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[Display omitted] • Comparative studies of planar and vesicular structures based on the same materials. • Characteristics of niosomes correlate with excess free energy of mixed monolayers. • Composition of shells determine morphology, polarity and microviscosity of niosomes. • Cholesterol increases the compatibility in monolayers and the stability of niosomes. In recent years, the study of niosomes as nanocarriers alternative to liposomes has received increasing attention. In contrast to well-studied liposome membranes, many aspects of the behavior of analogous niosome bilayers have not been studied. This paper considers one of these aspects related to the communication between the physicochemical properties of planar and vesicular objects. We present the first results of comparative studies of Langmuir monolayers of binary and ternary (with cholesterol) mixtures of non-ionic surfactants based on sorbitan esters and niosomal structures assembled from the same materials. The Thin-Film Hydration (TFH) method in the gentle shaking version was used to produce the particles of large sizes, while small unilamellar high quality vesicles with a unimodal distribution of particles were prepared by TFH using ultrasonic treatment and extrusion. An analysis of the structural organization and phase state of monolayers based on compression isotherms and supplemented by thermodynamic calculations, as well as the results of determining the particle morphology, polarity and microviscosity of niosome shells, made it possible to obtain fundamental data on the intermolecular interactions of the components and their packing in shells and to relate these data to the properties of niosomes. This relationship can be used to optimize the composition of niosome membranes and predict the behavior of these vesicular systems. It was shown that cholesterol excess creates regions of bilayers with increased rigidity (like "lipid rafts"), which hinders the process of folding film fragments into small niosomes. [ABSTRACT FROM AUTHOR]

[Display omitted] Unravelling the structural diversity of cellular membranes is a paramount challenge in life sciences. In particular, lipid composition affects the membrane collective behaviour, and its interactions with other biological molecules. Here, the relationship between membrane composition and resultant structural features was investigated by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry on in vitro membrane models of the mammalian plasma and endoplasmic-reticulum-Golgi intermediate compartment membranes in the form of Langmuir monolayers. Natural extracted yeast lipids were used because, unlike synthetic lipids, the acyl chain saturation pattern of yeast and mammalian lipids are similar. The structure of the model membranes, orthogonal to the plane of the membrane, as well as their lateral packing, were found to depend strongly on their specific composition, with cholesterol having a major influence on the in-plane morphology, yielding a coexistence of liquid-order and liquid-disorder phases. [ABSTRACT FROM AUTHOR]

[Display omitted] Lung surfactant protects lung tissue and reduces the surface tension in the alveoli during respiration. Particulate matter with an aerodynamic diameter of less than 2.5 μm (PM 2.5), which invades primely through inhalation, can deposit on and interact with the surfactant layer, leading to changes in the biophysical and morphological properties of the lung surfactant. Langmuir monolayers of 1,2-dipalmitoyl- sn - glycero -3-phosphatidylcholine (DPPC) and clinical surfactant Calsurf were investigated with a PM 2.5 model injected into the water subphase, which were characterized by surface pressure-area isotherms, Brewster angle microscopy, atomic force microscopy, fluorescent microscopy, and x-ray photoelectron spectroscopy. The binding between DPPC/Calsurf and PM 2.5 was studied using isothermal titration calorimetry. PM 2.5 induced the expansion of the monolayers at low surface pressure (п) and film condensation at high п. Aggregation of PM 2.5 mainly occurred at the interface of liquid expanded/liquid condensed (LE/LC) phases. PM 2.5 led to slimmer and ramified LC domains on DPPC and the reduction of nano-sized condensed domains on Calsurf. Both DPPC and Calsurf showed fast binding with PM 2.5 through complex binding modes attributed to the heterogeneity and amphiphilic property of PM 2.5. This study improves the fundamental understanding of PM 2.5 -lung surfactant interaction and shows useful implications of the toxicity of PM 2.5 through respiration process. [ABSTRACT FROM AUTHOR]

Dengue virus infection depends on its fusion with the host membrane, where the binding occurs through interaction between proteins on the virus cell surface and specific viral receptors on target membranes. This process is mediated by the fusion peptide located between residues 98 and 112 (DRGWGNGCGLFGKGG) that forms a loop in domain II of dengue E glycoprotein. In this study, we evaluated the role of fusion peptide surrounding regions (88–97 and 113–123) of the Dengue 2 subtype on its interaction with the membrane and fusion activity. These sequences are important to stabilize the fusion peptide loop and increase fusion activity. Three peptides, besides the fusion peptide, were synthesized by SPPS using the Fmoc chemical approach. The first contains the fusion peptide and the C-terminal region of the loop (sequence 98–123); another contains the N-terminal region (88–112) and the larger peptide contains both regions (88–123). The peptides were able to interact with a model membrane. Differences in morphology of the monolayer promoted by the peptides were assessed by Brewster Angle Microscopy (BAM). Our data indicated that the C-terminal region of fusion peptide loop is more efficient in promoting fusion and interacting with the membrane than the N-terminal sequence, which is responsible for the electrostatic initial interaction. We propose a 2-step mechanism for the interaction of the dengue virus fusion peptide with the host membrane, where the N-terminal sequence docks electrostatically on the headgroups and then the C-terminal interacts via hydrophobic forces in the acyl chains. [Display omitted] • 2-step mechanism for dengue virus fusion peptide. • N-terminal region can be related to the initial interaction in the membrane. • C-terminal is important for dengue virus fusion peptide. [ABSTRACT FROM AUTHOR]

[Display omitted] • EE2 interacts with both SM and SM/Chol monolayers at the air/water interface. • The morphology and permeability was induced by EE2 only to SM/Chol GUVs. • The L o phase regulate the permeability of the vesicles in presence of EE2. Hormone treatments are frequently associated with cardiovascular diseases and cancers in women. Additionally, the detrimental effects of their presence as contaminants in water remain a concern. The transport of hormones through cell membranes is essential for their biological action, but investigating cell permeability is challenging owing to the experimental difficulty in dealing with whole cells. In this paper, we study the interaction of the synthetic hormone 17α-ethynylestradiol (EE2) with membrane models containing the key raft components sphingomyelin (SM) and cholesterol (Chol). The models consisted of Langmuir monolayers and giant unilamellar vesicles (GUVs) that represent bilayers. EE2 induced expansion of SM monolayers upon interacting with the non-hydrated amide group of SM head, but it had practically no effect on SM GUVs because these group are not available for interaction in bilayers. In contrast, EE2 interacted with hydrated phosphate group ( P O 2 -) and amide group of SM/Chol mixture monolayer, which could explain the loss in phase contrast of liquid-ordered GUVs suggesting pore formation. A comparison with reported EE2 effects on GUVs in the fluid phase, for which no loss in phase contrast was observed, indicates that the liquid-ordered phase consisting of lipid rafts is relevant to be associated with the changes on cell permeability caused by the hormones. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The interaction of hydrophobic silver nanoparticles with different phospholipids and stratum corneum mimic (SCM) membranes is studied in Langmuir monolayers. Thus, silver nanoparticles coated with oleic acid (AgNP-OA) were synthesized, characterized and incorporated in Langmuir monolayers of single phospholipids –having different chain length, saturation degree and phase state– or of a SCM mixture. The incorporation of AgNP-OA to the lipid monolayers generated an expansion of the monolayers and a decrease of the surface compressional modulus compared to the pure lipid. X-ray photoelectron spectroscopy (XPS) suggested that the zwitterionic choline-phospholipids can be adsorbed onto the nanoparticles' surface, which is relevant considering that phospholipids are the major constituents of the cell membrane. We also studied the changes in the topography at the mesoscale level using Brewster angle microscopy. We found the most prominent changes in the lipids with liquid-condensed phase, such as SCM, showing segregation of their components. This could have major implications in the barrier function of the membrane, affecting for example the skin permeability towards hydrophobic nanoparticles. Finally, the capability of hydrophobic AgNP-OA for delivering Ag+ ions was studied in aqueous media in the absence and presence of phospholipids. In both conditions, AgNP-OA released Ag+ at reported-bactericidal concentrations, being double in the presence of phospholipids. [ABSTRACT FROM AUTHOR]

