Evaluation of 1-naphthol as a convenient fluorescent probe for monitoring ethanol-induced interdigitation in lipid bilayer membrane

Excited state proton transfer based fluorescent molecular probes and their application in studying lipid bilayer membranes

The distribution and prototropic equilibria of 1-naphthol (NpOH) in lipid bilayer membrane.

A molecular level understanding of interaction between FTY720 (Fingolimod hydrochloride) and DMPC multilamellar vesicles

This work focuses on the molecular level understanding of interaction between FTY720 (Fingolimod hydrochloride) and dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles (MLVs) as a drug molecule carrier by investigating the structural changes, solubilisation effect and thermotropic phase behaviour.

Bilayer interaction and protein kinase C-C1 domain binding studies of kojic acid esters

Synthesis of kojic acid ester analogues and their lipid bilayer interaction and PKC-C1 domain binding properties have been demonstrated in this present work.

Photophysical behavior of fisetin in dimyristoylphosphatidylcholine liposome membrane

A detailed photophysical study of the plant flavonoid fisetin in a dimyristoylphosphatidylcholine (DMPC) bilayer membrane has been carried out. Fisetin is found to partition well into the membrane (K(p) = (4.6 ± 0.5) × 10(5) in solid gel phase and (5.1 ± 0.5) × 10(5) in liquid crystalline phase). A fluorescence quenching study using cetylpyridinium chloride (CPC) as the quencher suggests that fisetin molecules are generally present near the head group region of the lipid bilayer membrane. The temperature dependence of the fluorescence lifetime indicates a local heterogeneity in the distribution of fisetin within the bilayer membrane. The phototautomer form of fisetin, which is the primary emitting species from the lipid membrane, has a large Stoke's shift (175 nm) and fluoresces with an intense green fluorescence, which can make the molecule a good dye for marker and bioimaging applications. Membrane-bound fisetin shows sensitive variations of fluorescence intensity, lifetime, and anisotropy parameters in cholesterol-containing DMPC membranes, in mixed phospholipids, and as a function of temperature. This suggests that fisetin can be an efficient fluorescent molecular probe for sensing lipid bilayer membrane related changes. The location of fisetin in the membrane and the observed cholesterol-induced expulsion of fisetin may possibly have implications in the antioxidant activity of fisetin.

Prototropism of 1-hydroxypyrene in liposome suspensions: implications towards fluorescence probing of lipid bilayers in alkaline medium

The partitioning efficiency of neutral and anionic prototropic forms of 1-hydroxypyrene in liposome suspensions has been studied. The high partition coefficient value of 1-hydroxypyrene indicates an easy incorporation of the molecule into the lipid bilayer. Detailed pH studies indicate that only the neutral form of 1-hydroxypyrene partitions into the membrane and appreciable spectral changes are observed in the pH range of 9.0-11.5 in Tris-NaOH buffer. However, at pH 11 the spectral changes are maximum. The possibility of using 1-hydroxypyrene as a fluorescent molecular probe for lipid bilayer membranes in alkaline media has been examined, by employing fluorescence intensity and fluorescence anisotropy as probe parameters. The neutral form fluorescence intensity as well as fluorescence anisotropy is sensitive to the changes in the membrane properties and is capable of sensing the phase-transition. This is also capable of monitoring the changes in the membrane due to incorporation of cholesterol and the ethanol-induced interdigitation. The time resolved fluorescence data and the quenching experiments show that 1-hydroxypyrene occupies the water inaccessible interior of the liposome. The high anisotropy value of 1-hydroxypyrene in liposome suggests that it resides in a considerably rigid environment and is very sensitive to the temperature-induced changes in the liposome.

Elasticity and phase behavior of DPPC membrane modulated by cholesterol, ergosterol, and ethanol

Giant vesicles formed of 1,2-dipalmitoylphosphatidylcholine (DPPC) and sterols (cholesterol or ergosterol) in water and water/ethanol solutions have been used to examine the effect of sterol composition and ethanol concentration on the area compressibility modulus (K(a)), overall mechanical behavior, vesicle morphology, and induction of lipid alkyl chain interdigitation. Our results from micropipette aspiration suggest that cholesterol and ergosterol impact the order and microstructure of the gel (L(beta)') phase DPPC membrane. At low concentration (10-15 mol%) these sterols disrupt the long-range lateral order and fluidize the membrane (K(a) approximately 300 mN/m). Then at 18 mol%, these sterols participate in the formation of a continuous cohesive liquid-ordered (L(o)) phase with a sterol-dependent membrane density (K(a) approximately 750 for DPPC/ergosterol and K(a) approximately 1100 mN/m for DPPC/cholesterol). Finally at approximately 40 mol% both cholesterol and ergosterol impart similar condensation to the membrane (K(a) approximately 1200 mN/m). Introduction of ethanol (5-25 vol%) results in drops in the magnitude of K(a), which can be substantial, and sometimes individual vesicles with lowered K(a) reveal two slopes of tension versus apparent area strain. We postulate that this behavior represents disruption of lipid-sterol intermolecular interactions and therefore the membrane becomes interdigitation prone. We find that for DPPC vesicles with sterol concentrations of 20-25 mol%, significantly more ethanol is required to induce interdigitation compared to pure DPPC vesicles; approximately 7 vol% more for ergosterol and approximately 10 vol% more for cholesterol. For lower sterol concentrations (10-15 mol%), interdigitation is offset, but by <5 vol%. These data support the idea that ergosterol and cholesterol do enhance survivability for cells exposed to high concentrations of ethanol and provide evidence that the appearance of the interdigitated (L(beta)I) phase bilayer is a major factor in the disruption of cellular activity, which typically occurs between approximately 12 and approximately 16 vol% ethanol in yeast fermentations. We summarize our findings by producing, for the first time, "elasticity/phase diagrams" over a wide range of sterol (cholesterol and ergosterol) and ethanol concentrations.