Chemistry in Australia December 2022
Luciferase-free firefly glow. Many of us cherish summer memories of firefly light shows – one of nature’s wonders. Electrochemical research has succeeded in capturing some of this eternal beauty ‘in a flask’. Light emission accompanying the enzymatic oxidation of luciferin – the firefly’s luminophore – by luciferase covers most of the visible spectrum, and is the basis of successful commercial assays for metabolic ATP production. But the chemical details of this light-emitting reaction and the mechanism of natural spectral tuning of luciferin are poorly understood. Addressing this knowledge gap has been hindered by a lack of laboratory model systems able to trigger luciferin luminescence in a simple reaction environment without the complexity of the enzyme active site. Recently, a team of researchers from Curtin University, Flinders University and the University of Bologna (Italy) reported luciferin electrochemiluminescence without the natural catalyst (Belotti M., El-Tahawy M.M.T., Yu L.-J., Russell I.C., Darwish N., Coote M.L., Garavelli M., Ciampi S. Angew. Chem. Int. Ed. 2022, 61, e202209670). Read More …
Chemistry in Australia March 2022
Light-driven carbonylation and cycloaddition. Photoenolisation of ortho-acetophenones and their derivatives is a powerful method for generating transient ortho-quinonedimethide intermediates that readily undergo [4+2]cycloadditions with dienophiles. The photoenolisation/ Diels–Alder (PEDA) sequence is increasingly finding high-profile applications in -natural-product synthesis, CO2 storage and photoligation, among others. However, to date these examples have been limited to carbonyl- containing aromatic ketones as pro-dienes. Now, researchers at the Australian National University have used theory, supported by experiment, to identify new opportunities for vastly expanding the synthetic scope of this sequence with respect to both the pro- diene and dienophile (Wang J.J., Blyth M.T., Sherburn M.S., Coote M.L. J. Am. Chem. Soc. 2022, 144, 1023–33). Read More …
Chemistry in Australia December 2021
Long-lived electric field of a liquid salt. Ionic liquids are organic salts that are liquid at room temperature. The adsorption of ionic liquids on metallic electrodes defines how these systems perform in applications ranging from energy storage to catalysis and lubrication. The electric-potential-driven ordering and subsequent relaxation of electrode–ionic-liquid interfaces are slower than for molecular solvents, but how slow has remained unclear. Methods currently
available to probe the dynamics of these interfaces, such as atomic force microscopy and neutron reflectometry, have shortcomings and are technically demanding. A team of researchers from Curtin University, ANU and Monash University has reported an extremely simple way to monitor the ordering of ionic liquid at interfaces using readily available open-circuit potentiometry Read More …
Chemistry in Australia March 2021
Charge up your photoinitiators. Oriented electric fields can influence chemical reactivity and recent research is applying this idea to enhance the performance of photoinitiators. Importantly for photoinitiators, shifts in the absorption transition must be considered along with shifts of other excited states that mediate activation (e.g. α-cleavage bond homolysis). Researchers at the University of Wollongong and Australian National University have shown how oriented electric fields, arising from single monatomic cations, can be used to tune the photodissociation of a common photoinitiator, Irgacure 2959. Read More …
Electrified Bubbles. The formation of bubbles at electrodes is a ubiquitous problem in technologies from batteries to industrial smelting. An adhering gas bubble will mask a portion of the electrode, preventing fresh solution from reaching it. Consequently, electrochemists and engineers unanimously regard surface bubbles as redox-inactive passivating entities. But now a team of researchers from Curtin University, the Australian National University, the University of New South Wales and the University of Western Australia has demonstrated that this is not case: bubbles adhering to an electrode surface initiate the oxidation of water-soluble species under conditions for which such reactions would normally be considered impossible. Read More …
Electrostatic Catalysis by Solvent Ordering. External electric fields have recently been shown to catalyse chemical reactions, but scaling these effects in practical experimental systems has been elusive. Now researchers from the ANU and Monash University have shown that ordered solvent environments can provide a way forward. This work takes advantage of the ability of solvents and ionic liquids to become ordered under external electric fields and, in the case of ionic liquids, to maintain that order for some time after the field is removed. This ordered solvent environment generates its own internal electric field that can be exploited for catalysis. Read More …