Abstract Tissue-nonspecific alkaline phosphatase (TNAP) is a key enzyme in the biomineralization process as it produces phosphate from a number of phospho-substrates stimulating mineralization while it also inactivates inorganic pyrophosphate, a potent mineralization inhibitor. We have previously reported on the reconstitution of TNAP on Langmuir monolayers as well as proteoliposomes. In the present study, thin films composed of dimyristoylphosphatidic acid (DMPA) were deposited on titanium supports by the Langmuir-Blodgett (LB) technique, and we determined preservation of TNAP's phosphohydrolytic activity after incorporation into the LB films. Increased mineralization was observed after exposing the supports containing the DMPA:TNAP LB films to solutions of phospho-substrates, thus evidencing the role of TNAP on the growth of calcium phosphates after immobilization. These coatings deposited on metallic supports can be potentially applied as osteoconductive materials, aiming at the optimization of bone-substitutes integration in vivo. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Epi -polygodial is isolated and presents Antitrypanosomal activity. • Epi -polygodial is incorporated in biointerface models. • Epi -polygodial changed the thermodynamic and structural properties of DPPE monolayers. • Changes in the monolayers can be associated to the interaction with membranes. Abstract Epi -polygodial, a drimane sesquiterpene was isolated from Drimys brasiliensis (Winteraceae). This compound demonstrated high parasite selectivity towards Trypanosoma cruzi trypomastigotes (IC 50 = 5.01 μM) with a selectivity index higher than 40. These results were correlated with the effects observed when this compound was incorporated in cellular membrane models of protozoans, represented by Langmuir monolayers of dipalmitoylphosphoethanolamine (DPPE). Surface pressure-area isotherms showed that epi -polygodial expands DPPE monolayers at higher areas and condenses them at lower areas, which was attributed to the preferential interaction with the polar heads of the lipid. This mechanism of action could be corroborated with Polarization-Modulation Reflection-Absorption Spectroscopy and Brewster Angle Microscopy. These results pointed to the fact that the interaction of epi -polygodial with DPPE monolayers at the air-water interface affects the physical chemical properties of the mixed film, which may be important to comprehend the interaction of this drug with cellular membranes at the molecular level. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hydroxymethyl and alkyl groups decrease IC 50 values and increase the selectivity. • Modifications modulate the interaction with the membrane at the air-water interface. • For tumorigenic cells models, the presence of the compounds expanded the monolayers. • For non-tumorigenic cells models, the compounds have condensed the monolayers. Abstract Twenty-one isovanillin derivatives were prepared in order to evaluate their cytotoxic properties against the cancer cell lines B16F10-Nex2, HL-60, MCF-7, A2058 and HeLa. Among them, seven derivatives exhibited cytotoxic activity. We observed that for obtaining smaller IC 50 values and for increasing the index of selectivity, two structural features are very important when compared with isovanillin (1); a hydroxymethyl group at C-1 and the replacement of the hydroxyl group at C-3 by different alkyl groups. As the lipophilicity of the compounds was changed, we decided to investigate the interaction of the cytotoxic isovallinin derivatives on cell membrane models through Langmuir monolayers by employing the lipids DPPC (1,2-diplamitoyl- sn - glycero -3-phosphocoline) and DPPS (1,2-diplamitoyl- sn - glycero -3-phosphoserine). The structural changes on the scaffold of the compounds modulated the interaction with the phospholipids at the air-water interface. These results were very important to understand the biophysical aspects related to the interaction of the cytotoxic compounds with the cancer cell membranes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calixarene pyrazoles show low hemolysis, low mutagenicity, and low in vivo toxicity. • NH-pyrazolated phenol ether and calixarenes stereoisomers inhibit M-HeLa cell growth. • Internal pathway of caspase-9 activation in M-HeLa cell lines treated by pyrazoles. • Upregulated DNA damage markers and M-HeLa cell-cycle halt after pyrazole treatment. • Monolayers of calixarene pyrazoles expand at air–water interface in presence of DNA. Tumor selectivity is yet a challenge in chemotherapy-based cancer treatment. A series of calixarenes derivatized at the lower rim with 3-phenyl-1H-pyrazole units with variable upper-rim substituent and conformations of macrocyclic core, alkyl chain length between heterocycle and core, as well as phenolic monomer (5-(4- tert -butylphenyloxy)methoxy-3-phenyl-1H-pyrazole) have been synthesized and characterized in a range of therapeutically relevant cellular models (M-HeLa, MCF7, A-549, PC3, Chang liver, and Wi38) from different target organs/systems. Specific cytotoxicity for M-HeLa cells has been observed in tert -butylcalix[4]arene pyrazoles in 1,3-alternate (compound 7b) and partial cone (compound 7c) conformations with low mutagenicity and haemotoxicity and in vivo toxicity in mice. Compounds 7b,c have induced mitochondrial pathway of apoptosis of M-HeLa cells through caspase-9 activation preceded by the cell cycle arrest at G0/G1 phase. A concomitant overexpression of DNA damage markers in pyrazole-treated M-HeLa cells suggests that calixarene pyrazoles target DNA, which was supported by the presence of interactions between calixarenes and ctDNA at the air–water interface. [ABSTRACT FROM AUTHOR]

The antimicrobial property of silver nanoparticles (AgNPs) is believed to be associated to their interaction with biointerfaces such as microbial cell membranes, encouraging research on the identification of membrane sites capable of AgNPs binding. Although significant progress has been made in that regard, the exact molecular mechanism of action is yet to be fully understood. In this study, AgNPs dispersed in aqueous media and stabilized with polyvinylpyrrolidone were incorporated in Langmuir monolayers of selected lipids that served as cell membrane models. Results from pressure-area isotherms, vibrational spectroscopy and Brewster angle microscopy revealed condensation of glycoside-free lipid monolayers, evidencing that the AgNPs interact mostly with the lipid hydrophilic head groups. In contrast, the monolayers of systems containing glycoside derivatives were found to expand upon AgNPs incorporation, indicating that the glycosidic compounds might facilitate the incorporation of these nanoparticles in cellular membranes. These data can be therefore correlated with the possible toxicity and microbicide effect of AgNPs in lipidic surfaces of mammalian and microbial membranes. [ABSTRACT FROM AUTHOR]

Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) monomer and an amphiphilic Hemicyanine dye derivative have been formed at the air/water interface. Two derivatives of docosylpyridinium have been used, with either one included in the monolayer in 1:1 molar ratio. The DA monomers within the mixed monolayers have been polymerized in situ at the air/water interface. The crystalline structure of the monolayer and the kinetics of polymerization have been probed by grazing incidence X-ray diffraction (GIXD). The polymerization of DA proceeds with no phase segregation, exclusively leading to the red polydiacetylene form. The kinetics of polymerization at the air/water interface has been monitored in situ by GIXD. The experimental results have been combined with Molecular Mechanics computer simulations, revealing that DA molecules are sequentially arranged with molecules of Hemicyanine dye in alternating rows. The hydrophobic chains of the dye molecules act as spacers between the DA monomers. Surprisingly, such molecular arrangement does not hinder the in situ photopolymerization of DA. The mechanism of polymerization of DA within the mixed Langmuir monolayers has been convincingly described in molecular detail. This approach for interfacial polymerization of DA holds great potential for optically active devices and nanostructures comprising self-assembled thin films based in polydiacetylene. [ABSTRACT FROM AUTHOR]

In this work, silver nanoparticles (AgNPs) dispersed in non-aqueous media and stabilized with polyether block polymers amide (PEBA) were incorporated in Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC), which served as a cell membrane model. The AgNPs presented surface activity, disturbing the viscoelastic properties of the floating film. They expanded the monolayers decreasing their surface elasticity as observed with surface pressure-area isotherms. Polarization modulation reflection-absorption spectroscopy showed that the permanence of AgNPs at the air-water interface is favored by PEBA, affecting both the hydrophilic and the hydrophobic groups of the phospholipid. Brewster angle microscopy showed that the AgNPs lead to the formation of aggregates at the air-water interface, establishing domains that shear with each other due to the low lateral viscosity of irregular and non-monomolecular domains. These data can be correlated to the possible toxicity and microbicide effect of AgNPs in lipidic surfaces such as in mammalian and microbial membranes. [ABSTRACT FROM AUTHOR]

Organic macromolecules with dendrimeric architectures are polymeric materials potentially useful as nanocarriers for therapeutic drugs. In this work, we evaluate a series of Newkome-type dendrons in Langmuir and Langmuir-Blodgett films as platforms capable of interacting with a potential antitumoral agent. The nanocomposite is proposed as model for the development of surface mediated drug delivery systems. We were successful in the formation and characterization of pure (dendrons) and composite (drug-dendron) stable and reproducible monolayers, and their transfer to solid substrates. A detailed study of topographic characteristics of the generated surfaces by atomic force microscopy was conducted. Furthermore, we probed dendron monolayer films as anchorage surfaces for mammalian cells. Normal cell attachment and proliferation on the surfaces were observed. No evident cytotoxic effects were detected, demonstrating the adequate biocompatibility of the surfaces. [ABSTRACT FROM AUTHOR]

Hypothesis Owing to structural similarities between sulfobetaine lipids and phospholipids it should be possible to form stable Langmuir monolayers from long tail sulfobetaines. By modification of the density of lipid tail group (number of carbon chains) it should also be possible to modulate the two-dimensional phase behaviour of these lipids and thereby compare with that of equivalent phospholipids. Potentially this could enable the use of such lipids for the wide array of applications that currently use phospholipids. The benefit of using sulfobetaine lipids is that they can be synthesised by a one-step reaction from cheap and readily available starting materials and will degrade via different pathways than natural lipids. The molecular architecture of the lipid can be easily modified allowing the design of lipids for specific purposes. In addition the reversal of the charge within the sulfobetaine head group relative to the charge orientation in phospholipids may modify behaviour and thereby allow for novel uses of these surfactants. Experiments Stable Langmuir monolayers were formed composed of single and double tailed sulfobetaine lipids. Surface pressure-area isotherm, Brewster Angle Microscopy and X-ray and neutron reflectometry measurements were conducted to measure the two-dimensional phase behaviour and out-of-plane structure of the monolayers as a function of molecular area. Findings Sulfobetaine lipids are able to form stable Langmuir monolayers with two dimensional phase behaviour analogous to that seen for the well-studied phospholipids. Changing the number of carbon tail groups on the lipid from one to two promotes the existence of a liquid condensed phase due to increased Van der Waals interactions between the tail groups. Thus the structure of the monolayers appears to be defined by the relative sizes of the head and tail groups in a predictable way. However, the presence of sub-phase ions has little effect on the monolayer structure, behaviour that is surprisingly different to that seen for phospholipids. [ABSTRACT FROM AUTHOR]

The molecular packing, thermodynamics and surface topography of binary Langmuir monolayers of Insulin and DPPC (dipalmitoylphosphatidylcholine) or POCP (1-palmitoyl-2-oleoylphosphatidylcholine) at the air/water interface on Zn 2+ containing solutions were studied. Miscibility and interactions were ascertained by the variation of surface pressure-mean molecular area isotherms, surface compressional modulus and surface (dipole) potential with the film composition. Brewster Angle Microscopy was used to visualize the surface topography of the monolayers. Below 20 mN/m Insulin forms stable homogenous films with DPPC and POPC at all mole fractions studied (except for films with X INS = 0.05 at 10 mN/m where domain coexistence was observed). Above 20 mN/m, a segregation process between mixed phases occurred in all monolayers without squeezing out of individual components. Under compression the films exhibit formation of a viscoelastic or kinetically trapped organization leading to considerable composition-dependent hysteresis under expansion that occurs with entropic–enthalpic compensation. The spontaneously unfavorable interactions of Insulin with DPPC are driven by favorable enthalpy that is overcome by unfavorable entropic ordering; in films with POPC both the enthalpic and entropic effects are unfavorable. The surface topography reveals domain coexistence at relatively high pressure showing a striped appearance. The interactions of Insulin with two major membrane phospholipids induces composition-dependent and long-range changes of the surface organization that ought to be considered in the context of the information-transducing capabilities of the hormone for cell functioning. [ABSTRACT FROM AUTHOR]

A series of semifluorinated thiols of the general formula C m F 2 m +1 C n H 2 n SH ( abbr . F m H n SH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F 10 ) and variable length of the hydrogenated part (H 6 , H 10 , H 12 ), and having identical hydrogenated segment (H 12 ) connected to a fluorinated moiety of different lengths (F 6 , F 8 , F 10 ). For the sake of comparison, an alkanethiol (H 18 SH) was also examined, and F 10 H 10 COOH and F 10 H 10 OH molecules were used for helping the assignment of SFG spectra of CH stretches. SFG was applied to investigate the hydrocarbon chain and the terminal CF 3 group, while PM-IRRAS was used to probe CF 2 groups. The number of gauche defects in the hydrocarbon chain increased with the increasing length of the molecule, either by elongation of the hydrogenated or perfluorinated part. SFG measurements recorded at three polarization combinations ( ppp , ssp , sps ) enabled us to estimate the tilt angle of the terminal CF 3 group in semifluorinated thiol molecules as ranging from 35° to 45°, which is consistent with nearly vertical fluorinated segments. Upon increasing the surface pressure, the fluorinated segment gets slightly more upright, but the hydrocarbon chain tilt increases while keeping the same average number of gauche defects. The extent of disorder in the hydrogenated segment may be controlled by varying the size of the fluorinated segment, and this could be exploited for designing functionalized surfaces with insertion of other molecules in the defect region. [ABSTRACT FROM AUTHOR]

Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air–water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air–water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces. [ABSTRACT FROM AUTHOR]

l -ascorbic acid alkyl esters (ASC n ) are molecules of pharmaceutical interest for their amphiphilic nature and proposed antioxidant power. In contrast to l -ascorbic acid, ASC n with different acyl chain lengths behaved stably upon oxidation and a tautomeric isomerization was observed. In Langmuir films, when the ascorbic ring has a negative charge, ASC 14 and ASC 16 form stable monolayers, contrary to ASC 10 and ASC 12 . ASC 16 films showed transition from liquid-expanded (LE) to liquid-condensed phase, whereas ASC 14 showed only an LE phase. When ASC n are mainly neutral, ASC 14 showed phase transition from LE to a crystalline phase, as previously reported for ASC 16 . The two-dimensional domains displayed crystal-like shapes with anisotropic optical activity when interacting with the polarized light under Brewster angle microscopy. The compounds with the longer acyl chain (ASC 16 , ASC 14 and ASC 12 ) exhibited good surface activity, forming Gibbs monolayers. They also were able to penetrate into phospholipid monolayers up to a critical point of 45–50 mN/m. The 1-palmitoyl-2-oleoylphosphatidylcholine/ASC n films showed LC and/or crystalline domains only for ASC 16 . This study provides valuable evidence regarding the stability and surface properties of this drug family, and casts light into the differential interaction of these drugs with lipid membranes, which is important for understanding its differential pharmacological activity. [ABSTRACT FROM AUTHOR]

Stability and reorganization in Langmuir films of PEO in PEO homopolymers and PPO–PEO block copolymers were investigated using film balance measurements. The apparent fractional losses of EO segments transferred into the subphase resulting from successive compression–expansion cycles have been estimated. The apparent loss is mainly Γ max , M n and time-dependent. At surface concentrations Γ ⩽ 0.32 mg/m 2 , PEO films are in equilibrium. For 0.32 ⩽ Γ ⩽ 0.7 mg/m 2 , the losses remain modest. Further compression leads to densification of the monolayer, requiring the interplay of thermodynamics and kinetic factors In the plateau regime, the loss is higher and constant for 1 ⩽ Γ max ⩽ 2 mg/m 2 upon maintaining the achieved surface area for 15 min. Similar losses were obtained for PEO homopolymers of high M n and PPO 353 –PEO 2295. It suggests that the PEO remains anchored in a metastable state at the air–water interface at surface concentration well above the onset of the plateau. Additional losses are incurred for PEO homopolymers for monolayers kept compressed in the plateau for 2 h. For the interpretation of these phenomena a combination of elements from self-consistent field theory and scaling is desirable with as a trend an increasing contribution of the latter with increasing surface concentration. [ABSTRACT FROM AUTHOR]

The antiparasitic properties of antiparasitic drugs are believed to be associated with their interactions with the protozoan membrane, encouraging research on the identification of membrane sites capable of drug binding. In this study, we investigated the interaction of mefloquine hydrochloride, known to be effective against malaria, with cell membrane models represented by Langmuir monolayers of selected lipids. It is shown that even small amounts of the drug affect the surface pressure-area isotherms as well as surface vibrational spectra of some lipid monolayers, which points to a significant interaction. The effects on the latter depend on the electrical charge of the monolayer-forming molecules, with the drug activity being particularly distinctive for negatively charged lipids. Therefore, the lipid composition of the monolayer modulates the interaction with the lipophilic drug, which may have important implications in understanding how the drug acts on specific sites of the protozoan membrane. [ABSTRACT FROM AUTHOR]

Highlights: [•] 1,4-Naphthoquinone is inserted in the subphase of lipid monolayers. [•] Drug condensed the monolayers to lower areas. [•] Effects of the drug are detected when cell cultures are spread. [•] Intermolecular interactions of the drug with monolayers are identified. [ABSTRACT FROM AUTHOR]

Highlights: [•] Li+ alters interfacial properties of layers of copolymers with PEO and/or PPO.. [•] Changes in monolayers behaviour are due to the formation of copolymer – Li+ complexes. [•] Typical Hofmeister series effects cannot explain the behaviour observed. [•] Contrary to the usual findings, added cations have a strong effect on the system. [•] Major importance of Li+ effect on elasticity of Langmuir layers as compared with adsorption layers. [ABSTRACT FROM AUTHOR]

Abstract: In contrast to classical surfactants, the knowledge about the self-organization of alkanes and their hydrophobic derivatives is still limited. In this paper, we present the results of the studies of self-assembly of long-chain dialkylthioethers at the air/water interface. The substitution of one methylene group by the thioether divalent sulfur introduces significant dipole moment to the alkane chain without affecting the hydrophobicity, which profoundly influences the self-assembly of these molecules. Depending on the location of the thioether group in the hydrophobic chain, the investigated molecules can form Langmuir monolayers, which are stabilized by the thioether-water H-bonds formation, or random multilayers. The structures of the monolayers were investigated with the application of Grazing Incidence X-ray Diffraction. To elucidate important structural differences between thioether and alkane monolalyers of the same hydrocarbon chain length, we applied the methods of quantum chemistry (ETS–NOCV calculations). It turned out that the introduction of one sulfur atom affects the distribution of electron density not only in the proximity of this atom but generally along the chain. The combination of experimental and calculation methods provides to the better understanding of the fundamental question of the self-organization of long-chain alkanes and their non-amphiphilic derivatives at interfaces. [Copyright &y& Elsevier]

Abstract: The dependence of the size of the cooperative unit (C.U.) of amphiphilic molecules on surface pressure (π) in the liquid expanded (LE)–liquid condensed (LC) phase coexistence region of Langmuir monolayers has been formulated and calculated using measured isotherm data. The C.U. size changes largely depending on the surface pressure in the coexistence region: these submicroscopic molecular aggregates are not static objects, but dynamic ones characterized by large fluctuations in size. It has been found that the C.U. size distribution can be a natural consequence of the significant change of monolayer compressibility, which reflects large molecular area density fluctuations, in the coexistence region. [Copyright &y& Elsevier]

