Search

Phospholipids are the most important structural elements of the bacterial cell wall, participate in the adaptation of microorganisms to the environment and can act as biomarkers for environmental changes and one of the components of environmental monitoring. Native phospholipids are used to form models of cell membranes, the biophysical properties of which can be studied by the Langmuir-Blodgett method. The aim of this work was to isolate and characterize the phospholipids of the cell membranes of the bacteria Staphylococcus aureus and Bacillus cereus and the formation of Langmuir monolayers based on them. The composition and ratio of fatty acids were determined by gas-liquid chromatography of fatty acid methyl esters. Fatty acids, found in the extract of the bacteria S. aureus 209-P and B. cereus 8035, are: hexadecanoic, trans-9-octadecenoic, octadecanoic, tetradecanoic, 13-methyltetradecanoic, 14-methylpentadecanoic, 15-methylhexadecanoic, cis-9-octadecanoic. To form a monolayer, a working solution of native phospholipids in chloroform with a concentration of C = 10-3 М was used. The monolayer formed when a 50 μl solution of a phospholipid mixture is applied to the surface has a more perfect structure, which is manifested in the constancy of its mechanical properties. The analysis of the obtained data has not yet revealed a clear dependence of the monolayer parameters on temperature. The changes in the compression modulus and compressibility were very minor. With an increase in the salt concentration, both an increase and a decrease in the compression modulus, and, consequently, the rigidity of the monolayer, is observed.

Surface pressure (π)–molecular area (A) isotherms were gathered to characterize the packing of binary mixed Langmuir monolayers of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphoethanolamine (DOPE) and one of two Gemini surfactants (GS), N,N‐bis(dimethyloctadecyl)‐1,7‐nonanediammonium dibromide (18‐7‐18) or 1,9‐bis(octadecyl)‐1,1,9,9‐tetramethyl‐5‐amino‐1,9‐nonanediammonium dibromide (18‐7NH‐18) of varying molar fractions. Information about miscibility behavior was derived from the π–A curves by examining the excess free energy of mixing (ΔGexc) that was calculated through the surface area additivity rule. Surface compressibility modulus (Cs−1) was also used to characterize intermolecular interactions. Mutual interactions between GS and DOPE were analyzed in terms of excess Gibbs energy of mixing and the value of this parameter depended strongly on the composition of the mixed film. GS and DOPE are generally miscible as DOPE reduces intermolecular repulsion between highly charged GS molecules leading to the formation of more densely packed mixed monolayers. However, GS and DOPE are immiscible in equimolar mixtures due to tail group packing mismatch between saturated and unsaturated alkyl chains. The prevalence of attractive synergistic interactions in the monolayers studied differs from a previous finding of antagonistic mixing behavior in GS/DOPE micelles. These results contribute to the understanding of GS‐lipid interactions and packing that are critical to the in vitro and in vivo stability of liposomes composed of these molecules used for non‐viral gene therapy applications. [ABSTRACT FROM AUTHOR]

LL-37 is the only member of the cathelicidin-type host defense peptide family in humans. It exhibits broad-spectrum bactericidal activity, which represents a distinctive advantage for future therapeutic targets. The presence of choline in the growth medium for bacteria changes the composition and physicochemical properties of their membranes, which affects LL-37's activity as an antimicrobial agent. In this study, the effect of the LL-37 peptide on the phospholipid monolayers at the liquid–air interface imitating the membranes of Legionella gormanii bacteria was determined. The Langmuir monolayer technique was employed to prepare model membranes composed of individual classes of phospholipids—phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL)—isolated from L. gormanii bacteria supplemented or non-supplemented with exogenous choline. Compression isotherms were obtained for the monolayers with or without the addition of the peptide to the subphase. Then, penetration tests were carried out for the phospholipid monolayers compressed to a surface pressure of 30 mN/m, followed by the insertion of the peptide into the subphase. Changes in the mean molecular area were observed over time. Our findings demonstrate the diversified effect of LL-37 on the phospholipid monolayers, depending on the bacteria growth conditions. The substantial changes in membrane properties due to its interactions with LL-37 enable us to propose a feasible mechanism of peptide action at a molecular level. This can be associated with the stable incorporation of the peptide inside the monolayer or with the disruption of the membrane leading to the removal (desorption) of molecules into the subphase. Understanding the role of antimicrobial peptides is crucial for the design and development of new strategies and routes for combating resistance to conventional antibiotics. [ABSTRACT FROM AUTHOR]

The antimicrobial and antibiofilm properties of arginine-based surfactants have been evaluated. These two biological properties depend on both the alkyl chain length and the spacer chain nature. These gemini surfactants exhibit good activity against a wide range of bacteria, including some problematic resistant microorganisms such us methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. Moreover, surfactants with a C10 alkyl chain and C3 spacer inhibit the (MRSA) and Pseudomonas aeruginosa biofilm formation at concentrations as low as 8 µg/mL and are able to eradicate established biofilms of these two bacteria at 32 µg/mL. The inhibitory activities of the surfactants over key enzymes enrolled in the skin repairing processes (collagenase, elastase and hyaluronidase) were evaluated. They exhibited moderate anti-collagenase activity while the activity of hyaluronidase was boosted by the presence of these surfactants. These biological properties render these gemini arginine-based surfactants as perfect promising candidates for pharmaceutical and biological properties. [ABSTRACT FROM AUTHOR]

