Microscopic Vibrational Circular Dichroism Enables Supramolecular Chirality Mapping

A two-dimensional map of proteins, including secondary structures, was obtained for the hindwings of an insect (Anomala albopilosa) at the spatial resolution of 100 µm. Mapping was achieved with the microscopic vibrational circular dichroism (VCD) system, which has been developed in our laboratory. As a result, the insect hindwing was revealed to be composed of segregated microdomains consisting of proteins with different secondary structures.

IR intensity mapping and VCD spectra of Anomala albopilosa

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 thesupramolecular 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 µm 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.

Published: 20 Aug 2021

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the Japan Science and Technology Agency JST MIRAI grants (JPMJMI18GC)