The induction of apoptosis in SGC-7901 cells through the ROS-mediated mitochondrial dysfunction pathway by a Ir(III) complex

A new ligand BTCP and its iridium(III) complex [Ir(ppy)₂(BTCP)]PF₆ (Ir-1) were synthesized and characterized by elemental analysis, ESI–MS, IR, ¹H NMR and ¹³C NMR. The cytotoxic activity in vitro of the ligand and its complex against SGC-7901, HeLa, HOS, PC-12, BEL-7402, MG-63, SiHa, A549, HepG2 and normal cell LO2 were evaluated by MTT method [MTT = (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)]. The apoptosis was assayed with AO/EB and Hoechst 33258 staining methods. The reactive oxygen species (ROS), mitochondrial membrane potential, autophagy and cell invasion were studied under fluorescent microscope. The expression of caspases and Bcl-2 family proteins were investigated by western blot. The IC₅₀ values of complex toward SGC-7901, BEL-7402 and MG-63 cells are 3.9 ± 0.5, 5.4 ± 1.2 and 4.2 ± 0.6 µM. The complex can increase the levels of ROS, and induce a decrease in the mitochondrial membrane potential. Ir-1 inhibits the cell growth at G0/G1 phase in SGC-7901 cells, and the complex can induce both autophagy and apoptosis and inhibit the cell invasion. And the complex induces apoptosis through a ROS-mediated mitochondrial dysfunction pathway.     

Synthesis, crystal structure and photoluminescent property of an iridium complex with coumarin derivative ligand

Novel iridium complex containing coumarin derivative as a cyclometalated ligand (L) and picolinate (pic) as the ancillary ligand, Ir(III)bis(3-(pyridin-2-yl)coumarinato N,C⁴)(picolinate) [Ir(L)₂(pic)], was synthesized and characterized. It was demonstrated that the iridium (III) ion in Ir(L)₂(pic) is hexacoordinated by two C atoms and two N atoms from 3-(pyridin-2-yl)coumarin ligands and one N atom and one O atom from picolinate ligand, displaying a distorted octahedral coordination geometry. The Ir(L)₂(pic) has very strong absorption and intensive emission at 532 nm. These results show the promising future of that Ir(L)₂(pic) in fabrication organic light-emitting diodes.     

Mitochondrial generation of reactive oxygen species is enhanced at the Q<Subscript>o</Subscript> site of the complex III in the myocardium of <Emphasis Type="Italic">Trypanosoma cruzi-</Emphasis>infected mice: beneficial effects of an antioxidant

In this study, we have characterized the cellular source and mechanism for the enhanced generation of reactive oxygen species (ROS) in the myocardium during Trypanosoma cruzi infection. Cardiac mitochondria of infected mice, as compared to normal controls, exhibited 63.3% and 30.8% increase in ROS-specific fluorescence of dihydroethidium (detects O₂ ^•−) and amplex red (detects H₂O₂), respectively. This increase in ROS level in cardiac mitochondria of infected mice was associated with a 59% and 114% increase in the rate of glutamate/malate- (complex I substrates) and succinate- (complex II substrate) supported ROS release, respectively, and up to a 74.9% increase in the rate of electron leakage from the respiratory chain when compared to normal controls. Inhibition studies with normal cardiac mitochondria showed that rotenone induced ROS generation at the Q_Nf-ubisemiquinone site in complex I. In complex III, myxothiazol induced ROS generation from a site located at the Q_o center that was different from the Q_i center of O₂ ^•− generation by antimycin. In cardiac mitochondria of infected mice, the rate of electron leakage at complex I during forward (complex I-to-complex III) and reverse (complex II-to-complex I) electron flow was not enhanced, and complex I was not the main site of increased ROS production in infected myocardium. Instead, defects of complex III proximal to the Q_o site resulted in enhanced electron leakage and ROS formation in cardiac mitochondria of infected mice. Treatment of infected mice with phenyl-α-tert-butyl-nitrone (PBN) improved the respiratory chain function, and, subsequently, decreased the extent of electron leakage and ROS release. In conclusion, we show that impairment of the Q_o site of complex III resulted in increased electron leakage and O₂ ^•− formation in infected myocardium, and was controlled by PBN.     

