Brewster Angle Microscopy Research Articles

Filling the gaps: Introducing plasticizers into π-conjugated OPE-NH2 Langmuir layers for defect-free anisotropic interfaces and membranes towards unidirectional mass, charge, or energy transfer

The construction of ultrathin membranes from linearly aligned π-electron systems is advantageous for targeted energy, charge, or mass transfer. The Langmuir-Blodgett (LB) technique enables the creation of such membranes, especially with amphiphilic π-electron systems. However, these systems often aggregate, forming rigid Langmuir monolayers with defects or holes. In this study we introduce plasticizers to effectively address this issue. To create anisotropic membranes, we used an oligo(phenylene ethynylene) derivative (OPE-NH2) as an linear amphiphile and bisphenol A di-tert-butyl ester (BPAE) as a plasticizer. We analyzed surface pressure (mean molecular area) (Π(mma)) isotherms and characterized Langmuir monolayers with Brewster Angle Microscopy (BAM), to determine the optimal miscibility of OPE-NH2 with BPAE. Detailed analysis of hole areas filled was performed through image binarization. We identified an optimal BPAE concentration of 4 mol-% in the OPE-NH2 Langmuir monolayer. Our BAM image evaluation via binarization determined the difference between the mean molecular areas of close-packed Langmuir domains and those quantified via the Π(mma) isotherm. This study presents an automated method for BAM image analysis and a new approach for fabricating defect-free anisotropic molecular monolayers of π-conjugated amphiphiles.

Interactions of sphingomyelin with biologically crucial side chain-hydroxylated cholesterol derivatives.

Oxysterols are interesting molecules due to their dual nature, reflecting beneficial and harmful effects on the body. An issue that still needs to be solved is how slight modification of their structure owing to the location of the additional polar group in the molecules affects their biological activity. With this in mind, we selected three side chain-hydroxylated oxysterols namely: 20(S)-hydroxycholesterol (20(S)-OH), 24(S)-hydroxycholesterol (24(S)-OH), and 27-hydroxycholesterol (27-OH), and examined their behavior in mixtures with the bioactive sphingolipid - sphingomyelin (SM). Our research was based on the Langmuir monolayer technique supplemented with molecular dynamics (MD) and microscopic observation of the films texture (Brewster angle microscopy, BAM, and atomic force microscopy, AFM). Additionally, since 20(S)-hydroxycholesterol has not been studied so far, we thoroughly characterized this oxysterol in one-component monolayers. Our studies showed differences in the interactions of the studied oxysterols and sphingomyelin. Namely, it was found that 20(S)-OH binds to SM, unlike 24(S)-OH and 27-OH, which both weakly interact with SM. This distinct behavior was interpreted within the molecular dynamics as being due to weak intermolecular interactions between 20(S)-OH molecules, which allowed easy incorporation of SM into the 20(S)-OH monolayer. In contrast, the strong oxysterol-oxysterol interactions occurring in monolayers with 24(S)-OH or 27-OH make this process more difficult. This may be important in the process of bone formation/resorption. Other aspects derived from our study are: (i) the tendency of oxysterols to incorporate into lipid rafts (leading to their modification in structure and function), as well as (ii) the formation of multilayer structures, in which oxysterols are arranged in the characteristic forms of "strings of beads", which may facilitate their transport across the membrane.

Optical anisotropy and surface phases of cholesterol derivative monolayer at air–water interface

Cholesterol and its derivatives play crucial roles in regulating processes of biological membranes. Langmuir monolayer can mimic a bio-membrane which can be used to investigate the molecular interaction governing the important physical phenomena. The cholesterol derivative exhibiting mesophases (CHLC molecules) was synthesized and spread at the air–water (A/W) interface to investigate the surface behavior. The monolayer exhibited a variety of surface phases such as gas, liquid expanded (LE), low density liquid like (L1) and liquid condensed (L2) phases. Treating the CHLC molecules to be rod-like, the average tilt of the molecules with respect to the surface normal in these phases are found to be different. The tilt angle decreases systematically from LE to L2 phase. The optical anisotropy of the ultrathin Langmuir-Blodgett (LB) films of CHLC molecules in these phases was measured using the surface plasmon resonance (SPR) spectroscopy. The high tilted molecules in the ultrathin LB film displayed a high value of optical anisotropy. The ultrathin film of CHLC molecules at different interfaces was investigated using Brewster angle microscopy, X-ray reflectivity (XRR), SPR spectroscopy and atomic force microscopy. This study is useful for the systems where the physical phenomena are governed by tilt of the molecules.

