What question did this study set out to answer?

The research aims to explore how multivalent anions affect the chiroptical signals of cyanine dye NK2707 in supramolecular assemblies.

July 4, 2026Langmuir0 citationsOpen Access

Multivalent-Anion-Induced Inversion of Chiroptical Signals in a Cyanine Dye Bound to Nanotubular Supramolecular Assemblies

MOMako OtsukiKumamoto University NHNanami HanoKumamoto University HIHirotaka IharaUniversity of Dhaka

Key Points

The research aims to explore how multivalent anions affect the chiroptical signals of cyanine dye NK2707 in supramolecular assemblies.
Investigated the effect of different salts on NK2707 bound to cationic glutamide lipids (G-Py + ) structures.
Examined J-aggregates and their circular dichroism (CD) signals upon adding sodium salt of multivalent anions and NaCl.
Analyzed changes in molecular orientation and aggregate formation at varying temperatures.
Addition of multivalent anions reversed CD signals from R-chiral to S-chiral, achieving unprecedented 10^6-level inversion.
NaCl did not cause significant spectral changes, indicating the effect is highly dependent on anion valence.
Na2SO4 maintained chiral orientation during phase transition and promoted new aggregate formations with substantial CD peaks.

Abstract

High Resolution Image Download MS PowerPoint Slide In this study, we investigated the effect of salts on the induced chirality of the cyanine dye NK2707 when bound to supramolecular assemblies formed by cationic glutamide lipids (G-Py + ). NK2707 bound to G-Py + self-assembled structures formed diverse aggregates and exhibited exceptionally large circular dichroism (CD) signals. The J -aggregates of NK2707 showed an unusually intense R -chiral-induced CD signal attributable to Davydov splitting; this signal reversed to an S -chiral CD response upon addition of the sodium salt of a multivalent anion. This inversion of a CD signal at the 10 6 level is unprecedented. In contrast, NaCl addition produced no appreciable spectral change, suggesting that this effect strongly depends on anion valence. We attribute the CD inversion to multivalent-anion bridging of pyridinium groups, which alters and stabilizes the chiral orientation of G-Py + and, in turn, reverses the induced CD. Furthermore, although molecular orientation typically decreases above the gel–liquid-crystal phase transition temperature, Na 2 SO 4 addition enabled G-Py + to retain its chiral orientation even in the liquid-crystal state. Na 2 SO 4 promoted J -aggregate formation in the gel state and H -aggregate formation in the liquid-crystal state, maintaining a CD peak on the order of 10 6 while shifting the wavelength by approximately 200 nm. Overall, the G-Py + /NK2707 system can be dynamically modulated by multivalent anions and temperature, providing a versatile platform for controlling chiroptical properties through salt-induced changes in molecular orientation.

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