Abstract: In this work the interaction between human serum albumin (HSA) and a monofluorinated phospholipid, 1-palmitoyl-2-[16-fluoropalmitoyl-phosphatidylcholine] (F-DPPC), was studied by using Langmuir monolayer and Brewster angle microscopy (BAM) techniques. Different amounts of F-DPPC were spread on a previously formed HSA monolayer located at the air/water interface at 25°C and the mixed monolayers thus obtained showed the existence of a liquid expanded–liquid condensed (LE–LC) phase transition (at 14mN/m), attributed to the pure F-DPPC monolayer, coexisting with a second transition (at 22–24mN/m) corresponding to the protein conformational change from an unfolded state to another in “loops” configuration. Relative thickness measurements recorded during the compression of the mixed monolayers showed the existence of an “exclusion” surface pressure (π exc), above which the protein is squeezed out the interface, but not totally. BAM images reveal that some protein molecules in a packed “loops” configuration remain at the interface at surface pressures higher than the “exclusion” surface pressure. The application of the Defay–Crisp phase rule to the phase diagram of the F-DPPC/HSA system can explain the existence of certain regions of surface pressure in which the mixed monolayer components are miscible, as well as those others that they are immiscible. [Copyright &y& Elsevier]

Abstract: Lupane type pentacyclic triterpenes (LTs) are pharmacologically active natural products isolated from different plants. They have broad spectrum of therapeutic action ranging from anticancer via anti-HIV, antibiotic to anti-inflammatory and anti-protozoal activity. Many scientific papers underline that the key stage in the LT mechanism of action is their incorporation into cellular membrane and the interaction with the structural lipids. In our research we apply Langmuir monolayers as a versatile platform for the investigation of these phenomena, since till now important aspects concerning this issue are incomprehensible. We focus our attention on the interactions of lupeol and betulinic acid with choline-headgroup structural lipids: a representative of saturated glycerophosphatidylcholines (DPPCs), and octadecyl-sphingomyelin, a representative of membrane sphingolipids. Application of complementary physicochemical techniques such as the Langmuir technique, Brewster angle microscopy, and grazing incidence X-ray diffraction supported by thermodynamic analysis enabled us to investigate the intermolecular interactions in such binary model systems. Our results corroborate that LT is miscible with the outer leaflet membrane phospholipids, both DPPC and SM in the whole range of mole ratios. Moreover, the introduction of LT into the phospholipid film, even in small proportion, leads to the loss of periodical ordering of the phospholipid molecules and the disappearance of the diffraction signal as observed by GIXD. Our results also proved that LT does not form any surface complexes of fixed stoichiometry resembling the well characterized lipid rafts. [Copyright &y& Elsevier]

Abstract: Chitosans have been widely exploited in biological applications, including drug delivery and tissue engineering, especially owing to their mucoadhesive properties, but the molecular-level mechanisms for the chitosan action are not known in detail. It is believed that chitosan could affect the mucus by interacting with the proteins mucins, in a process mediated by the cell membrane. In this study we used Langmuir monolayers of dimyristoylphosphatidic acid (DMPA) as simplified membrane models to investigate the interplay between the activity of mucins and chitosan. Surface pressure and surface potential measurements were performed with DMPA monolayers onto which chitosan and/or mucin was adsorbed. We found that the expanding effect from mucin was considerably reduced when chitosan was injected after mucin had been adsorbed on the DMPA monolayer. The results were consistent with the formation of complexes between mucin and chitosan, thus highlighting the importance of electrostatic interactions. Furthermore, chitosan could remove mucin that was co-deposited along with DMPA in Langmuir–Blodgett (LB) films, which could be ascribed to molecular-level interactions between chitosan and mucin inferred from the FTIR spectra of the LB films. In conclusion, the results with Langmuir and LB films suggest that electrostatic interactions are crucial for the mucoadhesive mechanism, which is affected by the complexation between chitosan and mucin. [Copyright &y& Elsevier]

Abstract: A recently described non-viral gene delivery system [dioctadecyldimethylammonium bromide (DODAB)/monoolein (MO)] has been studied in detail to improve knowledge on the interactions between lamellar (DODAB) and non-lamellar-forming (MO) lipids, as a means to enhance their final cell transfection efficiency. Indeed, the morphology, fluidity, and size of these cationic surfactant/neutral lipid mixtures play an important role in the ability of these systems to complex nucleic acids. The different techniques used in this work, namely dynamic light scattering (DLS), fluorescence spectroscopy, differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), light microscopy (LM), and surface pressure–area isotherms, allowed fully characterization of the phase behavior and aggregate morphology of DODAB/MO mixtures at different molar ratios. Overall, the results indicate that the final morphology of DODAB/MO aggregates depends on the balance between the tendency of DODAB to form zero-curvature bilayer structures and the propensity of MO to form non-bilayer structures with negative curvature. These results also show that in the MO-rich region, an increase in temperature has a similar effect on aggregate morphology as an increase in MO concentration. [Copyright &y& Elsevier]

Abstract: The interaction of monogalactosyldiacylglycerol (MGDG) with cytochrome b6f complex (cyt b6f), a major component of the photosynthetic apparatus, was studied in Langmuir monolayers during compression/expansion cycling and at constant surface pressure mode. The surface pressure/area isotherms of the mixed films were analyzed in terms of surface compressional modulus and two-dimensional virial equation of state. The morphology and the surface potential of the monolayers were monitored by Brewster angle microscopy and vibrating plate sensor respectively. Our results suggested that there is a specific interaction between MGDG and cyt b6f which resulted in depletion of lipid molecules from the interface. The current work sheds light on the still unclear question how b6f complex gets in touch with the major compound of the thylakoid membranes, the non-charged lipid MGDG. The interaction occured even at very low sub-nanomolar concentration of the complex. This effect most probably could be attributed to hydrogen bonding between the galactose headgroup of the lipid and the protein moiety of cyt b6f. [Copyright &y& Elsevier]

Abstract: Mesostructured silica films have attracted interest as potential platforms for sensing, molecular sieving, catalysis, and others. The fabrication of free-standing silica films on water, however, is challenging due to the need for scaffolding agents that would constitute effective templates. We describe the assembly of thin film at the air/water interface comprising quaternary silicates and polydiacetylene (PDA), a unique chromatic polymer forming two-dimensional conjugated networks, and the use of these films for biological sensing. PDA exhibits a dual role in the system—both as the amphiphilic matrix facilitating immobilization of the silicate colloidal units at the air/water interface and additionally a chromatic reporter that undergoes visible blue–red transitions, accompanied by fluorescence transformations, in the presence of analytes. We demonstrate the application of the silicate/PDA thin films for the detection of bacterial proliferation. [Copyright &y& Elsevier]

Abstract: To be suitable for reducing water evaporation, monolayers need to be easy to apply and also spread quickly across the surface of water. However, the choice of monolayer often involves a compromise between spreading rate and evaporation resistance. Because emulsions of the monolayer material have been suggested as a way to improve spreading, emulsions were made with the long-chain alcohols hexadecanol, octadecanol and eicosanol using the non-ionic surfactants Brij 78 and Tween 60 as emulsifying agents. The emulsions of octadecanol and eicosanol spread faster than the corresponding powder. However there was no improvement in the spreading of hexadecanol emulsion due to a significant amount of the material dispersing into the bulk water instead of spreading at the interface. The choice of emulsifier to stabilise the emulsions is critical for effective evaporation resistance. Whereas the octadecanol emulsion made with Brij 78 showed improved evaporation resistance, the emulsion with Tween 60 had an appreciably lower evaporation resistance than powdered octadecanol. One limitation of the emulsion application method is the poor spreading on surfaces with an already high surface pressure. [Copyright &y& Elsevier]