LL-37 is the only member of the cathelicidin-type host defense peptide family in humans. It exhibits broad-spectrum bactericidal activity, which represents a distinctive advantage for future therapeutic targets. The presence of choline in the growth medium for bacteria changes the composition and physicochemical properties of their membranes, which affects LL-37’s activity as an antimicrobial agent. In this study, the effect of the LL-37 peptide on the phospholipid monolayers at the liquid–air interface imitating the membranes of Legionella gormanii bacteria was determined. The Langmuir monolayer technique was employed to prepare model membranes composed of individual classes of phospholipids—phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL)—isolated from L. gormanii bacteria supplemented or non-supplemented with exogenous choline. Compression isotherms were obtained for the monolayers with or without the addition of the peptide to the subphase. Then, penetration tests were carried out for the phospholipid monolayers compressed to a surface pressure of 30 mN/m, followed by the insertion of the peptide into the subphase. Changes in the mean molecular area were observed over time. Our findings demonstrate the diversified effect of LL-37 on the phospholipid monolayers, depending on the bacteria growth conditions. The substantial changes in membrane properties due to its interactions with LL-37 enable us to propose a feasible mechanism of peptide action at a molecular level. This can be associated with the stable incorporation of the peptide inside the monolayer or with the disruption of the membrane leading to the removal (desorption) of molecules into the subphase. Understanding the role of antimicrobial peptides is crucial for the design and development of new strategies and routes for combating resistance to conventional antibiotics.

Understanding the mechanical behavior of biological membranes is of paramount importance in cell biophysics and in developing new biomaterials for medicine. In this study, we delve into the mechanical impact of β-escin, commonly referred to as escin, a naturally occurring biosurfactant derived from the seeds of the horse chestnut tree. To examine the modulable interaction between escin and dimyristoylphosphatidylcholine (DMPC), which is an archetypical fluid phospholipid and an essential constituent of the cellular fluid membrane, we have used artificial models based on the liquid crystal structure, such as bilayer vesicles and Langmuir monolayers. We have focused on the energetic and kinetic aspects of escin insertion when transversally adsorbed or longitudinally integrated within these model membranes. By employing surface microscopies of epifluorescence and Brewster angle reflectivity, we have elucidated the structural phase behavior of hybrid escin–phospholipid membranes, which exhibit dual mechanical properties characterized by high rigidity and reduced fluidity. Notably, at low temperatures, we observe a soft, glassy rheological behavior reminiscent of liquid crystalline ordered phases, which turns into a fluid-like viscoelasticity resembling more disordered phases at physiological temperatures. The hybrid membranes behave in one way or another as both are driven by an adsorption potential well imposed by escin cohesivity. These intriguing findings are discussed from a physicochemical perspective, highlighting their potential for future pharmacological designs and biomedical applications that exploit the dual mechanical impact of escin on biological membranes.

Among biodegradable polymers, polylactides (PLAs) have attracted considerable interest because the monomer can be produced from renewable resources. Since their initial degradability strongly affects commercial application fields, it is necessary to manage the degradation properties of PLAs to make them more commercially attractive. To control their degradability, poly(lactide-co-glycolide) (PLGA) copolymers of glycolide and isomer lactides (LAs) were synthesized, and their enzymatic and alkaline degradation rates of PLGA monolayers as functions of glycolide acid (GA) composition were systematically investigated by the Langmuir technique. The results showed that the alkaline and enzymatic degradations of PLGA monolayers were faster than those of l-polylactide (l-PLA), even though proteinase K is selectively effective in the l-lactide (l-LA) unit. Alkaline hydrolysis was strongly affected by their hydrophilicity, while the surface pressure of monolayers for enzymatic degradations was a major factor. [ABSTRACT FROM AUTHOR]

[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]

In this work, a sensitive coating based on Langmuir–Blodgett (LB) films containing monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) with an immobilized glucose oxidase (GOx) enzyme was created. The immobilization of the enzyme in the LB film occurred during the formation of the monolayer. The effect of the immobilization of GOx enzyme molecules on the surface properties of a Langmuir DPPE monolayer was investigated. The sensory properties of the resulting LB DPPE film with an immobilized GOx enzyme in a glucose solution of various concentrations were studied. It has shown that the immobilization of GOx enzyme molecules into the LB DPPE film leads to a rising LB film conductivity with an increasing glucose concentration. Such an effect made it possible to conclude that acoustic methods can be used to determine the concentration of glucose molecules in an aqueous solution. It was found that for an aqueous glucose solution in the concentration range from 0 to 0.8 mg/mL the phase response of the acoustic mode at a frequency of 42.7 MHz has a linear form, and its maximum change is 55°. The maximum change in the insertion loss for this mode was 18 dB for a glucose concentration in the working solution of 0.4 mg/mL. The range of glucose concentrations measured using this method, from 0 to 0.9 mg/mL, corresponds to the corresponding range in the blood. The possibility of changing the conductivity range of a glucose solution depending on the concentration of the GOx enzyme in the LB film will make it possible to develop glucose sensors for higher concentrations. Such technological sensors would be in demand in the food and pharmaceutical industries. The developed technology can become the basis for creating a new generation of acoustoelectronic biosensors in the case of using other enzymatic reactions. [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]

The antimicrobial and antibiofilm properties of arginine-based surfactants have been evaluated. These two biological properties depend on both the alkyl chain length and the spacer chain nature. These gemini surfactants exhibit good activity against a wide range of bacteria, including some problematic resistant microorganisms such us methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. Moreover, surfactants with a C10 alkyl chain and C3 spacer inhibit the (MRSA) and Pseudomonas aeruginosa biofilm formation at concentrations as low as 8 µg/mL and are able to eradicate established biofilms of these two bacteria at 32 µg/mL. The inhibitory activities of the surfactants over key enzymes enrolled in the skin repairing processes (collagenase, elastase and hyaluronidase) were evaluated. They exhibited moderate anti-collagenase activity while the activity of hyaluronidase was boosted by the presence of these surfactants. These biological properties render these gemini arginine-based surfactants as perfect promising candidates for pharmaceutical and biological properties.