Tuning Electrostatics to Promote Ordered Monolayers of Phosphole-Lipids.

Heteroatom-doped π-conjugated systems have been exploited for electronic device applications. Phosphole-containing backbones are particularly intriguing with regard to electron delocalization and ultimately control over the photophysical, redox, and charge transfer characteristics. However, practical application of these materials commonly relies on well-structured, thin film architectures. Self-assembly offers a route to generate ordered 2D structures deposited on solid substrates. The orientation of these deposited films can be manipulated by the introduction of alkyl chains of varying length (to form phosphole-based lipids) and chemical modification of the phosphole-derived headgroup. External controls can also be considered to tune these films' properties, e.g., the electrostatic interactions within the film can be controlled by varying the environment with the addition of simple salt counterions. A series of lipids with phosphole-based π-conjugated headgroups have been designed and exhibit intramolecular conformational changes in response to external conditions. Herein the 2D film structure in Langmuir and Langmuir-Blodgett films is reported in the presence and absence of halide salts. The film morphology obtained from Brewster angle and atomic force microscopy shows the formation of a condensed phase but also 3D aggregates, and grazing incidence X-ray diffraction confirmed the presence of untilted, hexagonally packed chains. The size of the counterion influences its ability to intercalate between the phosphole headgroups, which ultimately provides a means to induce the formation of a well-ordered, single monolayer film without aggregates that can be transferred to the solid substrate.

Small scale model for predicting transportation-induced particle formation in biotherapeutics

Understanding protein adsorption and aggregation at the air-liquid interfaces of protein solutions is an important open challenge in biopharmaceutical, medical, and biotechnological applications, among others. Proteins, being amphiphilic, adsorb at the surface, partially unfold, and form a viscoelastic film through non-covalent interactions. Mechanical agitation of the surface can break this film up, releasing insoluble protein particles into the solution. These aggregates are usually highly undesirable and even toxic in cases, such as for biopharmaceutical application. Therefore, it is imperative to be able to predict the behavior of such solutions undergoing surface agitation during handling, usually transport or mixing. We apply the findings on the viscoelastic protein film, formed at the air-liquid interface, to the prediction of surface mediated aggregation in selected protein solutions of direct biopharmaceutical relevance. Our broad study of Brewster angle microscopy and aggregation monitoring across multiple size ranges by micro-flow imaging, light scattering, and size exclusion chromatography shows that formation of protein particles is driven by the adsorption rate as compared to the rate of surface turnover and that surface film dynamics in the quiescent phase directly affect aggregation. We demonstrate how these learnings can be directly applied to the design of a novel small scale biopharmaceutical stability study, simulating relevant transport conditions. More generally, we show the impact of adsorption dynamics at the air-liquid interface on the stability of a distinct protein solution, as a general contribution to understanding different colloidal and biological interfacial systems.

Interfacial insights: [6]-Gingerol monolayers at the air-water interface and beyond

Ginger is a culinary spice with a millennia-old tradition due to its extensive therapeutic applications, recently validated by scientific studies. In particular [6]-Gingerol, a key active molecule in ginger, exhibits extraordinary capabilities in addressing a wide spectrum of health issues. However, its therapeutic potential is limited by its rather low bioavailability. The incorporation of [6]-Gingerol into membrane systems of liposomes, micelles, or exosomes is a promising strategy to overcome this limitation. In this contribution, we report the hitherto unexplored surface properties of [6]-Gingerol at the air-water interface. Our comprehensive study, which includes a detailed analysis of surface pressure and surface potential vs. area per molecule isotherms, surface compression modulus, and Brewster Angle Microscopy, demonstrates the capability of [6]-Gingerol to form Langmuir films. These films can be transferred onto solid substrates, forming remarkably homogeneous Langmuir-Blodgett films which have been characterized by Quartz Crystal Microbalance and Atomic Force Microscopy. This study may be of interest as it paves the way for future research on introducing [6]-Gingerol into membrane systems and transporting it into living cells.

