Chitosan as a subphase disturbant of membrane lipid monolayers. The effect of temperature at varying pH: I. DPPG

Effect of high sodium ion level on the interaction of AmB with a cholesterol-rich phospholipid monolayer

Invasive fungal infections are a primary reason for high mortality in immunocompromised people, especially in critically ill patients, such as intensive care unit (ICU) patients, advanced cancer patients, or severe burn patients. Hypernatremia also can increase mortality in severely ill patients. Amphotericin B (AmB) is the gold standard for treating infections, but in severely ill patients, AmB can cause hematotoxicity when administered intravenously due to its interaction with cholesterol on red blood cell membranes. This results in limited doses of AmB and affects the treatment of infections. The proportion of cholesterol molecules in membrane lipids in red blood cells is as high as 50 mol%, and the sodium ions can influence the interaction between AmB and lipids on the membrane. Therefore, in the complex clinical situation of a severely ill patient with a fungal infection and hypernatremia, the interaction between amphotericin B and the red blood cell membranes is worth studying in depth. In this work, the interaction between AmB and the dipalmitoyl phosphatidylcholine (DPPC)/cholesterol mixed monolayer in the presence of high sodium ion levels was studied when the proportion of cholesterol was 50%. The results show that the effect of AmB on reducing the monolayer's area at a high level of sodium ions is slightly stronger at 30 mN/m. The effect of AmB on reducing the elastic modulus of the DPPC/Chol monolayer is significantly weakened by a high sodium ion level, compared with the level of sodium ions at normal physiological concentration. The higher the sodium ion concentration, the weaker the intermolecular force of the DPPC/Chol/AmB mixed monolayers. The scanning electron microscope (SEM) and atomic force microscopy (AFM) observations suggest that at a high sodium ion level, the presence of AmB significantly reduces the surface roughness of the DPPC/Chol monolayer. AmB may bind to cholesterol molecules, and it isolates cholesterol from the monolayer, resulting in a reduced height of the cholesterol-rich monolayer and an increasingly dispersed monolayer region. The results are beneficial to understanding the mechanism of impact of a high sodium ion level on the relationship between AmB and red blood cell membranes rich in cholesterol and are valuable for understanding the hemolytic toxicity of AmB to red blood cells at a high sodium ion level.

Effect of Amphotericin B on the Thermodynamic Properties and Surface Morphology of the Pulmonary Surfactant Model Monolayer during Respiration

During the COVID-19 pandemic, the treatment of pulmonary fungal infection faced noteworthy challenges. Amphotericin B has shown promising therapeutic effects as an inhalation treatment for pulmonary fungal infections, especially those associated with the COVID-19 virus, due to its rare resistance. However, because the drug frequently produces renal toxicity, its effective dose is limited in clinical use. In this work, the DPPC/DPPG mixed monolayer was used as the pulmonary surfactant monolayer to study the interaction between amphotericin B and the pulmonary surfactant monolayer during inhalation therapy using the Langmuir technique and atomic force microscopy. The effects of different molar ratios of AmB on the thermodynamic properties and surface morphology of the pulmonary surfactant monolayer at different surface pressures was evaluated. The results showed that when the molar ratio of AmB to lipids in the pulmonary surfactant was less than 1:1, the main intermolecular force was attractive at a surface pressure greater than 10 mN/m. This drug had little effect on the phase transition point of the DPPC/DPPG monolayer, but decreased the height of the monolayer at 15 mN/m and 25 mN/m. When the molar ratio of AmB to lipids was greater than 1:1, the intermolecular force was mainly repulsive at a surface pressure greater than 15 mN/m, and AmB increased the height of the DPPC/DPPG monolayer at both 15 mN/m and 25 mN/m. These results are helpful in understanding the interaction between the pulmonary surfactant model monolayer and different doses of drugs at various surface tensions during respiration.

