Ionizable lipids are a class of pharmaceutical excipients with a main application in lipid nanoparticles for nucleic acid delivery. New ionizable lipids are needed to tune characteristics of lipid-based nucleic acid delivery systems, e.g. stability, nucleic acid loading capacity and binding strength, as well as bio-distribution. Herein, we present the synthesis of three novel ionizable lipids as putative excipients for lipid-based nucleic acid delivery systems. Langmuir monolayer experiments with classical surface pressure/area isotherm evaluation were used to understand the self-assembly behavior of the lipids. Additional experiments with surface sensitive techniques, namely grazing incidence x-ray scattering and infrared reflection-absorption spectroscopy (IRRAS), were performed to understand structural characteristics of lipid associates. The latter technique was also used to investigate the nucleic acid binding process between DNA and the ionizable lipids. Finally, first transfection experiments with the novel lipids formulated as cationic liposomes were performed providing first efficacy data. Although the alkyl chain pattern was comparable for all three ionizable lipids, the results demonstrated that with increasing head-group size the DNA binding capacity changed and the alkyl chain fluidity was increased. The lipid with the lowest phase transition temperature and the smallest packing parameter showed the highest DNA transfer efficiency.

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(CH3)3-C6H3)3Cl2] (1), [Ru(η6-p-cymene)P(3,5-CH3-C6H3)3Cl2] (2), [Ru(η6-p-cymene)P(4-CH3O-3,5-CH3-C6H2)3Cl2] (3), and [Ru(η6-p-cymene)P(4-CH3O-C6H4)3Cl2] (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.

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.

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.

The Langmuir monolayer technique has been successfully used for decades to model biological membranes and processes occurring at their interfaces. Classically, this method involves surface pressure measurements to study interactions within membrane components as well as between external bioactive molecules (e.g. drugs) and the membrane. In recent years, surface-sensitive techniques were developed to investigate monolayers in situ; however, the obtained results are in many cases insufficient for a full characterization of biomolecule-membrane interactions. As result, description of systems using parameters such as mixing or excess thermodynamic functions is still relevant, valuable and irreplaceable in biophysical research. This review article summarizes the theory of thermodynamics of single- and multi-component Langmuir monolayers. In addition, recent applications of this approach to characterize surface behaviour and interactions (e.g. orientation of bipolar molecules, drug-membrane affinity, lateral membrane heterogeneity) are presented.

The presence of an additional polar group in the cholesterol backbone increases the hydrophilicity of resulting compounds (oxysterols), determines their arrangement at the phase boundary, and interactions with other lipids and proteins. As a result, physicochemical properties of biomembranes (i.e., elasticity, permeability, and ability to bind proteins) are modified, which in turn may affect their functioning. The observed effect depends on the type of oxysterol and its concentration and can be both positive (e.g., antiviral activity) or negative (disturbance of cholesterol homeostasis, signal transduction, and protein segregation). The membrane activity of oxysterols has been successfully studied using membrane models (vesicles, monolayers, and solid supported films). Membrane models, in contrast to the natural systems, provide the possibility to selectively examine the specific aspect of biomolecule-membrane interactions. Moreover, the gradual increase in the complexity of the used model allows to understand the molecular phenomena occurring at the membrane level. The interest in research on artificial membranes has increased significantly in recent years, mainly due to the development of modern and sophisticated physicochemical methods (static and dynamic) in both the micro- and nanoscale, which are applied with the assistance of powerful theoretical calculations. This review provides an overview of the most important findings on this topic in the current literature.

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 (PO2-) 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.

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.

Influences of subphase pH and temperature on the interfacial aggregation behavior of two double hydrophilic hyperbranched copolymers of poly[oligo(ethylene glycol) methacrylate-co-(2-diisopropylamino)ethyl methacrylate] (P(OEGMA-co-DIPAEMA)) at the air/water interface are studied by the Langmuir film balance technique. Morphologies of their Langmuir-Blodgett (LB) films are characterized by atomic force microscopy (AFM). At the interface, P(OEGMA-co-DIPAEMA) copolymers tend to form a dense network structure of circular micelles composed of branching agent-connected carbon backbone cores and mixed shells of OEGMA and DIPAEMA segments (pendant groups). This network structure containing many honeycomb-like holes with diameters of 6-8 nm is identified for the first time and clearly observed in the enlarged AFM images of their LB films. Under acidic conditions, surface pressure versus molecular area isotherms of the two copolymers in the low-pressure region show larger mean molecular area than those under neutral and alkaline conditions due to the lack of impediment from DIPAEMA segments. Upon further compression, each isotherm exhibits a wide pseudo-plateau, which corresponds to OEGMA segments being pressed into the subphase. Furthermore, the isotherms under neutral and alkaline conditions exhibit the lower critical solution temperature behavior of OEGMA segments, and the critical temperature is lower when the hyperbranched copolymer contains higher OEGMA content.

In this work the cosmetic preservative based on a Ribes Nigrum (blackcurrant) plant extract (PhytoCide Black Currant Powder abbr. BCE) was investigated to evaluate its antibacterial effect and to gain an insight into its mechanism of action. The influence of this commercially available formulation on model Escherichia coli and Staphylococcus aureus lipid membranes was studied to analyze its interactions with membrane lipids at a molecular level. The mixed lipid monolayers and one component bacteria lipid films were used to investigate the effect of BCE on condensation and morphology of model systems and to study the ability of BCE components to penetrate into the lipid environment. The in vitro tests were also done on different bacteria species (E. coli, Enterococcus faecalis, S. aureus, Salmonella enterica, Pseudomonas aeruginosa) to compare antimicrobial potency of the studied formulation. As evidenced the in vitro studies BCE formulation exerts very similar antibacterial activity against E. coli and S. aureus. Moreover, based on the collected data it is impossible to indicate which bacteria: Gram-positive or Gram-negative are more susceptible to this formulation. Model membrane experiments evidenced that the studied preservative affects organization of both E. coli and S. aureus model system by decreasing their condensation and altering their morphology. BCE components are able to penetrate into the lipid systems. However, all these effects depend on the lipid composition and monolayer organization. The collected results were analyzed from the point of view of the mechanism of action of blackcurrant extract and the factors, which may determine the activity of this formulation.