Lipid Polar Head Groups Research Articles

Investigation of the Membrane Localization and Interaction of Selected Flavonoids by NMR and FTIR Spectroscopy.

In this report, we discuss the effects of undescribed flavone derivatives, HZ4 and SP9, newly isolated from the aerial parts of Hottonia palustris L. and Scleranthus perennis L. on membranes. Interaction of flavonoids with lipid bilayers is important for medicinal applications. The experiments were performed with FTIR and NMR techniques on liposomes prepared from DPPC (dipalmitoylphosphatidylcholine) and EYPC (egg yolk phosphatidylcholine). The data showed that the examined polyphenols incorporate into the polar head group region of DPPC phospholipids at both 25 °C and 45 °C. At the lower temperature, a slight effect in the spectral region of the ester carbonyl group is observed. In contrast, at 45 °C, both compounds bring about the changes in the spectral regions attributed to antisymmetric and symmetric stretching vibrations of CH2 and CH3 moieties. Similarly, as in DPPC lipids, the tested compounds interact with the fingerprint region of the polar head groups of the EYPC lipids and cause its reorganization. The outcomes obtained by NMR analyses confirmed the localization of both flavonoids in the polar heads zone. Unraveled effects of HZ4 and SP9 in respect to lipid bilayers can partly determine their biological activities and are crucial for their usability in medicine as disease-preventing phytochemicals.

Biological responses to imazapic and methyl parathion pesticides in bioinspired lipid membranes and Tilapia fish

Pesticide misuse has well-documented detrimental effects on ecosystems, with Nile tilapia (Oreochromis niloticus) being particularly vulnerable. The current study focuses on the impact of widely used sugarcane crop pesticides, Imazapic (IMZ) and Methyl Parathion (MP), on tilapia gill tissues and their lipid membranes. This investigation was motivated by the specific role of the lipid membrane in transport regulation. Bioinspired cell membrane models, including Langmuir monolayers and liposomes (LUVs and GUVs), were utilized to explore the interaction of IMZ and MP. The results revealed electrostatic interactions between IMZ and MP and the polar head groups of lipids, inducing morphological alterations in the lipid bilayer. Tilapia gill tissue exposed to the pesticides exhibited hypertrophic increases in primary and secondary lamellae, total lamellar fusion, vasodilation, and lifting of the secondary lamellar epithelium. These alterations can lead to compromised oxygen absorption by fish and subsequent mortality. This study not only highlights the harmful effects of the pesticides IMZ and MP, but also emphasizes the crucial role of water quality in ecosystem well-being, even at minimal pesticide concentrations. Understanding these impacts can better inform management practices to safeguard aquatic organisms and preserve ecosystem health in pesticide-affected environments.

Lipid-Specific Direct Translocation of the Cell-Penetrating Peptide NAF-144-67 across Bilayer Membranes.

The cell-penetrating peptide NAF-1 has recently emerged as a promising candidate for selective penetration and destruction of cancer cells. It displays numerous membrane-selective behaviors including cell-specific uptake and organelle-specific degradation. In this work, we explore membrane penetration and translocation of NAF-1 in model lipid bilayer vesicles as a function of lipid identity in zwitterionic phosphatidylcholine lipids mixed with anionic phosphatidylserine, phosphatidylglycerol, and phosphatidic acid lipids. By monitoring the digestion of NAF-1 using the protease trypsin located inside but not outside the vesicles, we determined that the translocation of NAF-1 was significantly enhanced by the presence of phosphatidic acid in the membrane compared to the other three anionic or zwitterionic lipids. These findings were correlated to fluorescence measurements of dansyl-labeled NAF-1, which revealed whether noncovalent interactions between NAF-1 and the bilayer were most stable either at the membrane/solution interface or within the membrane interior. Phosphatidic acid promoted interactions with fatty acid tails, while phosphatidylcholine, phosphatidylserine, and phosphatidylglycerol stabilized interactions with polar lipid headgroups. Interfacial vibrational sum frequency spectroscopy experiments revealed that the phosphate moiety on phosphatidic acid headgroups was better hydrated than on the other three lipids, which helped to shuttle NAF-1 into the hydrophobic region. Our findings demonstrate that permeation does not depend on the net charge on phospholipid lipid headgroups in these model vesicles and suggest a model wherein NAF-1 crosses membranes selectively due to lipid-specific interactions at bilayer surfaces.