The interactions of DNA with lysozyme in the surface layer were studied by performing infrared reflection–absorption spectroscopy (IRRAS), ellipsometry, surface tensiometry, surface dilational rheology, and atomic force microscopy (AFM). A concentrated DNA solution was injected into an aqueous subphase underneath a spread lysozyme layer. While the optical properties of the surface layer changed fast after DNA injection, the dynamic dilational surface elasticity almost did not change, thereby indicating no continuous network formation of DNA/lysozyme complexes, unlike the case of DNA interactions with a monolayer of a cationic synthetic polyelectrolyte. A relatively fast increase in optical signals after a DNA injection under a lysozyme layer indicates that DNA penetration is controlled by diffusion. At low surface pressures, the AFM images show the formation of long strands in the surface layer. Increased surface compression does not lead to the formation of a network of DNA/lysozyme aggregates as in the case of a mixed layer of DNA and synthetic polyelectrolytes, but to the appearance of some folds and ridges in the layer. The formation of more disordered aggregates is presumably a consequence of weaker interactions of lysozyme with duplex DNA and the stabilization, at the same time, of loops of unpaired nucleotides at high local lysozyme concentrations in the surface layer. [ABSTRACT FROM AUTHOR]

In this review, we present one of the main areas of the work of the Laboratory of Physical Chemistry of Supramolecular Systems, Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, devoted to studying monolayers and ultrathin films on liquid and solid surfaces. Numerous problems are discussed concerning the peculiarities of the supramolecular organization, behavior, and functional potential of these traditional colloidal systems. The article describes diverse examples of systems that form ultrathin organized films at different interfaces and the processes occurring in them, thereby reflecting the contemporary stage of the interconnection of related fields of science (colloid and supramolecular chemistry, nanotechnology, biomimetics, sensorics, etc.). Such a combination makes it possible to develop new intelligent nanostructured devices. Complexation in ultrathin layers of ligands on liquid and solid substrates is considered in connection with the use thereof as sensitive sensory elements in systems with reduced dimensionality. Substantial attention is focused on the aggregation behavior of diverse ligands and topochemical reactions in organized 2D ensembles, development of new methods for preparing two-dimensional organic networks, and creation of highly stable supramolecular devices based thereon. In the light of the features of 2D systems, several types of mechanochemical transformations occurring under the action of two-dimensional compression–expansion are considered: the phenomenon of redox isomerism in monolayers of lanthanide bis-phthalocyaninates, the phenomenon of forced axial coordination in tetrapyrrole complexes of nickel with a change in its spin number, and the phenomenon of the reversible formation of excimers. Especial attention is given to the problems concerning the behavior of organic photochromes at interfaces and the perspectives of developing molecular switches based on photosensitive compounds. [ABSTRACT FROM AUTHOR]

Possessing unique physicochemical properties, phthalocyanines are widely used as active components of supramolecular ensembles and nanomaterials. The functional properties of phthalocyanine-based materials are governed by not only the structure of their discotic molecules, but also the character of their intermolecular interactions, which determine both the self-assembly mechanism and the structure of such systems. This review discusses the experimental approaches, which are based on the notions of colloid and coordination chemistry that enable one to control intermolecular interactions in low-dimensional supramolecular ensembles based on phthalocyanines and metallocomplexes thereof. Using double-decker crown-substituted lanthanide phthalocyaninates as an example, it is shown how one- and two-dimensional nanomaterials with different properties can be obtained from the same type of building blocks employing a set of colloid-chemical methods. Such materials are, in particular, capable for controlled absorption of visible light in ultrathin films and can be employed as conducting one-dimensional components of planar elements for organic electronics. [ABSTRACT FROM AUTHOR]

The mitochondrion is an essential organelle enclosed by two membranes whose functionalities depend on their very specific protein and lipid compositions. Proteins from the outer mitochondrial membrane (OMM) are specialized in mitochondrial dynamics and mitophagy, whereas proteins of the inner mitochondrial membrane (IMM) have dedicated functions in cellular respiration and apoptosis. As for lipids, the OMM is enriched in glycerophosphatidyl choline but cardiolipin is exclusively found within the IMM. Though the lipid topology and distribution of the OMM and IMM are known since more than four decades, little is known about the interfacial and dynamic properties of the IMM and OMM lipid extracts. Here we build monolayers, supported bilayers and giant unilamellar vesicles (GUVs) of native OMM and IMM lipids extracts from porcine heart. Additionally, we perform a comparative analysis on the interfacial, phase immiscibility and mechanical properties of both types of extract. Our results show that IMM lipids form more expanded and softer membranes than OMM lipids, allowing a better understanding of the physicochemical and biophysical properties of mitochondrial membranes.

Among biodegradable polymers, polylactides (PLAs) have attracted considerable interest because the monomer can be produced from renewable resources. Since their initial degradability strongly affects commercial application fields, it is necessary to manage the degradation properties of PLAs to make them more commercially attractive. To control their degradability, poly(lactide-co-glycolide) (PLGA) copolymers of glycolide and isomer lactides (LAs) were synthesized, and their enzymatic and alkaline degradation rates of PLGA monolayers as functions of glycolide acid (GA) composition were systematically investigated by the Langmuir technique. The results showed that the alkaline and enzymatic degradations of PLGA monolayers were faster than those of l-polylactide (l-PLA), even though proteinase K is selectively effective in the l-lactide (l-LA) unit. Alkaline hydrolysis was strongly affected by their hydrophilicity, while the surface pressure of monolayers for enzymatic degradations was a major factor.

