Razão, religião e revolução: luzes e sombras nas telas de Jacques-Louis David

O artigo analisa a produção pictórica de Jacques-Louis David entre o final da década de 1770 e 1793, destacando o entrelaçamento entre arte, religião e política nas obras do artista francês. Em sua luta contra o Antigo Regime, “filósofos artistas”, como Jacques-Louis David, apossaram-se das armas que eram manipuladas, há séculos, por um de seus principais inimigos: a Igreja. A transmissão do ideário iluminista não poderia ficar restrita à “aridez” dos textos acadêmicos, devendo buscar na religião e nas artes o “encantamento” indispensável à conquista de olhos, ouvidos, cérebros e corações. Depois de recorrer aos heróis das antigas Grécia e Roma, Jacques-Louis David debruçou-se sobre os homens do seu tempo: os deputados de O juramento do jogo de pela e os mártires que sacrificaram suas vidas em prol da revolução. Entrelaçando a arte clássica com a cristã, razão, revolução e religião, Jacques-Louis David forjou estratégias que seriam mobilizadas na propagação de líderes e ideários políticos nos séculos XIX e XX.The article analyzes the pictorial production of Jacques-Louis David between the late 1770s and 1793, highlighting the links between art, religion and politics in the works of the French artist. In their struggle against the Old Regime “philosophers artists,” as Jacques-Louis David, they took possession of the weapons that were manipulated for centuries by one of its main enemies: the Church. The transmission of Enlightenment ideas could not be restricted to “aridity” of academic papers and should seek in religion and the arts the “enchantment” indispensable to the conquest of eyes, ears, brains and hearts. After resorting to the heroes of ancient Greece and Rome, Jacques-Louis David leaned across the men of his time: the deputies of Tennis Court Oath and the martyrs who sacrificed their lives for the sake of revolution. Interweaving classical art with Christian art, reason, revolution and religion, Jacques-Louis David forged strategies that would be mobilized in the spread of political leaders and ideologies in the nineteenth and twentieth centuries

The small molecule specific EphB4 kinase inhibitor NVP-BHG712 inhibits VEGF driven angiogenesis

EphB4 and its cognitive ligand ephrinB2 play an important role in embryonic vessel development and vascular remodeling. In addition, several reports suggest that this receptor ligand pair is also involved in pathologic vessel formation in adults including tumor angiogenesis. Eph/ephrin signaling is a complex phenomena characterized by receptor forward signaling through the tyrosine kinase of the receptor and ephrin reverse signaling through various protein–protein interaction domains and phosphorylation motifs of the ephrin ligands. Therefore, interfering with EphR/ephrin signaling by the means of targeted gene ablation, soluble receptors, dominant negative mutants or antisense molecules often does not allow to discriminate between inhibition of Eph/ephrin forward and reverse signaling. We developed a specific small molecular weight kinase inhibitor of the EphB4 kinase, NVP-BHG712, which inhibits EphB4 kinase activity in the low nanomolar range in cellular assays showed high selectivity for targeting the EphB4 kinase when profiled against other kinases in biochemical as well as in cell based assays. Furthermore, NVP-BHG712 shows excellent pharmacokinetic properties and potently inhibits EphB4 autophosphorylation in tissues after oral administration. In vivo, NVP-BHG712 inhibits VEGF driven vessel formation, while it has only little effects on VEGF receptor (VEGFR) activity in vitro or in cellular assays. The data shown here suggest a close cross talk between the VEGFR and EphR signaling during vessel formation. In addition to its established function in vascular remodeling and endothelial arterio-venous differentiation, EphB4 forward signaling appears to be an important mediator of VEGF induced angiogenesis since inhibition of EphB4 forward signaling is sufficient to inhibit VEGF induced angiogenesis

Density functional calculations of the structures and bond energies of Cr(CO)6 and (h6-C6H6)Cr(CO)2(CX) (X=O,S) complexes

Quantum chemical calculations based on density functional theory have been performed on Cr(CO)6, (eegr6-C6H6)Cr(CO)3 and (eegr6-C6H6)Cr(CO)2(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal-ligand binding energies. In particular, a comparison of metal-arene bond energies calculated for the (eegr6-C6H6)Cr(CO)3 and (eegr6-C6H6)Cr(CO)2(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger pgr-backbonding charge transfer to the CS ligand as compared with CO

