BackgroundReactors found in nature can be described as micro-heterogeneous systems, where media involved in each micro-environment can behave in a markedly different way compared with the properties of the bulk solution. The presence of water molecules in micro-organized assemblies is of paramount importance for many chemical processes, ranging from biology to environmental science. Self-organized molecular assembled systems are frequently used to study dynamics of water molecules because are the simplest models mimicking biological membranes. The hydrogen bonds between sucrose and water molecules are described to be stronger (or more extensive) than the ones between water molecules themselves. In this work, we studied the capability of sucrose moiety, attached to alkyl chains of different length, as a surface blocking agent at the water-interface and we compared its properties with those of polyethylenglycol, a well-known agent used for this purposes. Published studies in this topic mainly refer to the micellization process and the stability of mixed surfactant systems using glycosides. We are interested in the effect induced by the presence of sucrose monoesters at the interface (direct and reverse micelles) and at the palisade (mixtures with Triton X-100). We believe that the different functional group (ester), the position of alkyl chain (6-O) and the huge capability of sucrose to interact with water will dramatically change the water structuration at the interface and at the palisade, generating new possibilities for technological applications of these systems.ResultsOur time resolved and steady state fluorescence experiments in pure SEs micelles show that sucrose moieties are able to interact with a high number of water molecules promoting water structuration and increased viscosity. These results also indicate that the barrier formed by sucrose moieties on the surface of pure micelles is more effective than the polyoxyethylene palisade of Triton X-100. The fluorescence quenching experiments of SEs at the palisade of Triton X-100 micelles indicate a blocking effect dependent on the number of methylene units present in the hydrophobic tail of the surfactant. A remarkable blocking effect is observed when there is a match in size between the hydrophobic regions forming the apolar core (lauryl SE/ Triton X-100). This blocking effect disappears when a mismatch in size between hydrophobic tails, exists due to the disturbing effect on the micelle core.

Nanoscale organization of the membranes of living cells plays crucial roles in numerous vital processes, including during the activation of T-cells and their formation of the immunological synapse. However, the exact nature and function of reorganization of lipids during this key initiating event remain unclear. To gain further insight into this process, we employed two techniques that probe complementary properties of the membranes at the molecular level: 1) super-resolution STED-FCS to reveal detailed picture of the diffusion of the lipids, with additional information on spatial heterogeneity provided by the scanning mode; and 2) spectral (super-resolution STED) imaging with environment-sensitive membrane probes, i.e. fluorescence microspectroscopy, to map differences in local molecular order within the lipid bilayer. Using these methods, we monitored diffusion properties of lipids and molecular order of the plasma membrane of (Jurkat) T-cells over space and time upon their activation, revealing marked differences in lipid diffusion and molecular order. For the most informative and robust description of the latter, we systematically analyzed the benefits and pitfalls of the established representations, i.e. phasors, generalized polarization, and lineshape description.

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Design of new bio-nano hybrid systems calls for understanding and accounting for the influence of a nanostructured support and nanoconfinement on the structure and biophysical properties of lipid bilayer hybrid systems and membraneprotein interface. Here we report on spin-labeling EPR studies of pH-sensitive lipids and specifically labeled protein side chains to assess effects of solid inorganic interface, specifically, silica support in a form of monodispersed nanoparticles ranging from 20 to 300 nm in diameter on the surface electrostatic potential of lipid bilayers associated with the particles and effective pKa of the membrane-burred peptide ionisable sidechains. We have shown that bilayers formed from zwitterionic or mixed lipids on silica nanoparticle surfaces possess a higher negative electrostatic potential than the unsupported bilayers with the potential of mixed bilayers containing negatively charged lipids being significantly more sensitive to the silica support. Effect the silica nanoparticle size on the lipid bilayer surface electrostatic potential was also observed for particles smaller than 100 nm. pH-sensitive EPR probes were then employed to label model WALP peptide known to form an a-helix when integrated into a lipid bilayer. The silica support exerted pronounced effects on WALP dynamics and the effective pKa of the ionizable probe. It was demonstrated that the silica nanoparticles shift the effective pKa of the ionizable nitroxide probe in a membrane depth-dependent manner. Upon protonation of the membraneburred model ionisable sidechain the silica support caused significant changes in the membrane association of WALP peptide that are not observed when WALP is integrated into unilamellar phospholipid vesicles of similar curvature. Lipid metabolism is characterized by a complex set of sequential reactions which underpin many biological processes, including the maintenance of the cellular energy balance and the intercellular communication through the socalled lipid signalling. The lipid composition and distribution within cells change following chemical and physical interactions with the surrounding environment in response to specific needs or conditions, as is the case of the activation of lipolysis or storage pathways. The method here presented allows characterizing some of these processes through the evaluation of the microenvironment polarity within the cell membranes with a high spatial and temporal resolution. This is achieved by using an algorithm based on the phasor approach to the spectral imaging. As a result, a metabolic parameter is furnished to enable a quantitative assessment of the storage of fatty acids in triacylglycerols in the form of lipid droplets or the triacylglycerols hydrolysis in response to energetic demands, as well as changes in the global and local distribution of polar and non-polar lipids with a sub-micrometre resolution. The method has been applied both to tissues and cell cultures to study the reaction of the systems to lipid metabolism disorders or nutritional ...

Cells must be able to maintain and change membrane shape. This membrane curvature can be influenced by any lateral phase heterogeneity. Ternary mixtures of high-melting lipid, low-melting lipid, and cholesterol exhibit a region of liquid-ordered (Lo)þ liquid-disordered (Ld) phase coexistence analogous to raft þ non-raft behavior in cells. Although curvature can induce separation and sorting in vitro, a number of highly-curved membranes in vivo have raft-like composition, which is puzzling since the raft-like compositions have greater rigidity in lipid model mixtures. We find that including transmembrane helical

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