Microplastic leachates inhibit small-scale self-organization in mussel beds.

Self-organized spatial patterns are increasingly recognized for their contribution to ecosystem functioning. They can improve the ecosystem's ability to respond to perturbation and thus increase its resilience to environmental stress. Plastic pollution has now emerged as major threat to aquatic and terrestrial biota. Under laboratory conditions, we tested whether plastic leachates from pellets collected in the intertidal can impair small-scale, spatial self-organization and byssal threads production of intertidal mussels and whether the effect varied depending on where the pellets come from. Specifically, leachates originating from plastic pellets collected from relatively pristine and polluted areas respectively impaired and inhibited the ability of mussels to self-organize at small-scale and to produce byssal threads compared to control conditions (i.e., seawater without leaching solution). Limitations to natural self-organizing processes and threads formation may translate to a declined capacity of natural ecosystems to avoid tipping points and to a reduced restoration success of disturbed ecosystems.

Selective Nsp2 - and Csp2 - Photografting of Au-Surface by Aryldiazonium Salts and Arylazo Sulfonates.

Arylazo sulfonates (Ar-N=N-SO3 Na) have been found to undergo photografting on gold surface through both Au-Nsp2 - and Au-Csp2 - bond formation. The functionalized materials have been fully characterized by infrared reflection absorption spectroscopy (IRRAS), Raman, XPS, DFT calculations and UV-Vis absorption spectroscopy. These methods permit to evidence aromatic substituents (IRRAS), the Au-N=N signature (Raman and XPS spectroscopy), and the bond dissociation energy values of the two linkages (DFT calculation). The grafting proceeds through two competitive paths, namely a stepwise reaction involving an aryl radical (for the formation of the Au-Ar bonds) and a concerted reaction on the surface of gold (for Au-N=N-Ar bond formation). The occurrence of an aryl radical upon irradiation has been fully evidenced by EPR spectroscopy. Finally, E/Z photoisomerisation of the N=N bonds present on prepared few layer films has been observed by means of UV-Vis absorption spectroscopy.

Functionalized maghemite nanoparticles for enhanced adsorption of uranium from simulated wastewater and magnetic harvesting.

Maghemite (γ-Fe2O3) nanoparticles (MNPs) were functionalized with 3-aminopropyltriethoxysilane (APTES) to give APTES@Fe2O3 (AMNP) which was then reacted with diethylenetriamine-pentaacetic acid (DTPA) to give a nanohybrid DTPA-APTES@Fe2O3 (DAMNP). Nano-isothermal titration calorimetry shows that DTPA complexation with uranyl ions in water is exothermic and has a stoichiometry of two DTPA to three uranyl ions. Density functional theory calculations indicate the possibility of several complexes between DTPA and UO22+ with different stoichiometries. Interactions between uranyl ions and DAMNP functional groups are revealed by X-photoelectron and Fourier transform infrared spectroscopies. Spherical aberration-corrected Scanning Transmission Electron Microscopy visualizes uranium on the particle surface. Adsorbent performance metrics were evaluated by batch adsorption studies under different conditions of pH, initial uranium concentration and contact time, and the results expressed in terms of equilibrium adsorption capacities (qe) and partition coefficients (PC). By either criterion, performance increases from MNP to AMNP to DAMNP, with the maximum uptake at pH 5.5 in all cases: MNP, qe = 63 mg g-1, PC = 127 mg g-1 mM-1; AMNP, qe = 165 mg g-1, PC = 584 mg g-1 mM-1; DAMNP, qe = 249 mg g-1, PC = 2318 mg g-1 mM-1 (at 25 °C; initial U concentration 0.63 mM; 5 mg adsorbent in 10 mL of solution; contact time, 3 h). The pH maximum is related to the predominance of mono- and di-cationic uranium species. Uptake by DAMNPs follows a pseudo-first-order or pseudo-second-order kinetic model and fits a variety of adsorption models. The maximum adsorption capacity for DAMNPs is higher than for other functionalized magnetic nanohybrids. This adsorbent can be regenerated and recycled for at least 10 cycles with less than 10% loss in activity, and shows high selectivity. These findings suggest that DAMNP could be a promising adsorbent for the recovery of uranium from nuclear wastewaters.

