Thermal Transition of Bimetallic Metal–Phenolic Networks to Biomass‐Derived Hierarchically Porous Nanofibers

The development and utilization of biomass resources could contribute to new materials for long‐term sustainable energy storage and environmental applications, reduce environmental impacts, and meet the urgent need for green and sustainable development strategies. Herein, a bimetallic metal–phenolic network (MPN) was applied to incorporate different metallic element species into cattle skin and fabricate collagen‐fiber‐derived complex oxide nanofibers using natural polyphenols (Myrica tannins). Direct thermal transition of these biomass–MPN composites generates hierarchically porous nanofibers possessing micro‐ and mesoporous architectures along with a well‐preserved macroscopic structure. The pore system and complex oxide composition provide excellent photocatalytic performance. This low‐cost, simple, and readily scalable MPN‐based approach provides a straightforward route to synthesize nanostructured materials directly from biomass, which could play important roles in a wide range of potential applications.     

Crystal chemistry,magnetic, and electrical properties of the tetragonal plutonium oxide telluride Pu2O2Te

We describe the preparation and some physical properties of Pu₂O₂Te. The plutonium oxide telluride is isostructural with the corresponding rare-earth oxide tellurides which crystallize in the tetragonal system of La₂O₂Te-type. Magnetic susceptibility data from 4 K to room temperature are reported together with resistivity measurements. Pu₂O₂Te is found to be an antiferromagnet below 56 K and a semiconductor with an intrinsic energy gap of 0.65 eV. The magnetic behavior is interpreted in terms of superexchange coupling interactions via nonmetal p orbitals, i.e., in terms of 5f-p overlaps. This conclusion is supported by crystal chemistry considerations by comparison of cell volumes of Pu₂O₂Te and Nd₂O₂Te. In Pu₂O₂Te, the Pu crystal radius is found to be much lower than that of Nd in Nd₂O₂Te, suggesting some 5f electron “delocalization” leading to a crystal radius shrinkage. As for the hexagonal Pu₂O₂X compounds, with X = O, S, Se, the measured gap may be considered as the energy separation between the chalcogen np band and the 6d-7s conduction band, the occupied 5f states lying just below the np band with some 5f-np overlap.     

Simulation of small positively charged MgO clusters and study of their electronic densities

With the help of ab initio methods the clusters [(MgO)₁₃Mg] ^Q+ are simulated for Q = 0, 1, 2. Then, vacancy clusters [(MgO)₁₂Mg₂] ^Q+ obtained by removing one oxygen atom are computed for Q running from 0 to 4. These clusters exhibit a slight sphericity and generally shorter interatomic distances than in the crystal. The electronic densities variations are studied in function of Q. In particular, it is observed that the electronic density in the oxygen vacancy goes to a maximum when Q = 2. The ionisation potentials vary from approximately 4 to 14 eV when Q varies from 0 to 3, with a more rapid increase from Q = 1 to Q = 2. The stability study of vacancy clusters show that they experience a phase transition when their charge becomes equal to 2, in accordance with the features mentioned above. Received 14 September 1999 and Received in final form 2 December 1999     

Implementation of an adaptive finite-element approximation of the Mumford-Shah functional

Summary. We present and detail a method for the numerical solving of the Mumford-Shah problem, based on a finite element method and on adaptive meshes. We start with the formulation introduced in [13], detail its numerical implementation and then propose a variant which is proved to converge to the Mumford-Shah problem. A few experiments are illustrated. Received October 8, 1998 / Published online: April 20, 2000     

Fluorogenic Protein Probes with Red and Near-Infrared Emission for Genetically Targeted Imaging**

Fluorogenic probes are important tools to image proteins with high contrast and no wash protocols. In this work, we rationally designed and synthesized a small set of four protein fluorogens with red or near-infrared emission. The fluorophores were characterized in the presence of albumin as a model protein environment and exhibited good fluorogenicity and brightness (fluorescence quantum yield up to 36 %). Once conjugated to a haloalkane ligand, the probes reacted with the protein self-labeling tag HaloTag with a high fluorescence enhancement (up to 156-fold). The spectroscopic properties of the fluorogens and their reaction with HaloTag were investigated experimentally in vitro and with the help of molecular dynamics. The two most promising probes, one in the red and one in the near-infrared range, were finally applied to image the nucleus or actin in live-cell and in wash-free conditions using fluorogenic and chemogenetic targeting of HaloTag fusion proteins.     

