Pristine zinc-based layered double hydroxides (LDHs) possess remarkable antibacterial properties. The antibacterial activity of zinc-based LDHs could be explained by three possible mechanisms: (1) direct contact interactions between the LDH and bacterial surfaces, (2) release of antibacterial Zn2+ aq ions, and (3) generation of reactive oxygen species (ROS) by LDHs in response to irradiation by a suitable light source. In this work, the potential contribution of ROS generation in the antibacterial activity of ZnAl LDH nanoparticles (NPs) was determined by comparing their effect against Gram-positive Staphylococcus aureus bacteria in the presence and absence of UVA irradiation (λ = 365 nm, irradiation period = 4 h). The bactericidal efficacy of ZnAl LDH NPs was significantly enhanced in the presence of UVA light. The bactericidal activity was hindered in the presence of histidine acting as a ROS scavenger and giving indirect evidence of the role of ROS. Moreover, Fourier-transform infrared spectroscopy revealed denaturation and suppression of several structural components in S. aureus cells exposed to ZnAl LDH NPs under dark conditions and in the presence of UVA radiation, with more pronounced alterations for the latter. The impacts of such alterations on the topographical properties of S. aureus cells were determined by atomic force microscopy imaging. Treated cells with ZnAl LDH NPs were completely deformed and exhibited increased roughness, especially upon treatment in UVA conditions. All these results suggest the presence of a dual antibacterial effect between ZnAl LDH NPs and their generated ROS to provide amplified antibacterial activity.

This study investigated the speciation of hexavalent chromium (Cr(VI)) anion when inserted in layered double hydroxides (LDH). Nitrated magnesium/aluminum (Mg/Al-NO3) LDH nanoparticles (NP) were synthesized via fast coprecipitation followed by hydrothermal treatment with a Mg/Al molar ratio of 2. The saturation with hexavalent chromium (Cr(VI)) was easily performed by mixing the colloidal dispersion of LDH NP and a solution of chromate ion. Comprehensive characterization using powder X-ray diffraction (PXRD), Raman, Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), thermogravimetric analysis (TGA) were performed on LDH nano-particles in dry state. Ultraviolet-visible spectroscopy (UV-vis) captured the evolution of the Cr(VI) speciation during the hydration of the solid into colloidal aqueous suspension. The structural characterization data of both hydrated CrO42--LDH in colloidal state and dried Cr2O72--LDH nanoparticles in the solid state was interpreted with the help of density functional theory (DFT) calculation. Cr(VI) was demonstrated to keep its oxidation state and remain in the interlamellar space and not inserted in the cationic layer. The existence of Cr2O72-along with CrO42-in the dry state was unexpected, particularly when it was surrounded by hydroxide molecules in the interlamellar space of LDH, as this species is known to exist only in acidic solution. CrO42-became fully predominant upon hydration, indicating that study only on the dry solid, usually performed, could not be used to explain phenomenon in wet conditions such as the ionic exchange in LDH.

Green rust (GR) is a chemically reactive mineral of interest for environmental remediation. However, the lack of stability of this compound is a major drawback for practical applications. In this study, the precipitation of hydroxychloride green rust type 1 (GR1Cl) from soluble FeII and FeIII species was studied by analyzing pH titration curves and employing XRD, Raman and Mossbauer spectroscopies to find optimal conditions for synthesizing GR1Cl. Using the stoichiometric condition for FeII-FeIII corresponding to the [FeII3FeIII(OH)8]Cl compound, FeIIIO(OH)2.9Cl0.1 was formed in a first step during the addition of NaOH and then transformed into a mixture of GR1Cl and Fe3O4. The addition of phosphate anions (PO4) at a molar ratio PO4: Fe = 1: 10 in the initial solution was shown to avoid the formation of undesired magnetite. Interestingly, GR1Cl was also the only product without adding PO4 using an excess of FeII species in solution, i.e. for an initial ferric molar fraction x = FeIII: Fetot of 0.2. First experimental evidences of a hydroxyphosphate green rust type 2 GR2PO4 were also provided by XRD and Raman spectroscopy. Therefore, this work may attract interest for a better understanding of the geochemical cycle of iron and phosphate in natural environments such as hydromorphic soils or hydro- thermal chimneys where fougerite, the mineral homologue of synthetic GR, is supposed to play a significant role.