Chemistry World September 2020
The quest to control chemical reactions using interfacial electric fields. Electrostatic interactions underlie all of chemistry. Beyond the complicated chemical equations and reaction schemes that are used to describe chemical reactions, it is the rearrangement of charges and their associated electric fields that govern chemical reactivity. This is the conceptual understanding from which we derive our electron-pushing mechanisms and rationalise how we go from starting materials to products. Given that the probability and mechanism by which a reactant species is transformed into product is so dependent on the nature of the associated electric fields, it is not surprising that modulating the electric field environment surrounding a reacting system can influence its outcome. Read More …
New Scientist August 2020
Can static electricity make chemistry more efficient – and greener? It isn’t long after waking each day that we meet the handiwork of chemists. The flavourings in toothpaste, scents in shower gel, polyester in clothes – all have been created through the breaking and making of chemical bonds. The same goes for nearly all the materials on which the modern world relies. It isn’t easy work. Take remdesivir, the antiviral drug that could help us treat Covid-19. To make it, chemists begin with a small molecule called alanine and add a further 64 atoms to it over the course of 25 separate chemical reactions. Whew. Making such molecular marvels isn’t just taxing, it can also be a grubby affair. Synthetic chemists spend most of their time amid pastes, powders and bubbling solutions: it is a messy and often smelly craft. But perhaps there is a way to make it simpler and cleaner. More and more chemists are experimenting with a new tool of subtle power: the electric field. Not only does it promise to help us less damaging to the environment. If this works, chemistry will be transformed. Read More …
Enzyme-inspired self-assembling surfactant catalysts. Enzymes carry out their life-giving reactions by gathering together a remarkably intricate arrangement of functional groups. It is the precisely defined protein structure of enzymes that establishes these interactions. However, it is also this protein structure that makes enzymes susceptible to deactivation by heat, salts, and organic solvents. This problem has sparked interest in the design of enzyme-inspired catalysts that collect complimentary functionalities without relying on delicate protein asssemblies. A diverse team of researchers from the Australian National University and the University of Melbourne has recently developed a new, enzyme-inspired catalyst system that employs multi-functional surfactants to carry out catalysis. Read More …
Electric Fields Cooperatively Promote Ground and Excited State Reactivity. The demonstration that electric fields can be used to catalyse and control the reactivity of chemical reactions has recently sparked immense interest, with both theoreticians and experimentlaists exploring a range or avenues for harnessing these effects. Now, researchers from the Australian National University have shown that electric fields from remote charged functional groups can selectively and cooperatively promote both ground- and excited-state reactivity in the same system. Read More …
Chemistry in Australia November 2019
Electrophilic methylating agent activated by electrochemistry. Alkoxyamines are important compounds in polymer synthesis due to their ability to form a persistent nitroxide and a carboncentred radical at elevated temperatures, thus facilitating controlled radical polymerisation. However, using a combination of experimental and computational chemistry, researchers at the Australian National University recently showed that, by electrochemically oxidising these molecules, they can instead generate carbocations. Read More …
Stable contacts for molecular electronics. Single molecules are predicted to play a key role in the future of miniaturised electronics. One of the biggest challenges facing molecular electronics today is the lack of mechanically stable single molecule contacts to metal or semiconducting electrodes. In a study led by Nadim Darwish at Curtin University, single molecules, terminated by diazonium salts at both ends, were used to form covalent bonds to both gold and silicon electrodes, mimicking standard metal–insulator–semiconductor diodes. Read More …
ABC Science October 2019
Is a substitute for plastic coming anytime soon? For most of us, hearing the world plastic makes us think of single-use plastics like plastic bags or disposable plastic water bottles, but plastic covers a much wider variety of materials than that. They’re everywhere and have become an inescapable part of our lives, due to their versatility, flexibility, durability, affordability and because they’re relatively lightweight. Read More …
