Study of incompatibility of ammonium nitrate and its mechanism of decomposition by theoretical approach

International audienceThe dramatic accident involving ammonium nitrate (AN) that took place at Toulouse in September 2001 has once again focused attention to the complex hazards pertaining to this chemical. Despite the significant efforts made to increase AN safety over the whole supply chain, we are still facing insufficient knowledge of the actual mechanisms of ammonium nitrate decomposition that may take place in abnormal situations. The paper proposes a theoretical study of chemical incompatibilities of ammonium nitrate with the aim to better understand the driving mechanism(s) through which the explosive reaction takes place with the neat or contaminated substance, to identify what molecules can realistically be generated from this process and to estimate the energy involved. The results, coupled with experimental data, should allow a better understanding of ammonium nitrate hazard profile

Double-hybrid density functionals: merging wavefunction and density approaches to get the best of both worlds

We review why and how double-hybrid density functionals have become new leading actors in the field of computational chemistry, thanks to the combination of an unprecedented accuracy together with large robustness and reliability. Similar to their predecessors, the widely employed hybrid density functionals, they are rooted in the Adiabatic Connection Method from which they emerge in a natural way. We present recent achievements concerning applications to chemical systems of the most interest, and current extensions to deal with challenging issues such as non-covalent interactions and excitation energies. These promising methods, despite a slightly higher computational cost than other typical density-based models, are called to play a key role in the near future and can thus pave the way towards new discoveries or advances.The work in Alicante is supported by the “Ministerio de Educación y Ciencia” of Spain and the “European Regional Development Fund” through project CTQ2011-27253. The work in Paris is supported by the “Agence Nationale de la Recherche” of France through project DinfDNT ANR 2010 BLANC No. 0425 02 and by Sanofi-Aventis

The dosimetry of neutron fields of therapeutic complex based on the U-120 cyclotron

In this work, the characteristics of the treat beam's dosimetry of fast neutrons of the U-120 cyclotron have been analyzed with the help of the ionizing method. The fast neutrons with 6, 3 MeV as medium energy have been obtained in coordination of deuterons with the target made of beryllium and are meant to be used for treating the patients with malignant neoplasms. The capacity of the dose in the beam of fast neutrons has been measured by ionization chambers of different types. The research has been done with the consideration of co-occurring gamma rays. The monitoring indices needed for calculation the duration of therapy session at given therapy dose have also been specified

Development of a new QSPR based tool to predict explosibility properties of chemical substances within the framework of REACH and GHS

International audienceThe new European régulation of Chemicals named REACH (for "Registration, Evaluation and Authorization of Chemicals") turned out in the practical registration phase in December 2008. It requires the new assessment of hazard properties for up to 140000 substances. In this context, the development of alternative prédictive methods for assessing hazardous properties of chemical substances is promoted in REACH and in the related new European classification System of substances CLP (Classification, Labelling and Packaging of chemical substances and mixtures

Prediction of physico-chemical properties for REACH based on QSPR models

International audienceQuantitative Structure Property Relationship models have been developed for the prediction of flash points of two families of organic compounds selected in the PREDIMOL French Project: amines and organic peroxides. If the model dedicated to amines respected all OECD validation principles with excellent performances in predictivity, the one dedicated to organic peroxides was not validated on an external validation set, due to the low number of available data, but already presented high performances in fitting and robustness. This work highlighted the need of gathering experimental data, as in progress in the PREDIMOL project, to achieve validated reliable models that could be used in a regulatory framework, like REACH. Such models are expected to be submitted to the European Joint Research Comity (JRC) and to existing tools (like the OECD ECHA QSAR Toolbox) to be available for use by industrials and regulatory instances

Development of a QSPR model for predicting thermal stabilities of nitroaromatic compounds taking into account their decomposition mechanisms

International audienceThe molecular structures of 77 nitroaromatic compounds have been correlated to their thermal stabilities by combining the quantitative structure-property relationship (QSPR) method with density functional theory (DFT). More than 300 descriptors (constitutional, topological, geometrical and quantum chemical) have been calculated, and multilinear regressions have been performed to find accurate quantitative relationships with experimental heats of decomposition (deltaH). In particular, this work demonstrates the importance of accounting for chemical mechanisms during the selection of an adequate experimental data set. A reliable QSPR model that presents a strong correlation with experimental data for both the training and the validation molecular sets (R 2 = 0.90 and 0.84, respectively) was developed for non-ortho-substituted nitroaromatic compounds. Moreover, its applicability domain was determined, and the model's predictivity reached 0.86 within this applicability domain. To our knowledge, this work has produced the first QSPR model, developed according to the OECD principles of regulatory acceptability, for predicting the thermal stabilities of energetic compounds

