Effects of ethanol on the organization of phosphocholine lipid bilayers

Alkanols Regulate the Fluidity of Phospholipid Bilayer in Accordance to Their Concentration and Polarity

In spite of the widespread use of alkanols as penetration enhancers, their effect on vesicular formulations remains largely unexplored. These can affect the stability and integrity of the phospholipid bilayers. In this study, we have investigated the interaction of linear (ethanol, butanol, hexanol, octanol) and branched alkanols (t-amylol and t-butanol) with three phospholipids (soya lecithin, SL; soy L-α-phosphatidylcholine, SPC; and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC). Thermodynamic and structural aspects of these interactions were studied as a function of the alkanol concentration and chain length. Our interpretations are based on isothermal titration calorimetry (ITC) and dynamic light scattering (DLS) experiments. We observed one-site interactions wherein hydroxyl and acyl groups interacted with the polar and nonpolar regions of the phospholipid, respectively. The stability and structural integrity of bilayers appeared to be dependent upon (a) the hydrocarbon chain length and concentration of alcohols, and (b) the degree of unsaturation in the phospholipid molecule. We found that these interactions triggered a reduction in the enthalpy which was compensated by increased entropy, keeping free energy negative. Drop in enthalpy indicates reversible disordering of the bilayer which enables the diffusion of alcohol without triggering destabilization. Ethanol engaged predominantly with the interface, and it resulted in higher enthalpic changes. Interactions became increasingly unfavorable with longer alcohols - a cutoff point was recorded with hexanol. The overall sequence of membrane disordering capability was recorded as follows: ethanol < butanol < octanol < hexanol. Octanol's larger size restricted its penetration in the bilayer, and hence it caused less enthalpic changes relative to hexanol. This could also be verified from the trends in the area ratio of these vesicles obtained from the DLS data. Branched alkanols displayed a lower binding affinity with the phospholipids relative to their linear counterparts. These data are useful while contemplating the inclusion of short-chain alcohols as penetration enhancers in phospholipid vesicles.

Ethanol Inactivation of Enveloped Viruses: Structural and Surface Chemistry Insights into Phi6

Lipid-enveloped viruses, such as Ebola, influenza, or coronaviruses, are a major threat to human health. Ethanol is an efficient disinfectant that is widely used to inactivate these viruses and prevent their transmission. However, the interactions between ethanol and enveloped viruses leading to their inactivation are not yet fully understood. This study demonstrates the link between ethanol-induced viral inactivation and the nanostructural and chemical transformations of the model virus Phi6, an 85 nm diameter lipid-enveloped bacterial virus that is commonly used as surrogate for human pathogenic viruses. The virus morphology was investigated using small-angle X-ray scattering and dynamic light scattering and was related to its infectivity. The Phi6's surface chemistry was characterized by cryogenic X-ray photoelectron spectroscopy, and the modifications in protein structure were assessed by circular dichroism and fluorescence spectroscopy. Ethanol-triggered structural modifications were found in the lipid envelope, detaching from the protein capsid and forming coexisting nanostructures.

Bioinspired Antimicrobial Coatings from Peptide-Functionalized Liquid Crystalline Nanostructures

Surface-associated microbial infections and contaminations are a major challenge in various fields including the food and health sectors. This study demonstrates the design of antimicrobial coatings based on the self-assembly of the food-grade amphiphilic lipid glycerol monooleate with the human cathelicidin-derived antimicrobial peptide LL-37. Structural properties of the coating and their alterations with composition were studied using advanced experimental methods including synchrotron grazing-incidence small-angle X-ray scattering and ellipsometry. The integration of the LL-37 and its potential release from the nanostructured films into the surrounding solution was characterized with confocal Raman microscopy. Additional biological evaluation studies with clinically relevant bacterial strains, namely, Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive), were performed to investigate the antimicrobial activity of the coatings. Significant killing activity of the coating was found against both bacterial strains. The presented findings contribute to the fundamental understanding of lipid-peptide self-assembly on the surface and may open up a promising strategy for designing simple, sustainable antimicrobial coatings for medical and food applications.

Effects of ethanol and n-butanol on the fluidity of supported lipid bilayers

The interactions of molecules such as short-chain alcohols with the mammalian plasma membrane are thought to play a role in anesthetic effects. We have examined the concentration-dependent effects of ethanol and n-butanol on the fluidity of planar model lipid bilayer structures supported on mica. The supported model bilayer was composed of 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), cholesterol, and sphingomyelin, and the bilayers were formed by vesicle fusion from extruded unilamellar vesicles (133 nm diameter, polydispersity index of 0.17). Controlled amounts of ethanol and n-butanol were added during vesicle deposition. Translational diffusion constants were obtained utilizing fluorescence recovery after photobleaching (FRAP) measurements on the micrometer scale with perylene as the fluorophore. The translational diffusion constants increased and then decreased with increasing ethanol concentration, with the bilayer structure degrading at ca. 0.8 M ethanol. A similar trend was observed for n-butanol at lower alcohol concentrations owing to greater interactions with phospholipid bilayer constituents. For n-butanol, the integrity of the planar bilayer structure deteriorated at ca. 0.4 M n-butanol. The results are consistent with bilayer interdigitation.

