Uncovering potential mangrove microbial bioindicators to assess urban and agricultural pressures on Martinique island in the eastern Caribbean Sea.

Martinique's mangroves, which cover 1.85 ha of the island (<0.1 % of the total area), are considerably vulnerable to local urban, agricultural, and industrial pollutants.

Physicochemical surface properties of : a multiscale assessment, from electrokinetic and proton uptake descriptors to intermolecular adhesion forces.

Given the growing scientific and industrial interests in green microalgae, a comprehensive understanding of the forces controlling the colloidal stability of these bioparticles and their interactions with surrounding aqueous microenvironment is required. Accordingly, we addressed here the electrostatic and hydrophobic surface properties of from the population down to the individual cell levels. We first investigated the organisation of the electrical double layer at microalgae surfaces on the basis of electrophoresis measurements.

Photodegradation of disposable polypropylene face masks: Physicochemical properties of debris and implications for the toxicity of mask-carried river biofilms.

COVID-19 outbreak led to a massive dissemination of protective polypropylene (PP) face masks in the environment, posing a new environmental risk amplified by mask photodegradation and fragmentation. Masks are made up of a several kilometres long-network of fibres with diameter from a few microns to around 20 µm. After photodegradation, these fibres disintegrate, producing water dispersible debris.

Mangrove microbiota along the urban-to-rural gradient of the Cayenne estuary (French Guiana, South America): Drivers and potential bioindicators.

The microbial communities inhabiting the Atlantic-East Pacific (AEP) mangroves have been poorly studied, and mostly comprise chronically polluted mangroves. In this study, we characterized changes in the structure and diversity of microbial communities of mangroves along the urban-to-rural gradient of the Cayenne estuary (French Guiana, South America) that experience low human impact. The microbial communities were assigned into 50 phyla.

Phlorotannin and Pigment Content of Native Canopy-Forming Sargassaceae Species Living in Intertidal Rockpools in Brittany (France): Any Relationship with Their Vertical Distribution and Phenology?

Five native Sargassaceae species from Brittany (France) living in rockpools were surveyed over time to investigate photoprotective strategies according to their tidal position. We gave evidences for the existence of a species distribution between pools along the shore, with the most dense and smallest individuals in the highest pools. Pigment contents were higher in lower pools, suggesting a photo-adaptive process by which the decreasing light irradiance toward the low shore was compensated by a high production of pigments to ensure efficient photosynthesis.

Osmotic stress and vesiculation as key mechanisms controlling bacterial sensitivity and resistance to TiO nanoparticles.

Toxicity mechanisms of metal oxide nanoparticles towards bacteria and underlying roles of membrane composition are still debated. Herein, the response of lipopolysaccharide-truncated Escherichia coli K12 mutants to TiO nanoparticles (TiONPs, exposure in dark) is addressed at the molecular, single cell, and population levels by transcriptomics, fluorescence assays, cell nanomechanics and electrohydrodynamics. We show that outer core-free lipopolysaccharides featuring intact inner core increase cell sensitivity to TiONPs.

In situ determination of Si, N, and P utilization by the demosponge Tethya citrina: A benthic-chamber approach.

Sponges consume dissolved silicon (DSi) to build their skeletons. Few studies have attempted to quantify DSi utilization by these organisms and all available determinations come from laboratory measurements. Here we measured DSi consumption rates of the sponge Tethya citrina in its natural habitat, conducting 24h incubations in benthic chambers.

Remarkable reversal of electrostatic interaction forces on zwitterionic soft nanointerfaces in a monovalent aqueous electrolyte: an AFM study at the single nanoparticle level.

Soft (nano)colloids are increasingly used in medical applications due to the versatile options they offer in terms of e.g. tunable chemical composition, adaptable physical properties and (bio)functionalization perspectives.

Iron mineralogy as a fingerprint of former steelmaking activities in river sediments.

Submerged sediment cores were collected upstream of a dam in the Orne River, northeastern France. This dam was built in the context of steelmaking to constitute a water reservoir for blast furnace cooling and wet cleaning of furnace smokes. The dam also enhanced sediment deposition in the upstream zone.

Structural effects of soft nanoparticulate ligands on trace metal complexation thermodynamics.

Metal binding to natural soft colloids is difficult to address due to the inherent heterogeneity of their reactive polyelectrolytic volume and the modifications of their shell structure following changes in e.g. solution pH, salinity or temperature.

Structure of Multiresponsive Brush-Decorated Nanoparticles: A Combined Electrokinetic, DLS, and SANS Study.

Particles consisting of a glassy poly(methyl methacrylate) core (ca. 40 nm in radius) decorated with a poly(N-isopropylacrylamide) anionic corona are synthesized using either methacrylic acid (MA) or acrylic acid (AA) as reactive comonomers in the shell. The different reactivity ratios of MA and AA toward N-isopropylacrylamide originates p(MA-N) and p(N-AA) particles with carboxylate charges supposedly located, preferentially, in the close vicinity of the core and at the shell periphery, respectively.

NMR use to quantify phlorotannins: the case of Cystoseira tamariscifolia, a phloroglucinol-producing brown macroalga in Brittany (France).

Among the most renowned natural products from brown algae, phlorotannins are phloroglucinol polymers that have been extensively studied, both for their biotechnological potential and their interest in chemical ecology. The accurate quantification of these compounds is a key point to understand their role as mediators of chemical defense. In recent years, the Folin-Ciocalteu assay has remained a classic protocol for phlorotannin quantification, even though it frequently leads to over-estimations.

Electrokinetics as an alternative to neutron reflectivity for evaluation of segment density distribution in PEO brushes.