Development of an Enzyme-Inhibitor Reaction Using Cellular Retinoic Acid Binding Protein II for One-Pot Megamolecule Assembly

This paper presents an enzyme building block for the assembly of megamolecules. The system is based on the inhibition of the human-derived cellular retinoic acid binding protein II (CRABP2) domain. We synthesized a synthetic retinoid bearing an arylfluorosulfate group, which uses sulfur fluoride exchange click chemistry to covalently inhibit CRABP2. We conjugated both the inhibitor and a fluorescein tag to an oligo(ethylene glycol) backbone and measured a second-order rate constant for the protein inhibition reaction of approximately 3,600 M⁻¹s⁻¹. We used this new enzyme-inhibitor pair to assemble multi-protein structures in one-pot reactions using three orthogonal assembly chemistries to demonstrate exact control over the placement of protein domains within a single, homogeneous molecule. This work enables a new dimension of control over specificity, orientation, and stoichiometry of protein domains within atomically precise nanostructures.     

Charge kinetics in spinel and yttria-stabilized zirconia

Spinel and zirconia were studied by measuring the total secondary electron emission (SEE) yield σ in a dedicated scanning electron microscope (SEM) especially equipped to study the fundamental aspects of the charge trapping in insulating materials during a 1.1 keV electron irradiation at room temperature. The variation of the total SEE yield with the injected dose for both spinel and zirconia is different. In spinel the coefficient σ starts from its intrinsic value σ₀ = 4 and reaches a plateau at σ = 1 at the end of irradiation, which corresponds to the self-regulated regime. The continuity of the curves, shot after shot, proves that the trapped charges are stable and does not spread out in the material as injection proceeds. In this case spinel is called “trapper insulator”. In contrast with the spinel, σ in zirconia, never reaches unity while the injected charge increases: it evolves from its intrinsic yield σ₀ = 2.3 to a steady value a few percent above 1. The curve shows the relaxation of the positive generated charge. In this case zirconia is called “conductive insulator”. The difference in the charging kinetics of the two materials is attributed to the difference in conductivities.     

Alkaloids from the stem bark of Turraeanthus africanus (Meliaceae)

Fractionation of the methanol extract of the stem bark of Turraeanthus africanus led to the isolation of two new alkaloids designated turraeanthin A and B, together with two known alkaloids. The structures of the new alkaloids were elucidated by means of spectroscopic analysis and characterized as 10-O-demethyl-17-O-methyl isoarnottianamide and 11-demethoxyl-12-methoxyl oxynitidine respectively.     

Theoretical interpretation of the line shape of crystalline adipic acid

A general quantum theoretical approach of the upsilon(X-H) IR line shape of cyclic dimers of weakly H-bonded species in the crystal state is proposed. In this model, the adiabatic approximation (allowing to separate the high-frequency motion from the slow one of the H-bond bridge) is performed for each separate H-bond bridge of the dimer and a strong nonadiabatic correction is introduced into the model via the resonant exchange between the fast-mode excited states of the two moieties. Quantum indirect damping and Fermi resonances are taken into account. The present model reduces satisfactorily to many models in the literature dealing with more special situations. It has been applied to the cyclic dimers of adipic acid in the crystal phase. It correctly fits the experimental line shape of the hydrogenated compound and predicts satisfactorily the evolution in the line shapes with temperature and the change in the line shape with isotopic substitution.