Page 27 - University of Pretoria RESEARCH REVIEW 2016

LIGHT-HARVESTING
OUTSMARTING NATURE
“The more I understand physics, the more I become fascinated by life processes
– the detail, the remarkable efficiency, robustness, variety and elegance.”
This is how Dr Tjaart Krüger in the Department of Physics at UP introduces his research in the field
of molecular biophysics, a field that lies at the confluence of several scientific disciplines: physics, biology, chemistry, computer modelling and software engineering.
The natural environment is a rich source of adaptation, innovation and inspiration for numerous technologies, including solar technologies. Photosynthetic organisms convert solar energy
into ‘fuels’ with an extraordinary efficiency and adaptability, that have yet to be applied in even
the most advanced human-engineered energy technologies.
Dr Krüger’s research is focused on the primary processes of photosynthesis, where solar photons are absorbed by and transported within light- harvesting complexes (called ‘nano-antennae’)
and converted into transmembrane electron and proton gradients with an efficiency of close to 100%. However, because photosynthetic organisms have not been optimised for the production of fuels, there are significant energy losses that occur during the processes of energy storage and stabilisation. There is therefore much room available to engineer solar cells that outperform the natural systems.
Recent developments in molecular biology, as well as imaging and spectroscopy techniques, have pushed understanding of photosynthesis to the level where it allows, for the first time, considering the idea of redesigning photosynthesis and creating an artificial photosynthetic apparatus. The great advantage of such an artificial system would be that it could be adapted to specific circumstances. This approach holds great promise for advancing energy and agricultural technologies, in particular.
To guide this ambitious objective, it is important first to characterise natural photosynthetic systems in
great detail, and to decide which natural features need to be replicated in artificial photosystems in order to outperform natural structures. This is where biophysics comes into the picture, and Dr Krüger published, in 2016, a major review article in which he addressed some of these ideas.
Light-harvesting antennae, which consist of protein super-complexes that bind dense arrangements of pigment molecules, are some of the most complex molecular systems in the universe. But Dr Krüger’s research team is now at a stage where they are starting to understand many of the fundamental principles of these exceedingly complex systems. His approach is to develop and use advanced spectroscopy techniques to investigate the primary processes of photosynthesis. The two main techniques are single-molecule spectroscopy and ultrafast spectroscopy: methods that enable him to perform spectroscopy on individual molecules and at timescales as short as a few femtoseconds (i.e. 10–15 s). They are also developing ways to control various aspects of light-harvesting, using light, chemicals and nanostructures. Some of these complex experiments were reported in 2016 in the Journal of the American Chemical Society.
Dr Krüger’s research links a network of international collaborators in France, the Netherlands, England, Lithuania, Russia and Czech Republic, and includes one of the 2014 Nobel Laureates in Chemistry.
Asmita Singh, Tjaart Krüger and Alexander Paradzah
Tjaart Krüger
UP Research Review 2016 | 25