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Major leap forward in gold particle research – CSC's supercomputers used in computational tasks

Maria Virkkula

Researchers from the University of Jyväskylä's Nanoscience Center and Colorado State University have determined the structure of the ligand molecule layer that protects the surface of gold particles (Au102), and also its dynamics in water. A gold particle measures approximately one nanometre, that is, about one millionth of a millimetre.

A ligand molecule layer is formed from a number of organic molecules that bind to the surface of a gold nucleus. They are usually thiol molecules containing sulphur and organic carbon, and their sulphur head forms a chemical bond with the gold.

A metal's nucleus determines the particle's physical properties, while its protective layer determines the particle's chemical properties, such as whether the material is water-soluble or requires organic solvents, and how the particle interacts with its surroundings.

– Now that we have a detailed understanding of how the molecule layer protecting an Au102 particle behaves in water, we also have a much better idea of how the particle interacts with, for example, biological materials. This is a major leap forward in our research, says team leader, Academy Professor Hannu Häkkinen.

The gold particles he is studying may be of significant benefit in the development of new applications – for example, in catalysis or as pharmaceutical transporters, molecular electronic components, or biocompatible markers.

The nuclear magnetic resonance spectrum of an Au102 nanoparticle in water (left). The spectrum can be interpreted with the aid of the particle's crystal structure (right) and computational simulations.


Simulations facilitate interpretation of empirical results

It has been challenging to obtain accurate information about the structure of a gold particle's protective surface layer. Until now, all our information has been based on the structural analysis of particles packed in solid crystals. The crystalline structure of the Au102 particle was determined back in 2007, but this is the first time that data has been obtained about the ligand layer and the dynamics of its particles in the solution phase.

Several complementary methods were used during the research. The empirical experiments were performed using a spectroscopy method based on nuclear magnetic resonance. This data was interpreted using Density Functional Theory and simulations based on the molecular dynamics method. The simulations harnessed CSC's supercomputer resources.

– CSC's computing resources played a decisive role in our research. The ligand structure of an Au102 particle is extremely complex and generates dozens of signals in the measured nuclear magnetic resonance spectrum.

– No one had ever tried to study nuclear magnetic resonance computationally in such a complex system before. Post-doctoral Researcher Sami Malola first had to install our density functional code on Sisu and ensure that it would be possible to compute a theoretical spectrum in a massive parallel environment, says Häkkinen.

The atomic structure of a solid Au102 particle had already been published. With the aid of this information, they were able to make a final interpretation of the magnetic resonance results.

– We've been continually studying the Au102 particle and systems formed from it. This new information is extremely valuable when we are considering how to further functionalise the ligand layer in order to make the particles react with other particles or biological materials, and in particular proteins, says Häkkinen.

The research results were published in the journal 'Nature Communications' at the end of January. Read more here.

Academy Professor Hannu Häkkinen, Scientific Director of the Nanoscience Center, has previously used gold particles as virus markers in enterovirus research. Read more about this newly appointed Academy Professor and his groundbreaking research in CSC's online magazine.



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