Reversible photoswitching of spiropyran in biomolecular interfaces: A combined spectroscopy and computational study

The reversible photoswitching of nonactivated spiropyran viz., 1,3,3 Trimethylindolinobenzopyrylospiran (SP) is studied by employing UV-Vis spectroscopy and computational based calculations (DFT and MD simulation) under various environmental conditions. When SP resides at Histone (H1) interfaces, upon photoirradiation with UV 254 nm, it readily isomerizes to its merocyanine (MC) trans conformer which on exposure to visible light, reversibly cyclizes back to its original ring closure (SP) state with a rate constant of 2.8 min(-1). Furthermore, in the presence of negatively charged nucleic acid DNA, positively charged H1 protein form H1-DNA condensates. Noncovalently bound MC molecule, sandwiched between H1 protein and DNA at H1-DNA interfaces, with associated free energy of binding -8.3 kcal/mol, reveals very rigid attachment at the recognition sides. We believe that the significant structural isomerization of the non-substituted spiropyran at room temperature depending on its microenvironmental stimuli may find potential use in target-oriented drug delivery applications.

Automated summary

The reversible photoswitching behavior of nonactivated spiropyran was studied, revealing its ability to cyclize back under specific environmental conditions. Upon UV irradiation, spiropyran isomerizes to its merocyanine form, and upon visible light exposure, it reverts back to its original closed-ring state. These findings have potential implications for target-oriented drug delivery applications.