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

Abstract

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 (1H, 13C, and 119Sn), HRMS, UV/Vis spectroscopy, and fluorescence spectroscopy. All of the compounds in solution exhibited fluorescence with quantum yields (Φ) in the range 0.08 to 0.21. The cytotoxicities of 1–6 at 0.1 µg 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.

Organotin Dyes Bearing Anionic Boron Clusters as Cell‐Staining Fluorescent Probes

“…Recently,w eh ave been active in the design and synthesis of new fluorescent organoboron [21][22][23] and diorganotin derivatives bearing Schiff-base ligands. [24,25] Moreover,w eh ave demonstrated that fluorescent organotin derivatives I and J (Scheme 3) can be used as cytoplasm markersf or in vitro cell imaging. [26] When the electron-withdrawing group -NO 2 was appended to the ligand, aquenching of the fluorescencee mission (F < 3%)o ccurred.…”

“…Recently, we have been active in the design and synthesis of new fluorescent organoboron and diorganotin derivatives bearing Schiff‐base ligands . Moreover, we have demonstrated that fluorescent organotin derivatives I and J (Scheme ) can be used as cytoplasm markers for in vitro cell imaging .…”

Fluorescent boron Schiff bases dyes for staining silk fibroin: Green synthesis, structural characterization, DFT, and photophysical properties

“…A selection of several non‐fluorescent Bombyx mori cocoons was carried out for degumming and staining process. The staining process was achieved similarly to our previous report . After degumming of Bombyx mori cocoons, the immersion staining of silk fibroin was carried out applying the five‐different luminescent organoboron compounds.…”

“…However, due to the physical absorption, the intermolecular interaction protein‐pigment might be driven by both, Van der Waals and hydrophobic forces . We recently explained that interactions between fibroin and organotin complexes of the amino acid Schiff bases‐type are of non‐covalent interactions . It is worth mentioning that staining of the silk biopolymer with these new boron derivatives was successful and in particular that these boron complexes have not been applied as dyes.…”

“…For instance it was reported the silk fibroin stained with Rhodamines . Acridine orange, Stilben 420, Au nanoclusters, CdS, CdTe, Fluorene derivates, and recently with organotin compounds by our group. In that work, we developed luminescent silk fibroin by the immersion method, using an organotin compound as dye.…”