Abstract: The effect of temperature on the surface phase behavior of tetradecanoyl N-ethanolamide (NHEA-14) in Langmuir monolayers at the air–water interface has been investigated by film balance and Brewster angle microscopy (BAM). It has been observed that dendritic domains are formed in the coexistence region between liquid-expanded (LE) and liquid-condensed (LC) phases at different temperatures. At 10 and 15°C, the domains are four-armed dendrites having wide arms which have a tendency to be fractal while growing in size. At 20°C, five-armed dendritic domains are formed. At a temperature higher than 20°C, the domains are mainly six-armed dendrites having very narrow and sharp arms. The formation of dendritic domains should be due to the presence of interfacial hydrogen bonding among the head groups of the amphiphile. Increased dehydration of the head groups with an increase in the temperature should be responsible for the temperature dependency of the dendritic domain shapes in the monolayers of NHEA-14. [ABSTRACT FROM AUTHOR]

Abstract: We have carried out the analysis of liquid crystalline Langmuir monolayers at the air–water interface composed of the amphiphilic azobenzene derivative 8Az5COOH. By varying the temperature and the isomeric (trans–cis) composition, the monolayer behaviour has been studied in comparison with a shorter homologue, 8Az3COOH, by measuring the surface pressure–area isotherms along with Brewster angle microscopy (BAM). Our data with the pure trans isomer enable a posterior thermodynamic analysis, which was not feasible with the shorter homologue. For the mixed trans–cis monolayers, BAM observations reveal a phase segregation with trans enriched domains surrounded by a cis enriched matrix. Line tension between the two phases is lower than in the shorter homologue. The organisation of the rodlike molecules inside the trans domains results in highly symmetric textures that make the quantitative analysis of the BAM images possible, and a better understanding of the microscopic structure of the monolayer can be achieved. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between a hydrophobically modified 5,10,15,20-tetrakis(4-N-tetradecyl-pyridyl) porphyrin and three phospholipids: two negatively charged, DMPA (the sodium salt of dimyristoyl-sn-glycero-phosphatidyl acid) and DMPG (the sodium salt of 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]) and a zwitterionic DMPC (dimyristoyl-sn-glycero-phosphatidylcholine), were studied by means of surface pressure isotherms and spectroscopic methods. The interaction results in partial or total metallation of the porphyrin with zinc ions in the presence of negatively charged phospholipids, as attested by UV–vis and luminescence spectroscopy of the transferred films. In the presence of the zwitterionic phospholipid no insertion of zinc ion in the porphyrin ring is detected. These results are relevant for the understanding of photosensitizer-lipid-carrier binding for use in photodynamic therapy. [ABSTRACT FROM AUTHOR]

Abstract: Oligonucleotides have unique molecular recognition properties, being involved in biological mechanisms such as cell-surface receptor recognition or gene silencing. For their use in human therapy for drug or gene delivery, the cell membrane remains a barrier, but this can be obviated by grafting a hydrophobic tail to the oligonucleotide. Here we demonstrate that two oligonucleotides, one consisting of 12 guanosine units (G12), and the other one consisting of five adenosine and seven guanosine (A5G7) units, when functionalized with poly(butadiene), namely PB–G12 and PB–A5G7, can be inserted into Langmuir monolayers of dipalmitoyl phosphatidyl choline (DPPC), which served as a cell membrane model. PB–G12 and PB–A5G7 were found to affect the DPPC monolayer even at high surface pressures. The effects from PB–G12 were consistently stronger, particularly in reducing the elasticity of the DPPC monolayers, which may have important biological implications. Multilayers of DPPC and nucleotide-based copolymers could be adsorbed onto solid supports, in the form of Y-type LB films, in which the molecular-level interaction led to lower energies in the vibrational spectra of the nucleotide-based copolymers. This successful deposition of solid films opens the way for devices to be produced which exploit the molecular recognition properties of the nucleotides. [Copyright &y& Elsevier]

Abstract: A series of semifluorinated thiols of the general formula CF3(CF2) m −1(CH2) n SH (abbreviated to FmHnSH) have been synthesized and the Langmuir monolayers thoroughly characterized using surface pressure (π) and electric surface potential (ΔV) measurements. These data have been complemented with Brewster angle microscopy (BAM) visualization of the monolayers structure and IR spectroscopy (PM-IRRAS) analysis of the alkyl chain conformation. The investigated thiols (namely F4H10SH, F8H6SH, F6H10SH, F10H6SH, F6H11SH, F8H10SH and F10H10SH) differ in the length of the hydrophobic chain as well as in the degree of fluorination. Although the –SH group cannot form strong hydrogen bonds with the water subphase, thereby causing only weak anchoring, it has been found that all the investigated thiols, except for F4H10SH, are capable of stable Langmuir monolayer formation. The investigated thiols can be divided into two categories – thiols with longer alkyl chain (F10H10SH, F10H6SH, F8H10SH) and compounds with shorter hydrophobic part (F6H10SH, F6H11SH, F8H6SH). The monolayers of the latter thiols have their equilibrium surface pressure (ESP) comparable with the collapse pressure (π C) of their monolayers; thus these films are stable within the whole range of compression. On the contrary, thiols with longer perfluorinated fragments have considerably lower ESP than the π C of their monolayers; therefore, both stable and metastable regions can be distinguished in their π–A isotherms. Interestingly, for F8H6SH, a smectic ordering of molecules can be observed in monolayers as visualized with BAM. By comparing film-forming properties of the studied semifluorinated thiols with previously studied semifluorinated alkanes it has been found that the presence of –SH group facilitates spreading at the free water surface. Semifluorinated thiols have been found to maintain their monomolecular ordering in the presence of heavy metal cations in the aqueous subphase, contrary to their hydrogenated analogues, which have been reported to crystallize under the same conditions. [Copyright &y& Elsevier]

Abstract: A series of homologous alkyl thiols C n H2n+1SH (n =14–18, 20, 22) have been synthesized and Langmuir monolayers have been thoroughly characterized using surface pressure, electric surface potential measurements and Brewster angle microscopy. Although the –SH group cannot form strong hydrogen bonding with the water subphase, thereby causing weak anchoring, it has been found that alkyl thiols having more than 15 carbon atoms are capable of Langmuir monolayer formation at room temperature. The stability of the investigated films is not very high, however, but quite sufficient for LB transfer at low surface pressures. The increase in aliphatic chain length does not lead to any considerable improvement of the monolayer stability. The influence of subphase temperature and the presence of various cations in the aqueous subphase have also been studied. Contrary to literature, it has been found that the presence of alkaline earth metals cations does not improve the monolayer stability, and although the collapse pressure is higher, the equilibrium surface pressure remains the same as on pure water. [Copyright &y& Elsevier]