Effect of Trastuzumab on the thermodynamic behavior and roughness of fluid membrane using unsaturated phospholipid/cholesterol mixed monolayer model

The microenvironment near the receptor on biological membrane plays an important role in regulating drug-receptor interaction, and the interaction between drugs and lipids on membrane can also affect the microenvironment of membrane, which may affect drugs' efficacy or cause the drug resistance. Trastuzumab (Tmab) is a monoclonal antibody, used to treat early breast cancer associated with the overexpression of Human Epidermal growth factor Receptor 2 (HER2). But its effectiveness is limited due to its tendency to make tumor cells resistant to the drug. In this work, the monolayer mixed by unsaturated phospholipids (DOPC, DOPE and DOPS) and cholesterol were used as a model to simulate the fluid membrane region on biological membrane. The phospholipid/cholesterol mixed monolayers in molar ratio 7:3 and 1:1, were respectively used to simulate the one layer of simplified normal cell membrane and tumor cell membrane. The influence of this drug on the phase behavior, elastic modulus, intermolecular force, relaxation and the surface roughness of the unsaturated phospholipid/cholesterol monolayer was investigated. The results show that at 30 mN/m the increase or decrease of the elastic modulus and surface roughness of the mixed monolayer caused by Tamb depends on the type of phospholipid, but the intensity of the effect depends on the content of cholesterol, and the intensity of influence is more significant at the presence of 50% cholesterol. However, the effect of Tmab on the ordering of the DOPC/cholesterol or DOPS/cholesterol mixed monolayer is stronger when the content of cholesterol is 30%, but it was stronger for the DOPE/cholesterol mixed monolayer when the content of cholesterol is 50%. This study is helpful to understand the effects of anticancer drugs on microenvironment of cell membrane, and it has a certain reference value for the design of drug delivery system and drug target identification.

Surface characterization and interfacial activity of chitinase chi18-5 against chitosan in langmuir monolayers

One of the challenges for producing active chitinase formulations relies on the gap between the laboratory tests and the biological scenarios where the enzyme will perform its function. In this work, we have employed different Langmuir monolayer arrays to evaluate the interfacial behavior of a recently purified recombinant chitinase, Chi18-5. We have demonstrated that two conformations exist for the chitinase at pH values close to its pI, showing very distinct structural properties at the air/aqueous interface. Enzyme activity was assessed by implementing different kinetic approaches and using a chitosan-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed film as organized substrate model membrane. Combining these strategies, we demonstrated that better catalytic efficiencies can be obtained for Chi18-5 at pH 5. Moreover, the chitinase activity at the air/aqueous interface can be tuned by introducing in situ pH modifications over the surrounding milieu. We also studied the changes in the topography at the mesoscale level using Brewster Angle Microscopy (BAM). We found that Chi18-5 segregated onto the chitosan domains of the membrane, showing differences in homogeneity depending on the pH imposed. Alternatively, pure Chi18-5 was tested for immobilization onto a hydrophilic activated solid support using the Langmuir-Blodgett technique. Atomic Force Microscopy (AFM) analyses showed successfully stabilization and preservation of molecular features attributed to the pH at which the enzyme deposition was performed.

Regulation of calcium ions on the interaction between amphotericin B and cholesterol-rich phospholipid monolayer in LE phase and LC phase

Amphotericin B, as a "gold standard", is used to treat invasive fungal infections. The AmB molecule can bind easily to cholesterol and damage cell membranes, so it produces the toxicity on cell membrane, which limits its clinical dose. However, the interaction between AmB and cholesterol-rich membrane is unclear now. The phase state of the membrane and the metal cation outside cell membrane may affect the interaction between AmB and the membrane. In this work, the effects of amphotericin B on the mean molecular area, elastic modulus and stability of mammalian cell membrane rich in cholesterol in the presence of Ca²⁺ ions were studied using DPPC/Chol mixed Langmuir monolayer as a model. The Langmuir-Blodgett method and AFM test were used to study the effects of this drug on the morphology and height of cholesterol-rich phospholipid membrane in the presence of Ca²⁺ ions. The influence of calcium ions on the mean molecular area and the limiting molecular area was similar in LE phase and in LC phase. The calcium ions made the monolayer more condensed. However, calcium ions can weaken the shortening effect of AmB on the relaxation time of the DPPC/Chol mixed monolayer in LE phase but enhance it in LC phase. Interestingly, calcium ions caused a LE-LC coexistence phase to occur in the DPPC/Chol/AmB mixed monolayers at 35mN/m, which was confirmed by atomic force microscopy. The results can help to understand the interaction between amphotericin B and cell membrane rich in cholesterol in the calcium ions environment.