Identification of a broad lipid repertoire associated to the endothelial cell protein C receptor (EPCR)

Evidence is mounting that the nature of the lipid bound to the endothelial cell protein C receptor (EPCR) has an impact on its biological roles, as observed in anticoagulation and more recently, in autoimmune disease. Phosphatidylethanolamine and phosphatidylcholine species dominate the EPCR lipid cargo, yet, the extent of diversity in the EPCR-associated lipid repertoire is still unknown and remains to be uncovered. We undertook mass spectrometry analyses to decipher the EPCR lipidome, and identified species not yet described as EPCR ligands, such as phosphatidylinositols and phosphatidylserines. Remarkably, we found further, more structurally divergent lipids classes, represented by ceramides and sphingomyelins, both in less abundant quantities. In support of our mass spectrometry results and previous studies, high-resolution crystal structures of EPCR in three different space groups point to a prevalent diacyl phospholipid moiety in EPCR’s pocket but a mobile and ambiguous lipid polar head group. In sum, these studies indicate that EPCR can associate with varied lipid classes, which might impact its properties in anticoagulation and the onset of autoimmune disease.

Molecular organization of dengue fusion peptide in phospholipid monolayers revealed by tensiometry and vibrational spectroscopy

The interaction of Dengue fusion peptide (FLAg) in selected lipid Langmuir monolayers was characterized with surface pressure-area isotherms and infrared spectroscopy to investigate the role of the membrane charge and molecular organization in the peptide-lipid binding. Surface pressure-area isotherms were employed to analyze the thermodynamic and mechanical properties of the FLAg-lipid monolayer, showing that charged lipid monolayers showed different peptide adsorption patterns for an optimized peptide concentration (maximum membrane adsorption). Polarization modulation infrared reflection-absorption spectroscopy pointed out that incorporating FLAg changed the dipole orientations for the lipid polar head groups, as confirmed in PG-containing monolayers. Also, FLAg reorients the lipid film when it interacts with the phosphate and choline groups. Finally, analysis of the 310-helix bands suggests that FLAg assumes a configuration as a hairpin, an essential premise for the beginning of the membrane fusion process.

Sample Preparation using a Lipid Monolayer Method for Electron Crystallographic Studies

Electron crystallography is a powerful tool for high-resolution structure determination. Macromolecules such as soluble or membrane proteins can be grown into highly ordered two-dimensional (2D) crystals under favorable conditions. The quality of the grown 2D crystals is crucial to the resolution of the final reconstruction via 2D image processing. Over the years, lipid monolayers have been used as a supporting layer to foster the 2D crystallization of peripheral membrane proteins as well as soluble proteins. This method can also be applied to 2D crystallization of integral membrane proteins but requires more extensive empirical investigation to determine detergent and dialysis conditions to promote partitioning to the monolayer. A lipid monolayer forms at the air-water interface such that the polar lipid head groups remain hydrated in the aqueous phase and the non-polar, acyl chains, tails partition into the air, breaking the surface tension and flattening the water surface. The charged nature or distinctive chemical moieties of the head groups provide affinity for proteins in solution, promoting binding for 2D array formation. A newly formed monolayer with the 2D array can be readily transfer into an electron microscope (EM) on a carbon-coated copper grid used to lift and support the crystalline array. In this work, we describe a lipid monolayer methodology for cryogenic electron microscopic (cryo-EM) imaging.

Probing Water State during Lipidic Mesophases Phase Transitions.

We investigate the static and dynamic states of water network during the phase transitions from double gyroid (Ia3‾d ) to double diamond (Pn3‾m ) bicontinuous cubic phases and from the latter to the reverse hexagonal (H II) phase in monolinolein based lipidic mesophases by combining FTIR and broadband dielectric spectroscopy (BDS). In both cubic(s) and H II phase, two dynamically different fractions of water are detected and attributed to bound and interstitial free water. The dynamics of the two water fractions are all slower than bulk water due to the hydrogen‐bonds between water molecules and the lipid's polar headgroups and to nanoconfinement. Both FTIR and BDS results suggest that a larger fraction of water is hydrogen‐bonded to the headgroup of lipids in the H II phase at higher temperature than in the cubic phase at lower temperature via H‐bonds, which is different from the common expectation that the number of H‐bonds should decrease with increase of temperature. These findings are rationalized by considering the topological ratio of interface/volume of the two mesophases.

