Double proton transfer in a polar nano-droplet: Phototautomerization of alloxazine in AOT/alkane reverse micelles containing water or glycerol

Alloxazine phototautomerization is believed to occur through an excited state double proton transfer (ESDPT) mechanism involving cyclic intermolecular H-bonded complexes between Alloxazine and hydroxylic solvents like water and alcohols. In AOT/alkane dispersions in the absence of any polar liquid, Alloxazine molecules reside inside the polar core of the AOT reverse micelle nanoparticles, where they involve in H-bonding with the anionic sulfonate head-groups of the AOT molecules, but are unable to generate the appropriate cyclic intermolecular H-bonded complexes conducive to ESDPT. However, tautomerization is switched on with addition of water and formation of water nano-droplet at the core of reverse micelle. Evidently, the Alloxazine center dot center dot center dot center dot AOT H-bonds are now replaced by Alloxazine... Water H bonds, promoting ESDPT. On the other hand, Alloxazine phototautomerization is hindered in Glycerol, irrespective of whether the latter is in the bulk liquid state or in the form of a polar nano-droplet. This may be explained by steric considerations. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

Alloxazine phototautomerization occurs through an excited state double proton transfer mechanism involving cyclic intermolecular hydrogen-bonded complexes with hydroxylic solvents. In AOT/alkane dispersions, water addition switches on the tautomerization process by forming water nano-droplets, while phototautomerization is hindered in Glycerol due to steric considerations.