Hevea brasiliensis rubber particles' fluid interfaces reveal size impact on early coagulation steps

Natural rubber originates from the coagulation of rubber particles (RP) from Hevea brasiliensis latex. The size distribution of Hevea RP is bimodal with the presence of small rubber particles (SRP) and large rubber particles (LRP). This study aims at getting a better understanding of the early coagulation steps of Hevea RP taking into account the particle size. SRP and LRP were obtained by centrifugation of freshly tapped ammonia-free latex from RRIM600 clone. Size and zeta potential measurements showed that both RP fractions were efficiently separated and stable in basic buffer. SRP and LRP dispersions were placed in a Langmuir trough and RP were let to adsorb at the air-liquid interface to form interfacial films. Surface tension and ellipsometry indicate that the formation kinetics and the stabilization of the film at the air-liquid interface are faster for SRP than LRP. Moreover, the arrangement of RP at the interface differs between SRP and LRP, as shown by Brewster angle microscopy, atomic force microscopy and confocal laser scanning microscopy. First, the RP membrane and cis-1,4-polyisoprene core spread at the air-liquid interface before clustering. Then, while the SRP fuse, the LRP keep their structure in individual particles in floating aggregate. The role of the non-isoprene molecules on the different organization of SRP and LRP films is discussed, the one of the two major RP proteins, SRPP1 (Small Rubber Particle Protein) and Rubber Elongation Factor (REF1) in the early coagulation steps.

Exploring the influence of acetylenic acetogenin unsaturation patterns on lipid interface interactions: Insights from surface chemistry, rheology, and spectroscopy

This study explores how the unsaturation patterns of three acetogenins from Porcelia macrocarpa (2S,3R,4R)-3-hydroxy-4-methyl-2-(eicos-11′-yn-19′-enyl)-butanolide (1), (2S,3R,4R)-3-hydroxy-4-methyl-2-(eicos-11′-ynyl)-butanolide (2), and (2S,3R,4R)-3-hydroxy-4-methyl-2-eicosyl-butanolide (3)—affect their interactions with lipid interfaces, using Langmuir monolayers of dipalmitoyl-phosphoethanolamine (DPPE) as a model for protozoal membranes. The hypothesis posits that unsaturated acetogenins (1 and 2) will exhibit distinct behaviors compared to the saturated acetogenin (3) due to structural differences. Experiments incorporated each acetogenin into DPPE monolayers, employing techniques like tensiometry, dilatational rheology, infrared spectroscopy, and Brewster angle microscopy (BAM) to assess interactions and changes in film properties. Results showed that unsaturated acetogenin 1, active against Leishmania infantum and Trypanosoma cruzi, destabilized the film and induced rapid molecular reorganization, while acetogenin 2, inactive against these parasites, uniquely increased the viscous contribution to viscoelasticity. Saturated acetogenin 3 did not integrate into the film. All acetogenins enhanced fluidity, reducing elasticity and viscosity, with BAM revealing phase separation only in acetogenin 2. Infrared spectroscopy underscored the impact of drug-lipid interactions, leading to the conclusion that unsaturated acetogenins 1 and 2 have a more significant influence on thermodynamic and structural properties than acetogenin 3, offering insights into their potential therapeutic mechanisms.

