Low Surface Pressure Research Articles

Driving Coordination Polymer Monolayer Formation by Competitive Reactions at the Air/Water Interface.

We have developed a novel approach enabling us to follow and facilitate the formation of two-dimensional coordination polymer monolayers directly at the air/water interface without the need of complex instrumentation. The method is based on the use of a surface active ligand that, when spread at the air/water interface, progressively undergoes hydrolysis with consequent gradual decrease in surface pressure. Notably, if the aqueous subphase contains metal ions capable of coordinating the ligand, coordination competes with hydrolysis, resulting in a lower surface pressure decrease. As a consequence, the formation of the coordination polymer monolayer can be verified simply by surface pressure measurements. Competition between hydrolysis and coordination was investigated as a function of the main experimental parameters affecting the two reactions, enabling the formation of stable coordination polymer monolayers with controlled density. Finally, the formation of continuous rigid 2D layers was confirmed by compression isotherms and ex situ morphological characterization. This work will simplify the verification of coordination polymer monolayer formation; thus, it will boost the synthesis of novel and innovative 2D materials.

Phase Behavior of GM1-Containing DMPC-Cholesterol Monolayer: Experimental and Theoretical Study.

Organization and distribution of lipids in cellular membranes play an important role in a diverse range of biological processes, such as membrane trafficking and signaling. Here, we present the combined experimental and simulated results to elucidate the phase behavioral features of ganglioside monosialo 1 (GM1)-containing mixed monolayer of the lipids 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and cholesterol (CHOL). Two monolayers having compositions DMPC-CHOL and GM1-DMPC-CHOL are investigated at air-water and air-solid interfaces using Langmuir-Blodgett experiments and scanning electron microscopy (SEM), respectively, to ascertain the phase behavior change of the monolayers. Surface pressure isotherms and SEM imaging of domain formation indicate that addition of GM1 to the monolayer at low surface pressure causes a fluidization of the system but once the system attains the surface pressure corresponding to its liquid-condensed phase, the monolayer becomes more ordered than the system devoid of GM1 and interacts among each other more cooperatively. Besides, the condensing effect of cholesterol on the DMPC monolayer was also verified by our experiments. Apart from these, the effects induced by GM1 on the phase behavior of the binary mixture of DMPC-CHOL were studied with and without applying liquid-expanded (LE)-liquid-condensed (LC) equilibrium surface pressure using molecular dynamics (MD) simulation. Our molecular dynamics (MD) simulation results give an atomistic-level explanation of our experimental findings and furnish a similar conclusion.

Effects of saturated and polyunsaturated fatty acids on interactions with cholesterol versus 7-ketocholesterol in Langmuir monolayers and their potential biological implications.

In this work the Langmuir monolayer technique was used to study interactions between cholesterol (chol) and 7-ketocholesterol (7-KC) with saturated (arachidic acid, AA) and polyunsaturated fatty acids (PUFAs) (ω-3 α-linolenic acid, α-LA,and ω-6 γ- linolenic, γ-LA) in order to get insight into their potential role in atherosclerosis. For this study, surface pressure (π)-area (A) isotherms, compressibility modulus (Cs-1) versus π plots, Brewster angle microscopy (BAM) images and excess functions (Aexc and ΔGexc) were analysed. Different behaviour has been observed. For cholesterol/AA mixed monolayers, components immiscibility occurs, whatever the surface pressure or the mixtures composition is, whereas for the 7-KC/AA mixed system, ideal behaviour was observed at low and high surface pressures for all the investigated compositions. However, the remaining mixed studied systems (sterol/PUFA) exhibit negative deviations from the ideality, although some differences do occurr. The magnitude of these deviations depend on the kind of a PUFA (for ω-3 PUFA greater than for ω-6) - attributed to the different geometry of their acyl chains- and the type of a sterol (for 7-KC greater than for cholesterol).The strength of attractive interactions followed the order: chol/ γ-LA <7-KC/γ-LA < chol/α-LA < 7-KC/ α-LA, postulating the formation of stable complexes of 1:2 stoichiometry for 7-KC/α-LA mixed monolayers and 1:1 stoichiometry for chol/α-LA mixed films. For 7-KC/γ-LA system, the formation of a low stability complex of 2:1 stoichiometry was suggested. The existence of these complexes can play an important role in diminishing the circulating sterols in the blood stream, thus decreasing the probability of atherosclerotic plaques formation.