Effect of naproxen on the model lipid membrane formed on the water-chitosan subphase

Non steroidal anti-inflammatory drugs (NSAIDs) are those of the most common over the counter (OTC) medications widely used by millions of people every day. Unfortunately, despite their popularity those drugs can cause serious side effects in the digestive system (ulcers, bleeding, and pain). These inconveniences are caused by the changes in the structures of the outer phospholipid layers of gastric mucus and mucosa. As a result the H⁺ ions from the stomach acid can pass easily through these natural protective barriers and damage the epithelial cells which causes ulcers and bleeding. Chitosan as a polysaccharide known for its unique biocompatibility, drug delivery possibilities and wound healing effect has been chosen to examine if it can induce the reduction of undesirable effects of naproxen. This paper focuses on the interactions of the naproxen with a model biological membrane with and without the presence of chitosan. Applying the Langmuir technique coupled with the surface potential measurements and the Brewster angle microscope imaging allowed to characterize successfully examined systems in terms of the monolayer compressibility, thickness, stability, electric properties and morphology. The results proved that the presence of naproxen alters the mechanical and electrical properties of the model membrane depending on its surface pressure. Moreover, the addition of chitosan to the lipid-drug system causes significant changes in the properties of the layer, i.e. a reduction of its compressibility, thickness and morphology modification. Nevertheless, chitosan suppresses some changes induced by naproxen such as alteration of the apparent dipole moment and film stability.

Interaction mechanism of chitosan oligomers in pure water with cell membrane models studied by SFG vibrational spectroscopy

Chitosan is a versatile and biocompatible cationic antimicrobial polymer obtained from sustainable sources that is effective against a wide range of microorganisms. Although it is soluble only at low pH, chitosan oligomers (ChitO) are soluble in pure water and thus more appropriate for antibacterial applications. Although there is a vast literature on chitosan's antimicrobial activity, the molecular details of its interaction with biomembranes remain unclear. Here we investigate these molecular interactions by resorting to phospholipid Langmuir films (zwitterionic DPPC and anionic DPPG) as simplified membrane models (for mammalian and bacterial membranes, respectively), and using SFG vibrational spectroscopy to probe lipid tail conformation, headgroup dynamics and interfacial water orientation. For comparison, we also investigate the interactions of another simple cationic antimicrobial polyelectrolyte, poly(allylamine) hydrochloride - PAH. By forming the lipid films over the polyelectrolyte solutions, we found that both have only a very small interaction with DPPC, but PAH adsorption is able to invert the interfacial water orientation (membrane potential). This might explain why ChitO is compatible with mammalian cells, while PAH is toxic. In contrast, their interaction with DPPG films is much stronger, even more so for ChitO, with both insertion within the lipid film and interaction with the oppositely charged headgroups. Again, PAH adsorption inverts the membrane potential, while ChitO does not. Finally, ChitO interaction with DPPG is weaker if the antimicrobial is injected underneath a pre-assembled Langmuir film, and its interaction mode depends on the time interval between end of film compression and ChitO injection. These differences between ChitO and PAH effects on the model membranes highlight the importance of molecular structure and intermolecular interactions for their bioactivity, and therefore this study may provide insights for the rational design of more effective antimicrobial molecules.

Chitosan effects on monolayers of zwitterionic, anionic and a natural lipid extract from E. coli at physiological pH

Langmuir monolayers are used to simulate the biological membrane environment, acting as a mimetic system of the outer or the inner membrane leaflet. Herein, we analyze the interaction of membrane models with a partially N-acetylated chitosan (Ch35%) possessing a quasi-ideal random pattern of acetylation, full water solubility up to pH ≈ 8.5 and unusually high weight average molecular weight. Lipid monolayers containing dipalmitoyl phosphatidyl choline (DPPC), dipalmitoyl phosphatidyl ethalonamine (DPPE), dipalmitoyl phosphatidyl glycerol (DPPG) or E. coli total lipid extract were spread onto subphases buffered at pH 4.5 or 7.4. The incorporation of Ch35% chitosan caused monolayer expansion and a general trend of decreasing monolayer rigidity with Ch35% concentration. Due to its relatively high content of N-acetylglucosamine (GlcNAc) units, Ch35% interactions with negatively charged monolayers and with E. coli extract were weaker than those involving zwitterionic monolayers or lipid rafts. While the smaller interaction with negatively charged lipids was unexpected, this finding can be attributed to the degree of acetylation (35%) which imparts a small number of charged groups for Ch35% to interact. Chitosan properties are therefore determinant for interactions with model cell membranes, which explains the variability in chitosan bactericide activity in the literature. This is the first study on the effects from chitosans on realistic models of bacterial membranes under physiological pH.

