Photoswitchable Tetraethynylethene‐Dihydroazulene Chromophores

The synthesis, characterization, and photophysical as well as electrochemical properties of the photochromic hybrid systems 11 – 16 and 18 , which contain photoswitchable tetraethynylethene (TEE; 3,4‐diethynylhex‐3‐ene‐1,5‐diyne) and dihydroazulene (DHA) moieties, are presented. The molecular photoswitches were synthesized by a Sonogashira cross‐coupling reaction between an appropriate TEE precursor ( 6 – 10 and 17 ) and an iodinated DHA 1 or its vinylheptafulvene (VHF) isomer ( 4 ) (Schemes 5 – 7). X‐Ray crystal structures of five DHA derivatives ( 1 , trans‐ 11a , cis‐ 11a , 12 , and 13 ) are discussed (Figs. 2 – 5). In all compounds, the cyclohexatriene moiety of the DHA chromophore adopts a clear boat conformation (Table 1). Presumably due to crystal‐packing effects, the arylated TEE moieties in the hybrid systems show substantial distortions from planarity, with the dihedral angles between the planes of the central TEE core and the adjacent aryl substituents amounting to 44°. The switching properties were investigated by electronic absorption spectroscopy. Upon light absorption, DHAs 1 , 12 – 16 , and 18 underwent retro‐electrocyclization in solution to give the corresponding VHFs (Figs. 6, 11, and 12). The reaction is thermally reversible, with half‐lives τ_1/2 between 3.9 and 5.8 h at 25° in CH₂Cl₂ (Figs. 7 and 13 and Table 3). A comparatively slower (E)→(Z) isomerization process about the central C=C bond of the TEE moiety was also observed. The N,N‐dimethylanilino‐(DMA) substituted TEE‐DHA hybrid systems trans‐ 11a and cis‐ 11a did not react to the corresponding VHFs upon irradiation (Scheme 9). Instead, only the reversible (E)→(Z) photoisomerization of the TEE core occurred (Fig. 16 and Table 4). This process was further investigated for photofatigue by electronic‐emission spectroscopy (Fig. 17). After protonation of the DMA group, the usual DHA→VHF photoreaction took place. Compound 11 represents a three‐way chromophoric molecular switch with three addressable sub‐units (TEE core, DHA/VHF moiety, and proton sensitive DMA group) that can undergo individual, reversible switching cycles (Scheme 9). A process modeling the function of an `AND' logic gate (Fig. 19) and three write/erase processes could be performed with this system. Cyclic and linear sweep‐voltammetry studies in CH₂Cl₂ (+Bu₄NPF₆) revealed the occurrence of characteristic first‐reduction steps in the TEE‐DHA hybrid systems between −1.6 and −1.8 V vs. Fc/Fc⁺ (ferrocene/ferricinium couple) (Table 5). Oxidations occur at ca. +1.10 V. After photoisomerization to the VHF derivatives, reduction steps at more positive and oxidation steps at more negative potentials were recorded. No DHA→VHF isomerization took place upon electrochemical oxidation or reduction (Fig. 20).     

Glyphosate–Exonuclease Interactions: Reduced Enzymatic Activity as a Route to Glyphosate Biosensing

N-phosphonomethyle-glycine (glyphosate) is the most widely used pesticide worldwide due to its effectiveness in killing weeds at a moderate cost, bringing significant economic benefits. However, owing to its massive use, glyphosate and its residues contaminate surface waters. On site, fast monitoring of contamination is therefore urgently needed to alert local authorities and raise population awareness. Here the hindrance of the activity of two enzymes, the exonuclease I (Exo I) and the T5 exonuclease (T5 Exo) by glyphosate, is reported. These two enzymes digest oligonucleotides into shorter sequences, down to single nucleotides. The presence of glyphosate in the reaction medium hampers the activity of both enzymes, slowing down enzymatic digestion. It is shown by fluorescence spectroscopy that the inhibition of ExoI enzymatic activity is specific to glyphosate, paving the way for the development of a biosensor to detect this pollutant in drinking water at suitable detection limits, i.e., 0.6 nm .     

Asymmetric Organocatalyzed Intermolecular Functionalization of Cyclohexanone-Derived Dienones

Over the past decades, the advent of asymmetric organocatalysis has changed the way chemists think about creating or breaking chemical bonds, enabling new enantioselective strategies for functionalized molecules. The success of asymmetric organocatalysis is notably based on the existence of various activation modes, leading to countless transformations, and on the vast array of available chiral organic catalysts. Breakthroughs in this area have also been driven by selective functionalization of compounds with multiple activation sites such as cyclohexanone-derived dienones. These platforms can undergo diverse transformations such as Michael addition, Friedel-Crafts alkylation or Diels-Alder cycloaddition that offer new opportunities for reaching natural products and biologically relevant compounds. Amongst cyclohexanone-derived dienones, the 2,5-cyclohexadienone motif has received a great deal of attention due to its reactivity pattern and recently, (cross)-conjugated cyclohexanone-derived substrates have also been considered. In this review, we discuss the intermolecular functionalization of (cross)-conjugated cyclohexanone-derived compounds employing asymmetric organocatalysis.     

Cobalt Nanoparticles Formed upon Reaction of Cp*Co(III) Metallacycles with Na[BHEt3] Show Catalytic Activity in the Hydrosilylation of Aryl Ketones,Aldehydes and Nitriles

The reactivity of the 2-phenylpyridine-derived [Cp*CoI(phpy-κ^C,N)] metallacycle towards Et₃SiH and hydrides was evaluated. The treatment of the same Co(III) complex with Na[BHEt₃] resulted in its decomposition into cobalt nanoparticles. The hydride-promoted decomposition of the metallacycle involves the transient formation of an elusive hydrido-cobalt(III) intermediate, the traces of which were detected by ¹H NMR spectroscopy at sub-ambient temperature. The Co nanoparticles produced from a 5 mol% and 10 mol% load of cobaltacycle and Na[BHEt₃] respectively contain Co(0) that is responsible for the hydrosilylation by Et₃SiH of arylketones into silylalkyl ethers. To minimize the residual side reduction of carbonyls by Na[BHEt₃], a mixture of 5 mol% of the latter with 5 mol% of BEt₃ was found to produce optimal hydrosilylation yields at 40 °C in 2 h. Under similar conditions, several arylnitriles were mono-hydrosilylated into N-silyl-imines in yields ranging from 68 to 100 %.