Simple encapsulation using chiral capsules made from terpenes enables non-chiral organic dyes to exhibit chiroptical characteristics in water without complex chemical changes, according to a recent report by scientists. These molecular innovations may lead to significant advancements in various optical technologies relevant to fields like digital storage, biomedicine, and catalysis, among others.
Chirality is a vital feature in biology, with the molecular components of key biological structures, such as DNA and proteins, being chiral. A chiral molecule cannot be superimposed onto its mirror image, similar to the way your left hand cannot match up perfectly with your right hand. Notably, chirality can influence how a molecule or assembly interacts with light, particularly when it comes to circularly polarized light.
As the demand for advanced optical technologies grows, components that are ‘chiroptically active’ could be utilized in today’s displays, optical storage systems, analytical devices, and biomedicine. Therefore, scientists have been looking for innovative methods to make traditional non-chiral dyes act like chiroptically active molecules. By utilizing “chirality transfer,” non-chiral dyes encapsulated within chiral molecular structures can gain chiroptical qualities. However, creating practical chiral capsules has been difficult due to the complexity and inflexibility of existing designs.
In a recent publication in the Journal of the American Chemical Society, a team led by Assistant Professor Yuya Tanaka and Yoshihisa Hashimoto from the Institute of Science Tokyo introduced a new and simpler solution. They designed innovative chiral capsules derived from terpenes, natural compounds found in plants. These terpene-based capsules provide an efficient and adaptable method for imparting chirality to different non-chiral dyes inside their cavities.
The new chiral capsules are made from terpene-based bent amphiphilic molecules, developed through multiple chemical modifications of menthol. Due to their hydrophilic and hydrophobic structures, these chiral amphiphiles naturally form spherical shapes called terpene capsules when combined with water. When a non-chiral dye is mixed with these amphiphiles, a host-guest composite is created, where the dyes fit into the chiral cavity.
Through thorough experimentation, the researchers demonstrated that chirality was effectively transferred from the capsule to various non-chiral dyes. For instance, fluorescent dyes, such as polyaromatic and BODIPY compounds, showed strong induced circular dichroism and circularly polarized fluorescence. Unlike previously reported chiral hosts, this new structure is highly adaptable and straightforward to produce. Dr. Tanaka noted, “Our terpene capsules allow for the easy creation of well-defined host−guest composites with adjustable chiroptical properties through the simple inclusion of various non-chiral dyes, unlike most previously reported hosts with rigid chiral cavities.” Importantly, another benefit of this chiral capsule is that the resulting composites can be utilized in water, eliminating the need for organic solvents, which has been a drawback of other models.
In summary, this research could lead to cost-effective, high-performance chiroptically active composites, potentially spurring progress in advanced optical technologies. “Our approach enables the easy introduction of chirality to diverse non-chiral dyes without complex synthetic modifications, which may be valuable for polymer materials and catalysts,” Dr. Tanaka concludes. He also hints at ongoing exploration in his lab, focusing on multicomponent host−guest systems with enhanced chiroptical functions.
