Correlated ab Initio Study of the Excited State of the Iron-Coordinated-Mode Noninnocent Glyoxalbis(mercaptoanil) Ligand

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How do structural factors determine the linear and non-linear optical properties of fluorene-containing quadrupolar fluorophores? A theoretical answer

International audienceA large series of push-push and pull-pull quadrupolar fluorophore derivatives with conjugated rods made from arylene-vinylene (PV) or arylene-ethynylene (PE) building blocks, bearing different electron-releasing or electron-withdrawing end-groups, were theoretically investigated using DFT and TD-DFT computations. These compounds, which exhibit good transparency in the visible region, are very promising for various applications, especially for optical limitation. Their absorption and photoluminescence as well as their two-photon absorption (TPA) properties in the near infrared (NIR) region were systematically investigated in order to derive structure-property relationships. The results indicate that (i) for all the studied compounds, the lowest excited state reached by the TPA is the S-2 state, corresponding to the HOMO-1 to LUMO electronic transition, (ii) push-push molecules are found to be more efficient than pull-pull molecules, (iii) an increase of the strength of the donor terminal group (OPh, OMe, NH2, NPh2, and NBu2) enhances the TPA cross-section, and (iv) replacement of PV by PE always leads to an increase of TPA cross-sections in the NIR region

Theoretical investigation on two different mechanisms of fulleropyrrolidine formation

International audienceFulleropyrrolidine synthesis by photo-addition of glycine methyl ester (GME) to [60] fullerene has been recently realized and experimentally studied. Two possible hypotheses were suggested for its formation pathway, but there was no consensus about the most favorable one. Thus, in order to find the most probable mechanism, we performed a detailed theoretical investigation of the reaction between GME and [60] fullerene studying both mechanisms suggested experimentally. The first hypothesis involves two additions of two GME radicals in two steps to C-60 followed by a NH3 departure, whereas the second one involves azomethine ylide formation in a first step and followed by a cycloaddition to [60] fullerene. All the transition states and the intermediates in the reaction steps for both mechanisms were determined. The energetic profiles of both mechanisms were drawn and compared. Several levels of theory were used for the purpose, with the aim to investigate which low-cost level is sufficient to settle and which mechanism is probably involved. For the purpose, semiempirical (AM1), DFT on geometries optimized at AM1 level, and finally DFT on geometries optimized at DFT level were considered. At DFT level, GGA (PBE), hybrid (PBE0) and meta-GGA (M06-2X) were used, with a 6-31+ G(d) basis set. We proved that the release of NH3 and the ring formation step in the first mechanism require a higher energy barrier compared to the second mechanism reaction steps like tautomerization and H2O departure. Thus, we can conclude that the second mechanism involving in a first step the azomethine ylide formation is more favorable than the first mechanism. The interest in using in a first step a semiempirical determination of reaction paths is highlighted, and the choice of the exchange-correlation functional is discussed

Multifunctional isoxazolidine derivatives as α-amylase and α-glucosidase inhibitors

International audienceA series of novel isoxazolidines based on benzaldehyde derivatives have been synthesized from the cycloaddition of chiral menthone-based nitrone and allyl phenyl ethers. All synthetic compounds were assessed for their in vitro PPA, HPA and HLAG inhibitory activity. The results revealed that all targets exhibited better inhibitory effect against PPA (12.3 < IC50 < 38.2 μM), HPA (10.1±0.4< IC50 < 26.8±0.2 μM) and HLAG (65.4±1.2< IC50 < 274.8±1.1μM) when compared with the reference inhibitor, acarbose (IC50=284.6±0.3 μM for PPA, 296.6±0.8 μM for HPA, 780.4±0.3 μM for HLAG) with the highest PPA inhibitory activity was ascribed to compound 3g against both PPA and HPA, and 3b against HLAG enzymes, respectively. Structural activity relationships (SARs) were also established for all synthesized compounds and the interaction modes of the most potent inhibitor (3g) and the active site with residues of three enzymes were confirmed through molecular docking studies. Furthermore, a combination of molecular docking analysis with the in vitro activities can help to improve prediction success and encourages the uses of some of these molecules as potential alternatives toward the modulation of T2D

A Reversible Optical Sensor Film for Mercury Ions Discrimination Based on Isoxazolidine Derivative and Exhibiting pH Sensing

