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ERC

CAPRI — Result In Brief

Project ID: 290966
Funded under: FP7-IDEAS-ERC
Country: United Kingdom
Domain: Fundamental Research

Pioneering molecular movies yields insights into chemical reactions in liquids

The EU-funded CAPRI project successfully used ultrafast laser pulses to shed light on mechanisms of chemical reactions in liquids in unprecedented detail, with potential for leaner and greener industrial chemistry.
Pioneering molecular movies yields insights into chemical reactions in liquids
Despite much of the world’s most significant chemistry (both for the living environment and industry) taking place in liquids, research has typically studied chemical reactions in the gas phase. Accurate observation of reactive molecular encounters during chemical synthesis in liquids has been hampered by the constant motion of the solvent molecules, coupled with the process speed. Bonds can be severed, and new ones created, at intervals faster than a trillionth of a second.

The EU-funded CAPRI project used laser pulses - shorter in time than the collision intervals of molecules - to successfully capture snapshots of chemical reactions in liquids, in unparalleled detail. By joining the snapshots and using computer simulations, the team created step-by-step visualisations. The leading science magazine ‘Scientific American’, has credited the team’s approach as constituting a ‘World Changing Idea’.

Explaining the motivation for CAPRI, the project coordinator Professor Andrew Orr-Ewing recalls, ‘It was partly fundamental curiosity about the largely unexplored question of what happens to reacting molecules dissolved in a liquid solvent, and partly a recognition that most chemistry carried out in research labs and in industry requires use of liquid solvents.’

Getting the picosecond snapshots

The project team studied the molecules using absorption spectroscopy. By using ultrafast laser pulses (in the Infra Red or Ultra Violet regions) they measured the amount of light absorbed at different wavelengths by short-lived species, intermediate between reactants and final products, The professor elucidates that, ‘We measured these transient spectra at different time delays to watch the growth and decay of the reaction intermediates. The spectra revealed the reaction pathways and the motions of the molecules during reaction.’

The experiments were conducted in common solvents including water, Deuterium Oxide (D2O), Acetonitrile, Chloroform and Dichloromethane. CAPRI also looked at the less common liquid Perfluorocarbons which are chemically inert, interacting only weakly with solvent molecules, but which allow very detailed measurements of dissolved molecule behaviour.

As Professor Orr-Ewing summarises, ‘The experiments were pioneering because they demonstrated for the first time that studies of reactions in solution could approach the level of detail for those performed on isolated molecules in the gas phase.’ He goes on to conclude that, ‘One important surprise from the experiments was that reactions in solution cannot simply be modelled using statistics to predict where the excess energy of reactions might end up. The actual experimental insights really were key.’

Towards a future of leaner and greener industrial chemistry

CAPRI offers a better understanding of energy flows sparked by chemical reactions. New chemical pathways have been tracked, including ways in which molecules dissipate excess energy from absorption of ultraviolet radiation to avoid being damaged. Over and above CAPRI’s fundamental scientific research objective, the project’s findings have direct benefits for synthetic and industrial chemistry.

Results will improve simulations, inputting to various fields including drug design. CAPRI also offers the prospect of improved industrial processing of fine chemicals and pharmaceuticals, for example through the use of flow chemistry in photochemical reactors, driven by cheap and efficient light sources such as Light Emitting Diodes (LEDs). Then there is the contribution to ‘green chemistry’. As the professor elaborates, ‘We are applying this strategy to understand reactions of importance to synthetic organic chemists and to chemists using catalytic cycles activated by light absorption, avoiding toxic or scarce metal based catalysts.’

The team is now expanding the work to look at more complex molecular systems as well as specific phenomena, such as how biologically important molecules interact with ultraviolet light and resist photochemical damage.

Keywords

CAPRI, In liquid chemical reactions, solvents, picosecond, green chemistry, solvent molecules, short-lived intermediate species, laser pulses, absorption spectroscopy, pharmaceuticals, catalytic cycles, flow chemistry, ultraviolet radiation
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