Ceramide-mediation of diffusion in supported lipid bilayers

The fluidity and compositional heterogeneity of the mammalian plasma membrane play deterministic roles in a variety of membrane functions. Designing model bilayer systems allows for compositional control over these properties. Ceramide is a phospholipid capable of extensive headgroup-region hydrogen bonding, and we report here on the role of ceramide in planar model bilayers. We use fluorescence recovery after photobleaching (FRAP) to obtain translational diffusion constants of two chromophores in supported model bilayers composed of cholesterol, 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), sphingomyelin, and ceramide. FRAP data for perylene report on the acyl chain region of the model bilayer and FRAP data for 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) sense diffusional dynamics in the bilayer headgroup region. Dynamics in the headgroup region exhibit anomalous diffusion behavior that is characteristic of spatially heterogeneous media.

Embedding calix[4]resorcinarenes in liposomes: Experimental and computational investigation of the effect of resorcinarene inclusion on liposome properties and stability

Two calix[4]resorcinarenes, which differ in the length of the alkyl chain on the methylene bridge between the aromatic rings, have been embedded in unilamellar liposomes prepared from 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine in three host/guest ratios, following two different procedures. The effect of the insertion of the guests has been evaluated through the measurements of the viscosity and the kinetic stability of the liposomal systems by means of the fluorescent probes pyrene and 5(6)-carboxyfluorescein. The presence of the guests reduces the viscosity of the liposomes, suggesting a modification of the bilayer structure. However, this does not affect liposome stability. A calix[4]resorcinarene cavitand with a more rigid conformation compared to the parent resorcinarene, has been also synthetized and embedded in liposomes. The free energy of the insertion of the substrates in the lipid bilayer has been evaluated through Molecular Dynamics simulations.

Magnetic polymer microcapsules loaded with Nile Red fluorescent dye

Fabrication of multifunctional smart vehicles for drug delivery is a fascinating challenge of multidisciplinary research at the crossroads of materials science, physics and biology. We demonstrate a prototypical microcapsule system that is capable of encapsulating hydrophobic molecules and at the same time reveals magnetic properties. The microcapsules are prepared using a templated synthesis approach where the molecules to be encapsulated (Nile Red) are present in the organic droplets that are suspended in the polymerization solution which also contains magnetic nanoparticles. The polymer (polypyrrole) grows on the surface of organic droplets encapsulating the fluorescent dye in the core of the formed microcapsule which incorporates the nanoparticles into its wall. For characterization of the resulting structures a range of complementary physicochemical methodology is used including optical and electron microscopy, magnetometry, ¹H NMR and spectroscopy in the visible and X-ray spectral ranges. Moreover, the microcapsules have been examined in biological environment in in vitro and in vivo studies.

Interface-mediation of lipid bilayer organization and dynamics

We report on the morphology and dynamics of planar supported lipid bilayer structures as a function of pH and ionic strength of the aqueous overlayer. Supported lipid bilayers composed of three components (phosphocholine, sphingomyelin and cholesterol) are known to exhibit phase segregation, with the characteristic domain sizes dependent on the amount and identity of each constituent, and the composition of the aqueous overlayer in contact with the bilayer. We report on fluorescence anisotropy decay imaging measurements of a rhodamine chromophore tethered to the headgroup of a phosphoethanolamine, where anisotropy decay images were acquired as a function of solution overlayer pH and ionic strength. The data reveal a two-component anisotropy decay under all conditions, with the faster time constant being largely independent of pH and ionic strength and the slower component depending on pH and ionic strength in different manners. For liposomes of the same composition, a single exponential anisotropy decay was seen. We interpret this difference in terms of bilayer curvature and support surface-bilayer interactions, and the pH and ionic strength dependencies in terms of ionic screening and protonation in the bilayer headgroup region.

Formation of highly ordered liquid crystalline coatings – an in situ GISAXS study

In situ GISAXS and AFM reveal the formation of highly geometrically organized glycerol monooleate based liquid crystalline films on silicon wafers.

