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New insight into the chiral world

EU-funded scientists developed a new class of stable chiral macromolecules – alleno-acetylenic oligomers – in their quest to investigate what causes high optical activity. These materials are of interest to chemistry as much for their outstanding chiro-optical properties as for a number of other applications.
New insight into the chiral world
Optical activity describes the phenomenon by which chiral molecules are observed to rotate polarised light in either a clockwise or counterclockwise direction. As chiral molecules, alleno-acetylenes are enantiopure and very optically active.

Within HELICALLENES (Helical alleno-acetylenic oligomers with high chiroptical activity), researchers successfully formed supramolecular assemblies of alleno-acetylenes in an effort to study their structure-property relations.

In a combined computational and experimental study of alleno-acetylenic macrocycles and oligomers with different linkers, scientists demonstrated that the strong Cotton effect is a hallmark of alleno-acetylenic molecules. Research also provided evidence that these molecules adopt a helical structure, and 'handedness' depends on the chirality of the constituting monomers.

Another finding was that enantiopure alleno-acetylenic ligands assemble in a diastereoselective way when adding zinc(II) salt, forming triple-stranded helicates. However, what was remarkable and rare was that this helical structure was sufficiently large for encapsulating organic molecules. The circular dichroism spectra of helicates were found to be extremely sensitive to the nature of the guest molecules.

Demonstrating particular affinity towards non-chromophoric, achiral guests typically found in water, this proves that such chiral materials can function as detectors for various molecules.

The project team then synthesised extended helical structures, bearing two separated cavities. Small guests binding independently to the two cavities should be the first reported example of multiple guests binding inside enantiopure helicates. The Cotton effect was stronger compared to the case of shorter helical structures.

Enantiopure strands of alleno-acetylenes were found to assemble upon adding silver(I) salt, forming double-stranded helicates. After increasing the solvent polarity, these helicates formed interlocked structures of unique morphology that demonstrated a significant increase in the Cotton effect.

The great socioeconomic impact of using these chiral materials stems from their potential application as sensitive and selective sensors for analyte detection in aqueous solutions. In addition, the ability to assemble when using certain salts, combined with the outstanding chiro-optical properties makes these materials useful for use in future optoelectronic devices.

Related information


Alleno-acetylenic oligomers, supramolecular chemistry, molecular recognition, optical activity, chiral molecules, enantiopure, Cotton effect, analyte detection
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