Probing Water State during Lipidic Mesophases Phase Transitions

AbstractWe investigate the static and dynamic states of water network during the phase transitions from double gyroid ( ) to double diamond ( ) bicontinuous cubic phases and from the latter to the reverse hexagonal (HII) phase in monolinolein based lipidic mesophases by combining FTIR and broadband dielectric spectroscopy (BDS). In both cubic(s) and HII phase, two dynamically different fractions of water are detected and attributed to bound and interstitial free water. The dynamics of the two water fractions are all slower than bulk water due to the hydrogen‐bonds between water molecules and the lipid's polar headgroups and to nanoconfinement. Both FTIR and BDS results suggest that a larger fraction of water is hydrogen‐bonded to the headgroup of lipids in the HII phase at higher temperature than in the cubic phase at lower temperature via H‐bonds, which is different from the common expectation that the number of H‐bonds should decrease with increase of temperature. These findings are rationalized by considering the topological ratio of interface/volume of the two mesophases.

Direct evidence of acid-base interactions in gecko adhesion.

While it is generally accepted that van der Waals (vdW) forces govern gecko adhesion, several studies indicate contributions from non-vdW forces and highlight the importance of understanding the adhesive contact interface. Previous work hypothesized that the surface of gecko setae is hydrophobic, with nonpolar lipid tails exposed on the surface. However, direct experimental evidence supporting this hypothesis and its implications on the adhesion mechanism is lacking. Here, we investigate the sapphire-setae contact interface using interface-sensitive spectroscopy and provide direct evidence of the involvement of acid-base interactions between polar lipid headgroups exposed on the setal surface and sapphire. During detachment, a layer of unbound lipids is left as a footprint due to cohesive failure within the lipid layer, which, in turn, reduces wear to setae during high stress sliding. The absence of this lipid layer enhances adhesion, despite a small setal-substrate contact area. Our results show that gecko adhesion is not exclusively a vdW-based, residue-free system.

Effects of insecticide acephate on membrane mimetic systems: The role played by electrostatic interactions with lipid polar headgroups

Pesticides are important agrochemicals to yield high crop productivity but their indiscriminate use may harm the environment and human health. In order to seek a compromise between effectiveness as insecticide and safety for humans, it is essential to correlate their physiological action with molecular-level interaction with cell membranes. In this study, we found that acephate interacts preferentially with positively charged Langmuir monolayers that represent simplified cell membranes. This was proven by comparing surface pressure-molecular area (π-A) isotherms and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) data on monolayers of the zwitterionic 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC), the cationic dimethyldioctadecyl ammonium bromide (DODAB) and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), and the anionic dihexadecyl phosphate (DHP) and 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA). While acephate induced a closer packing of DODAB and DPTAP monolayers upon binding to their quaternary ammonium and choline groups, respectively, almost no effects were observed in the π-A isotherms of the other lipids. Such preferred interaction between acephate and the positively-charged groups was confirmed with density-functional theory (DFT) calculations. Acephate also changed the size and zeta potential of large unilamellar vesicles (LUVs) formed with cationic lipids. Taken together these results point to a physiological action related to acephate binding to positively charged groups owing to its negative character, which may help establish conditions for the safe use of this insecticide.

Interaction of Ionenes with Lipid Membrane: Unusual Impact of Charge Density.

Synthetic water-soluble polymers are increasingly used for gene delivery, stabilization, and delivery of proteins, and as prospective antimicrobial and antiviral agents. Therefore, study of their interaction with lipid membranes is of special importance. Herein, we studied interaction of aliphatic cationic ionenes (recently tested for gene delivery efficiency) differed in the length of spacer between charged groups (and therefore in charge density) with anionic lipid membrane. A range of approaches such as measurement of particle size and electrophoretic mobility, liposome integrity, ATR-FTIR spectroscopy, isothermal titration calorimetry as well as atomistic molecular modeling was used. Ionene with a spacer of 10 methylene groups has been shown to be incorporated into membrane and interact with its inner hydrophobic part in contrast to ionenes with shorter spacer, which interacted only with outer polar head groups of lipids staying at the water-membrane interface. It affects membrane integrity and results in a different behavior of the polymer-liposome complexes. These findings are relevant for potential biomedical application of ionenes, including creation of composite polymer-liposome systems for drug delivery.