Abstract: Intermolecular interactions lie at the root of many fundamental processes in nature. For example, they define membrane formation and crystallisation processes. Here, using Langmuir monolayers, we have investigated the role of intermolecular interactions in defining non-equilibrium monolayer structure and response, specific to a nucleating subphase chemistry. In particular, the interactions in mixed alcohol/carboxylic acid systems have been explored on four different subphases: ultrapure water, calcium chloride, sodium bicarbonate and a calcium carbonate crystallising subphase. Area per molecule, surface pressure and surface potential were analysed as a function of mol% ratio of acid to alcohol on each of the subphases. Comparison of the data across the subphases showed that three main interactions dictate the behaviour of the monolayer: (1) formation of a hydrogen-bonding network (predominantly dominating intramonolayer structure), (2) electrostatic interactions between the charged monolayer and strongly binding counterions and (3) the formation of a hydrogen-bonded soap network induced by the presence of bicarbonate coions. The latter provides a potential mechanism for defining directionality of interfacial interactions, and therefore face-selective nucleation. [Copyright &y& Elsevier]

Abstract: Two semifluorinated alkanes (SFAs), differing in their fluorinated segment lengths (F6H18 and F10H19), were compared with typical surfactants (F8H10OH and C18OH) as regards their collapse mechanism. It has been found that analysis of the isotherms under different experimental conditions is insufficient for a reliable description of the collapse phenomenon, and the importance of the relaxation experiments complemented with Brewster angle microscopy observation has been emphasized in this respect. The applied nucleation–growth–collision model points out differences between typical (alcohols) and nontypical (SFAs) surfactants as regards the collapse mechanism. Our results indicate that for the collapse process the presence of the polar head group in the molecule is more important than the structure of the hydrophobic chain. [Copyright &y& Elsevier]

Abstract: A glycosylphosphatidylinositol (GPI)-anchored enzyme (rat osseous plate alkaline phosphatase—OAP) was studied as monolayer (pure and mixed with lipids) at the air–water interface. Surface pressure and surface potential–area isotherms showed that the enzyme forms a stable monolayer and exhibits a liquid-expanded state even at surface pressure as high as 30 mN m−1. Isotherms for mixed dimyristoylphosphatidic acid (DMPA)–OAP monolayer showed the absence of a liquid-expanded/liquid-condensed phase transition as observed for pure DMPA monolayer. In both cases, pure or mixed monolayer, the enzyme preserves its native conformation under compression at the air–water interface as observed from in situ p-polarized light Fourier transform-infrared reflection–absorption spectroscopic (FT-IRRAS) measurements. Changes in orientation and conformation of the enzyme due to the presence or absence of DMPA, as well as due to the surface compression, are discussed. [Copyright &y& Elsevier]

Abstract: Thermodynamic and morphological properties of Langmuir monolayers of di-n-dodecyl hydrogen phosphate (DDP) have been studied by film balance and Brewster angle microscopy (BAM) over a wide range of temperature between 5 and 40 °C. From isotherms, a generalized phase diagram consisting of gas (G), liquid expanded (LE) and liquid condensed (LC) phases is constructed for the DDP monolayers. The BAM images show the formation of gas bubble in the bright background of LE phase during G–LE phase transitions and fingering LC domains during LE–LC phase transitions. The shapes of these domains are independent of temperature, showing a sharp contrast to the temperature-dependent monolayer morphologies of amphiphilic systems where the shape of the LC domains changes either from compact circular to fingering or from irregular or spiral to compact patterns with increasing temperature. In addition, the domains do not show any change in their shapes with decreasing the compression rate. Since the two-alkyl chains are directly attached by covalent bonds to the phosphate group, the rearrangement of the molecules needs to move the whole molecules including the hydration sphere. The difficulty related to such a movement of the molecules causes the fingering domains, which are independent of external variables. Although the domains are formed in a fingering shape, the equilibrium shape can be attained by about 120 min at 15 °C indicating a rather slow relaxation rate. [Copyright &y& Elsevier]

Abstract: Mixed monolayers of gramicidin A (GA) and three alcohols, differing in the degree of fluorination, namely C18OH, F18OH, and F8H10OH have been investigated by means of: surface manometry ( isotherms) and Brewster angle microscopy (BAM) aiming at finding appropriate molecules for incorporating gramicidin A for a biosensor design. Our results proved that only the semifluorinated alcohol is appropriate material for this purpose since it forms miscible and homogeneous monolayers with GA within the whole concentration range. The experimental results have been supported by the calculations of van der Waals energy profiles using the Insight II program. Both the hydrogenated and perfluorinated alcohols were found to aggregate at higher surface pressures, which exclude their application for gramicidin-based biosensor construction. [Copyright &y& Elsevier]

Abstract: The surface phase behavior of di-n-dodecyl hydrogen phosphate (DDP) in Langmuir monolayer and its interactions with l-arginine (l-arg) have been investigated by measuring isotherms with a film balance and observing monolayer morphology with a Brewster angle microscopy (BAM). The DDP monolayers on pure water show a first-order liquid expanded–liquid condensed (LE–LC) phase transition and form fingering LC domains having uniform brightness at different temperatures. At 15 °C, the isotherms on pure water and on different concentration solutions of l-arg show a limiting molecular area at . With increasing the subphase concentration of l-arg up to , the LE and the LE–LC coexistence regions shift to larger molecular areas and higher surface pressures, respectively. With a further increase in the concentration of l-arg beyond this critical concentration, these isotherms show little or no more expansion. These results have been explained by considering the fact that the l-arg undergoes complexation with the DDP to form l-arg–DDP that remains in equilibrium with the components at the air–water interface. As the concentration of l-arg in the subphase increases, the equilibrium shifts towards the complex. At a concentration of , the DDP monolayers get saturated and show the characteristics of the new amphiphile, l-arg–DDP. BAM is applied to confirm the above results. When the concentration of the l-arg is , domains always start forming at an area of , which is the critical molecular area for the phase transition in the DDP monolayers on pure water. In contrast, when the monolayers are formed on a solution containing l-arg, comparatively smaller size domains are formed after the appearance of a new cusp point at . With an increase in the concentration of l-arg in the subphase, the size of the domains decreases indicating that the fraction of the DDP gradually decreases, whereas the fraction of the complex gradually increases. In addition, a very simple procedure for determination of the stability constant, which is at 15 °C, has been suggested. [Copyright &y& Elsevier]

Abstract: Surface phase behavior of di-n-tetradecyl hydrogen phosphate, DTP, has been studied by measuring isotherms with a film balance and observing monolayer morphology with a Brewster angle microscopy (BAM) at different temperatures. A generalized phase diagram, which shows a triple point for gas (G), liquid-expanded (LE) and liquid-condensed (LC) phases at about 32 °C, is constructed for the amphiphile. Below the triple point, a first-order G–LC phase transition has been shown to occur, whereas a first-order G–LE phase transition followed by another first-order LE–LC transition has been found to take place at a temperature above the triple point. The amphiphile shows the fingering LC domains with uniform brightness indicating the presence of untilted molecules. The domain shapes are independent of the change in temperature and compression rate. The existence of similar fingering domains over a wide range of temperature is rather uncommon in the monolayer systems and is considered to be due to the restricted movement of the molecules incorporating into the LC phase. Because the two-alkyl chains are directly attached to two covalent bonds of the phosphate head group, the rearrangement of the molecules, which is an essential condition for the circular domain formation, needs the movement of the whole molecules including the hydration sphere. The difficulty related to such a movement of the molecules causes fingering domains, which are independent of external variables. [Copyright &y& Elsevier]