In this work, a sensitive coating based on Langmuir–Blodgett (LB) films containing monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) with an immobilized glucose oxidase (GOx) enzyme was created. The immobilization of the enzyme in the LB film occurred during the formation of the monolayer. The effect of the immobilization of GOx enzyme molecules on the surface properties of a Langmuir DPPE monolayer was investigated. The sensory properties of the resulting LB DPPE film with an immobilized GOx enzyme in a glucose solution of various concentrations were studied. It has shown that the immobilization of GOx enzyme molecules into the LB DPPE film leads to a rising LB film conductivity with an increasing glucose concentration. Such an effect made it possible to conclude that acoustic methods can be used to determine the concentration of glucose molecules in an aqueous solution. It was found that for an aqueous glucose solution in the concentration range from 0 to 0.8 mg/mL the phase response of the acoustic mode at a frequency of 42.7 MHz has a linear form, and its maximum change is 55°. The maximum change in the insertion loss for this mode was 18 dB for a glucose concentration in the working solution of 0.4 mg/mL. The range of glucose concentrations measured using this method, from 0 to 0.9 mg/mL, corresponds to the corresponding range in the blood. The possibility of changing the conductivity range of a glucose solution depending on the concentration of the GOx enzyme in the LB film will make it possible to develop glucose sensors for higher concentrations. Such technological sensors would be in demand in the food and pharmaceutical industries. The developed technology can become the basis for creating a new generation of acoustoelectronic biosensors in the case of using other enzymatic reactions.

The Fe(III) complexes of branched asymmetric dendrimers were obtained by a one-step reaction as the second-generation architectures. Mesomorphic behavior was found for complexes with PF6− and BF4− counter-ions. To obtain knowledge about the existence of HS and LS fractions of iron(III) ion and their evolution with temperature, EPR methods were used. It was demonstrated that compounds contain one low-spin (LS, S = 1/2) and two HS-spin (HS, S = 5/2) of Fe(III) centers and are packed into two magnetic sub-lattices. A floating layers of Fe(III) complexes and Langmuir–Blodgett films on their base were formed and investigated in the presence of a magnetic field. [ABSTRACT FROM AUTHOR]

The application of surface rheology and Brewster angle microscopy on mixed monolayers of DPPC and polymeric nanoparticles (cationic and anionic) showed that the sign of the particle charge affects the dynamic properties of the monolayers less than the nanoparticles' ability to aggregate. Under almost physiological conditions, the effect of nanoparticles on the elasticity of DPPC monolayer is insignificant. However, the particles prevent the surface tension from decreasing to extremely low values. This effect could affect the functionality of pulmonary surfactants. [ABSTRACT FROM AUTHOR]

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

Polychlorinated cyclodiene pesticides (CP) are persistent organic pollutants causing widespread soil contamination. CPs-contaminated soils could be purified by mycoremediation, i.e. the introduction of CP-degrading fungal strains into the soils. However, not all mycoremediation attempts are effective, and the microbial cells introduced into the soil die. CP molecules are highly hydrophobic, therefore, their toxicity may largely result from membrane activity, i.e. from the incorporation of CP molecules into membranes disturbing their functions. To test this hypothesis and shed light on the interactions of CPs with plasma membranes, we used lipid Langmuir monolayers and unilamellar liposomes as models of fungal membranes. In our research, we included the four most common CPs polluting soils: aldrin, endrin, endosulfan, and chlordecone. Our studies have shown that CPs can be incorporated into the membranes up to the molar ratio of approximately 0.15. In the case of Langmuir monolayers, greater effects were observed for the model composed of saturated lipids. For this model, however, X-ray diffraction studies have shown that CPs are incorporated into the ergosterol-enriched amorphous phase without disturbing the formation of crystalline phospholipid nanodomains. Langmuir monolayer studies showed that chlordecone disturbs the physical properties of the model membrane to the greatest extent. However, liposome studies have shown that the effect of all CPs is similar – their presence increases the fluidity of the bilayer. Our studies confirmed CPs' membrane activity, however, also showed that the presence of CP molecules in lipid membranes does not cause drastic changes in their physical properties. [Display omitted] • Cyclodiene pesticides are incorporated into model fungal membranes • Cyclodiene pesticides do not disturb the formation of phospholipid crystalline nanodomains • Chlordecone has the greatest impact on the physical properties of Langmuir monolayers • All studied cyclodiene pesticides fluidize the lipid bilayer in liposomes [ABSTRACT FROM AUTHOR]