Role of mitochondria in ultraviolet‐induced oxidative stress

The biological effects of ultraviolet radiation (UV), such as DNA damage, mutagenesis, cellular aging, and carcinogenesis, are in part mediated by reactive oxygen species (ROS). The major intracellular ROS intermediate is hydrogen peroxide, which is synthesized from superoxide anion (^•O₂⁻) and further metabolized into the highly reactive hydroxyl radical. In this study, we examined the involvement of mitochondria in the UV‐induced H₂O₂ accumulation in a keratinocyte cell line HaCaT. Respiratory chain blockers (cyanide‐p‐trifluoromethoxy‐phenylhydrazone and oligomycin) and the complex II inhibitor (theonyltrifluoroacetone) prevented H₂O₂ accumulation after UV. Antimycin A that inhibits electron flow from mitochondrial complex III to complex IV increased the UV‐induced H₂O₂ synthesis. The same effect was seen after incubation with rotenone, which blocks electron flow from NADH‐reductase (complex I) to ubiquinone. UV irradiation did not affect mitochondrial transmembrane potential (ΔΨ_m). These data indicate that UV‐induced ROS are produced at complex III via complex II (succinate‐Q‐reductase). J. Cell. Biochem. 80:216–222, 2000. © 2000 Wiley‐Liss, Inc.     

Metal-Enhanced Photosensitization of Singlet Oxygen (ME1O2) from Brominated Carbon Nanodots on Silver Nanoparticle Substrates

The deleterious effects of reactive oxygen species (ROS), including singlet oxygen (¹O₂), on biological systems have cultivated widespread interest in fields ranging from therapeutic techniques to sterilization materials. Researchers have, for example, sought to capitalize on the oxidative damage from singlet oxygen to treat tumors as well as to kill antibiotic resistant bacteria. To generate ¹O₂ in a controllable manner, photosensitizers are optimized to generate ¹O₂ from ground state oxygen (³O₂) when excited by light. When considering applications of photosensitization, favorable properties include high ¹O₂ yield, low synthetic complexity, and minimal cost. Previously, studies have shown that plasmonic nanoparticles are able to amplify the photosensitization of ¹O₂ from small molecule photosensitizers in a mechanism similar to metal-enhanced fluorescence (MEF), thereby improving yield. A recent study from our lab has demonstrated that brominated carbon nanodots, which are an inexpensive and simple-to-collect as a hydrocarbon combustion byproduct, generate reactive oxygen species that can be used for antimicrobial photodynamic inactivation of bacteria. Herein we investigate the combination of these advantageous properties. Using the turn-on fluorescent probe Singlet Oxygen Sensor Green™ to detect ¹O₂, we report the metal-enhanced photosensitization of ¹O₂ by brominated dots in silvered Quanta Plate™ wells. These results provide a promising direction for the potential optimization of carbon nanodot-based agents in light-activated antimicrobial materials.

     

Mitochondrial handling of excess Ca2+ is substrate-dependent with implications for reactive oxygen speciesgeneration

The mitochondrial electron transport chain is the major source of reactive oxygen species (ROS) during cardiac ischemia. Several mechanisms modulate ROS production; one is mitochondrial Ca²⁺ uptake. Here we sought to elucidate the effects of extramitochondrial Ca²⁺ (e[Ca²⁺]) on ROS production (measured as H₂O₂ release) from complexes I and III. Mitochondria isolated from guinea pig hearts were preincubated with increasing concentrations of CaCl₂ and then energized with the complex I substrate Na⁺ pyruvate or the complex II substrate Na⁺ succinate. Mitochondrial H₂O₂ release rates were assessed after giving either rotenone or antimycin A to inhibit complex I or III, respectively. After pyruvate, mitochondria maintained a fully polarized membrane potential (ΔΨ; assessed using rhodamine 123) and were able to generate NADH (assessed using autofluorescence) even with excess e[Ca²⁺] (assessed using CaGreen-5N), whereas they remained partially depolarized and did not generate NADH after succinate. This partial ΔΨ depolarization with succinate was accompanied by a large release in H₂O₂ (assessed using Amplex red/horseradish peroxidase) with later addition of antimycin A. In the presence of excess e[Ca²⁺], adding cyclosporin A to inhibit mitochondrial permeability transition pore opening restored ΔΨ and significantly decreased antimycin A-induced H₂O₂ release. Succinate accumulates during ischemia to become the major substrate utilized by cardiac mitochondria. The inability of mitochondria to maintain a fully polarized ΔΨ under excess e[Ca²⁺] when succinate, but not pyruvate, is the substrate may indicate a permeabilization of the mitochondrial membrane, which enhances H₂O₂ emission from complex III during ischemia.     

