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The effects of four cryoprotectants (dimethylformamide (DMF), ethylene glycol (EG), glycerol and dimethyl sulfoxide (DMSO)) on monolayers of four phospholipids were investigated at high cryoprotectant concentration (10% v/v) relevant to cryoprotection, and compared with previous work at lower concentrations (5% v/v). The results show that the interactions between cryoprotective agents (CPAs) and lipids are complex, with significant differences identified as functions of CPA, concentration and phospholipid species. It was observed that generally DMF and EG cause monolayer compaction, whereas glycerol causes expansion (penetrating the monolayer), although each exhibited subtle differences with different phospholipids. DMSO showed significant differences depending on the headgroup (phosphatidylcholine vs phosphatidylethanolamine) and the physical state of the monolayer. In addition, it was found that DMF was the only CPA capable of penetrating monolayers at physiologically relevant lateral pressures. The results highlight that conclusions based on a single model system (e.g. DPPC) should not be extrapolated to other lipids, and there is a need to study a wider range of lipid species and CPA concentrations in order to understand their mechanisms of action more fully. The interactions between four cryoprotectants and monolayers of four phospholipids were investigated. Significant differences are observed as functions of cryoprotectant, lipid species and physical state of the monolayer, highlighting that results based on a single model system are insufficient to understand the mechanisms of action of cryoprotectants. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] Pseudomonas aeruginosa bacteria originate severe infections in hospitalized patients and those with chronic debilitating diseases leading to increased morbidity and mortality, longer hospitalization and huge financial burden to the healthcare system. The clinical relevance of P. aeruginosa infections is increased by the capability of this bacterium to grow in biofilms and develop multidrug resistant mechanisms that preclude conventional antibiotic treatments. Herein, we engineered novel multimodal nanocomposites that integrate in the same entity antimicrobial silver nanoparticles (NPs), the intrinsically antimicrobial, but biocompatible biopolymer chitosan, and the anti-infective quorum quenching enzyme acylase I. Acylase present in the NPs specifically degraded the signal molecules governing bacterial cell-to-cell communication and inhibited by ∼ 55 % P. aeruginosa biofilm formation, while the silver/chitosan template altered the integrity of bacterial membrane, leading to complete eradication of planktonic bacteria. The innovative combination of multiple bacteria targeting modalities resulted in 100-fold synergistic enhancement of the antimicrobial efficacy of the nanocomposite at lower and non-hazardous towards human skin cells concentrations, compared to the silver/chitosan NPs alone. [ABSTRACT FROM AUTHOR]

Classical and atomistic nucleation models have been tested in several aqueous systems dealing with electrocrystallisation. A lot of reported experimental nucleation data have been used and in a wide range of overpotentials. The critical nucleus size has been calculated in those cases not reported in the original work, and the results obtained with the classical and atomistic models have been tabulated, compared and discussed. Small values for the critical nucleus size occur in most of the systems. [ABSTRACT FROM AUTHOR]

Abstract: Ubiquinone and plastoquinone are two of the main electron and proton shuttle molecules in biological systems, and monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in the thylakoid membrane of chloroplasts. Saturated MGDG, ubiquinone-10 (UQ) and MGDG:UQ mixed monolayers at the air/water interface have been studied using surface pressure–area isotherms and Brewster Angle Microscopy. Moreover, the transferred Langmuir–Blodgett films have been observed by Atomic Force Microscopy. The results show that MGDG:UQ mixtures present more fluid phase than pure MGDG, indicating a higher order degree for the later. It is also observed an important influence of UQ on the MGDG matrix before UQ collapse pressure and a low influence after this event, due to UQ expulsion from the MGDG matrix. This expulsion leads to a similar remaining UQ content for all the tested mixtures, indicating a limiting content of this molecule in the MGDG matrix at high surface pressures. The thermodynamic studies confirm the stability of the MGDG:UQ mixtures at low surface pressures, although presenting a non-ideal behaviour. Results point to consider UQ as a good candidate for studies of artificial photosynthesis. [Copyright &y& Elsevier]

• 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]

Abstract: The interaction of 1-palmitoy-2-oleoyl-sn-glycero-3-phosphocoline (POPC) and 1-palmitoy-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), two of the major components in biological membranes, were investigated using the monolayer technique at the air–water interface. The pressure–area isotherms indicate that both phospholipids are miscible through all range of compositions. POPE–POPC form stable mixtures, with a minimum for the Gibbs energy of mixing at X POPC =0.4. A virial equation of state was fitted to the experimental values. Positive values found for the second virial coefficient indicate repulsion between POPC and POPE. The interaction parameter was evaluated which indicated that a corresponding decrease in the repulsion occurs when POPC molar fraction is low. This effect suggests the existence of hydrogen bonds between POPE and the water beneath the interface. [Copyright &y& Elsevier]

