A gel made from urea has molecules that resemble friendship bracelets

https://www.newscientist.com/article/2195598-a-gel-made-from-urea-has-molecules-that-resemble-friendship-bracelets/

Urine in a pot

A gel can be made from urea

Arindam Ghosh / Alamy

A gel made from the main compound in urine looks just like a friendship bracelet. It is formed of minuscule fibres that spontaneously form braids and could be used to engineer new medicines.

Jonathan Steed at Durham University in the UK and his colleagues created the gel using urea. On a molecular level, the gel assembles itself into four-stranded braids, in two different configurations.

The simplest four-stranded braid is a quadruple helix – similar to the double helix of DNA, but with four strands winding in parallel. The other is in the form of two double helices weaving in and out of one another.

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“We’ve designed a toy molecule that we can watch forming these rather beautiful braids,” says Steed.

Although their molecule was engineered, braids like this can appear naturally. For example, in mad cow disease, fibres of amyloid proteins form braids and clump together.

SEM images illustrating branching of gel fibres due to braiding defects. showing that the separation of branch points in dried gel samples is highly variable.

Braids made using urea

Christopher D. Jones

The team has used similar urea-based gels to produce pharmaceuticals with different properties.

“We crystallise new drug molecules within them and sometimes find different crystal packing arrangements,” says Steed. The different resulting structures can alter the drug’s solubility and how much of it reaches a person’s bloodstream after it is taken.

The new molecule is stickier than gels the researchers have previously produced and may help to better control the properties of the molecules they design.

“You might imagine a situation where, for example, you can braid fibres in one way and you get something which is ketchup-like and you can braid them another way and you get something that’s like a rubber ball,” says Steed. “If you can produce different microstructures with the same molecule, then you can get materials with different properties.”

Journal reference: Nature Chemistry , DOI: 10.1038/s41557-019-0222-0

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