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Chemical Sensing

Supramolecular sensor detects glycolipids

Assembly overcomes challenges of binding the molecules’ hydrophilic and hydrophobic portions

by Celia Arnaud
August 19, 2018

20180819lnp1-sensor.jpg
Credit: Adapted from Angew. Chem. Int. Ed.
A supramolecular assembly of a cucurbituril, a carbohydrate receptor, and an indicator dye detects glycolipids.

Sensors that selectively detect glycolipids—molecules that are involved in infection, inflammation, and cancer progression—are hard to make. Most sensors target either the hydrophilic sugar head group or the hydrophobic lipid tail. A new supramolecular sensor has components that bind both parts of the glycolipid, researchers reported at the American Chemical Society national meeting in Boston on Sunday. Timothy E. Glass of the University of Missouri described the sensor in a presentation in the Division of Analytical Chemistry. The work was also published earlier this month (Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201807221).

Glass’s supramolecular sensor comprises a hydrophobic cavity made from a barrel-shaped cucurbituril molecule, a boronic acid-based carbohydrate receptor, and a fluorescent indicator dye. The receptor stays put in the cavity because a bis-pyridinium group anchors it there. This positively charged anchor region also quenches the dye, which accompanies the receptor in the cavity. When the boronic acid receptor binds the sugar head group of a glycolipid, the lipid tail displaces the dye, which is then free to fluoresce.

“One of my students had the idea that maybe we could self-assemble something, so we don’t have to worry about making a single molecule with all the components we need,” Glass said. “We had to go through a dozen other permutations that didn’t work very well to find one that did.” For instance, some unsuccessful combinations included two receptor elements, leaving no room in the cavity for either the indicator or the lipid tail.

“If anybody thinks it’s easy to recognize both domains of a glycolipid and couple them to a signal, well, I invite them to try,” Julius Rebek Jr., supramolecular expert at Scripps Research Institute California, said. “Dr. Glass has devised a system that works and is modular. The components can be engineered, which offers the potential for even more selective glycolipid detection. Good job!”

So far, the sensor works only with non-natural glycolipids. Natural glycolipids have such hydrophobic tails that they pull the entire assembly out of solution. Glass’s group is collaborating with other researchers to make cucurbiturils and receptors that are more water soluble. He eventually hopes to use the assemblies to shuttle natural glycolipids between cells.

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