Organocatalytic regio- and asymmetric C-selective S(N)Ar reactions-stereoselective synthesis of optically active spiro-pyrrolidone-3,3'-oxoindoles

The first example of catalytic enantioselective nucleophilic aromatic substitution of beta-dicarbonyl compounds is presented. An O-benzoylated cinchona alkaloid derivative catalyst gave a selective C-arylation reaction compared to, e.g., the corresponding benzylated catalyst which provided a 1:1 mixture of the C- and O-arylation products. The reaction proceeds well for various aromatic compounds with different 1,3-dicarbonyl compounds, and the optically active products are obtained in very high yields and with up to 92% ee. One further scope of the organocatalytic enantioselective nucleophilic aromatic substitution reaction is demonstrated by the synthesis of the optically active spiro-pyrrolidone-3,3'-oxoindole structure.     

Quaternary ammonium substituted agarose as surface coating for capillary electrophoresis

A novel positively charged polymer of quaternary ammonium substituted agarose (Q-agarose) has been synthesized and explored for use as a coating in capillary electrophoresis. The fast and simple coating procedure is based on a multi-site electrostatic interaction between the polycationic agarose polymer and the negatively charged fused-silica surface. By simply flushing fused-silica capillaries with hot polymer solution a positively charged, hydrophilic deactivation layer is achieved. The polymer surface provides an intermediate electroosmotic flow of reversed direction, over a range of pH 2-11, compared to unmodified fused-silica. The coating procedure was highly reproducible with an RSD of 4%, evaluated as the electroosmotic flow mobility for 30 capillaries prepared at 10 different occasions. The application of Q-agarose coated capillaries in separation science was investigated using a set of basic drugs and model proteins and peptides. Due to the intermediate electroosmotic flow generated, the resolution of basic drugs could be increased, compared to using bare fused-silica capillaries. Moreover, the coating enabled separation of proteins and peptides with efficiencies up to 300.000 plates m(-1).     

5-Hydroxy-2H-pyrrol-2-ones and not 2-aminofurans are the cycloaddition products between alkyl isocyanides and benzyliden-1,3-diketones

New insights into the cycloaddition reaction between alkyl isocyanides and benzyliden-1,3-diketones are reported. 5-Hydroxy-N-substituted-2H-pyrrol-2-ones and not substituted furans, as previously reported, are formed. The proof of the structure relies on a thorough analytical investigation and X-ray crystallography.     

Studying and switching electron transfer: from the ensemble to the single molecule

We report here on the systematic investigation of photoinduced intramolecular electron transfer (IET) in a series of donor-bridge-acceptor molecules as a means of understanding electron transport through the bridge. Perylenebisimide chromophores connected by various oligophenylene bridges are studied because their electron-transfer behavior can readily be monitored by following changes in the fluorescence intensity. We find dramatic switching of the IET behavior as the solvent polarity (dielectric constant) is increased. By combining steady-state and time-resolved fluorescence spectroscopy in a variety of solvents at multiple temperatures with standard theories of electron transfer, we determine parameters governing the IET behavior of these dimers, such as the electronic coupling through the bridges. We also deploy available ab initio quantum chemical methods to calculate the through-space component of the electronic coupling matrix element. Single-molecule investigations of the electron-transfer behavior also show that IET can be switched reversibly by a similar mechanism in an isolated individual molecule.     

Synthesis,characterization, and ecotoxicity of CeO<Subscript>2</Subscript> nanoparticles with differing properties

CeO₂ nanoparticles with various characteristics find an increasing number of applications in the electronic, medical, and other industries and are therefore likely released in the environment. This calls for investigations linking the physicochemical properties of these particles with their potential environmental impacts. In this study, CeO₂ nanoparticle powders were prepared using three different precursors [Ce(NO₃)₃, CeCl₃, and Ce(CH₃COO)₃] and annealing temperatures (300, 500, and 700 °C). This procedure resulted in nine different types of nanoparticles with differing size (5–90 nm), morphology, surface Ce³⁺/Ce⁴⁺ ratio, and slightly different crystal structures as characterized using transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, and X-ray diffraction measurements with Rietveld refinement. These CeO₂ nanoparticles underwent toxicity testing at concentrations up to 64 mg L^?1 using Daphnia magna. Toxic effects were observed for three particle types with EC50 values between 5 and 64 mg L^?1. No clear correlation was observed between the physicochemical properties (size, shape, oxygen occupancy, Ce³⁺/Ce⁴⁺ ratio) of the nanoparticles and their toxicity. However, toxicity was correlated with the amount of Ce remaining suspended in the test medium after 24 h. This indicated that toxic effects may depend on the colloidal stability of CeO₂ nanoparticles during the first day of exposure. Therefore, being readily suspended and remaining stable for several days in the aquatic media increases the likelihood that CeO₂ nanoparticles will cause unwanted adverse effects.     

