Robinson, DM, Go Y B, Greenblatt M, Dismukes CG.  2010.  Water Oxidation by λ-MnO2: Catalysis by the Cubical Mn4O4 Subcluster Obtained by Delithiation of Spinel LiMn2O4. Journal of the American Chemical Society. 132:11467-11469. AbstractWebsite
Dismukes, CG, Brimblecombe R, Felton GAN, Pryadun RS, Sheats JE, Spiccia L, Swiegers GF.  2009.  Development of Bioinspired Mn4O4−Cubane Water Oxidation Catalysts: Lessons from Photosynthesis. Accounts of Chemical Research. 42:1935-1943. AbstractWebsite
Brimblecombe, R, Bond AM, Dismukes CG, Swiegers GF, Spiccia L.  2009.  Electrochemical investigation of Mn4O4-cubane water-oxidizing clusters. Physical Chemistry Chemical Physics. 11:6441-6449. AbstractWebsite
High valence states in manganese clusters are a key feature of the function of one of the most important catalysts found in nature, the water-oxidizing complex of photosystem II. We describe a detailed electrochemical investigation of two bio-inspired manganese-oxo complexes, [Mn4O4L6] (L = diphenylphosphinate (1) and bis(p-methoxyphenyl)phosphinate (2)), in solution, attached to an electrode surface and suspended within a Nafion film. These complexes contain a cubic [Mn4O4]6+ core stabilized by phosphinate ligands. They have previously been shown to be active and durable photocatalysts for the oxidation of water to dioxygen. A comparison of catalytic photocurrent generated by films deposited by two methods of electrode immobilization reveals that doping of the catalyst in Nafion results in higher photocurrent than was observed for a solid layer of cubane on an electrode surface. In dichloromethane solution, and under conditions of cyclic voltammetry, the one-electron oxidation processes 1/1+ and 2/2+ were found to be reversible and quasi-reversible, respectively. Some decomposition of 1+ and 2+ was detected on the longer timescale of bulk electrolysis. Both compounds also undergo a two-electron, chemically irreversible reduction in dichloromethane, with a mechanism that is dependent on scan rate and influenced by the presence of a proton donor. When immersed in aqueous electrolyte, the reduction process exhibits a limited level of chemical reversibility. These data provide insights into the catalytic operation of these molecules during photo-assisted electrolysis of water and highlight the importance of the strongly electron-donating ligand environment about the manganese ions in the ability of the cubanes to photocatalyze water oxidation at low overpotentials.
Swiegers, G F, Huang J, Brimblecombe R, Chen J, Dismukes CG, Mueller-Westerhoff U T, Spiccia L, Wallace G G.  2009.  Homogeneous Catalysts with a Mechanical (“Machine-like”) Action. Chemistry – A European Journal. 15:4746-4759.Website
Carrieri, D, McNeely K, De Roo AC, Bennette N, Pelczer I, Dismukes CG.  2009.  Identification and quantification of water-soluble metabolites by cryoprobe-assisted nuclear magnetic resonance spectroscopy applied to microbial fermentation. Magnetic Resonance in Chemistry. 47:S138-S146.Website
Brimblecombe, R, Dismukes CG, Swiegers GF, Spiccia L.  2009.  Molecular water-oxidation catalysts for photoelectrochemical cells. Dalton Transactions. :9374-9384. AbstractWebsite
Photoelectrochemical cells that efficiently split water into oxygen and hydrogen, "the fuel of the future", need to combine robust water oxidation catalysts at the anode (2H2O [rightward arrow] O2 + 4H+ + 4e-) with hydrogen reduction catalysts at the cathode (2H+ + 2e-[rightward arrow] H2). Both sets of catalysts will, ideally, operate at low overpotentials and employ light-driven or light-assisted processes. In this Perspective article, we focus on significant efforts to develop solid state materials and molecular coordination complexes as catalyst for water oxidation. We briefly review the field with emphasis on the various molecular catalysts that have been developed and then examine the activity of molecular catalysts in water oxidation following their attachment to conducting electrodes. For such molecular species to be useful in a solar water-splitting device it is preferable that they are securely and durably affixed to an electrode surface. We also consider recent developments aimed at combining the action of molecular catalysts with light absorption so that light driven water oxidation may be achieved.