DFT Simulations as Valuable Tool to Support NMR Characterization of Halide Perovskites: the Case of Pure and Mixed Halide Perovskites

International audienceSolid state NMR spectroscopy is swiftly emerging as useful tool to characterize the structure, composition and dynamic properties of lead halide perovskites. On the other hand, interpretation of solid state NMR signatures is often challenging, because of the potential presence of many overlapping signals in small range of chemical shifts, hence complicating the extraction of detailed structural features. Here, we demonstrate the reliability of periodic Density Functional Theory in providing theoretical support for the NMR characterization of halide perovskite compounds, considering nuclei with spin I=1/2. For light H-1 and C-13 nuclei, we predict NMR chemical shifts in good agreement with experiment, further highlighting the effects of motional narrowing. Accurate prediction of the NMR response of Pb-207 nuclei is comparably more challenging, but we successfully reproduce the downshift in frequency when changing the halide composition from pure iodine to pure bromine. Furthermore, we confirm NMR as ideal tool to study mixed halide perovskite compounds, currently at the limelight for tandem solar cells and color-tunable light emission

Solid state NMR structural characterization of halide perovskites: the potential contribution of atomistic DFT modeling

International audienceHalide perovskites are a complex class of semiconductors whose structure features two apparently contradictory properties: long-range order associated to the regular crystalline structure,[1] and short-range dynamic disorder, related to the soft nature of the lattice and the libration motion of the organic cations.[2] While the former feature is routinely addressed via X-ray diffraction techniques, the latter requires more local “probes”, with solid state Nuclear Magnetic Resonance (NMR) being an ideal method-of-choice, in light of its sensitivity to local chemical composition and environment, as demonstrated in the recent literature [3-6]. However, the complex line-shapes of solid state NMR measurements, as due to the inherent anisotropic response of this technique, make their interpretation usually a delicate task, hence calling for additional supportive tools.Here we show how periodic DFT simulations can ease the interpretation of the NMR spectroscopic features, providing a complementary perspective to experiments. Targeting nuclei with spin-quantum number I=1/2 for 3D methylammonium lead iodide, bromide and mixed halide systems, we demonstrate the reliability of DFT in reproducing experimental signatures of 13C and 1H light-atoms, with prospects in supporting the characterization of dimensionally confined or hollow perovskite architectures, where the organic component has more important structural/templating role. Quantitative prediction of 207Pb nuclei is more challenging but the different response from pure phase iodide and bromide lead perovskites is well reproduced by DFT simulations. This motivated us to investigate on mixed halide compositions, confirming the sensitivity of NMR to the halide composition,[6-7] and segregation, already at the scale of the individual PbX6 octahedron.[8] Our results open the prospect for joint theoretical-experimental investigations of halide perovskite materials, that combine solid state NMR and periodic DFT simulations. [1] Weller, M. T.; Weber, O. J.; Frost, J. M.; Walsh, A. Cubic Perovskite Structure of Black Formamidinium Lead Iodide, α‐[HC(NH2)2]PbI3, at 298 K, J. Phys. Chem. Lett. 2015, 6, 3209-3212.[2] Quarti, C.; Mosconi, E.; De Angelis, F. Structural and electronic properties of organo-halide hybrid perovskites from ab initio molecular dynamics, Phys. Chem. Chem. Phys., 2015, 17, 9394-9409. [3] Piveteau, L.; Morad, V.; Kovalenko, M. V. Solid-State NMR and NQR spectroscopy of lead-halide perovskite materials, J. Am. Chem. Soc. 2020, 142, 19413-19437.[4] Kubicki, D. J.; Prochowicz, D.; Hofstetter, A.; Zakeeruddin, S. M.; Grätzel, M.; Emsley, L.; Phase Segregation in Cs‐, Rb- and K‐Doped Mixed-Cation (MA)x(FA)1−xPbI3 Hybrid Perovskites from Solid-State NMR’, J. Am. Chem. Soc. 2017, 139, 14173–14180.[5] Milic, J. V.; Im, J.-H.; Kubicki, D. J.; Ummadisingu, A.; Seo, J.-Y.; Li, Y. Ruiz-Preciado, M. A.; Ibrahim Bar, M.; Zakeeruddin, S. M.; Emsley, L.; Grätzel, M. Supramolecular Engineering for Formamidinium-Based Layered 2D Perovskite Solar Cells: Structural Complexity and Dynamics Revealed by Solid-State NMR Spectroscopy, Adv. Energy Mater. 2019, 9, 1900284.[6] Rosales, B. A.; Men, L.; Cady, S.; Hanrahan, M. P.; Rossini, A. J.; Vela, J. Persistent Dopants and Phase Segregation in Organolead Mixed- Halide Perovskites, Chem. Mater. 2016, 28, 6848–6859.[7] Roiland, C.; Trippé-Allard, G.; Jemli, K.; Alonso, B.; Ameline, J.-C.; Gautier, R.; Bataille, T.; Le Pollès, L.; Deleporte, E.; Even, J.; Katan, C. Multinuclear NMR as a tool for studying local order and dynamics in CH3NH3PbX3 (X = Cl, Br, I) hybrid perovskites, Phys. Chem. Chem. Phys. 2016, 18, 27133–27142.[8] Quarti C., Furet E., Katan C., DFT simulations as valuable tool to support NMR characterization of halide perovskites: the case of pure and mixed halide perovskites, submitted under invitation to Helvetica Chimica ActaAcknowledgements This work has been supported by Agence Nationale de la Recherche, project ANR-18-CE05-0026 (MORELESS)

