Unveiling the mysterious world of molecules – scientists confirm a decades-old theory

Scientists have confirmed a decades-old theory about the non-uniform distribution of electron density in aromatic molecules, expanding the possibilities for designing new nanomaterials. This research builds on their previous work and uses advanced scanning electron microscopy for subatomic analysis.

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

Researchers from IOCB Prague, the Institute of Physics of the Czech Academy of Sciences, and Palatski University Olomouc have once again made great progress in unlocking the mysteries of the world of molecules and atoms. They experimentally verified a long-standing theory that electron density is not uniformly distributed in aromatic molecules.

This phenomenon greatly affects the physical and chemical properties of molecules and their interactions. This research expands the possibilities for designing new nanomaterials and is the subject of a just-published paper Nature Communications.

The same team of authors in its previous pilot study published in Sciences Describe the irregular distribution of electrons in corn, the so-called σ hole. Now researchers have confirmed the existence of a so-called π hole. In aromatic hydrocarbons, electrons are found in clouds above and below the plane of the carbon atoms. If we replace the surrounding hydrogen atoms with more electronegative atoms or groups of atoms that pull the electrons away, the originally negatively charged clouds turn into positively charged electron holes.

Pavel Hobza

Professor Pavel Hobza, Distinguished Chair and Head of the Non-Covalent Interactions Group at IOCB Prague. Credit: Thomas Bellon/IOCB Prague

Scientists have taken the advanced method of scanning electron microscopy and pushed its capabilities even further. This method works with subatomic resolution, and thus can image not only atoms in molecules, but also the structure of an atom’s electron shell. As one of the co-authors, Bruno de la Torre of the Czech Institute for Advanced Technology and Research (CATRIN) at Palatski University Olomouc, points out, the success of the experiment described here is mainly due to the excellent facilities at his home institution and the institute’s excellent Ph.D. participation. students.

“Thanks to our previous experience with Kelvin probe force microscopy (KPFM) technology, we were able to improve our measurements and obtain very complete datasets that helped us deepen our understanding not only of how charge is distributed in molecules. But also of what can observed using this technique.

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: chemical structure of the investigated molecule, computed electrostatic potential map of the molecule, experimental Kelvin probe force micrograph (KPFM), and simulated KPFM image. Credit: IOCB Prague

Modern force microscopy has long been the domain of researchers at the Institute of Physics. Not only in the case of molecular structures, they used the unprecedented spatial resolution to its fullest extent. Some time ago they confirmed the existence of an irregular distribution of electron density around halogen atoms, the so-called σ holes. This achievement was published in 2021 by Sciences. The previous and current research was greatly contributed by one of the most cited Czech scientists today, Professor Pavel Hobza of 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 precedes it, fully illustrates the quality of the theoretical predictions of quantum chemistry, which have been responsible for both phenomena for decades. It shows that they can be relied upon even in the absence of available experiments,” says Pavel Hobza. .

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

A better knowledge of the electron’s charge distribution will help the scientific community understand many chemical and biological processes in the first place. On a practical level, this will translate into the ability to build new supermolecules and subsequently develop advanced nanomaterials with improved properties.

Reference: “Visualization of a π-hole in Molecules by Kelvin-Probe Force Microscopy” by B. Mallada, M. Ondráček, M. Lamanec, A. Gallardo, A. Jiménez-Martín, B. de la Torre, P. Hobza and B. . Jelinek, Aug. 16, 2023, Available here. Nature Communications.
doi: 10.1038/s41467-023-40593-3

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