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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]

Fatty acids, cholesterol, and phospholipids are amphiphilic compounds of biological interest, which form ordered monolayers mimicking biomembranes, and can be studied with the Langmuir technique using surface pressure-area isotherms and compressibility plots. Proteins are also components of biomembranes or are present in body fluids. In this study, the influence of lysozyme on different films of a fatty acid (stearic acid or oleic acid), cholesterol, a phospholipid (dipalmitoylphosphatidylcholine, DPPC, or palmitoyloleoylphosphatidylcholine, POPC), and mixtures of them is presented using a 0.9% saline solution as subphase. Results show that the presence of lysozyme alters the lipid monolayer formation in an important way at the beginning (low surface pressures) and the middle (intermediate surface pressures) parts of the isotherm. At high surface pressures, the phospholipids DPPC and POPC and the saturated fatty acid, stearic acid, expel lysozyme from the surface, while oleic acid and cholesterol permit the presence of lysozyme on it. The mixtures of oleic acid-DPPC also expel lysozyme from the surface at high surface pressures, while mixtures of oleic acid-POPC and cholesterol-POPC permit the presence of lysozyme on it. The compressibility of the monolayer is affected in all cases, with an important reduction in the elastic modulus values and an increase in the fluidity, especially at low and intermediate surface pressures. [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]

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]

• 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]

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]