Détermination d’une couche superficielle de sol favorable au transfert du Trichloréthylène (TCE) vers l’atmosphère

L’intérêt de cet article est de montrer qu’il existe une couche superficielle dans la zone non saturée du sol à l’intérieur de laquelle les mécanismes de transport du trichloréthylène (TCE) vers l’atmosphère sont favorables. En prenant en compte dans un modèle de simulation certains paramètres clés du sol déterminés expérimentalement, on a pu non seulement montrer que les effets hygroscopiques modifient le comportement du TCE mais aussi et surtout que ces mécanismes de transfert sont plus favorables dans une couche limite qu’on a appelée couche superficielle. Les résultats montrent clairement que les transferts sont plus importants dans une couche limite du sol au de-là de laquelle ce transfert s’amenuise. En d’autres termes, l’atmosphère ambiante influence les mécanismes d’évaporation par l’intermédiaire de la température et de l’humidité relative lorsque celui-ci se trouve dans la couche dite couche superficielle. En revanche, cette influence de l’atmosphère ambiante se réduit à mesure que le TCE s’infiltre en profondeur. Au de-là de 0,8 mètre de profondeur, le milieu ambiant semble jouer un rôle moins important et les mécanismes d’atténuation naturelles sont d’avantage très faibles favorisant ainsi la persistance du TCE dans le sol.Mots-clés : couche superficielle, trichloréthylène, transfert, sol, atténuation naturelle

Dual EZH2 and EHMT2 histone methyltransferase inhibition increases biological efficacy in breast cancer cells

Background: Many cancers show aberrant silencing of gene expression and overexpression of histone methyltransferases. The histone methyltransferases (HKMT) EZH2 and EHMT2 maintain the repressive chromatin histone methylation marks H3K27me and H3K9me, respectively, which are associated with transcriptional silencing. Although selective HKMT inhibitors reduce levels of individual repressive marks, removal of H3K27me3 by specific EZH2 inhibitors, for instance, may not be sufficient for inducing the expression of genes with multiple repressive marks. Results: We report that gene expression and inhibition of triple negative breast cancer cell growth (MDA-MB-231) are markedly increased when targeting both EZH2 and EHMT2, either by siRNA knockdown or pharmacological inhibition, rather than either enzyme independently. Indeed, expression of certain genes is only induced upon dual inhibition. We sought to identify compounds which showed evidence of dual EZH2 and EHMT2 inhibition. Using a cell-based assay, based on the substrate competitive EHMT2 inhibitor BIX01294, we have identified proof-of-concept compounds that induce re-expression of a subset of genes consistent with dual HKMT inhibition. Chromatin immunoprecipitation verified a decrease in silencing marks and an increase in permissive marks at the promoter and transcription start site of re-expressed genes, while Western analysis showed reduction in global levels of H3K27me3 and H3K9me3. The compounds inhibit growth in a panel of breast cancer and lymphoma cell lines with low to sub-micromolar IC50s. Biochemically, the compounds are substrate competitive inhibitors against both EZH2 and EHMT1/2. Conclusions: We have demonstrated that dual inhibition of EZH2 and EHMT2 is more effective at eliciting biological responses of gene transcription and cancer cell growth inhibition compared to inhibition of single HKMTs, and we report the first dual EZH2-EHMT1/2 substrate competitive inhibitors that are functional in cells

Capillary cohesion and mechanical strength of polydisperse granular materials

We investigate the macroscopic mechanical behaviour of wet polydisperse granular media. Capillary bonding between two grains of unequal diameters is described by a realistic force law implemented in a molecular-dynamics algorithm together with a protocol for the distribution of water in the bulk. Axial-compression tests are simulated for granular samples at different levels of water content, and compared to experiments performed in similar conditions. We find good agreement between numerical and experimental data in terms of the rupture strength as a function of water content. Our results show the importance of the distribution of water for the mechanical behaviour

