Chengzhi Jin

Cyclometalated Iridium(III) Complexes as Two-Photon Phosphorescent Probes for Specific Mitochondrial Dynamics Tracking in Living Cells

Five cyclometalated iridium(III) complexes with 2-phenylimidazo[4,5-f][1,10]phenanthroline derivatives (IrL1-IrL5) were synthesized and developed to image and track mitochondria in living cells under two-photon (750 nm) excitation, with two-photon absorption cross-sections of 48.8-65.5 GM at 750 nm. Confocal microscopy and inductive coupled plasma-mass spectrometry (ICP-MS) demonstrated that these complexes selectively accumulate in mitochondria within 5 min, without needing additional reagents for membrane permeabilization, or replacement of the culture medium. In addition, photobleaching experiments and luminescence measurements confirmed the photostability of these complexes under continuous laser irradiation and physiological pH resistance. Moreover, results using 3D multicellular spheroids demonstrate the proficiency of these two-photon luminescent complexes in deep penetration imaging. Two-photon excitation using such novel complexes of iridium(III) for exclusive visualization of mitochondria in living cells may substantially enhance practical applications of bioimaging and tracking.

Azo-Based Iridium(III) Complexes as Multicolor Phosphorescent Probes to Detect Hypoxia in 3D Multicellular Tumor Spheroids.

Hypoxia is an important characteristic of malignant solid tumors and is considered as a possible causative factor for serious resistance to chemo- and radiotherapy. The exploration of novel fluorescent probes capable of detecting hypoxia in solid tumors will aid tumor diagnosis and treatment. In this study, we reported the design and synthesis of a series of “off-on” phosphorescence probes for hypoxia detection in adherent and three-dimensional multicellular spheroid models. All of the iridium(III) complexes incorporate an azo group as an azo-reductase reactive moiety to detect hypoxia. Reduction of non-phosphorescent probes Ir1-Ir8 by reductases under hypoxic conditions resulted in the generation of highly phosphorescent corresponding amines for detection of hypoxic regions. Moreover, these probes can penetrate into 3D multicellular spheroids over 100 μm and image the hypoxic regions. Most importantly, these probes display a high selectivity for the detection of hypoxia in 2D cells and 3D multicellular spheroids.

Synthesis, characterization and biological evaluation of mixed-ligand ruthenium(II) complexes for photodynamic therapy

This study investigated the photodynamic therapy (PDT) and anticancer activity of mixed ligand Ru(ii) terpyridyl complexes (Ru1-Ru3). The photophysical and photochemical properties, hydrophobic properties, DNA binding and DNA transcription inhibition abilities, cell uptake efficiency, cellular localization and photo-cytotoxicity were investigated. Ru1-Ru3 exhibited red luminescence between 670-710 nm and functioned as photo-sensitizers (PSs) by generating both singlet oxygen and radical ions. Without light activation, Ru1-Ru3 were located at the cytoplasm and were nontoxic to cells. However, upon light activation, Ru1-Ru3 exhibited significant photocytotoxicity. After PDT treatment, mitochondria alteration and nuclear membrane disruption occurred, which resulted in relocalization of the complexes from the cytoplasm to the nucleus. Moreover, high cellular oxidative stress caused cell necrocytosis after PDT treatment.

Cyclometalated Iridium(III) Complexes as AIE Phosphorescent Probes for Real-Time Monitoring of Mitophagy in Living Cells

Mitophagy, which is a special autophagy that removes damaging mitochondria to maintain sufficient healthy mitochondria, provides an alternative path for addressing dysfunctional mitochondria and avoiding cellular death. In the present study, by coupling the triphenylamine group with 2-phenylimidazo[4,5-f][1,10]phenanthroline derivatives, we synthesized five Ir(III) complexes with an AIE property that are expected to fulfill requirements for real-time monitoring of mitophagy. Ir1-Ir5 were exploited to image mitochondria with a short incubation time by confocal microscopy and inductive coupled plasma–mass spectrometry (ICP-MS). Due to aggregation-induced emission (AIE), Ir1-Ir5 exhibited excellent photostability compared to MitoTracker Green (MTG). Moreover, Ir1-Ir5 manifested satisfactory photostability in the mitochondrial physiological pH range. In addition, the uptake mechanism of Ir1 was investigated using confocal microscopy and flow cytometry analysis. Finally, using both Ir1 and LysoTracker Green, we were able to achieve real-time monitoring of mitophagy.

Interfering with DNA High‐Order Structures using Chiral Ruthenium(II) Complexes

In this work, it was found that DNA can undergo B-Z transformational changes and compaction in the presence of DNA intercalators such as ruthenium(II) polypyridyl complexes. The link between B-Z transition and condensation is weak but can be strengthened under certain circumstances with slight alterations to the structures of the ruthenium(II) complexes. Here, following on from previous research, this work reports a series of ruthenium(II) complexes with imidazophenanthroline ligands, which vary in size and planarity. The complexes exhibit distinct effects on DNA structures, ranging from little impact to the transformation of DNA secondary structures to the formation of higher-order DNA structures. Further studies on DNA morphological changes induced by chiral ruthenium(II) complexes are observed by atomic force microscopy and transmission electron microscopy.

Super-Resolution Tracking of Mitochondrial Dynamics with An Iridium(III) Luminophore

Combining luminescent transition metal complex with super-resolution microscopy is an excellent strategy for the long-term visualization of the dynamics of subcellular structures in living cells. However, it remains unclear whether iridium(III) complexes are applicable for a particular type of super-resolution technique, structured illumination microscopy (SIM), to image subcellular structures. Herein, an iridium(III) dye, to track mitochondrial dynamics in living cells under SIM is described. The dye demonstrates excellent specificity and photostability and satisfactory cell permeability. While using SIM to image mitochondria, an ≈80 nm resolution is achieved that allows the clear observation of the structure of mitochondrial cristae. The dye is used to monitor and quantify mitochondrial dynamics relative to lysosomes, including fusion involved in mitophagy, and newly discovered mitochondria-lysosome contact (MLC) under different conditions. The MLC remains intact and fusion vanishes when five receptors, p62, NDP52, OPTN, NBR1, and TAX1BP1, are knocked out, suggesting that these two processes are independent.