Calcium bridging drives polysaccharide co-adsorption to a proxy sea surface microlayer

Saccharides comprise a significant mass fraction of organic carbon in sea spray aerosol (SSA), but the mechanisms through which saccharides are transferred from seawater to the ocean surface and eventually into SSA are unclear. It is hypothesized that saccharides cooperatively adsorb to other insoluble organic matter at the air/sea interface, known as the sea surface microlayer (SSML). Using a combination of surface-sensitive infrared reflection-absorption spectroscopy and all-atom molecular dynamics simulations, we demonstrate that the marine-relevant, anionic polysaccharide alginate co-adsorbs to an insoluble palmitic acid monolayer via divalent cationic bridging interactions. Ca2+ induces the greatest extent of alginate co-adsorption to the monolayer, evidenced by the ∼30% increase in surface coverage, whereas Mg2+ only facilitates one-third the extent of co-adsorption at seawater-relevant cation concentrations due to its strong hydration propensity. Na+ cations alone do not facilitate alginate co-adsorption, and palmitic acid protonation hinders the formation of divalent cationic bridges between the palmitate and alginate carboxylate moieties. Alginate co-adsorption is largely confined to the interfacial region beneath the monolayer headgroups, so surface pressure, and thus monolayer surface coverage, only changes the amount of alginate co-adsorption by less than 5%. Our results provide physical and molecular characterization of a potentially significant polysaccharide enrichment mechanism within the SSML.

Aligned Assembly in a 2-D Gel of a Water-Soluble Peptide

We demonstrate the assembly of a compact, gel-like Langmuir-Blodgett film of rods formed by self-assembly of a β-sheet-forming water-soluble peptide, Ac-IKHLSVN-NH₂, at the surface of aqueous electrolytes. We characterize surface pressure hysteresis and demonstrate shear stiffening of the surface caused by area cycling, which we interpret as due to rearrangement and alignment of the rods. We show strong effects of the electrolyte on the assembly of the elementary rods, which can be related to the Hofmeister series and interpreted by effects on the interaction energies mediated by ions and water. Formation of β-sheet structures and assembly of these into surface-segregated semicrystalline gels was strongly promoted by ammonium sulfate electrolyte. With ammonium sulfate electrolyte as subphase for Langmuir-Blodgett film deposition, shear stiffening by surface area cycling resulted in very compact films on transfer to a substrate.

Study of the Mechanism of the Antimicrobial Activity of Novel Water Soluble Ammonium Quaternary Benzanthrone on Model Membranes

The increasing resistance of many pathogens to most of the common antimicrobials requires the development of new substances with more effective antimicrobial properties. In the present work, we investigated the mechanism of the antimicrobial activity of novel water soluble ammonium quaternary benzanthrone (Compound B) on model membranes, composed of dipalmitoylphosphatidylcholine, 1-palmitoyl-2-oleoylphosphatidylcholine, dipalmitoylphosphatidylglycerol, 1-palmitoyl-2-oleoylphosphatidylglycerol, and dipalmitoylphosphatidylethanolamine (DPPE). The lipids were chosen to represent a model of a bacterial membrane. The changes in surface pressure of the model membranes, before and after the addition of Compound B, were studied by the Langmuir's monolayer method, and the compressional modulus for each monolayer was determined. In addition, the surface morphology of the lipid monolayers before and after injection of Compound B was monitored by Brewster Angle Microscopy. The results showed that Compound B penetrated all the monolayers studied. The most noticeable effects were found with the negatively charged phosphatidylglycerols and with DPPE leading to the conclusion that the electrostatic interactions between the compound and the lipid head groups and the possible formation of hydrogen bonds between the amino group of the ethanolamine and the keto groups in the structure of Compound B are of great importance. In addition, the penetration ability of the benzoquinone with all phospholipids studied was stable even at higher values of the surface pressure, i.e. thicker monolayers, due to the hydrophobic interaction, which plays also an important role for the antimicrobial activity of Compound B.

Interaction of Silver-Lignin Nanoparticles With Mammalian Mimetic Membranes

Silver nanoparticles (AgNPs) have broad spectrum antibacterial activity, but their toxicity to human cells has raised concerns related to their use as disinfectants or coatings of medically relevant surfaces. To address this issue, NPs comprising intrinsically bactericidal and biocompatible biopolymer and Ag with high antibacterial efficacy against common pathogens and compatibility to human cells have been engineered. However, the reason for their lower toxicity compared to AgNPs has not yet been elucidated. This work studies the in vitro interaction of AgLNPs with model mammalian membranes through two approaches: (i) Langmuir films and (ii) supported planar bilayers studied by quartz crystal microbalance and atomic force spectroscopy. These approaches elucidate the interactions of AgLNPs with the model membranes indicating a prominent effect of the bioresourced lignin to facilitate the binding of AgLNPs to the mammalian membrane, without penetrating through it. This study opens a new avenue for engineering of hybrid antimicrobial biopolymer – Ag or other metal NPs with improved bactericidal effect whereas maintaining good biocompatibility.