The mechanism of chemotherapeutic action of Ru-based drugs involves plasma membrane disruption and valuable insights into this process may be gained using cell membrane models. The interactions of a series of cytotoxic η6- p -cymene ruthenium(II) complexes, [Ru(η6- p -cymene)P(3,5-C(CH 3) 3 -C 6 H 3) 3 Cl 2 ] (1) , [Ru(η6- p -cymene)P(3,5-CH 3 -C 6 H 3) 3 Cl 2 ] (2) , [Ru(η6- p -cymene)P(4-CH 3 O-3,5-CH 3 -C 6 H 2) 3 Cl 2 ] (3) , and [Ru(η6- p -cymene)P(4-CH 3 O-C 6 H 4) 3 Cl 2 ] (4) , were examined using Langmuir monolayers as simplified healthy and cancerous outer leaflet plasma membrane models. The cancerous membrane (CM1 and CM2) models contained either 40 % 1,2- dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) or 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC), 30 % cholesterol (Chol), 20 % 1,2-dipalmitoyl- sn -glycero-3-phosphoethanolamine (DPPE), and 10 % 1,2-dipalmitoyl- sn -glycero-3-phospho- l -serine (DPPS). Meanwhile, the healthy membrane (HM1 and HM2) models were composed of 60 % DPPC or DOPC, 30 % Chol and 10 % DPPE. The complexes affected surface pressure isotherms and decreased compressional moduli of cancerous and healthy membrane models, interacting with the monolayers headgroup and tails according to data from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). However, the effects did not correlate with the toxicity of the complexes to cancerous and healthy cells. Multidimensional projection technique showed that the complex (1) induced significant changes in the CM1 and HM1 monolayers, though it had the lowest cytotoxicity against cancer cells and is not toxic to healthy cells. Moreover, the most toxic complexes (2) and (4) were those that least affected CM2 and HM2 monolayers. The findings here support that the ruthenium complexes interact with lipids and cholesterol in cell membrane models, and their cytotoxic activities involve a multifaceted mode of action beyond membrane disruption. [Display omitted] • Ru complexes interact with both healthy and cancer plasma membrane models. • The cytotoxicity of Ru complexes in unrelated to their effect on membrane models. • Ru complexes either cross or penetrate the cell membrane. • The mechanism of action of Ru complexes goes beyond simple cell membrane disruption. [ABSTRACT FROM AUTHOR]

The study aimed to synthesize and characterize the magnetic drug carrier modified with terbium (III) ions. The addition of terbium extends the possibilities of their applications for targeted anticancer radiotherapy as well as for imaging techniques using radioisotopes emitting β+, β−, α, and γ radiation. The synthesis of iron oxide nanoparticles stabilized with citrates using the co-precipitation method (IONP @ CA) was carried out during the experimental work. The obtained nanoparticles were used to synthesize a conjugate containing terbium ions and guanosine-5′-monophosphate as an analog of drugs from the thiopurine group. Conjugates and their components were characterized using Transmission Electron Microscopy, infrared spectroscopy, X-ray microanalysis, spectrofluorimetry, and thermogravimetric analysis. The hybrid was also investigated with Langmuir layers to check the interaction with analogs of biological membranes. [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]

The results of a systematic study on the adsorption of polylysine molecules of different lengths on the surface of a 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) monolayer in the liquid (LE) and condensed (LC) states are presented. A compressibility diagram and the Volta potential were recorded with the Langmuir monolayer technique and further analyzed with the empirical approach. The structure of the monolayer films with adsorbed polypeptides was studied with synchrotron X-ray reflectometry. Two- and three-layer slab models describe the reflectivity data fairly well and reveal both the significant structural changes and the dehydration of the polar groups induced by all polylysines used at the maximal coverage of the monolayer interface in both the LE and LC states. On the one hand, in the LE phase of the monolayer (area per molecule A ≅ 70 Ǻ2), the integrated electron density of the lipid headgroup region is approximately half the density contained in the clean monolayer. This indicates both significant compaction and dehydration in the polar groups of the lipids, caused by the adsorption of polypeptides. On the other hand, in the LC state (A ≅ 40 Ǻ2), the degree of the hydration of the polar region is similar to that for the initial DMPS monolayer. However, both the electron density and the thickness of the head group region differ significantly from the values of these parameters for the clean monolayer in the LC state.

1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleyl-sn-glycerol-3-phosphorcholine (POPC) are important components in pulmonary surfactants (PSs), of which the relative content is related to lung compliance. Herein, the phase behavior and thermodynamic structure of mixed DPPC/POPC monolayers were studied to elucidate the intermolecular interaction between DPPC and POPC molecules. Surface pressure–molecular area isotherms demonstrated that POPC significantly affected the phase behavior of the lipid domain structure as a function of its concentration. The compression modulus of the mixed monolayers reduced with the increase in POPC proportion, which can be attributed to the intermolecular repulsion between DPPC and POPC. Brewster angle microscopy analysis showed that the ordered structure of the monolayers trended toward fluidization in the presence of POPC. Raman spectroscopy results revealed that the change in C–C skeleton stretching vibration was the main cause of the decrease in the monolayer packing density. These findings provide new insights into the role of different phospholipid components in the function of PS film at a molecular level, which can help us to understand the synergy effects of the proportional relationship between DPPC and POPC on the formation and progression of lung disease and provide some references for the synthesis of lung surfactants.

The interactions of DNA with lysozyme in the surface layer were studied by performing infrared reflection–absorption spectroscopy (IRRAS), ellipsometry, surface tensiometry, surface dilational rheology, and atomic force microscopy (AFM). A concentrated DNA solution was injected into an aqueous subphase underneath a spread lysozyme layer. While the optical properties of the surface layer changed fast after DNA injection, the dynamic dilational surface elasticity almost did not change, thereby indicating no continuous network formation of DNA/lysozyme complexes, unlike the case of DNA interactions with a monolayer of a cationic synthetic polyelectrolyte. A relatively fast increase in optical signals after a DNA injection under a lysozyme layer indicates that DNA penetration is controlled by diffusion. At low surface pressures, the AFM images show the formation of long strands in the surface layer. Increased surface compression does not lead to the formation of a network of DNA/lysozyme aggregates as in the case of a mixed layer of DNA and synthetic polyelectrolytes, but to the appearance of some folds and ridges in the layer. The formation of more disordered aggregates is presumably a consequence of weaker interactions of lysozyme with duplex DNA and the stabilization, at the same time, of loops of unpaired nucleotides at high local lysozyme concentrations in the surface layer.