On the prediction of thermal stability of nitroaromatic compounds using quantum chemical calculations

International audienceThis work presents a new approach to predict thermal stability of nitroaromatic compounds based on quantum chemical calculations and on quantitative structure-property relationship (QSPR) methods. The data set consists of 22 nitroaromatic compounds of known decomposition enthalpy (taken as a macroscopic property related to explosibility) obtained from differential scanning calorimetry. Geometric, electronic and energetic descriptors have been selected and computed using density functional theory (DFT) calculation to describe the 22 molecules. First approach consisted in looking at their linear correlations with the experimental decomposition enthalpy. Molecular weight, electrophilicity index, electron affinity and oxygen balance appeared as the most correlated descriptors (respectively R2 = 0.76, 0.75, 0.71 and 0.64). Then multilinear regression was computed with these descriptors. The obtained model is a six-parameter equation containing descriptors all issued from quantum chemical calculations. The prediction is satisfactory with a correlation coefficient R2 of 0.91 and a predictivity coefficient R2(cv) of 0.84 using a cross validation method

Theoretical Exploration of Type I/Type II Dual Photoreactivity of Promising Ru(II) Dyads for PDT Approach

Ru(II)-dyads are a class of bioactive molecules of interest as anticancer agents obtained incorporating an organic chromophore in the light-absorbing metallic scaffold. A careful DFT and TDDFT investigation of the photophysical properties of a series of Ru(II)-polypiridyl dyads containing polythiophene chains of different lengths bound to a coordinating imidazo[4,5-f][1,10]phenantroline ligand, is herein reported. The modulation of the crucial chemical and physical properties of the photosensitizer with the increasing number of thiophene units, has been accurately described investigating the UV-Vis spectra, Type I and Type II photoreactions, also including spin orbit coupling values (SOC). Results show that the low-lying 3IL states afforded as the number of the thiophene ligands increases (n=3,4) are energetically high enough to ensure the singlet oxygen production and can be also involved in electron transfer reaction, showing a dual type I/typeII photeoreactivity

Rationale for a new class of double-hybrid approximations in density-functional theory

We provide a rationale for a new class of double-hybrid approximations introduced by Br\'emond and Adamo [J. Chem. Phys. 135, 024106 (2011)] which combine an exchange-correlation density functional with Hartree-Fock exchange weighted by \l and second-order M{\o}ller-Plesset (MP2) correlation weighted by \l^3. We show that this double-hybrid model can be understood in the context of the density-scaled double-hybrid model proposed by Sharkas et al. [J. Chem. Phys. 134, 064113 (2011)], as approximating the density-scaled correlation functional E_c[n_{1/\l}] by a linear function of \l, interpolating between MP2 at \l=0 and a density-functional approximation at \l=1. Numerical results obtained with the Perdew-Burke-Ernzerhof density functional confirms the relevance of this double-hybrid model.Comment: 4 pages, 2 figures, to appear in Journal of Chemical Physic

A mechanistic and experimental study of the diethyl ether oxidation

International audienceThis work presents the results of the theoretical investigations on autoxidation process of diethyl ether (DEE), a chemical largely used as solvent in laboratories and considered to be responsible for various accidents. Based on Density Functional Theory (DFT) calculations, the aims of this study were the identification of all the most probable reaction paths involved in DEE oxidation (at ambient temperature and under conditions that reflect normal storage conditions) and the characterization of products and all potential hazardous intermediates, such as peroxides. Results indicate that industrial hazards could be related to hydroperoxide formation and accumulation during the chain propagation step. A detailed kinetics model of DEE oxidation in the gas phase was then developed from all energetic and kinetics parameters collected during the mechanistic study. Outputs of the kinetics model, in terms of time of evolution of product concentrations, have been then compared with the experimentally measured concentration of products (notably hydroperoxides) issued from tests on DEE oxidation conducted under accelerated conditions with autoclaves