The Surface Structure of a TiNi-Based Powder Alloy Manufactured by the Method of Diffusion Sintering

Russian Physics Journal - The structural features of the surface of a TiNi-based powder alloy produced by diffusion sintering are studied. Two-dimensional porous samples based on a TiNi powder...     

Electronic Transitions in Different Redox States of Trinuclear 5,6,11,12,17,18-Hexaazatrinaphthylene-Bridged Titanium Complexes: Spectroelectrochemistry and Quantum Chemistry

Multinuclear transition metal complexes bridged by ligands with extended π-electronic systems show a variety of complex electronic transitions and electron transfer reactions. While a systematic understanding of the photochemistry and electrochemistry has been attained for binuclear complexes, much less is known about trinuclear complexes such as hexaphenyl-5,6,11,12,17,18-hexaazatrinaphthylene-tristitanocene [(Cp₂Ti)₃HATN(Ph)₆]. The voltammogram of [(Cp₂Ti)₃HATN(Ph)₆] shows six oxidation and three reduction waves. Solution spectra of [(Cp₂Ti)₃HATN(Ph)₆] and of the electrochemically formed oxidation products show electronic transitions in the UV, visible and the NIR ranges. Density functional theory (DFT) and linear response time-dependent DFT show that the three formally titanium(II) centers transfer an electron to the HATN ligand in the ground state. The optically excited transitions occur exclusively between ligand-centered orbitals. The charged titanium centers only provide an electrostatic frame to the extended π-electronic system. Complete active self-consistent field (CASSCF) calculation on a structurally simplified model compound, which considers the multi-reference character imposed by the three titanium centers, can provide an interpretation of the experimentally observed temperature-dependent magnetic behavior of the different redox states of the title compound in full consistency with the interpretation of the electronic spectra.     

In Situ Generated Gold Nanoparticles on Active Carbon as Reusable Highly Efficient Catalysts for a C −C Stille Coupling

Gold nanoparticle catalysts are important in many industrial production processes. Nevertheless, for traditional C ?C cross‐coupling reactions they have been rarely used and Pd catalysts usually give a superior performance. Herein we report that in situ formed gold metal nanoparticles are highly active catalysts for the cross coupling of allylstannanes and activated alkylbromides to form C ?C bonds. Turnover numbers up to 29 000 could be achieved in the presence of active carbon as solid support, which allowed for convenient catalyst recovery and reuse. The present study is a rare case where a gold metal catalyst is superior to Pd catalysts in a cross‐coupling reaction of an organic halide and an organometallic reagent.     

Thermally Rearranged Polymer Membranes Containing Tröger's Base Units Have Exceptional Performance for Air Separations

The influence of segmental chain motion on the gas separation performance of thermally rearranged (TR) polymer membranes is established for TR polybenzoxazoles featuring Tröger's base (TB) monomer subunits as exceptionally rigid sites of contortion along the polymer backbone. These polymers are accessed from solution‐processable ortho‐acetate functionalized polyimides, which are readily synthesized as high‐molecular‐weight polymers for membrane casting. We find that thermal rearrangement leads to a small increase in d‐spacing between polymer chains and a dramatic pore‐network reconfiguration that increases both membrane permeability and O₂/N₂ selectivity, putting its performance above the 2015 upper bound.     

Nonclassical SNAPFL analogue as a Cy5 resonance energy transfer partner

We have synthesized a new SNAPFL analogue (1) that exhibits a large Stokes shift (78 nm) (abs. 542 nm, em. 620 nm) and a good quantum yield. Because of the large overlap between the emission spectrum of 1 and the absorption spectrum of Cy5, 1 functions well as a fluorescence donor to Cy5 and has been used in FRET-based experiments using estrogen receptor site-specifically labeled with Cy5 and a receptor ligand conjugated to SNAPFL.     

Control over binding stoichiometry and specificity in the supramolecular immobilization of cytochrome c on a molecular printboard

Here, the stepwise assembly of an electroactive bionanostructure on a molecular printboard is described. The system consists of a cyclodextrin receptor monolayer (molecular printboard) on glass, a divalent linker, streptavidin (SAv), and biotinylated cytochrome c (cyt c). The divalent linker consists of a biotin moiety for binding to SAv and two adamantyl moieties for supramolecular host-guest interaction at the cyclodextrin molecular printboard. The binding of biotinylated cyt c onto a SAv layer bound to preadsorbed linker appeared to be highly specific. The coverages of cyt c as assessed by UV-vis spectroscopy and scanning electrochemical microscopy (SECM) appeared to be identical indicating that all cyt c units remained active. Moreover, the coverage values corresponded well with an estimate based on steric requirements, and the binding stoichiometry was therefore found to be by two biotin moieties of cyt c per one SAv molecule.