Meuser, JE, Ananyev GM, Wittig LE, Kosourov S, Ghirardi ML, Seibert M, Dismukes CG, Posewitz MC.  2009.  Phenotypic diversity of hydrogen production in chlorophycean algae reflects distinct anaerobic metabolisms. Journal of Biotechnology. 142:21-30.Website
Brimblecombe, R, Kolling DRJ, Bond AM, Dismukes CG, Swiegers GF, Spiccia L.  2009.  Sustained Water Oxidation by [Mn4O4]7+ Core Complexes Inspired by Oxygenic Photosynthesis. Inorganic Chemistry. 48:7269-7279. AbstractWebsite
Dismukes, GC, Carrieri D, Bennette N, Ananyev GM, Posewitz MC.  2008.  Aquatic phototrophs: efficient alternatives to land-based crops for biofuels. Curr Opin Biotechnol. 19:235-40. AbstractWebsite
To mitigate some of the potentially deleterious environmental and agricultural consequences associated with current land-based-biofuel feedstocks, we propose the use of biofuels derived from aquatic microbial oxygenic photoautotrophs (AMOPs), more commonly known as cyanobacteria, algae, and diatoms. Herein we review their demonstrated productivity in mass culturing and aspects of their physiology that are particularly attractive for integration into renewable biofuel applications. Compared with terrestrial crops, AMOPs are inherently more efficient solar collectors, use less or no land, can be converted to liquid fuels using simpler technologies than cellulose, and offer secondary uses that fossil fuels do not provide. AMOPs pose a new set of technological challenges if they are to contribute as biofuel feedstocks.
Bartlett, JE, Baranov SV, Ananyev GM, Dismukes GC.  2008.  Calcium controls the assembly of the photosynthetic water-oxidizing complex: a cadmium(II) inorganic mutant of the Mn4Ca core. Philosophical Transactions of the Royal Society B-Biological Sciences. 363:1253-1261. AbstractWebsite
Perturbation of the catalytic inorganic core (Mn4Ca1OxCly) of the photosystem II-water-oxidizing complex (PSII-WOC) isolated from spinach is examined by substitution of Ca2+ with cadmium(II) during core assembly. Cd2+ inhibits the yield of reconstitution of O-2-evolution activity, called photoactivation, starting from the free inorganic cofactors and the cofactor-depleted apo-WOC-PSII complex. Ca2+ affinity increases following photooxidation of the first Mn2+ to Mn3+ bound to the 'high-affinity' site. Ca2+ binding occurs in the dark and is the slowest overall step of photoactivation (IM1/IM*(1) -> step). Cd2+ competitively blocks the binding of Ca2+ to its functional site with 10-to 30-fold higher affinity, but does not influence the binding of Mn2+ to its high-affinity site. By contrast, even 10-fold higher concentrations of Cd2+ have no effect on O-2-evolution activity in intact PSII-WOC. Paradoxically, Cd2+ both inhibits photoactivation yield, while accelerating the rate of photoassembly of active centres 10-fold relative to Ca2+. Cd2+ increases the kinetic stability of the photooxidized Mn3+ assembly intermediate(s) by twofold (mean lifetime for dark decay). The rate data provide evidence that Cd2+ binding following photooxidation of the first Mn3+, IM1/IM*(1), causes three outcomes: (i) a longer intermediate lifetime that slows IM1 decay to IM0 by charge recombination, (ii) 10-fold higher probability of attaining the degrees of freedom (either or both cofactor and protein d.f.) needed to bind and photooxidize the remaining 3 Mn2+ that form the functional cluster, and (iii) increased lability of Cd2+ following Mn-4 cluster assembly results in (re) exchange of Cd2+ by Ca2+ which restores active O-2-evolving centres. Prior EPR spectroscopic data provide evidence for an oxo-bridged assembly intermediate, Mn3+ (mu-O2-) Ca2+, for IM*(1). We postulate an analogous inhibited intermediate with Cd2+ replacing Ca2+.