Internal heavy atom effect of Au(III) and Pt(IV) on hypocrellin A for enhanced in vitro photodynamic therapy of cancer

Hypocrellin A (HA), an a natural perylene quinine photosensitizers (PSs), can chelate with heavy metal ions, including Au(III) and Pt(IV), to form a 1:2 complex, which exhibits enhanced ¹O₂ generation quantum yield through the increased intersystem crossing efficiency mediated by internal heavy atom effect. Besides, the chelate process greatly improved the water solubility of HA. Comparative studies with HA and complexes have demonstrated that the heavy-atom effect on HA molecules enhances the efficiency of in vitro photodynamic (PDT) efficacy.     

Ambivalent effects of diazoxide on mitochondrial ROS production at respiratory chain complexes I and III

Background

Reactive oxygen species (ROS) are among the main determinants of cellular damage during ischemia and reperfusion. There is also ample evidence that mitochondrial ROS production is involved in signaling during ischemic and pharmacological preconditioning. In a previous study we analyzed the mitochondrial effects of the efficient preconditioning drug diazoxide and found that it increased the mitochondrial oxidation of the ROS-sensitive fluorescent dye 2′,7′-dichlorodihydrofluorescein (H₂DCF) but had no direct impact on the H₂O₂ production of submitochondrial particles (SMP) or intact rat heart mitochondria (RHM).

Methods

H₂O₂ generation of bovine SMP and tightly coupled RHM was monitored under different conditions using the amplex red/horseradish peroxidase assay in response to diazoxide and a number of inhibitors.

Results

We show that diazoxide reduces ROS production by mitochondrial complex I under conditions of reverse electron transfer in tightly coupled RHM, but stimulates mitochondrial ROS production at the Q_o site of complex III under conditions of oxidant-induced reduction; this stimulation is greatly enhanced by uncoupling. These opposing effects can both be explained by inhibition of complex II by diazoxide. 5-Hydroxydecanoate had no effect, and the results were essentially identical in the presence of Na⁺ or K⁺ excluding a role for putative mitochondrial K_ATP-channels.

General significance

A straightforward rationale is presented to mechanistically explain the ambivalent effects of diazoxide reported in the literature. Depending on the metabolic state and the membrane potential of mitochondria, diazoxide-mediated inhibition of complex II promotes transient generation of signaling ROS at complex III (during preconditioning) or attenuates the production of deleterious ROS at complex I (during ischemia and reperfusion).     

Generator-specific targets of mitochondrial reactive oxygen species

To understand the role of reactive oxygen species (ROS) in oxidative stress and redox signaling it is necessary to link their site of generation to the oxidative modification of specific targets. Here we have studied the selective modification of protein thiols by mitochondrial ROS that have been implicated as deleterious agents in a number of degenerative diseases and in the process of biological aging, but also as important players in cellular signal transduction. We hypothesized that this bipartite role might be based on different generator sites for “signaling” and “damaging” ROS and a directed release into different mitochondrial compartments. Because two main mitochondrial ROS generators, complex I (NADH:ubiquinone oxidoreductase) and complex III (ubiquinol:cytochrome c oxidoreductase; cytochrome bc₁ complex), are known to predominantly release superoxide and the derived hydrogen peroxide (H₂O₂) into the mitochondrial matrix and the intermembrane space, respectively, we investigated whether these ROS generators selectively oxidize specific protein thiols. We used redox fluorescence difference gel electrophoresis analysis to identify redox-sensitive targets in the mitochondrial proteome of intact rat heart mitochondria. We observed that the modified target proteins were distinctly different when complex I or complex III was employed as the source of ROS. These proteins are potential targets involved in mitochondrial redox signaling and may serve as biomarkers to study the generator-dependent dual role of mitochondrial ROS in redox signaling and oxidative stress.     

