Luminescent Silk Fibroin with Organotin Compounds from Amino Acid Schiff Bases - Microwave-Assisted Synthesis, Chemo-Optical Characterization, Cytotoxicity, and Confocal Microscopy

In this work, we report the microwave-assisted synthesis of six new pentacoordinate and chiral organotin compounds (1-6) derived from amino acid based Schiff bases. The syntheses were achieved through multicomponent reactions (MCRs) of L-amino acids (tryptophan, tyrosine, and phenylalanine), 2-hydroxy-1-naphthaldehyde, and the corresponding diorganotin oxide (R2SnO, R = nBu or Ph). These compounds were characterized by NMR spectroscopy (H-1, C-13, and Sn-119), HRMS, UV/Vis spectroscopy, and fluorescence spectroscopy. All of the compounds in solution exhibited fluorescence with quantum yields (Phi) in the range 0.08 to 0.21. The cytotoxicities of 1-6 at 0.1 mu g mL(-1) were investigated, and they are practically harmless to melanoma B16F10 cells. The fluorescent staining ability of the organotin compounds toward silk fibroin was investigated by the immersion method and analyzed by confocal microscopy, which showed the efficient and uniform integration of the luminescent compounds. DFT calculations of the interactions of a truncated organotin-fibroin complex are also reported.