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An understanding of the mechanism of action of antimicrobial peptides is fundamental to the development of new and more active antibiotics. In the present work, we use a wide range of techniques (SANS, SAXD, DSC, ITC, CD, and confocal and electron microscopy) in order to fully characterize the interaction of a cecropin A-melittin hybrid antimicrobial peptide, CA(1-7)M(2-9), of known antimicrobial activity, with a bacterial model membrane of POPE/POPG in an effort to unravel its mechanism of action. We found that CA(1-7)M(2-9) disrupts the vesicles, inducing membrane condensation and forming an onionlike structure of multilamellar stacks, held together by the intercalated peptides. SANS and SAXD revealed changes induced by the peptide in the lipid bilayer thickness and the bilayer stiffening in a tightly packed liquid-crystalline lamellar phase. The analysis of the observed abrupt changes in the repeat distance upon the phase transition to the gel state suggests the formation of an L$_γ$ phase. To the extent of our knowledge, this is the first time that the $_γ$ phase is identified as part of the mechanism of action of antimicrobial peptides. The energetics of interaction depends on temperature, and ITC results indicate that CA(1-7)M(2-9) interacts with the outer leaflet. This further supports the idea of a surface interaction that leads to membrane condensation and not to pore formation. As a result, we propose that this peptide exerts its antimicrobial action against bacteria through extensive membrane disruption that leads to cell death.

The decrease of the lattice size of periodic mesoporous organosilicas (PMOs) is one important goal in obtaining a microporous material for storage or adsorption of small molecules. To determine the influence of different synthesis parameters in the lattice size, here we performed in situ small-angle X-ray diffraction studies and show that a variation of the surfactant's headgroup size is not directly followed by the lattice parameter of the resulting structure. We show that in the surfactant series of penta-, hexa-, hepta-, octa-, nona-, and decaethylene glycol monododecyl ether (C12(EO)n, n = 5, 6, 7, 8, 9, 10) the lattice size decreases between n = 5 and n = 8 and then increases, while the ordering of the materials is always cubic (space group Fd3m). This size effect is due to the ethylene oxide (EO) chain conformation that changes as the number of EO groups increases. Short ethylene oxide chains tend to have a so-called "zigzag" conformation while an increase of the chain length leads to a "Mäander" (coiling) conformation. Although this phenomenon is most commonly observed for chains consisting of more than 10 ethylene oxide units, we found a minimum PMO lattice size for 8 EO units and intermediate values for 6 and 7 EO units. The increase of the lattice parameter for more than 9 EO units is attributed to the increasing number of "Mäander" configurated EO units.

International audience; The coagulation of sodium montmorillonite by inorganic salts (NaNO3, Ca(NO3)(2) and La(NO3)(3)) was studied by combining classical turbidity measurements with wide-angle-X-ray scattering (WAXS), small-angle-X-ray scattering (SAXS), and transmission X-ray microscopy (TXM). Using size-selected samples, such a combination, associated with an original quantitative treatment of TXM images, provides a true multiscale investigation of the formed structures in a spatial range extending from a few angstroms to a few micrometers. We then show that, at neutral pH and starting with fully Na-exchanged samples, coagulation proceeds via the formation of stacks of particles with a slight mismatch between layers. These stacks arrange themselves into larger porous anisotropic particles, the porosity of which depends on the valence of the cation used for coagulation experiments. Face-face coagulation is clearly dominant under those conditions, and no evidence for significant face-edge coagulation was found. These structures appear to arrange as larger clusters, the organization of which should control the mechanical properties of the flocs.

We synthesize and characterize alkylthiohydroquinones (ATHs) in order to investigate their interactions with lipid model membranes, POPE and POPC. We observe the formation of structures with different morphologies, or curvature of the lipid bilayer, depending on pH and increasing temperature. We attribute their formation to changes in the balance charge/polarity induced by the ATHs. Mixtures of ATHs with POPE at pH 4 form two cubic phases, P4(3)32 and Im3m, that reach a maximum lattice size at 40 °C while under basic conditions these phases only expand upon heating from room temperature. The cubic phases coexist with lamellar or hexagonal phases and are associated with inhomogeneous distribution of the ATH molecules over the lipid matrix. The zwitterionic POPC does not form cubic phases but instead shows lamellar structures with no clear influence of the 2,6-BATH.

The combination of physisorption experiments with simultaneous in situ small-angle X-ray and neutron scattering (SAXS/SANS) was used to elucidate the porosity in mesoporous silica with a trimodal pore structure. The material ("KLE-IL") contains spherical mesopores of 14 nm in diameter, worm-like mesopores (2-3 nm), and micropores, templated by a block copolymer and an ionic liquid surfactant, while the micropores originate from the hydrophilic block of the block copolymer. The main objective of the study was the quantification of the microporosity and the small mesopores and to find out if they are indeed located between the larger, spherical mesopores. Our in situ SAXS/SANS experiments took advantage of contrast matching of nitrogen (SANS, T = 77 K) and dibromomethane (SAXS, T = 290 K). By using the latter gas with a slightly larger kinetic diameter, it was possible to judge the accessibility of the pores under ambient conditions. The in situ experiments were supported by high-precision ex situ physisorption. Using suitable approaches for the SAXS/SANS analysis, it was possible to separate the content of the micropores and small mesopores.