A team of researchers at the University of Vermont have invented a new tool – they call it a “nanocage” – that can capture and straighten out molecular sizes of polymers.
When a messy polymer strand – whether made of protein or plastic – is opened “we can activate only the polymers we want, leaving the rest alone,” says UVM chemist Severin Schneebeli, who led the new research. This tool – which works as a thread with a needle hole – opens up a new way to create custom materials that have never been made before, he says. These may include nanoscale pill coatings that wrap around single molecules of medicine or new industrial products composed of precisely arranged plastic strands in the atomic scale.
The tool, which consists of molecular edges with special “shape-directing” hydrogen bonds – and thousands of times smaller than a needle head – can select shorter strands of a polymer, leaving longer, which demonstrates that the nanocage can be used to selectively find particular molecular sizes in a soup with material. “It’s selective and it’s never been done before,” Schneebeli says. This research is the first time that science has been able to distinguish and activate different polymer chains in a laboratory – opening the door to new opportunities for precision chemistry.
The new research was published in the June issue of the magazine Chem.
Nanocage’s abilities are new to science – but not to nature. For billions of years, life has evolved to pick just one piece of a protein or other biological node that it wants to loosen and turn on – what scientists call “functionalization.” But people have had a hard time doing the same. “Despite many examples in biology,” the UVM researchers write, “efficient and selective modification of human bodies is still difficult.”
Whether changing biological strands, like DNA, or industrial materials, like plastic, the new tetrahedron-shaped tool promises to let scientists do what nature is already doing well. “It took years of hard work in the lab to assemble this tetrahedron before we could test it,” said Mona Sharafi, lead author of the new study, and postdoctoral researcher at Unversity of Vermont who came to the United States from Iran. “It’s entirely human,” she says, “but inspired by nature.”
The word polymer comes from a few Greek words meaning “many parts.” And polymers are just that: materials made of huge molecules that consist of many repeating parts. They are available in many everyday products. Some are natural, like rubber and shellac. Many are synthetic and are used to produce much of the material in everyday life – from shopping bags to diapers, clothes to water lines. Polymers can be found in nice long strands at the molecular level – or they can be tied up in good knots like a billion strands of micro-spaghetti
Nature has had eons to find out how to synthesize these huge molecules – biopolymers, like DNA – and how to edit and activate selected parts. People have become quite good at creating new synthetic polymers – but not so good at choosing and editing them. Many scientists and engineers – working with new renewable energy applications (such as next-generation solar cells), precision medicine (such as delivering cancer drugs to targeted parts of the body) and advanced electronics (including flexible devices) – would like greater control and efficiency that works with what the UVM team calls “functional polymers with complex topologies.” With support from the National Science Foundation and the National Institute of Health (which supported the computational studies, directed by UVM chemist Jianing Li), nanocage research provides a new tool to do so – “to loosen the knot, open polymers that would have been inaccessible earlier, says UVM’s Mona Sharafi. “We have opened something big.”
Growing polymers of different lengths
Mona Sharafi et al, size-selective catalytic polymer acylation with a molecular tetrahedron, Chem (2020). DOI: 10.1016 / j.chempr.2020.05.011
Provided by the University of Vermont
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