Crystals redux: X-ray buckyball revelation

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  • Published: Oct 1, 2016
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Crystals redux: X-ray buckyball revelation

Crystal wisdom

The century-old received wisdom concerning crystallography may have been turned over by an international twenty strong team of scientists who have found a way to make a new type of crystal using a high-intensity light source. Brian Abbey of La Trobe University, in Melbourne, Australia and colleague Harry Quiney of the University of Melbourne report details in the journal Science Advances. (Graphic created by DB using Chemspider)

The century-old received wisdom concerning crystallography may have been turned over by an international twenty strong team of scientists who have found a way to make a new type of crystal from the all-carbon molecule, buckminsterfullerene, using a high-intensity light source. Brian Abbey of La Trobe University, in Melbourne, Australia and colleague Harry Quiney of the University of Melbourne report details in the journal Science Advances.

The team experimented with a crystalline sample of the carbon allotrope buckminsterfullerene, colloquially known as buckyballs for their soccer ball shape that resembles the structures of geodesic domes created by architect Richard Buckminster Fuller that so delighted the late Harry Kroto, discoverer of these molecules. They exposed the compound, more formally known as [60]fullerene, to the intense radiation from the hard X-ray free electron laser (XFEL) at the SLAC National Accelerator Laboratory in the USA and examined the kickback from the molecular soccer balls.

Sledgehammer

Earlier experiments with far dimmer, but nevertheless powerful, sources such as the Australian Synchrotron simply led to the melting and consequent destruction of the fullerenes despite their relative weakness. It was assumed that the XFEL would be even more rapidly destructive so it was a big surprise to find that the XFEL didn't immediately burst the buckyballs. Above a critical energy level, radiation apparently led to the spontaneous rearrangement of the electrons in the molecules rebuilding the material into an entirely novel structure shaped not like a spherical soccer ball but the ovoid shape of an Australian or American football. The shape-shifting buckyballs have very different optical and physical properties to their spherical symmetrical chemical cousins and also generate an entirely different diffraction pattern.

"It was like smashing a walnut with a sledgehammer and instead of destroying it and shattering it into a million pieces, we instead created a different shape - an almond!" Abbey enthuses. "We were stunned, this is the first time in the world that X-ray light has effectively created a new type of crystal phase," adds physicist Quiney.

Spheres to ovoids

The team points out that the ovoid buckyball nanocrystals exist for a tiny fraction of a second but just long enough for the requisite observations to prove that the X-rays themselves have changed the electronic structure dramatically from its original form. "This change means that when we use XFELs for crystallography experiments we will have to change the way we interpret the data," Abbey adds. "The results give the 100-year-old science of crystallography a new, exciting direction." The discovery could change the way many different types of study from small molecules to biomacromolecules such as proteins are investigated with such bright X-ray sources. "Currently, crystallography is the tool used by biologists and immunologists to probe the inner workings of proteins and molecules - the machines of life. Being able to see these structures in new ways will help us to understand interactions in the human body and may open new avenues for drug development," Abbey adds.

"This research is a first step to understanding the interactions involving complex materials and ultra-bright, ultra-short X-ray pulses," Quiney told SpectroscopyNOW. "When we achieve that goal, we will be able to construct molecular movies that capture chemical and biological processes with atomic resolution and on timescales an order of magnitude less than the typical vibrational period of a molecule." He adds that, "Advances in the biological and medical sciences over the past few centuries have been very closely linked to improvements in the resolving power of microscopes. If we can understand the fundamental physics involved in using the X-ray free-electron laser as a molecular microscope, we will push molecular imaging to even smaller distances and shorter timescales than is possible at present and in environments that more closely resemble those that are encountered in living systems."

The team used buckyballs as a convenient source of stable molecules built from carbon to examine whether widely held assumptions about how they ought to behave really were correct. "In conventional crystallography, the system is assumed to behave like a regular superposition of atoms, and so any carbon-based system should have been as good as any other to test what we were looking for," Quiney told us. "But, what we saw wasn't what we expected at all; it really was a discovery...something new and quite unexpected." He adds that his colleagues have already seen something unusual in studies with proteins containing heavy elements and so they are now investigating further. 

The research involved scientists at the ARC Centre of Excellence in Advanced Molecular Imaging, at La Trobe, the University of Melbourne, Imperial College London, the CSIRO, the Australian Synchrotron, Swinburne Institute of Technology, the University of Oxford, Brookhaven National Laboratory, SLAC, the BioXFEL Science and Technology Centre, Uppsala University and the Florey Institute of Neuroscience and Mental Health.

Related Links

Sci Adv 2016, 2(9), e1601186: "X-ray laser-induced electron dynamics observed by femtosecond diffraction from nanocrystals of Buckminsterfullerene"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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