed by phospholipids. We conclude that LAURDAN in these lipid aggregates resides in sites containing different amounts of water. The dimension of these sites increases with the size of the GSLs polar headgroup. The GP function reports on the concentration and dynamics of water molecules in these sites. Upon addition of cholesterol to Gg4Cer, the fluorescence behavior of LAURDAN was similar to that of pure cerebrosides and sphingomyelin vesicles. This observation was attributed to a change in the interfacial hydration as well as changes in the shape and size of the Gg4Cer aggregates in the presence of cholesterol. After the addition of cholesterol to gangliosides, the changes in the LAURDAN's spectral parameters decrease progressively as the polar headgroup of these lipids becomes more complex. This finding suggests that the dehydration effect of cholesterol depends strongly on the curvature radius and the extent of hydration of these lipid aggregates. In the gel phase of phrenosine, GalCer, Gg3Cer, sulfatide, and sphingomyelin, the excitation red band (410 nm) of LAURDAN was reduced with respect to that of LAURDAN in the gel phase of pure phospholipids. This observation indicates a local environment that interacts differently with the ground state of LAURDAN in GSLs when compared with LAURDAN in phospholipids
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Effect of solvent polarity and lipid chemical structure on naphthalene derivatives excitation spectra.
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A model for the interaction of 6-lauroyl-2-(N,N-dimethylamino)naphthalene with lipid environments: implications for spectral properties.
Although 6-lauroyl-2-(N,N-dimethylamino)naphthalene (LAURDAN) is now widely used as a probe for lipid systems, most studies focus on the effect of the lipid environment on its emission properties but not on the excitation properties. The present study is intended to investigate the excitation properties of LAURDAN in diverse lipid environments. To this end, the fluorescence properties of LAURDAN were studied in synthetic ester and ether phosphatidylcholines and sphingomyelin vesicles below, at and above the corresponding lipid main phase-transition temperature. The excitation spectra of LAURDAN in these environments always show at least two well-resolved bands. In the different lipid vesicles the behavior of the red band in the LAURDAN excitation spectra is sensitive to the lipid chemical environment near the probe fluorescent moiety and to the packing of the different lipid phases (gel and liquid crystalline). We propose that the interaction between the LAURDAN dimethylamino group and the ester linkage of ester phospholipids is responsible for the strong stabilization of LAURDAN's red excitation band in the gel phase of ester phospholipid vesicles. We discuss the consequence of these proposed ground-state interactions on LAURDAN's emission generalized polarization function. In the context of variable excitation wavelengths, information concerning solvent dipolar relaxation through excitation generalized polarization function is also discussed