Synthesis of 2(1H)-pyrazinone phosphonates via an Arbuzov-type reaction

A simple and catalyst-free method for the synthesis of phosphonated 2(1H)-pyrazinones is described starting from 3,5-dichloropyrazinones. The method also works for 3-bromo- and 3-iodopyrazinones. Classical heating conditions as well as microwave-enhanced reaction conditions were tested.     

Temporary silicon-tethered ring-closing metathesis: recent advances in methodology development and natural product synthesis

Temporary silicon-tethered ring-closing metathesis represents an important cross-coupling strategy for the formation of medium-sized silacycles. These intermediates are valuable synthons in organic synthesis due to their propensity to undergo a facile refunctionalization through protodesilylation, oxidation, silane-group transfer or transmetallation. A particularly attractive utility of this methodology is an application in the synthesis of biologically important natural products. The purpose of this review article is to highlight the recent progress in methodology development and its strategic application toward the target-directed synthesis.     

HOMOGENIZATION,SYMMETRY, AND PERIODIZATION IN DIFFUSIVE RANDOM MEDIA

We present a systematic study of homogenization of diffusion in random media with emphasis on tile-based random microstructures.We give detailed examples of several such media starting from their physi...     

Synthesis and acid functionalization of cerium oxide nanoparticles

Colloidal cerium oxide has been obtained by controlled oxidation of soluble Ce(III) salts in hydrothermal conditions. The homogeneous nucleation of CeO₂ through thermolysis of this oxidizing solution allows the formation of well dispersed colloidal particles. Under optimal conditions, well crystallized particles with an average size of 8 nm are obtained. The surface is terminated by acetate groups which can be substituted by grafting phosphonic acids or phosphoric acids. Particularly, the grafting of 2-carboxyethylphosphonic acid or phosphonoacetic acid increases the acidic character of the surface as observed by impedance spectroscopy.     

Parameters for Irreversible Inactivation of Monoamine Oxidase

The irreversible inhibitors of monoamine oxidases (MAO) slow neurotransmitter metabolism in depression and neurodegenerative diseases. After oxidation by MAO, hydrazines, cyclopropylamines and propargylamines form a covalent adduct with the flavin cofactor. To assist the design of new compounds to combat neurodegeneration, we have updated the kinetic parameters defining the interaction of these established drugs with human MAO-A and MAO-B and analyzed the required features. The K_i values for binding to MAO-A and molecular models show that selectivity is determined by the initial reversible binding. Common to all the irreversible inhibitor classes, the non-covalent 3D-chemical interactions depend on a H-bond donor and hydrophobic-aromatic features within 5.7 angstroms apart and an ionizable amine. Increasing hydrophobic interactions with the aromatic cage through aryl halogenation is important for stabilizing ligands in the binding site for transformation. Good and poor inactivators were investigated using visible spectroscopy and molecular dynamics. The initial binding, close and correctly oriented to the FAD, is important for the oxidation, specifically at the carbon adjacent to the propargyl group. The molecular dynamics study also provides evidence that retention of the allenyl imine product oriented towards FADH⁻ influences the formation of the covalent adduct essential for effective inactivation of MAO.     

Phase diagram of epidemic spreading — unimodal vs. bimodal probability distributions

Disease spreading on complex networks is studied in SIR model. Simulations on empirical complex networks reveal two specific regimes of disease spreading: local containment and epidemic outbreak. The variables measuring the extent of disease spreading are in general characterized by a bimodal probability distribution. Phase diagrams of disease spreading for empirical complex networks are introduced. A theoretical model of disease spreading on m-ary tree is investigated both analytically and in simulations. It is shown that the model reproduces qualitative features of phase diagrams of disease spreading observed in empirical complex networks. The role of tree-like structure of complex networks in disease spreading is discussed.     

Symmetries of Equivelar 4-Toroids

We derive some general results on the symmetries of equivelar toroids and provide detailed analysis of the subgroup lattice structure of the dihedral group D ₄ and of the octahedral group to complete classification by symmetry type of those in ranks 3 and 4.     

Ultrasensitive Anion Detection by NMR Spectroscopy: A Supramolecular Strategy Based on Modulation of Chemical Exchange Rate

NMR spectroscopy is a powerful tool for monitoring molecular interactions and is widely used to characterize supramolecular systems at the atomic level. NMR is limited for sensing purposes, however, due to low sensitivity. Dynamic processes such as conformational changes or binding events can induce drastic effects on NMR spectra in response to variations in chemical exchange (CE) rate, which can lead to new strategies in the design of supramolecular sensors through the control and monitoring of CE rate. Here, we present an indirect NMR anion sensing technique in which increased CE rate, due to anion‐induced conformational flexibility of a relatively rigid structure of a novel sensor, allows ultrasensitive anion detection as low as 120 nM .