This study presents a new approach to designing a lithocholic acid functionalized oligomer (OLithocholicAA-X) that can be used as a drug carrier with additional, beneficial activity. Namely, this novel oligomer can incorporate an anti-cancer drug due to the application of an effective backbone as its component (lithocholic acid) alone is known to have anticancer activity. The oligomer was synthesized and characterized in detail by nuclear magnetic resonance, attenuated total reflectance Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, thermal analysis, and mass spectrometry analysis. We selected lipid rafts as potential drug carrier-membrane binding sites. In this respect, we investigated the effects of OLithocholicAA-X on model lipid raft of normal and altered composition, containing an increased amount of cholesterol (Chol) or sphingomyelin (SM), using Langmuir monolayers and liposomes. The surface topography of the studied monolayers was additionally investigated by atomic force microscopy (AFM). The obtained results showed that the investigated oligomer has affinity for a system that mimics a normal lipid raft (SM:Chol 2:1). On the other hand, for systems with an excess of SM or Chol, thermodynamically unfavorable fluidization of the films occurs. Moreover, AFM topographies showed that the amount of SM determines the bioavailability of the oligomer, causing fragmentation of its lattice. [Display omitted] • The synthesis and physicochemical characterization of OLithocholicAA-X was presented • OLithocholicAA-X can act as a drug carrier with double activity • Model membrane systems were used to study OLithocholicAA-X binding into membrane • OLithocholicAA-X shows affinity to model lipid rafts • SM determines the bioavailability of the oligomer causing fragmentation of its lattice [ABSTRACT FROM AUTHOR]

The Fe(III) complexes of branched asymmetric dendrimers were obtained by a one-step reaction as the second-generation architectures. Mesomorphic behavior was found for complexes with PF6− and BF4− counter-ions. To obtain knowledge about the existence of HS and LS fractions of iron(III) ion and their evolution with temperature, EPR methods were used. It was demonstrated that compounds contain one low-spin (LS, S = 1/2) and two HS-spin (HS, S = 5/2) of Fe(III) centers and are packed into two magnetic sub-lattices. A floating layers of Fe(III) complexes and Langmuir–Blodgett films on their base were formed and investigated in the presence of a magnetic field.

One of the main known effects of cholesterol is to rigidify the cell membrane throughout the so-called condensing effect. Although many studies have been done in mixtures of cholesterol with different membrane lipids, there are not many studies in a wide concentration range of cholesterol or at physiological conditions. In this work, we studied mixtures of DMPC/Cholesterol monolayers to determine the effect of cholesterol, from very low to physiological concentrations and two pHs. We use a Langmuir balance and Brewster angle microscopy to study their thermodynamic behavior at 37.0 ± 0.1°C at the air/solution interface. From the analysis of the (π−A) isotherms, we determined the excess area and the compressibility elastic modulus to determine the monolayers mechanical properties. Surprisingly, we found three main effects of cholesterol: The first one is a fluidization effect of the monolayer at all cholesterol concentrations. The second effect is the so-called condensing effect that appears due to the non-ideality of the mixture. The third effect is a stiffness of the monolayer as the cholesterol concentration increases. These effects are stronger in pure water, pH ≈ 6.6, than on buffer at physiological pH = 7.4. We also found that all mixtures are thermodynamically stable at all concentrations at a surface pressure of 30.1 ± 1.6 and 27.4 ± 3.2 mN/m in pure water and buffer, respectively. Furthermore, we compared this stability with a fatty acid monolayer that shows a much lower surface pressure equilibrium value that DMPC or its mixtures with cholesterol, indicating a possibly reason why double chain lipids are better than single chain lipids to made up the cell membrane.

Langmuir and Langmuir-Blodgett films holding a synthetic bioinspired wound healing active compound were used as drug-delivery platforms. Palmitic acid Langmuir monolayers were able to incorporate 2-methyltriclisine, a synthetic Triclisine derivative that showed wound healing activity. The layers proved to be stable and the nanocomposites were transferred to solid substrates. Normal human lung cells (Medical Research Council cell strain 5, MRC-5) were grown over the monomolecular Langmuir-Blodgett films that acted as a drug reservoir and delivery system. The proliferation and migration of the cells were clearly affected by the presence of 2-methyltriclisine in the amphiphilic layers. The methodology is proposed as a simple and reliable model for the study of the effects of bioactive compounds over cellular cultures.

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]

Hypothesis: Amphotericin B (AmB) is a highly effective antimicrobial, with broad antimycotic and antiparasitic effect. However, AmB poor water-solubilisation and aggregation tendency limits its use for topical applications. We studied the capacity of nanostructures formed by alkyl esters of L-ascorbic acid (ASCn) to solubilise AmB and tested the relationship between the prevalence of the monomeric form of AmB and its effectiveness as antimicrobial agent. Experiments: We developed self-assembled nanostructures formed by the commercial compound, palmitoyl ascorbic acid, as well as the shorter chained myristoyl and lauroyl ascorbic acid. AmB loaded ASCn nanostructures were studied by a combination of spectroscopic techniques, together with particle analysis, differential scanning calorimetry, microbiological tests, and Langmuir monolayer visualisation. Findings: We found no direct relation between the antimicrobial capacity and the prevalence of the monomeric form of the drug. However, the later was related to chemical stability and colloidal robustness. Nanostructures formed by ASC16 in its anionic state provide an appropriate environment for AmB in its monomeric form, maintaining its antimicrobial capacity. Langmuir film visualisation supports spectrophotometric evidence, indicating that ASC16 allows the in-plane solubilisation of AmB. Coagels formed by ASC16 appear as promising for carrying AmB for dermal delivery.