Sbraccia, C, Zipoli F, Car R, Cohen MH, Dismukes CG, Selloni A.  2008.  Mechanism of H2 Production by the [FeFe]H Subcluster of Di-Iron Hydrogenases: Implications for Abiotic Catalysts. The Journal of Physical Chemistry B. 112:13381-13390. AbstractWebsite
Ananyev, GM, Carrieri D, Dismukes GC.  2008.  Optimization of metabolic capacity and flux through environmental cues to maximize hydrogen production by the cyanobacterium "Arthrospira (Spirulina) maxima". Applied and Environmental Microbiology. 74:6102-6113. AbstractWebsite
Environmental and nutritional conditions that optimize the yield of hydrogen (H-2) from water using a two-step photosynthesis/ fermentation (P/F) process are reported for the hypercarbonate-requiring cyanobacterium "Arthrospira maxima." Our observations lead to four main conclusions broadly applicable to fermentative H-2 production by bacteria: (i) anaerobic H-2 production in the dark from whole cells catalyzed by a bidirectional [NiFe] hydrogenase is demonstrated to occur in two temporal phases involving two distinct metabolic processes that are linked to prior light-dependent production of NADPH (photosynthetic) and dark/anaerobic production of NADH (fermentative), respectively; (ii) H-2 evolution from these reductants represents a major pathway for energy production (ATP) during fermentation by regenerating NAD(+) essential for glycolysis of glycogen and catabolism of other substrates; (iii) nitrate removal during fermentative H-2 evolution is shown to produce an immediate and large stimulation of H-2, as nitrate is a competing substrate for consumption of NAD(P) H, which is distinct from its slower effect of stimulating glycogen accumulation; (iv) environmental and nutritional conditions that increase anaerobic ATP production, prior glycogen accumulation (in the light), and the intracellular reduction potential (NADH/NAD(+) ratio) are shown to be the key variables for elevating H-2 evolution. Optimization of these conditions and culture age increases the H-2 yield from a single P/F cycle using concentrated cells to 36 ml of H-2/g (dry weight) and a maximum 18% H-2 in the headspace. H-2 yield was found to be limited by the hydrogenase-mediated H-2 uptake reaction.
Dasgupta, J, Ananyev GM, Dismukes GC.  2008.  Photoassembly of the water-oxidizing complex in photosystem II. Coordination Chemistry Reviews. 252:347-360. AbstractWebsite
The light-driven steps in the biogenesis and repair of the inorganic core comprising the O-2-evolving center of oxygenic photosynthesis (photosystem II water-oxidation complex, PSII-WOC) are reviewed. These steps, known collectively as photoactivation, involve the photoassembly of the free inorganic cofactors to the cofactor-depleted PSII-(apo-WOC) driven by light and produce the active O-2-evolving core comprised of Mn4CaOxCly. We focus on the functional role of the inorganic components as seen through the competition with non-native cofactors ("inorganic mutants") on water oxidation activity, the rate of the photoassembly reaction, and on structural insights gained from EPR spectroscopy of trapped intermediates formed in the initial steps of the assembly reaction. A chemical mechanism for the initial steps in photoactivation is given that is based on these data. Photoactivation experiments offer the powerful insights gained from replacement of the native cofactors, which together with the recent X-ray structural data for the resting holoenzyme provide a deeper understanding of the chemistry of water oxidation. We also review some new directions in research that photoactivation studies have inspired that look at the evolutionary history of this remarkable catalyst. (c) 2007 Elsevier B.V. All rights reserved.