Getting a Grip on Static Electricity. Electrically insulating objects gain a net electrical charge when brought into and out of contact. This phenomenon – triboelectricity – involves the flow of charged species, but to conclusively establish their nature has proven extremely difficult. A team of researchers from Curtin University, the Australian National University and the University of New South Wales has studied the redox growth of metal nanoparticles on electrostatically charged polymers. They have described for the first time, a material-specific relationship between the tribocharging magnitude and the extent of redox word that can be harvested from tribocharged polymers. Read More …
Chemistry in Australia May 2019
Australian Journal of Chemistry’s 70th Birthday Edition. To celebrate its 70th birthday, the Australian Journal of Chemistry has released a special online collection of published papers. CSIRO Publishing’s Jennifer Foster highlights some of the selections, including a “landmark paper by Michelle Coote and co-workers, (Aust. J. Chem. 2005, 58, 437-441) describing a viable synthetic route to a novel class of RAFT agents bearing a fluorine Z-group.” Read More …
Altering photochemistry with static electric fields. It has recently been shown that static electric fields can be used to catalyse non-electrochemical reactions, opening up a new approach to chemical catalysis. Now, researchers at the Australian National University have expanded electrostatic catalysis into the realm of molecular excited states. Using state-of- the-art computational methods, they have shown that static electric fields can be used as an approach to modifying the relative energies of different types of excited state in a predictable and significant manner. Read More …
Discrete and stereospecific oligomers as natural biopolymer mimics. Natural biopolymers such as DNA and proteins have uniform microstructures with defined molecular weight, precise monomer sequence, and stereoregularity along the polymer main chain, which endows them with unique biological functions. Mimicking natural biopolymers, Jiangtao (Jason) Xu and co-workers at the University of New South Wales and their collaborators from the Australian National University, CSIRO, University of California, Santa Barbara, USA, and Nagoya University, Japan, recently established a new method to prepare discrete and stereospecific oligomers using sequential and alternating photoinduced RAFT single-unit monomer insertion (Photo-RAFT SUMI). Read More …
Eureka Prize Finalists July 2018
Eureka Prize for Scientific Research Finalists Announced: The Invisible Catalyst Team. Developing efficient ways to catalyse reactions has been an important quest for scientific research. The Invisible Catalyst Team, Professor Michelle Coote, Dr Simone Ciampi and Dr Nadim Darwish, has shown that electric fields can be used to manipulate chemical reactions. This breakthrough may enable greener and safer methods for fabricating materials, from drugs to plastics. Watch Video …
Triggering bond cleavage with electric fields. Electricity has long been used in chemistry to trigger electrochemical reactions, but only recently have static electric fields been shown to catalyse non-electrochemical reactions. But implementation has to date required scanning tunnelling microscopy (STM) to orient the reagents appropriately in the electric field. Now, a team of researchers from Curtin University, the Australian National University, the University of Wollongong, ANSTO, the Silesian University of Technology, Poland, and the University of Murcia, Spain, has shown that electrostatic factors contribute to the catalysis of a chemical process that follows an anodic reaction in an electrochemical cell. Read More …
When electrochemical measurement artefacts are real. Electricity has long been used in chemistry to trigger electrochemical reactions, but only recently have static
electric fields been shown to catalyse non-electrochemical reactions. But implementation has to date required scanning tunnelling microscopy (STM) to
orient the reagents appropriately in the electric field. Now a team of researchers from Curtin University, the University of Murcia, Spain, the University of Wollongong, the Australian National University and the University of New South Wales have been able to reproduce and explain the often puzzling behaviour of electrons that enter or leave semiconductor materials. Read More …
Light, reactivity, action! Efficient light-induced ligation protocols are valuable tools for functional materials design. The teams of Christopher Barner-Kowollik and James Blinco, at the Queensland University of Technology and the Karlsruhe Institute of Technology, Germany, and Michelle Coote at the Australian National University have investigated two highly efficient photoligation reactions involving photoenols and nitrile imines in a combined experimental and theoretical studyriggering bond cleavage with electric fields. Read More …
Chemistry World January 2018
