Ethylbenzene to chemicals: Catalytic conversion of ethylbenzene into styrene over metal-containing MCM-41

Isomorphously substituted (MeDM) and impregnated metal-containing MCM-41 (MeO_x/IM) catalysts, in which Me = Co, Cu, Cr, Fe or Ni, have been prepared. Structural and textural characterizations of the catalysts were performed by means of X-ray diffraction (XRD), chemical analysis, Raman spectroscopy, electron paramagnetic resonance (EPR), N₂ adsorption isotherms and temperature programmed reduction (TPR). Cu²⁺, Co²⁺, and Cr⁴⁺/Cr³⁺ species were found over the catalysts as cations incorporated in the MCM-41 structure (MeDM) or highly dispersed oxides on the surface (MeO_x/IM). The MeDM catalysts exhibited a good performance in the dehydrogenation of ethylbenzene with CO₂. However, MeO_x/IM catalysts had a low performance in styrene production (activity less than 15 × 10^?3 mmol h^?1 and selectivity for styrene less than 80%) due to the high reducibility of the metals species. However, Ni²⁺ or Fe³⁺ coordinated with the MCM-41 framework, as well as NiO_x and Fe₂O₃ extra-framework species, is continuously oxidized by the CO₂ to maintain the active sites for dehydrogenating ethylbenzene. Deactivation studies on the FeDM sample showed that Fe³⁺ species produced active sp² carbon compounds, which are removed by CO₂; the referred sample is catalytically selective for styrene and stable over 24 h of reaction. In contrast, highly active Ni²⁺ and Ni⁰ species produced a large amount of polyaromatic carbonaceous deposits from styrene, as identified by TPO, TG and Raman spectroscopy. An acid–base mechanism is proposed to operate to adsorb ethylbenzene and abstract the β-hydrogen. CO₂ plays a role in furnishing the lattice oxygen to maintain the Fe³⁺ active sites in the dehydrogenation of ethylbenzene to form styrene.     

Development and validation of a sensitive and selective method using GC/MS-MS for quantification of 5-fluorouracil in hospital wastewater

Pollution of the environment by pharmaceuticals is a subject of growing scientific and societal concern. However, few quantitative data have been reported concerning hospital wastewater contamination. Among the different molecules used at hospital, antineoplastic drugs appear to be of special interest, and 5-fluorouracil (5-FU) can be considered as a key compound of this therapeutic class. To monitor this pharmaceutical in hospital wastewater, a highly specific and selective method was developed using gas chromatography tandem mass spectrometry after solid-phase extraction. This sensitive method (limit of quantification = 40 ng L⁻¹) was then applied to assess sewage contamination of a middle-size hospital with oncology service located in Paris, France. Native 5-FU was detectable in 12 of the 14 analysed samples. In positive samples, concentration range was measured from 0.09 to 4.0 μg L⁻¹. Finally, a predicting model for the hospital wastewater concentrations is presented, and results of this model are discussed.     

Stereoselective synthesis of N-aryl proline amides by biotransformation-Ugi-Smiles sequence

An efficient combination of MAO-N-catalyzed desymmetrization of cyclic meso-amines with Ugi-Smiles multicomponent chemistry produced optically pure N-aryl proline amides. This method represents the first report of a fully asymmetric Ugi-Smiles process.     

A mild hydrolysis of esters mediated by lithium salts

When treated with amine bases such as triethylamine and various lithium salts in wet solvents, esters are efficiently hydrolyzed to the corresponding acids in good yields. Esters incorporating an α- or β-heteroatom with respect to the ester carbonyl group are hydrolyzed rapidly even at room temperature. To further demonstrate the usefulness of this method, one example is provided where hydrolysis of acetylated camphorsultam is mediated by LiBr.     

Residue-specific pKa determination of lysine and arginine side chains by indirect 15N and 13C NMR spectroscopy: application to apo calmodulin

Electrostatic interactions in proteins can be probed experimentally through determination of residue-specific acidity constants. We describe here triple-resonance NMR techniques for direct determination of lysine and arginine side-chain protonation states in proteins. The experiments are based on detection of nonexchangeable protons over the full range of pH and temperature and therefore are well suited for pKa determination of individual amino acid side chains. The experiments follow the side-chain 15Nzeta (lysine) and 15Nepsilon or 13Czeta (arginine) chemical shift, which changes due to sizable changes in the heteronuclear electron distribution upon (de)protonation. Since heteronuclear chemical shifts are overwhelmed by the charge state of the amino acid side chain itself, these methods supersede 1H-based NMR in terms of accuracy, sensitivity, and selectivity. Moreover, the 15Nzeta and 15Nepsilon nuclei may be used to probe changes in the local electrostatic environment. Applications to three proteins are described: apo calmodulin, calbindin D9k, and FKBP12. For apo calmodulin, residue-specific pKa values of lysine side chains were determined to fall between 10.7 and 11.2 as a result of the high net negative charge on the protein surface. Ideal two-state titration behavior observed for all lysines indicates the absence of significant direct charge interactions between the basic residues. These results are compared with earlier studies based on chemical modification.     

Three Redox States of Nitrosyl: NO+, NO., and NO−/HNO Interconvert Reversibly on the Same Pentacyanoferrate(II) Platform

Not so elusive : [Fe^II(CN)₅(HNO)]^3? has been characterized spectroscopically after the two‐electron reduction of nitroprusside (see scheme). The complex is stable at pH 6, slowly decomposing to [Fe(CN)₆]^4? and N₂O. It is deprotonated at increasing pH value with oxidation of bound NO^? to [Fe^II(CN)₅(NO)]^3?. [Fe^II(CN)₅(HNO)]^3? is the first non‐heme iron–nitroxyl complex prepared in aqueous solution that is reversibly redox‐active under biologically relevant conditions.

     

Loading of Exponentially Grown LBL Films with Silver Nanoparticles and Their Application to Generalized SERS Detection

Feature film : Thin films made by exponential layer‐by‐layer growth display high diffusivity and can be readily infiltrated with inorganic nanoparticles. They can sequestrate molecular systems from solution as a function of the composition of their layers, while providing intense surface‐enhanced Raman scattering (SERS) signals (see picture).

     

Epothilone Analogues with Benzimidazole and Quinoline Side Chains: Chemical Synthesis,Antiproliferative Activity,and Interactions with Tubulin

A series of epothilone B and D analogues bearing isomeric quinoline or functionalized benzimidazole side chains has been prepared by chemical synthesis in a highly convergent manner. All analogues have been found to interact with the tubulin/microtubule system and to inhibit human cancer cell proliferation in vitro, albeit with different potencies (IC₅₀ values between 1 and 150 nM ). The affinity of quinoline‐based epothilone B and D analogues for stabilized microtubules clearly depends on the position of the N‐atom in the quinoline system, while the induction of tubulin polymerization in vitro appears to be less sensitive to N‐positioning. The potent inhibition of human cancer cell growth by epothilone analogues bearing functionalized benzimidazole side chains suggests that these systems might be conjugated with tumor‐targeting moieties to form tumor‐targeted prodrugs.