According to the academy, the X-ray structures of halogen-bonded crystals have so far indirectly indicated the existence of a sigma hole. These revealed the surprising fact that the chemically bonded halogen atoms of one molecule and the nitrogen or oxygen atoms of the other molecule that should be repelled are in close proximity and thus attract. The observations contradicted the assumption that these atoms carry a homogeneous negative charge and repel due to electrostatic force.
The researchers therefore decided to investigate the subatomic structure of halogen using a Kelvin force microscopy probe. First, they developed a theory that describes the atomic resolution mechanism of the probe. It allowed them to adjust the experimental conditions to display the sigma-hole. The team then combined experimental measurements and advanced quantum-chemical techniques. And this led them to a breakthrough in observation and also to the definitive confirmation of the concept of halogen bonds.
According to Bruno de la Torre of CATRIN and FZÚ, the researchers increased the sensitivity of scanning microscopy by modifying the probe tip. The researcher noted that the research pushed the boundaries of the experiment and expanded the possibilities for other researchers.
“I’ve been dealing with non-covalent interactions all my life, and it’s a satisfaction to me that we can now observe what we’ve only ‘seen’ in theory so far, and that experimental measurements confirm our theoretical predictions of sigma-hole existence and shape perfectly. This will also allow us to better understand these interactions and interpret them, “says computer chemist Pavel Hobza from IOCB, who performed advanced quantum-chemical calculations on supercomputers at the IT4Inovations center in Ostrava.
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What is it for?
This basic research is important for the very knowledge of our world, but scientists already know that it can help in practice. According to the academy, the discovery will make it possible, for example, to better understand the reactions of individual molecules and the reason for the arrangement of different molecular structures.
The new imaging method also paves the way for improving the material and structural properties of a number of physical, biological and chemical systems that have an impact on people’s daily lives.
Researchers from the Czech Institute of Research and Advanced Technologies (CATRIN) at Palacký University in Olomouc, the Institute of Physics of the Academy of Sciences, IOCB and the IT4Inovations Center at the University of Mining – Technical University of Ostrava collaborated on the large-scale project.
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