Activation of Bismuth(III) Derivatives in Ionic Liquids: Novel and Recyclable Catalytic Systems for Friedel−Crafts Acylation of Aromatic Compounds

The activity of four bismuth(III) derivatives when employed as Friedel−Crafts catalysts for the acylation of aromatics was found to increase dramatically when dissolved in ionic liquids. Solutions of bismuth oxide or triflate in [emim][NTf2] and [bmim][NTf2] are the most efficient catalytic systems, with catalyst loading as low as 1% leading to clean, high-yielding acylation of a variety of benzene derivatives. These improved Friedel−Crafts catalytic systems can also be efficiently recycled as opposed to traditional systems

Specific Effects of Room Temperature Ionic Liquids on Cleavage Reactivity: Example of the Carbon−Halogen Bond Breaking in Aromatic Radical Anions

Specific solvation effects of ionic liquids have been evidenced on the chemical reactivity of radical anions with three different ionic liquids (1-butyl-3-methylimidazolium, trimethylbutylammonium, and triethylbutylammonium cations associated with the same anion (bis(trifluoromethylsulfonyl)imide). Large modifications depending on the localization of the negative charge in the radical anions and, to a less extent, on the nature of the ionic liquids cations are reported. When the charge is spread out over the entire molecule as in the 9-chloroanthracene radical anion, an acceleration of the carbon−halogen bond cleavage when passing from acetonitrile to the ionic liquid is observed. On the contrary, in the case of 4-chlorobenzophenone radical anion where the negative charge is more localized on the oxygen atom of the carbonyl group, a large decrease of the C−Cl cleavage rate occurs in relation with a positive shift of the reduction standard potentials. These effects can be explained by specific ion-pair associations between the radical anion and the cation of the ionic liquid that stabilizes the unpaired electron in the π* orbital of the aromatic system and thus decreases its presence in the σ* bond breaking. The experimental results can be rationalized using Marcus-type formalism (Savéant's model describing the dynamics of electron transfers and bond cleavage) and agree well with the calculated ion-pair stabilization energies estimated with density functional theory (B3LYP). Besides the decrease of the cleavage rate, the ion pairing favors the dimerization between two radical anions that prevails over the cleavage reaction, leading to a different mechanism

Strong Modulation of Two-Photon Excited Fluorescence of Quadripolar Dyes by (De)Protonation

Two quadripolar dyes have been designed and synthesized that present large cross sections for two-photon excitation and whose fluorescence responds strongly to (de)protonation. These dyes are considered as prototypes of molecular pH probes for multiphoton fluorescence microscopy

Ionic Liquid Droplet as e-Microreactor

A powerful approach combining a droplet-based, open digital microfluidic lab-on-a-chip using task-specific ionic liquids as soluble supports to perform solution-phase synthesis is reported as a new tool for chemical applications. The negligible volatility of ionic liquids enables their use as stable droplet reactors on a chip surface under air. The concept was validated with different ionic liquids and with a multicomponent reaction. Indeed, we showed that different ionic liquids can be moved by electrowetting on dielectric (EWOD), and their displacement was compared with aqueous solutions. Furthermore, we showed that mixing ionic liquids droplets, each containing a different reagent, in “open” systems is an efficient way of carrying supported organic synthesis. This was applied to Grieco's tetrahydroquinolines synthesis with different reagents. Analysis of the final product was performed off-line and on-line, and the results were compared with those obtained in a conventional reaction flask. This technology opens the way to easy synthesis of minute amounts of compounds ad libitum without the use of complex, expensive, and bulky robots and allows complete automation of the process for embedded chemistry in a portable device. It offers several advantages, including simplicity of use, flexibility, and scalability, and appears to be complementary to conventional microfluidic lab-on-a-chip devices usually based on continuous-flow in microchannels

Synchronous Photoinitiation of Endothelial NO Synthase Activity by a Nanotrigger Targeted at Its NADPH Site

We designed a new nanotrigger to synchronize and monitor an enzymatic activity interacting specifically with the conserved NADPH binding site. The nanotrigger (NT) combines a docking moiety targeting the NADPH site and a chromophore moiety responsive to light excitation for efficient electron transfer to the protein. Specific binding of the nanotrigger to the reductase domain of the endothelial nitric oxide synthase (eNOSred) was demonstrated by competition between NADPH and the nanotrigger on the reduction of eNOSred flavin. A micromolar Ki was estimated. We had monitored initiation of eNOSred activity by ultrafast transient spectroscopy. The transient absorption spectrum recorded at 250 ps fits the expected sum of the reduced and oxidized species, independently obtained by other chemical methods, in agreement with a photoinduced electron transfer from the excited nanotrigger to the flavin moiety of eNOSred. The rate of electron transfer from the excited state of the nanotrigger (NT*) to the protein is estimated to be kET = (7 ± 2) × 109 s-1 using the decay of oxidized eNOSred-bound nanotrigger compared against prereduced eNOSred or glucose 6-P dehydrogenase as controls. This fast electron transfer bypasses the slow hydride transfer to initiate NOS catalysis as shown by ultrafast kinetics using the eNOSred mutated in the regulatory F1160 residue. The selective targeting of the nanotrigger to NADPH sites should allow controlled initiation of the enzymatic activity of numerous proteins containing an NADPH site