Linear preservers of row-dense matrices

Let M_m,n be the set of all m × n real matrices. A matrix A ∈ M_m,n is said to be row-dense if there are no zeros between two nonzero entries for every row of this matrix. We find the structure of linear functions T: M_m,n → M_m,n that preserve or strongly preserve row-dense matrices, i.e., T(A) is row-dense whenever A is row-dense or T(A) is row-dense if and only if A is row-dense, respectively. Similarly, a matrix A ∈ M_n,m is called a column-dense matrix if every column of A is a column-dense vector. At the end, the structure of linear preservers (strong linear preservers) of column-dense matrices is found.     

Glivenko sequent classes in the light of structural proof theory

In 1968, Orevkov presented proofs of conservativity of classical over intuitionistic and minimal predicate logic with equality for seven classes of sequents, what are known as Glivenko classes. The proofs of these results, important in the literature on the constructive content of classical theories, have remained somehow cryptic. In this paper, direct proofs for more general extensions are given for each class by exploiting the structural properties of G3 sequent calculi; for five of the seven classes the results are strengthened to height-preserving statements, and it is further shown that the constructive and minimal proofs are identical in structure to the classical proof from which they are obtained.     

Computer‐Assisted Synthetic Planning: The End of the Beginning

Exactly half a century has passed since the launch of the first documented research project (1965 Dendral) on computer‐assisted organic synthesis. Many more programs were created in the 1970s and 1980s but the enthusiasm of these pioneering days had largely dissipated by the 2000s, and the challenge of teaching the computer how to plan organic syntheses earned itself the reputation of a “mission impossible”. This is quite curious given that, in the meantime, computers have “learned” many other skills that had been considered exclusive domains of human intellect and creativity—for example, machines can nowadays play chess better than human world champions and they can compose classical music pleasant to the human ear. Although there have been no similar feats in organic synthesis, this Review argues that to concede defeat would be premature. Indeed, bringing together the combination of modern computational power and algorithms from graph/network theory, chemical rules (with full stereo‐ and regiochemistry) coded in appropriate formats, and the elements of quantum mechanics, the machine can finally be “taught” how to plan syntheses of non‐trivial organic molecules in a matter of seconds to minutes. The Review begins with an overview of some basic theoretical concepts essential for the big‐data analysis of chemical syntheses. It progresses to the problem of optimizing pathways involving known reactions. It culminates with discussion of algorithms that allow for a completely de novo and fully automated design of syntheses leading to relatively complex targets, including those that have not been made before. Of course, there are still things to be improved, but computers are finally becoming relevant and helpful to the practice of organic‐synthetic planning. Paraphrasing Churchill's famous words after the Allies’ first major victory over the Axis forces in Africa, it is not the end, it is not even the beginning of the end, but it is the end of the beginning for the computer‐assisted synthesis planning. The machine is here to stay.     

Enhancing elementary-school mathematics teachers' efficacy beliefs: a qualitative action research

Individuals and societies that can use mathematics effectively in this period of rapid changes will have a voice on increasing the opportunities and potentials which can shape their future. This has brought affective characteristics, such as self-efficacy, that affect mathematics achievement into focus of the research. Teacher efficacy refers to the extent to which a teacher feels capable to help students learn, influence students’ performance and commitment, and thus plays a crucial role in developing the student in all aspects. In this study, we used two sources of efficacy beliefs, mastery experiences and physiological and emotional states, in an interesting and challenging seven month workshop, as tools to foster teacher efficacy for six elementary-school teachers who were frustrated and wanted to leave their job. Our aim was to study the nature of these teachers’ efficacy in order to change it. In this qualitative action research, we used open interviews, non-participant observations and field notes. Results show that these teachers became efficacious, their students’ achievements and motivation were enhanced, and the school climate was changed. Qualitative inquiry of this construct sheds light on efficacy beliefs of mathematics teachers. Nurturing teacher efficacy has borne much fruit in the field of mathematics in school.     

Gelatin—Hyaluronic Acid Hydrogels with Tuned Stiffness to Counterbalance Cellular Forces and Promote Cell Differentiation

Cells interact mechanically with their environment, exerting mechanical forces that probe the extracellular matrix (ECM). The mechanical properties of the ECM determine cell behavior and control cell differentiation both in 2D and 3D environments. Gelatin (Gel) is a soft hydrogel into which cells can be embedded. This study shows significant 3D Gel shrinking due to the high traction cellular forces exerted by the cells on the matrix, which prevents cell differentiation. To modulate this process, Gel with hyaluronic acid (HA) has been combined in an injectable crosslinked hydrogel with controlled Gel–HA ratio. HA increases matrix stiffness. The addition of small amounts of HA leads to a significant reduction in hydrogel shrinking after cell encapsulation (C2C12 myoblasts). We show that hydrogel stiffness counterbalanced traction forces of cells and this was decisive in promoting cell differentiation and myotube formation of C2C12 encapsulated in the hybrid hydrogels.