Textural,structural and catalytic properties of zirconia doped by heteropolytungstic acid: a comparative study between aerogel and xerogel catalysts

Zirconia doped by heteropolytungstic acid HPW have been synthesized by sol–gel method using two drying techniques of the solvent evacuation. Samples were analyzed with adsorption–desorption of N₂ at 77 K, and the aerogel catalyst was found to exhibit a higher surface area and a higher average pore diameter compared to xerogel. XRD results show that aerogel develops ZrO₂ tetragonal phase, whereas xerogel is amorphous. The thermal analysis studies show that the aerogel’s thermal stability is better than the xerogel one. The catalytic behavior of the aerogel and xerogel toward the nature of the isomerization products probably depends on the acidity and the presence of carbide species. This has been explained by XPS and isopropanol dehydration reaction. In fact, the deconvolution aerogel’s Cls bands reveals the presence of four carbon species assigned to C–C, C=O, C–O and carbide species.     

The Electronic Structure of Some Cyanohydrins—A Spectroscopically Under‐Investigated Family of Compounds

Cyanohydrins are usually formed by addition of hydrogen cyanide to aldehydes or ketones while the elimination of HCN from cyanohydrins is easily observed upon heating. The low thermal stability of these highly boiling compounds leads to difficult studies in the gas phase where partial or complete decomposition is usually observed. Consequently, the reported physicochemical properties of such compounds in the gas phase are still scarce. Keeping with this, four simple cyanohydrins, the glycolonitrile and methyl, vinyl and ethynyl derivatives, have been selected. These are possible candidates for the Interstellar Medium, where the corresponding aldehydes and HCN have been detected, and could have played an important role in prebiotic chemistry, as already proposed for some of them. Three well‐suited spectroscopic techniques, namely, UV photoelectron, infrared, and Raman spectroscopies, in tandem with quantum calculations, have been chosen for the structure analysis. Photoelectron spectroscopy, successfully performed with gaseous compounds, provides the first comparative study on cyanohydrins in the gas phase.     

Mechanochromic Luminescence of Copper Iodide Clusters

Luminescent mechanochromic materials are particularly appealing for the development of stimuli‐responsive materials. Establishing the mechanism responsible for the mechanochromism is always an issue owing to the difficulty in characterizing the ground phase. Herein, the study of real crystalline polymorphs of a mechanochromic and thermochromic luminescent copper iodide cluster permits us to clearly establish the mechanism involved. The local disruption of the crystal packing induces changes in the cluster geometry and in particular the modification of the cuprophilic interactions, which consequently modify the emissive states. This study constitutes a step further toward the understanding of the mechanism involved in the mechanochromic luminescent properties of multimetallic coordination complexes.     

Controlled Release of Encapsulated Bioactive Volatiles by Rupture of the Capsule Wall through the Light‐Induced Generation of a Gas

The encapsulation of photolabile 2‐oxoacetates in core–shell microcapsules allows the light‐induced, controlled release of bioactive compounds. On irradiation with UVA light these compounds degrade to generate an overpressure of gas inside the capsules, which expands or breaks the capsule wall. Headspace measurements confirmed the light‐induced formation of CO and CO₂ and the successful release of the bioactive compound, while optical microscopy demonstrated the formation of gas bubbles, the cleavage of the capsule wall, and the leakage of the oil phase out of the capsule. The efficiency of the delivery system depends on the structure of the 2‐oxoacetate, the quantity used with respect to the thickness of the capsule wall, and the intensity of the irradiating UVA light.     

Rhodamine B nanocrystals: elaborations,characterizations and functionalizations for biosensing applications

A biological sensor based on fluorescent organic nanocrystals (NCs) of Rhodamine B grown in sol–gel thin films was developed. The original signalization function is based on fluorescence contrasts of NCs, which exhibit a simple fluorescence signature, good photostability and higher fluorescence intensities compared to dispersed dye molecules. Thanks to a well-controlled dissolution process of the sol–gel surface, accurately followed by atomic force microscopy, the NCs were made emerging just a few nanometers above the silicate thin films to be directly accessible to biological macromolecules. Thus, hairpin-shaped DNA, functionalized by a probe-molecule (DNA probe), has been grafted onto nanocrystal surfaces leading to a fluorescence quenching by Forster resonance energy transfer. After hybridization of these hairpin-shaped DNA probes with their complementary DNA-target, the molecular probes and NCs are pulled apart, stopping thus the quenching. This “turn-on” of nanocrystal fluorescence allows thus a label-free DNA detection. The preparation methodology of the signalization function, its functionalization by hairpin-shaped DNA probes and first DNA-sensor experiments are presented.     

Cycloaddition of keteniminium with terminal alkynes toward cyclobuteniminium and their use in Diels–Alder reactions

An efficient access to cyclobutanone derivatives has been developed via a ‘one-pot’ [2+2]/[4+2] sequence involving keteniminium and cyclobuteniminium salts as key intermediates. A broad range of novel cyclobuteniminium salts have been prepared via [2+2] cycloaddition of keteniminium salts and alkynes. The resulting [2+2] adducts were then further transformed by Diels–Alder reaction with various dienes to afford cyclobutanone derivatives in good yields. A density functional theory (DFT) based computational study has been performed to obtain insight into the nature of the cycloaddition reactions and to investigate the difference in reactivity of cyclobuteniminium salts. Finally, the usefulness of cyclobutanone derivatives has been demonstrated by ring expansion reactions affording lactone, lactame, and cyclopentanone derivatives.     

Electrochemical sensing of nitric oxide for biological systems: methodological approach and new insights in examining interfering compounds

We report here on the appropriate analysis of some examples of interfering compounds that should be done to assess the specificity of the electrochemical sensing of nitric oxide in solution. To do so, we describe the design of a nickel porphyrin and Nafion®-coated carbon microfibre and discuss the methodological approach in examining interfering compounds.     

Diastereoselective synthesis of a conformationally restricted dinucleotide with predefined alpha and beta torsional angles for the construction of alpha,beta-constrained nucleic acids (alpha,beta-CNA)

[reaction: see text] The synthesis of a diastereopure 1,3,2-dioxaphosphorinane linkage in which two, alpha and beta, out of six torsion angles of the natural phosphodiester backbone are constrained with predefined values of ca. +60 degrees (g(+)) and 180 degrees (t), respectively, is described. The stable and unstrained six-membered cyclic phosphotriester structure represents the smallest possible ring allowing the conformational locking of the alpha torsion angle at a significant positive value that is typical of many bulged regions of nucleic acids.     

Increased catalytic activity of surface-immobilized palladium complexes in the fluorogenic deprotection of an alloc-derivatized coumarin

Catalytic surfaces have been prepared by complexation of palladium on self-assembled terpyridine monolayers on silicon. A reaction-based fluorogenic probe was developed to allow facile visualization of the catalytic potential of the surface. Superior activity of the immobilized catalyst compared with the homogeneous control reactions is demonstrated.