Mutations in the rfa operon leading to severely truncated lipopolysaccharide (LPS) structures are associated with pleiotropic effects on bacterial cells, which in turn generates a complex phenotype termed deep-rough. Literature reports distinct behavior of these mutants in terms of susceptibility to bacteriophages and to several antibacterial substances. There is so far a critical lack of understanding of such peculiar structure-reactivity relationships mainly due to a paucity of thorough biophysical and biochemical characterizations of the surfaces of these mutants. In the current study, the biophysicochemical features of the envelopes of Escherichia coli deep-rough mutants are identified from the molecular to the single cell and population levels using a suite of complementary techniques, namely microelectrophoresis, Atomic Force Microscopy (AFM) and Isobaric Tag for Relative and Absolute Quantitation (iTRAQ) for quantitative proteomics. Electrokinetic, nanomechanical and proteomic analyses evidence enhanced mutant membrane destabilization/permeability, and differentiated abundances of outer membrane proteins involved in the susceptibility phenotypes of LPS-truncated mutants towards bacteriophages, antimicrobial peptides and hydrophobic antibiotics. In particular, inner-core LPS altered mutants exhibit the most pronounced heterogeneity in the spatial distribution of their Young modulus and stiffness, which is symptomatic of deep damages on cell envelope likely to mediate phage infection process and antibiotic action.

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The distribution of edge and basal surface areas of phyllosilicate particles is an essential parameter for understanding the interaction mechanisms at solid/gas or solid/liquid interfaces. Among the techniques proposed to determine the geometrical heterogeneities of flat solids, low-pressure argon adsorption and AFM analysis are the most promising to derive the weight-averaged values of specific surface areas. A series of publications have recently been dedicated to the combination of both methods showing the correlation between the two approaches. As obtaining a large set of high-resolution AFM images is time-consuming, it is necessary to test the ability of AFM routine analysis to derive surface areas and aspect ratio systematically and statistically, with all possible experimental and instrumental artefacts. In the present study, the expected agreement was found between AFM and argon adsorption determination for total, basal, and edge-specific surface areas of nonswelling clay minerals, except for one kaolinite, which is very heterogeneous in size. In addition, it was observed that for a given sample, individual particles present similar shapes, whatever their size, making it possible to derive a statistical relationship between AFM basal and total surface areas. On the basis of the obtained results, recommendations are given to derive accurate edge, basal, and total specific surface areas of phyllosilicates by combining conventional gas adsorption (nitrogen BET) and routine AFM techniques.

… From a geometrical point of view, it is thought that clay destabilization is mainly 36 controlled by phenomena starting at the edge faces of the particles. 37In the present work, the rates of the smectite-Fe(0) reaction at 80°C was assessed by XRD, 38 Mössbauer and CEC analyses for three smectites. The investigations show marked 39 differences in the degree of stability, which can not be explained by the crystal-chemistry 40 rules established in previous studies. Therefore, the Fe(0)-smectite interactions were studied 41 in view of textural and energetic surface quantitative analyses. The studied smectites have 42 equivalent nitrogen BET specific surface areas, equivalent argon edge surface areas and 43 slightly different basal surface areas. This similarity in particle shape indicates that the edge 44 surface area can not be accounted for when explaining the observed differences in reactivity. 45However, a correlation is obtained between smectite reactivity and the energetic 46 heterogeneity of its edge faces. This is interpreted in terms of a multiplication of the number 47 of sites on the edge faces, where the electron transfer between Fe(0) and the smectite 48 structure can occur. 49 3 50 INTRODUCTION 51 52Iron-clay reactions are of great importance in soils and in sedimentary and diagenetic 53 processes. In soils, the evolution of clay minerals is mainly controlled by oxidation-reduction 54 reactions. Kaolinite is very reactive in media under varying redox conditions, but Fe-rich 55 TOT clay minerals are even more reactive, and great changes in their properties may occur 56 (e.g. Favre et al. 2002). Low temperature, iron-rich, clayey environments are also described 57 in sedimentary verdine facies (Bailey 1988; Odin 1988; Odin 1990), in diagenetic oolitic 58 ironstones (Bhattacharyya 1983; Bhattacharyya 1986) and in sandstones (Hornibrook and 59 Longstaffe 1996;Aagaard et al. 2000; Hillier and Velde 1992;Hillier 1994). In these natural 60 systems, iron is present as iron oxides and/ or hydroxides (e.g. Odin 1988;Buatier et al. 1989; 61 Walker and Thompson 1990;Hornibrook and Longstaffe 1996), although metallic iron, 62Fe(0), has only been identified in contact with clay in extraterrestrial materials, such as CM 63 carbonaceous chondrites. In this case, when heating of the asteroid induces fusion of accreted 64 ice, cronstedtite, a Fe-rich 7Å mineral, is formed by interaction between olivine and FeNi 65 metal (Zolensky and McSween 1988;Brearley 1997;Zega and Buseck. 2003 Other possible controlling parameters, which were not analyzed in Lantenois' work, are those 95 describing the surface properties. Indeed, phyllosilicate surfaces have strong differential 96 reactivity because of the extreme anisotropy of their structure (Cases et al., 1986; Bickmore 97 et al., 2001), the irregular surface topography (e.g., kinks, edges and adatoms) and the 98 5 presence of defects (Metz et al., 2005). For example, concerning the alkaline dissolution of 99 smectites (Sato et al. 2003), it has been confirmed t...