Phospholipase A2 way to hydrolysis: Dint formation, hydrophobic mismatch, and lipid exclusion

Phospholipase A2 (PLA2) exerts a wide range of biological effects and attracts a lot of attention of researchers. Two sites are involved in manifestation of PLA2 enzymatic activity: catalytic site responsible for substrate binding and fatty acid cleavage from the sn-2 position of a glycerophospholipid, and interface binding site (IBS) responsible for the protein binding to lipid membrane. IBS is formed by positively charged and hydrophobic amino acids on the outer surface of the protein molecule. Understanding the mechanism of PLA2 interaction with the lipid membrane is the most challenging step in biochemistry of this enzyme. We used a combination of experimental and computer simulation techniques to clarify molecular details of bee venom PLA2 interaction with lipid bilayers formed by palmitoyloleoylphosphatidylcholine or dipalmitoylphosphatidylcholine. We found that after initial enzyme contact with the membrane, a network of hydrogen bonds was formed. This led to deformation of the interacting leaflet and dint formation. The bilayer response to the deformation depended on its phase state. In a gel-phase bilayer, diffusion of lipids is restricted therefore chain melting occurred in both leaflets of the bilayer. In the case of a fluid-phase bilayer, lateral diffusion is possible, and lipid polar head groups were excluded from the contact area. As a result, the bilayer became thinner and a large hydrophobic area was formed. We assume that relative ability of a bilayer to come through lipid redistribution process defines the rate of initial stages of the catalysis.

Partitioning of Benzoic Acid into 1,2-Dimyristoyl-sn-glycero-3-phosphocholine and Blood-Brain Barrier Mimetic Bilayers.

Using an all-atom explicit water model and replica exchange umbrella sampling simulations, we investigated the molecular mechanisms of benzoic acid partitioning into two model lipid bilayers. The first was formed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids, whereas the second was composed of an equimolar mixture of DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine, palmitoylsphingomyelin, and cholesterol to constitute a blood-brain barrier (BBB) mimetic bilayer. Comparative analysis of benzoic acid partitioning into the two bilayers has revealed qualitative similarities. Partitioning into the DMPC and BBB bilayers is thermodynamically favorable although insertion into the former lowers the free energy of benzoic acid by approximately an additional 1 kcal mol-1. The partitioning energetics for the two bilayers is also largely similar based on the balance of benzoic acid interactions with apolar fatty acid tails, polar lipid headgroups, and water. In both bilayers, benzoic acid retains a considerable number of residual water molecules until reaching the bilayer midplane where it experiences nearly complete dehydration. Upon insertion into the bilayers, benzoic acid undergoes several rotations primarily determined by the interactions with the lipid headgroups. Nonetheless, in addition to the depth of the free energy minimum, the BBB bilayer differs from the DMPC counterpart by a much deeper location of the free energy minimum and the appearance of a high free energy barrier and positioning of benzoic acid near the midplane. Furthermore, DMPC and BBB bilayers exhibit different structural responses to benzoic acid insertion. Taken together, the BBB mimetic bilayer is preferable for an accurate description of benzoic acid partitioning.

Structural modifications of lipid membranes exposed to statins – Langmuir monolayer and PM-IRRAS study

The effects of selected statins on the structure and properties of lipid membranes composed of zwitterionic (1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine, DMPE) or anionic (1,2-dimyristoyl-sn-glycero-3-phospho-l-serine, DMPS) lipids were studied for the first time by Langmuir technique combined with polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and Brewster angle microscopy (BAM). The interactions of statins of different hydrophobicity: pravastatin, fluvastatin, and cerivastatin with the polar region of the lipids forming the membrane were monitored by PM-IRRAS and the changes of the overall monolayer structure and organization were described on the basis of surface pressure vs. area per molecule measurements and Brewster angle microscopy. Large differences in the action of each of the statins on the lipid monolayers were observed and explained by their different hydrophobicity combined with the different degree of hydration of the lipid polar headgroups in the monolayer. Monolayer fluidizing effect was connected with the interaction of statins in the headgroup region of the membrane affecting the original hydrogen bonding in the lipid layers. The most hydrophilic pravastatin interacted only with the polar head groups of the monolayer and affected the organization of the polar part of the lipid membrane by increasing the headgroups hydration. In the case of DMPS, the contribution of electrostatic interactions between the negatively charged headgroups and the drug was observed, and for this lipid especially strong dehydration effect of cerivastatin was revealed. It facilitated the incorporation of the hydrophobic part of the drug into the nonpolar region of the DMPS layer and in this case there was almost no fluidization of the layer. Strong dehydration effects may be dangerous for the lipid membranes and may also be one of the reasons to avoid cerivastatin in the therapies, despite its known efficacy especially in view of the large doses and prolonged application that are usually needed.