Molecular Dynamics of POPC Phospholipid Bilayers through the Gel to Fluid Phase Transition: An Incoherent Quasi-Elastic Neutron Scattering Study

The microscopic dynamics for the gel and liquid-crystalline phase of highly aligned D2O-hydrated bilayers of 1-palmitoyl-oleoyl-sn-glycero-phosphocholine (POPC) were investigated in the temperature range from 248 to 273 K by using incoherent quasi-elastic neutrons scattering (QENS). We develop a model for describing the molecular motions of the liquid phase occurring in the 0.3 to 350 ps time range. Accordingly, the complex dynamics of hydrogen are described in terms of simple dynamical processes involving different parts of the phospholipid chain. The analysis of the data evidences the existence of three different motions: the fast motion of hydrogen vibrating around the carbon atoms, the intermediate motion of carbon atoms in the acyl chains, and the slower translational motion of the entire phospholipid molecule. The influence of the temperature on these dynamical processes is investigated. In particular, by going from gel to liquid-crystalline phase, we reveal an increase of the segmental motion mainly affecting the terminal part of the acyl chains and a change of the diffusional dynamics from a localized rattling-like motion to a confined diffusion.

Effect of ethanol perturbation on viscosity and permeability of an inner membrane in Bacillus subtilis spores

In this work, we investigated how a combination of ethanol and high temperature (70°C), affect the properties of the inner membrane of Bacillus subtilis spores. We observed membrane permeabilization for ethanol concentrations ≥50%, as indicated by the staining of the spores' DNA by the cell impermeable dye Propidium Iodide. The loss of membrane integrity was also confirmed by a decrease in the peak corresponding to dipicolinic acid using infrared spectroscopy. Finally, the spore refractivity (as measured by phase contrast microscopy) was decreased after the ethanol-heat treatment, suggesting a partial rehydration of the protoplast. Previously we have used fluorescent lifetime imaging microscopy (FLIM) combined with the fluorescent molecular rotor Bodipy-C12 to study the microscopic viscosity in the inner membrane of B. subtilis spores, and showed that at normal conditions it is characterized by a very high viscosity. Here we demonstrate that the ethanol/high temperature treatment led to a decrease of the viscosity of the inner membrane, from 1000cP to 860cP for wild type spores at 50% of ethanol. Altogether, our present work confirms the deleterious effect of ethanol on the structure of B. subtilis spores, as well as demonstrates the ability of FLIM - Bodipy-C12 to measure changes in the microviscosity of the spores upon perturbation.

MALDI ionization mechanisms investigated by comparison of isomers of dihydroxybenzoic acid

Matrix-assisted laser desorption/ionization (MALDI) ion formation mechanisms were investigated by comparison of isomers of dihydroxybenzoic acid (DHB). These exhibit substantially different MALDI performance, the basis for which was not previously understood. Luminescence decay curves are used here to estimate excited electronic state properties relevant for the coupled chemical and physical dynamics (CPCD) model. With these estimates, the CPCD predictions for relative total ion and analyte ion yields are in good agreement with the data for the DHB isomers. Predictions of a thermal equilibrium model were also compared and found to be incompatible with the data. Copyright © 2015 John Wiley & Sons, Ltd.

Excited state dynamics in the matrix-assisted laser desorption/ionization matrix 2,4,6-trihydroxyacetophenone: evidence for triplet pooling charge separation reactions

RATIONALE

Excited state pooling reactions are a central part of some models of ultraviolet matrix-assisted laser desorption/ionization (MALDI) mechanisms. Evidence has been found for pooling in several matrix materials, but a recent report of pure exponential fluorescence decay at MALDI-relevant laser fluences suggested that 2,4,6-trihydroxy-acetophenone (THAP) may be an example of a matrix in which pooling does not occur (Lin et al., Rapid Commun. Mass Spectrom. 2014, 28, 77). However, those data were instrumentally limited in dynamic range and signal/noise ratio, and the conclusion does not take into account several aspects of THAP excited state dynamics.

METHODS

Using time-correlated single photon counting, and absorption and emission spectroscopies, the excited state dynamics of THAP are reexamined.

RESULTS

Like many other aromatic ketones and acetophenone, isolated THAP molecules undergo very efficient intersystem crossing. No fluorescence is observed in dilute solution. In the solid state, efficient fluorescence reappears, but is non-exponential even at very low excitation intensity. The solvent used for sample preparation was found to have a large effect on the spectra and decay curves. Needle-like crystals seem to be correlated with reduced intersystem crossing.

CONCLUSIONS

THAP solid state fluorescence is entirely due to intermolecular interactions. Activation of fluorescence, instead of quenching, is a clear indicator of delocalized excited state phenomena in THAP. Contrary to the conclusions of Lin et al., the greatly increased singlet lifetime in the solid state substantially increases the probability that pooling-type reactions are indeed involved in ionization processes. The sensitivity of fluorescence and phosphorescence on sample morphology appears to reflect changes in intermolecular interactions due to crystal packing. Pooling charge separation pathways based on known triplet-triplet ionization reactions of aromatic ketones are proposed.

