Dimerization of aldehydes to carboxylic esters catalyzed by K2[Fe(CO)4]–crown ether system

K₂[Fe(CO)₄] (1) with a crown ether was found to be an efficient catalyst for the dimerization of aldehydes to carboxylic esters. Several aromatic aldehydes including furfural gave the corresponding esters in good yields. This reaction also proceeded intramolecularly to give phthalide from phthalaldehyde. However, aliphatic aldehydes gave aldol-condensation products instead of the corresponding esters. In the reactions of p-substituted benzaldehydes with 1, the reactivity decreased with increase of the electron-releasing ability of the substituents. On the basis of these results, the reaction mechanism including the nucleophilic attack of tetracarbonylferrate dianion to the carbonyl carbon is discussed.     

Nucleophilic reactivity of the gold atom in a diarylborylgold(i) complex toward polar multiple bonds

A di(o-tolyl)borylgold complex was synthesized via the metathesis reaction of a gold alkoxide with tetra(o-tolyl)diborane(4). The resulting diarylborylgold complex exhibited a Lewis acidic boron center and a characteristic visible absorption that arises from its HOMO–LUMO excitation, which is narrower than that of a previously reported dioxyborylgold complex. The diarylborylgold complex reacted with isocyanide in a stepwise fashion to afford single- and double-insertion products and a C–C coupled product. Reactions of this diarylborylgold complex with C O/N double bond species furnished addition products under concomitant formation of Au–C and B–O/N bonds, which suggests nucleophilic reactivity of the gold metal center. DFT calculations provided details of the underlying reaction mechanism, which involves an initial coordination of the C O/N bond to the boron vacant p-orbital of the diarylboryl ligand followed by a migration of the gold atom from the tetracoordinate sp³-hybridized boron center, which is analogous to the reactivity of the conventional sp³-hybridized borate species. The DFT calculations also suggested a stepwise mechanism for the reaction of this diarylborylgold complex with isocyanide, which afforded three different reaction products depending on the applied reaction conditions.

A di(o-tolyl)borylgold complex added to C O/N double bond to form Au–C and B–O/N bonds. DFT calculations revealed a two-step mechanism consisting of the coordination of O/N atom to B atom followed by nucleophilic migration of Au atom.     

Orientation selective bond cleavage reactions of biphenyl-fused 1,2-diphenylcyclobutanes initiated by electron transfer

Biphenyl-fused 1,2-diphenylcyclobutanes underwent orientation selective bond cleavage in the photosensitized reactions using DCA as a sensitizer or aminium cation radical catalysed reactions.     

Methoxyquinoline-diethylenetriamine conjugate as a fluorescent zinc sensor

A 6-methoxyquinoline conjugated diethylenetriamine derivative, N,N'-bis(6-methoxy-2-quinolylmethyl)diethylenetriamine (6-MeOBQDIEN) has been synthesized and its fluorescent response toward zinc ion was investigated. In the presence of zinc ion, 6-MeOBQDIEN exhibits fluorescence (λ(ex) = 329 nm, λ(em) = 418 nm, φ = 0.039). The fluorescent intensity of the zinc complex of the compound is two times higher than the parent BQDIEN (φ = 0.021) under the same conditions. The crystal structure of 6-MeOBQDIEN-Zn complex shows that all five nitrogen atoms participate to the metal coordination in a distorted square-pyramidal geometry (τ = 0.145) with the aliphatic nitrogen in an apical position. Fluorescent microscopic analysis using 6-MeOBQDIEN reveals the zinc ion concentration change in living cells.     

Different modes of cyclization in zoanthamine alkaloid system, bisaminal versus spiroketal formation

Bisaminal cyclization in the zoanthamine alkaloid system was strongly affected by the stereochemistry of the C4 methyl. While cyclization of the (4S)-methyl precursor gave only a bisaminal compound, cyclization of the (4R)-methyl isomer produced both spiroketal and bisaminal products.     

Optimization of in situ derivatization SPME by experimental design for GC-MS multi-residue analysis of pharmaceutical drugs in wastewater

This paper presents the development of a procedure, which enables the analysis of nine pharmaceutical drugs in wastewater using gas chromatography‐mass spectrometry (GC‐MS) associated with solid‐phase microextraction (SPME) for the sample preparation. Experimental design was applied to optimize the in situ derivatization and the SPME extraction conditions. Ethyl chloroformate (ECF) was employed as derivatizing agent and polydimethylsiloxane‐divinylbenzene (PDMS‐DVB) as the SPME fiber coating. A fractional factorial design was used to evaluate the main factors for the in situ derivatization and SPME extraction. Thereafter, a Doehlert matrix design was applied to find out the best experimental conditions. The method presented a linear range from 0.5 to 10 μg/L, and the intraday and interday precision were lower than 16%. Applicability of the method was verified from real influent and effluent samples of a wastewater treatment plant, as well as from samples of an industry wastewater and a river.     

Evidence for crystal-face-dependent TiO2 photocatalysis from single-molecule imaging and kinetic analysis

According to the concept of active sites, the activity of heterogeneous catalysts correlates with the number of available catalytic sites and the binding affinity of the substrates. Herein, we report a single-molecule, single-particle fluorescence approach to elucidate the inherent photocatalytic activity of exposed surfaces of anatase TiO(2), a promising photocatalyst, using redox-responsive fluorogenic dyes. A single-molecule imaging and kinetic analysis of the fluorescence from the products shows that reaction sites for the effective reduction of the probe molecules are preferentially located on the {101} facets of the crystal rather than the {001} facets with a higher surface energy. This surprising discrepancy can be explained in terms of face-specific electron-trapping probability. In situ observation of the catalytic events occurring at the solid/solution interfaces reveals the hidden role of the crystal facets in chemical reactions and their impact on the efficiency and selectivity of heterogeneous (photo)catalysts.     

Shock stand-off distance of a solid sphere decelerating in transonic velocity range

The shock stand-off distance of a spherical model flying with transonic speeds is determined through numerical simulations. The model decelerates due to drag forces caused by the pressure and viscous shear stress at the model surface. Two-dimensional axisymmetric numerical codes with numerical grids fixed to the flying spherical model are used in the simulations. Numerically determined shock stand-off distances are compared with experimental data obtained in a previous study as well as with those obtained in our ballistic-range experiments. The numerical results and the experimental data are found to be in good agreement. In addition, the time-dependent shock stand-off distance of a decelerating model is investigated.     

Paramagnetic-diamagnetic phase transition accompanied by coordination bond formation-dissociation in the dithiolate complex Na[Ni(pdt)2]·2H2O

Bis(2,3-pyrazinedithiolate)nickel complex Na[Ni(pdt)(2)]·2H(2)O formed one-dimensional stacks of the Ni(pdt)(2) units and showed strong antiferromagnetic interactions along the stacking direction. A first-order phase transition between the paramagnetic and diamagnetic states, which was driven by dimerization of the Ni(pdt)(2) units, accompanied by coordination bond formation, was observed.