Interaction of chitosan derivatives with cell membrane models in a biologically relevant medium

HYPOTHESIS

The interaction of chitosan, a natural biopolymer with various biomedical applications, with lipid Langmuir films has been widely investigated as a simple model for cell membranes. However, to ensure polymer solubility, up to now only acidic subphases with pH significantly below biological fluids have been used. To increase the biological significance of these investigations, here we evaluated the effects of two chitosan derivatives (low molecular weight - CH, and positively charged - CH-P40) on phospholipid films (either zwitterionic DPPC or anionic DPPG) using phosphate buffered saline solutions (PBS) as a subphase.

EXPERIMENTS

Surface pressure - area (π-A) isotherms were used to evaluate the expansion and changes in film elasticity, while Sum-Frequency Generation (SFG) vibrational spectroscopy provided information about the chain conformation of lipids.

FINDINGS

It was found that chitosans caused a small expansion of the DPPC film by its insertion within the monolayer. In contrast, they distinctly expanded DPPG monolayers by both chitosan insertion within the lipid monolayer and by interacting with the anionic head group. Therefore, PBS buffer can be used as a subphase for more biologically relevant studies of chitosan interactions with Langmuir films, shedding light on why chitosan is antibacterial but not toxic to mammals, as the interaction mechanism depends on lipid headgroup charge.

Functionalization of LC molecular films with nanocrystalline cellulose: A study of the self-assembly processes and molecular stability

The bottom-up approach in designing and synthesis of materials using nanoparticles of different size-, shape- or chemical composition is an extreme challenge. However, in this way, new task-specific or general use nanocomposites can be obtained. This work presents, the investigations of the preparation procedures and molecular stability of Langmuir films based on cellulose nanocrystals (CNC) and different liquid crystals. The CNC-based nanocomposite with the 5CB, 5OCB, 5FCB, and 5PCH liquid crystals, have been obtained by the modified Langmuir technique. The investigations of the Langmuir monolayers gives an excellent model system for studying intermolecular interactions at the interface, which allows analyzing the ordering, sorption, desorption, association and phase separation phenomena determining physical and chemical properties of studied systems. The process of self-assembly and molecular organization on the air-liquid interphase was studied for different compositions of LC/CNC films. The compressibility profiles and the mean molecular area have been calculated. The stability of prepared monolayers has been studied to investigate the sorption and desorption processes. The morphology of the prepared systems was determined by Brewster Angle Microscopy (BAM), and the influence of the CNC on LC organization in molecular monolayers on the air-liquid interphase has been studied.

Enhanced antioxidant and antifungal activity of chitosan derivatives bearing 6-O-imidazole-based quaternary ammonium salts

In this paper, a series of 6-O-imidazole-based quaternary ammonium chitosan derivatives via 6-O-chloroacetyl chitosan (CAClC) were successfully designed and synthesized. Detailed structural characterization was carried out by means of FT-IR and ¹H NMR spectroscopy, and elemental analysis. Furthermore, the antioxidant property against hydroxyl radicals, superoxide radicals, and DPPH radicals was evaluated in vitro. 2-(N,N,N-trimethyl)-6-O-(2-aminobenzimidazole)acetyl chitosan chloride (2NPhMC) and 2-(N,N,N-trimethyl)-6-O-(1-butylimidazole)acetyl chitosan chloride (NBMC) showed more than 90% scavenging indices at 1.6 mg/mL. Besides, the antifungal activity against Botrytis cinerea and Gibberella zeae was estimated using in vitro MIC and hypha measurements. Most of the quaternized chitosan derivatives especially with the long length alkyl chain and primary amino group showed an inhibitory index of > 85% at 1.0 mg/mL against Botrytis cinerea. Besides, the cytotoxicity of chitosan and all the quaternized chitosan derivatives was evaluated in vitro on HaCaT cells and all the quaternized chitosan derivatives bearing 6-O-imidazole exhibited low cytotoxicity. These results suggested that chitosan derivatives bearing 6-O-imidazole-based quaternary ammonium salts may be used as good biomaterials.