The application of surface rheology and Brewster angle microscopy on mixed monolayers of DPPC and polymeric nanoparticles (cationic and anionic) showed that the sign of the particle charge affects the dynamic properties of the monolayers less than the nanoparticles’ ability to aggregate. Under almost physiological conditions, the effect of nanoparticles on the elasticity of DPPC monolayer is insignificant. However, the particles prevent the surface tension from decreasing to extremely low values. This effect could affect the functionality of pulmonary surfactants.

Sulfur-containing groups preorganized on macrocyclic scaffolds are well suited for liquid-phase complexation of soft metal ions; however, their binding potential was not extensively studied at the air–water interface, and the effect of thioether topology on metal ion binding mechanisms under various conditions was not considered. Herein, we report the interface receptor characteristics of topologically varied thiacalixarene thioethers (linear bis-(methylthio)ethoxy derivative L2, O2S2-thiacrown-ether L3, and O2S2-bridged thiacalixtube L4). The study was conducted in bulk liquid phase and Langmuir monolayers. For all compounds, the highest liquid-phase extraction selectivity was revealed for Ag+ and Hg2+ ions vs. other soft metal ions. In thioether L2 and thiacalixtube L4, metal ion binding was evidenced by a blue shift of the band at 303 nm (for Ag+ species) and the appearance of ligand-to-metal charge transfer bands at 330–340 nm (for Hg2+ species). Theoretical calculations for thioether L2 and its Ag and Hg complexes are consistent with experimental data of UV/Vis, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffractometry of Ag–thioether L2 complexes and Hg–thiacalixtube L4 complex for the case of coordination around the metal center involving two alkyl sulfide groups (Hg2+) or sulfur atoms on the lower rim and bridging unit (Ag+). In thiacrown L3, Ag and Hg binding by alkyl sulfide groups was suggested from changes in NMR spectra upon the addition of corresponding salts. In spite of the low ability of the thioethers to form stable Langmuir monolayers on deionized water, one might argue that the monolayers significantly expand in the presence of Hg salts in the water subphase. Hg2+ ion uptake by the Langmuir–Blodgett (LB) films of ligand L3 was proved by X-ray photoelectron spectroscopy (XPS). Together, these results demonstrate the potential of sulfide groups on the calixarene platform as receptor unit towards Hg2+ ions, which could be useful in the development of Hg2+-selective water purification systems or thin-film sensor devices.

The study aimed to synthesize and characterize the magnetic drug carrier modified with terbium (III) ions. The addition of terbium extends the possibilities of their applications for targeted anticancer radiotherapy as well as for imaging techniques using radioisotopes emitting β+, β−, α, and γ radiation. The synthesis of iron oxide nanoparticles stabilized with citrates using the co-precipitation method (IONP @ CA) was carried out during the experimental work. The obtained nanoparticles were used to synthesize a conjugate containing terbium ions and guanosine-5′-monophosphate as an analog of drugs from the thiopurine group. Conjugates and their components were characterized using Transmission Electron Microscopy, infrared spectroscopy, X-ray microanalysis, spectrofluorimetry, and thermogravimetric analysis. The hybrid was also investigated with Langmuir layers to check the interaction with analogs of biological membranes.

[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]

Cationic lipids are synthetic compounds of amphiphilic character used in Drug Delivery Systems (DDS), especially in gene therapy, as the carriers of genetic material. As it is known, the main limitation of the application of cationic lipids in DDS is their high cytotoxicity after in vivo administration and low bioactivity. This is probably related to not fully known the relationship between the lipid structure and its activity as well as the mechanism of lipofection or drug delivery. Therefore, in this work we determined the impact of a selected group of cationic lipids - triesters of phosphatidylcholine (Et-PCs) - differing in their hydrophobic structure on model mammalian membranes. In the research, as model systems, Langmuir monolayers and liposomes were applied. It was shown that the incorporation of Et-PCs into model mammalian membranes weakens interactions between lipids, causing the increase of fluidity, disordering degree and permeability of membrane. The destabilization of the membrane in this way can facilitate the entry of drugs, carried inside cationic liposomes, into the pathological cell. Moreover, the studies prove that the structure of the hydrophobic part of cationic lipids also affects the properties of lipid membranes. [Display omitted] • The interactions of Et-PCs with mammalian membranes depend on their composition. • The hydrophobic structure of Et-PCs effects on the properties of lipid membranes. • Et-PCs increase the disordering degree of molecules in model mammalian membranes. • Et-PC with unsaturated bonds in hydrophobic part fluidizes lipid membranes more. • EDOPC increases more the permeability of the model membrane than EDPPC. [ABSTRACT FROM AUTHOR]

