On the Use of Amine–Borane Complexes To Synthesize Iron Nanoparticles

The effectiveness of amine–borane as reducing agent for the synthesis of iron nanoparticles has been investigated. Large (2–4 nm) Fe nanoparticles were obtained from [Fe{N(SiMe₃)₂}₂]. Inclusion of boron in the nanoparticles is clearly evidenced by extended X‐ray absorption fine structure spectroscopy and Mössbauer spectrometry. Furthermore, the reactivity of amine–borane and amino–borane complexes in the presence of pure Fe nanoparticles has been investigated. Dihydrogen evolution was observed in both cases, which suggests the potential of Fe nanoparticles to promote the release of dihydrogen from amine–borane and amino–borane moieties.     

Nanoscale Chemical Imaging Using Tip‐Enhanced Raman Spectroscopy: A Critical Review

Methods for chemical analysis at the nanometer scale are crucial for understanding and characterizing nanostructures of modern materials and biological systems. Tip‐enhanced Raman spectroscopy (TERS) combines the chemical information provided by Raman spectroscopy with the signal enhancement known from surface‐enhanced Raman scattering (SERS) and the high spatial resolution of atomic force microscopy (AFM) or scanning tunneling microscopy (STM). A metallic or metallized tip is illuminated by a focused laser beam and the resulting strongly enhanced electromagnetic field at the tip apex acts as a highly confined light source for Raman spectroscopic measurements. This Review focuses on the prerequisites for the efficient coupling of light to the tip as well as the shortcomings and pitfalls that have to be considered for TERS imaging, a fascinating but still challenging way to look at the nanoworld. Finally, examples from recent publications have been selected to demonstrate the potential of this technique for chemical imaging with a spatial resolution of approximately 10 nm and sensitivity down to the single‐molecule level for applications ranging from materials sciences to life sciences.     

Serial coupling of RP and zwitterionic hydrophilic interaction LC–MS: Suspects screening of diclofenac transformation products by oxidation with a boron‐doped diamond electrode

The presence of pollutants and their transformation products (TPs) in the water system is a big concern because of possible adverse effects on the aquatic environment. Their identification is still a challenge that requires the combination of different chromatographic techniques. In the current research, serial coupling of RPLC and zwitterionic hydrophilic interaction LC with TOF‐MS was investigated as a single separation technique for the screening of suspected TPs from electrochemical oxidation of diclofenac using a boron‐doped diamond electrode. Diclofenac oxidation was performed in three water matrices in order to study its transformation in different chemical contexts. 47 TPs resulting from similar oxidation methods were selected from the literature. As in most cases standards were not available, an identification procedure based on accurate mass data and chromatographic behavior was proposed. According to this procedure, 11 suspected TPs, previously analyzed by LC, GC, or ion chromatography, were detected in a single injection. The method was proved to be reliable and versatile and it could be efficiently employed as a comprehensive analytical tool for the simultaneous analysis of compounds in a wide polarity range.     

Transition‐Metal‐Free Oxidative Cross‐Coupling of Tetraarylborates to Biaryls Using Organic Oxidants

Readily prepared tetraarylborates undergo selective (cross)‐coupling through oxidation with Bobbitt's salt to give symmetric and unsymmetric biaryls. The organic oxoammonium salt can be used either as a stoichiometric oxidant or as a catalyst in combination with in situ generated NO₂ and molecular oxygen as the terminal oxidant. For selected cases, oxidative coupling is also possible with NO₂/O₂ without any additional nitroxide‐based cocatalyst. Transition‐metal‐free catalytic oxidative ligand cross‐coupling of tetraarylborates is unprecedented and the introduced method provides access to various biaryl and heterobiaryl systems.     