• 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]

Abstract.: Artificial lipid bilayers have been extensively studied as models that mimic natural membranes (biomimetic membranes). Several attempts of biomimetic membranes inserting ubiquinone (UQ) have been performed to enlighten which the position of UQ in the lipid layer is, although obtaining contradictory results. In this work, pure components (DPPC and UQ) and DPPC:UQ mixtures have been studied using surface pressure-area isotherms and Langmuir-Blodgett (LB) films of the same compounds have been transferred onto solid substrates being topographically characterized on mica using atomic force microscopy and electrochemically on indium tin oxide slides. DPPC:UQ mixtures present less solid-like physical state than pure DPPC indicating a higher-order degree for the latter. UQ influences considerably DPPC during the fluid state, but it is mainly expelled after the phase transition at $ \approx$ 26 mN·m^-1 for the 5:1 ratio and at $ \approx$ 21 mN·m^-1 for lower UQ content. The thermodynamic studies confirm the stability of the DPPC:UQ mixtures before that event, although presenting a non-ideal behaviour. The results indicate that UQ position can be tuned by means of the surface pressure applied to obtain LB films and the UQ initial content. The UQ positions in the biomimetic membrane are distinguished by their formal potential: UQ located in 'diving' position with the UQ placed in the DPPC matrix in direct contact with the electrode surface ( -0.04±0.02 V), inserted between lipid chains without contact to the substrate ( 0.00±0.01 V) and parallel to the substrate, above the lipid chains ( 0.09±0.02 V). Graphical abstract: [ABSTRACT FROM AUTHOR]

In this work biomimetic monolayers of a MGDG, monogalactosyldiacylglycerol, and DGDG, digalactosyldiacylglycerol mixture (MD), in a ratio close to that of the thylakoid membranes of oxygenic photosynthetic organisms, have been prepared. The lipid mixture incorporates plastoquinone-9 (PQ), that is the electron and proton shuttle of the photosynthetic reaction centres. The MD:PQ mixtures have been firstly studied using surface pressure-area isotherms. Langmuir-Blodgett (LB) films of those mixtures have been transferred onto a substrate forming a monolayer that mimics one of the bilayer sides of the thylakoid membranes. These monolayers have been characterized topographically and electrochemically. The results show the influence of PQ in the MD matrix and its partial expulsion when increasing the surface pressure, obtaining two main PQ positions in the MD matrix. The calculated apparent electron transfer rate constants indicate a different kinetic control for the reduction and the oxidation of the PQ/PQH 2 couple, being k Rapp (I) = 0.7 · 10 − 6 s − 1 , k Rapp (II) = 2.2 · 10 − 9 s − 1 , k Oapp (I) = 7.4 · 10 − 4 s − 1 and k Oapp (II) = 5.2 · 10 − 5 s − 1 , respectively. The comparison of the different galactolipid:PQ systems that our group has studied is also presented, concluding that the PQ position in the galactolipid matrix can be tuned according to several controlled variables. [ABSTRACT FROM AUTHOR]

Abstract.: The relevance of biomimetic membranes using galactolipids has not been expressed in any extensive experimental study of these lipids. Thus, on the one hand, we present an in-depth article about the presence and role of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) in thylakoid membranes, their physical states and their applications. On the other hand, we use the Langmuir and Langmuir-Blodgett (LB) techniques to prepare biomimetic monolayers of saturated galactolipids MGDG, DGDG and MGDG:DGDG 2:1 mixture (MD)--biological ratio--. These monolayers are studied using surface pressure-area isotherms and their data are processed to enlighten their physical states and mixing behaviour. These monolayers, once transferred to a solid substrate at several surface pressures are topographically studied on mica using atomic force microscopy (AFM) and using cyclic voltammetry for studying the electrochemical behaviour of the monolayers once transferred to indium-tin oxide (ITO), which has good optical and electrical properties. Moreover, MD presents other differences in comparison with its pure components that are explained by the presence of different kinds of galactosyl headgroups that restrict the optimal orientation of the MGDG headgroups. Graphical abstract: [ABSTRACT FROM AUTHOR]