Field of Influence. Chemists are used to harnessing all sorts of subtle and not-so-subtle tools to choreograph the dance of molecules, from lasers to microwaves to plain old heating and stirring. But now, in a few labs around the world, an unusual new idea is crackling and sparking into life: chemists are starting to explore whether electric fields can be used to control reactions too. Read More …
Chemical and Engineering News January 2018
What will be chemistry’s next big thing? Michelle Coote, professor, Research School of Chemistry, Australian National University; associate editor, Journal of the American Chemical Society What? Electric fields as catalysts. Why? The use of electric fields as catalysts is not yet commonplace. The first paper demonstrating the process in a nonredox reaction was published in 2016 in Nature. “But I think the potential is enormous and we are just starting to explore it,” Coote says. “The timing is also fantastic, as the use of electrochemistry to trigger chemical reactions is also starting to gain traction as a routine tool for organic synthesis.” Read more…
Electrical Mechanochemistry. Normally one assumes that the redox potential of a molecule is a unique property of the molecule, its solvent environment and the temperature. However, researchers from the Arizona State University, The Australian National University and Curtin University have now demonstrated that mechanical force can also be used to manipulate electron transfer reactions. Read More …
Chemistry in Australia September 2017
2017 ARC Laureate Fellowships announced. Professor Michelle Coote FRACI CChem (pictured) from the ANU Research School of Chemistry has received the Georgina Sweet Australian Laureate Fellowship for science and technology for a project to establish a new approach to chemical catalysis. Read More …
Controlling electroactivity of surface-tethered radicals Cyclic voltammetry is a well-established form of electrochemical ‘spectroscopy’ that yields a great wealth of mechanistic and thermodynamic information from the analysis of a current flowing across an electrified interface. A team of researchers from the University of Wollongong, the Australian National University, the University of New South Wales, Institut de Bioenginyeria de Catalunya and ANSTO has used this technique to show how a seemingly simple ‘dynamic’ current−potential trace can yield quantitative insights into the ‘electrostatic’ environment around a surface- tethered nitroxide radical. Read More …
Chemical Free Catalysis. It is often thought that the ability to control reaction rates with an applied electrical potential gradient is unique to redox systems. However, the researchers from the Australian National University, the University of Wollongong and the University of Barcelona have recently demonstrated that a simple Diels-Alder reaction can be catalyzed with an oriented electric field Read More …
Nature News and Views:
Xiang, L.; Tao, N.J., Reactions triggered by electricity, Nature (2016) 531, 38-39.
Where macromolecules cleave: entropic selectivity for chain scission. Reversible covalent and supramolecular bonding is increasingly being employed in applications such as self-healing and stimuli-responsive materials, complex macromolecular architectures and protein mimics. Normally, dynamic ligation equilibria are tuned by modifying the ligating functional groups to alter their electronic properties and thus reaction enthalpy. However, researchers from the Karlsruhe Institute of Technology, the Australian National University and the Leibniz Institute for Polymer Research have demonstrated that the equilibria can be tuned by altering the molecular weight and chain stiffness of the linking groups without changing the actual bonding motifs, thus taking advantage of their effect on entropy instead of enthalpy. They showed that an important consequence of these entropic effects is a significant preference for cleavage of macromolecules in the middle of long chains, rather than at the ends. Read More …
Chemical and Engineering News March 2016
Zapping Diels-Alder reactions. In a discovery that might come as a shock—or, at the very least, an electric shock—chemists have found that a properly oriented external electric field can nudge two reagents to hook up with one another in a Diels-Alder reaction. The fundamental discovery expands chemists’ knowledge of how electricity can drive synthesis and catalysis. Chemists have long used electricity to trigger redox reactions. And theorists have suggested that electric fields could spur on non-redox transformations, but until now, no one had shown this was possible with a bimolecular system. “What is particularly striking is that we chose a really simple nonpolar carbon-carbon-bond-forming reaction—a Diels-Alder reaction—for which there are no formal zwitterionic intermediates involved,” says Michelle L. Coote, a professor at Australian National University who coauthored the study. “So we think these electric field effects could be very general.” Read More …
Chemistry World March 2016