Synthesis, characterization, and antifungal evaluation of diethoxyphosphoryl polyaminoethyl chitosan derivatives

Botrytis cinerea, Phytophthora capsici Leonian, and Fusarium solani are important plant pathogenic fungi which can cause great crop losses worldwide, but their control methods are limited. It is necessary to develop efficient and green fungicides from abundant marine resources. Chitosan is a non-toxic, biodegradable, biocompatible marine polysaccharide which has prospective applications in agriculture. In this paper, to increase the antifungal activity of chitosan for application, novel water-soluble functional chitosan derivatives were synthesized by grafting polyaminoethyl and diethoxyphosphoryl groups in accordance with a strategy of improving protonation potential. The derivatives were characterized by FTIR, NMR, XRD, SEM, Gaussian 09 and elemental analysis. The antifungal activities against the three fungi and the cytotoxicity were estimated in vitro. The results showed that the derivatives had better antifungal activities and water solubility than chitosan, and had good biocompatibility. They confirmed that these chitosan derivatives can be developed as antifungal agents for plant protection purposes.

The interaction between BSA and DOTAP at the air-buffer interface

In this article, the interaction between bovine serum albumin (BSA) and the cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) at the air-buffer interface was investigated at different subphase's pH values (pH = 3, 5 and 10). Surface pressure measurements (π - A) and penetration kinetics process (π - t) were carried out to reveal the interaction mechanism and the dynamical behavior. The data showed that π - A isotherms moved towards larger mean molecular area when the concentration of BSA ([BSA]) increased, the amount of BSA adsorbed onto DOTAP monolayer reached a threshold value at a [BSA] of 5 × 10^-8 M, and BSA desorbed from the lipid monolayer as time goes by. The results revealed that the association of BSA with DOTAP at the air-buffer interface was affected by the subphase's pH value. When pH = 10, the interaction mechanism between them was a combination of hydrophobic interaction and electrostatic attraction, so BSA molecules could be well separated and purified from complex mixtures. AFM images demonstrated that pH value and [BSA] could affect the morphology feature of DOTAP monolayer and the adsorption and desorption processes of BSA. So the study provides an important experimental basis and theoretical support for learning the interaction mechanism among biomolecules in separation and purification of biomolecules and biosensor.

Effect of Laminaria japonica polysaccharides on lipids monolayers at the air-water surface

In this paper, we examined the effect of Laminaria japonica polysaccharides (LJP) on cationic 1,2-Dioleoyl-3-Trimethylammonium-Propane (DOTAP) and anionic 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-1-glycerol] (DPPG) monolayers at the air-water interface by the pressure-area isotherms (π-A), adsorption curves (π-t) and morphology measurements with atomic force microscopy (AFM) technique. The π-A curves revealed that the isotherms shifted to larger mean molecular area with progressive addition of LJP into subphase for both DOTAP and DPPG monolayers. And the compression modulus Cs-1 obtained from π-A curves showed that the elasticity of the films decreased with the addition of LJP. Adsorption curves were measured at the surface pressure of 10 and 20mN/m, which were fitted by the adsorption kinetics equation. It revealed that DOTAP monolayer changed into a mixed film with the insertion of polysaccharides molecules. However, there was no significant effect on the surface pressure for DPPG monolayer. Besides, surface morphology was observed by AFM, which was consistent with the results of fitted adsorption curves.

Synthesis of Benzyl Acetate Catalyzed by Lipase Immobilized in Nontoxic Chitosan-Polyphosphate Beads

Enzymes serve as biocatalysts for innumerable important reactions, however, their application has limitations, which can in many cases be overcome by using appropriate immobilization strategies. Here, a new support for immobilizing enzymes is proposed. This hybrid organic-inorganic support is composed of chitosan-a natural, nontoxic, biodegradable, and edible biopolymer-and sodium polyphosphate as the inorganic component. Lipase B from Candida antarctica (CALB) was immobilized on microspheres by encapsulation using these polymers. The characterization of the composites (by infrared spectroscopy, thermogravimetric analysis, and confocal Raman microscopy) confirmed the hybrid nature of the support, whose external part consisted of polyphosphate and core was composed of chitosan. The immobilized enzyme had the following advantages: possibility of enzyme reuse, easy biocatalyst recovery, increased resistance to variations in temperature (activity declined from 60 °C and the enzyme was inactivated at 80 °C), and increased catalytic activity in the transesterification reactions. The encapsulated enzymes were utilized as biocatalysts for transesterification reactions to produce the compound responsible for the aroma of jasmine.