Oxygen Sensitivity of Mitochondrial Reactive Oxygen Species Generation Depends on Metabolic Conditions

The mitochondrial generation of reactive oxygen species (ROS) plays a central role in many cell signaling pathways, but debate still surrounds its regulation by factors, such as substrate availability, [O₂] and metabolic state. Previously, we showed that in isolated mitochondria respiring on succinate, ROS generation was a hyperbolic function of [O₂]. In the current study, we used a wide variety of substrates and inhibitors to probe the O₂ sensitivity of mitochondrial ROS generation under different metabolic conditions. From such data, the apparent K_m for O₂ of putative ROS-generating sites within mitochondria was estimated as follows: 0.2, 0.9, 2.0, and 5.0 μm O₂ for the complex I flavin site, complex I electron backflow, complex III Q_O site, and electron transfer flavoprotein quinone oxidoreductase of β-oxidation, respectively. Differential effects of respiratory inhibitors on ROS generation were also observed at varying [O₂]. Based on these data, we hypothesize that at physiological [O₂], complex I is a significant source of ROS, whereas the electron transfer flavoprotein quinone oxidoreductase may only contribute to ROS generation at very high [O₂]. Furthermore, we suggest that previous discrepancies in the assignment of effects of inhibitors on ROS may be due to differences in experimental [O₂]. Finally, the data set (see supplemental material) may be useful in the mathematical modeling of mitochondrial metabolism.The production of reactive oxygen species (ROS)² by mitochondria has been implicated in numerous disease states, including but not limited to sepsis, solid state tumor survival, and diabetes (1). In addition, mitochondrial ROS (mtROS) play key roles in cell signaling (reviewed in Refs. 2 and 3). There exist within mitochondria several sites for the generation of ROS, with the most widely studied being complexes I and III of the electron transport chain (ETC). However, there is currently some debate regarding the relative contribution of these complexes to overall ROS production (4–9) and the factors that may alter this distribution. One such factor considered herein is [O₂]. Estimates of physiological [O₂] within tissues (i.e. interstitial [O₂]) range from 37 down to 6 μm at 5–40 μm away from a blood vessel (10). More recently, EPR oximetry has estimated tissue [O₂] to be in the 12–60 μm range (11). In addition, elegant studies with hepatocytes have shown that O₂ gradients exist within cells, such that an extracellular [O₂] of 6–10 μm yields an [O₂] of ∼5 μm close to the plasma membrane, dropping to 1–2 μm close to mitochondria deep within the cell (12). In cardiomyocytes, at an extracellular [O₂] of 29 μm, intracellular [O₂] varied in the range 6–25 μm (13). Clearly, different tissues consume O₂ at different rates, so these gradients can vary considerably between tissue and cell types.By definition, the generation of reactive oxygen species by any mechanism, is an O₂-dependent process. However, measurements in intact cells have indicated that mtROS generation increases at lower O₂ levels (1–5% O₂) (14). Proponents of an increase in mtROS in response to hypoxia suggest that under such conditions, reduction of the ETC results in increased leakage of electrons to O₂ at the Q_O site of complex III (14). Such a model posits that increased hypoxic ROS is a mitochondria-autonomous signaling mechanism (i.e. it is an inherent property of the mitochondrial ETC). Therefore, mtROS generation should increase in hypoxia regardless of the experimental system being studied, including isolated mitochondria. In contrast to this hypothesis, we and others have demonstrated that ROS generation by mitochondria is a positive function of [O₂] across a wide range of values (0.1–1000 μm O₂) (15–18), suggesting that signaling mechanisms external to mitochondria may be required to facilitate the increased hypoxic mtROS production observed in cells.One limitation of our previous work (15) was that only a single respiratory condition was studied, namely succinate as respiratory substrate (feeding electrons into complex II) plus rotenone to inhibit backflow of electrons through complex I (5, 7). The possibility exists that under different metabolic conditions, which may lead to differential redox states between the cytochromes in the ETC (19, 20), ROS generation may exhibit a different response to [O₂]. Thus, in the current study, we examined