Unravelling details of charge, structure and molecular interactions of functional polymer coatings defines an important analytical challenge that requires the extension of current methodologies. In this article we demonstrate how streaming current measurements interpreted with combined self consistent field (SCF) and soft surface electrokinetic theories allow the evaluation of the segment distribution within poly(ethylene oxide) (PEO) brushes beyond the resolution limits of neutron reflectivity technique.

Effects of added silica nanoparticles on the nematic liquid crystal phase formation in beidellite suspensions.

In this article, we present a study of the liquid crystal phase behavior of mixed suspensions of the natural smectite clay mineral beidellite and nonadsorbing colloidal silica particles. While virtually all smectite clays dispersed in water form gels at very low concentrations, beidellite displays a first order isotropic-nematic phase transition before gel formation (J. Phys.

Coagulation of Na-montmorillonite by inorganic cations at neutral pH. A combined transmission X-ray microscopy, small angle and wide angle X-ray scattering study.

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 ångstroms 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.

In-situ SAXS study of aqueous clay suspensions submitted to alternating current electric fields.

Aqueous colloidal suspensions of clay platelets display a sol/gel transition that is not yet understood. Depending on the nature of the clay, liquid-crystalline behavior may also be observed. For example, the suspensions of beidellite display a nematic phase whereas those of montmorillonite do not.

Tailoring highly oriented and micropatterned clay/polymer nanocomposites by applying an a.c. electric field.

Clay/polymer nanocomposites have recently raised much interest because of their widespread industrial applications. Nevertheless, controlling both clay platelet exfoliation and orientation during polymerization still remains challenging. Herein, we report the elaboration of clay/polymer nanocomposite hydrogels from aqueous suspensions of natural swelling clays submitted to high-frequency a.

Aqueous suspensions of natural swelling clay minerals. 2. Rheological characterization.

We report in this article a comprehensive investigation of the viscoelastic behavior of different natural colloidal clay minerals in aqueous solution. Rheological experiments were carried out under both dynamic and steady-state conditions, allowing us to derive the elasticity and yield stress. Both parameters can be renormalized for all sizes, ionic strength, and type of clay using in a first approach only the volume of the particles.

Aqueous suspensions of natural swelling clay minerals. 1. Structure and electrostatic interactions.

In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only.

Orientational order of colloidal disk-shaped particles under shear-flow conditions: a rheological-small-angle X-ray scattering study.

The structure of a colloidal dispersion consisting of anisometric natural clay particles (beidellite) was followed under shear-flow conditions by small-angle X-ray scattering (SAXS) measurements in a Couette-type cell. It is shown that in this shear-thinning dispersion an orientational order develops with increasing shear rate. By use of two different geometrical configurations for SAXS measurements, corresponding to incident beam parallel and perpendicular to flow velocity gradient (radial and tangential configurations, respectively), it is observed that SAXS patterns are anisotropic in both geometries, meaning that particles tend to align along a preferred orientation with their normal in velocity gradient direction, and further they partly rotate around flow streamlines.

Sol-gel and isotropic/nematic transitions in aqueous suspensions of natural nontronite clay. Influence of particle anisotropy. 2. Gel structure and mechanical properties.

After size-selection, the phase behavior of aqueous suspensions of nontronite clay was analyzed by osmotic pressure measurements, rheological experiments, and small-angle X-ray scattering. All the measurements confirm that for ionic strength < or =10(-3) M/L, the system is purely repulsive. By combining results from osmotic pressure measurements and X-ray scattering, it appears that the pressure of the system can be well-described using a simple Poisson-Boltzmann treatment based on the interaction between charged infinite parallel planes.

Sol/gel and isotropic/nematic transitions in aqueous suspensions of natural nontronite clay. Influence of particle anisotropy. 1. Features of the i/n transition.

The phase behavior of a natural nontronite clay was studied for size-selected particles by combining osmotic pressure measurements, visual observations under polarized light, and rheological experiments. In parallel, the positional and orientational correlations of the particles were analyzed by small-angle X-ray scattering. Aqueous suspensions of nontronite exhibit a true isotropic/nematic (I/N) transition that occurs before the sol/gel transition, for ionic strengths below 10(-3) M/L.

Liquid-crystalline aqueous clay suspensions.

This article demonstrates the occurrence of a true isotropic/nematic transition in colloidal Brownian aqueous suspensions of natural nontronite clay. The liquid-crystalline character is further evidenced by polarized light microscopy and small-angle x-ray scattering experiments in the presence and absence of modest external magnetic fields. The complete phase diagram ionic strength/volume fraction then exhibits a clear biphasic domain in the sol region just before the gel transition in contrast with the situation observed for other swelling clays in which the sol/gel transition hinders the isotropic/nematic transition.

Hydration of a synthetic clay with tetrahedral charges: a multidisciplinary experimental and numerical study.

The interaction of water with a synthetic saponite clay sample, with a layer charge of 1 per unit cell (0.165 C m(-2)), was investigated by following along water adsorption and desorption in the relative pressure range from 10(-6) to 0.99 (i) the adsorbed amount by gravimetric and near-infrared techniques, (ii) the basal distance and arrangement of water molecules in the interlayer by X-ray and neutron diffraction under controlled water pressure, and (iii) the molecular structure and interaction of adsorbed water molecules by near-infrared (NIR) and Raman spectroscopy under controlled water pressure.

Synthesis of NiGa layered double hydroxides. A combined EXAFS, SAXS, and TEM study. 3. Synthesis at constant pH.

The present paper focuses on the direct synthesis of NiGa layered double hydroxides (LDHs) by concomitant addition of Ni and Ga chloride in solution with NaOH solution, at a constant pH value of 6.5. Various Ni/Ga ratios (Ni/Ga = 2, Ni/Ga = 4, or Ni/Ga = 6) were investigated, and samples were collected after successive additions.