The influence of blackcurrant extract–based cosmetic antimicrobial agent on skin cells and skin model membranes

The components of blackcurrant extract are known for their antimicrobial properties and the lipid membrane is the important target in terms of the activity of these compounds. In this work, a commercially available product that is PhytoCide Black Currant Powder (BCE), which can be used as a soothing, conditioning and antimicrobial agent in cosmetics, was investigated. The aim of this study was to explore its effect on skin cells and gain insight into the mechanism of its selectivity. The influence of this formulation on keratinocyte and fibroblast cells in in vitro tests was studied and the effect of BCE on model keratinocyte and fibroblast membranes was investigated. As model systems, the lipid monolayers of different compositions were used. The experiments involved the surface pressure/area measurement, penetration studies and Brewster angle microscopy experiments. The BCE formulation was shown to be non-toxic to the skin cells at the concentrations applied. Model membrane experiments confirmed that BCE components do not incorporate into keratinocyte and fibroblast membranes at membrane-related conditions. However, they alter morphology of the studied systems by acting in the region of polar head. Significant differences were found in the affinity of the BCE formulation for bacteria compared to skin lipids, consistent with the proven antibacterial effect of the preservative while lacking toxicity to skin cells. Thus, the membrane of the cell may be critical to the selectivity of the chemicals being tested.

PH-dependent self-assembly of an acid derivative of cholesterol at interfaces

Understanding and control over the self-assembly of molecules is desirable in many physico-chemical processes. Functional groups responsive to a pH change offer immense scope in driving selective molecular self-assembly. pH-dependent self-assembly of an aromatic acid derivative of cholesterol, 4-(6-(cholest-5-ene-3-yloxy)-5-(oxopentyloxy)) benzoic acid, ChBA, is investigated at the air-aqueous interface and characterized using different interface-sensitive techniques. Evidence for the presence of unstable films of ChBA at the air-water interface or for pH < 10 emerges from the surface pressure – area per molecule isotherm, surface pressure relaxation, and Brewster angle microscopy studies. In contrast, for pH > 10.6, ChBA forms a relatively stable film with a higher magnitude of the collapse pressure (45 mN/m). The compressional moduli and the textures obtained using Brewster angle microscopy reveal the presence of two phases (L1 and L2), which are also highly stable with temperature. The surface topography of ChBA films transferred from the air-water interface reveals the presence of multilayers of different thicknesses, for film transferred at pH 11 reveals primarily a uniform and homogenous monolayer. Based on the dependence of the collapse pressure with pH, the surface pKa of ChBA is estimated to be about 10.6. Our studies show that the undissociated ChBA spontaneously forms multilayers, whereas partially or fully dissociated ChBA forms distinct and ordered monolayer phases, highlighting the role of electrostatic interactions.

Oxidation of lipid membrane cholesterol by cholesterol oxidase and its effects on raft model membrane structure

The effects of a peripheral protein – cholesterol oxidase (3β-hydroxysteroid oxidase, ChOx) on the characteristics of model lipid membranes composed of cholesterol, cholesterol:sphingomyelin (1:1), and the raft model composed of DOPC:Chol:SM (1:1:1) were investigated using two membrane model systems: the flat monolayer prepared by the Langmuir technique and the curved model consisting of liposome of the same lipids. The planar monolayers and liposomes were employed to follow membrane cholesterol oxidation to cholestenone catalyzed by ChOx and changes in the lipid membrane structure accompanying this reaction. Changes in the structure of liposomes in the presence of the enzyme were reflected in the changes of hydrodynamic diameter and fluorescence microscopy images, while changes of surface properties of planar membranes were evaluated by grazing incidence X-ray diffraction (GIXD) and Brewster angle microscopy. UV-Vis absorbance measurements confirmed the activity of the enzyme in the tested systems. A better understanding of the interactions between the enzyme and the cell membrane may help in finding alternative ways to decrease excessive cholesterol levels than the common approach of treating hypercholesterolemia with statins, which are not free from undesirable side effects, repeatedly reported in the literature and observed by the patients.

