Synchronizing Substrate Activation Rates in Multicomponent Reactions with Metal–Organic Framework Catalysts

A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In₈(OH)₆(popha)₆(H₂O)₄]?3 H₂O ( InPF‐16 ), [In(popha)(2,2′‐bipy)]?3 H₂O ( InPF‐17 ), [In₃(OH)₃(popha)₂(4,4′‐bipy)]?4 H₂O ( InPF‐18 ), [In₂(popha)₂(4,4′‐bipy)₂]?3 H₂O ( InPF‐19 ), [In(OH)(Hpopha)]?0.5 (1,7‐phen) ( InPF‐20 ), and [In(popha)(1,10‐phen)]?4 H₂O ( InPF‐21 ) (InPF=indium polymeric framework, H₃popha=5‐(4‐carboxy‐2‐nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent‐free cyanosilylation of carbonyl compounds, the one pot Passerini 3‐component (P‐3CR) and the Ugi 4‐component (U‐4CR) reactions. In addition, InPF‐17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α‐aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven‐coordinated indium framework of the catalyst InPF‐17 . This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF‐based heterogeneous catalyst for multicomponent reactions.     

XANES speciation of mercury in three mining districts – Almadén,Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.     

ESR EVIDENCE OF AN ELECTRON TRANSFER BETWEEN ARYLPHOSPHINES AND ARYLNITROSO COMPOUNDS

Abstract

Electron transfer between arylphosphines and arylnitroso compounds gives rise to the formation of free radicals which have been characterized by esr     

Highly Diastereoselective [3+2] Cycloadditions Between Non-Racemic p-Tolylsulfinimines and Iminoesters: An Efficient Entry to Enantiopure Imidazolidines and Vicinal Diaminoalcohols

Abstract

Readily available p-tolylsulfinimines undergo highly stereoselective [3 + 2] cycloadditions with azomethine ylides generated from α -iminoesters and LDA to produce N-sulfinylimidazolidines. In the presence of Lewis acids, p-tolylsulfinimines react with glycine iminoester enolates to produce N-sulfinylimidazolidines, after cyclization of open chain intermediates. These mechanistically diverse processes take place with excellent regio-, stereo-, and facial selectivities, and the latter is opposite to most known reactions involving sulfinimines. Some of the resulting imidazolidines have been transformed into examples of a novel class of nonsymmetrical vicinal diamines using reductive and/or hydrolytic protocols.     

Structural Basis for Carbapenemase Activity of the OXA-23 β-Lactamase from Acinetobacter baumannii

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Hydration of high alumina cement–silica fume composite with addition of Portland cement or sodium polyphosphate under hydrothermal treatment

Various hydrothermal curing regimes were used to investigate the hydration and physical characteristics of two kinds of inorganic binder composites: high alumina cement–silica fume–Portland cement and high alumina cement–silica fume–sodium polyphosphate. Simultaneous thermal analysis (DTA and TG) was used to identify temperature ranges of thermal decomposition of cured samples and to characterize the nature of hydrate products. Two kinds of products are formed. The first ones consist of C₃AH₆, AH₃, calcium carbonate (C–C) as a product of carbonation, and C₃AH_1.5 resulted from the partial decomposition of C₃AH₆ under higher hydrothermal pressure. The second ones are the products formed by acid–base reaction between monocalcium aluminate and sodium polyphosphate to form NaCaPO₄·xH₂O and Al₂O₃·xH₂O that could convert to chemically bonded ceramic binders like hydroxyapatite (Ca₅(PO₄)₃OH) and gibbsite (Al(OH)₃). These two hydroceramic products formed under these conditions act also as binder and could be useful as cement binders for the protection of petroleum, gas, or geothermal wells. Mercury intrusion porosimeter was used for the estimation of the pore structure parameters of the composites. It turned up that longer curing time coupled with higher hydrothermal pressure has improved the pore structure of the first composite, while that of the second has remained unchanged.     

Chemoselective hydrosilylation of hydroxyketones

A chemoselective method for the hydrosilylation of ketones has been developed, using the combination of triphenylsilane and a catalyst prepared from Ni(COD)₂ and the simple N-heterocyclic carbene IMes. The most notable feature of this method is that free hydroxyls are largely unaffected, thus providing a simple one-step procedure for the conversion of hydroxyketones to mono-protected diols, wherein the protecting group is exclusively installed on the ketone-derived hydroxyl. The process is typically high yielding with both simple ketones and more complex hydroxyketone substrates.     

ADSORPTION OF METAL IONS ON STEARIC ACID-NONADECANE PARTICLES IN AQUEOUS SOLUTION

The adsorption of metal ions at the stearic acid/electrolyte and nnonadccane-stearic acid mixture/electrolyte interface was investigated by means of the potentiometric titration, zeta potential and adsorption measurements. It was found that the studied colloidal suspensions exhibited an adsorption affinity towards multivalent metal ions. The adsorption of Ca²⁺, Cd²⁺ and Al³⁺ ions caused a strong decrease of surface charge density and zeta potential values in this systems. The adsorption reactions occur by way of cation exchange with protons from two surface carboxyl groups. Al high metal concentrations, in adsorption reactions there are involved also carboxyl groups from the subsurface layer. On the basis of the adsorption data, the cation surface complexation constants were calculated by Shindler's method.