Crystal chemistry,magnetic, and electrical properties of hexagonal plutonium oxide chalcogenides: Pu2O2X, X = O,S, Se

A study was made of the influence of the chalcogen X on the magnetic and electrical properties of Pu₂O₂X (X = O, S, Se) compounds and on bonding in these hexagonal compounds, isostructural with the corresponding rare-earth compounds. The comparison of the cell volumes of Nd₂O₂X and Pu₂O₂X compounds showed that the Pu³⁺ crystal radius decreased from β-Pu₂O₃ to Pu₂O₂Se as “5f delocalization” and 5f-p overlap increased. These plutonium compounds were all found to be antiferromagnetic. This was caused by superexchange coupling interactions via p orbitals of the oxygen and chalcogen ions. The Néel temperature increased from β-Pu₂O₃ (26 K) to Pu₂O₂S (28 K) then to Pu₂O₂Se (34 K) showing that 5f-p covalency was enhanced as the chalcogen electronegativity decreased and the p radial extent increased. The hexagonal β-Pu₂O₃ was found to be an insulator while both other compounds were semiconductors with gaps around 0.5 eV. These gaps were interpreted as the energy separation between the 6d-7s conduction band and the np band of the chalcogen X with some overlap of the occupied 5f states and the np band. A simple electron band scheme of these compounds is proposed on such assumptions.     

Theoretical interpretation of the infrared lineshape of liquid and gaseous acetic acid

We have applied a model used recently [P. Blaise, M.J. Wojcik, O. Henri-Rousseau, J. Chem. Phys. 122 (2005) 64306] to unpolarized ν_X–H infrared lineshapes of cyclic (CH₃COOH)₂ in liquid and gaseous phases and (CD₃COOH)₂ in gaseous phase and taking into account the IR A_g forbidden transition. This model incorporates (i) the anharmonic coupling between the high frequency mode and the H-bond bridge, (ii) the Davydov coupling between the excited states of the two moieties, (iii) the quantum direct and indirect dampings. The approach reproduces satisfactorily the main features of the experimental lineshapes by using a minimum number of independant parameters.     

Hydrogen Peroxide-Responsive Triggers Based on Borinic Acids: Molecular Insights into the Control of Oxidative Rearrangement

Arylborinic acids represent new, efficient, and underexplored hydrogen peroxide-responsive triggers. In contrast to boronic acids, two concomitant oxidative rearrangements are involved in the complete oxidation of these species, which might represent a major limitation for an efficient effector (drug or fluorophore) release. Herein, a comprehensive study of H₂O₂-mediated unsymmetrical arylborinic acid oxidation to investigate the factors that could selectively guide their oxidative rearrangement is described. The o-CF₃ substituent was found to be an excellent directing group allowing a complete regioselectivity on borinic acid models. This result was successfully applied to synthesizing new borinic acid-based fluorogenic probes, which exclusively release the fluorescent moiety upon H₂O₂ treatment. These compounds maintained their superior kinetic properties compared to boronic acids, thus further enhancing the potential of arylborinic acids as valuable new H₂O₂-sensitive triggers.     

Characterizing Enzyme Cooperativity with Imaging SAMDI-MS

This paper describes a method that combines a microfluidic device and self-assembled monolayers for matrix-assisted laser desorption/ionization mass spectrometry (SAMDI) mass spectrometry to calculate the cooperativity in binding of calcium ions to peptidylarginine deiminase type 2 (PAD2). This example uses only 120 μL of enzyme solution and three fluidic inputs. This microfluidic device incorporates a self-assembled monolayer that is functionalized with a peptide substrate for PAD2. The enzyme and different concentrations of calcium ions are flowed through each of eight channels, where the position along the channel corresponds to reaction time and position across the channel corresponds to the concentration of Ca²⁺. Imaging SAMDI (iSAMDI) is then used to determine the yield for the enzyme reaction at each 200 μm pixel on the monolayer, providing a time course for the reactions. Analysis of the peptide conversion as a function of position and time gives the degree of cooperativity (n) and the concentration of ligand required for half maximal activity (K_0.5) for the Ca²⁺ – dependent activation of PAD2. This work establishes a high-throughput and label-free method for studying enzyme-ligand binding interactions and widens the applicability of microfluidics and matrix-assisted laser desorption/ionization mass spectrometry (MALDI) imaging mass spectrometry.     

Recurrence-Based Synchronization Analysis of Weakly Coupled Bursting Neurons under External ELF Fields

We investigate the response characteristics of a two-dimensional neuron model exposed to an externally applied extremely low frequency (ELF) sinusoidal electric field and the synchronization of neurons weakly coupled with gap junction. We find, by numerical simulations, that neurons can exhibit different spiking patterns, which are well observed in the structure of the recurrence plot (RP). We further study the synchronization between weakly coupled neurons in chaotic regimes under the influence of a weak ELF electric field. In general, detecting the phases of chaotic spiky signals is not easy by using standard methods. Recurrence analysis provides a reliable tool for defining phases even for noncoherent regimes or spiky signals. Recurrence-based synchronization analysis reveals that, even in the range of weak coupling, phase synchronization of the coupled neurons occurs and, by adding an ELF electric field, this synchronization increases depending on the amplitude of the externally applied ELF electric field. We further suggest a novel measure for RP-based phase synchronization analysis, which better takes into account the probabilities of recurrences.     

Preparation of 5-Alkylthio and 5-Arylthiotetrazoles from Thiocyanates Using Phase Transfer Catalysis

A very efficient method of preparation for 5-alkyl and 5-arylthiotetrazoles from the corresponding alkyl or aryl halides is described. The halides are first transformed into thiocyanates which further react with azide, yielding the corresponding tetrazoles with [2+3] polar cycloaddition. All synthetic transformations are performed under phase transfer catalytic conditions. The yields vary from good to excellent except for the preparation of 5-benzylthiotetrazole, where the reaction between benzyl thiocyanate and azide [2+3] cycloaddition is in competition with nucleophilic substitution, with benzyl azide as product.     

Vinyl-triphenylamine dyes, a new family of switchable fluorescent probes for targeted two-photon cellular imaging: from DNA to protein labeling

On the basis of our previous work on vinyl-triphenylamine derived DNA fluorophores we explored the structure space around this core by coupling it to diverse cationic, anionic and zwitterionic groups in the aim of targeting different classes of biomolecules. In parallel core modifications were performed to optimize the photophysical properties (quantum yield, two-photon absorption). The resulting water soluble π-conjugated molecules are called TP dyes and display an exceptional combination of optical properties: high two-photon absorption cross-section, high photostability, no self-quenching, and switchable fluorescence emission when bound to a biopolymer matrix. The linear and nonlinear optical properties of the TP dyes were studied in vitro in presence of DNA and in presence of a model protein (human serum albumin) using complementary absorption and fluorescence spectroscopy characterization tools. Structure modifications enabled to switch from DNA probes (cationic TP-pyridinium series) to protein probes (anionic TP-rhodanine series) without affecting the optical properties. Finally most TP compounds appear cell-permeant and show an intracellular localization consistent with their in vitro target specificity.