Self-assembled structures having a regular hollow icosahedral form (such as those observed for proteins of virus capsids) can occur as a result of biomineralization processes, but are extremely rare in mineral crystallites. Compact icosahedra made from a boron oxide have been reported, but equivalent structures made of synthetic organic components such as surfactants have not hitherto been observed. It is, however, well known that lipids, as well as mixtures of anionic and cationic single chain surfactants, can readily form bilayers that can adopt a variety of distinct geometric forms: they can fold into soft vesicles or random bilayers (the so-called sponge phase) or form ordered stacks of flat or undulating membranes. Here we show that in salt-free mixtures of anionic and cationic surfactants, such bilayers can self-assemble into hollow aggregates with a regular icosahedral shape. These aggregates are stabilized by the presence of pores located at the vertices of the icosahedra. The resulting structures have a size of about one micrometre and mass of about 1010 daltons, making them larger than any known icosahedral protein assembly or virus capsid. We expect the combination of wall rigidity and holes at vertices of these icosahedral aggregates to be of practical value for controlled drug or DNA release.

Mixtures of cationic and anionic surfactants crystallized at various ratios in the absence of added salt form micrometer-sized colloids. Here, we propose and test a general mechanism explaining how this ratio controls the shape of the resulting colloidal structure, which can vary from nanodiscs to punctured planes; during cocrystallization, excess (nonstoichiometric) surfactant accumulates on edges or pores rather than being incorporated into crystalline bilayers. Molecular segregation then produces a sequence of shapes controlled by the initial mole ratio only. Using freezefracture electron microscopy, we identified three of these states and their corresponding coexistence regimes. Fluorescence confocal microscopy directly showed the segregation of anionic and cationic components within the aggregate. The observed shapes are consistently reproduced upon thermal cycling, demonstrating that the icosahedral shape corresponds to the existence of a local minimum of bending energy for facetted icosahedra when the optimal amount of excess segregated material is present.C ontrolling both size and shape of colloidal particles is a major challenge to the predictable formulation of mixed systems consisting of surfactants, polymers, and inorganic solids. Successful control of size and shape requires simultaneous knowledge of the mixture's equilibrium phase behavior and the mechanism of formation. The aim of this article is to describe and test hypotheses based on bending energy to control a general sequence of colloidal shapes, from large discs to punctured planes.If the elemental building blocks of a complex colloidal aggregate are amphiphilic molecules, the basic concept used to rationalize self-assembly is the concept of spontaneous curvature originating from the surface-to-volume ratio of the surfactant film (1). Common single-chain ionic amphiphiles have a spontaneous radius of curvature equivalent to one surfactant length (2) and therefore form globular micelles. Decreasing monolayer curvature obtained by mixing surfactants first produces giant cylindrical and finally locally flat bilayers.When the elementary building block is a fragment of a bilayer, line tension of pores, or rims of discs, and elastic energy associated to dihedral angles on the contact line between adjacent facets need to be considered (3). The crystallization͞ segregation should be consistent with the sequence of shapes observed with strongly interacting charged colloids in the absence of salt. Molecular segregation is demonstrated by specificity of labeling with a dye and direct observation, and we show finally that the resulting shapes correspond to local minima of energy of formation. Mechanism of Shape Control Through Molecular SegregationConsider an initial state of the dispersion with unilamellar vesicles in the fluid state. In the fluid state of mixed vesicles, the two components exhibit in-plane miscibility.Y Upon cooling, nucleation and growth of planar crystals occur in the form of polygonal frozen bilayers, which can only form at a fixe...