Electronic Finetuning of a Bio‐inspired Iron(II) tetra‐NHC Complex by trans Axial Isocyanide Substitution

The synthesis of trans axially substituted mono‐ ( 1 a ) and bis(tert‐butylisocyanide) ( 1 b ) derivatives of the highly active homogeneous bio‐inspired iron(II) olefin epoxidation (pre‐)catalyst 1 bearing an equatorial macrocyclic tetra N‐heterocyclic carbene and two trans axial labile acetonitrile ligands is reported. NMR spectroscopy and SC‐XRD indicate a considerable π‐backdonation from the iron(II) centres to the isocyanide ligand(s). The impact of isocyanide substitution on the electronic features of the complexes is studied by cyclic voltammetry revealing a significant increase in half‐cell potential assignable to the reversible Fe(II)/Fe(III) redox couple with an increasing number of isocyanides as a result of their π‐accepting properties: E_1/2=0.15 V ( 1 ), E_1/2=0.35 V ( 1 a ), E_1/2=0.44 V ( 1 b ).     

One-pot azidochlorination of glycals

A simple one-pot azidochlorination for the preparation of nitrogen-containing Koenigs-Knorr glycosyl donors proceeds upon reaction of protected glycals with sodium azide, ferric chloride, and hydrogen peroxide. Different mono- and disaccharide galactals and glucals are converted in a highly α-selective manner to the 2-azido glycosyl chlorides. Starting from disaccharide galactals, building blocks for the synthesis of the T-antigen are obtained in a straightforward manner. The simplicity of the reaction conditions allows for an efficient and scalable α-selective synthesis of 2-azido substituted glycosyl chlorides.     

Solvent enhancement of reaction selectivity: a unique property of cationic chiral dirhodium carboxamidates

1,3-Dipolar cycloaddition reactions of nitrones with α,β-unsaturated aldehydes catalyzed by a cationic chiral dirhodium(II,III) carboxamidate with (R)-menthyl (S)-2-oxopyrrolidine-5-carboxylate ligands in toluene increase reaction rates, give optimum regioselectivities, and enhance stereoselectivities compared to the same reactions performed in traditionally used halocarbon solvents. Rate and enantioselectivity enhancements were also obtained in hetero-Diels-Alder and carbonyl-ene reactions performed in toluene over those obtained in dichloromethane using the diastereomeric chiral cationic dirhodium(II,III) carboxamidate with (S)-menthyl (S)-2-oxopyrrolidine-5-carboxylate ligands. These enhancements are attributed to diminished or absent association of toluene with the catalyst which lessens the relative importance of the uncatalyzed background reaction, and they may also be a consequence of different coordination angles for aldehyde association with rhodium in the different solvent environments. Overall, the enhancement of reaction rates and selectivities with cationic chiral dirhodium(II,III) carboxamidates in toluene suggests broad applications for them in Lewis acid catalyzed reactions.     

Lattice Boltzmann model for thermal free surface flows with liquid-solid phase transition

Purpose

The main objective of this work is to develop an algorithm to use the Lattice Boltzmann method for solving free surface thermal flow problems with solid/liquid phase changes.

Approach

A multi-distribution function model is applied to simulate hydrodynamic flow and the coupled thermal diffusion-convection problem.

Findings

The free surface problem, i.e. the reconstruction of the missing distribution functions at the interface, can be solved by applying a physical transparent momentum and heat flux based methodology. The developed method is subsequently applied to some test cases in order to assess its computational potentials.

Practical implications

Many industrial processes involve problems where non-isothermal motion and simultaneous solidification of fluids with free surface is important. Examples are all castings processes and especially foaming processes which are characterized by a huge and strongly changing surface.

Value

A reconstruction algorithm to treat a thermal hydrodynamic problem with free surfaces is presented which is physically transparent and easy to implement.     

Inclusion of chemotherapeutic agents in substituted ��-cyclodextrin derivatives

The stabilities of the inclusion compounds of three chemotherapeutic agents, camptothecin (CPT), docetaxel (DOC) and idarubicin (IDA), plus a model compound 1,4-dihydroxyanthraquinone (DHA) with several ??-cyclodextrin (??-CD) derivatives were investigated by solubility measurements, isothermal titration microcalorimetry and fluorescence anisotropy measurements. Ionic heptakis-(6-deoxy-6-thioethers) of ??-CD were found to exhibit very high binding potentials for these drugs making them to good candidates for advanced drug delivery.