Impact of arctic oscillation on Indian winter monsoon

The Himalayas in the north part of Indian sub-continent is characterized by variable topography, heterogeneous landuse and climate variations. It acts as a barrier to atmospheric circulation for Indian summer and winter monsoon, thus modulating the associated precipitation over these regions. Western disturbances embedded in Indian winter monsoon (IWM) arriving from Mediterranean region result in one-third of annual precipitation over Himalayas. In the recent decade, studies have shown increased forcings associated with Arctic Oscillations (AOs). In the present study, impact of AO on IWM (December, January, February—DJF) is analyzed. During positive AO years, Polar region is having low surface pressure and colder conditions in comparison with higher pressure with cold surges to midlatitudes during negative AO years. For detailed analysis, National Center of Environmental Prediction/National Center for Atmospheric Research, US reanalysis data is used. Analysis of positive and negative AO year composites shows stronger westerlies over Arabian Sea and neighboring Indian region. Stronger north–south temperature gradient due to warmer Indian Ocean and colder Tibetan region is seen during positive AO years. In addition, weakening of Hadley circulation is seen during positive AO years. This weakening helps in Polar and/or extratropical mass to move southwards having mid-latitude interactions leading to enhanced precipitation over Indian regions. Extensive and intense wave train seen during positive AO years indicates Rossby wave response. Such forcings associated with AOs led to increased precipitation over the northern Indian region.

Stabilizing mixed fatty acid and phthalate ester monolayer on artificial seawater

Phthalate esters which are widely used as industrial chemicals have become widespread contaminants in the marine environment. However, little information is available on the interfacial behavior of phthalate esters in the seawater, where contaminants generally occur at elevated concentrations and have the potential to transfer into the atmosphere through wave breaking on sea surface. We used artificial seawater coated with fatty acids to simulate sea surface microlayer in a Langmuir trough. The interactions of saturated fatty acids (stearic acid (SA) and palmitic acid (PA)) with one of the most abundant phthalate esters (di-(2-ethylhexyl) phthalate (DEHP)), were investigated under artificial seawater and pure water conditions. Pure DEHP monolayer was not stable, while more stable mixed monolayers were formed by SA and DEHP on the artificial seawater at relatively low surface pressure. Sea salts in the subphase can lower the excess Gibbs free energy to form more stable mixed monolayer. Among the ten components in the sea salts, Ca2+ ions played the major role in condensation of mixed monolayer. The condensed characteristic of the mixed SA (or PA)/DEHP monolayers suggested that the hydrocarbon chains were ordered on artificial seawater. By means of infrared reflection-absorption spectroscopy (IRRAS), we found that multiple sea salt mixtures induced deprotonated forms of fatty acids at the air–water interface. Sea salts can improve the stability and lifetime of mixed fatty acid and phthalate ester monolayer on aqueous droplets in the atmosphere. Interfacial properties of mixed fatty acid and phthalate ester monolayers at the air–ocean interface are important to help understand their behavior and fate in the marine environment.

Earth analogue testing and analysis of Martian duricrust properties

Previous and current Mars rover missions have noted a nearly ubiquitous presence of duricrusts on the planet surface. Duricrusts are thin, brittle layers of cemented regolith that cover the underlying terrain. In some cases, the duricrust hides safe or relatively safe underneath the top soil. However, as was observed by both Mars exploration rovers, Spirit and Opportunity, such crusts can also hide loose, untrafficable terrain, leading to Spirit becoming permanently incapacitated in 2009. Whilst several reports of the Martian surface have indicated the presence of duricrusts, none have been able to provide details on the physical properties of the material, which may indicate the level of safe traversability of duricrust terrains. This paper presents the findings of testing terrestrially-created duricrusts with simulated Martian soil properties, in order to determine the properties of such duricrusts and to discover what level of hazard that they may represent (e.g. can vehicles traverse the duricrust surface without penetration to lower sub-surface soils?). Combinations of elements that have been observed in the Martian soil were used as the basis for forming the laboratory-created duricrusts. Variations in duricrust thickness, water content, and the iron oxide compound were investigated. As was observed throughout the testing process, duricrusts behave in a rather brittle fashion and are easily destroyed by low surface pressures. This indicates that duricrusts are not safe for traversing and they present a definite hazard for travelling on the Martian landscape when utilising only visual terrain classification, as the surface appearance is not necessarily representative of what may be lying beneath.

