Tobacco cutworms insert oxygen into nanocarbon hoops and rings

A team of chemists in Japan have traded in their round-bottom flasks for a squirmier reaction vessel—the tobacco cutworm Spodoptera litura. In a preprint that has not yet been peer-reviewed, the researchers report that when they fed a mix of agar, boiled kidney beans, and nanocarbon hoops and rings to these larvae and extracted the chemicals from their excrement, they found the critters had inserted an oxygen atom into a C–C bond in the nanocarbon structures (ChemRxiv 2024, DOI: 10.26434/chemrxiv-2024-1zd0b).

This was a surprise, says Riken’s Kenichiro Itami, one of the study’s leaders. Cytochrome P450 enzymes, which are probably performing the oxidation in the tobacco cutworm, typically insert oxygen atoms in C–H bonds. “When looking at the X-ray crystal structure of the product, everyone was so shocked,” Itami says in an email. “We realized that there is something very special and unique going on in the insect.”

The chemists, who were also led by Nagoya University’s Takeshi Yanai, Kazuhiro J. Fujimoto, and Atsushi Usami, did the “in-insect” chemistry on methylene-bridged [6]cycloparaphenylene ([6]MCPP, shown). They also fed the larvae cycloparaphenylene (CPP) rings of various sizes but found that only [6]CPP was oxidized.

Initially, the chemists tried using silkworms, but the nanocarbons proved to be toxic to them. Tobacco cutworms are voracious eaters known to feed on a wide variety of crops, and they consumed the nanocarbons without problems. The chemists used about 50 cutworm chemists for most of their syntheses, but for larger experiments they used up to 200 of them, Itami says.

Lawrence T. Scott, a chemistry professor at Boston College who was not involved in the research but has collaborated with Itami, says the work represents out-of-the-box thinking. “This is a really unusual unnatural compound that Itami and his group have chosen to feed to the insect,” Scott says. And the chemistry the insect does would not be easy to do in a typical laboratory reaction, he says.

“We are not saying the in-insect synthesis can replace the in-flask synthesis. But we learned that in-insect offers very exciting opportunity!” Itami says. “We demonstrated the transformations of some selected molecular nanocarbons, but the potential substrates are virtually unlimited.”