Damaged plants and fake perfumes can be identified rapidly and reliably in real time
The chiral signature of a fragrance can reveal whether a perfume is real or fake. Likewise, the chiral signature of a plant’s emissions can provide information about whether the plant is healthy or diseased. 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 such chiral signatures. Most natural chirals are found in two mirror image forms that are present in different relative amounts. Therefore, each plant and each perfume must have its own individual chiral characteristic. Using their new approach, the research team has for the first time been able to identify chiral compounds in complex gas mixtures with high 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 that “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 collaborating partners have already applied for a patent for their technology.
Naturally occurring fragrances are different from synthetic fragrances
Chirality is a fundamental property of nature. Our right and left hands are an expression of this. Most importantly, different biomolecules exist in two mirror image forms that cannot be superimposed — in the same way that a right hand cannot fit into 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 prominent example is the chiral molecule pinene, which is responsible for the characteristic odor of conifers and pines. The relative proportions of the two enantiomers of pinene vary naturally in the emissions from such plants, but are largely dependent on the health status of the plant.
The same principle applies in the case of complex mixtures of natural and synthetic components, such as in the case of perfumes. All chiral ingredients will exist in both the D and L isomers, but in different relative amounts depending on whether they come from natural sources or synthetic ones. Because it is often the case that natural components are replaced by synthetics in fake/counterfeit perfumes, fake perfumes will have a chiral signature that is different from that of the originals.
Research under the auspices of the ULTRACHIRAL project funded by the European Union
The Mainz-based researchers have developed a cavity-enhanced polarimetric method for optical chiral analysis as part of the EU-sponsored ULTRACHIRAL project. They were able to detect the different optical rotational effects of chiral molecules under polarized light. To do this, they transferred a sample of a plant or perfume scent to a small room that they exposed to polarized light. They then used a new chirality-sensitive optical polarimeter to accurately and accurately measure the induced rotation of the polarized light. The researchers have been able to achieve a sensitivity several orders of magnitude better than that of the current state-of-the-art equipment.
“Our new approach to chiral analysis provides us with accurate results, faster and with better sensitivities than traditional techniques, without the need for any calibration for each measurement run. In addition, our technique has been combined for the first time with gas chromatography to combine the individual components in a complex mixture. As a result, the chiral form of any component present in a complex mixture of gases can be identified instantly and accurately,” explains JGU physicist Dr. Lykourgos Bougas, lead author of the paper recently published in scientific progress† In their publication, the team of authors propose a whole range of possible new applications for their detection method.
One is the quality control of perfumes, currently a very complex process because perfumes contain hundreds or even thousands of different – natural and synthetic – compounds. To demonstrate the effectiveness of their technique, the researchers compared four authentic, high-quality commercial perfumes with their inexpensive counterfeits. The Mainz-based team was able to distinguish the high-quality original perfumes from their imitations based on their chiral signatures using a single quick measurement.
Potential use in crop cultivation to monitor plant and pest health
The technique can also be of great importance in the field of agriculture. By taking a young coniferous plant, the team was able to show that the chiral signature of the plant’s emissions suddenly changed once the plant was damaged. Similar chiral features have already been observed in plants subject to drought or disease. In practice, these signatures can be used, for example, to continuously monitor arable plants and to sound the alarm if they are infested by insects, have a water shortage or become unhealthy.
The method can also help to gain more insight into the physical and chemical processes that take place 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 not only affect the chemistry and physics of the air around us, but also our climate. VOCs may also be the precursors of secondary organic aerosols that affect the Earth’s solar radiation budget. “We are still largely unaware of the role chirality plays in all of these processes. To better understand this, we need new tools and new approaches, like those of our study,” Bougas concluded.
In order to make the new method easier to implement in the various fields of application, Dr. Lykourgos Bougas and Professor Jonathan Williams that a portable version of the device will be developed in the future.
Metamaterial significantly improves chiral nanoparticle signals
Lykourgos Bougas et al, Absolute Optical Chiral Analysis Using Cavity Enhanced Polarimetry, scientific progress (2022). DOI: 10.1126/sciadv.abm3749
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