Driven by curiosity, Barnes only began to look at the radical chemistry of the ring cyclobis (paraquat-p-phenylene) two years ago, nearly 25 years after the ring was first made.
"I wondered what would happen if we took it all the way to the max," said Barnes, the paper's first author and a member of Stoddart's group. "Can we take two of these rings, each with four positive charges, and make them live together?"
The rings repel each other like the positive poles of two magnets. Barnes saw an opportunity where he thought he could tweak the chemistry by using radicals to overcome the hate between the two rings.
"We made these rings communicate and love each other under certain conditions, and once they were mechanically interlocked, the bond could not be broken," Barnes said.
Barnes' first strategy -- adding electrons to temporarily reduce the charge and bring the two rings together -- worked the first time he tried it. He, Stoddart and their colleagues started with a full ring and a half ring that they then closed up around the first ring (using some simple chemistry), creating the mechanical bond.
When the compound is oxidized and electrons lost, the strong positive forces come roaring back -- "It's hate on all the time," Barnes said -- but then it is too late for the rings to be parted. "That's the beauty of this system," he added.
Most organic radicals possess short lifetimes, but this unusual radical compound is stable in air and water. The compound tucks the electrons away inside the structure so they can't react with anything in the environment. The tight mechanical bond endures despite the unfavorable electrostatic interactions.
The two interlocked rings house an immense amount of charge in a mere cubic nanometer of space. The compound, a homocatenane, can adopt one of six oxidation state
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