Stress relaxation in quasi-two-dimensional self-assembled nanoparticle monolayers.

We experimentally probed the stress relaxation of a monolayer of iron oxide nanoparticles at the water-air interface. Upon drop-casting onto a water surface, the nanoparticles self-assembled into islands of two-dimensional hexagonally close packed crystalline domains surrounded by large voids. When compressed laterally, the voids gradually disappeared as the surface pressure increased. After the compression was stopped, the surface pressure (as measured by a Wilhelmy plate) evolved as a function of the film aging time with three distinct timescales. These aging dynamics were intrinsic to the stressed state built up during the non-equilibrium compression of the film. Utilizing x-ray photon correlation spectroscopy, we measured the characteristic relaxation time (τ) of in-plane nanoparticle motion as a function of the aging time through both second-order and two-time autocorrelation analysis. Compressed and stretched exponential fitting of the intermediate scattering function yielded exponents (β) indicating different relaxation mechanisms of the films under different compression stresses. For a monolayer compressed to a lower surface pressure (between 20 mN/m and 30 mN/m), the relaxation time (τ) decreased continuously as a function of the aging time, as did the fitted exponent, which transitioned from being compressed (>1) to stretched (<1), indicating that the monolayer underwent a stress release through crystalline domain reorganization. However, for a monolayer compressed to a higher surface pressure (around 40 mN/m), the relaxation time increased continuously and the compressed exponent varied very little from a value of 1.6, suggesting that the system may have been highly stressed and jammed. Despite the interesting stress relaxation signatures seen in these samples, the structural ordering of the monolayer remained the same over the sample lifetime, as revealed by grazing incidence x-ray diffraction.

Response of the Asian summer monsoons to idealized precession and obliquity forcing in a set of GCMs

We examine the response of the Indian and East Asian summer monsoons to separate precession and obliquity forcing, using a set of fully coupled high-resolution models for the first time: EC-Earth, GFDL CM2.1, CESM and HadCM3. We focus on the effect of insolation changes on monsoon precipitation and underlying circulation changes, and find strong model agreement despite a range of model physics, parameterization, and resolution. Our results show increased summer monsoon precipitation at times of increased summer insolation, i.e. minimum precession and maximum obliquity, accompanied by a redistribution of precipitation and convection from ocean to land. Southerly monsoon winds over East Asia are strengthened as a consequence of an intensified land-sea pressure gradient. The response of the Indian summer monsoon is less straightforward. Over south-east Asia low surface pressure is less pronounced and winds over the northern Indian Ocean are directed more westward. An Indian Ocean Dipole pattern emerges, with increased precipitation and convection over the western Indian Ocean. Increased temperatures occur during minimum precession over the Indian Ocean, but not during maximum obliquity when insolation is reduced over the tropics and southern hemisphere during northern hemisphere summer. Evaporation is reduced over the northern Indian Ocean, which together with increased precipitation over the western Indian Ocean dampens the increase of monsoonal precipitation over the continent. The southern tropical Indian Ocean as well as the western tropical Pacific (for precession) act as a moisture source for enhanced monsoonal precipitation. The models are in closest agreement for precession-induced changes, with more model spread for obliquity-induced changes, possibly related to a smaller insolation forcing. Our results indicate that a direct response of the Indian and East Asian summer monsoons to insolation forcing is possible, in line with speleothem records but in contrast to what most marine proxy climate records suggest.

Effect of Oil Hydrophobicity on the Adsorption and Rheology of β-Lactoglobulin at Oil-Water Interfaces.

