Characterization and Fate of Hydrogen-Bonded Free-Radical Intermediates and Their Coupling Products from the Hydrogen Atom Transfer Agent 1,8-Naphthalenediol.

1,8-Naphthalenediol (dihydroxynaphthalene, 1,8-DHN) has been shown to be a potent hydrogen atom transfer (HAT) antioxidant compound because of the strong stabilization of the resulting free radical by intramolecular hydrogen bonding. However, the properties, reactivity, and fate of the 1,8-DHN phenoxyl radical have remained so far uncharted. Herein, we report an integrated experimental and computational characterization of the early intermediates and dimer products that arise by the oxidation of 1,8-DHN. Laser flash photolysis (LFP) studies of HAT from 1,8-DHN to the cumyloxyl and aminoxyl radicals showed the generation of a transient species absorbing at 350, 400, and >600 nm attributable to the 1,8-DHN phenoxyl radical. Peroxidase/H2O2 oxidation of 1,8-DHN was found to proceed via an intense blue intermediate (λmax 654 nm) preceding precipitation of a black melanin-like polymer. By halting the reaction in the early stages, three main dimers featuring 2,2'-, 2,4'-, and 4,4'-bondings could be isolated and characterized in pure form. Density functional theory calculations supported the generation of the 1,8-DHN phenoxyl radical and its subsequent coupling via the 2- and 4-positions giving extended quinone dimers with intense transitions in the visible range, consistent with UV-vis and LFP data. Overall, these results allowed to elucidate the mechanism of oxidative polymerization of 1,8-DHN of possible relevance to melanogenesis in fungi and other processes of environmental and astrochemical relevance.

Just Add Salt: A Mass Spectrometric Analysis Method for Imaging Anion-Exchanged Poly(Ionic Liquid)s.

We report the first mass spectrometric analysis of poly(ionic liquid)s (PILs) containing weakly coordinating anions introduced by a fast, simple, and quantitative postmodification method on the example of the hydrophilic, well-defined poly(vinylbenzylpyridinium chloride) p([VBPy]Cl) species, analyzed with an in-source collision induced dissociation-Orbitrap mass spectrometry (MS) protocol. Using the MS approach allows for the precise structural elucidation of ion-exchanged p([VBPy]Cl) utilizing AgX (X = NO3- , CF3 CO2- , BF4- ) salts. The anion exchange is shown to be quantitative - without observing residual chlorinated PIL - on rapid time scales, using only filtration as a standard procedure during sample preparation. In addition, the influence of weakly coordinating anions on the ionization behavior of PILs is studied in detail.

Universal mass spectrometric analysis of poly(ionic liquid)s.

We introduce a universal high resolution mass spectrometric method for the analysis of poly(ionic liquid)s (PILs), which belong to the most challenging polyelectrolytes from an analytical perspective, by fusing high resolution collision-induced dissociation (CID)-Orbitrap mass spectrometry (MS) with supercharging agents as well as quadrupole time-of-flight (QToF) MS. The study includes a wide array of hydrophilic halide-containing PILs, which were analyzed in negative mode. The influence of the core structures (based on imidazolium, triazolium, ammonium, phosphonium and pyridinium moieties), and variable styrene-, acrylate- and vinyl-type IL polymers on the ionization behavior is mapped in detail. Variable end group functionalities were introduced via functional chain transfer agents (CTA) in reversible addition-fragmentation chain transfer (RAFT) polymerization to study their behavior during the MS analysis. Furthermore, the demanding class of vinylimidazolium halide IL polymers was investigated. The current contribution thus introduces a new analytical technology platform for an entire polymer class.