Nanocarbon synthesis in Spodoptera litura (tobacco cutworm)

A research group led by Designated Assistant Professor Atsushi Usami at the Institute for Advanced Research, Nagoya University, has achieved the world's first synthesis of a functional nanocarbon^*1 in insects by harnessing their xenobiotic metabolism. When belt-shaped nanocarbons were fed to the larvae of S. litura^*2, a new compound was recovered from their frass. Analysis revealed that oxygen atoms were inserted into the nanocarbon in the larvae, thereby endowing it with fluorescent properties. This study demonstrates that insect metabolic systems can be exploited to impart new functions to nanocarbons.

*1 Nanocarbon
Nanometer-scale carbon material. Used in electronic components, batteries, etc.

*2 Spodoptera litura
A moth known as an agricultural pest

Selective oxygen introduction into nanocarbons is difficult with conventional methods

Until now, pharmaceuticals and functional materials have been produced by chemical synthesis in flasks or by utilizing enzymes in vitro. However, special nanocarbons such as fullerenes^*3 have unique structures that make regioselective functionalization difficult, thus limiting their use as starting materials for synthesis.

In contrast, insects possess a wide variety of enzymes in their bodies, enabling them to perform complex chemical reactions with precision and efficiency. In particular, they have developed sophisticated detoxification systems over a long evolutionary history to cope with harmful substances such as plant toxins and pesticides. Therefore, the research group hypothesized that, if living insects could be used as a reaction environment, the regioselective oxygenation of nanocarbons, which has been considered quite difficult, might be achievable in a single step.

*3 Fullerene
A molecule consisting of carbon atoms arranged in a spherical structure that resembles a soccer ball

Unprecedented in vivo synthesis

Successful synthesis in Spodoptera litura larvae

The research group orally administered [6]MCPP (methylene-bridged [6]cycloparaphenylene), a belt-shaped nanocarbon, to S. litura larvae by mixing it into their feed. Two days after administration, a novel derivative [6]MCPP-oxylene, which acquired fluorescent properties through the introduction of an oxygen atom, was recovered from the frass (Fig. 1).

Lepidopteran-specific genes are involved in the synthesis

Analysis of gene functions in the intestinal tissue of S. litura revealed that cytochrome P450 (CYP)^*4 enzymes, a family of metabolic enzymes, play a key role in oxygenation. In particular, knockdown of the Lepidopteran-specific genes CYP X2 and X3 significantly reduced [6]MCPP-oxylene production, suggesting that these genes play especially important roles in the oxygen incorporation reaction.

*4 Cytochrome P450 (CYP)
A superfamily of enzymes found in nearly all living organisms. They play a central role in the breakdown of foreign substances that enter the body.

Selective reactivity toward specific molecular sizes

Similar experiments were carried out using [6]CPP([6]cycloparaphenylene), a cyclic nanocarbon corresponding to a partial structure of [6]MCPP, as well as [5]CPP and [7]–[12]CPP, which differ in ring size. Oxygen incorporation was observed only for [6]CPP. This revealed that nanocarbon size is a key determinant of enzyme activity.

To clarify the reaction mechanism, the research group performed computer simulations. The results showed that CYP X2 and X3 can accommodate two [6]MCPP molecules simultaneously.

Furthermore, the reaction was found to proceed through a previously unknown mechanism: direct insertion of an oxygen atom into the carbon–carbon bond, bypassing the intermediate stages expected in conventional chemical reactions.

Creating new materials using living organisms

This study presents a new strategy for materials science by demonstrating that biological systems can be used to create functional molecules, in contrast to conventional approaches based on chemical and physical methods. In the future, combining this approach with gene-editing technologies and methods for artificially enhancing enzyme performance may expand its applicability to a much broader range of molecules.