The adsorption of protein layers at oil-water interfaces is critical to the formation and stability of various emulsions in, for example, technical applications as well as in biological lipid storage. Effects of ionic strength, pH, temperature, and pretreatments of the proteins are well-known. However, the oil phase has been regarded as exchangeable and its role in protein adsorption has been widely ignored. Herein, the influence of systematically selected oil interfaces of high purity on the formation and properties of β-lactoglobulin (β-lg) adsorption layers was evaluated. Droplet profile tensiometry and interfacial rheometry were employed to determine the adsorption kinetics and dilatational and interfacial shear moduli. We show that depending on the molecular size, flexibility, hydrophobicity, polarity, and polarizability of the oils, globular proteins adsorb distinctively. Stronger interactions of polar oils with the hydrophilic exterior of the native β-lg lead to decelerated protein unfolding. This results in lower surface pressures and slower formation of viscoelastic networks. In addition, polar oils interact stronger with the protein network by hydrophilic bonding and thereby act as softening agents. The observed effects of hydrophobic subphases on the adsorbed protein layers provide knowledge, which promotes higher reproducibility in rheological studies and precise tailoring of interfacial films for enhanced formation and stability of emulsions.

Mixed Monolayer of Amphiphilic Schiff Base of ortho-Vaniline and Stearic Acid: Isotherms and Thermodynamic Properties

Surface pressure-area isotherms of pure 2-methoxy-6-[(n-octadecylimino)methyl]phenol (MODIMP) and its mixture with stearic acid are reported. While the monolayer of pure MODIMP is unstable, mixing it with stearic acid stabilizes and condenses it. As the proportion of stearic acid in the solution being spread increases, the monolayer gets progressively more condensed and the surface pressure-area isotherm shows a decreased compressibility. Values of excess area per molecule of the mixed monolayer compared to the individual components give an indication about the possible interactions between the molecules of the two components and their orientation at the interface. At lower surface pressures, interactions between the molecules of different components are stronger than those in the pure monolayer, while opposite is the case at higher surface pressures. DOI: http://dx.doi.org/10.17807/orbital.v10i2.1078

Evolution and mechanics of mixed phospholipid fibrinogen monolayers.

All mammals depend on lung surfactant (LS) to reduce surface tension at the alveolar interface and facilitate respiration. The inactivation of LS in acute respiratory distress syndrome (ARDS) is generally accompanied by elevated levels of fibrinogen and other blood plasma proteins in the alveolar space. Motivated by the mechanical role fibrinogen may play in LS inactivation, we measure the interfacial rheology of mixed monolayers of fibrinogen and dipalmitoylphosphatidylcholine (DPPC), the main constituent of LS, and compare these to the single species monolayers. We find DPPC to be ineffective at displacing preadsorbed fibrinogen, which gives the resulting mixed monolayer a strongly elastic shear response. By contrast, how effectively a pre-existing DPPC monolayer prevents fibrinogen adsorption depends upon its surface pressure. At low DPPC surface pressures, fibrinogen penetrates DPPC monolayers, imparting a mixed viscoelastic shear response. At higher initial DPPC surface pressures, this response becomes increasingly viscous-dominated, and the monolayer retains a more fluid, DPPC-like character. Fluorescence microscopy reveals that the mixed monolayers exhibit qualitatively different morphologies. Fibrinogen has a strong, albeit preparation-dependent, mechanical effect on phospholipid monolayers, which may contribute to LS inactivation and disorders such as ARDS.

