Change the laterality of molecules
KANAZAWA, Japan, March 9, 2022 /PRNewswire/ — Researchers from Kanazawa University report in Proceedings of the National Academy of Sciences a reactive molecular system which, through chemical reactions, reverses its chirality before becoming racemic.
Molecules that have the ability to change their structure in response to a chemical or physical stimulus are called “reactive molecules”. This type of molecule plays an important role in signal transduction at the nanoscale. The typical time profile of a structural change in a sensitive molecule follows exponential relaxation. However, molecular systems with atypical temporal responses, such as chemical oscillators (whose structure periodically switches between two states), offer advanced functionality and are also intensively studied. Shigehisa Akine and her colleagues at Kanazawa University have now designed a particular sensitive molecule in which the chirality (“laterality”) changes non-exponentially. This achievement is a breakthrough in the field of reactive systems, because the change in chirality occurs in a unimolecular system – and not, as has often been the case before, in supramolecular assemblies.
The researchers’ sensitive molecule has six exchangeable sites; it can be written as [LCo3X6]3+, where X represents a ligand at each of the six sites. The molecule has two forms, a “left-handed” (abbreviated ‘M‘) and a ‘right-handed’ (abbreviated ‘P‘) version. In solution, both forms will occur, in a given ratio. Akine and his colleagues started from the molecule where X is a particular chiral amine labeled A (chiral means that the ligand and its mirror image cannot be superimposed, and amine refers to a type of nitrogen-containing molecular group). In a methanol solution, the P/M a ratio of [LCo3A6]3+ was 88:12, meaning the right-handed version was dominant. The scientists then examined what happened during the exchange of the chiral A groups with piperidine (another amine, but achiral).
Due to the achirality of the piperidine groups, the [LCo3(piperidine)6]3+ the solution must become “racemic”, which means that all the effects of chirality are compensated. This is what happened, but the researchers discovered that before reaching the racemic state after two days, the solution first passed from origin P-dominant at M-dominant after 7 minutes, with maximum M-dominance after 60 – 120 minutes. Remarkably, a similar transient chirality reversal was not observed for the reverse reaction, [LCo3(piperidine)6]3+ for [LCo3A6]3+for which the solution changed monotonically from racemic to P-dominant.
Akine and his colleagues note that their [LCo3X6]3+ The reactive molecule is the first unimolecular platform displaying transient chirality reversal, and that the single chirality change occurs on a timescale of minutes to hours, which could be potentially useful for functional materials dependent on time related to human activity. Quoting the scientists: “This result will provide important insight into the science of autonomously driven materials.”
An enantiomer (sometimes called an optical isomer) is one of two molecules that are mirror images of each other but are not superimposable, just like left and right hands. The two members of a pair of enantiomers are also called enantiomorphs.
In symmetric environments, the enantiomers have identical physical properties except for one: the ability to rotate a particular form of polarized light (called plane-polarized light) by equal amounts but in opposite directions. The enantiomers are therefore called optically active. A mixture consisting of an equal number of the two enantiomorphs of a pair of enantiomers is called a racemic mixture; a racemic mixture is never optically active.
Shigehisa Akine and colleagues at Kanazawa University have now discovered a molecular system in solution that, through chemical reactions, changes its overall “chirality” (chirality) from right to left, before becoming racemic.
Yoko Sakata, Shunsuke Chibaand Shigehisa Akine, Inversion of transient chirality during the racemization of a helical cobalt(III) complex, proc. Natl Acad. science, 119 (11) e2113237119, March 2022
Figure 1. Transient chirality inversion in this study.
A right-handed helical cobalt(III) complex underwent chirality inversion to give the left-handed form before full racemization upon removal of the chiral source.
About the Nano Life Science Institute (WPI-NanoLSI)
The Nano Life Science Institute (NanoLSI) at Kanazawa University is a research center established in 2017 under the World Premier International Research Center Initiative of the Ministry of Education, Culture, Sports, Science and Technology. The objective of this initiative is to create world-class research centres. NanoLSI combines the most advanced knowledge of biological probe microscopy to establish “nano-endoscopic techniques” to directly image, analyze and manipulate biomolecules to better understand the mechanisms governing life phenomena such as diseases.
About Kanazawa University
As the leading comprehensive university in the sea of Japan coast, Kanazawa University has contributed greatly to higher education and academic research in Japan since its inception in 1949. The University has three colleges and 17 schools offering courses in subjects including medicine, computer engineering, and humanities.
The University is located on the sea coast of Japan in Kanazawa – a city rich in history and culture. The city of Kanazawa has had a highly respected intellectual profile since the time of the feud (1598-1867). The University of Kanazawa is divided into two main campuses: Kakuma and Takaramachi for its approximately 10,200 students, including 600 foreigners.
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