G. Charles Dismukes

Sustained water oxidation by [Mn4O4]7+ core complexes inspired by oxygenic photosynthesis

The bioinspired Mn-oxo cubane complex, [Mn(4)O(4)L(6)](+) 1b(+) (L = (p-MeO-Ph)(2)PO(2)), is a model of the photosynthetic O(2)-evolving complex. It is able to electro-oxidize water at 1.00 V (vs Ag/AgCl) under illumination by UV-visible light when suspended in a proton-conducting membrane (Nafion) coated onto a conducting electrode. Electrochemical measurements, and UV-visible, NMR, and EPR spectroscopies are interpreted to indicate that 1b(+) is the dominant electro-active species in the Nafion, both before and after catalytic cycling, and thus correlates closely with activity. The observation of a possible intermediate and free phosphinate ligand within the Nafion suggests a catalytic mechanism involving photolytic disruption of a phosphinate ligand, followed by O(2) formation, and subsequent reassembly of the cubane structure. Several factors that influence catalytic turnover such as the applied potential, illumination wavelength, and energy have been examined in respect of attaining optimum catalytic activity. Catalytic turnover frequencies of 20-270 molecules O(2) h(-1) catalyst(-1) at an overpotential of 0.38 V plus light (275-750 nm) and turnovers numbers >1000 molecules O(2) catalyst(-1) are observed. The 1b(+)-Nafion system is among the most active and durable molecular water oxidation catalysts known.

The Origin and Evolution of Photosynthetic Oxygen Production

This chapter reviews some of the evidence and the postulated proposals for how oxygenic photosynthesis first emerged as a distinct form of photoautotrophic metabolism using water as an electron donor. This form of photosynthesis is the most successful photoautotrophic metabolism in the contemporary biosphere and is found in all higher plants, green and red algae and both cyano- and oxyphoto-bacteria. We summarize the timetable for emergence and the biogeochemical consequences of oxygenic photosynthesis. Particular attention is paid to evolution of the inorganic core of the enzyme that catalyzes water oxidation, chemical speciation of the inorganic cofactors and possible alterative substrates. We discuss possible mineral remnants of early oxygenic photosynthesis and the emerging role of bicarbonate in assembly of the inorganic core and as an hypothesized evolutionary cofactor.

Homogeneous catalysts with a mechanical ("machine-like") action.

Chemical reactions may be controlled by either: 1) the minimum threshold energy that must be overcome during collisions between reactant molecules/atoms (the activation energy, E(a)), or: 2) the rate at which reactant collisions occur (the collision frequency, A)--for reactions with low E(a). Reactions of type 2 are governed by the physical, mechanical interaction of the reactants. Such mechanical processes are unusual, but not unknown in molecular catalysts. In this work we examine the machine-like nature of the action in various abiological mechanical catalysts and consider the implications for mimicry of biological catalysts.

Warwick Hillier: a tribute

Warwick Hillier (October 18, 1967–January 10, 2014) made seminal contributions to our understanding of photosynthetic water oxidation employing membrane inlet mass spectrometry and FTIR spectroscopy. This article offers a collection of historical perspectives on the scientific impact of Warwick Hillier’s work and tributes to the personal impact his life and ideas had on his collaborators and colleagues.