Studying the interaction between triazines and humic substances--a new approach using open tubular capillary electrochromatography

The strength of the interaction between a pesticide and the soil organic matter is a key parameter to assess the risk of it reaching to groundwater with potentially harmful effects to human health. In this work, a new approach that allows measuring such interactions in a few minutes using a purified fraction of the soil organic matter (humic substances) is detailed. The strength of sorption is assessed via the normalised difference of elution (retention factor, k′) between the chemical of interest and a neutral marker transported via electroosmotic flow through an open tubular column supporting the immobilised humic substances (open tubular capillary electrochromatography). The immobilisation was achieved by incubating a capillary, pre-coated with a monolayer of humic acid, with an acidic solution of humic substances. This induces the formation of a supramolecular structure of humic substances as it occurs in soils. This aggregate can easily be removed using alkaline solutions, and a new structure assembled using other humic substances (HS) or different incubations conditions. The whole procedure takes 2 h. This approach has been tested using five triazines and three types of humic substances. The order of the strength of sorption of the triazines as expected from relevant literature and the relative standard deviation of k′ was between 1 and 6%. Good repeatability was also observed after long period of wash, between re-coating and repeating of the full coating with a new capillary.     

Straightforward and efficient synthesis of 3-benzyloxy-4-bromopicolinate ester and 3-benzyloxy-5-bromopicolinate ester, common building blocks for pharmaceuticals and agrochemicals

A practical and rapid preparation of 3-benzyloxy-4-bromo and 3-benzyloxy-5-bromopicolinate esters 10 and 16 was developed in four steps, respectively, in 38% and 31% overall yield. Then their viability as partners for cross-coupling reactions has been evaluated in Suzuki-Miyaura, Hartwig-Buchwald, and Sonogashira reactions to synthesize biologically relevant targets. The preparation of these two highly functionalizable pyridines 10 and 16 has been never described to date in the literature and could be used as common building block for the preparation of several biologically active compounds or agrochemical products.     

Weak interactions modulating the dimensionality in supramolecular architectures in three new nickel(II)-hydrazone complexes, magnetostructural correlation, and catalytic potential for epoxidation of alkenes under phase transfer conditions

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL(1)), 2-hydroxyacetophenone (HL(2)), and 2, 3-dihydroxybenzaldehyde (HL(3)). These tridentate ligands are reacted with Ni(OOCCF(3))(2)·xH(2)O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L(1))(OOCCF(3))(CH(3)OH)](2) (1), [Ni(L(2))(OOCCF(3))(H(2)O)](2) (2), and [Ni(L(3))(L(3)H)](OOCCF(3))(H(2)O)(1.65)(CH(3)OH)(0.35) (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV-vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O-H···O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand backbone provoke differences in the supramolecular architectures of the complexes, leading to a variety of one, two, and three-dimensional hydrogen bonded networks in complexes 1-3 respectively. Variable temperature magnetic susceptibility measurements reveal that moderate antiferromagnetic interactions operate between phenoxo bridged Ni(II) dimers in 1 and 2 whereas very weak antiferromagnetic exchange occurs through hydrogen bonding and π-π stacking interactions in 3. All complexes are proved to be efficient catalysts for the epoxidation of alkenes by NaOCl under phase transfer condition. The efficiency of alkene epoxidation is dramatically enhanced by lowering the pH, and the reactions are supposed to involve high valent Ni(III)-OCl or Ni(III)-O· intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396).     

Thermodynamic optimization of the (Na2O + SiO2 + NaF + SiF4) reciprocal system using the Modified Quasichemical Model in the Quadruplet Approximation

All available thermodynamic and phase diagram data for the condensed phases of the ternary reciprocal system (NaF + SiF₄ + Na₂O + SiO₂) have been critically assessed. Model parameters for the unary (SiF₄), the binary systems and the ternary reciprocal system have been found, which permit to reproduce the most reliable experimental data. The Modified Quasichemical Model in the Quadruplet Approximation was used for the oxyfluoride liquid solution, which exhibits strong first-nearest-neighbor and second-nearest-neighbor short-range ordering. This thermodynamic model takes into account both types of short-range ordering as well as the coupling between them. Model parameters have been estimated for the hypothetical high-temperature liquid SiF₄.     

Slow quench dynamics of a one-dimensional Bose gas confined to an optical lattice

We analyze the effect of a linear time variation of the interaction strength on a trapped one-dimensional Bose gas confined to an optical lattice. The evolution of different observables such as the experimentally accessible on site particle distribution are studied as a function of the ramp time by using time-dependent numerical techniques. We find that the dynamics of a trapped system typically displays two regimes: For long ramp times, the dynamics is governed by density redistribution, while at short ramp times, local dynamics dominates as the evolution is identical to that of an homogeneous system. In the homogeneous limit, we also discuss the nontrivial scaling of the energy absorbed with the ramp time.     

Strongly coupled chameleons and the neutronic quantum bouncer

We consider the potential detection of chameleons using bouncing ultracold neutrons. We show that the presence of a chameleon field over a planar plate would alter the energy levels of ultracold neutrons in the terrestrial gravitational field. When chameleons are strongly coupled to nuclear matter, β?10(8), we find that the shift in energy levels would be detectable with the forthcoming GRANIT experiment, where a sensitivity of the order of 1% of a peV is expected. We also find that an extremely large coupling β?10(11) would lead to new bound states at a distance of order 2 μm, which is already ruled out by previous Grenoble experiments. The resulting bound, β?10(11), is already 3 orders of magnitude better than the upper bound, β?10(14), from precision tests of atomic spectra.     

Layered hydroxide hybrid nanostructures: a route to multifunctionality

Today, seeking new materials for tailor-made applications and new devices leads to explore the potential offered by various kinds of functional building blocks. Hence, it concerns not only solid-state chemists, physicists or materials engineers, but also the area of (supra)molecular chemistry, and biochemistry as well. This is especially clear in the field of hybrid multifunctional materials. Indeed, their design requires investigating new concepts derived from principles developed in these different disciplines. The aim of this critical review is to present the last achievements concerning transition metal hydroxide hybrids, their synthesis, flexibility and functional properties. They often provide nice model systems for understanding the correlation between structure and physical properties brought by the molecular moieties grafted onto the metal hydroxide basis layers. The contribution of the atomic scale modelling to the electronic structure calculations and structural optimization is also reported (216 references).     

Ring-rearrangement metathesis of nitroso Diels-Alder cycloadducts

Strained nitroso Diels–Alder bicyclo[2.2.1] or [2.2.2] adducts functionalized with alkene side chains of diverse length undergo a ring‐rearrangement metathesis process with external alkenes and Grubbs II or Hoveyda–Grubbs II ruthenium catalysts, under microwave irradiation or classical heating, to deliver cis‐fused bicycles of various ring sizes, which contain a N? O bond. These scaffolds are of synthetic relevance for the generation of molecular diversity and to the total synthesis of alkaloids. The observation of unexpected reactions, such as epimerization or one‐carbon homologation of the alkene side chain, is also reported.