The behavior of amphiphilic molecules such as lipids, peptides and their mixtures at the air/water interface allow us to evaluate and visualize the arrangement formed in a confined and controlled surface area. We have studied the surface properties of the zwitterionic DPPC lipid and Aβ(1–40) amyloid peptide in mixed films at different temperatures (from 15 to 40 °C). In this range of temperature the surface properties of pure Aβ(1–40) peptide remained unchanged, whereas DPPC undergoes its characteristic liquid-expanded → liquid-condensed bidimensional phase transition that depends on the temperature and lateral pressure. This particular property of DPPC makes it possible to dynamically study the influence of the lipid phase state on amyloid structure formation at the interface in a continuous, isothermal and abrupt change on the environmental condition. As the mixed film is compressed the fibril-like structure of Aβ(1–40) is triggered specifically in the liquid-expanded region , independently of temperature, and it is selectively excluded from the well-visible liquid condensed domains of DPPC. The Aβ amyloid fibers were visualized by using BAM and AFM and they were Thio T positive. In mixed DPPC/Aβ(1–40) films the condensed domains (in between 11 mN/m to 20 mN/m) become irregular probably due to the fibril-like structures is imposing additional lateral stress sequestering lipid molecules in the surrounding liquid-expanded phase to self-organize into amyloids. [Display omitted] • Βeta amyloid peptide forms fibril-like structures in phospholipid liquid phase. • Lipid phase acts as an amyloid inductor in biomembranes. • Fibril-like structures can be triggered by the interfacial condition. [ABSTRACT FROM AUTHOR]

Phosphatidic acid (PA) is one of the simplest membrane phospholipids, yet it plays a crucial role in various biologically relevant processes that take place in cells. Since PA generation may be triggered by a variety of factors, very often of antagonistic character, the specific nature of physiological responses driven by PA is not clear. In order to shed more light on these issues, we carried out a systematic characterization of membranes containing one of the three biologically significant PA molecular species. The effect of these molecules on the properties of membranes composed of phosphatidylcholine and/or cholesterol was assessed in a multidisciplinary approach, including molecular dynamic simulations, flicker noise spectroscopy, and Langmuir monolayer isotherms. The first enables the determination of various macroscopic and microscopic parameters such as lateral diffusion, membrane thickness, and defect analysis. The obtained data revealed a strong interaction between unsaturated PA species and phosphatidylcholine. On the other hand, the behavior of saturated PA was greatly influenced by cholesterol. Additionally, a strong effect on mechanical properties was observed in the case of three-component systems, which could not be explained by the simple extrapolation of parameters of the corresponding two-component systems. Our data show that various PA species are not equivalent in terms of their influence on lipid mono- and bilayers and that membrane composition/properties, particularly those related to the presence of cholesterol, may strongly modulate PA behavior.

The formation of ordered 2D nanostructures of double stranded DNA molecules at various interfaces attracts more and more focus in medical and engineering research, but the underlying intermolecular interactions still require elucidation. Recently, it has been revealed that mixtures of DNA with a series of hydrophobic cationic polyelectrolytes including poly(N,N-diallyl-N-hexyl-N-methylammonium) chloride (PDAHMAC) form a network of ribbonlike or threadlike aggregates at the solution—air interface. In the present work, we adopt a novel approach to confine the same polyelectrolyte at the solution—air interface by spreading it on a subphase with elevated ionic strength. A suite of techniques–rheology, microscopy, ellipsometry, and spectroscopy–are applied to gain insight into main steps of the adsorption layer formation, which results in non-monotonic kinetic dependencies of various surface properties. A long induction period of the kinetic dependencies after DNA is exposed to the surface film results only if the initial surface pressure corresponds to a quasiplateau region of the compression isotherm of a PDAHMAC monolayer. Despite the different aggregation mechanisms, the micromorphology of the mixed PDAHMAC/DNA does not depend noticeably on the initial surface pressure. The results provide new perspective on nanostructure formation involving nucleic acids building blocks.

Stimulus-responsive liposomes (L) for triggering drug release to the target site are particularly useful in cancer therapy. This research was focused on the evaluation of the effects of cholesterol levels in the performance of gold nanoparticles (AuNPs)-functionalized L for controlled doxorubicin (D) delivery. Their interfacial and morphological properties, drug release behavior against temperature changes and cytotoxic activity against breast and ovarian cancer cells were studied. Langmuir isotherms were performed to identify the most stable combination of lipid components. Two mole fractions of cholesterol (3.35 mol% and 40 mol%, L1 and L2 series, respectively) were evaluated. Thin-film hydration and transmembrane pH-gradient methods were used for preparing the L and for D loading, respectively. The cationic surface of L allowed the anchoring of negatively charged AuNPs by electrostatic interactions, even inducing a shift in the zeta potential of the L2 series. L exhibited nanometric sizes and spherical shape. The higher the proportion of cholesterol, the higher the drug loading. D was released in a controlled manner by diffusion-controlled mechanisms, and the proportions of cholesterol and temperature of release media influenced its release profiles. D-encapsulated L preserved its antiproliferative activity against cancer cells. The developed liposomal formulations exhibit promising properties for cancer treatment and potential for hyperthermia therapy.

Langmuir monolayers containing different amounts of cholesterol and cholesteryl stearate were studied at two different temperatures (24 °C and 35 °C). The main goal was to contribute towards the understanding of how the variations in the chemical composition may affect the physico-chemical properties of these specific lipid monolayers. The model mixture was chosen considering that cholesteryl esters are present in cell membranes and some other biological systems, including human tear lipids. Therefore, an investigation into the effect of the lipid monolayer composition on their interfacial properties may elucidate some of the fundamental reasons for the deficiencies in cell membranes and tear film functioning in vivo. The experimental results have shown that the molar ratio of the mixture plays a crucial role in the modulation of the Langmuir film properties. The condensing effects of the cholesterol and the interactions between the lipids in the monolayer were the main factors altering the monolayer response to dilatational deformation. The modification of the mixture compositions leads to significant changes in the Langmuir films and the mechanical performance, altering the ability of the monolayer to reduce the surface tension and the viscoelastic properties of the monolayers. This suggests that subtle modifications of the biomembrane composition may significantly alter its physiological function.