Macromolecular Crowding Affects Voltage-Dependent Alamethicin Pore Formation in Lipid Bilayer Membranes.

Macromolecular crowding is known to modulate chemical equilibria, reaction rates, and molecular binding events, both in aqueous solutions and at lipid bilayer membranes, natural barriers that enclose the crowded environments of cells and their subcellular compartments. Previous studies on the effects of macromolecular crowding in aqueous compartments on conduction through membranes have focused on single-channel ionic conduction through previously formed pores at thermodynamic equilibrium. Here, the effects of macromolecular crowding on the mechanism of pore formation itself were studied using the droplet interface bilayer (DIB) technique with the voltage-dependent pore-forming peptide alamethicin (alm). Macromolecular crowding was varied using 8 kDa molecular weight polyethylene glycol (PEG8k) or 500 kDa dextran (DEX500k) in two aqueous droplets on both sides of the bilayer membrane. In general, voltage thresholds for pore formation in the presence of crowders in the droplets decreased compared to their values in the absence of crowders, due to excluded volume effects, water binding by PEG, and changes in the ordering of water molecules and hydrogen-bonding interactions involving the polar lipid headgroups. In addition, asymmetric crowder loading (e.g., PEG8k-DEX500k on either side of the membrane) resulted in transmembrane osmotic pressure gradients that either enhanced or degraded the ionic conduction through the pores.

Thermodynamic Investigation of the Mechanism of Heat Production During Membrane Depolarization.

When an action potential passes through a neuron, heat is first produced and then reabsorbed by the neuronal membrane, resulting in a small measurable temperature spike. Here, we describe the thermodynamics and molecular features of the heat production using a coarse-grained molecular dynamics approach. We study a simple unicomponent lipid bilayer membrane surrounded by physiological salt solution with and without an external electric field, which represents an imbalanced charge across the membrane. We show that the temperature increases significantly upon removal of the electric field under constant pressure conditions. The potential energy converted to heat is initially stored mainly in the imbalanced ion distribution across the membrane and the elastic energy of the membrane has only a minor role to play. We demonstrate that the mechanism of heat production involves interaction between ions as well as lipid headgroup dipoles while the interactions between polar water molecules and lipid headgroup dipoles absorbs a considerable portion of such produced heat upon removal of the electric field. Our data provide novel thermodynamic insights into the molecular processes governing membrane reorganization upon discharging of lipid membranes and insight into energy metabolism in nerves.

The Role of a Crystallographically Unresolved Cytoplasmic Loop in Stabilizing the Bacterial Membrane Insertase YidC2

YidC, a bacterial member of the YidC/Alb3/Oxa1 insertase family, mediates membrane protein assembly and insertion. Cytoplasmic loops are known to have functional significance in membrane proteins such as YidC. Employing microsecond-level molecular dynamics (MD) simulations, we show that the crystallographically unresolved C2 loop plays a crucial role in the structural dynamics of Bacillus halodurans YidC2. We have modeled the C2 loop and used all- atom MD simulations to investigate the structural dynamics of YidC2 in its apo form, both with and without the C2 loop. The C2 loop was found to stabilize the entire protein and particularly the C1 region. C2 was also found to stabilize the alpha-helical character of the C-terminal region. Interestingly, the highly polar or charged lipid head groups of the simulated membranes were found to interact with and stabilize the C2 loop. These findings demonstrate that the crystallographically unresolved loops of membrane proteins could be important for the stabilization of the protein despite the apparent lack of structure, which could be due to the absence of the relevant lipids to stabilize them in crystallographic conditions.

