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"iridium"
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Eccentric orbits : the Iridium story
\"How the largest man-made constellation in the heavens was built by dreamers in the Arizona Desert, targeted for destruction by panicked executives, and saved by a single Palm Beach retiree who battled Motorola, cajoled the Pentagon, wrestled with thirty banks, survived an attack by Congress, infiltrated the White House, found allies through the Black Entertainment Network, and wooed a mysterious Arab prince to rescue the only phone that links every inch of the planet.\"
Book
Metallopolymer strategy to explore hypoxic active narrow-bandgap photosensitizers for effective cancer photodynamic therapy
Practical photodynamic therapy calls for high-performance, less O
2
-dependent, long-wavelength-light-activated photosensitizers to suit the hypoxic tumor microenvironment. Iridium-based photosensitizers exhibit excellent photocatalytic performance, but the in vivo applications are hindered by conventional O
2
-dependent Type-II photochemistry and poor absorption. Here we show a general metallopolymerization strategy for engineering iridium complexes exhibiting Type-I photochemistry and enhancing absorption intensity in the blue to near-infrared region. Reactive oxygen species generation of metallopolymer
Ir-P1
, where the iridium atom is covalently coupled to the polymer backbone, is over 80 times higher than that of its mother polymer without iridium under 680 nm irradiation. This strategy also works effectively when the iridium atom is directly included (
Ir-P2
) in the polymer backbones, exhibiting wide generality. The metallopolymer nanoparticles exhibiting efficient O
2
•−
generation are conjugated with integrin αvβ3 binding cRGD to achieve targeted photodynamic therapy.
Iridium-based photosensitizers exhibit good photocatalytic performance, but the in vivo applications are hindered by conventional O
2
-dependent Type-II photochemistry and poor absorption. Here, the authors report a general metallopolymerization strategy for engineering iridium complexes exhibiting Type-I photochemistry and enhancing absorption intensity in the blue to near-infrared region.
Journal Article
Potent anticancer activity of a novel iridium metallodrug via oncosis
Oncosis (from Greek
ónkos
, meaning “swelling”) is a non-apoptotic cell death process related to energy depletion. In contrast to apoptosis, which is the main form of cell death induced by anticancer drugs, oncosis has been relatively less explored but holds potential to overcome drug resistance phenomena. In this study, we report a novel rationally designed mitochondria-targeted iridium(III) complex (
OncoIr3
) with advantageous properties as a bioimaging agent.
OncoIr3
exhibited potent anticancer activity in vitro against cancer cells and displayed low toxicity to normal dividing cells. Flow cytometry and fluorescence-based assays confirmed an apoptosis-independent mechanism involving energy depletion, mitochondrial dysfunction and cellular swelling that matched with the oncotic process. Furthermore, a
Caenorhabditis elegans
tumoral model was developed to test this compound in vivo, which allowed us to prove a strong oncosis-derived antitumor activity in animals (with a 41% reduction of tumor area). Indeed,
OncoIr3
was non-toxic to the nematodes and extended their mean lifespan by 18%. Altogether, these findings might shed new light on the development of anticancer metallodrugs with non-conventional modes of action such as oncosis, which could be of particular interest for the treatment of apoptosis-resistant cancers.
Graphical abstract
Journal Article
Phototoxicity of cyclometallated Ir(III) complexes bearing a thio-bis-benzimidazole ligand, and its monodentate analogue, as potential PDT photosensitisers in cancer cell killing
Two novel cyclometallated iridium(III) complexes have been prepared with one bidentate or two monodentate imidazole-based ligands, 1 and 2, respectively. The complexes showed intense emission with long lifetimes of the excited state. Femtosecond transient absorption experiments established the nature of the lowest excited state as 3IL state. Singlet oxygen generation with good yields (40% for 1 and 82% for 2) was established by detecting 1O2 directly, through its emission at 1270 nm. Photostability studies were also performed to assess the viability of the complexes as photosensitizers (PS) for photodynamic therapy (PDT). Complex 1 was selected as a good candidate to investigate light-activated killing of cells, whilst complex 2 was found to be toxic in the dark and unstable under light. Complex 1 demonstrated high phototoxicity indexes (PI) in the visible region, PI > 250 after irradiation at 405 nm and PI > 150 at 455 nm, in EJ bladder cancer cells.
