Some molecules exist in two forms so their structures and mirror images are not perfect, like our left and right hands. Called chirality, it is a property of these molecules due to their asymmetry. Chiral molecules tend to be transparent because of how they interact with light. Usually, only one type of chiral molecule exists in nature, for example, DNA. Interestingly, if a chiral molecule works well as a drug, its mirror image may not be useful in medicine.
In an attempt to create chirality in the lab, a team led by chemists at the University of California, Riverside, has discovered that the magnetic distribution is the only one.
“We discovered that the magnetic field of any magnet, including a bar magnet, has chirality,” said Yadong Yin, professor of chemistry, who led the team. “Furthermore, we were also able to use the magnetic field distribution to induce the nanoparticles to form chiral structures.”
Traditionally, researchers use “tempplating” to create a chiral molecule. A chiral molecule is first used as a template. Achiral (or non-chiral) nanoparticles are assembled on this template, allowing them to mimic the structure of a chiral molecule. The drawback of this method is that it cannot be used universally, depending heavily on the structure of the molecular template. Another drawback is that the newly created chiral structure cannot be fixed at a specific location, say, on an electronic device.
“But in order to get a good shape, you need a chiral molecule to be in a certain position on the device,” Yin said. “Our method overcomes these difficulties. We are able to quickly create chiral structures by assembling magnetic materials of any type of chemical at scales ranging from molecules to nano- and microstructures.”
Yin explained that his team’s method uses permanent magnets that rotate continuously in space to create chirality. He said that transferring chirality to chiral molecules is done by doping, which includes guest species, such as metals, polymers, semiconductors, and dyes in magnetic nanoparticles that are used to induce chirality.
The results of the study appear today in the journal Science.
Yin said that chiral materials have optical properties when they interact with polarized light. In polarized light, the light waves vibrate in one plane, reducing the intensity of the light. As a result, polarized lenses in sunglasses cut light into our eyes, while non-polarized lenses do not.
“If we change the magnetic field that makes the material chiral, we can change the chirality, which creates different colors that can be seen through polarized glasses,” said Yin. “This color change is instantaneous. Chirality can also be eliminated instantaneously with our method, allowing for rapid control.”
The findings can be used in anti-fraud technology. The chiral pattern that shows the reliability of an object or document cannot be seen with the naked eye but is visible when viewed with polarized glasses. Other applications that have been found are in sensing and the field of optoelectronics.
Zhiwei Li, the first author of the paper and a former student in Yin’s lab said: “More advanced devices can be made using the technological advantages that our method allows.” “Where it is concerned, our method can be used to quickly find chiral or achiral molecules that are associated with other diseases, such as cancer and viral diseases.”
Yin and Li were joined in this research by a group of graduate students in Yin’s lab, including Qingsong Fan, Zuyang Ye, Chaolumen Wu, and Zhongxiang Wang. Li is now a postdoctoral researcher at Northwestern University in Illinois.
This research was supported by a grant to Yin from the National Science Foundation. The UCR Office of Technology Partnerships has filed a patent application related to this project.
The research paper is titled “A magnetic assembly approach to chiral superstructures.”
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