Electrostatic field powers up reaction rate. Applying electrical potential to Diels-Alder system confirms prediction of catalytic effect that defies received chemical wisdom. Scientists in Australia and Spain have shown electrostatic fields can speed up simple carbon—carbon bond-forming reactions, overturning a long-held chemical assumption. Michelle Coote from the Australian National University in Canberra and her coworkers changed reaction rate with the flick of a switch, giving organic chemists a potentially powerful new tool. Read More …
See also: IFLScience
Chemoselective switch in asymmetric organocatalysis Most chemical reactions are straightforward and furnish only one set of products. However, a holy grail in synthesis is to design reactions that can be readily ‘tuned’ to deliver different product sets that can be selected according to the reaction conditions, reagents, catalysts and even post purification strategies. This task is even more challenging when enantio- and diastereo- discrimination is required. Collaborative work by researchers from Henan University and Australian National University. Read More …
ANU Reporter March 2016
Supercharging Efficiency. Solar panels adorn the rooftops of more than one million Australian homes and the industry is booming. Yet most commercial solar cells are often relatively inefficient. Many solar panels only convert up to 15 per cent of the sunlight received into electricity but ANU scientists are working on improving this rat Research by Professor Michelle Coote and a team of eight scientists from the ANU Research School of Chemistry has led to the doubling of the efficiency of solar cells using the National Computational Infrastructure (NCI) at ANU. Read more …
Chemistry in Australia October 2015
Experimental Demonstration of pH-Dependent Electrostatic Catalysis of Radical Reactions. It is normally assumed that the ability to use electric fields to accelerate chemical reactions is limited to redox processes occurring at electrode surfaces. However, in theory, electric fields should be able to catalyse non-electrochemical reactions by electrostatically stabilising high-energy charge-separated resonance contributors to the transition state. In practice, the challenge is orienting the field relative to the reaction centre. One solution is to use charged functional groups within the substrate, auxiliary, or catalyst whose electric field is relatively localised but can be precisely aligned with respect to the reaction centre. Read More …
Ring closing highlights hydrogen bonding. Colourless spiropyrans undergo ring opening to form brightly coloured merocyanines on exposure to UV light. Merocyanines are thermally unstable and relax back to the colourless spiropyrans over time. The merocyanines designed by Simone Ciampi, from the University of Wollongong, Australia, and his colleagues contain a catechol group that can form intramolecular hydrogen bonds, which stabilises the open form and slows down discolouration. However, polar solvents can out-compete intramolecular hydrogen bond formation, and speed up discolouration. In this way, Ciampi’s team were able to visualise the hydrogen bonding character of solvents by adding their dye and observing the rate at which it discoloured. Read More …
The Canberra Times February 2014
Top thinkers entered into Australian Academy of Science. A self-described “discovery-junkie” with a passion for biodiversity will take his place among Australia’s scientific elite this May. Of 21 researchers who have been elected fellows of the Australian Academy of Science, more than a third are based in Canberra. Read More …
See also: Science at the Shine Dome
Non-directional polar effects on radical stability. Polar effects on radical stability are traditionally attributed either to resonance effects or to dipole effects. The former involves donor-acceptor interactions between specific functional groups that are conjugated or hyperconjugated with one another; the latter involves through space electrostatic interactions between charged (or partially charge-separated) functional groups. Both types of effects are strongly directional. However, researchers from the Australian National University have now discovered a third type of polar effect that is in principle non-directional and requires no conjugation or permanent dipoles (G. Gryn’ova, M. L. Coote J. Am. Chem. Soc. 2013, 135, 15392). When a localised anion is placed in the vicinity of a delocalised radical, the radical is strongly stabilized compared with its corresponding non-radical derivatives. The effect arises in the enhanced polarisability (i.e., ability to redistribute the electron density in response to an external electric field) of delocalised radicals compared with their corresponding closed-shell counterparts. In this way the destabilising interaction between a remote negative charge and an unpaired electron is minimised and a greater overall stabilisation of the species (through charge-nuclei attraction) is achieved. The resulting polar effects are surprisingly large and long-range, and are likely to be useful in synthesis and harnessed in enzyme catalysis.
