ASSOCIATE PROFESSOR STEVE COLBRAN

SCHOOL OF CHEMISTRY

UNIVERSITY OF NEW SOUTH WALES

( s.colbran@unsw.edu.au )

COLBRAN GROUP

CHEMISTRY FOR A SUSTAINABLE FUTURE insight, design, synthesis, reactions, redox, catalysis, knowledge

Team Colbran – 2011

Cytochome c oxidase — heme-copper catalytic centre turning oxygen into water to make you go, now, always

turning water into energy/fuel … a new proton reduction catalyst

an original twist to making NH3 … requires a new N2-reduction catalyst

Why? To discover the hottest, most reactive, coolest catalysts for…

CO2 → methanol (= a transport fuel !)

(turning a ‘greenhouse’ problem into an ‘oil-crisis’ solution)

N2 → ammonia efficiently!

(cheap fertilizer to grow the food to feed >½ world’s population)

chemical reduction

(new non-wasteful, ‘sustainable’ technology for global industry)

Biomimicry & Catalysis

Cutting-edge chemistry for a sustainable

future for us all: we …

Study and learn from metallo-proteins,

the nifty molecules in you and all other

life that catalyze all the interesting

biological chemistry

Apply the insights learnt to design

smart catalysts to make important

reactions go at maximum efficiency

What’s involved

Synthesis = we make metal-containing

molecules, new, never seen before,

exciting stuff

Electrochemistry & spectroscopy

= we zap the new molecules, with light

and electricity, to see how they wiggle

Reactivity and catalysis = we hit the

new molecules with reagents, other

molecules, to see what new reactions

happen — all sorts of fun new stuff

A/Prof. Steve Colbran (Chemical & Biological Catalysis Cluster, School of Chemistry, UNSW)

Research Projects Research in my group starts with developing understanding of how Nature employs metal centres to catalyse difficult multi-electron processes. We use new insights obtained from biology to design, synthesise and study new biomimetic catalysts. By way of example, some recent research highlights and some research projects currently underway are summarised in the figures and text below. Aerobic respiration. So just how is the molecular oxygen that you breathe used? Well all aerobes —that's all life you can see unaided with your eyes — convert oxygen to water in the Fea3...CuB catalytic centre of a respiratory heme-copper oxidase (HCO). Simple? No — not at all! The structure(s) of these complex respiratory enzymes have been known in atomic detail for many years now, but how they work remains a complete puzzle, one of life's mysteries. HCO's are transducers. The Fea3...CuB catalytic centre

(shown) couples exergonic 4e–

reduction of molecular oxygen to trans-membrane proton pumping. It has many unusual and unique features including redox-active tyrosine and tryptophan residues. Our biomimetic studies of carefully designed radical models and theoretical calculations continue to provide new insights into how this catalytic centre for multi-electron reduction and proton-pumping works.

Post-doctoral associate: Dr Sang-Tae Lee Selected publication: ... Valence Tautomerism and Coordinative Lability in Copper(II)-Imidazolyl-Semiquinonate Anion Radical Models for the CuB Center in Cytochrome c Oxidases. J. Amer. Chem. Soc. 2007, 129, 5800. Funding: Australian Research Council (ARC) – Discovery Grant

Oxidising organic substrates. Selective oxidation of inert organic substrates such as alkanes is a key process in the petrochemical industry and in life. Living organisms use enzymes called non-heme iron oxygenases to perform this task with activities and specificities unmatched in lab-constructed oxidation catalysts. In collaboration with A/Prof. Steve Blanksby at the University of Wollongong, we have used state-of-the-art mass spectrometry to generate the key, highly reactive metal(IV)-oxo species, not only for iron as found throughout biology but for all first-row transition metals Ti–Cu. The gas-phase reactivities of the metal(IV)-oxo species with organic substrates have been studied, trends ascertained, and we have used density functional theory calculations to provide insights into reaction pathways. The results point to optimum metal-ligand sets for peak activity and selectivity in oxidation catalysts. Now we just have to make the synthetic ('real, in-a-bottle') catalysts!

