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Highlights • Biomimetic membranes are prepared using the natural myriad of each lipid structures that constitute the bacterial membrane. • The biomimetic membranes are very elastic due to the presence of several unsaturations in the lipids structures. • The model membranes present the same physical state and minor rigidity differences regardless the PE:PG or PE:CL ratio. • The similar rigidity suggests that the changes in the lipid composition may influence the membrane proteins function. Abstract Novel antimicrobial agents are focused to interact with the bacterial membrane whose lipid composition (number and position of unsaturations and lipid headgroup) is adapted according to environmental signals. The anticipation of the adapted membrane properties is of high relevance to increase the targetability of such drugs. Herein, natural lipids extracted from Escherichia coli -phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL)- are used to form biomimetic membranes constituted by several PE:lipid ratios using the Langmuir and Langmuir-Blodgett techniques. The use of these techniques and the natural myriad of each lipid structures that constitute the biological E.coli membrane establishes a simple and reproducible model to evaluate the lipid-lipid interactions. PE and PG present similar shape and size, thus establish ideal and fluid -liquid expanded (LE) state - mixtures, whereas the differences between PE and CL motivate the formation of non-ideal and fluid (LE state) mixtures. The same physical state and the minor differences in elasticity (differences in the inverse of the compressibility modulus < 15 mN·m−1) between both systems regardless the PE content in the (PE:lipid) mixture suggest that the changes in the lipid composition influence the membrane proteins function rather than affecting the rigidity of the bacterial membrane. [ABSTRACT FROM AUTHOR]

The transformation of penicillin G into nano/micro-sized spheres (nanopenicillin) using sonochemical technology was explored as a novel tool for the eradication of Gram-negative bacteria and their biofilms. Known by its effectiveness only against Gram-positive microorganisms, the penicillin G spherization boosted the inhibition of the Gram-negative Pseudomonas aeruginosa 10-fold (from 0.3 to 3.0 log-reduction) and additionally induced 1.2 log-reduction of Escherichia coli growth. The efficient penetration of the spheres within a Langmuir monolayer sustained the theory that nanopenicillin is able to cross the membrane and reach the periplasmic space in Gram-negative bacteria where they inhibit the β-lactam targets: the transferases that build the bacteria cell wall. Moreover, it considerably suppressed the growth of both bacterial biofilms on a medically relevant polystyrene surface, leaving majority of the adhered cells dead compared to the treatment with the non-processed penicillin G. Importantly, nanopenicillin was found innocuous towards human fibroblasts at the antibacterial-effective concentrations. [ABSTRACT FROM AUTHOR]

• Lipid-containing artificial tears can be studied with the Langmuir technique. • Interactions between natural tear components and lipid tears can be investigated. • Albumin and lysozyme proteins interact strongly with lipid tear products. • The influence of albumin and lysozyme on lipid π-A isotherms, at pH of 7.4, is opposite. • The natural tear components affects the fluidity of the lipid layer. We studied the behaviour of three lipid tear products, commercialised by the same brand, as Langmuir films at the air/liquid interface to simulate the ocular environment. No significant differences were observed in the surface behaviour of two of them disclosing the same composition, but commercialised for different applications. The interaction of several subphases, namely sodium chloride, glucose, albumin and lysozyme present in the natural tear, with the lipid films was assessed at room temperature and the temperature of human tear using surface pressure-area isotherms and elastic modulus plots. There is a notable influence of sodium chloride and the proteins albumin and lysozyme on the surface pressure-area isotherm of the lipid Langmuir films. Albumin shifted this isotherm to lower areas while an opposite shift was caused by lysozyme. These studies could be useful for the formulation of new lipid-containing artificial tears, and for increasing the confidence of the customers in commercial eye care formulations. [ABSTRACT FROM AUTHOR]