Abstract: A series of semifluorinated alcohols differing in the proportion of the perfluorinated to hydrogenated chains length was synthesized and investigated in Langmuir monolayers using surface pressure and surface potential measurements. All the investigated semifluorinated alcohols were found to be capable of stable floating monolayer formation. The stability of monolayers was found to be higher upon increasing the length of the perfluorinated segment. A lower stability of the monolayers from alcohols having shorter perfluorinated fragment was attributed to the aggregation process, which was visualized with Brewster angle microscopy (BAM). Most condensed monolayers were formed by compounds with longer perfluorinated moiety, whereas monolayers composed by molecules with an iso-branched perfluorinated segment were found to be more expanded. The change of electric surface potential was negative along the whole compression. The maximum absolute values of ΔV varies, depending on the number of CF2 groups, from ca. for F6H10OH to ca. for F10H10OH. The dipole moments of free molecules were calculated with Hyperchem, and the obtained values were approximately the same (within the experimental error), i.e., 2.8D for all the investigated molecules, independently on the perfluorinated fragment length. The dipole moment vector was found to be virtually aligned to the main molecular axis for the studied compounds. Therefore, the observed differences in the measured values of ΔV can result from a different dielectric permittivity of a particular monolayer. [Copyright &y& Elsevier]

Abstract: A series of semifluorinated n-alkanes (SFAs), of the general formula: (CF3)2–CF–(CF2)6–(CH2)HnH (in short iF9Hn), n=11-20, have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were performed in addition to Brewster angle microscopy results, which enabled both direct visualization of the monolayers structure and estimation of the monolayer thickness at different stages of compression. Our paper was aimed at investigating the influence of the iso-branching of the perfluorinated fragment of the SFA molecule on the surface behavior of these molecules at the air/water interface. It occurred that iF9 SFAs with the number of carbon atoms in the hydrogenated moiety from 11 to 20 are capable of Langmuir monolayer formation. Monolayers from iF9H11 to iF9H13 are instable, whereas those formed by iF9 SFAs with longer hydrogenated chains form stable films at the free surface of water. As compared to SFAs containing perfluorinated chain in a normal arrangement, iso-branched molecules have a greater tendency to aggregate. Lower stability of monolayers formed by iF9 SFAs as compared to F10 SFAs originated from the surface nucleation observed in BAM images, even at the very initial stages of compression. The dipole moment vector for iso-branched SFAs was found to be virtually aligned with the main axis of the molecule, contrary to F10 SFAs, where the dipole moment vector was calculated to be tilted with respect to the main molecular axis. Quantitative Brewster angle microscopy measurements (relative reflectivity experiments) enabled us to monitor the changes of monolayer thickness at different stages of monolayer compression. [Copyright &y& Elsevier]

Abstract: We study the surface phase behavior in Langmuir monolayers of 1-O-hexadecyl-rac-glycerol (C16G) by film balance and Brewster angle microscopy over a wide range of temperatures. A cusp point followed by a pronounced plateau region in the pressure–area (π–A) isotherm indicates a first-order phase transition between a lower density liquid expanded (LE) phase and a higher density liquid condensed (LC) phase at the air–water interface. A wide variety of condensed domains are found to form just after the appearance of the cusp point. The observed surface morphology was compared with that of ethylene glycol mono-n-hexadecyl ether (C16E1) that bears an ethylene oxide (EO) unit in the head-group. As usually observed, the domains of C16E1 are found to be circular at lower temperatures and fractal at higher temperatures. Contrary to this usual behavior, the domains of C16G are found to be strip-like structures at lower temperatures, which attain increasingly compact shape as the temperature increases and finally attain faceted structures at . It is concluded that a higher degree of dehydration around the head-group region of C16G appreciably reduces the hydration-induced repulsive interactions between the head-groups and imparts to the molecules an increase in hydrophobicity, thereby a closer molecular packing. As a result, the molecules form increasingly compact domains as the temperature increases. Since the head-group of C16E1 is much smaller than that of C16G, dehydration effect cannot appreciably increase its hydrophobic character. Rather, increases in subphase temperature result in a decrease in the line tension of the interface giving fractal structures at higher temperatures. In addition, the changes in enthalpy and entropy values were also calculated to understand the thermodynamic nature of condensation of the molecules in the LE–LC transition region. [Copyright &y& Elsevier]

Abstract: We study the surface phase behavior in Langmuir monolayers of a series of nonionic surfactants of the general formula CnE1 with , 16, and 18 by film balance and Brewster angle microscopy (BAM) over a wide range of temperatures. A cusp point followed by a pronounced plateau region in the pressure–area () isotherms indicates a first-order phase transition in the coexisting state between a lower density liquid expanded (LE) phase and a higher density liquid condensed (LC) phase at the air–water interface. The formation of bright two-dimensional (2D) LC domains in a dark background visualized by BAM further confirms this observation. In addition to the cusp point at the onset of the LE–LC coexistence state, another cusp point followed by a small plateau is observed for the C14E1 and C18E1 monolayers, indicating a second phase transition between two condensed phases of different compressibility and tilt orientation of the molecules. This unusual two-step phase transition is explained by the Ostwald step rule. The C16E1 and C18E1 monolayers show a kink in their respective isotherms, after which the surface pressure increases steeply with only a little decrease in the molecular area, suggesting that the molecules undergo a transition from a tilted to an almost vertical orientation with respect to the water surface. The thermodynamic parameters for the condensation of the molecules in the LE–LC coexistence state were calculated by employing the 2D Clapeyron equation. The temperature coefficient of the critical surface pressure values shows a decreasing trend from C14E1 to C18E1, suggesting that the condensation process becomes less and less prone to thermal perturbation as the chain length increases. For all the amphiphiles, the ΔH values are found to be negative, suggesting an exothermic nature of condensation. The negative ΔS values obtained from the relation probably come from the restriction on the rotational and translational motion of the molecules constrained in a confined area in the LE–LC transition region. [Copyright &y& Elsevier]

Abstract: N-(1-Piperidinepropionyl)amphotericin B methyl ester (in short, PAME), a low-toxicity amphotericin B derivative, has been investigated in Langmuir monolayers at the air/water interface alone and in mixtures with cellular membrane sterols (a mammalian sterol, cholesterol, and a fungal sterol, ergosterol) and a model phospholipid (DPPC). The analysis of the strength of interaction between PAME and both sterols as well as DPPC was based, on surface pressure measurements and analysis of the isothermal compressibility (), the mean area per molecule (), the excess free energy of mixing () and the total free energy of mixing (). It has been found that the interactions between PAME and sterols are attractive; however, their strength is significantly weaker for mixtures of PAME with cholesterol than with ergosterol. This casts light on the improved selectivity of PAME toward fungal cells. The strongest interactions, found for PAME/DPPC mixtures, proved an important role of DPPC in the mechanism of reduced toxicity of PAME as compared to amphotericin B. Due to stable complex formation between PAME and DPPC the antibiotic is immobilized with DPPC molecules, which reduces the concentration of free antibiotic, which is capable of interacting with membrane sterols. [Copyright &y& Elsevier]