Facile preparation and study of supramolecular architecture of an efficient nanocomposite LB film AHSM/SA based on azo-functionalized hockey stick-shaped mesogen at air-water and air-solid interface

Hockey stick-shaped mesogens are fascinating thermotropic liquid crystal systems owing to their exceptional supramolecular assembly properties and shape anisotropy compared to conventional rod-and bent-shaped mesogens. In this article, we present an investigation of the supramolecular organization of a new azo-functionalized hockey stick-shaped mesogen with stearic acid at the air-water interface and air-solid interfaces by applying the Langmuir-Blodgett film deposition method. The incorporation of stearic acid can change the molecular organization of azo-functionalized hockey stick-shaped mesogen at an aqueous interface through hydrophobic-hydrophobic interactions and form a supramolecular nanostructure at the solid interface. The interfacial nature of the Langmuir monolayer was studied by recording the isotherm (surface pressure area, π–A), which was further analyzed by using Brewster angle microscopy. The significant reduction in molecular area, increased surface pressure, and lower isotherm slope of the AHSM/SA composite mixture indicate the hybrid AHSM/SA monolayer's greater stability compared to pure AHSM. BAM images of the AHSM/SA composite signify nanostructure aggregates formed by the interaction of AHSM and SA molecules at the air-water interface. Field emission scanning electron microscopic analysis of composite films revealed the formation of supramolecular domains. The impact of changing the surface pressure and the number of depositions on the morphology of the composite film surface was monitored using field emission scanning electron microscopy. The supramolecular H-type aggregation of azo-functionalized hockey stick-shaped mesogen and stearic acid molecules in the composite LB film was characterized using UV–visible absorption and steady-state fluorescence spectroscopy. The adsorption of stearic acid onto azo-functionalized hockey stick-shaped mesogen via hydrophobic interactions was confirmed by Fourier transform infrared spectroscopy of the composite Langmuir Blodgett film. Further, Raman spectroscopy of the LB films of the AHSM/SA composites is distinct from the pristine film components due to the merging of signals at similar wave numbers for both SA and AHSM with a lack of typical packing pattern further supported by PXRD studies of the films.

Langmuir monolayers provide an effective strategy for studying molecular recognition of nucleobases using alkylated nucleotides

Molecular Recognition in nucleotides is crucial for medicine, underpinning precise interactions in genetic replication and therapy. Alkylated nucleotides, in particular, play a key role in modifying DNA to inhibit cancer cell growth. In this study, we focused on an alkylated nucleotide, PNM2 (3′,4′,6’-O-tristearoyl uridine or uridine tri-stearate), to investigate the interaction between adenine molecules in the aqueous subphase and PNM2 Langmuir monolayers. Utilizing techniques such as tensiometry, Brewster angle microscopy, infrared spectroscopy, surface potential measurements, and dilatational surface rheology, we found compelling evidence of molecular Recognition between the polar head of the insoluble amphiphile (uridine) in the monolayer and adenine in the aqueous subphase, attributed to hydrogen bonding. These interactions significantly influenced the physicochemical properties of the air-water interface, including monolayer expansion upon molecular recognition, decreased dilatational modulus, increased tensiometric stability of the monolayer when compressed to relevant surface pressures, and decreased surface potential. These findings are noteworthy for drug development, providing crucial insights into the mechanisms of nucleotide interactions.

Nanostructured films of PM6 and Y6 and their assembly using Langmuir–Schaefer technique

This study investigates the molecular-level assembly and electronic properties of Langmuir and Langmuir–Schaefer (LS) films formed from Y6 (a non-fullerene electron acceptor) and PM6 (a wide bandgap electron donor polymer). We employ a variety of techniques including surface pressure-area isotherms, Brewster angle microscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, and electrical characterizations to explore the behavior of these films. Our findings reveal that the films exhibit a tendency to aggregate and form non-homogeneous layers, which impacts their optical and electrical properties. The LS films show a significant sensitivity to solar radiation, which is evident from the changes in conductivity under illumination. This study highlights the potential of these materials in the development of photovoltaic applications, emphasizing the importance of molecular packing and film morphology in optimizing device performance.

Line tension and line entropy associated with the monolayer/trilayer boundary of smectic liquid crystal at the air-water interface.

