Service Interdisciplinaire sur les Systèmes Moléculaires et les Matériaux

A blooming tree illustrates how CO2 can be recycled to a variety of chemicals based on a strategy discussed by T. Cantat and co-workers in their Communication on page 187 ff. The approach relies on the simultaneous use of a functionalizing reagent and a reductant that can be independently adjusted to access a variety of molecules from CO2. The direct conversion of CO2, amines, and silanes to formamides is reported.

The radiolysis of water due to ionizing radiation results in the production of electrons, H· atoms, ·OH radicals, H3O+ ions and molecules (dihydrogen H2 and hydrogen peroxide H2O2). A brief history of the development of the understanding of water radiolysis is presented, with a focus on the H2 production. This H2 production is strongly modified at oxide surfaces. Different parameters accounting for this behavior are presented.

Lateral thinking: A diagonal approach to CO2 recycling has been explored for the formation of both functionalized and energetic chemicals featuring a reduced carbon center. The strategy relies on the tandem use of a functionalization reagent and a reductant that can be independently modified to access a wide spectrum of chemicals from CO2. It is exemplified with an organocatalytic process to convert CO2 into formamides (see picture). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The Geant4-DNA project proposes to develop an open-source simulation software based and fully included in the general-purpose Geant4 Monte-Carlo simulation toolkit. The main objective of this software is to simulate biological damages induced by ionizing radiations at the cellular and sub-cellular scale. This project was originally initiated by the European Space Agency for the prediction of the deleterious effects of radiations that may affect astronauts during future long duration space exploration missions. In this paper, the Geant4-DNA collaboration presents an overview of the whole on-going project, including its most recent developments that are available in the Geant4 toolkit since December 2009 (release 9.3), as well as an illustration example simulating the direct irradiation of a biological chromatin fiber. Expected extensions involving several research domains, such as particle physics, chemistry and cellular and molecular biology, within a fully interdisciplinary activity of the Geant4 collaboration are also discussed.

PURPOSE: The GEANT4 general-purpose Monte Carlo simulation toolkit is able to simulate physical interaction processes of electrons, hydrogen and helium atoms with charge states (H0, H+) and (He0, He+, He2+), respectively, in liquid water, the main component of biological systems, down to the electron volt regime and the submicrometer scale, providing GEANT4 users with the so-called "GEANT4-DNA" physics models suitable for microdosimetry simulation applications. The corresponding software has been recently re-engineered in order to provide GEANT4 users with a coherent and unique approach to the simulation of electromagnetic interactions within the GEANT4 toolkit framework (since GEANT4 version 9.3 beta). This work presents a quantitative comparison of these physics models with a collection of experimental data in water collected from the literature. METHODS: An evaluation of the closeness between the total and differential cross section models available in the GEANT4 toolkit for microdosimetry and experimental reference data is performed using a dedicated statistical toolkit that includes the Kolmogorov-Smirnov statistical test. The authors used experimental data acquired in water vapor as direct measurements in the liquid phase are not yet available in the literature. Comparisons with several recommendations are also presented. RESULTS: The authors have assessed the compatibility of experimental data with GEANT4 microdosimetry models by means of quantitative methods. The results show that microdosimetric measurements in liquid water are necessary to assess quantitatively the validity of the software implementation for the liquid water phase. Nevertheless, a comparison with existing experimental data in water vapor provides a qualitative appreciation of the plausibility of the simulation models. The existing reference data themselves should undergo a critical interpretation and selection, as some of the series exhibit significant deviations from each other. CONCLUSIONS: The GEANT4-DNA physics models available in the GEANT4 toolkit have been compared in this article to available experimental data in the water vapor phase as well as to several published recommendations on the mass stopping power. These models represent a first step in the extension of the GEANT4 Monte Carlo toolkit to the simulation of biological effects of ionizing radiation.

Unprecedented transformations have been developed over the last years to convert amines to formamides, formamidines and methylamines, in the presence of CO₂ as a reagent. These emerging technologies are reviewed in this perspective and the opportunities and challenges facing the practical use of CO₂ in the production of nitrogen molecules are discussed.

A highly active organocatalytic system based on N-heterocyclic carbenes has been designed for the formylation of N-H bonds in a large variety of nitrogen molecules and heterocycles, using two chemical wastes: CO(2) and polymethylhydrosiloxane (PMHS).

A novel catalytic reaction has been designed to utilize, for the first time, CO2 as a C1 feedstock in the synthesis of N-methylamines. Simple zinc catalysts, based on commercially available zinc salts and ligands, prove highly efficient in promoting both a 6 electron reduction of carbon dioxide and the formation of a C–N bond, using hydrosilanes and amines.

