Alain Walcarius

Factors affecting the reactivity of thiol-functionalized mesoporous silica adsorbents toward mercury(II).

Numerous mercaptopropyl-functionalized silica spheres have been prepared by either post-synthesis grafting of MCM-41 and MCM-48 or self-assembly co-condensation of mercaptopropyltrimethoxysilane (MPTMS) or mercaptopropyltriethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. These materials of approximately the same particle size and morphology featured different functionalization levels, various degrees of structural order, and variable distribution of thiol groups in the mesopores. Their reactivity in solution has been studied using Hg(II) as model analyte. Total accessibility (on a 1:1 S:Hg stoichiometry basis) was demonstrated and quantified for well-ordered materials whereas less open and less organized structures with high degrees of functionalization were subject to less-than-complete loadings. Capacities measured at pH 2 were lower than at pH 4 because of distinct mercury-binding mechanisms. Kinetics associated to the uptake process were studied by in situ electrochemical monitoring of Hg(II) consumption from aqueous suspensions containing the various adsorbents. They indicate only little difference between materials of the MCM-41 and MCM-48 series at similar functionalization levels, fast mass transport in well-ordered mesostructures in comparison to the poorly or non-ordered ones (except at pH 2 where charge formation induced some restriction in materials characterized by long-range structural order), and even faster processes in the wormlike frameworks (characterized by shorter range structural order). Hg(II) binding to thiol-functionalized materials obtained by post-synthesis grafting was found to occur more rapidly in the early beginning of the uptake process as a result of a higher concentration of binding sites at the pore entrance in comparison to the more homogeneous distribution of these groups in the mesochannels of materials obtained by co-condensation.

Electrochemical analysis of methylparathion pesticide by a gemini surfactant-intercalated clay-modified electrode.

In this study, an hybrid material obtained by the intercalation of a gemini surfactant between the layers of smectite-type clay, was fully characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and N(2) adsorption-desorption experiments (BET method). To ascertain the intercalation process of the starting clay by the dimeric surfactant, the permselectivity and ion exchange properties of the organoclay were investigated by ion exchange voltammetry using [Fe(CN)(6)](3-) and [Ru(NH(3))(6)](3+) as redox probes, by the means of a clay film-modified electrode. Due to its organophilic character, the surfactant-intercalated complex was evaluated as electrode modifier for the accumulation of methylparathion (MP) pesticide. The electroanalytical procedure involves two steps: preconcentration under open-circuit followed by voltammetric detection by square wave voltammetry: the peak current obtained (after 5min preconcentration in 4x10(-5)molL(-1)MP) on a glassy carbon electrode coated by a thin film of the modified clay was more than five times higher than that exhibited by the same substrate covered by a film of the pristine clay. This opens the way to the development of a sensitive method for the detection of the pesticide. Many parameters that can affect the stripping response (surfactant loading of the hybrid material, film composition, pH of the detection medium, preconcentration time, electrolysis potential and duration as well as some other instrumental parameters) were systematically investigated to optimize the sensitivity of the organoclay-modified electrode. After optimization, a linear calibration curve for MP was obtained in the concentration range from 4x10(-7) to 8.5x10(-6)molL(-1) in acetate buffer (pH 5), with a detection limit of 7x10(-8)molL(-1) (signal-to-noise ratio equal to 3). The interference effect of various inorganic ions likely to influence the stripping determination of the pesticide was also examined, and the described method was applied to spring water analysis.

Investigation of alendronate-doped Apatitic Cements as a Potential Technology for the Prevention of Osteoporotic Hip Fractures: Critical Influence of the Drug Introduction Mode on the In Vitro Cement Properties.

Combination of a bisphosphonate (BP) anti-osteoporotic drug, alendronate, with an apatitic calcium phosphate cement does not significantly affect the main properties of the biomaterial, in terms of injectability and setting time, provided that the BP is introduced chemisorbed onto calcium-deficient apatite, one of the components of the cement. In contrast to other modes of introducing the BP into the cement formulation, this mode allows to minimize alendronate release in the cement paste, thus limiting the setting retardant effect of the BP. An original approach based on high frequency impedance measurements is found to be a convenient method for in situ monitoring of the cement setting reaction. The release profile of the drug from a cement block under continuous flow conditions can be well described using a coupled chemistry/transport model, under simulated in vivo conditions. The results show that the released alendronate concentration is expected to be much lower than the cytotoxic concentration.

Positronium reemission yield from mesostructured silica films

The reemission yield of ortho-positronium (o-Ps) into vacuum outside mesoporous silica films on glass is measured in reflection mode with a specially designed lifetime (LT) spectrometer. Values as high as 40% are found. The intensity of the 142 ns vacuum LT is recorded as a function of reemission depth. The LT depth profiling is correlated to the 2gamma and 3gamma energy ones to determine the annihilation characteristics inside the films. Positron lifetime in capped films is used to determine the pore size. For the first time, a set of consistent fingerprints for Ps annihilation, o-Ps reemission into vacuum, and pore size, is directly determined in CTACl-TEOS films.