We developed a new optical sensor for tracing Hg(II) ions. The detection affinity examines within a concentration range of 0–4.0 µM Hg(II). The sensor film is based on Methyl 2-hydroxy-3-(((2S,2’R,3a’S,5R)-2-isopropyl-5,5’-dimethyl-4’-oxotetrahydro-2’H-spiro[cy-clohexane-1,6’-im-idazo[1,5-b]isoxazol]-2’-yl)methyl)-5-methylbenzoate (IXZD). The novel synthesized compound could be utilized as an optical turn-on chemosensor for pH. The emission intensity is highly enhanced for the deprotonated form concerning the protonated form. IXZD probe has a characteristic fluorescence peak at 481 nm under excitation of 351 nm with large Stocks shift of approximately 130 nm. In addition, the binding process of IXZD:Hg(II) presents a 1:1 molar ratio which is proved by the large quench of the 481 nm emission peak of IXZD and the growth of a new emission peak at 399 nm (blue shift). The binding configurations with one Hg(II) cation and its electronic characteristics were investigated by applying the Density Functional Theory (DFT) and the time-dependent DFT (TDDFT) calculations. Density functional theory (DFT) and the time-dependent DFT (TDDFT) theoretical results were provided to examine Hg(II)-IXZD structures and their electronic properties in solution. The developed chemical sensor was offered based on the intramolecular charge transfer (ICT) mechanism. The sensor film has a significantly low limit of detection (LOD) for Hg(II) of 0.025 μM in pH 7.4, with a relative standard deviation RSDr (1%, n = 3). Lastly, the IXZD shows effective binding affinity to mercury ions, and the binding constant Kb was estimated to be 5.80 × 105 M−1. Hence, this developed optical sensor film has a significant efficiency for tracing mercury ions based on IXZD molecule-doped sensor film

Rapid Access to Ground- and Excited-State Properties of Gold Nanoclusters Coated with Organic Ligands: Evaluation of the DFTB Method Performance

International audienceGold nanoclusters stand as promising building blocks for solar energy harvesting applications, luminescent materials, and catalytic devices. At the frontier between molecular metallic structures, their large number of electrons prevent use ab initio quantum mechanics method to rationalize predict structure–property relationships, especially when fully coated with organic ligands. Using an approximate DFT-based scheme, namely, density functional tight-binding (DFTB), we demonstrate that it is possible rapidly access ground- (geometry electronic structure) excited-state (UV–visible absorption) properties these nano-objects without sacrificing qualitative accuracy its parent DFT, paving way toward a material design gold-organic nanodevices

Photoinduced charge-transfer in chromophore-labeled gold nanoclusters: quantum evidence of the critical role of ligands and vibronic couplings

International audienceThe electron flow between a metallic aggregate and an organic molecule after excitation with light is a crucial step on which hybrid photovoltaic nanomaterials are based. So far, designing such devices with the help of theoretical approaches has been heavily limited by the computational cost of quantum dynamics models able to track the evolution of the excited states over time. In this article, we present the first application of the time-dependent density functional tight-binding (TD-DFTB) method for an experimental nanometer-sized gold-organic system consisting of a hexyl-protected Au25 cluster labelled with a pyrene fluorophore, in which the fluorescence quenching of the pyrene is attributed to the electron transfer from the metallic cluster to the dye. The full quantum rationalization of the electron transfer is attained through quantum dynamics simulations, highlighting the crucial role of the protecting ligand shell in electron transfer, as well as the coupling with nuclear movement. This work paves the way towards the fast and accurate theoretical design of optoelectronic nanodevices

Physicochemical properties and theoretical studies of novel fragile ionic liquids based on N-allyl-N,N-dimethylethylammonium cation

International audienceA series of novel ionic liquids (ILs) based on N-allyl-N,N-dimethylethylammonium (N112A+) are synthesized and characterized. Their physical properties and electrochemical stabilities are investigated and discussed toward the anion constituents. Herein, four anions are studied including one planar non-fluorinated anion (DCA−) and three fluorinated anions (TFSI−, OTf−, TFA−). The experimental properties are compared to those predicted by density functional theory (DFT) calculations. All salts are found to be low melting compounds while being liquid at room temperature. N112A-TFSI is the most thermally stable (Td = 329 °C) and N112A-TFA is the least stable (Td = 158 °C). The temperature effect on ILs transport properties is determined and discussed using the ionicity and Angell's fragility concepts. Among the good and fragile prepared ILs, N112A –DCA exhibits outstanding transport properties thanks to the low dynamic viscosity (19.97 mPa·s) and high ionic conductivity (19.20 mS·cm−1) reached at 298 K. These suitable properties are explained, from theoretical calculations, by the lower intermolecular interactions of ion-pairs in N112A –DCA and quantified by the decreased value of dispersion ion-pairs interaction energy (−6 kJ·mol−1). The electrochemical stability window (ESW) of selected ILs is strongly affected by the anion structure. The ESW values are found to decrease in the following order N112A-TFSI (4.40 V) > N112A-OTf (3.80 V) > N112A-DCA (3.00 V) > N112A-TFA (2.18 V). Taking into account the most likely oxidation and reduction reactions, the ESWs are discussed and validated by the density-based solvent model (SMD). The experimental values of ESWs are very close to the predicted ones