High-Entropy-Alloy Nanocrystal Based Macro- and Mesoporous Materials.

High-entropy-alloy (HEA) nanoparticles are attractive for several applications in catalysis and energy. Great efforts are currently devoted to establish composition-property relationships to improve catalytic activity or selectivity. Equally importantly, developing practical fabrication methods for shaping HEA-based materials into complex architectures is a key requirement for their utilization in catalysis. However, shaping nano-HEAs into hierarchical structures avoiding demixing or collapse remains a great challenge. Herein, we overcome this issue by introducing a simple soft-chemistry route to fabricate ordered macro- and mesoporous materials based on HEA nanoparticles, with high surface area, thermal stability, and catalytic activity toward CO oxidation. The process is based on spray-drying from an aqueous solution containing five different noble metal precursors and polymer latex beads. Upon annealing, the polymer plays a double role: templating and reducing agent enabling formation of HEA nanoparticle-based porous networks at only 350 °C. The formation mechanism and the stability of the macro- and mesoporous materials were investigated by a set of in situ characterization techniques; notably, in situ transmission electron microscopy unveiled that the porous structure is stable up to 800 °C. Importantly, this process is green, scalable, and versatile and could be potentially extended to other classes of HEA materials.

Extending nanoscale patterning with multipolar surface plasmon resonances.

Plasmonic excitation of metallic nanoparticles can trigger chemical reactions at the nanoscale. Such optical effects can also be employed to selectively and locally graft photopolymer layers at the nanostructure surface, and, when combined with a surface functionalization agent, new pathways can be explored to modify the surface of a plasmonic nanoparticle. Among these approaches, diazonium salt chemistry is seen as an attractive strategy due to the high photoinduced reactivity of these salts. In this work, we demonstrate that it is possible to trigger the site-selective grafting of aryl films derived from diazonium salts on distinct nano-localized area of single gold nanotriangles, by taking advantage of their multipolar localized surface plasmon modes. It is shown the aryl film will preferentially graft in areas where the electric field enhancement is maximum, independently of the considered excited surface plasmon mode. These experimental findings are in very good qualitative agreement with the calculations of the local electric field, using the finite-difference time-domain (FDTD) method. We believe that this plasmonic-based approach will not only pave a new way for the spatially controlled surface functionalization of plasmonic nanoparticles, but also provide a general strategy to attach distinct molecules to hot spot regions on a single nanoparticle, opening promising prospects in sensing and multiplexing, and optically nano-scale patterning of functional groups.

Grafting TRAIL through Either Amino or Carboxylic Groups onto Maghemite Nanoparticles: Influence on Pro-Apoptotic Efficiency.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF cytokine superfamily. TRAIL is able to induce apoptosis through engagement of its death receptors DR4 and DR5 in a wide variety of tumor cells while sparing vital normal cells. This makes it a promising agent for cancer therapy. Here, we present two different ways of covalently grafting TRAIL onto maghemite nanoparticles (NPs): (a) by using carboxylic acid groups of the protein to graft it onto maghemite NPs previously functionalized with amino groups, and (b) by using the amino functions of the protein to graft it onto NPs functionalized with carboxylic acid groups. The two resulting nanovectors, NH-TRAIL@NPs-CO and CO-TRAIL@NPs-NH, were thoroughly characterized. Biological studies performed on human breast and lung carcinoma cells (MDA-MB-231 and H1703 cell lines) established these nanovectors are potential agents for cancer therapy. The pro-apoptotic effect is somewhat greater for CO-TRAIL@NPs-NH than NH-TRAIL@NPs-CO, as evidenced by viability studies and apoptosis analysis. A computational study indicated that regardless of whether TRAIL is attached to NPs through an acid or an amino group, DR4 recognition is not affected in either case.