Interactions between model cell membranes and the neuroactive drug propofol

Vibrational sum frequency spectroscopy (VSFS) complemented by surface pressure isotherm and neutron reflectometry (NR) experiments were employed to investigate the interactions between propofol, a small amphiphilic molecule that currently is the most common general anaesthetic drug, and phospholipid monolayers. A series of biologically relevant saturated phospholipids of varying chain length from C18 to C14 were spread on either pure water or propofol (2,6-bis(1-methylethyl)phenol) solution in a Langmuir trough, and the change in the molecular structure of the film, induced by the interaction with propofol, was studied with respect to the surface pressure. The results from the surface pressure isotherm experiments revealed that propofol, as long as it remains at the interface, enhances the fluidity of the phospholipid monolayer. The VSF spectra demonstrate that for each phospholipid the amount of propofol in the monolayer region decreases with increasing surface pressure. Such squeeze out is in contrast to the enhanced interactions that can be exhibited by more complex amphiphilic molecules such as peptides. At surface pressures of 22–25 mN m−1, which are relevant for biological cell membranes, most of the propofol has been expelled from the monolayer, especially in the case of the C16 and C18 phospholipids that adopt a liquid condensed phase packing of its alkyl tails. At lower surface pressures of 5 mN m−1, the effect of propofol on the structure of the alkyl tails is enhanced when the phospholipids are present in a liquid expanded phase. Specifically, for the C16 phospholipid, NR data reveal that propofol is located exclusively in the head group region, which is rationalized in the context of previous studies. The results imply a non-homogeneous distribution of propofol in the plane of real cell membranes, which is an inference that requires urgent testing and may help to explain why such low concentration of the drug are required to induce general anaesthesia.

Adsorption kinetics of the partially protonated cationic surfactant dodecylamine

The adsorption kinetics of the partially protonated cationic surfactant dodecylamine (C12H27N) in a 50mM NaCl solution was examined. The dynamic and equilibrium surface tensions (STs) were measured using a video-enhanced pendant bubble tensiometer with a modified cell system. The equilibrium and complete ST relaxation profiles were compared with the theoretical profiles predicted from the non-ionic, partially ionized and fully ionized ionic models. A quasi-equilibrium approach was used in the ionic model to describe the electric field in the electrical double layer. In the very low surface pressure regime (π<2mN/m), the dynamic ST data were compared with the theoretical ST predicted by the ionic (partially or fully ionized) Frumkin model under a diffusion-controlled condition. The fitted theoretical profiles produced a diffusivity value of 0.6–1.0×10−6cm2/s, which is much lower than the diffusivity calculated using the Wilke-Chang equation, which was D=5.6×10−6cm2/s. Therefore, it could be concluded that in the low surface pressure regime, the controlling mechanism of the adsorption process exhibits a mixed diffusive-kinetic control model.

Emergence of Strong Nonlinear Viscoelastic Response of Semifluorinated Alkane Monolayers.

Viscoelasticity of monolayers of fluorocarbon/hydrocarbon tetrablock amphiphiles di(FnHm) ((CnF2n+1CH2)(Cm-2H2m-3)CH-CH(CnF2n+1CH2)(Cm-2H2m-3)) was characterized by interfacial dilational rheology under periodic oscillation of the moving barriers at the air/water interface. Because the frequency dispersion of the response function indicated that di(FnHm) form two-dimensional gels at the interface, the viscosity and elasticity of di(FnHm) were first analyzed with the classical Kelvin-Voigt model. However, the global shape of stress response functions clearly indicated the emergence of a nonlinearity even at very low surface pressures (π ≈ 5 mN/m) and small strain amplitudes (u0 = 1%). The Fourier-transformed response function of higher harmonics exhibited a clear increase in the intensity only from odd modes, corresponding to the nonlinear elastic component under reflection because of mirror symmetry. The emergence of strong nonlinear viscoelasticity of di(FnHm) at low surface pressures and strain amplitudes is highly unique compared to the nonlinear viscoelasticity of other surfactant systems reported previously, suggesting a large potential of such fluorocarbon/hydrocarbon molecules to modulate the mechanics of interfaces using the self-assembled domains of small molecules.

