Trans-cis Photoisomerization of a biomimetic cyclocurcumin analogue rationalized by molecular modelling.

Raúl Losantos,Stéphane Parant,Jérémy Pecourneau,Maxime Mourer,Andreea Pasc,Antonio Monari

doi:10.1039/d1cp01224j

Abstract

Cyclocurcumin is a natural compound extracted from turmeric and showing, in addition to antiinfective, antibacterial, and intinflammatory capabilities, solvent-dependent phtoswitching ability. The solvent-dependent photochemistry of cyclocurcumin has been rationalized on the basis of a competition between π-π* and n-π* states. Recently we have reported the synthesis of a biomimetic analogue showing enhanced photochemical properties and in particular presenting photoswitching capacity in various media. In the present contribution we rely on the use of molecular modeling and simulation, incuding density functional and wavefunction based methods to explore the excited states potential energy surface landscape. We see that the addition of a carbon-carbon double bond to the core of the natural compounds favors the population of the π-π* state, whatever the choice of the solvent, and hence leads to photoisomerisation, with fluorescence reduced to only a minor channel, rationalizing the experimental observations. In addition, the two photon absorption cross section is also strongly increased compared to the parent compound, paving the way to the use in biologically oriented applications.

Highlights

Curcumin is a natural compound which can be isolated from turmeric rhizome[1] (Curcuma longa), and is widely used as a spice and culinary condiment.[2]
Despite the fact that natural CC has a relatively high two-photon absorption (TPA) cross-section compared to simple and small organic compounds, having been computationally estimated at 14 GM, its value is still too low for practical exploitation.[15]. With all these motivations in mind, we recently reported the design and synthesized a biomimetic analogue based on natural CC showing improved non-linear absorption properties, especially concerning significantly increased TPA cross-section, while keeping the main photoswitchable characteristics of the natural CC.[19]
We reported the first bioinspired photoswitch derived from cyclocurcumin (CC) showing that trans–cis photo-isomerization is possible and rather solvent independent

Summary

Introduction

Curcumin is a natural compound which can be isolated from turmeric rhizome[1] (Curcuma longa), and is widely used as a spice and culinary condiment.[2]. Despite the fact that natural CC has a relatively high TPA cross-section compared to simple and small organic compounds, having been computationally estimated at 14 GM, its value is still too low for practical exploitation.[15] With all these motivations in mind, we recently reported the design and synthesized a biomimetic analogue based on natural CC showing improved non-linear absorption properties, especially concerning significantly increased TPA cross-section, while keeping the main photoswitchable characteristics of the natural CC.[19] As a matter of fact, the combination of a biomimetic strategy using synthetic and molecular design has emerged as a clearly advantageous procedure in the improvement of the photoswitching capabilities.[20,21] we reported the first bioinspired photoswitch derived from cyclocurcumin (CC) showing that trans–cis photo-isomerization is possible and rather solvent independent. A detailed knowledge of these factors is crucial and instrumental to further improve the generations of CC biomimetics yielding to more efficient photoswitches to be used in a broad spectrum of applications

Results and discussion

Conclusions

Computational methodology