Antifungal resistance has become a very serious concern, and Candida albicans is considered one of the most opportunistic fungal pathogens responsible for several human infections. In this context, the use of new antifungal agents such as zinc-based layered double hydroxides to fight such fungal pathogens is considered one possible means to help limit the problem of antifungal resistance. In this study, we show that ZnAl LDH nanoparticles exhibit remarkable antifungal properties against C. albicans and cause serious cell wall damage, as revealed by growth tests and atomic force microscopy (AFM) imaging. To further link the antifungal activity of ZnAl LDHs to their adhesive behaviors toward C. albicans cells, AFM-based single-cell spectroscopy and single-particle force spectroscopy were used to probe the nanoscale adhesive interactions. The force spectroscopy analysis revealed that antimicrobial ZnAl LDHs exhibit specific surface interactions with C. albicans cells, demonstrating remarkable force magnitudes and adhesion frequencies in comparison with non-antifungal negative controls, e.g., Al-coated substrates and MgAl LDHs, which showed limited interactions with C. albicans cells. Force signatures suggest that such adhesive interactions may be attributed to the presence of agglutinin-like sequence (Als) adhesive proteins at the cell wall surface of C. albicans cells. Our findings propose the presence of a strong correlation between the antifungal effect provided by ZnAl LDHs and their nanoscale adhesive interactions with C. albicans cells at both the single-cell and single-particle levels. Therefore, ZnAl LDHs could interact with C. albicans fungal pathogens by specific adhesive interactions through which they adhere to fungal cells, leading to their damage and subsequent growth inhibition.

Due to the constraints associated with diffusion and mixing time, traditional kinetic and thermodynamic approaches were inadequate for probing the true mechanism of interaction between chromate and Layered Double Hydroxide (LDH). To circumvent these limitations, colloidal suspensions of Mg/Al-NO3 LDH, characterized by a positively charged surface (approximately +50 mV) in ultrapure water and a mean average diameter of 140 nm, allowing the formation of stable suspensions for days, were swiftly mixed with Cr(VI) suspensions at both pH = 4 and 9 using a stopped flow technique. This rapid mixing, accomplished in <5 milliseconds, enabled the examination of the initial stages of interaction between the toxic anion and the host compound. Two distinct steps in the adsorption process were identified: a very fast step (completed in <5 ms), representing up to 80% of the measured variation, and a slower step lasting up to 100 s. The fast step assumed to be driven by electrostatic interaction (zeta similar to +50 mV) with the surface, and sites close to the surface are easily accessible to the chromate anions. The slower step corresponded to a diffusion process close or inside the particles. Chromate extraction efficiency was investigated through ultrafiltration tests, varying the LDH and chromate amounts, indicating that 2 nitrate ions are exchanged for 1 chromate, regardless of the pH considered, and a total exchange can be fulfilled with 0.1 g L-1 of LDH within the explored concentration range.

Resistance to antimicrobial agents is responsible for major social and economic losses. The World Health Organization estimated 700,000 global deaths a year due to antimicrobial resistance. The use of layered double hydroxides (LDHs) as antibacterial materials could present a way to reduce the risk of bacterial infections and antibacterial resistance, by partial release of metallic ions in aqueous dispersion. The partial dissolution of different synthetic LDHs M-II-Al-III (M = Zn, Cu, Ni, Co, Mg) was studied in Lysogeny Broth (LB) and Tryptic Soy Broth (TSB), growth media of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria, respectively. The influence of several parameters (crystallinity, M-II:Al-III ratio, type of intercalated anion {CO32-, Cl-, NO3-, ClO4-} and nature of M-II cations) was investigated. In the absence of any post-synthetic hydrothermal treatment, Zn-II-Al-III LDH showed a release of Zn-III ions 6 times enhanced. Upon increasing Zn-II:Al-III molar ratio to 3: 1 and exchanging carbonate anions with other anions having lower intercalating affinities, a similar effect was observed. The dissolution properties of M-II-Al-III LDHs were correlated with the thermodynamic stability of their M-II(OH)(2) hydroxide counterparts with the exception of Cu-II-based LDH, which showed an amplified release of Cu-II due to its irregular structure presenting defects. Finally, the antibacterial activity was only noted for Zn-II and Cu-II-based LDHs. The antimicrobial effect of the studied LDHs was linked in the first place to the nature of divalent metal itself, and to the amount of released M-II ions into the culture media in the second place. This effect was more easily identified in Zn-II-Al-III LDHs whose minimum inhibitory concentration was decreased significantly from 12 to 0.375 mg.mL(-1) when higher amounts of Zn-II ions were released.