Structural disruption of phospholipid bilayers over a range of length scales by n-butanol

We report on the exposure of planar multicomponent lipid bilayers supported on mica to n-butanol. The bilayer contains 49 mol % 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), 10 mol % cholesterol, 40 mol % sphingomyelin, and 1 mol % sulforhodamine-tagged 1,2-dioleoyl-sn-phosphatidylethanolamine (SR-DOPE). Phase separation of the cholesterol domains is seen within the bilayer structure, and exposure of this supported bilayer to controlled amounts of n-butanol in the aqueous overlayer produces morphological changes over a range of length scales. We report steady state fluorescence imaging, fluorescence lifetime imaging, and fluorescence anisotropy decay imaging for these bilayers. These data are consistent with literature reports on the interactions of lipid bilayers with n-butanol and provide molecular-scale insight relative to bilayer organization that has not been available to date. The exposure of these bilayers to n-butanol leads to more extensive disruption of the bilayer than is seen for their exposure to ethanol.

Ethanol-induced perturbations to planar lipid bilayer structures

We report on the formation of planar lipid bilayer structures on mica where the bilayer contains the phosphocholine 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), cholesterol, sphingomyelin and sulforhodamine-tagged-1,2-dioleoyl-sn-phosphatidylethanolamine (SR-DOPE). Phase separation is seen for the cholesterol domains within the bilayer structure, and exposure of this supported bilayer to controlled concentrations of ethanol reveals organizational changes on both the micrometer- and molecular-length scales. We report steady state fluorescence imaging, fluorescence lifetime imaging, and fluorescence anisotropy decay imaging for these bilayers. These data are complementary to existing information on the interactions of lipid bilayers with ethanol and point to subtle but important changes in the molecular-scale organization of these structures.

n-Butanol partitioning into phase-separated heterogeneous lipid monolayers

Cellular adaptation to elevated alcohol concentration involves altering membrane lipid composition to counteract fluidization. However, few studies have examined the biophysical response of biologically relevant heterogeneous membranes. Lipid phase behavior, molecular packing, and elasticity have been examined by surface pressure-area (π-A) analysis in mixed monolayers composed of saturated dipalmitoylphosphatidylcholine (DPPC) and unsaturated dioleoylphosphatidylcholine (DOPC) as a function of DOPC and n-butanol concentration. n-Butanol partitioning into DPPC monolayers led to lipid expansion and increased elasticity. Greater lipid expansion occurred with increasing DOPC concentration, and a maximum was observed at equimolar DPPC:DOPC consistent with n-butanol partitioning between coexisting liquid expanded (LE, DOPC) phases and liquid condensed (LC, DPPC) domains. This led to distinct changes in the size and morphology of LC domains. In DOPC-rich monolayers the effect of n-butanol adsorption on π-A behavior was less pronounced due to DOPC tail kinking. These results point to the importance of lipid composition and phase coexistence on n-butanol partitioning and monolayer restructuring.

Lipid adlayer organization mediated by a liquid overlayer

We report on the formation of a chemically bound 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) monolayer on modified Au and silica surfaces, and changes in the organization of the interfacial lipid layer associated with immersion in aqueous solution. We have studied the interface using steady state and time resolved fluorescence spectroscopy, water contact angle and optical ellipsometry measurements, and electrochemical methods. Our data reveal that the DMPC adlayer in contact with air forms a relatively well organized interface that mediates the rotational motion of perylene. In the presence of an aqueous overlayer, perylene reorientation becomes more rapid, consistent with a reduction in the organization of the interfacial lipid adlayer. One implication of this finding is that the interfacial adlayer is less than a uniform monolayer, which is confirmed by electrochemical data. Our data underscore the importance of water in mediating the organization of interfacial lipid adlayers.

Pyrene-loaded polypyrrole microvessels

The encapsulation of guest molecules within polymeric hollow nano- or microscale structures is a rapidly developing field of interdisciplinary research due to a variety of applications ranging from drug delivery and sensor fabrication to nanoscale synthesis and bioinspired mineralization. We report on the encapsulation of pyrene within three-dimensional polypyrrole microvessels synthesized by precipitation polymerization of pyrrole onto toluene droplets that contain pyrene. Steady state and time-resolved fluorescence measurements show that the optical response and dynamics of encapsulated pyrene is significantly different from that in the free solution, likely due to interactions with oligomeric species generated during the polymerization process that partition into the organic core of the microvessel. Our results indicate that the encapsulation process can have a significant influence on the local environment of encapsulated species, an issue that is critical from the perspective of potential synthetic or medical applications.