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Real-time monitoring of chirality

Artist’s impression of a time-resolved circular dichroism measurement of a photoexcited spin-crossover complex. Credit: Ella Maru Studio, Inc.

A pair of chiral molecules has two forms, known as enantiomers, that are mirror images of one another but cannot be superimposed. Enantiomers can have negative impacts on (bio)chemical processes, despite the fact that they share many chemical and physical features. Enantiomeric forms of a target molecule may only be bound by a certain protein or enzyme. To create (bio)chemical substances, for example, in the food, fragrance, and pharmaceutical sectors, the detection and management of chirality is often critical.

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Chiral materials absorb left- and right-circularly polarized light differently, allowing for direct identification of enantiomers. This technique is known as circular dichroism. Because of its chiral reaction, circular dichroism has become a prominent analytical method in the (bio)chemical sciences for resolving a molecule’s conformation.

Circular dichroism, on the other hand, has thus far been limited in terms of time resolution and spectral spectrum. Malte Oppermann and Majed Chergui’s group at EPFL have developed a new time-resolved instrument that measures circular dichroism changes in fractions of a picosecond (one trillionth of a second), which means that it can take ultrafast snapshots of a molecule’s (bio)chemical activity at the nanosecond scale. In this way, the chirality of photoexcited molecules can be captured and the conformational motion driving light absorption can be resolved.

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The new method was used to investigate the magnetic-switching dynamics of so-called “iron-based spin-crossover complexes,” an important class of metallo-organic molecules with promising applications in magnetic data storage and processing devices, in collaboration with the groups of Jérôme Lacour at the University of Geneva and Francesco Zinna at the University of Pisa. Despite its usefulness for magnetic data storage, the deactivation mechanism of their magnetic state remains unsolved after decades of research.

Scientists used a time-resolved circular dichroism experiment to discover that the chiral symmetry of the molecule is twisted, causing the loss of magnetization. When the researchers adjusted complexes, they discovered that they were also able to slow down their magnetic decay by reducing their twisting motions.

As Malte Oppermann points out, “These ground-breaking investigations indicate that time-resolved circular dichroism is ideally adapted to record the molecular motion that drives many (bio)chemical processes.” An entirely new method for studying dynamic processes, such as the rapid rotation of synthetic molecular motors, and the conformational changes of proteins and enzymes in their original liquid environment, has been developed.”

Nature Chemistry has published the research.

Further information: Malte Oppermann, Chiral control of spin-crossover dynamics in Fe(II) complexes, Nature Chemistry (2022). DOI: 10.1038/s41557-022-00933-0www.nature.com/articles/s41557-022-00933-0

Journal information: Nature Chemistry

Source: Ecole Polytechnique Federale de Lausanne

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