Selective Lanthanides Sequestration Based on a Self‐Assembled Organosilica

In this paper, we investigate the cation‐exchange properties of a self‐assembled hybrid material towards trivalent ions, lanthanides (La³⁺, Eu³⁺, Gd³⁺, Yb³⁺) and Fe³⁺. The bis‐zwitterionic lamellar material was prepared by sol–gel process from only 3‐aminopropyltriethoxysilane (APTES), succinic anhydride, and ethylenediamine. In ethanol heated under reflux, the exchange ethylenediammonium versus Ln³⁺ proved to be complete by complexometry measurements and elemental analyses, one Cl^? ion per one Ln^III remaining as expected for charge balance. In aqueous solution at 20 °C, the material was found to be selective towards lanthanide in spite of the similarity of their ionic radii. The cation uptake depends on the nature of the salt, the difference between two lanthanides reaching up to 20 % in some cases. Finally, ion‐exchange reaction with FeCl₃ was chosen as a probe to get more information on the material after incorporation of trivalent ions. Based on Mössbauer spectroscopic investigations on the resulting material in conjunction with the XRD analysis of materials containing trivalent ions, a structural model was proposed to describe the incorporation of trivalent ions by exchange reaction within the original zwitterionic material.     

Dirac particles in a gravitational field

The semiclassical approximation for the Hamiltonian of Dirac particles interacting with an arbitrary gravitational field is investigated. The time dependence of the metric leads to new contributions to the in-band energy operator in comparison to previous works in the static case. In particular we find a new coupling term between the linear momentum and the spin, as well as couplings that contribute to the breaking of the particle–antiparticle symmetry.     

Nevanlinna counting function and Carleson function of analytic maps

We show that the maximal Nevanlinna counting function and the Carleson function of analytic self-maps of the unit disk are equivalent, up to constants.     

Bargaining among groups: an axiomatic viewpoint

We introduce a model of bargaining among groups, and characterize a family of solutions using a Consistency axiom and a few other invariance and monotonicity properties. For each solution in the family, there exists some constant α ≥ 0 such that the “bargaining power” of a group is proportional to c ^α , where c is the cardinality of the group.     

Surface orbital magnetism

We compute the surface correction to the density of states of a particle in a convex box subjected to a magnetic field. Applying these results to orbital magnetism, we find that at high temperatures or weak magnetic fields the surface magnetization is always paramagnetic, but oscillations appear at low temperatures. In two dimensions they can give very large paramagnetic contributions near integer values of the filling factor. Explicit formulas are given for the zero-field susceptibility and for samples with a cylindrical shape in arbitrary magnetic field.     

Le traitement des formes en chimie analytique

(Signal-shape processing in analytical chemistry.) When signal evolution (e.g., spectra) has to be detected or measured, shape processing can be useful. The distribution function method enables all the information in the signal shape to be utilized, by working with normalized integrals. The concept of shape also helps in estimating resolution parameters of overlapped peaks. The principles are outlined and some applications in chromatography and Mössbauer spectrography are summarized.     

Insights into the Catalytic Activity of Nitridated Fibrous Silica (KCC‐1) Nanocatalysts from 15N and 29Si NMR Spectroscopy Enhanced by Dynamic Nuclear Polarization

Fibrous nanosilica (KCC‐1) oxynitrides are promising solid‐base catalysts. Paradoxically, when their nitrogen content increases, their catalytic activity decreases. This counterintuitive observation is explained here for the first time using ¹⁵N‐solid‐state NMR spectroscopy enhanced by dynamic nuclear polarization.     

Macrocyclic Gd3+ Complexes with Pendant Crown Ethers Designed for Binding Zwitterionic Neurotransmitters

A series of Gd³⁺ complexes exhibiting a relaxometric response to zwitterionic amino acid neurotransmitters was synthesized. The design concept involves ditopic interactions 1) between a positively charged and coordinatively unsaturated Gd³⁺ chelate and the carboxylate group of the neurotransmitters and 2) between an azacrown ether appended to the chelate and the amino group of the neurotransmitters. The chelates differ in the nature and length of the linker connecting the cyclen‐type macrocycle that binds the Ln³⁺ ion and the crown ether. The complexes are monohydrated, but they exhibit high proton relaxivities (up to 7.7 mM ^?1 s^?1 at 60 MHz, 310 K) due to slow molecular tumbling. The formation of ternary complexes with neurotransmitters was monitored by ¹H relaxometric titrations of the Gd³⁺ complexes and by luminescence measurements on the Eu³⁺ and Tb³⁺ analogues at pH 7.4. The remarkable relaxivity decrease (≈80 %) observed on neurotransmitter binding is related to the decrease in the hydration number, as evidenced by luminescence lifetime measurements on the Eu³⁺ complexes. These complexes show affinity for amino acid neurotransmitters in the millimolar range, which can be suited to imaging concentrations of synaptically released neurotransmitters. They display good selectivity over non‐amino acid neurotransmitters (acetylcholine, serotonin, and noradrenaline) and hydrogenphosphate, but selectivity over hydrogencarbonate was not achieved.     

[2+1] Cycloaddition Affording Methylene‐ and Vinylidenecyclopropane Derivatives: A Journey around the Reactivity of Metal‐Phosphinito–Phosphinous Acid Complexes

Metal–phosphinito–phosphinous acid complexes are interesting catalysts exhibiting unique reactivities. In this account, we intend to provide a clear overview of palladium– and platinum–phosphinito–phosphinous acid complexes, their preparation from secondary phosphine oxides, and their applications in catalysis. They have been mainly used to develop [2+1] cycloadditions to afford methylenecyclopropane derivatives using norbornenes and various alkynes as partners. As a function of the catalyst, the reaction conditions, or the nature of the reagents, different synthetic transformations have been observed: [2+1] cycloadditions, giving rise to either alkylidenecyclopropanes or vinylidenecyclopropanes; tandem [2+1]/[3+2] cycloadditions, and so forth. The mechanisms of these reactions have been studied to rationalize the different reactivities observed.