Surface Enhanced Raman Scattering on Regular Arrays of Gold Nanostructures: Impact of Long-Range Interactions and the Surrounding Medium.

Long-range interaction in regular metallic nanostructure arrays can provide the possibility to manipulate their optical properties, governed by the excitation of localized surface plasmon (LSP) resonances. When assembling the nanoparticles in an array, interactions between nanoparticles can result in a strong electromagnetic coupling for specific grating constants. Such a grating effect leads to narrow LSP peaks due to the emergence of new radiative orders in the plane of the substrate, and thus, an important improvement of the intensity of the local electric field. In this work, we report on the optical study of LSP modes supported by square arrays of gold nanodiscs deposited on an indium tin oxyde (ITO) coated glass substrate, and its impact on the surface enhanced Raman scattering (SERS) of a molecular adsorbate, the mercapto benzoic acid (4-MBA). We estimated the Raman gain of these molecules, by varying the grating constant and the refractive index of the surrounding medium of the superstrate, from an asymmetric medium (air) to a symmetric one (oil). We show that the Raman gain can be improved with one order of magnitude in a symmetric medium compared to SERS experiments in air, by considering the appropriate grating constant. Our experimental results are supported by FDTD calculations, and confirm the importance of the grating effect in the design of SERS substrates.

On the importance of the crystalline surface structure on the catalytic activity and stability of tailored unsupported cobalt nanoparticles for the solvent-free acceptor-less alcohol dehydrogenation.

Unsupported nanoparticles are now recognized as model catalysts to evaluate the intrinsic activity of metal particles, irrespectively of that of the support. Co nanoparticles with different morphologies, rods, diabolos and cubes have been prepared by the polyol process and tested for the acceptorless catalytic dehydrogenation of alcohols under solvent-free conditions. Rods crystallize with the pure hcp structure, diabolos with a mixture of hcp and fcc phases, while the cubes crystallize in a complex mixture of hcp, fcc and ε-Co phases. All the cobalt particles are found to be highly selective towards the oxidation of a model secondary alcohol, octan-2-ol, into the corresponding ketone while no significant activity is found with octan-1-ol. Our results show the strong influence of particle shape on the activity and catalytic stability of the catalysts: Co nanorods display the highest conversion (85%), selectivity (95%) and recyclability compared to Co diabolos and Co cubes. We correlate the nanorods excellent stability with a strong binding of carboxylate ligands on their {1 1 2¯ 0} facets, preserving their crystalline superficial structure, as evidenced by phase modulation infrared reflection absorption spectroscopy.

Visible-light-driven CO2 reduction on dye-sensitized NiO photocathodes decorated with palladium nanoparticles.

The thin-layer-stacked dye-sensitized NiO photocathodes decorated with palladium nanoparticles (nPd) can be used for the visible-light-driven selective reduction of CO2, mostly to CO, at potentials starting as low as 0 V vs. RHE (compared to -0.6 V in the dark for electrocatalysis). The photosensitization of NiO by the organic dye P1, with a surface coverage of 1.5 × 10-8 mol cm-2, allows the hybrid material to absorb light in the 400-650 nm range. In addition, it improves the stability and the catalytic activity of the final material decorated with palladium nanoparticles (nPd). The resulting multi-layered-type photocathode operates according to the electron-transfer-cascade mechanism. On the one hand, the photosensitizer P1 plays a central role as it generates excited-state electrons and transfers them to nPd, thus producing the catalytically active hydride material PdH x . On the other hand, the dispersed nPd, absorb/adsorb hydrogen and accumulate electrons, thus easing the reductive electrocatalysis process by further driving the separation of charges at the photoelectrochemical interface. Surface analysis, morphology, and roughness have been assessed using SEM, EDS, and AFM imaging. Both conventional electrochemical and photoelectrochemical experiments have been performed to confirm the catalytic activity of hybrid photocathodes toward the CO2 reduction. The recorded cathodic photocurrents have been found to be dependent on the loading of Pd nanoparticles. A sufficient amount of loaded catalyst facilitates the electron transfer cascade, making the amount of dye grafted at the surface of the electrode the limiting parameter in catalysis. The formation of CO as the main reaction product is postulated, though the formation of traces of other small organic molecules (e.g. methanol) cannot be excluded.