The effect of chitin nanoparticles on surface behavior of DPPC/DPPG Langmuir monolayers

The effect of chitin nanoparticles on surface behavior of lipid systems containing dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) is studied by surface pressure (π)-area (A) isotherms, polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS), Brewster angle microscopy (BAM). The variation of surface behavior of DPPC/DPPG monolayers is induced mainly by electrostatic interactions between nanoparticles and head groups of phospholipids. At lower surface pressure, nanoparticles can penetrate into the monolayers and the positive charges carried by nanoparticles benefits the enrichment of phospholipid molecules at surface, which not only increases the mean molecular area but also hinders the formation of phospholipid liquid-condensed (LC) phase. However, when surface pressure is higher, the nanoparticles flee away from the surface and some of the phospholipid molecules are pulled out of the monolayers together to the subphase and decrease the order degree of the monolayers. Moreover, nanoparticles can destroy the hydrogen-bond between water molecules and phosphate head groups and thus lead to the dehydration of phosphate groups. This work confirms that chitin nanoparticles can affect the surface behavior of DPPC/DPPG monolayers. Furthermore, the results obtained using mixed monolayer containing two major lung surfactants DPPC/DPPG and nanoparticles will be helpful for deep understanding the harm of PM2.5 to lung health.

Chitosan-fatty acid interaction mediated growth of Langmuir monolayer and Langmuir-Blodgett films

The interaction of chitosan with bio-membranes, which plays important role in deciding its use in biological applications, is realized by investigating the interaction of chitosan with stearic acid (fatty acid) in Langmuir monolayers (at air–water interface) and Langmuir-Blodgett (LB) films (after transferring it onto solid substrate). It is found from the pressure-area isotherms that the chitosan insertion causes an expansion of chitosan-fatty acid hybrid monolayers, which reduces the elasticity and make the film heterogeneous. It is likely that at low surface pressure chitosan is situated at the interface, interacting with stearic acid molecules via electrostatic and hydrophobic interactions whereas at high pressure chitosan mainly located at subsurface beneath stearic acid molecules. In the latter case the interaction is predominantly electrostatic yielding very small contribution to the surface pressure. The reduction of temperature of the subphase water allows more number of chitosan molecules to reach surface to increase the pressure/interaction. On the other hand, although pure chitosan is found difficult to relocate on the substrate from air-water interface due to its hydrophilic-like nature, it alongside stearic acid (amphiphilic molecules) can be transferred onto substrate using LB technique as evident from infrared spectra. Their out-of-plane and in-plane structures, as extracted from two complementary surface sensitive techniques- X-ray reflectivity and atomic force microscopy, are found strongly dependent on the chitosan mole fraction and the deposition pressure. These analysis of the film-structure will essentially allow one to model the system better and provide better insight into the interaction.

Effect of saturation in phospholipid/fatty acid monolayers on interaction with amyloid β peptide

The effect of the saturation of fatty acid (FA) in 1,2-dimyristoyl-sn-glycero-3-phosphocoline (DMPC)/FA membrane on the interaction between lipid membrane and amyloid β monomer was investigated by using the Langmuir monolayer technique. The surface pressure (Π)-mean molecular area (A) isotherms and fluorescent measurements reveal that DMPC and octadecanoic acid (stearic acid, SA) molecules were somewhat miscible in the mixed membrane, which was maintained to homogeneous gel phase by enhance of the intermolecular hydrophobic interactions because of the all trans acyl chains. On the other hand, DMPC and 9Z,12Z-octadecadienoic acid (linoleic acid, LA) molecules were considered to be well miscible in the mixed membrane, where the membrane partially transferred from gel phase to liquid-crystalline phase. The Π-A isotherms of the monolayers on amyloid β-peptide (Aβ) solution indicated that Aβ monomers tend to be inserted into the saturated acyl chain region of monolayers at low surface pressure and that the Aβ monomers were then extruded from the monolayer at higher surface pressure. It was observed that behaviors of Aβ monomers at higher surface pressure depended on membrane microstructures. In the DMPC/SA monolayers, Aβ aggregated and then was extruded from monolayers at about 20mNm-1 of surface pressure irrespective of the SA proportion. On the other hand, in the DMPC/LA monolayers, Aβ, which favors to interact with DMPC, is dispersed in the monolayer even at high surface pressure because DMPC and LA molecules were well miscible in the monolayer.