Molecularly thin films of the smectic liquid crystal 4'-octyl-4-biphenylcarbonitrile (8CB) at the air-water interface phase separate into regions with different numbers of layers, in analogy with freestanding smectic liquid crystalline films. This paper reports the line tension associated with the boundary of coexisting trilayer and monolayer phases of in Langmuir films of 8CB at the air-water interface as a function of temperature and humidity and infers information on the boundary profile between the coexisting phases. Two complementary techniques are used to characterize the 8CB thin films: surface pressure-area isotherm and Brewster angle microscopy (BAM). We determine the line tension by stretching isolated domains from their equilibrium circular shape and analyzing the free relaxation with a hydrodynamic model. Then, we interpret the line tension vs temperature data in terms of an excess line entropy for the domain boundary, which requires careful consideration of the thermodynamics of inhomogeneous monolayer systems.

Impact of the nature of the linker on the 2D and 3D organization of lipid-phenalenone conjugates

A series of phenalenone-lipid conjugates (1A, 1B, 1C, 2) have been synthesized to compensate for the poor water solubility of the photosensitizer phenalenone (PN) and promote the formation of nano-assemblies. We show that the organization and structure of monolayers upon compression strongly depend on the nature of the linker connecting PN to the lipid backbone, and the number of C18 chains. Monolayer properties at the air-water interface were analyzed by surface pressure measurements, Brewster angle and atomic force microscopies, grazing incidence X-ray diffraction, and X-ray reflectivity. Whereas conjugate 1C (ester bond) organizes into multilayers upon compression, conjugates 1A, 1B, and 2 form stable monolayers whose structure is controlled by van der Waals (vdW) interactions between C18 chains, intermolecular H-bonding involving the linker, and for 1B, π-π stacking of PN moieties. Conjugate 1A (amide-triazole linker) is structured into a rectangular network of chains with an order that extends only to the molecule of the adjacent cell. Conjugate 1B (amide bond) forms two incommensurate networks, one for the chains and the other for the headgroups. The distance between molecules in the next near neighbor chain lattice and the sufficient degree of freedom of PN groups allow the latter to pile up via π-π interactions below the chains in a rectangular cell. Conjugate 2 with its double chain adopts a similar behavior to that of a saturated phospholipid. Strong vdW interactions predominate and allow, at high surface pressure, hexagonal packing with no chain tilt. The distance between molecules prevents PN stacking. The identified PN derivative structures explain the linker’s impact on the formation and stability of nano-assemblies.

Effects of the ametryn pesticide on biomembrane models based on Langmuir films and giant unilamellar vesicles (GUVs)

The plasma membrane plays a crucial role in regulating various physiological processes within cells, controlling the flow of substances in and out of the cell. It primarily comprises lipids, oligosaccharides, sterols, and proteins, which are responsible for its functionalization. In this study, we utilized 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) to create mono and bilayers as mimetic systems for the lipid structure of cell plasma membranes. This approach constitutes the initial phase of comprehending the impact of contaminants on in vivo systems. Thus, the impact of the pesticide ametryn (AMT) on DPPC monolayers, which were formed using Langmuir films at the air/water interface, as well as on DPPC bilayers formed by giant unilamellar vesicles (GUVs), was investigated. The use of Brewster Angle Microscopy revealed a significant influence of AMT when in the water subphase on the morphology of DPPC aggregates in Langmuir monolayers, whose surface pressure vs. mean molecular area (π-A) isotherms are shifted to larger areas for higher AMT concentrations. Phase modulation infrared reflection-absorption spectroscopy indicated interactions between AMT and DPPC in Langmuir films, specifically involving the phosphate and choline DPPC head groups. Basically, the negatively charged hydrophilic portion of AMT (SCH3) would be oriented towards the DPPC choline group. At the same time, the AMT triazine ring would be positioned closer to the DPPC phosphate group, leading also to a slight disturb of the vertical orientation of the DPPC alkyl chains. In line with the findings from the monolayer experiments, the confocal microscopy images obtained through phase contrast revealed that the presence of AMT resulted in approximately 85 % of the DPPC GUVs losing their phase contrast. This loss can be attributed to the exchange between the inner and outer contents of the DPPC bilayer.