MECHANICAL BEHAVIOR OF ANNULUS FIBROSUS TISSUE: IDENTIFICATION OF A PORO-HYPER-ELASTIC MODEL FROM EXPERIMENTAL MEASUREMENTS

Annulus fibrosus (AF) is the outer tissue of intervertebral disc (IVD) which is a highly specialized element of the spine that provides flexibility and dissipative capacities. When mechanical loads are transmitted along the spine, IVD mainly supports compression an

A New Experimental Method to Determine the Henry’s Law Constant of a Volatile Organic Compound Adsorbed in Soil

This paper presents a new mechanical method to determine Henry’s law constant (HLC) of a volatile organic compound (VOC). This method is an extension of the one proposed by Ouoba et al. (2010) to determine the water activity in porous media. This work focuses on TCE and aims at characterizing its liquid-vapor equilibrium in various cases in the form of a pure liquid phase or dissolved in an aqueous solution, adsorbed or not in a natural soil. A liquid phase is disposed in a closed chamber whose volume can be incrementally increased. The recording of the total gas pressure leads to evaluating the vapor partial pressure of a volatile compound even in the case of an aqueous solution. This method has been validated using various aqueous solutions of TCE and the HLC obtained is in agreement with the literature. Then, the validity of Henry’s law has been asserted in the case of an aqueous solution of TCE adsorbed in a hygroscopic soil. Indeed, a linear relation between the vapor partial pressure of TCE and its concentration has been obtained while the HLC is about 16% lower. This result highlights the influence of adsorption phenomena on vapor/liquid equilibrium

Comparison of theory and experiment for a two-region solute transport model

International audienceIn this work we compare the recently developed two-region mass transfer theory reported by Ahmadi et al. [A. Ahmadi, M. Quintard, S. Whitaker (1998), Transport in chemically and mechanically heterogeneous porous media, V, two-equation model for solute transport with adsorption, Adv. Water Resour. 1998;22:59–86] with experimental results reported by Zinn et al. [Zinn, B., L. C. Meigs, C. F. Harvey, R. Haggerty, W. J. Peplinski, C. F. Von Schwerin. Experimental visualization of solute transport and mass transfer processes in two-dimensional conductivity fields with connected regions of high conductivity. Environ Sci Technol 2004;38:3916–3926]. We find that the constant mass transfer coefficient predicted by the steady-state closure to the theory, when used with the macroscale transport equation, provides a reasonable prediction of the observed breakthrough curve. However, the use of a constant mass transfer coefficient does not allow good representation of the tailing that is observed in the data. We show that the mass transfer coefficient can be represented in terms of the eigenvalue expansion of a Green's function. For a steady solution to the closure problem, this expansion leads to the effective mass transfer coefficient being defined in terms of the harmonic average of the eigenvalues of the expansion; this is consistent with previous work on this topic. To further investigate the influence of using a single, constant value for the mass transfer coefficient, we examine the solution to the mass transfer problem in terms of a mixed model, where the eigenvalues of one region (the inclusions) are kept, while the second region (the matrix) is treated as a homogenized material. The results from this comparison indicate that the mass transfer coefficient predicted via volume averaging using a quasi-steady closure could potentially be improved upon by development of new methods that retain more of the eigenvalues of the system

On the histone lysine methyltransferase activity of fungal metabolite chaetocin.

Histone lysine methyltransferases (HKMTs) are an important class of targets for epigenetic therapy. 1 (chaetocin), an epidithiodiketopiperazine (ETP) natural product, has been reported to be a specific inhibitor of the SU(VAR)3-9 class of HKMTs. We have studied the inhibition of the HKMT G9a by 1 and functionally related analogues. Our results reveal that only the structurally unique ETP core is required for inhibition, and such inhibition is time-dependent and irreversible (in the absence of DTT), ultimately resulting in protein denaturation. Mass spectrometric data provide a molecular basis for this effect, demonstrating covalent adduct formation between 1 and the protein. This provides a potential rationale for the selectivity observed in the inhibition of a variety of HKMTs by 1 in vitro and has implications for the activity of ETPs against these important epigenetic targets