The global estimation of microplastic afloat in the ocean is only approximately 1% of annual global plastic inputs. This reflects fundamental knowledge gaps in the transformation, fragmentation, and fates of microplastics in the ocean. In order to better understand microplastic fragmentation we proceeded to a thorough physicochemical characterization of samples collected from the North Artlantic subtropical gyre during the sea campaign Expedition seventh Continent in May 2014. The results were confronted with a mathematical approach. The introduction of mass distribution in opposition to the size distribution commonly proposed in this area clarify the fragmentation pattern. The mathematical analysis of the mass distribution points out a lack of debris with mass lighter than 1 mg. Characterization by means of microscopy, microtomography, and infrared microscopy gives a better understanding of the behavior of microplastic at sea. Flat pieces of debris (2 to 5 mm in length) typically have one face that is more photodegraded (due to exposure to the sun) and the other with more biofilm, suggesting that they float in a preferred orientation. Smaller debris, with a cubic shape (below 2 mm), seems to roll at sea. All faces are evenly photodegraded and they are less colonized. The breakpoint in the mathematical model and the experimental observation around 2 mm leads to the conclusion that there is a discontinuity in the rate of fragmentation: we hypothesized that the smaller microplastics, the cubic ones mostly, are fragmented much faster than the parallelepipeds.

No abstract

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Estimates of cumulative plastic inputs into the oceans are e:xpressed in hundred million tons, whereas the total R = ,,fITF mass of microplastics afl oat at sea is 3 orders of magnitude twt In couni. l.ottrge pla.<_; tki, (1-f> mm) below this. This l arg e gap is evidence of our ignorance about the fate of plastics, as well as transformations and sinks in the oceans. One of the current challenges consists of identifying and quantifying plastic particles at the microscale, the small Il"' �'• Sphcrc Microplastic Ellip,oid �! n ��"pl�!�, � (� 6 ln mass Smnll plastics Large 1>laslks (251un-l mm) (1-5 mm) microplastics (SMP, 25-1000 µm). The aim of the present study is to investigate SMP concentration in count and in mass at the sea surface in the North Atlantic subtropical gyre during the sea campaign Expedition i h Continent After isolation, From plastic dcbris SMP were characterized by micro Fourier transform infrared to models Rise velocities 1\, ficroplo.stics corroetcd concentrations spectroscopy. Microplastic distribution was modeled by a wind driven vertical mixing correction mode! taking into account individual particle properties (dimension, shape and density). We demonstrate that SMP buoyancy is significantly decreased compared to the l arg e microplastics (LMP, 1-5 mm) and consequently more susceptible to vertical transport. The uncorrected LMP concentration in count was between 13 000 and 174000 pieces 1an-2 , and was between 5 and 170 times more abundant for SMP. With a wind driven vertical mixing correction, we estimated that SMP were 300 to 70 000 times more abundant than LMP. When discussing this in terms of weight after correction, LMP concentrations were between 50 and 1000 g 1an-2 , and SMP concentrations were between 5 and 14000 g 1an-2 _

New double-chain and gemini catanionic analogues of the glycolipid galβ1ceridentified as a cell receptor of the HIV-1 viruswere easily prepared in two steps from unprotected lactose. Due to their sugar moiety, these new catanionic surfactants were able to be cationized by sodium ions and therefore to be characterized in their monomeric forms by electrospray mass spectrometry. To our knowledge, this is the first time that catanionic surfactants have been directly observed, proving undoubtedly their existence as monomeric species. These new catanionic glycolipids showed interesting anti-HIV-1 activities, acting as monomeric analogues of galβ1cer. Finally, these new catanionic glycolipids were characterized by their surface active properties, by lamellar mesophases, and by their aptitude to spontaneously form vesicles.

There are fundamental gaps in our understanding of the fates of microplastics in the ocean, which must be overcome if the severity of this pollution is to be fully assessed. The predominant pattern is high accumulation of microplastic in subtropical gyres. Using in situ measurements from the 7th Continent expedition in the North Atlantic subtropical gyre, data from satellite observations and models, we show how microplastic concentrations were up to 9.4 times higher in an anticyclonic eddy explored, compared to the cyclonic eddy. Although our sample size is small, this is the first suggestive evidence that mesoscale eddies might trap, concentrate and potentially transport microplastics. As eddies are known to congregate nutrients and organisms, this phenomenon should be considered with regards to the potential impact of plastic pollution on the ecosystem in the open ocean.