The electrochemical behaviour of biomimetic monolayers of monogalactosyldiacylglycerol (MGDG) incorporating ubiquinone-10 (UQ) has been investigated. MGDG is the principal component in the thylakoid membrane and UQ seems a good substitute for plastoquinone-9, involved in photosynthesis chain. The monolayers have been performed using the Langmuir and Langmuir–Blodgett (LB) techniques and the redox behaviour of the LB films, transferred at several surface pressures on a glass covered with indium–tin oxide (ITO), has been characterized by cyclic voltammetry. The cyclic voltammograms show that UQ molecules present two redox processes (I and II) at high UQ content and high surface pressures, and only one redox process (I) at low UQ content and low surface pressures. The apparent rate constants calculated for processes I and II indicate a different kinetic control for the reduction and the oxidation of UQ/UQH 2 redox couple, being k Rapp (I) = 2.2 · 10 − 5 s − 1 , k Rapp (II) = 5.1 · 10 − 14 k Oapp (I) = 3.3 · 10 − 3 s − 1 and k Oapp (II) = 6.1 · 10 − 6 s − 1 , respectively. The correlation of the redox response with the physical states of the LB films allows determining the positions of the UQ molecules in the biomimetic monolayer, which change with the surface pressure and the UQ content. These positions are known as diving and swimming. [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]

Photosyntheticorganisms use light to convert the inorganic matterin organic one. Photosynthetic process consists on several steps,and one of them involves plastoquinone (PQ) that acts as electronand proton shuttle between photosystem II and cytochrome. We preparedmembranes that mimic the characteristics and composition of naturalphotosynthetic membranes and we characterized them using several techniquesin order to obtain both the PQ molecules disposition in the membraneand their electrochemical behavior. The selected lipid was monogalactosyldiacylglycerol(MGDG) that represents the 50% of the lipid content of the thylakoidmembrane. Both MGDG and PQ, and the MGDG:PQ mixtures have been studiedusing surface pressure–area isotherms and the presence of PQalters the physical state and compactness of the MGDG matrix. Langmuir–Blodgett(LB) films have been obtained by transferring a monolayer that mimicshalf of the bilayer of a biological membrane. The AFM topographicalcharacterization of the monolayers on mica indicates the presenceof differentiated domains, corresponding to different physical stateslinked to the influence of the PQ content. Moreover, the electrochemicalbehavior of the monolayers has been studied when transferred on ITO,observing one main electrochemical process that is due to the divingposition of PQ molecules in the lipid matrix. [ABSTRACT FROM AUTHOR]

The objective of this work is to apply Atomic Force Microscopy in Peak Force mode to obtain topographic characteristics (mean roughness, root-mean-square roughness, skewness and kurtosis) and mechanical characteristics (adhesion, elastic modulus) of Siloxane-Hydrogel Soft Contact Lenses (CLs) of two different materials, Lotrafilcon B of Air Optix (AO) and Asmofilcon A of PremiO (P), after use (worn CLs). Thus, the results obtained with both materials will be compared, as well as the changes produced by the wear at a nanoscopic level. The results show significant changes in the topographic and mechanical characteristics of the CLs, at a nanoscopic level, due to wear. The AO CL show values of the topographic parameters lower than those of the P CL after wear, which correlates with a better comfort qualification given to the former by the wearers. A significant correlation has also been obtained between the adhesion values found after the use of the CLs with tear quality tests, both break-up-time and Schirmer. [ABSTRACT FROM AUTHOR]

Bacterial-mediated diseases are amajor healthcare concern worldwide due to the rapid spreadof antibiotic-resistant bacteria. One strategy to manage the bacterialinfections while avoiding the emergence of resistant strains impliesspecific targeting and disruption of bacteria membranes. This workevaluates the potential of nanostructured biopolymer derivatives,nanocapsules (NCs), to disrupt the bacteria cell walls and effectivelykill planktonic microorganisms. Two biopolymers, chitosan and cellulose,were chemically modified to synthesize derivatives with improved cationiccharacter (thiolated chitosan and aminocellulose) prior to their processinginto nanocapsules via a one-step sonochemical process. The interactionsof NCs, displaying an average size of around 250 nm, with bacteriamembrane were evaluated using two membrane models: Langmuir monolayersand liposome bilayers composed of a l-α-phosphatidylglycerolphospholipid extracted from Escherichia coli. NCs possessed improved membrane disturbing capacity in comparisonto the nonprocessed biopolymer derivatives, by drastically increasingthe monolayer fluidity and inducing more than 50% leakage of a dyeinserted in the bilayered liposomes. In addition, membrane disturbancewas directly proportional to the NCs cationic charge. Whereas evidenceshowed that thiolated chitosan and aminocellulose interacted withthe bacteria membrane through a “carpet model”, theNCs were found to induce larger surface defects and high local perturbancethrough a “detergent model”. Importantly, the degreeof disruption caused by the biopolymer derivatives and NCs correlatedwell with the antimicrobial capacity against Escherichiacoli, selectively killing bacteria cells without impartingtoxicity to human fibroblasts. [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]

