Learning from similarities and differences: a reflection on the potentials and constraints of cross-national studies in mathematics

Research in mathematics education that crosses national boundaries provides new insights into the development and improvement of the teaching and learning of mathematics. In particular, cross-national comparisons lead researchers to more explicit understanding of their own implicit theories about how teachers teach and how children learn mathematics in their local contexts as well as what is going on in school mathematics in other countries. Further, when researchers from multiple countries and regions study collaboratively aspects of teaching and learning of mathematics, the taken-for-granted familiar practices in the classroom can be questioned. Such cross-national comparisons provide opportunities for researchers and educators to probe typical dichotomies such as “high-performing” versus “low performing”, “teacher-centred versus student-centred”, or even “East versus West”, in searching for similarities and differences in educational policies and practices in different cultural contexts.     

Label-free molecular imaging of immunological synapses between dendritic and T cells by Raman micro-spectroscopy

Confocal Raman micro-spectroscopy (CRMS) was used to measure spectral images of immunological synapse formation between dendritic and T cells without using molecular labels or other invasive procedures. The purpose-built inverted CRMS instrument integrated an environmental enclosure and a near-infrared laser to allow measurements on live cells maintained under physiological conditions. The integration of the wide-field fluorescence also enabled viability assays and direct comparison between Raman spectral images and gold-standard immuno-fluorescence images for specific molecules. Raman spectral images of nucleus and proteins were built by fuzzy c-mean clustering method. The Raman images were found to be in good correspondence with the immuno-fluorescence images of DNA and actin. These results indicate that actin is a main contributor to the Raman spectrum of the cytoplasm of dendritic and T cells. While for control cells the Raman spectral images of proteins indicated a more homogeneous distribution of proteins in the cytoplasm of dendritic cells, they indicated a higher accumulation of proteins at the immunological synapses when dendritic cells were pre-treated with laminin. These conclusions were also supported by confocal immuno-fluorescence imaging after cell fixation and labelling. This study demonstrates the potential of CRMS for label-free non-invasive imaging of junctions between live cells. Therefore, this technique may become a useful tool for studying cellular processes in live cells and where non-invasive molecular specific imaging is desirable, such as cell-cell interactions.     

A Rare Cyclic Dimolybdenum Triad with Three Weakly Interacting Unpaired Electrons

Oxidation of α-[Mo₂(cis-DAniF)₂]₃(μ-F)₆ with an excess of FeCp₂BF₄ produces the triply oxidized species {β-[Mo₂(cis-DAniF)₂]₃(μ-F)₆}(BF₄)₃. During the oxidation process, the conformation in the α triangular species changes from an arrangement in which two dimetal units are parallel and the third one essentially orthogonal to a structure in which all three dimetal units are parallel. Furthermore, upon removal of three electrons, the Mo–Mo distances increase by about 0.05–0.06 Å and the Mo–F bond distances decrease by 0.04 Å. The structural data, as well as EPR, are consistent with an electronically localized system and a decrease in bond order from 4 to 3.5 for each dimetal unit.     

A chromogenic calixarene hydroxamic acid for the sequential separation of Ti(IV) and Zr(IV)

A new chromogenic calixarene with hydroxamic acid as chelating agent was synthesized by partial reduction of nitrocalixarene which was subsequently coupled with coumarin chloride. The reagent showed selective and quantitative extraction of Ti(IV) into chloroform at 6 M HCl and that of Zr(IV) at 0.5 M HCl. A facile liquid-liquid extraction method for the separation and spectrophotometric determination of Ti(IV) and Zr(IV) has been proposed. The validity of the method was checked by separating several synthetic mixtures. The method was successfully applied to the analysis of piezoelectric lead-zirconium-titanate (PZT) samples. The method shows remarkable simplicity and selectivity. The method can also be used for the determination of Ti(IV) and Zr(IV) in various environmental samples. The article is published in the original.     

Substituent effect on anthracene-based bisboronic acid glucose sensors

Earlier we communicated an anthracene-based bisboronic acid sensor for glucose. Aimed at understanding the substituent effect, we have introduced various functional groups, such as the cyano, nitro, and fluoro group on the boronic acid moiety of this glucose sensor. Fluorescent binding studies indicated that the cyano-substituted sensor (4a) has the highest affinity (K 2540 M⁻¹) for glucose, but the lowest selectivity (three-fold over fructose); the fluoro-substituted compound (4c) shows the lowest affinity (630 M⁻¹) and a modest selectivity (15-fold over fructose); and the unsubstituted one (1a) shows the highest selectivity over fructose (43-fold) and a modest affinity (1472 M⁻¹).     

Importance of selenium in antioxidant behavior of ebselen: A theoretical study

The electronic structure, geometrical parameters, proton affinities, lone pair occupancies, and orbital interactions have been explored to understand the antioxidant behavior of ebselen at B3LYP/6-31+G1 level. The role of substituents in the nucleophilicity of selenium in eight model molecules containing SeN bond has been analyzed in terms of relative proton affinities. The free energy changes associated with probable catalytic reaction steps have also been evaluated.     

Synthesis and reactivity of novel 3-isothiocyanatopropylsilatrane derived from aminopropylsilatrane: X-ray crystal structure and theoretical studies

A novel silatrane containing Si ← N bond (2.160 Å), has been synthesized by the reaction of 3-aminopropylsilatrane (1), dicyclohexylcarbodiimide (2) and CS₂. The structure was established by elemental analysis, spectroscopic methods (IR, ¹H NMR, ¹³C NMR and Mass spectroscopy) and X-ray crystallography. It was correlated with theoretical studies such as semiempirical (AM1, PM3, PM3MM and MNDO), Density Functional Theory (B3LYP) and Hartree-Fock at 3-21+G^∗ and 6-31G^∗(d) levels. The reactivity of compound 3 was studied with some Lewis acids and bases that showed the formation of corresponding adducts (4-7), which were characterized by elemental analysis, IR and NMR (¹H, ¹³C) spectroscopy.     

Origin of 1,3-induction in the addition of alkyl lithium to imines bearing an N-stereogenic center

The origin of diastereoselectivity in the addition of alkyl lithium to chiral Schiff bases has been investigated experimentally and theoretically and the formation of the major diastereomer can be explained from the energy minimized structure of the Schiff base in which the phenyl group has been found to orient in such a manner that it posed lesser steric hindrance to the incoming nucleophile as compared to the alkyl group.     

Nickel catalysis: six membered heterocycle syntheses

Abstract

The investigation of methods for the chemical synthesis is a growing area of interest due to increasing environmental issues. The use of catalysts in organic reactions has gained extensive interest. Metal and nonmetal catalysts provide a new improved alternative to traditional methods in modern synthetic chemistry. The aim of present review is to focus on the applications of nickel for the synthesis of six membered heterocylces.