the response of mtROS generation to [O₂] under 11 different conditions, using a variety of respiratory substrates and inhibitors (for a thorough review of electron entry points to the ETC under various substrate/inhibitor combinations, see Ref. 21). Fig. 1 shows a schematic of the mitochondrial ETC, highlighting sites of electron entry resulting from various substrates, binding sites of inhibitors, and major sites of ROS generation. Fig. 2 shows the specific details of each experimental condition, indicating the predicted sites of ROS generation resulting from the use of each substrate/inhibitor combination. The legend to Fig. 2 provides an explanation of each condition.Open in a separate windowFIGURE 1.Mitochondrial pathways of electron flow resulting from the substrates and inhibitors used in this study. Substrates used were glutamate/malate (which generates NADH via the tricarboxylic acid cycle, feeding into complex I), succinate (which feeds electrons directly into complex II), and palmitoyl-carnitine (which feeds electrons into the ETC via acyl-CoA dehydrogenase as well as through the β-oxidation pathway). (For a more thorough explanation, refer to Ref. 21.) Inhibitors used were rotenone (which inhibits at the downstream Q binding site of complex I (9)), malonate (a competitive inhibitor of complex II (25, 26)), and antimycin A (a complex III inhibitor that prevents electron flow to the Q_I site of complex III, thus stabilizing QH^˙ at the Q_O site (6, 28)).Open in a separate windowFIGURE 2.Pathways of electron flow for the substrate/inhibitor combinations used in conditions A–L. Each panel includes the respective maximal respiration rate (VO_{2 max}; nmol of O₂/min/mg of protein) measured under each condition. A, glutamate/malate/malonate. Electrons enter through complex I, whereas electron entry at complex II is inhibited by malonate. ROS generation occurs at the FMN site of complex I as well as the Q_O site of complex III. B, glutamate/malate/malonate/rotenone. Electrons enter through complex I. Electron passage through complex I is inhibited by rotenone binding at the downstream Q site, resulting in maximal ROS production at the FMN site of complex I. ROS production at the Q_O site of complex III is prevented due to no electrons reaching the complex from either complexes I or II, both of which are inhibited. C, glutamate/malate/malonate/antimycin A. Electrons enter through complex I only, since complex II is blocked. Flow of electrons is inhibited by the complex III inhibitor antimycin A, resulting in ROS production at the Q_O site of complex III, as well as the FMN site of complex I. D, succinate. Electrons enter at complex II. ROS is generated by the flow of electrons though the Q_O site of complex III as well as the backflow of electrons through complex I. E, succinate/rotenone. Electrons enter at complex II, and ROS is generated at the Q_O site of complex III, because rotenone is present to inhibit backflow of electrons through complex I. F, succinate/antimycin A. Electrons enter through complex II. ROS is generated at both complex I via backflow and complex III Q_O, with an increased rate at the latter due to inhibition by antimycin A. G, succinate/rotenone/antimycin A. Electrons enter through complex II. Backflow of electrons through complex I is inhibited by rotenone, whereas ROS generation at complex III Q_O is augmented due to the presence of antimycin A. H, glutamate/malate/succinate. Electrons enter at both complexes I and II. ROS is generated from the complex I FMN site and the complex III Q_O site. J, glutamate/malate/succinate/antimycin A. Electrons enter at complexes I and II. ROS generation occurs at the complex I FMN and is augmented at the complex III Q_O site by antimycin A. K, palmitoyl-carnitine. Electrons enter at the ETFQOR. ROS is generated at the ETFQOR as well as complex I via backflow and at the complex III Q_O site. L, palmitoyl-carnitine/rotenone. Electron entry is at the ETFQOR. ROS is generated at the ETFQOR as well as at the complex III Q_O site, whereas ROS due to complex I backflow is blocked by rotenone. Glu, glutamate; Mal, malate; Suc, succinate; PC, palmitoyl-carnitine; Rot, rotenone; AntiA, antimycin A; Malon, malonate.The results of these studies indicated that although ROS generation under all experimental conditions exhibited the same overall response to [O₂] (i.e. hyperbolic, with decreased ROS at low [O₂]), the apparent K_m for O₂ varied widely between metabolic states.     