Calcium silicate hydrate (C-S-H) is the main constituent of hydrated cement paste and determines its cohesive properties. Because of the environmental impact of cement industry, it is more and more common to replace a part of the clinker in cement by secondary cementitious materials (SCMs). These SCMs are generally alumina-rich and as a consequence some aluminum is incorporated into the C-S-H. This may have consequences on the cohesion and durability of the material, and it is thus of importance to know the amount and the location of Al in C-S-H and what the parameters are that control these features. The present paper reports the (29)Si and (27)Al MAS NMR analyses of well-characterized C-A-S-H samples (C-S-H containing Al). These samples were synthesized using an original procedure that successfully leads to pure C-A-S-H of controlled compositions in equilibrium with well-characterized solutions. The (27)Al MAS NMR spectra were quantitatively interpreted assuming a tobermorite-like structure for C-A-S-H to determine the aluminum location in this structure. For this purpose, an in-house written software was used which allows decomposing several spectra simultaneously using the same constrained spectral parameters for each resonance but with variable intensities. The hypothesis on the aluminum location in the C-A-S-H structure determines the proportion of each silicon site. Therefore, from the (27)Al NMR quantitative results and the chemical composition of each sample, the intensity of each resonance line in the (29)Si spectra was set. The agreement between the experimental and calculated (29)Si MAS NMR spectra corroborates the assumed C-A-S-H structure and the proposed Al incorporation mechanism. The consistency between the results obtained for all compositions provides another means to assess the assumptions on the C-A-S-H structure. It is found that Al substitutes Si mainly in bridging positions and moderately in pairing positions in some conditions. Al in pairing site is observed only for Ca/(Si+Al) ratios greater than 0.95 (equivalent to 4 mmol.L(-1) of calcium hydroxide). Finally, the results suggest that penta and hexa-coordinated aluminum are adsorbed on the sides of the C-A-S-H particles.

This review presents an overview of the different techniques developed over the last decade to regulate the temperature within microfluidic systems. A variety of different approaches has been adopted, from external heating sources to Joule heating, microwaves or the use of lasers to cite just a few examples. The scope of the technical solutions developed to date is impressive and encompasses for instance temperature ramp rates ranging from 0.1 to 2,000 °C/s leading to homogeneous temperatures from -3 °C to 120 °C, and constant gradients from 6 to 40 °C/mm with a fair degree of accuracy. We also examine some recent strategies developed for applications such as digital microfluidics, where integration of a heating source to generate a temperature gradient offers control of a key parameter, without necessarily requiring great accuracy. Conversely, Temperature Gradient Focusing requires high accuracy in order to control both the concentration and separation of charged species. In addition, the Polymerase Chain Reaction requires both accuracy (homogeneous temperature) and integration to carry out demanding heating cycles. The spectrum of applications requiring temperature regulation is growing rapidly with increasingly important implications for the physical, chemical and biotechnological sectors, depending on the relevant heating technique.

The Seebeck coefficients of the nonaqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide, and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol, and ethylene-glycol are measured in a temperature range from T = 30 °C to T = 45 °C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1 M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or "structure making" effects of tetraalkylammonium ions on the structure of alcohols.

Up to 2 million tons per year of titanium dioxide (TiO₂) nanoparticles (NP) are produced worldwide. This extensive production is postulated to result in release into the environment with subsequent contamination of soils and plants; however, few studies have examined TiO₂-NP uptake and impact on plants. In this study, wheat and rapeseed plantlets were exposed to 14 nm or 25 nm anatase TiO₂-NP in hydroponics conditions, either through root or leaf exposure. Microparticle-induced x-ray emission (μPIXE) coupled with Rutherford backscattering spectroscopy (RBS) was used to quantify absorbed titanium (Ti). Micro x-ray fluorescence (μXRF) based on synchrotron radiation was used to evaluate Ti distribution in roots and leaves. Our results show that both TiO₂-NP are accumulated in these plantlets upon root exposure and that Ti content is higher in rapeseed than wheat. Ti distribution in root cross sections depended on NP agglomeration state. NP are also accumulated in plantlets upon leaf exposure. Finally, it was found that TiO₂-NP exposure induced increased root elongation but did not affect germination, evapotranspiration, and plant biomass. Taken together, these results confirm that TiO₂-NP may be accumulated in plant crops but may only moderately impact plant development.

Gold nanorods in aqueous solution are generally surrounded by surfactants or capping agents. This is crucial for anisotropic growth during synthesis and for their final stability in solution. When CTAB is used, a bilayer has been evidenced from analytical methods even though no direct morphological characterization of the precise thickness and compactness has been reported. The type of surfactant layer is also relevant to understand the marked difference in further self-assembling properties of gold nanorods as experienced using 16-EO(1)-16 gemini surfactant instead of CTAB. To obtain a direct measure of the thickness of the surfactant layer on gold nanorods synthesized by the seeded growth method, we coupled TEM, SAXS, and SANS experiments for the two different cases, CTAB and gemini 16-EO(1)-16. Despite the strong residual signal from micelles in excess, it can be concluded that the thickness is imposed by the chain length of the surfactant and corresponds to a bilayer with partial interdigitation.

