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Polymer chains are already often used in drug delivery, pointed out
Malcolm Chisholm, Distinguished Professor of Mathematical and Physical
Sciences and professor of chemistry at Ohio State. Polymer rings could
have similar uses. "These rings could encapsulate certain molecules,
transport them somewhere, and release them at a specific time," he
said.
The technique may eventually be used in drug design. The kind of ring
molecules grown in this study, known as depsipeptides, are similar to
some natural compounds produced by microorganisms that are employed as
antibiotics, such as valinomycin. Scientists are also studying
depsipeptides as possible anti-cancer agents.
Chisholm hit upon the idea for the new process when he decided to
capitalize on what some chemists would call a "bad" reaction.
"A bad chemical reaction is a competing reaction," he said. "So if I'm
trying to grow polymer chains, and for some reason a side reaction
occurs that chops up my chains, or grows some rings instead, that's a
bad reaction. And I thought, if we could control the bad reaction to
be selective, to do just one thing for us, then we'd actually have a
new kind of process, something that would be completely different from
everybody else's."
Chisholm doesn't want to oversell the technology.
"This project is really just beginning, and so there won't be any
immediate applications. But there could be potential for future
applications in medicine, because these molecules can be varied to
perform specific functions," he said.
He described how the ring-making technique works. A catalyst - an
added chemical substance that enables the reaction - reacts with a
single ring-shaped molecule, and multiplies it many times over,
spawning rings of many different sizes. He likened the process to a
child blowing a cascade of bubbles.
The rings form, break apart, and reform, until the chemists introduce
a compound that specifically binds with one size ring in particular,
and removes it from the mix. Then all the other rings assume the size
and shape of the ring that was removed.
"It's as if all the bubbles in the end collapse to that one particular
bubble you were looking for," he said.
While there are other methods for making polymer rings and chains,
this is the only one that solely makes rings. It's also the only one
for which the catalyst is reusable indefinitely, which Chisholm counts
as a significant advantage.
Next, the chemists would like to bind their rings to other charged
atoms, such as ions of potassium and lithium.
Ohio State coauthors on the paper included Judith C. Gallucci, a
senior research associate, and Hongfeng Yin, a postdoctoral researcher,
both in chemistry.
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