Color tunable phosphorescent iridium complexes with substituted 2-phenylthiazoles as the cyclometalated ligands

Several new iridium complexes with substituted 2-phenylthiazoles as the cyclometalated ligands have been synthesized and characterized to try to investigate the effect of the size of the π system and substituent groups on physical properties. The complexes have the general structure of (C^∧N)₂Ir(acac), where the C^∧N are 2-phenylthiazole (ptz), 2-(4-methylphenyl)thiazole (mptz), 2-(4-ethylphenyl)thiazole (eptz). The absorption, emission, cyclic voltammetry and thermostability of the complexes were systematically investigated. The experimental results revealed that the maximum emission wavelength in CH₂Cl₂ at room temperature are in the range 542-547 nm, which is blue shift than that of the known iridium(III) bis(2-phenylbenzothiazolato-N,C^2′) acetyl acetonate (bt)₂Ir(acac) due to decreasing the size of the π system in the benzothiazole portion of 2-phenylbenzothiazole ligand.     

Photoluminescence imaging of europium (III)‐doped γ‐Al2O3 nanofiber structures

Aluminium oxide (Al₂O₃) has widely been used for catalysts, insulators, and composite materials for diverse applications. Herein, we demonstrated if γ‐Al₂O₃ was useful as a luminescence support material for europium (Eu) (III) activator ion. The hydrothermal method and post‐thermal treatment at 800°C were employed to synthesize Eu(III)‐doped γ‐Al₂O₃ nanofibre structures. Luminescence characteristics of Eu(III) ions in Al₂O₃ matrix were fully understood by taking 2D and 3D‐photoluminescence imaging profiles. Various sharp emissions between 580 to 720 nm were assigned to the ⁵D₀→⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu(III) activators. On the basis of X‐ray diffraction crystallography, Auger elemental mapping and the asymmetry ratio, Eu(III) ions were found to be well doped into the γ‐Al₂O₃ matrix at a low (1 mol%) doping level. A broad emission at 460 nm was substantially increased upon higher (2 mol%) Eu(III) doping due to defect creation. The first 3D photoluminescence imaging profiles highlight detailed understanding of emission characteristics of Eu(III) ions in Al oxide‐based phosphor materials and their potential applications.     

Opening of the mitoKATP channel and decoupling of mitochondrial complex II and III contribute to the suppression of myocardial reperfusion hyperoxygenation

Diazoxide, a mitochondrial ATP-sensitive potassium (mitoK_ATP) channel opener, protects the heart from ischemia–reperfusion injury. Diazoxide also inhibits mitochondrial complex II-dependent respiration in addition to its preconditioning effect. However, there are no prior studies of the role of diazoxide on post-ischemic myocardial oxygenation. In the current study, we determined the effect of diazoxide on the suppression of post-ischemic myocardial tissue hyperoxygenation in vivo, superoxide (O₂ ^??) generation in isolated mitochondria, and impairment of the interaction between complex II and complex III in purified mitochondrial proteins. It was observed that diazoxide totally suppressed the post-ischemic myocardial hyperoxygenation. With succinate but not glutamate/malate as the substrate, diazoxide significantly increased ubisemiquinone-dependent O₂ ^?? generation, which was not blocked by 5-HD and glibenclamide. Using a model system, the super complex of succinate-cytochrome c reductase (SCR) hosting complex II and complex III, we also observed that diazoxide impaired complex II and its interaction with complex III with no effect on complex III. UV–visible spectral analysis revealed that diazoxide decreased succinate-mediated ferricytochrome b reduction in SCR. In conclusion, our results demonstrated that diazoxide suppressed the in vivo post-ischemic myocardial hyperoxygenation through opening the mitoK_ATP channel and ubisemiquinone-dependent O₂ ^?? generation via inhibiting mitochondrial complex II-dependent respiration.     