Harnessing Entropy to Direct the Bonding/Debonding of Self-Healing Polymers. Self-healing polymers are based on stimuli responsive, dynamically bonding functional groups that allow the material to undergo reversible debonding in response to a pre-selected trigger such as heat, light or pH. Currently, the method for tuning the debonding point of such materials is to design the reversibly bonding functional groups (i.e., the chemistry), which essentially requires new monomers to be synthesized each time an adjustment of the debonding point is desired. However, scientists from the Australian National University, the Karlsruhe Institute of Technology, the University of Dresden and Evonik Industries report that the debonding temperature of a polymer can also be tuned by changing the chain length of the polymer building blocks, thus altering the entropy released on debonding (Guimard N.K., Ho J., Brandt J., Lin C.Y., Namazian M., Mueller J.O., Oehlenschlager K.K., Hilf S., Lederer A., Schmidt F.G., Coote M.L., and Barner-Kowollik C. Chem. Sci., 2013, 4, 2752-2759). In this work, entropy driven debonding is predicted theoretically and demonstrated experimentally for two Diels-Alder polymer systems, each based on a different difunctional diene and a common difunctional dienophile. This finding has the potential to fundamentally transform the approach polymer and materials chemists take to designing dynamically bonding materials
Chemistry in Australia August 2013
See also Nature Chemistry News and Views
Radical orbital switching. A recent discovery made by researchers from Australian National University and University of Wollongong (Gryn’ova G., Marshall D.L., Blanksby S.J., Coote M.L., Nature Chem. 2013, 5, 474–481) appears to challenge several cornerstones of chemical reactivity. According to the aufbau principle, the unpaired electron of a free radical should occupy the highest-energy orbital. However, the authors show that a broad range of distonic radical anions display so-called orbital energy-level conversion, in which their singly-occupied orbital is energetically lower than the doubly-occupied orbital(s) of the anionic functional group. As a result, the one-electron oxidation of such compounds produces high-spin species with potential applications in molecular electronics. Moreover, it is generally assumed that remote charges (beyond ca. 5Å separation) do not significantly affect the stability and reactivity of radicals (and vice versa), yet these distonic radical anions are more stable than their closed-shell or protonated counterparts by as much as 4 orders of magnitude. This ability to pH-switch radical reactivity can be harnessed to develop radical protecting groups for free-radical polymerization and organic synthesis, and is likely to be important in radical biochemistry and particularly enzyme catalysis.
Chemistry Australia October 2012
Extraordinary Efficiency of Amine Antioxidants Explained. Hindered Amine Light Stabilizers (HALSs) are remarkably effective radical-trapping antioxidants; however, the precise mechanism of their protective action has long been debated. Researchers from Australian National University, and Canada National Research Council, have used high-level quantum-chemical calculations to uncover the autocatalytic cycle in which these antioxidants inhibit the thermo- and photooxidative degradation of polymers and other organic materials (Gryn’ova G., Ingold K.U., Coote M.L. J. Am. Chem. Soc. 2012, 134, 12979–88). Their work finally explains a number of experimental observations, including the regeneration of the main active species, a nitroxide radical R1R2NO•, and the selective formation of secondary amines, R1R2NH, as by-products. The key step in the new catalytic cycle is the abstraction of a β-hydrogen atom from alkoxyamine, R1R2NOCHR3R4, which is found to be energetically feasible for a wide range of substrates. The authors also discovered that alternative, more energetically demanding catalytic cycles operate in the systems without abstractable β-hydrogens, which explains why standard HALSs are less effective in such cases. These findings are crucial for future design of effective radical-trapping antioxidants and longer-lasting polymers.