Investigation of Surface Behavior of DPPC and Curcumin in Langmuir Monolayers at the Air-Water Interface

Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a mixture of DPPC with curcumin (CUR) have been investigated at the air-water interface through a combination of surface pressure measurements and atomic force microscopy (AFM) observation. By analyzing the correlation data of mean molecular areas, the compressibility coefficient, and other thermodynamic parameters, we obtained that the interaction between the two components perhaps was mainly governed by the hydrogen bonding between the amino group of DPPC and the hydroxyl groups of CUR. CUR markedly affected the surface compressibility, the thermodynamic stability, and the thermodynamic phase behaviors of mixed monolayers. The interaction between CUR and DPPC was sensitive to the components and the physical states of mixed monolayers under compression. Two-dimensional phase diagrams and interaction energies indicated that DPPC and CUR molecules were miscible in mixed monolayers. AFM images results were in agreement with these analyses results of experimental data. This study will encourage us to further research the application of CUR in the biomedical field.

Essential oils as food eco-preservatives: Model system studies on the effect of temperature on limonene antibacterial activity

Antimicrobial properties of essential oils predestine these substances to be used as ecological food preservatives. However, their activity is determined by variety of factors among which external conditions and food properties are highly important. Herein the influence of limonene on artificial membranes was studied to verify the effect of temperature on the incorporation of this compound into model bacterial membrane. The investigations were done on lipid monolayers and the experiments involved the surface pressure-area measurements, penetration studies and Brewster Angle Microscopy analysis. It was found that limonene incorporates into lipid monolayers causing their fluidization. However, the magnitude of alterations depends on limonene concentration, model membrane composition and, for a given composition, on system condensation. Moreover, the influence of limonene is stronger at lower temperatures and, in the light of collected data, this may be a consequence of strong volatility and evaporation of limonene increasing with temperature.

Co-assembly in chitosan-surfactant mixtures: thermodynamics, structures, interfacial properties and applications

In this review, different aspects characterizing chitosan-surfactant mixtures are summarized and compared. Chitosan is a bioderived cationic polysaccharide that finds wide-ranged applications in various field, e.g., medical or food industry, in which synergistic effects with surfactant can play a fundamental role. In particular, the behavior of chitosan interacting with strong and weak anionic, nonionic as well as cationic surfactants is reviewed. We put a focus on oppositely charged systems, as they exhibit the most interesting features. In that context, we discuss the thermodynamic description of the interaction and in particular the structural changes as they occur as a function of the mixed systems and external parameters. Moreover, peculiar properties of chitosan coated phospholipid vesicles are summarized. Finally, their co-assembly at interfaces is briefly reviewed. Despite the behavior of the mentioned systems might strongly differ, resulting in a high variety of properties, few general rules can be pointed out which improve the understanding of such complex systems.

Insights into chitosan multiple functional properties: the role of chitosan conformation in the behavior of liposomal membrane

Interactions of chitosan with liposomes correlate with multiple functionalities. Chitosan chains can self-aggregate above a critical aggregation concentration. The physical properties of liposomes are affected by chitosan conformation. Chitosan displays “polymeric surfactant property” in the form of coils.

Electrospinning an essential oil: cinnamaldehyde enhances the antimicrobial efficacy of chitosan/poly(ethylene oxide) nanofibers

Due to the persistent spread of antibiotic resistance, commercial antibiotic treatments are proving ineffective. Cinnamaldehyde (CA), a volatile essential oil, eradicates pathogens non-specifically. However, the ability to incorporate essential oils into nanofiber mats has not yet been demonstrated, and, only six studies have electrospun two immiscible phases. Here, CA (0.5 and 5.0%) was incorporated into chitosan/poly(ethylene oxide) (PEO) solutions that were successfully electrospun into mats with ∼ 50 nm fiber diameters. Solid-state NMR results corroborated with release studies wherein the 5.0% CA mats released a statistically higher amount of CA-liquid (545% more) and CA-vapor (279% more) than the 0.5% CA mats. In time dependent cytotoxicity studies, the intrinsic antibacterial activity of chitosan along with the quick release of CA enabled high inactivation rates against Escherichia coli and Pseudomonas aeruginosa. For the first time we have demonstrated chitosan/CA/PEO nanofiber mats can serve as CA delivery vehicles that potentially eradicate pseudomonas infections.