Synthesis, structures and properties of new cyclometalated iridium(III) complexes of 3-methoxy-6-methyl-2-(naphthalen-2-yl)pyridine

The reaction between 3-methoxy-6-methyl-2-(naphthalen-2-yl)pyridine 1 and IrCl₃ was performed in an attempt to synthesize a cyclometalated Ir(III) Cl-bridged dimer 2. An unexpected Ir(III) complex 3 was isolated, which was a five-coordinate bis-cyclometalated Ir(III) complex. The complexes 2 and 3 were converted to the same mononuclear complex 4 upon reacting with acetylacetonate (acac), respectively. All of the new compounds have been fully characterized by elemental analysis, IR, ¹H, ¹³C{¹H} NMR and ESI-MS. Additionally, the crystal structures and properties of these Ir(III) complexes are investigated. The most striking common features of the structures of 2 and 3 is intramolecular C-H···Cl hydrogen bonds. The complex 4 shows yellow phosphorescence with structureless emission peaks at about 556 nm.     

Synthesis of a novel tris-cyclometalated iridium(III) complex containing triarylamine unit and its application in OLEDs

The synthesis of the tris-cyclometalated iridium(III) complex [Ir(DCP)₃] (HDCP = 1-(N,N-diphenyl-amino)-4-(4-chlorophenyl)-phthalazine) from hydrated iridium(III) chloride and the ligand HDCP under mild reaction conditions was described. The photophysical, electrochemical and electrophosphorescent properties of this complex were investigated. Organic light-emitting diodes (OLEDs) using the complex as a dopant and a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD) as a host exhibited bright red emission at 620 nm with the Commission Internationale de l’Eclairage (CIE) coordinate of (0.67, 0.32). A maximum external quantum efficiency of 13.6% photos/electron with a luminous efficiency of 7.4 cd/A at a current density of 0.73 mA/cm², and a maximum luminance of 2941 cd/m² at 99 mA/cm² were obtained in the device at 4 wt% doping concentration.     

A stopped‐flow study of the dual chemiluminescence for the luminol–KIO4–Mn2+ system in strong alkaline solutions

A novel phenomenon of dual chemiluminescence (CL) was observed for the KIO₄–luminol–Mn²⁺ system in strong alkaline solutions using the stopped‐flow technique. Scavenging study of the reactive oxygen species (ROS) suggested that the two CL peaks originated from different CL pathways precipated by distinct ROS (O₂^? and ^?OH for the first peak, mainly ¹O₂ for the second peak). Generation of these ROS at different time intervals from the reactions involving IO₄^?, O₂, and Mn²⁺ and their subsequent reactions with luminol induced the intense CL emission. The relative intensity of the two CL peaks can be tuned over a wide range by varying the concentrations of Mn^2?, luminol and KIO₄. Because of the involvement of different ROS in each pathway, the two CL peaks could respond quite differently to various substances. Moreover, variation of the intensity ratio of the two CL peaks altered the relative proportions of the corresponding ROS, thereby changing their responses to a given substance. The dual CL emission acts like a pair of tunable probes and it is believed that this CL system has great potential in analytical applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis, crystallography and photoluminescence of a new pyrazolonato iridium complex

By using 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone (pmip) as the ancillary ligand, the cyclometalated complex: bis-(2-phenylpyridine)-(pmip)-iridium [(ppy)₂Ir(pmip)] was synthesized. Its crystal structure, absorption and emission were compared with those of its analogue, the frequently used electrophosphorescent material (ppy)₂Ir(dbm) [bis-(2-phenylpyridine)-(dibenzoylmethane) iridium]. For (ppy)₂Ir(pmip) in dichloromethane, the emission is highly structured and the intensity is 5 times higher than that of (ppy)₂Ir(dbm). It is a result of the higher triplet energy level of pmip relative to that of dbm. In solid state, green emission of (ppy)₂Ir(pmip) peaked at 550 nm was observed with a quantum efficiency 0.31% in contrast to the emission at 626 nm with a quantum efficiency of 0.76% for (ppy)₂Ir(dbm). The bathochromical shift and higher efficiency in crystallized (ppy)₂Ir(dbm) was explained by the stronger π-π intermolecular interactions which is unique to in solid state (ppy)₂Ir(dbm) crystals.     

