Ergothioneine and related histidine derivatives in the gas phase: tautomer structures determined by IRMPD spectroscopy and theory

L-Ergothioneine (ET) is a sulfur-containing derivative of the amino acid histidine that offers unique antioxidant properties. The enzyme independent redox-chemistry of ET relies on the availability of the thiol tautomer to allow oxidative formation of disulfide bridges, i.e., the tautomeric equilibrium. To study the intrinsic properties of ET the tautomeric equilibrium is studied in the gas-phase by infrared multiphoton dissociation (IRMPD) spectroscopy. The IR ion spectra of isolated molecular ions of ET and of the biosynthetic precursors of ET, i.e., hercynine and Nε-methyl-hercynine are acquired. The analyte structures are independently investigated by density functional theory (DFT) and computed linear IR-spectra of tautomer ion structures are compared with the gas-phase spectra for identification. For the molecular ion of ET the simulated IR spectra of thione and thiol structures match the recorded IRMPD spectrum and that prevents an individual structure assignment. On the other hand, theory suggests that ET adopts a thione tautomer in MeOH solution which could be carried over from the condensed phase to gas phase and could be kinetically trapped after effective electrospray phase transfer and desolvation. Such a non-thermal behavior is also found for the molecular ions of protonated hercynine and Nε-methyl-hercynine. Contrary to that, the sodium complex ions of ET, hercynine and Nε-methyl-hercynine adopt the respective ground structures predicted by theory, which are reliably identified spectroscopically. For ET the thione tautomer is by far the most stable isomer in the sodium complex molecular ion

Competitive interplay of deposition and etching processes in atomic layer growth of cobalt and nickel metal films

Atomic layer deposition ALD of air stable cobalt and nickel complexes based on tridentate enaminones N,N 4,4,4 trifluorobut 1 en 3 on dimethylethyldiamine Htfb dmeda and N,N 4,4,4 trifluorobut 1 en 3 on dimethylpropyldiamine Htfb dmpda successfully produced metallic cobalt and nickel thin films. Detailed X ray photoelectron spectroscopy XPS studies on the binding interaction of the first precursor monolayer with the surface functional groups elucidated the chemisorption behavior of the new precursor systems. A reactive remote hydrogen plasma was used as the co reactant to activate the precursor decomposition yielding metal hydroxide intermediates. Subsequent hydrogen plasma etching of as deposited films resulted in phase pure metallic films through a recrystallization process, verified by surface and sub surface XPS. Scanning electron microscopy SEM and atomic force microscopy AFM analyses revealed pinhole free films, with low surface roughness 0.2 0.06 nm root mean square, RMS for both, cobalt and nickel thin films. Herein, the competitive role of hydrogen as etchant and reactant was demonstrated as prolonged plasma exposure time periods resulted in the formation of metal hydrides. This is mostly due to the catalytic dissociation of molecular hydrogen on transition metal surfaces, which already occurs upon low energy inpu