Investigating the effects of different natural molecules on the structure and oligomerization propensity of hen egg-white lysozyme.

The formation of amyloid aggregates is the hallmark of systemic and neurodegenerative diseases, also known as amyloidosis. Many proteins have been found to aggregate into amyloid-like fibrils and thus process is recognized as general tendency of polypeptides. Inhibition of protein aggregation and fibril formation is thus one of the important strategies in the prevention and treatment of such disease. There is a growing interest of identification of small molecules mainly natural compounds that can prevent or delay amyloid fibril formation. In this work, we report the effect of various compounds from different groups on the amyloid fibrillation of hen egg white lysozyme, a model protein for amyloid formation. Herein, a range of biophysical techniques have been employed in order to establish a systematic approach to study the effect of candidate inhibitors on amyloid aggregation. Results demonstrated that the strategy used show that the different techniques are complimentary in order to elucidate a complete in vitro picture of the effect of the used compounds on HEWL aggregation. Moreover, compared to the data obtained by other groups for the inhibition of lysozyme fibril formation, this work provides new insights into the structural changes (local, secondary, oligomeric, fibrillar structures) undergone by HEWL during aggregation in the presence and absence of inhibitors.

Removal of lead and cadmium from aqueous solutions by using 4-amino-3-hydroxynaphthalene sulfonic acid-doped polypyrrole films.

Water pollution by heavy metals is a great health concern worldwide. Lead and cadmium are among the most toxic heavy metals because they are dangerous for the human and aquatic lives. In this work, the removal of lead and cadmium from aqueous solutions has been studied using electrosynthesized 4-amino-3-hydroxynaphthalene-1-sulfonic acid-doped polypyrrole (AHNSA-PPy) films as a new adsorbent. Two distinct methods, including the immersion method, based on the Pb2+ and Cd2+ spontaneous removal by impregnation of the polymer in the solution, and the electro-elimination method, consisting of removal of Pb2+ and Cd2+ ions from the solution by applying a small electrical current (5 mA) to the polymer film, were developed: the evolution of Pb2+ and Cd2+ concentrations with time was monitored by inductively coupled plasma optical emission spectrometry (ICP-OES). The effect of pH on the adsorption and electro-elimination of Pb2+ and Cd2+ using the AHNSA-PPy film was investigated and optimized, showing that the ionic adsorption and electro-elimination processes were highly pH-dependent. The kinetics of Pb2+ and Cd2+ adsorption and electro-elimination were found to follow second-order curves. The maximum adsorption capacity values of the AHNSA-PPy film were 64.0 and 50.4 mg/g, respectively, for Pb2+ and Cd2+. The removal efficiency values were, respectively, for Pb2+ and Cd2+, 80 and 63% by the immersion method, and 93 and 85% by the electro-elimination method. Application of both methods to Senegal natural waters, fortified with Pb2+ and Cd2+, led to removal efficiency values of, respectively for Pb2+ and Cd2+, 76-77 and 58-59% by the immersion method, and of 82-90 and 80-83%, by the electro-elimination method.

Removal of Cr(VI) from aqueous solution using electrosynthesized 4-amino-3-hydroxynaphthalene-1-sulfonic acid doped polypyrrole as adsorbent.