The ubiquity of the cyclopentadienyl ligand permits us to use its complexes as representative examples for the description of recent highlights in organometallic and more generally in coordination chemistry of the actinides. Uranium(III) complexes exhibit a remarkable reactivity, especially in the activation of small molecules, and are valuable precursors of higher valent derivatives. Using redox-active ligands led to the design of reactive complexes which have been considered as “synthons” of AnII and AnIII (An = Th, U). Studies of low-valent compounds gave a better insight into lanthanide(III)/actinide(III) differentiation. Organoactinide(IV) complexes with the bis-Cp* platform play a major role in the synthesis of a variety of compounds containing single and double metal–ligand bonds, revealing novel structures and reactions. The bis(cyclopentadienyl) uranium(IV) and thorium(IV) complexes were also found to be quite efficient in catalytic processes. Cyclopentadienyl complexes afford systems in which actinide ions potentially engage in magnetic exchange interactions. Organoactinide complexes in the +5 and +6 oxidation states remain relatively rare, and most of these are cyclopentadienyl derivatives with oxo and imido ligands.

Abstract The aim of inverting seismic waveforms is to obtain the "best" earth model. The best model is defined as the one producing seismograms that best match (usually under a least-squares criterion) those recorded. Our approach is nonlinear in the sense that we synthesize seismograms without using any linearization of the elastic wave equation. Since we use rather complete data sets without any spatial aliasing, we do not have the problem of secondary minima (Tarantola, 1986). Nevertheless, our gradient methods fail to converge if the starting earth model is far from the true earth (Mora, 1987; Kolb et al., 1986; Pica et al., 1989).

An efficient H/D exchange method allowing the deuteration of pyridines, quinolines, indoles, and alkyl amines with D2 in the presence of Ru@PVP nanoparticles is described. By a general and simple procedure involving mild reaction conditions and simple filtration to recover the labeled product, the isotopic labeling of 22 compounds proceeded in good yield with high chemo- and regioselectivity. The viability of this procedure was demonstrated by the labeling of eight biologically active compounds. Remarkably, enantiomeric purity was conserved in the labeled compounds, even though labeling took place in the vicinity of the stereogenic center. The level of isotopic enrichment observed is suitable for metabolomic studies in most cases. This approach is also perfectly adapted to tritium labeling because it uses a gas as an isotopic source. Besides these applications to molecules of biological interest, this study reveals a rich and underestimated chemistry on the surface of ruthenium nanoparticles.

Catalytic hydrosilylation of CO₂ is an efficient and selective approach to form chemicals. Herein, we describe the first iron catalysts able to promote the reductive functionalization of CO₂ using hydrosilanes as reductants. Iron(<sc>ii</sc>) salts supported by phosphine donors enable the conversion of CO₂ to formamide and methylamine derivatives under mild reaction conditions.

The activity of cerium alkoxide complexes supported by a Schiff base ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The rate of L-lactide polymerization was modified by switching in situ between the cerium(III) and cerium(IV) species.

An integrated computational method that couples classical molecular dynamics simulations with density functional theory calculations has been used to simulate the solid-state 17O and 23Na MQMAS, 29Si, 31P, and 23Na static and MAS NMR spectra of the 45S5 Bioglass structural models with up to 248 atoms. Comparison with the experimental spectra collected in this work (the 17O MQMAS spectrum of the 45S5 Bioglass is reported for the first time in the literature) shows an excellent agreement. The results provide deep insights into fundamental open questions regarding the atomic-scale structural details of this glass of great medical interest. In particular, the host silica network, described by the Qn distribution (a Qn species is a network-forming ion bonded to n bridging oxygens), consists of chains and rings of Q2Si (67.2%) SiO4 tetrahedra cross-linked with Q3Si (22.3%) species and terminated by a low quantity of Q1Si (10.1%) species. No Si−O−P bridges have been detected by both 31P NMR and 17O MQMAS experiments, and therefore isolated orthophosphate units are able to form nanodomains that subtract sodium and calcium cations from their network modifying role into the silicate network. Finally, both the experimental and theoretical results show a mixture of dissimilar cations (Na,Ca) around NBO, according to a nonrandom distribution of these species.

Boron speciation was investigated in soda‐lime borosilicate glass containing zirconium. In such compositions, competition between charge compensators (here, sodium and calcium) can occur for the compensation of tetrahedral boron or octahedral zirconium units. 11 B MAS NMR is particularly suitable for obtaining data on preferential compensation behavior that directly affects the boron coordination number. In addition to the classical proportions of tri‐ and tetrahedral boron, additional data can be obtained on the contributions involved in these two coordination numbers. An approach is described here based on simultaneous MAS spectrum analysis of borosilicate glass with variable Zr/Si and Ca/Na ratios at two magnetic field strengths (11.7 and 18.8 T), with constraints arising from MQMAS spectroscopy, detailed analysis of satellite transitions, and spin‐echo experiments. New possibilities of 11 B NMR were presented for improving the identification and quantification of the different contributions involved in tri‐ and tetrahedral boron coordination. Both NMR and Raman revealed a trend of decreased tetrahedral boron proportion with the increase of Ca/Na ratio or the Zr/Si ratio. This strongly suggests that zirconium compensation takes preference over boron compensation, and that zirconium and boron are both compensated mainly by sodium rather than calcium.