A new combined approach to investigate stacking faults in lamellar compounds

International audienceA new combined approach based on DFT calculations and X-ray powder diffraction allowing the investigation of stacking faults is herein presented. In a first step, most probable stacking faults vectors are computed using first-principles calculations. The favoured layer translations are then considered for the crystal structure refinement using the DIFFaX+ program. As a test case, this method was validated on β-Ni(OH)2 lamellar structure in which the stacking faults have been unambiguously described. Some lamellar vanadophosphates have been investigated using this combined approach

Application of a modified EHMO-ASED formalism to the determination of the structural parameters of organometallics

The parametrization of the EHMO-ASED method we have recently suggested for organometallics is shown to be also applicable, in principle without any modification, to derive the major structural parameters of second-row transition metal systems such as carbonyls or metallocenes. Furthermore, this model leads to satisfactory results when used to calculate the structure of compounds as large as (N-methylindole)tricarbonylchromium(0) or (phenylo.xazoline) tricarbonylchromlum(0) with full geometry optimization of the ligands

VOPO4*H2O: a stacking faults structure studied by X-ray powder diffraction and DFT-D calculations.

International audienceThe dehydration process of VOPO(4)*2H(2)O occurs in two steps corresponding to successive elimination of the two crystallographically distinct water molecules. The intermediate phase VOPO(4)*H(2)O has been stabilized for X-ray powder diffraction studies. The resulting data suggest a tetragonal cell (a = 6.2203(2) Å and c = 6.18867(7) Å), but an important anisotropy in the line broadening points out the necessity of considering a not perfectly organized structure. Because of the layered structure of this compound, density functional theory calculations including dispersion corrections have been carried out to evaluate the possible presence of stacking faults. The results of these calculations give information about the nature of the translations and their probabilities using a Boltzmann distribution. DIFFaX+ simulations of the X-ray powder diffraction pattern have been carried out using the results of the theoretical calculations and confirm the presence and nature of stacking faults

Analysis and Prediction of Stacking Sequences in Intercalated Lamellar Vanadium Phosphates

International audienceAn approach is presented that enables the analysis and prediction of stacking sequences in intercalated lamellar vanadium phosphates. A comparison of previously reported vanadium phosphates reveals two modes of intercalation: (i) 3d transition metal ions intercalated between VOPO4 layers and (ii) alkali/alkaline earth metal ions between VOPO4·H2O layers. Both intercalations were investigated using DFT calculations in order to understand the relative shifts of the vanadium phosphate layers. These calculations in addition to an analysis of the stacking sequences in previously reported materials enable the prediction of the crystal structures of Mx(VOPO4)·yH2O (M = Cs+, Cd2+ and Sn2+). Experimental realization and structural determination of Cd(VOPO4)2·4H2O by single-crystal X-ray diffraction confirmed the predicted stacking sequences