Home Science & Technology Discovering the mysterious world of molecules – scientists confirm a theory known for several decades

Discovering the mysterious world of molecules – scientists confirm a theory known for several decades

Discovering the mysterious world of molecules – scientists confirm a theory known for several decades

Molecule velocity studies

Scientists have confirmed the decades-old theory of the uneven distribution of electron density in aromatic molecules, expanding the possibilities of designing new nanomaterials. This research builds on their previous work and used advanced scanning electron microscopy to achieve subatomic resolution.

Scientists have experimentally verified a long-standing theory that assumed that electron density is unevenly distributed in aromatic molecules.

Scientists from the IOCB in Prague, the Institute of Physics of the Czech Academy of Sciences and Palacky University in Olomouc have once again made significant progress in unraveling the mysteries of the world of molecules and atoms. They experimentally verified a long-standing theory suggesting that electron density is not evenly distributed in aromatic molecules.

This phenomenon significantly affects the physicochemical properties of molecules and their mutual interaction. This research broadens the possibilities for designing new nanomaterials and is the subject of a paper just published in the journal Nature communication.

The same team of authors in their previous landmark study published in Science described the uneven distribution of electrons in a molecule atom, so-called σ-hole. Now researchers have confirmed the existence of the so-called holes π. In aromatic hydrocarbons, electrons are found in clouds above and below the plane of the carbon atoms. If we replace the peripheral hydrogen atoms with more electronegative atoms or groups of atoms that withdraw electrons, the originally negatively charged clouds turn into positively charged electron holes.

Paul Hobza

Prof. Pavel Hobza, Distinguished Chairman and Head of the Non-Covalent Interaction Group at IOCB Prague. Source: Tomáš Belloň / IOCB Prague

Scientists used an advanced method of scanning electron microscopy and developed its capabilities. The method works with subatomic resolution and therefore can image not only atoms in molecules, but also the structure of the electron shell of an atom. As one of the researchers involved, Bruno de la Torre from the Czech Institute for Advanced Technologies and Research (CATRIN) of Palacky University in Olomouc, points out, the success of the experiment described here is mainly due to the excellent equipment of his home institution and the participation of excellent doctoral students.

“With our previous experience with the Kelvin Probe Force Microscopy (KPFM) technique, we were able to refine our measurements and obtain very complete datasets that helped us improve our understanding of not only how charge distribution in molecules but also what can be observed with this technique,” ​​says Bruno de la Torre.

Experimental measurements confirmed theoretical predictions of the existence of a π hole

Experimental measurements confirmed theoretical predictions of the existence of a π hole. From left to right: the chemical structure of the molecule under study, the calculated electrostatic potential map of the molecule, an experimental Kelvin probe force microscopy (KPFM) image, and a simulated KPFM image. Source: IOCB Prague

Contemporary force microscopy has long been the domain of researchers at the Institute of Physics. Not only in the case of molecular structures, unprecedented spatial resolution was fully exploited. Some time ago, they confirmed the existence of an uneven distribution of electron density around halogen atoms, the so-called σ-holes. This achievement was published in 2021 by Science. One of the most cited contemporary Czech scientists, Prof. Pavel Hobza from the Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences (IOCB Prague).

“The confirmation of the existence of the π hole, as well as the σ hole that preceded it, fully demonstrates the quality of the quantum chemistry theoretical predictions that have explained both phenomena for decades. It shows that they can be relied on even in the absence of available experiments,” says Pavel Hobza.

The results of research by Czech scientists at the subatomic and submolecular level can be compared to the discovery of cosmic black holes. They were also theorized about for decades before their existence was confirmed by experiments.

A better understanding of electron charge distribution will help the scientific community understand many chemical and biological processes in the first place. In practice, this will translate into the possibility of building new supramolecules, and then into the development of advanced nanomaterials with improved properties.

Reference: “Visualization of the π hole in molecules by Kelvin probe force microscopy”: B. Mallada, M. Ondráček, M. Lamanec, A. Gallardo, A. Jiménez-Martín, B. de la Torre, P. Hobza, and P Jelinek, August 16, 2023, Nature communication.
DOI: 10.1038/s41467-023-40593-3


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