Microwave-assisted synthesis, characterization and molecular docking of two C2-symmetric Schiff bases as fluorescent dye for silk fibroin

Using non-cytotoxic fluorescent materials for staining Bombyx mori silk fibroin holds great promise for tissue engineering and regenerative medicine, as it could be used as a scaffold and monitor for cell growth. Here, we report the microwave-assisted synthesis of two fluorescent Schiff bases in short reaction time and good yields. Detailed characterization of the synthesized compounds using NMR (¹H, ¹³C NMR, and 2D NMR experiments), HRMS (DART+), UV/Vis, fluorescence spectroscopy, and X-ray diffraction studies. The Schiff base molecular structures showed a non-planar arrangement with the C₂ point group. Both compounds showed low cytotoxicity on colon carcinoma cells (Caco2, ATCCHTB-37) at different concentrations (1 to 5 μg/mL). Notably, Schiff bases exhibit good fluorescent staining of Bombyx mori silk fibroin by the immersion method and were analyzed by confocal microscopy. The fluorescent staining ability of the Schiff bases toward the silk fibroin was explored by molecular docking, where two predominant binding sites were identified, and H-bonding and other polar interactions were found to stabilize the binding modes of the compounds. From the remarkable findings and to the best of our knowledge, this is the first report on Schiff bases as a fluorescent dye of this biomaterial.