The influence of Leucidal, a natural cosmetic preservative, on fibroblast and keratinocytes. Studies on cells and on model membrane systems

The aim of this work was to investigate the influence of Leucidal® Liquid (abbr. Leucidal), which is recommended as a natural cosmetic ingredient of antimicrobial properties, on model membranes of keratinocytes and fibroblasts. The toxicity tests on cell lines were also performed to allow for a more detailed discussion of the results. As model membrane systems the lipid Langmuir monolayers were applied. During the investigations, the surface pressure/area measurements, penetration studies and Brewster Angle Microscopy (BAM) visualization were performed for one component and mixed lipid monolayers.It was evidenced that at the membrane – corresponding conditions, the components of Leucidal do not penetrate either model keratinocyte and fibroblast membranes or one component films composed of the major lipids of skin cell membranes. Leucidal makes these systems slightly more expanded and less stable, however this is not reflected in the changes in the film morphology. Only the ceramide systems were sensitive to the presence of Leucidal, i.e. the incorporation of Leucidal components manifested well in the decrease of the films’ condensation and alterations in their morphology. The tests on cells demonstrated that Leucidal is non toxic for these types of cells at the concentrations suggested by the producer. A thorough comparison of these results with those published for bacteria model membranes enabled us to discuss them in the context of the mechanism of action of Leucidal components. It was concluded that Leucidal components are of low affinity to the skin cellular model membranes of low content of Leucidal-sensitive ceramides and are not toxic for fibroblast and keratinocyte cell lines. Moreover, the lipid composition of the membrane and its molecular organization can be important targets for Leucidal components, decisive from the point of view of the activity and selectivity of the studied composition.

Unveiling Texture and Topography of Fatty Acid Langmuir Films: Domain Stability and Isotherm Analysis.

3D texturing by self-assembly at the air-water interface has recently been proposed. The hypothesis of this work is that, if this is true, such domain formation should be inferable directly from pressure-area isotherms and be thermodynamically stable. Monolayers of branched fatty acid mixtures with straight chain analogues and their stability are thus studied using a combination of pressure-area isotherms, thermodynamic analysis, in situ Brewster angle microscopy, and atomic force microscopy of both LB-deposited and drop-cast films on silicon wafers. Isotherms reflecting the behavior of monodisperse 3D domains are shown to be independent of compression rate and display long-term stability. Gibbs analysis further confirms the thermodynamic rather than kinetic origin of such novel species by revealing that deviations from ideal mixing can be explained only a priori by differences in the topography of the water surface, thus also indirectly confirming the self-assembly deformation of the water interface. The intrinsic self-assembly curvature and miscibility of the two fatty acids is confirmed by drop-casting, which also provides a rapid, tunable thin-film preparation approach. Finally, the longevity of the nanostructured films is extraordinary, the long-range order of the deposited films increases with equilibration time at the water interface, and the integrity of the nanopatterns remains intact on the scale of years.

GMP affected assembly behaviors of phosphatidylethanolamine monolayers elucidated by multi-resolved SFG-VS and BAM

The interaction between nucleotide molecules and lipid molecules plays important roles in cell activities, but the molecular mechanism is very elusive. In the present study, a small but noticeable interaction between the negatively charged phosphatidylethanolamine (PE) and Guanosine monophosphate (GMP) molecules was observed from the PE monolayer at the air/water interface. As shown by the sum frequency generation (SFG) spectra and Pi-A isotherm of the PE monolayer, the interaction between the PE and GMP molecules imposes very small changes to the PE molecules. However, the Brewster angle microscopy (BAM) technique revealed that the assembly conformations of PE molecules are significantly changed by the adsorption of GMP molecules. By comparing the SFG spectra of PE monolayers after the adsorption of GMP, guanosine and guanine, it is also shown that the hydrogen bonding effect plays an important role in the nucleotide-PE interactions. These results provide fundamental insight into the structure changes during the nucleotide-lipid interaction, which may shed light on the molecular mechanism of viral infection, DNA drug delivery, and cell membrane curvature control in the brain or neurons.