• DMSO expands the area per lipid for DPPC, but causes compression for POPC, highlighting species dependent effects. • Ethylene glycol and glycerol expand monolayers regardless of lipid species, implying they insert into the headgroup region. • Dimethylformamide compresses the monolayer for all lipid species, implying it dehydrates the lipid head groups. • Under physiological conditions, the penetrating action of cryoprotectants may only occur for unsaturated phospholipids. The influence of four common cryoprotectants (dimethyl sulfoxide, glycerol, ethylene glycol and dimethylformamide) on monolayers of four common phospholipids (DPPC, DOPC, POPC and POPE) have been studied using Langmuir isotherms and monolayer insertion experiments. The cryoprotectant concentrations were chosen to be directly relevant to cryoprotection. We show that DMSO causes an expansion of the DPPC area per lipid (in contrast to previous work at higher concentrations). However, it caused compression for POPC, and had little effect for POPE or DOPC. As most previous studies have involved only DPPC, this highlights the importance of studying different lipid types as these may have a significant effect on the interactions. We show that both ethylene glycol and glycerol cause a small expansion of the monolayer at fixed pressure, implying that they insert into the headgroup regions, regardless of lipid species, and consistent with their ability to penetrate membranes. By contrast, dimethylformamide causes monolayer compression for all lipid species, implying it dehydrates the lipid head groups. Membrane insertion experiments at physiological values of lateral pressure highlight that DPPC is the most difficult lipid to penetrate, implying that the penetrating action of cryoprotectants may only occur for unsaturated phospholipids. Thus, extrapolations of results based solely on the DPPC need to be made with care. [ABSTRACT FROM AUTHOR]

The photosynthesis is the process used by plants and bacteria cells to convert inorganic matter in organic thanks to the light energy. This process consist on several steps, being one of them the electronic transport from the photosystem II to the cytochrome thanks to plastoquinone-9 (PQ). Here we prepare membranes that mimic the characteristics and composition of natural photosynthetic cell membranes and we characterize them in order to obtain the PQ molecules position in the membrane and their electrochemical behaviour. The selected galactolipid is digalactosyldiacylglycerol (DGDG) that represents the 30% of the thylakoid membrane lipid content. The results obtained are worthful for several science fields due to the relevance of galactolipids as anti-algal, anti-viral, anti-tumor and anti-inflammatory agents and the antioxidant and free radical scavenger properties of prenylquinones. Both pure components (DGDG and PQ) and the DGDG:PQ mixtures have been studied using surface pressure–area isotherms. These isotherms give information about the film stability and indicate the thermodynamic behaviour of the mixture and their physical state. The Langmuir–Blodgett (LB) film has been transferred forming a monolayer that mimics the bottom layer of the biological membranes. This monolayer on mica has been topographically characterized using AFM and both the height and the physical state that they present have been obtained. Moreover, these monolayers have been transferred onto ITO that is a hydrophilic substrate with good optical and electrical features, so that, it is suitable for studying the electrochemical behaviour of these systems and it is a good candidate for energy producing devices. [ABSTRACT FROM AUTHOR]

The antibacterial activity of chitosan modified with the thiol-containing 2-iminothiolane HCl (TC-IMI) and N-acetyl-l-cysteine (TC-NAC) was studied by Langmuir film balance technique using a dipalmitoylphosphatidylglycerol (DPPG) monolayer bacterial membrane model. The interactions of the biopolymer with the membrane model were assessed by monitoring the differences in the shape of the compression isotherms recorded in the absence and presence of chitosan and thiolated conjugates in the subphase. A low molecular weight chitosan (15kDa) shifted the compression isotherms of DPPG monolayers towards larger areas (A 0,CS =145Å2), confirming its membrane disturbance capacity. Further thiolation induced higher yield of expansion, more pronounced in the case of TC-IMI. The expansion of the monolayer increased significantly (A 0,TC-NAC =150Å2 vs A 0,TC-IMI =175Å2) and the elasticity at a surface pressure of 30mN/m, typical for bio-membranes decreased to a greater extent =120mN/mvs =87mN/m) in presence of TC-IMI. Antibacterial tests against a Gram-negative Escherichia coli and a Gram-positive Staphylococcus aureus were in good agreement with these findings, suggesting that chitosan thiolated with 2-iminothiolane HCl acts as a bactericide disrupting the integrity of the bacterial cell membrane. [ABSTRACT FROM AUTHOR]