Effect of structure on the interactions between five natural antimicrobial compounds and phospholipids of bacterial cell membrane on model monolayers

Monolayers composed of bacterial phospholipids were used as model membranes to study interactions of the naturally occurring phenolic compounds 2,5-dihydroxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde, and the plant essential oil compounds carvacrol, cinnamaldehyde, and geraniol, previously found to be active against both Gram-positive and Gram-negative pathogenic microorganisms. The lipid monolayers consist of 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE), 1,2-dihexa- decanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), and 1,1',2,2'-tetratetradecanoyl cardiolipin (cardiolipin). Surface pressure–area (π-A) and surface potential–area (Δψ-A) isotherms were measured to monitor changes in the thermodynamic and physical properties of the lipid monolayers. Results of the study indicated that the five compounds modified the three lipid monolayer structures by integrating into the monolayer, forming aggregates of antimicrobial –lipid complexes, reducing the packing effectiveness of the lipids, increasing the membrane fluidity, and altering the total dipole moment in the monolayer membrane model. The interactions of the five antimicrobial compounds with bacterial phospholipids depended on both the structure of the antimicrobials and the composition of the monolayers. The observed experimental results provide insight into the mechanism of the molecular interactions between naturally-occurring antimicrobial compounds and phospholipids of the bacterial cell membrane that govern activities.

Processing of α-chitin nanofibers by dynamic high pressure homogenization: characterization and antifungal activity against A. niger

Chitin nano-objects become more interesting and attractive material than native chitin because of their usable form, low density, high surface area and promising mechanical properties. This work suggests a straightforward and environmentally friendly method for processing chitin nanofibers using dynamic high pressure homogenization. This technique proved to be a remarkably simple way to get α-chitin into α-chitin nanofibers from yellow lobster wastes with a uniform width (bellow 100 nm) and high aspect ratio; and may contributes to a major breakthrough in chitin applications. Moreover, the resulting α-chitin nanofibers were characterized and compared with native α-chitin in terms of chemical and crystal structure, thermal degradation and antifungal activity. The biological assays highlighted that the nano nature of chitin nanofibers plays an important role in the antifungal activity against Aspergillus niger.

Insights on the interactions of chitosan with phospholipid vesicles. Part I: Effect of polymer deprotonation

Interactions between the polysaccharide chitosan and negatively charged phospholipid liposomes were studied as a function of compositional and environmental conditions. Using isothermal titration calorimetry, different levels of deprotonation of chitosan in acidic solutions were attained with titration of the fully protonated polymer at pH 4.48 into solutions with increasing pH. The process was found to be highly endothermic. We then examined the interaction of the polymer with vesicles in solutions of different pH. Even when partially deprotonated, the chitosan chains retain their affinity to the negatively charged liposomes. However, the stronger adsorption results in lower organization of the chains over the membrane.

Interaction of O-acylated chitosans with biomembrane models: probing the effects from hydrophobic interactions and hydrogen bonding

One of the major challenges in establishing the mechanisms responsible for the chitosan action in biomedical applications lies in the determination of the molecular-level interactions with the cell membrane. In this study, we probed hydrophobic interactions and H-bonding in experiments with O,O'-diacetylchitosan (DACT) and O,O'-dipropionylchitosan (DPPCT) incorporated into monolayers of distinct phospholipids, the zwitterionic dipalmitoyl phosphatidyl choline (DPPC), and the negatively charged dipalmitoyl phosphatidyl glycerol (DPPG) and dimyristoyl phosphatidic acid (DMPA). The importance of hydrophobic interactions was confirmed with the larger effects observed for DACT and DPPCT than for parent chitosan (Chi), particularly for the more hydrophobic DPPCT. Such larger effects were noted in surface pressure isotherms and elasticity of the monolayers. Since H-bonding is hampered for the chitosan derivatives, which have part of their hydroxyl groups shielded by O-acylation, these effects indicate that H-bonding does not play an important role in the chitosan-membrane interactions. Using polarization-modulated infrared reflection absorption (PM-IRRAS) spectroscopy, we found that the chitosan derivatives were incorporated into the hydrophobic chain of the phospholipids, even at high surface pressures comparable to those in a real cell membrane. Taken together, these results indicate that the chitosan derivatives containing hydrophobic moieties would probably be more efficient than parent chitosan as antimicrobial agents, where interaction with the cell membrane is crucial.