Damaged plants and false scents can be identified quickly and reliably in real time

image: At the heart of the new device is a chiral optical polarimeter with which it is possible to determine the chiral signature of components precisely and accurately even in the gas phase.
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Credit: photo/©: Lykourgos Bougas, JGU

A perfume’s chiral signature can reveal whether a perfume is genuine or fake. Likewise, the chiral signature of a plant’s emissions can provide information about plant health or disease. Researchers from Johannes Gutenberg University Mainz (JGU) and the Max Planck Institute for Chemistry (MPIC) have developed an innovative approach capable of identifying and monitoring these chiral signatures. Most natural chiral substances are found in two mirror image forms present in different relative amounts. Therefore, each plant and each fragrance must have its own individual chiral mark. Thanks to their new approach, the research team was able, for the first time, to identify chiral compounds within complex mixtures of gases with a high level of sensitivity and in real time.

“Our new technique has enormous potential, especially in agriculture and the chemical industry,” said Dr. Lykourgos Bougas of JGU. Professor Jonathan Williams of MPIC added: “In addition to commercial applications, this technique will also allow us to decode chiral signals in the air around us, allowing us to better understand the chemistry of the atmosphere.” The cooperating partners have already filed a patent application for their technique.

Natural odors differ from synthetic odors

Chirality is a fundamental property of nature. Our right and left hands are a manifestation of this. More importantly, several biomolecules exist in two mirror-image forms that are not superimposable – in the same way that a right hand will not fit in a left-handed glove. This can affect the biochemical activity of these molecules. A unique example is plant emissions. These contain several chiral compounds that are naturally present in both chiral forms, the D and L isomers or enantiomers. A striking example is the chiral molecule pinene, which is responsible for the characteristic smell of conifers and pines. The relative ratios of the two enantiomers of pinene vary naturally in the emissions of these plants, but they depend critically on the state of health of the plant.

The same principle applies in the case of complex mixtures of natural and synthetic components, as in the case of perfumes. All chiral ingredients will appear in both D and L isomers, but in different relative amounts depending on whether they come from natural or synthetic sources. As it often happens that natural components are replaced by synthetic substances in counterfeit or counterfeit perfumes, the fake perfumes will have a different chiral signature than the originals.

Research under the aegis of the ULTRACIRAL project funded by the European Union

The Mainz-based researchers developed an improved cavity polarimetric method for optical chiral analysis as part of the EU-sponsored ULTRACHIRAL project. They were able to detect the different optical rotation effects of chiral molecules under polarized light. For this, they transferred a sample of a plant odor or perfume into a small chamber which they exposed to polarized light. They then used a new chirality-sensitive optical polarimeter to precisely and accurately measure the induced rotation of polarized light. The researchers were able to achieve orders of magnitude better sensitivity than current state-of-the-art equipment.

“Our new approach to chiral analysis provides us with accurate, faster results at better sensitivities than traditional techniques, without requiring calibration before each measurement. In addition, our technique has been combined for the first time with chromatography in the gas phase to separate the individual components in a complex mixture. As a result, the chiral form of each constituent present in a complex mixture of gases can be identified directly and accurately,” explained JGU physicist Dr Lykourgos Bougas, lead author of the recently published article. Scientists progress. In their publication, the team of authors proposes a whole range of possible new applications for their method of detection.

Among these, the quality control of perfumes, a process currently particularly complex because perfumes contain several hundred or even thousands of different compounds – natural and synthetic. To demonstrate the effectiveness of their technique, the researchers compared four authentic, high-quality commercial perfumes with their low-cost counterfeits. The Mainz-based team was able to differentiate high-quality original fragrances from their knockoffs based on their chiral signatures using just one quick measurement.

Potential use in growing crops to monitor plant health and pest infestations

The technique could also be of considerable interest in the field of agriculture. By taking a young conifer, the team was able to show that the chiral signature of the plant’s emissions suddenly changed as soon as the plant was damaged. Similar chiral signatures have already been observed in plants prone to drought or disease. These signatures can be used in practice, for example, to continuously monitor cultivated plants and trigger an alarm if they are infested with insects, suffer from a lack of water or become ill.

The method can also help to better understand the physical and chemical processes that occur in our atmosphere. Forests are known to release large amounts of volatile organic compounds (VOCs) into the environment, many of which are chiral. These molecules affect not only the chemistry and physics of the air around us, but also our climate. VOCs can also be precursors to secondary organic aerosols that influence the Earth’s solar radiation balance. “We still largely ignore the role that chirality plays in all these processes. In order to better understand this, we need new instruments and new approaches, such as those provided by our research,” Bougas concluded.

In order to allow easier implementation of the new method in the different fields of application, Dr. Lykourgos Bougas and Professor Jonathan Williams hope that a portable version of the device will be developed in the future.

Related links:
https://www.mpic.de/2285/en – Max Planck Institute of Chemistry;
https://cordis.europa.eu/project/id/737071 – ULTRACHIRAL project

Dr Lykourgos Bougas
Quantum, Atomic and Neutronic Physics (QUANTUM)
Institute of Physics
Johannes Gutenberg University Mainz (JGU)
and the Helmholtz Institute Mainz (HIM)
55099 Mainz
phone: +49 6131 39-29633
E-mail: lybougas@uni-mainz.de

Professor Dr. Jonathan Williams
Atmospheric chemistry
Max Planck Institute for Chemistry
Hahn-Meitner-Weg 1
55128 Mainz
phone: +49 6131 3054500
E-mail: jonathan.williams@mpic.de

Read more:
https://www.uni-mainz.de/presse/aktuell/13510_ENG_HTML.php – press release “The metabolite fumarate may reveal cellular damage: Presentation of a new fumarate generation method for MRI” (April 27, 2021);
https://www.uni-mainz.de/presse/aktuell/13224_ENG_HTML.php – press release “Magnetic resonance imaging of the hyperpolarized proton used to observe metabolic processes in real time” (March 11, 2021);
https://www.uni-mainz.de/presse/aktuell/13025_ENG_HTML.php – press release “Venus flytrap producing magnetic fields” (2 Feb. 2021);
https://www.uni-mainz.de/presse/aktuell/11825_ENG_HTML.php – press release “A new NMR method makes it possible to monitor chemical reactions in metal containers” (July 15, 2020);
https://www.uni-mainz.de/presse/aktuell/11370_ENG_HTML.php – press release “New simple method for measuring the state of lithium-ion batteries” (May 7, 2020);
https://www.uni-mainz.de/presse/20145_ENG_HTML.php – press release “EU funding for excellent young researchers in physics” (23 February 2016)

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