Electrochemical response of ascorbic and uric acids at organoclay film modified glassy carbon electrodes and sensing applications

A naturally occurring Cameroonian smectite clay has been grafted with trimethylpropylammonium groups and the resulting organoclay deposited as thin film onto a glassy carbon electrode (GCE) surface. It was then exploited as a suitable matrix for the accumulation and the electrochemical detection of ascorbic acid (AA) and uric acid (UA). Cyclic voltammetry revealed an increase in oxidation peak responses along with a negative shift of the corresponding anodic peak potential for both AA and UA species when using the organoclay coated GCE in comparison with the bare electrode. The electroanalytical response was improved by coating the electrode surface with a first layer of sublimed ferrocene (FC(s)), and then overcoating with the organoclay film to avoid the mediator leaching. The resulting bilayer film exhibited good characteristics such as extended linear range and high sensitivities for AA and UA, in cyclic voltammetry and amperometry. Interestingly, the redox mediator FC(s) was likely to lower overpotentials for AA oxidation (but not for UA), making possible the selective detection of these species in a mixture. The developed method could be used for the determination of AA in a pharmaceutical preparation and for UA in urine.

A Scheme To Produce The Antihydrogen Ion H̄+ For Gravity Measurements

We propose to use the charge exchange reaction of antiprotons with positronium atoms in order to produce antihydrogen atoms, H, and H+ ions. The ions can be cooled down to μK temperatures and then ionized to recover an ultra slow neutral H atom. Its acceleration is then measured by time of flight. Results on the conversion of slow positrons into positronium are presented. This is a first step towards the creation of a dense cloud of positronium atoms to be used as a target for the antiprotons. The source of positrons is based on a 6 MeV industrial electron linac with 0.2 mA average current to be installed in CEA‐Saclay. Equipped with a tungsten target and a moderator, it is aimed at producing rates of order 108 s−1 slow positrons.

Electrochemistry within template nanosystems

Nanostructuration of electrode surfaces via bottom-up approaches has becoming a well-established area of modern electrochemistry. Among them, the use of templates such as supramolecular assemblies, packed colloidal crystals or hard porous materials, appear to be increasingly attractive to generate nanosystems with ordered pore structure at the meso- or macro-scale. This review highlights the features of both electrically conducting and non-conducting organized materials prepared by a template approach, in connection to their possible application in various fields of electrochemical science. On the basis of selected examples, it discusses the main advantages of templated macro- and mesoporous metals, metal oxides and carbon materials in terms of designing new types of porous electrodes exhibiting high performance. The improvements are related to electroactive surface areas larger than the geometric one, fast mass transport owing to widely open porous structures, and/or good ionic or electronic conductivity.

A straightforward approach to enhance the textural, mechanical and biological properties of injectable calcium phosphate apatitic cements (CPCs): CPC/blood composites, a comprehensive study

Two commercial formulations of apatitic calcium phosphate cements (CPCs), Graftys® Quickset (QS) and Graftys® HBS (HBS), similar in composition but with different initial setting time (7 and 15min, respectively), were combined to ovine whole blood. Surprisingly, although a very cohesive paste was obtained after a few minutes, the setting time of the HBS/blood composite dramatically delayed when compared to its QS analogue and the two blood-free references. Using solid state NMR, scanning electron microscopy and high frequency impedance measurements, it was shown that, in the particular case of the HBS/blood composite, formation of a reticulated and porous organic network occurred in the intergranular space, prior to the precipitation of apatite crystals driven by the cement setting process. The resulting microstructure conferred unique biological properties to this material upon implantation in bone defects, since its degradation rate after 4 and 12weeks was more than twice that for the three other CPCs, with a significant replacement by newly formed bone. STATEMENT OF SIGNIFICANCE A major challenge in the design of bone graft substitutes is the development of injectable, cohesive, resorbable and self-setting calcium phosphate cement (CPC) that enables rapid cell invasion with initial mechanical properties as close as bone ones. Thus, we describe specific conditions in CPC-blood composites where the formation of a 3D clot-like network can interact with the precipitated apatite crystals formed during the cement setting process. The resulting microstructure appears more ductile at short-term and more sensitive to biological degradation which finally promotes new bone formation. This important and original paper reports the design and in-depth chemical and physical characterization of this groundbreaking technology.

1,8-Bis[3-(triethoxy­silyl)prop­yl]-1,8-diazo­niatricyclo­[9.3.1.14,8]hexa­decane diiodide

The organic molecule of title compound, C30H66N4O6Si2 2+·2I−, is located around a centre of symmetry. The structure exhibits disorder of the triethoxy groups with the ratios 0.78 (1)/0.22 (1), 0.67 (1)/0.33 (1) and 0.58 (1)/0.42 (1).