Recent advancements of fluorescent tin(IV) complexes in biomedical molecular imaging

In the last few years, tin(IV) complexes have emerged as very attractive candidates in the field of molecular imaging due to their unique photophysical properties. Despite the few reviews published to date covering the chemistry of organotin and tin complexes and their cytotoxic potential, there are no reviews devoted to their live cell imaging properties. Therefore, this feature article summarizes the discussion of the fundamental photophysical properties of fluorescent tin metal complexes focusing on their recent advances in "biomedical molecular imaging". A debate on the design of tin complexes as cellular imaging agents relating to their chemical, electronic and photophysical properties is enclosed. This paper also discusses the imaging applications of tin complexes in cells, tissues, and organisms via confocal and multiphoton imaging for sensing mechanisms in cellular media, bioimaging, and therapeutic labeling. In addition, it explores and explains the current challenges and prospects associated with these tin complexes as emerging luminescent cellular agents for potential clinical use.

Mitochondria-Targeted Luminescent Organotin(IV) Complexes: Synthesis, Photophysical Characterization, and Live Cell Imaging

Five fluorescent ONO donor-based organotin(IV) complexes, [Sn^IV(L^1-5)Ph₂] (1-5), were synthesized by the one-pot reaction method and fully characterized spectroscopically including the single-crystal X-ray diffraction studies of 2-4. Detailed photophysical characterization of all compounds was performed. All the compounds exhibited high luminescent properties with a quantum yield of 17-53%. Additionally, the results of cellular permeability analysis suggest that they are lipophilic and easily absorbed by cells. Confocal microscopy was used to examine the live cell imaging capability of 1-5, and the results show that the compounds are mostly internalized in mitochondria and exhibit negligible cytotoxicity at imaging concentration. Also, 1-5 exhibited high photostability as compared to the commercial dye and can be used in long-term real-time tracking of cell organelles. Also, it is found that the probes (1-5) are highly tolerable during the changes in mitochondrial morphology. Thus, this kind of low-toxic organotin-based fluorescent probe can assist in imaging of mitochondria within living cells and tracking changes in their morphology.

Organotin Schiff bases as halofluorochromic dyes: green synthesis, chemio-photophysical characterization, DFT, and their fluorescent bioimaging in vitro

Fluorescent bioimaging is an excellent tool in cellular biology, and it will be a powerful technique in modern medicine as a noninvasive imaging technology where tumoral and normal cells must be distinguished. One of the differences between normal and cancer cells is the intracellular pH. Therefore, the design and synthesis of pH-responsive fluorescent materials are required. Organotin Schiff bases showed halofluorochromic behavior in solution. Microwave-assisted synthesis showed better reaction times and chemical yields compared with conventional heating. All compounds were fully characterized by spectroscopic and spectrometric techniques. The halofluorochromism study showed that some molecules in acidic media have the maximum luminescence intensity due to protonation. All the fluorescent tin complexes showed cell staining on hepatocyte and MCF-7 cells by confocal microscopy. The theoretical study has enabled us to rationalize the optical properties and the halofluorochromism for compounds 1 and 2 synthesized in this work. Our results showed that the emission decrease, in the acid and basic media for compounds 1 and 2, respectively, is caused by intramolecular charge transfer (ICT) deactivation.

Novel triorganotin complexes based on phosphonic acid ligands: Syntheses, structures and in vitro cytostatic activity

Six novel organotin phosphonate complexes, [(Me₃Sn)₄(HL¹)₄]_n1, [(Me₃Sn)₂(HL²)₂]_n2, [(Me₃Sn)₂L³(H₂O)]_n3, [(Ph₃Sn)(HL¹)]₆4, [(Ph₃Sn)₂L²]_n5 and [(Ph₃Sn)₂L³]₆6, derived from phosphonic acid ligands [NaHL¹ = 1-C₁₀H₇OPO₂(OH)Na, H₂L² = 1-C₁₀H₇PO(OH)₂, H₂L³ = 2-C₁₀H₇PO(OH)₂], have been synthesized and characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C, ³¹P and ¹¹⁹Sn) spectroscopy and X-ray crystallography. The structural analysis reveals that complexes 1 and 5 display 1D infinite zig-zag chain structures, and complex 2 shows 1D right-handed helical chain structure, while complex 3 displays 1D left-handed helical chain structure. Complexes 4 and 6 are 24-membered macrocyclic rings interconnected by P, O and Sn atoms. Additionally, the molecules of complexes 1 and 3 are further linked through intermolecular π···π and O-H···O interaction into supramolecular structures, respectively. Furthermore, we preliminarily estimated in vitro cytostatic activity of complexes 1-6 against the human cervix tumor cells (HeLa), human hepatocellular carcinoma cells (HepG-2) and human normal breast cells (HBL-100). Importantly, the anti-proliferative properties and possible pathway of complex 6 are investigated, and the results demonstrate that complex 6 could induce apoptotic cell death via an overload of intracellular reactive oxygen species (ROS) levels and the dysfunctional depolarization of mitochondrial membranes.