Silver nanoparticles (Ag NPs) appeared as promising antimicrobial candidates to face the development of antibiotic resistance. Although reported as toxic towards mammalian cells, their combination with biomolecules have shown reduced toxicity, while maintaining the antimicrobial function. Herein, hyaluronic acid (HA) with low (40 kDa), medium (200 and 600 kDa) and high (2 MDa) molecular weight (Mw) was modified with adipic acid dihydrazide (ADH) and used as reducing and capping agents to synthesise antimicrobial hybrid Ag NPs. The Mw of the polymer played a crucial role in the morphology, size and antibacterial activity of the Ag NPs. The 600 and 200 kDa HA-ADH-Ag NPs were able to reduce the Escherichia coli and Staphylococcus aureus concentration by more than 3 logs, while the 40 kDa NPs reached ~2 logs reduction. The 2 MDa HA-ADH failed to form homogenous NPs with strong bactericidal activity. A mechanistic study of the interaction with a model bacterial membrane using Langmuir isotherms confirmed the greater interaction between bacteria and higher Mw polymers and the effect of the NP's morphology. The nanocomposites low toxicity to human skin cells was demonstrated in vitro, showing more than 90% cell viability after incubation with the NPs. [ABSTRACT FROM AUTHOR]

Abstract: The structure and the electrochemical behaviour of Langmuir and Langmuir–Blodgett (LB) films of the biological ubiquinone-10 (UQ) and a mixture of dipalmytoilphosphatidylcholine (DPPC) and UQ at the molar ratios DPPC:UQ 5:1 and 10:1 have been investigated. The surface pressure-area isotherms of the Langmuir films and the AFM images of the LB films show the formation of a monolayer in the DPPC:UQ mixture till a certain surface pressure is attained, and then at higher surface pressures the UQ is progressively expelled. The cyclic voltammograms of DPPC:UQ LB films formed on indium tin oxide, ITO, at different surface pressures show one reduction and one oxidation peak at low surface pressures, but two or even more reduction and oxidations peaks at medium and high surface pressures. The electrochemical behaviour is correlated with the film structure. [Copyright &y& Elsevier]

Abstract The severity and cost of wound infections strongly demands for simple and fast methods for wound infection determination. Point-of-care testing devices play a crucial role in order to achieve a fast diagnosis and early treatment. Myeloperoxidase (MPO) enzyme, detected in fluids of infected wounds has been postulated as a suitable biomarker for wound diagnostics. Here we present a new system for MPO detection, based on enzyme-catalysed oxidative synthesis of a dye that can be incorporated into paper-based point of care devices. Visual MPO detection has been achieved through the use of phenylenediamine, a common colourless hair dye precursor. MPO oxidation of these compounds yielded bright coloured products distinguishable from the colour of the wound environment. Immobilisation of the MPO substrates on paper strips was achieved through in situ interaction of the oxidised coloured product with branched polyethyleneimine. The colour reaction of the immobilized substrates, detectable by naked eye, responds to the MPO levels present in infected wound fluids revealing an easy system for incorporation of MPO detection in paper based diagnostic devices. Graphical abstract fx1 Highlights • A new sensitive MPO detection method for wound infection diagnose. • Fast visual detection of MPO levels corresponding to infected wounds avoiding haemoglobin cross-reaction. • A new detection method easily transferable to paper-based point of care diagnostic devices. [ABSTRACT FROM AUTHOR]

Ubiquinone (UQ) is one of the mainelectron and proton shuttlemolecules in biological systems, and dipalmitoylphosphatidylcholine(DPPC) is one of the most used model lipids. Supported planar bilayers(SPBs) are extensively accepted as biological model membranes. Inthis study, SPBs have been deposited on ITO, which is a semiconductorwith good electrical and optical features. Specifically, topographicatomic force microscopy (AFM) images and force curves have been performedon SPBs with several DPPC:UQ ratios to study the location and theinteraction of UQ in the SPB. Additionally, cyclic voltammetry hasbeen used to understand the electrochemical behavior of DPPC:UQ SPBs.Obtained results show that, in our case, UQ is placed in two maindifferent positions in SPBs. First, between the DPPC hydrophobic chains,fact that originates a decrease in the breakthrough force of the bilayer,and the second between the two leaflets that form the SPBs. This secondposition occurs when increasing the UQ content, fact that eventuallyforms UQ aggregates at high concentrations. The formation of aggregatesproduces an expansion of the SPB average height and a bimodal distributionof the breakthrough force. The voltammetric response of UQ dependson its position on the bilayer. [ABSTRACT FROM AUTHOR]