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Plasma electrolytic oxidation (PEO) coatings fabricated on 6061 aluminum alloy under different applied voltages (400 V, 500 V and 600 V) were used to investigate the plasma discharge induced ‘local over-growth’ characteristics across substrate/coating interface. The instant microdischarges across the local plasma channels induce the ‘micro molten pool’ products and then solidify rapidly to form ‘over-growth’ oxides region extending into substrate. A thin bonding layer composed of nanocrystalline and amorphous Al2O3 with a constant thickness of ~600 nm is always forming on the interface. The intact interface structure of the “local over-growth” characteristic patterns was presented perfectly by both microdischarge-sculpted substrate side ‘pits’ and electrochemically detached coating side ‘protrusions’. The patterns demonstrate that the over-growth ‘pits’ and ‘protrusions’ gradually grow up with increasing applied voltage, which is attributed to the larger discharge channels and molten pools caused by the increased size and intensity of plasma discharges. The speculative ‘over-growth’ mechanism of discharge event during plasma electrolytic oxidation process is described. This work provides insights to control ‘over-growth’ characteristics of substrate/coating interface by tailoring electrical parameters or electrolytes composition. And this strategy has a potential application to fabricate micro-nano structure or optimize outstanding performance of PEO coatings.

Iodotyrosine deiodinase (IYD) is unusual for its reliance on flavin and ability to promote reductive dehalogenation under aerobic conditions. As implied by the name, this enzyme was first discovered to catalyze iodide elimination from iodotyrosine for recycling iodide during synthesis of tetra- and triiodothyronine collectively known as thyroid hormone. However, IYD likely supports many more functions and has been shown to debrominate and dechlorinate bromo- and chlorotyrosines. A specificity for halotyrosines versus halophenols is well preserved from humans to bacteria. In all examples to date, the substrate zwitterion establishes polar contacts with both the protein and the isoalloxazine ring of flavin. Mechanistic data suggest dehalogenation is catalyzed by sequential one electron transfer steps from reduced flavin to substrate despite the initial expectations for a single two electron transfer mechanism. A purported flavin semiquinone intermediate is stabilized by hydrogen bonding between its N5 position and the side chain of a Thr. Mutation of this residue to Ala suppresses dehalogenation and enhances a nitroreductase activity that is reminiscent of other enzymes within the same structural superfamily.