Preparation and Characterization of Persistent Maltose-Conjugated Triphenylmethyl Radicals

The condensation reaction of d-maltose to free radicals of the series of tris­(2,4,6-trichlorophenyl)­methyl (TTM) and tris­(perchlorophenyl)­methyl (PTM) has been described for the first time. The new persistent radicals <b>1</b> and <b>2</b> are very stable and have been characterized by EPR. Their cyclic voltammograms show a quasi-reversible process in the cathode, being reduced to the corresponding anions, with redox potentials a little lower than those of TTM and PTM, respectively. Their oxidant activity is in close relation with their reduction potentials. Therefore, while <b>2</b> is reduced by ascorbic acid, <b>1</b> remains unaltered

Punicalagin and Catechins Contain Polyphenolic Substructures That Influence Cell Viability and Can Be Monitored by Radical Chemosensors Sensitive to Electron Transfer

Plant polyphenols may be free radical scavengers or generators, depending on their nature and concentration. This dual effect, mediated by electron transfer reactions, may contribute to their influence on cell viability. This study used two stable radicals (tris­(2,3,5,6-tetrachloro-4-nitrophenyl)­methyl (TNPTM) and tris­(2,4,6-trichloro-3,5-dinitrophenyl)­methyl (HNTTM)) sensitive only to electron transfer reduction reactions to monitor the redox properties of polyphenols (punicalagin and catechins) that contain phenolic hydroxyls with different reducing capacities. The use of the two radicals reveals that punicalagin’s substructures consisting of gallate esters linked together by carbon–carbon (C–C) bonds are more reactive than simple gallates and less reactive than the pyrogallol moiety of green tea catechins. The most reactive hydroxyls, detected by TNPTM, are present in the compounds that affect HT-29 cell viability the most. TNPTM reacts with C–C-linked gallates and pyrogallol and provides a convenient way to detect potentially beneficial polyphenols from natural sources

Scalable Synthesis of Carbon-Supported Platinum–Lanthanide and −Rare-Earth Alloys for Oxygen Reduction

Platinum–rare-earth alloys have proven to be both active and stable under accelerated stability tests in their bulk polycrystalline form. However, a scalable method for the synthesis of a high-surface-area supported catalyst of these alloys has so far not been presented. Herein we discuss the thermodynamics relevant for the reduction conditions of the rare earths to form alloys with platinum. We show how the tolerance for water and oxygen severely limits the synthesis parameters and how under certain conditions the thermal reduction of YCl₃ with H₂ is possible from 500 °C. From the insight gained, we synthesized a Pt_<i>x</i>Y/C catalyst by modifying a Pt/C catalyst and confirmed alloy formation by both X-ray diffraction and X-ray photoelectron spectroscopy measurements. These reveal crystalline intermetallic phases and the metallic state of yttrium. Without any optimization of the method, the catalyst has an improved mass activity in comparison to the unmodified catalyst, proving the viability of the method. Initial work based on thermodynamic equilibrium calculations on reduction time show promise in controlling the phase formed by tuning the parameters of time, temperature, and gas composition