A study gives a detailed look at an interesting property of chiral materials

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In nature, many molecules possess a property called immiscibility, which means that they cannot be superimposed on their mirror images (such as left and right hand).

Alternative effects can affect function, affecting pharmaceutical or enzyme efficacy, for example, or the perceived aroma of a compound.

Now a new study is advancing scientists ’understanding of another feature linked to vitality: How light interacts with chiral materials under a magnetic field.

Previous research has shown that in such a system, the left and right forms of material absorb light differently, in ways that mirror each other when light flowing parallel to an external magnetic field changes direction, adopting an antiparallel flux. This phenomenon is called magneto-chiral dichroism (MChD).

There is, however, no confirmation from past experiments that experimental observations are consistent with predictions made by MChD theory – a necessary step to test the theory and understand the effects that scientists have observed.

The new newspaper, which will appear on April 21 in Scientific Advances, changes this. The study was led by Geert LJA Rikken, Ph.D., director of the Laboratoire National des Champs Magnétiques Intenses in France, and Jochen Autschbach, Ph.D., Larkin professor of histemia at the University of Buffalo in the United States. The first authors were Matteo Atzori, a doctor, a researcher at the Laboratoire National des Champs Magnétiques Intenses, and a doctor of chemistry from UB student Herbert Ludowieg.

“The first theoretical predictions of MChD for light appeared in the 1980s. Since then, an increasing number of observations on the effect have been reported, but no quantitative analysis has been able to confirm whether the underlying theory of MChD is correct,” says Rikken. “The new study presents detailed measurements of two well-defined model systems, and advanced quantum chemistry calculations on one of them.”

“Dr. Rikken’s team made the first experimental observation of MChD in 1997 and has since reported other experimental studies on the effect on different systems,” says Autschbach. “However only now is a direct comparison between experiment and ab-initio-quantum theoretical calculations possible, for confirmation of MChD theory.”

The research focused on crystals consisting of the mirrored forms of two compounds: nitrate of tris (1,2-diaminoethane) nickel (II), and nitrate of tris (1,2-diaminoethane) cobalt (II). As Autschbach explains, “the molecular form of the tris (1,2-diaminoethane) metal (II) ion in the crystal has a helix-like shape. Helices also come in pairs of mirror images that cannot be superimposed.”

Rikken’s laboratory performed detailed experimental measurements for both systems studied, while Autschbach’s group exploited UB’s supercomputer facility, the Center for Computational Research, to perform difficult quantochemical calculations related to light absorption of nickel. II) compound.

The results, as explained in the Scientific Advances paper: “We report the experimental low-temperature MChD spectra of two archetypal chiral paramagnetic crystals taken as model systems, tris (1,2-diaminoethane) nickel (II) and cobalt (II) nitrate, for light propagating parallel or perpendicular to c- axis of the crystals, and the calculation of the MChD spectra for the Ni (II) derivative by state-of-the-art quantum chemical chemistry calculations.

“By adding vibronic coupling, we find a good consensus between experiment and theory, which paves the way for MChD to develop into a powerful chiral spectroscopic tool and provide fundamental information for the chemical design of new magnetocirculation materials for technological applications.”

While the study is in the realm of basic science, Rikken notes the following regarding the future potential of MChD: “We find experimentally that (for the materials we studied), at low temperatures, the difference in light distribution is parallel and against – parallel to a modest magnetic field of 1 Tesla, barely more than what a refrigerator magnet produces can reach 10% Our calculations allow us to understand this in detail.The magnitude of the effect and its detailed understanding now opens the door. future applications of MChD that could range from optical diodes to new optical data storage methods. ”


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Additional information:
Validation of microscopic magnetocirical dichroic theory, Scientific Advances (2021). DOI: 10.1126 / sciadv.abg2859, advances.sciencemag.org/content/7/17/eabg2859

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Quote: Study gives detailed look at interesting property of chiral materials (2021, April 21) taken April 21, 2021 from https://phys.org/news/2021-04-intriguing-property-chiral-materials.html

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