On the mechanism of hydrogen peroxide-, superoxide-, and ultraviolet light-induced DNA cleavages of inactive bleomycin-iron (III) complex

The ³²P-labeled DNA cleavage experiments showed that the biological activity of the bleomycin(BLM)-Fe(III)OH^? complex is evidently induced by addition of H₂O₂ and KO₂, or by irradiation of UV light. Hydrogen peroxide contributes to the conversion from the inactive BLM-Fe(III)OH^? complex to the active BLM-Fe(III)O₂H^? complex, and UV light to the reduction of the BLM-Fe(III)OH^? complex to the BLM-Fe(II) complex. The proposed hypothetical mechanism for cyclic function of BLM-iron complex is similar to that of certain heme-oxygenases and heme-oxidases.     

Blue phosphorescent iridium complexes based on 2-(fluoro substituted phenyl)-4-methylpyridines: Synthesis, crystal structure, and photophysics

A series blue phosphorescent emitting materials based on 2-(fluoro substituted phenyl)-4-methylpyridine as the cyclometalated ligands have been synthesized and characterized. The complexes have the general structure (C^{^}N)₂Ir(pic), where C^{^}N is a monoanionic cyclometalating ligand (e.g., 2-(2,4-difluorophenyl)-4-methylpyridine (24f₂pmpyH), 2-(3,4-difluorophenyl)-4-methylpyridine (34f₂pmpyH), 2-(3,5-difluorophenyl)-4-methylpyridine (35f₂pmpyH), and 2-(3,4,5-trifluorophenyl)-4-methyl-pyridine (345f₃pmpyH)), pic is 2-picolinic acid. The absorption, emission, cyclic voltammetry and thermostability of the complexes were systematically investigated. The (46f₂pmpy)₂Ir(pic) has been characterized using X-ray crystallography and the electronic ground state calculated using B3LYP density functional theory. HOMO levels are a mixture of Ir and 2-(fluoro phenyl)-4-methylpyridine ligand orbitals, while the LUMO is predominantly pic ligand based. Introduction of fluorine atoms and methyl group into ppy ligand and changing in position of F substituents in phenyl ring can finely tune emission of the complexes, showing bright blue-to-green luminescence at a wavelength of 463-501 nm at room temperature in CH₂Cl₂.     

Syntheses and crystal structures of the first iridium complexes with m- and p-terphenyl (tp). {[Ir2(p-tp)(cod)2](BF4)2 · 2CH2Cl2}3 and [Ir(m-tp)(η-C5Me5)](BF4)2

Novel two iridium terphenyl complexes were prepared and their structures were characterized crystallographically. The reaction of [Ir(cod)₂]BF₄ with p-terphenyl (p-tp) in CH₂Cl₂ was carried out to afford dinuclear Ir(I) complex {[Ir₂(p-tp)(cod)₂](BF₄)₂ · 2CH₂Cl₂}₃ (cod=1,5-cyclooctadiene) (1 · 2CH₂Cl₂), whereas the reaction of the intermediate [Ir(η⁵-C₅Me₅)(Me₂CO)₃]³⁺ in Me₂CO with m-terphenyl (m-tp) was done to provide mononuclear Ir(III) complex [Ir(m-tp)(η⁵-C₅Me₅)](BF₄)₂ (2). In complex 1 · 2CH₂Cl₂, two Ir atoms are η⁶-coordinated to both sides of terminal benzene rings from the upper and lower sides in the p-tp ligand, while one Ir atom is η⁶-coordinated to one side of the terminal benzene ring in the m-tp ligand in complex 2. Each crystal structure describes the first coordination mode found in metal complexes with the m- and p-tp ligands.