Solvatochromic Modeling of Laurdan for Multiple Polarity Analysis of Dihydrosphingomyelin Bilayer

Abstract

The hydration properties of the interface between lipid bilayers and bulk water are important for determining membrane characteristics. Here, the emission properties of a solvent-sensitive fluorescence probe, 6-lauroyl-2-dimethylamino naphthalene (Laurdan), were evaluated in lipid bilayer systems composed of the sphingolipids D-erythro-N-palmitoyl-sphingosylphosphorylcholine (PSM) and D-erythro-N-palmitoyl-dihydrosphingomyelin (DHPSM). The glycerophospholipids 1-palmitoyl-2-palmitoyl-sn-glycero-3-phosphocholine and 1-oleoyl-2-oleoyl-sn-glycero-3-phosphocholine were used as controls. The fluorescence properties of Laurdan in sphingolipid bilayers indicated multiple excited states according to the results obtained from the emission spectra, fluorescence anisotropy, and the center-of-mass spectra during the decay time. Deconvolution of the Laurdan emission spectra into four components based on the solvent model enabled us to identify the varieties of hydration and the configurational states derived from intermolecular hydrogen bonding in sphingolipids. Sphingolipids showed specific, interfacial hydration properties stemming from their intra-and intermolecular hydrogen bonds. Particularly, the Laurdan in DHPSM revealed more hydrated properties compared to PSM, even though DHPSM has a higher T m than PSM. Because DHPSM forms hydrogen bonds with water molecules (in 2NH configurational functional groups), the interfacial region of the DHPSM bilayer was expected to be in a highly polar environment. The careful analysis of Laurdan emission spectra through the four-component deconvolution in this study provides important insights for understanding the multiple polarity in the lipid membrane.

Influence of Membrane Phase on the Optical Properties of DPH

“…Fluorescence spectroscopies are nowadays one of the techniques of choice for the analysis of the behavior of probes in different membrane phases, due to the different responses related to the anisotropy decay [ 51 , 52 , 53 , 54 , 55 , 56 , 57 ]. We focus on the decay time and the fluorescence anisotropy decay as model analyses which can be obtained by computations [ 29 , 30 , 31 , 33 , 34 ].…”

Lipid Clustering in Mycobacterial Cell Envelope Layers Governs Spatially Resolved Solvation Dynamics

“…[13] These results suggest that multiple hydration states existed for Laurdan in Msm outer and inner membranes, consistent with a recent multi-polarity study of Laurdan within lipid bilayers. [14] Addition of PAL and man-LAM to outer membrane lipids had a minor effect on Laurdan emission. The small shift in the blue emission spectrum in Msm membranes suggests the presence of a non-polar microenvironment in mycobacterial membranes and could be attributed to differences in lateral organization between Msm lipid phases and DPPC.…”

“…[14] The broad Laurdan emission spectra makes conventional generalized polarization (GP) analysis challenging [17] and raises the need for multiple deconvolution steps that rely on the correlation between the Laurdan emission peaks and dielectric constant (ɛ) of various solvents. [14] We observed peak positions at < 440 nm for non-polar regions (e. g., lipid chains), 440-480 nm for membrane regions with low polarity (e. g., interfacial acyl region), and > 480 nm for membrane regions with high polarity (e. g., lipid headgroups) (Figure 3A). These observations confirm previous correlations of Laurdan emission peaks at 440 nm and 490 nm with hydrated and less-hydrated states, respectively.…”

“…The excitation spectra at λ em = 475 nm showed a decreased blue-edge intensity in the outer membrane and mycomembrane, suggestive of the different localizations of Laurdan within these Msm cell envelope bilayers. [14] The broad Laurdan emission spectra makes conventional generalized polarization (GP) analysis challenging [17] and raises the need for multiple deconvolution steps that rely on the correlation between the Laurdan emission peaks and dielectric constant (ɛ) of various solvents. [14] We observed peak positions at < 440 nm for non-polar regions (e. g., lipid chains), 440-480 nm for membrane regions with low polarity (e. g., interfacial acyl region), and > 480 nm for membrane regions with high polarity (e. g., lipid headgroups) (Figure 3A).…”

Membrane Surface-Enhanced Raman Spectroscopy for Cholesterol-Modified Lipid Systems: Effect of Gold Nanoparticle Size

“…Then, the fluorescence spectrum of Laurdan was recorded with an excitation wavelength of 340 nm, at emission wavelengths from 400 to 600 nm. The membrane polarity (GP 340 ) at different temperatures was determined from 35,38,39 where I 440 and I 490 are the emission intensities of Laurdan at 440 and 490 nm wavelengths, respectively.…”