Microscopic vibrational circular dichroism enables supramolecular chirality mapping

Insect wings are interesting and attractive as unique examples of bioinspired and biomimetic materials. They exhibit multi-functional features and provide a natural model for developing a functional device based on organic polymers. Although there are many studies on the structures of insect wings using spectroscopic or morphological methods, only a few focused on their chiral properties.

The present work is unprecedented in that it focused on the supramolecular chiral aspect of a targeted insect hindwing sample. We report the application of a multi-dimensional vibrational circular dichroism system (MultiD-VCD) to the hindwings of an insect (Anomala albopilosa (male) ). The MultiD-VCD system with a QCL (quantum cascade laser) was recently developed for the microscopic two-dimensional mapping of VCD signals. The mapping was performed at the spatial resolution of 100 mm on insect hindwing tissue. As a result, it was revealed that the insect hindwing is composed of segregated microdomains consisting of proteins with different secondary structures. The uniqueness of the present method is demonstrated by the following aspects: (i) the observed microscopic distribution of proteins is unattainable by conventional FT-IR spectroscopy; (ii) the identification of a secondary structure of a protein is realized in situ with no pretreatment of the biological sample, such as coating, grinding or solvent extraction.