Synthesis and characterization of acetyl curcumin-loaded core/shell liposome nanoparticles via an electrospray process for drug delivery, and theranostic applications

Despite substantial advancements in divergent drug delivery systems (DDS), there is still room for novel and innovative nanoparticle-mediated drug delivery methodologies such as core/shell liposomes to deliver drugs in a kinetically controlled manner into the active site without any side effects. Herein, ((1E,6E)-3,5-dioxohepta-1,6-diene-1,7-diyl) bis (2-methoxy-4,1-phenylene) diacetate acetyl curcumin (AC)-loaded poly(lactic-co-glycolic acid) (PLGA) core/shell liposome nanoparticles (ACPCSLNPs) were prepared using an electron spray method under an applied electric field, which facilitated the uniform formation of nano-sized liposome nanoparticles (LNPs). Then, kinetically controlled and sustained drug release profiles were investigated using the as-prepared ACPCSLNPs. Moreover, the inner polymeric core could not only induce the generation of electrostatic interactions between the polymer and drug molecules but could also affect the prominent repulsions between the polar head groups of lipids and the nonpolar drug molecules. As a result, the sustained maximum release of the drug molecules (~48.5%) into the system was observed over a long period (~4 days). Furthermore, cell cytotoxicity studies were conducted in a human cervical cancer cell line (HeLa) and a healthy human dermal fibroblast cell line (HDFa) by employing all AC loaded LNPs along with free drugs. Multicolor cell imaging was also observed in HeLa cells using ACPCSLNPs. Notably, more curcumin was released from the ACPCSLNPs than AC due to the presence of polar group attractions and polar-polar interactions between the lipid head groups and curcumin since curcumin is more soluble than AC in aqueous medium. In addition, the predictions of the release kinetic patterns were also investigated thoroughly using the exponential-based Korsmeyer-Peppas (K-P) and Higuchi models for drug-loaded LNPs and PLGA NPs, respectively.

Molecular-Level Insight into the Interactions of DNA/Polycation Complexes with Model Cell Membranes.

The interactions of DNA/polycation complexes (polyplexes) with cell membranes are crucial for understanding the molecular mechanisms behind polycation-mediated delivery of nucleic acid therapeutics into the target cells. In this study, we employed both biased and unbiased atomic-scale computer simulations to get an insight into such interactions. To this end, we considered complexes of DNA with linear polyethylenimine (PEI) with various polycation contents, ranging from an almost fully neutralized DNA to a highly overcharged polyplex. Our findings clearly show that the free energy gradually increases when a polyplex approaches the surface of a zwitterionic (neutral) phospholipid membrane from bulk water, implying the lack of attractive polyplex/membrane interactions. Remarkably, overcharging of DNA molecules by polycations enhances the repulsion between the polyplex and the zwitterionic lipid membrane. The observed repulsion is most likely driven by the dehydration of a polyplex upon its partitioning into the zwitterionic lipid membrane as well as by the loss of conformational entropy of PEI chains. We also demonstrate that cationic polymer chains are able to protect DNA from the dehydration as well as from contacts with lipid molecules. Interestingly, the absence of local minima in the free energy profiles does not exclude transient weak adsorption of a polyplex on the zwitterionic membrane surface. We show that such spontaneous adsorption can indeed be initiated by the interactions of loose polycation chains of the polyplex with polar head groups of lipids. Overall, our computational findings contribute considerably to the understanding of the initial stages in polycation-mediated DNA transfection. In particular, we demonstrate that a zwitterionic lipid bilayer represents an energetic barrier for polyplexes, so that a proper model of the cell membrane should account for the anionic surface charge of the membrane (e.g., due to the presence of proteoglycans).

Interactions of Lipid Polar Headgroups with Carbendazim Fungicide.

Carbendazim (MBC) is a fungicide widely used in agriculture which allows the high productivity of several cultures, a necessary condition considering the growing of the world population. Moreover, MBC has environmental impact mainly on the soil and water sources, and consequently, on animal and human lives. However, even though the toxicity of fungicides is well established, their action mechanism in cell membranes are not completely understood. Herein, we investigate the interaction of different polar headgroups: dimethyldioctadecylammonium bromide (DODAB), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG); and different chain unsaturation degrees DPPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) with MBC. Lipid monolayers at the air/water interface were applied as mimetic systems of cell membranes to investigate the interaction with MBC dissolved in the ultrapure water subphase. It was found that the interaction is driven preferably by electrostatic forces of the headgroups, with higher affinity for DODAB (cationic), intermediate for DPPC (zwitterionic), and absent for DPPG (anionic), considering the monolayer in the condensed phase. DODAB-MBC electrostatic interaction was consistent with FTIR (cast films). We also investigated giant unilamellar vesicles (GUVs) of zwitterionic lipids (DPPC, POPC, and DOPC) with distinct chain unsaturations in the presence of MBC by confocal microscopy and molecular dynamic (MD) simulations. The results indicate that, unlike the chain unsaturation, the polar headgroups play key role on the lipid-MBC interaction.