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Membrane-embedded pyrophosphatase (M-PPase) hydrolyzes pyrophosphate to drive ion (H+ and/or Na+) translocation. We determined crystal structures and functions of Vigna radiata M-PPase (VrH+-PPase), the VrH+-PPase–2Pi complex and mutants at hydrophobic gate (residue L555) and exit channel (residues T228 and E225). Ion pore diameters along the translocation pathway of three VrH+-PPases complexes (Pi-, 2Pi- and imidodiphosphate-bound states) present a unique wave-like profile, with different pore diameters at the hydrophobic gate and exit channel, indicating that the ligands induced pore size alterations. The 2Pi-bound state with the largest pore diameter might mimic the hydrophobic gate open. In mutant structures, ordered waters detected at the hydrophobic gate among VrH+-PPase imply the possibility of solvation, and numerous waters at the exit channel might signify an open channel. A salt-bridge, E225–R562 is at the way out of the exit channel of VrH+-PPase; E225A mutant makes the interaction eliminated and reveals a decreased pumping ability. E225–R562 might act as a latch to regulate proton release. A water wire from the ion gate (R-D-K-E) through the hydrophobic gate and into the exit channel may reflect the path of proton transfer.

Molecular phosphorescent heteroleptic bis-tridentate iridium(III) emitters have been prepared via n1-arene intermediates. In the presence of 4.0 mol of AgOTf, the complex [(IrCl{k3-N, C, N-(pyC6HMe2py)})(µ-Cl)]2 (1; pyC6H2Me2py=1, 3-di(2-pyridyl)-4, 6-dimethylbenzene) reacted with 9-(6-phenylpyridin-2-yl)-9H-carbazole (PhpyCzH) and 2-phenoxy-6-phenylpyridine (PhpyOPh) to give [Ir{k3-N, C, N-(pyC6HMe2py)}{k3-C, N, C'-(C6H4pyCzH)}]OTf (2) and [Ir{k3-N, C, N-(pyC6HMe2py)}{k3-C, N, C'-(C6H4pyOPh)}]OTf (3). The X-ray diffraction structures of 2 and 3 reveal that the carbazolyl and phenoxy substituents of the C, N, C' ligand coordinate to the metal center to form an n1-arene p bond. Treatment of 2 and 3 with KOtBu led to the deprotonation of the coordinated carbon atom of the n1-arene group to afford the molecular phosphorescent [5t+4t'] heteroleptic iridium(III) complexes [Ir{k3-N, C, N-(pyC6HMe2py)}{k3-C, N, C'-(C6H4pyCz)}] (4) and [Ir{k3-N, C, N-(pyC6HMe2py)}{k3-C, N, C'-(C6H4pyOC6H4)}] (5). These complexes are green emitters that display short lifetimes and high quantum yields of 0.73 (4) and 0.87 (5) in the solid state.

Membrane-bound pyrophosphatases (M-PPases), which couple proton/sodium ion transport to pyrophosphate synthesis/hydrolysis, are important in abiotic stress resistance and in the infectivity of protozoan parasites. Here, three M-PPases structures in different catalytic states show that closure of the substrate-binding pocket by helices 5-6 affects helix 13 in the dimer interface and causes helix 12 to move down. This springs a "molecular mousetrap", repositioning a conserved aspartate and activating the nucleophilic water. Corkscrew motion at helices 6 and 16 rearranges the key ionic gate residues and leads to ion pumping. The pumped ion is above the ion gate in one of the ion-bound structures, but below it in the other. Electrometric measurements show a single-turnover event with a non-hydrolysable inhibitor, supporting our model that ion pumping precedes hydrolysis. We propose a complete catalytic cycle for both proton and sodium-pumping M-PPases, and one that also explains the basis for ion specificity.