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The interaction of biomolecules at the mineral-water interface could have played a prominent role in the emergence of more complex organic species in life's origins. Serpentinite-hosted hydrothermal vents may have acted as a suitable environment for this process to occur, although little is known about biomolecule-mineral interactions in this system. We used batch adsorption experiments and surface complexation modeling to study the interaction of L-aspartate onto a thermodynamically stable product of serpentinization, brucite [Mg(OH) 2 ], over a wide range of initial aspartate concentrations at four ionic strengths governed by [Mg 2+ ] and [Ca 2+ ]. We observed that up to 1.0 µmol of aspartate adsorbed per m 2 of brucite at pH~10.2 and low Mg 2+ concentrations (0.7x10-3 M), but surface adsorption decreased at high Mg 2+ concentrations (5.8x10-3 M). At high Ca 2+ concentrations (4.0x10-3 M), aspartate surface adsorption doubled (to 2.0 µmol•m-2), with Ca 2+ adsorption at 29.6 µmol•m-2. We used the extended triple-layer model (ETLM) to construct a quantitative thermodynamic model of the adsorption data. We proposed three surface reactions involving the adsorption of aspartate (HAsp-) and/or Ca 2+ onto brucite: 2>SOH + H + + HAsp-= >SOH 2 + >SAsp-+ H 2 O, >SOH + HAsp-+ Ca 2+ = >SO-_Ca(HAsp) + + H + , and >SOH + Ca 2+ + 2H 2 O = >SOH 2 + _ Ca(OH) 2 + H +. We used the ETLM to predict that brucite particle surface charge becomes more negative with increasing [Mg 2+ ], creating an unfavorable electrostatic environment for a negativelycharged aspartate molecule to adsorb. In contrast, our addition of Ca 2+ to the system resulted in Ca 2+ adsorption and development of positive surface charge. Our prediction of surface speciation of aspartate on brucite with Ca 2+ revealed that the calcium-aspartate complex is the predominant surface aspartate species, which suggests that the increase in aspartate adsorption with Ca 2+ is primarily driven by calcium adsorption. The cooperative effect of Ca 2+ and the inhibitive effect of Mg 2+ on aspartate adsorption onto brucite indicate that serpentinite-hosted hydrothermal fluids provide an ideal environment for these interactions to take place.

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The aim of this study was to provide new insight into the evaluation of the effect of the crystallinity, size, and morphology of TiO2-anatase nanoparticles on their acid–base properties at the solid–liquid interface. This was achieved through monitoring the evolution in the surface charge density with the solution acidity and point of zero net proton charge (PZNPC) for a set of anatase nanoparticles with a mean size in the 5–20 nm range and various shapes. Different anatase nanoparticles were obtained by a sol–gel synthesis approach using different precursors, pH conditions, and various inorganic or organic additives. The measured PZNPC values were found to vary more than one pH unit depending on the degree of crystallinity and presence of differently exposed surfaces. To discriminate slight differences in the surface reactivity at the solid–water interface, high-resolution titration curves of surface charge for each anatase sample were recorded, and a fine analysis by the titration derivative isotherm summation (TDIS) method and proton affinity distributions (PADs) was performed. They provided accurate data on the strength (pK position) of various local domains of proton adsorption with their relative surface contributions in relation with the particle morphology. The increase in the proportion of sites that are more present on the {101} faces or that of medium acid sites largely present on the {100} faces shifted the point of zero net proton charge to more acidic pH values for particles possessing a majority of such surfaces. In addition to these experiments, the relative acidity of the surface sites on the different surfaces of anatase was evaluated with the multisite complexation model (i.e., MUSIC model) applied to the theoretically optimized surfaces, and a comparison was drawn.