This article reports for the first time the synthesis of an LDH using only manganese as the divalent and trivalent metallic ion. Analysis of the pH, redox potential, and chemical composition during the oxidation of a manganese basic salt using persulfate indicates the oxidation of 1/3 of the initial MnII ions, in agreement with the paramagnetic structure and XPS analysis. Infrared, Raman spectra and thermogravimetric analysis results were similar to the ones obtained with Fe-LDH also known as green rust. X-Ray diffractograms and Rietveld refinement were used to determine the structure of this solid. Thermodynamic considerations predict that this solid could reduce nitrate into gaseous nitrogen without further reduction to ammonium or ammonia unlike what is observed for Fe-LDH.

Encapsulation of active substances in biopolymer beads becomes a widely developed approach to gain efficiency for many applications. However, the characterization of such aqueous materials in their early stage of production is very delicate regarding their textural properties. The classical tools such as gas adsorption and Hg porosimetry can hardly provide relevant information since they require the removal of water, which is yet a fundamental part of the sample that drives its structure. In this article, we used small angle x-ray scattering (SAXS) as a tool in order to determine the specific surface area (SSA) of alginate microbeads in solution. This has been made possible by a careful procedure of SAXS measurements, involving calibration samples, allowing writing intensities in absolute units. Therefore, the Porod limit theory was used to calculate the SSA from the scattering length contrast and the measured absolute intensity. In addition, we compared the SSA of microbeads obtained from pure water and from a widely used cell culture medium, and we followed the textural evolution of a water alginate sample during the first step of a gentle drying process. Our results show that SAXS should be considered as a valuable tool for physico-chemists and food formulators in order to extract in situ dimensional and textural information of hydrogels during the formulation. It enables them to figure out the real surface available for the sorption of additive or active molecules in the formulation of biopolymers such as alginates, empowering them to better control encapsulation processes.

Infections by pathogenic bacteria have been threatening several fields as food industries, agriculture, textile industries and healthcare products. Layered double hydroxides materials (LDHs), also called anionic clays, could be utilized as efficient antibacterial materials due to their several interesting properties such as ease of synthesis, tunable chemical composition, biocompatibility and anion exchange capacity. Pristine LDHs as well as LDH-composites including antibacterial molecules and nanoparticles loaded-LDHs were proven to serve as efficient antibacterial agents against various Gram-positive and Gram-negative bacterial strains. The achieved antibacterial effect was explained by the following mechanisms: (1) Direct contact between the materials and bacterial cells driven by electrostatic interactions between positively charged layers and negatively charged cell membranes, (2) Dissolution and gradual release over time of metallic ions or antibacterial molecules, (3) Generation of reactive oxygen species.

Understanding the mechanisms of the interactions between zinc-based layered double hydroxides (LDHs) and bacterial surfaces is of great importance to improve the efficiency of these antibiotic-free antibacterial agents. In fact, the role of surface interactions in the antibacterial activity of zinc-based LDH nanoparticles compared to that of dissolution and generation of reactive oxygen species (ROS) is still not well documented. In this study, we show that ZnAl LDH nanoparticles exhibit a strong antibacterial effect against Staphylococcus aureus by inducing serious cell wall damages as revealed by the antibacterial activity tests and atomic force microscopy (AFM) imaging, respectively. The comparison of the antibacterial properties of ZnAl LDH nanoparticles and micron-sized ZnAl LDHs also demonstrated that the antibacterial activity of Zn-based LDHs goes beyond the simple dissolution into Zn2+ antibacterial ions. Furthermore, we developed an original approach to functionalize AFM tips with LDH films in order to probe their interactions with living S. aureus cells by means of AFM-based force spectroscopy (FS). The force spectroscopy analysis revealed that antibacterial ZnAl LDH nanoparticles show specific recognition of S. aureus cells with high adhesion frequency and remarkable force magnitudes. This finding provides a first insight into the antibacterial mechanism of Zn-based LDHs through direct surface interactions by which they are able to recognize and adhere to bacterial surfaces, thus damaging them and leading to subsequent growth inhibition.