Carrieri, D, Ananyev GM, Costas AMG, Bryant DA, Dismukes GC.  2008.  Renewable hydrogen production by cyanobacteria: Nickel requirements for optimal hydrogenase activity. International Journal of Hydrogen Energy. 33:2014-2022. AbstractWebsite
Some species of cyanobacteria naturally produce hydrogen gas as a byproduct of anaerobic fermentation at night using fixed-carbon compounds that are produced photosynthetically in daylight under aerobic conditions. The nutrient requirements for optimal activity of these two systems of metabolic energy production are different and in some cases incompatible. Resolving these conflicting needs has not been widely considered, yet is critical for application of cyanobacteria as efficient cell factories for hydrogen production. The filamentous nondiazotrophic cyanobacterium Arthrospira maxima ferments in the dark both intracellular fixed-carbon compounds and added glucose, producing hydrogen exclusively via a bidirectional NiFe hydrogenase. We show that the hydrogenase activity in cell extracts (in vitro) and whole cells (in vivo) correlates with the amount of Ni2+ in the growth medium (saturating activity at 1.5 mu M Ni2+). This and higher levels of nickel in the medium during photoautotrophic growth cause stress leading to chlorophyll degradation and a retarded growth rate that is severe at ambient solar flux. We show that A. maxima acclimates to micromolar nickel concentrations at reduced light intensity after a delay which minimizes chlorophyll degradation and restores normal growth rate. Nickel adaptation permits normal biomass accumulation while significantly increasing the rate of fermentative hydrogen production. Relative to nickel-free media (only extraneous Ni2+), the average hydrogenase activity in cell extracts (in vitro) increases by 18-fold, while the average rate of intracellular H-2 production within intact cells increases 6-fold. Nickel is inferred to be a limiting cofactor for hydrogenase activity in many cyanobacteria grown using photoautotrophic conditions, particularly those lacking a high-affinity Ni2+ transport system. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Brimblecombe, R, Swiegers G F, Dismukes  CG, Spiccia L.  2008.  Sustained Water Oxidation Photocatalysis by a Bioinspired Manganese Cluster. Angewandte Chemie International Edition. 47:7335-7338.Website
Carrieri, D, Ananyev GM, Brown T, Dismukes GC.  2007.  In vivo bicarbonate requirement for water oxidation by Photosystem II in the hypercarbonate-requiring cyanobacterium Arthrospira maxima. J Inorg Biochem. 101:1865-74. AbstractWebsite
While the presence of inorganic carbon in the form of (bi)carbonate has been known to be important for activity of Photosystem II (PSII), the vast majority of studies on this "bicarbonate effect" have been limited to in vitro studies of isolated thylakoid membranes and PSII complexes. Here we report an in vivo requirement for bicarbonate that is both reversible and selective for this anion for efficient water oxidation activity in the hypercarbonate-requiring cyanobacterium Arthrospira (Spirulina) maxima, originally isolated from highly alkaline soda lakes. Using a non-invasive internal probe of PSII charge separation (variable fluorescence), primary electron acceptor (Q(A)(-)/Q(A)) reoxidation rate, and flash-induced oxygen yield, we report the largest reversible bicarbonate effect on PSII activity ever observed, which is due to the requirement for bicarbonate at the water-oxidizing complex. Temporal separation of this donor side bicarbonate requirement from a smaller effect of bicarbonate on the Q(A)(-) reoxidation rate was observed. We expect the atypical way in which Arthrospira manages intracellular pH, sodium, and inorganic carbon concentrations relative to other cyanobacteria is responsible for this strong in vivo bicarbonate requirement.
Yu, Y, Dubey M, Bernasek SL, Dismukes CG.  2007.  Self-Assembled Monolayer of Organic Iodine on a Au Surface for Attachment of Redox-Active Metal Clusters. Langmuir. 23:8257-8263. AbstractWebsite
Dasgupta, J, Tyryshkin AM, Kozlov YN, Klimov VV, Dismukes CG.  2006.  Carbonate Complexation of Mn2+ in the Aqueous Phase:  Redox Behavior and Ligand Binding Modes by Electrochemistry and EPR Spectroscopy. The Journal of Physical Chemistry B. 110:5099-5111. AbstractWebsite
Carrieri, D, Kolling D, Ananyev GM, Dismukes C.  2006.  Prospecting for biohydrogen fuel. Industrial Biotechnology. 2:40-43.
Hillier, W, McConnell I, Badger MR, Boussac A, Klimov VV, Dismukes CG, Wydrzynski T.  2006.  Quantitative Assessment of Intrinsic Carbonic Anhydrase Activity and the Capacity for Bicarbonate Oxidation in Photosystem II†. Biochemistry. 45:2094-2102. AbstractWebsite
Tyryshkin, AM, Watt RK, Baranov SV, Dasgupta J, Hendrich MP, Dismukes CG.  2006.  Spectroscopic Evidence for Ca2+ Involvement in the Assembly of the Mn4Ca Cluster in the Photosynthetic Water-Oxidizing Complex†. Biochemistry. 45:12876-12889. AbstractWebsite
Ananyev, GM, Nguyen T, Putnam-Evans C, Dismukes GC.  2005.  Mutagenesis of CP43-arginine-357 to serine reveals new evidence for (bi)carbonate functioning in the water oxidizing complex of Photosystem II. Photochemical & Photobiological Sciences. 4:991-998.Website
Ananyev, GM, Dismukes GC.  2005.  How fast can Photosystem II split water? Kinetic performance at high and low frequencies Photosynthesis Research. 84:355-365.Website