Polypyrrole (PPy) conducting films, doped with 4-amino-3-hydroxynaphthalene sulfonic acid (AHNSA), were electrosynthesized by anodic oxidation of pyrrole on Pt and steel electrodes in aqueous medium (0.01 M AHNSA +0.007 M NaOH, using cyclic voltammetry (CV), and their electrochemical properties were studied. Fourier-transform infrared (FT-IR) spectroscopy confirmed the formation of AHNSA-PPy films. Their morphology was characterized by scanning electron microscopy (SEM), and their optical properties, including UV-VIS absorption and fluorescence spectra, were also investigated. AHNSA-PPy films were used for the removal of chromium(VI) from aqueous solution, by means of the immersion method and the Cr(VI) electro-reduction method. The effect of various experimental parameters, including the adsorbent (polymer) mass, pH, type of electrodes, and current intensity, on the adsorption of chromium by the polymer was performed and optimized. The adsorption and electro-reduction of (Cr VI) on the AHNSA-PPy film surface were found to be highly pH-dependent, and the kinetics of Cr(VI) adsorption and electro-reduction followed second-order kinetic curves. Apparent second-order rate constants were about three times higher for the Cr(VI) electro-reduction method than for the immersion method, indicating that the use of electro-reduction method significantly accelerated the chromium adsorption process on polymer. The maximum adsorption capacity of the AHNSA-PPy film for chromium was 224 mg g-1. A 96% chromium removal from pure aqueous solution was reached within about 48 h by the immersion method, but only within about 6 h by the Cr(VI) electro-reduction method. Application of both methods to Cr(VI) fortified natural waters of Senegal led to chromium removal efficiency high values (93 to 96% according to the type of natural water).

Insights into Kinetics of Agitation-Induced Aggregation of Hen Lysozyme under Heat and Acidic Conditions from Various Spectroscopic Methods.

Protein misfolding and amyloid formation are an underlying pathological hallmark in a number of prevalent diseases of protein aggregation ranging from Alzheimer's and Parkinson's diseases to systemic lysozyme amyloidosis. In this context, we have used complementary spectroscopic methods to undertake a systematic study of the self-assembly of hen egg-white lysozyme under agitation during a prolonged heating in acidic pH. The kinetics of lysozyme aggregation, monitored by Thioflavin T fluorescence, dynamic light scattering and the quenching of tryptophan fluorescence by acrylamide, is described by a sigmoid curve typical of a nucleation-dependent polymerization process. Nevertheless, we observe significant differences between the values deduced for the kinetic parameters (lag time and aggregation rate). The fibrillation process of lysozyme, as assessed by the attenuated total reflection-Fourier transform infrared spectroscopy, is accompanied by an increase in the ß-sheet conformation at the expense of the α-helical conformation but the time-dependent variation of the content of these secondary structures does not evolve as a gradual transition. Moreover, the tryptophan fluorescence-monitored kinetics of lysozyme aggregation is described by three phases in which the temporal decrease of the tryptophan fluorescence quantum yield is of quasilinear nature. Finally, the generated lysozyme fibrils exhibit a typical amyloid morphology with various lengths (observed by atomic force microscopy) and contain exclusively the full-length protein (analyzed by highly performance liquid chromatography). Compared to the data obtained by other groups for the formation of lysozyme fibrils in acidic pH without agitation, this work provides new insights into the structural changes (local, secondary, oligomeric/fibrillar structures) undergone by the lysozyme during the agitation-induced formation of fibrils.

Powerful Surface Chemistry Approach for the Grafting of Alkyl Multilayers on Aluminum Nanoparticles.

The synthesis of aluminum nanoparticles (Alnp) has raised promising perspectives these past few years for applications in energetic materials. However, because of their high reactivity, it is crucial to functionalize them before their use. In this work, we propose an original and simple chemical approach to graft spontaneously alkyl layers derived from alkyl halides at the surface of Alnp, by relying on the highly reductive character of these nanoparticles, when they are in the unoxidized form. Alnp were prepared in a glovebox and reacted with alkyl halides (RI and RBr) to give modified Alnp-R, as shown by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction, thermogravimetric analysis (TGA), and microscopy. The coating is made of alkyl multilayers, which were found to be strongly anchored at the Alnp surface, as it resisted 2 h of rinsing in toluene. An electrocatalytic electron transfer promoted by Alnp is proposed to describe the mechanism of this grafting reaction.