Caseinate-Induced Competitive Displacement of Whey Protein from Interfaces

The caseinate-induced competitive displacement of whey protein from planar air-water interfaces was investigated based on atomic force microscopy (AFM) imaging and that from the surfaces of oil droplets immersed in aqueous solution based on AFM force spectroscopy. After the addition of sodium caseinate to the sub-phase, the surface pressure of planar interfacial films of pre-adsorbed whey protein increased from 8 mN/m to up to 21 mN/m. The thicknesses of interfacial films were uniform and remained to be approximately 2 nm at relatively low surface pressures up to 18 mN/m, while they became uneven at higher surface pressures and increased to up to 7.1 nm, presumably due to the compression of interfacial whey protein networks by adsorbed caseinate. The rigidity of oil droplets coated with protein adsorbed to their surfaces was then evaluated based on the slope of approximately linear force-distance curves obtained by pressing an oil droplet against another. The adsorption of whey protein to oil droplet surfaces increased droplets’ rigidity. The subsequent addition of caseinate to the bulk solution surrounding oil droplets coated with pre-adsorbed whey protein further increased droplets’ rigidity. The present results suggest that caseinate adsorbed to an interface to which whey protein had adsorbed in advance did not completely expel pre-adsorbed whey protein molecules into the aqueous phase but caused a compaction of interfacial whey protein networks and thereby strengthened the interfacial film.

Daunorubicin and doxorubicin molecular interplay with 2D membrane models

The anthracyclines daunorubicin and doxorubicin are widely used antineoplastic agents due to their therapeutic activity against a broad variety of human cancers. Although, the classical model to explain anthracyclines’ cytotoxicity has been based in the direct interference with nucleic acid function, evidence suggests that the plasma membrane is also involved in the drug’s mechanism of action.In this work, the interaction of these drugs with two-dimensional membrane models were studied in order to gain further insights at the molecular level regarding anthracyclines membrane interactions. For that purpose, Langmuir monolayers composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), sphingomyelin (SM) and cholesterol (Chol) were used, since these are the most common lipids found in biological membranes. Several biophysical techniques were employed: surface pressure (π) – area (A) isotherms measurements were used to investigate the adsorption and penetration of drugs, polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to acquire structural information and Brewster angle microscopy (BAM) to record images of the monolayers on the micrometer scale.The interactions of anthracyclines were assessed by alterations in the monolayers’ shape, characteristic parameters (Cs−1 values and area per lipid molecule at 30mN·m−1 and under maximum packing conditions) and morphology of each 2D model studied. The presence of the drugs in the interface led to the production of less ordered monolayers, as evidenced by the decrease in the compressibility modulus. In addition, the drugs’ effect on the membrane organization is related with their chemical structure and depends on the membraneś phase. For lower surface pressures, both electrostatic and hydrophobic interactions led to significant modifications in the monolayer order. With further compression, the impact of such interactions is reduced, resulting in the squeezing-out of some drug molecules from the interface. Furthermore, BAM images showed a clear anticancer drug interplay with the lipid monolayer by changes in the domains shape and appearance of bright dots, which are located in the frontier between the condensed and expanded lipid phases.

Transfer of molecular chirality to spiral nanostructure in the interfacial mixed amphiphilic diacetylene/histidine monolayers via in situ topochemical photopolymerization

The photopolymerization in the monolayers consisted of an equivalent mixture of 10, 12-pentacosadiynoic acid and amphiphilic histidine derivatives L-HC18 or D-HC18 has been investigated. It is found that the diacetylene derivatives can be incorporated into the monolayer and polymerized to polydiacetylene (PDA) backbone with a red phase by in situ UV irradiation at the air/water interface. The chiral amphiphiles L-HC18 or D-HC18 can transfer the molecular chirality to PDA through the ordered alignments of the two components. AFM images of the transferred films further revealed the chiral nanostructures from PDA/L-HC18 or PDA/D-HC18. The topochemical polymerization of the mixed films at a low surface pressure as a function of time is carried out to characterize crimp behaviors from straight nanobelts to more curly bands even spiral nanostructures in a clockwise or anti-clockwise direction, in which the curling direction is depended on the molecular chirality of the two enantiomers. The research has well established the connection between molecular chirality and mesoscopic chirality using the Langmuir as well as Langmuir-Blodgett methods.