PhD student: Mr Ivan Taylor Selected publication: ... Production and Isolation of Ligated Metal(IV)-Oxo Ions by Tandem Mass Spectrometry, Rapid Commun. Mass Spectrom., 2010, 24, 1142–1146. Funding: American Chemical Society – Petroleum Research Fund AC Grant

Turning light into electricity. Dye-sensitised solar cells (DSSCs) offer the possibility of converting everyday building surfaces — roofs, walls, even windows — into sun-driven electricity generators. The problem is that at present they are all too costly for too low efficiency. Working with Dr Andrew McDonagh at UTS, we characterised the electrochemistry and spectroscopy of new ruthenium phthalocyanin-

based dyes. Studies of the new dyes in DSSCs revealed important interplays between dye redox-properties, sizes and coverage, and light-driven electricity generation efficiencies.

Collaborators: McDonagh Group, UTS Selected publication: ... Ruthenium Phthalocyanine-Bipyridyl Dyads as Sensitizers for Dye-Sensitized Solar Cells: Dye Coverage versus Molecular Efficiency, Inorg. Chem., 2009, 48, 3215–3227.

Towards efficient multi-electron reduction catalysts. Industrialisation, anthropogenic fixation of molecular nitrogen to produce ammonia (the Haber-Bosch process), and fossil fuels for cheap energy have allowed the world's human population to burgeon. We, now, should all be aware that this comes at a heavy price — overwhelming, and possibly irreversible, environmental degradation (which includes carbon dioxide-driven climate change). One giant leap forward would be discovery of an efficient solar-driven process for electro-reduction of atmospheric nitrogen to ammonia. Ammonia is the source of the fertiliser that grows the food for half the world's population — one in two nitrogen atoms in you is industrial in origin! Ammonia is also a storable energy-dense fuel — cheap ammonia could replace fossil fuels thus eliminating carbon dioxide emissions. However, the Haber-Bosch industrial process is energy demanding (it accounts for ~ 2% of global energy consumption), wasteful (overall more carbon dioxide than ammonia is produced) and is ultimately unsustainable (as molecular hydrogen, the key reagent, is sourced from dwindling natural gas reserves). Motivated by current and future need, the focus of current research in my group is discovery of catalysts for electro-reduction of small molecules such as molecular nitrogen and carbon dioxide. Two approaches, both biology-inspired, are being explored: (a) Employing a central light p-block atom to hold together novel multi-iron clusters that store multiple electrons for difficult reduction processes. The syntheses, reactions and (spectro-) electrochemistries of the targeted multi-iron clusters are being thoroughly examined. The multi-iron clusters are important because they share common structural features with the FeMo-cofactor that is the active site of the

enzyme nitrogenase. This enzyme 'fixes' atmospheric nitrogen as ammonia by an as yet unknown mechanism, and is the natural route for entry of nitrogen into the biosphere. We believe research into similar clusters may lead to energy-efficient routes to ammonia and to other multi-electron reduction processes affording new alternative fuels.

Post-Doctoral Associate: Dr Carolina Gimbert-Suriñach Funding: ARC – Discovery Grant

(b) Developing a first chemistry for transition metal complexes with nicotinamide-functionalised ligands. The nicotinamides NAD(P)+/H are Natures' carriers of hydride ion (H–). In many enzyme-catalysed reductions, a substrate that is polarised, and thus activated, by binding to a metal centre is reduced by the direct transfer of hydride ion from NAD(P)H to it. We have synthesised a new class of robust transition metal complexes functionalised with nicotinamide substituents, and we are now investigating their reactions in an attempt to emulate biological catalytic reduction processes. Prospects for exciting new chemistry are excellent.

PhD Student: Mr Alex McSkimming Selected Publication: ... Hydride Ion-Carrier Ability in Rh(I) Complexes of a Nicotinamide-Functionalised N-Heterocyclic Carbene Ligand, Dalton Trans. 2010, 39, 10581–10584.

Interested? Come & chat. I'm always looking for good students interested in a research project.

My office is in the Dalton Bldg, Rm 225; e-mail: s.colbran@unsw.edu.au; phone: +61-(0)2-93854737