It is expected that during a titration using a basic NaOH solution, the pH can only increase. In this article the formation of two different solids during the precipitation of a MnSO4 solution is discussed. The formation of a new compound Mn-4(OH)(6)SO4 center dot nH(2)O instead of Mn(OH)(2) is evidenced by the quantification of the remaining ions in solution as well as by X-Ray Diffraction, Raman and infrared spectroscopies. The transformation of this solid into Mn(OH)(2) after a sursaturation of the solid in OH can explain a drop of the pH in the titration curve.

Iron and cobalt monometallic Layered Double Hydroxide (LDH), combining divalent and trivalent cations of the same chemical element, are commonly used respectively for nitrate reduction and oxygen evolution reaction. This article reports the first synthesis of a LDH using only manganeseas metallic ion. X-Ray diffractograms, infrared and Raman spectra show that the structure obtained through the oxidation of a basic MnII salt with persulfate is comparable to the structure of Fe-LDH also known as Green Rust. XPS shows that in this solid coexist MnII and MnIII states. Thermodynamic considerations predict that this solid can reduce nitrate into gaseous nitrogen without further reductioninto ammonium or ammonia unlike what is observed for Fe-LDH.

The hydrogenation of triple and double carbon-carbon bonds in C4 molecules containing a single unsaturation has been investigated for the lowest index surfaces of the triad Ni, Pd, and Pt through first-principles simulations. Both low and high hydrogen coverage have been explored to identify the nature of the selectivity found in the experiments. The adsorption behavior of the alkynes and alkenes at high hydrogen concentrations differs from the structures in the infinite dilution-limit coverage which makes a significant contribution to selectivity. Structure sensitivity is also a consequence of the hydrogen coverage, at high contents (111) surfaces cannot trap the C4 molecules efficiently, and thus, the reactivity mainly occurs on the more open (100) surfaces. The combination of fast/slow elementary steps, crucial to eliminate trans-alkenes that are health threatening, is not possible for any of the metals studied, although some metals present slightly better behavior. Our study paves the way towards an integrative analysis of the hydrogenation process that accounts for high surface coverage, preferential adsorption, and kinetic contributions.

Catalysts with the strongest basic properties are not always the most efficient ones for transesterification, a series of magnesium-based materials, exhibiting a large range of acido–basic properties, was investigated.

This article describes the main strategies to activate and convert carbon dioxide (CO2 ) into valuable chemicals over catalytic surfaces. Coherent elements such as common intermediates are identified in the different strategies and concisely discussed based on the reactivity of CO2 with the aim to understand the decisive factors for selective and efficient CO2 conversion.

This study aims to reveal how water adsorbed on to a solid can influence its catalytic properties for transesterification in liquid phase. A commercial magnesium silicate was subjected to a range of thermal pretreatments and used for the transesterification of ethyl acetate with methanol. Conversion of ethyl acetate decreased with increasing pretreatment temperature, in direct relation to the release of the water content of the magnesium silicate. Thermogravimetric analysis, diffuse reflectance infrared Fourier transform (DRIFT), and H-1 NMR spectroscopies revealed that physically adsorbed water had little influence on the reactivity. The water incorporated within the catalysts, however, which desorbs at higher temperatures, played a key role on the conversion. Calorimetry, in situ DRIFT spectroscopy, and H-1 NMR characterization indicate that two kinds of active site exist. These are created from the water coordinated to magnesium located on the edge of the clay-like particles or in the defects present in the silicate layer, respectively. Their role could be to stabilize methanol deprotonated by basic MgOH groups, activate the ester, or help the departure of the alkoxyl moiety.

The Cover Feature portrays the four main means (heroes), namely heat, light, electric and solar power, to activate CO2 for its transformation to useful chemicals. This Concept article describes unifying theoretical views of CO2 activation over catalytic surfaces and how product selectivity arises in a general manner. More information can be found in the Concept by A. Álvarez et al. on page 3135 in Issue 22, 2017 (DOI: 10.1002/cphc.201700782).

We present the first in situ W-band (94-GHz) electron paramagnetic resonance (EPR) study of a trapped electron center in thin MgO(001) films. The improved resolution of the high-field EPR experiments proves that the signal originate from a well-defined species present in the bulk of the films, whose projection of the principal g-tensor components onto the (001) plane are oriented along the [110] direction of the MgO lattice. Based on a comparison between the structural properties of the films, knowledge of the ability of bulk defects to trap electrons, and the properties of the EPR signal, it is possible to propose that the paramagnetic species are located at the origin of a screw dislocation in the bulk of the film.