Journal Article
Enantioselective remote C–H activation directed by a chiral cation
Chiral cations have been used extensively as organocatalysts, but their application to rendering transition metal–catalyzed processes enantioselective remains rare. This is despite the success of the analogous charge-inverted strategy in which cationic metal complexes are paired with chiral anions. We report here a strategy to render a common bipyridine ligand anionic and pair its iridium complexes with a chiral cation derived from quinine. We have applied these ion-paired complexes to long-range asymmetric induction in the desymmetrization of the geminal diaryl motif, located on a carbon or phosphorus center, by enantioselective C–H borylation. In principle, numerous common classes of ligand could likewise be amenable to this approach.
Journal Article
Photosensitized, energy transfer-mediated organometallic catalysis through electronically excited nickel(II)
Transition metal catalysis has traditionally relied on organometallic complexes that can cycle through a series of ground-state oxidation levels to achieve a series of discrete yet fundamental fragment-coupling steps. The viability of excited-state organometallic catalysis via direct photoexcitation has been demonstrated. Although the utility of triplet sensitization by energy transfer has long been known as a powerful activation mode in organic photochemistry, it is surprising to recognize that photosensitization mechanisms to access excited-state organometallic catalysts have lagged far behind. Here, we demonstrate excited-state organometallic catalysis via such an activation pathway: Energy transfer from an iridium sensitizer produces an excited-state nickel complex that couples aryl halides with carboxylic acids. Detailed mechanistic studies confirm the role of photosensitization via energy transfer.
Journal Article
Mitochondria-targeted phosphorescent cyclometalated iridium(III) complexes: synthesis, characterization, and anticancer properties
Cyclometalated iridium(III) complexes represent a promising approach to developing new anticancer metallodrugs. In this work, three phosphorescent cyclometalated iridium(III) complexes
Ir1–Ir3
have been explored as mitochondria-targeted anticancer agents. All three complexes display higher antiproliferative activity than cisplatin against the cancer cells screened, and with the IC
50
values ranging from 0.23 to 5.6 μM. Colocalization studies showed that these complexes are mainly localized in the mitochondria. Mechanism studies show that these complexes exert their anticancer efficacy through initiating a series of events related to mitochondrial dysfunction, including depolarization of mitochondrial membrane potential (MMP), elevation of intracellular reactive oxygen species (ROS) levels, and induction of apoptosis.
Graphic abstract
Mitochondria-targted cyclometalated iridium complexes induce apoptosis through depolarized mitochondria, elevation of intracellular ROS and activated caspase.
Journal Article
New iridium bis‐terpyridine complexes: synthesis, characterization, antibiofilm and anticancer potentials
This study represents synthesis, characterization, screening of antibiofilm efficacy, and cytotoxicity of iridium bis-terpyridine complexes. The complexes were characterized by NMR, MS, FTIR, UV/Visible, and fluorescence spectroscopies. The efficacy of biofilm inhibition and eradication of iridium complexes was evaluated using a crystal violet assay test and verified by fluorescence microscopy. Cytotoxicity and apoptosis analysis of iridium complexes were determined in this study. The results of our study revealed that three iridium complexes had the potential to inhibit biofilm formation and moderate the ability to destroy pre-formed biofilm of
S. aureus
ATCC 29,213. 250 µM concentration of synthesized complexes showed the highest antibiofilm activity (75% for Ir1, 90% for Ir2, and 71% for Ir3). The significant inhibition obtained at 6.25 µM concentration of Ir2 and Ir3 revealed the potential of our samples. Also, Ir1 and Ir2 complexes had a good capacity to destroy pre-formed biofilm. The results clearly showed that iridium complexes have cytotoxic activity towards colon cancer (Caco-2) and liver cancer (HepG2) cell lines without affecting non-cancerous cells (HEK293) at applied doses. Moreover, tested compounds induced apoptosis in these cancer cells. All of these results showed that iridium complexes had possessed the ability to inhibit or destroy pre-formed biofilm and could be developed as an effective agent against bacterial biofilms. Moreover, these pure substances may have valuable anti-cancer activity and it should be confirmed with further studies for therapeutic effects.
Journal Article
Copper’s rapid ascent in visible-light photoredox catalysis
Photoredox catalysis relies on visible-light excitation to accelerate a burgeoning number of chemical reactions. Initially, the technique relied primarily on complexes of precious metals, such as ruthenium or iridium, to absorb the light. Hossain et al. review recent progress in the use of copper complexes as an alternative. In addition to its Earth abundance, copper opens up a variety of distinct mechanisms involving electron transfer within the coordination sphere. Science , this issue p. eaav9713 Visible-light photoredox catalysis offers a distinct activation mode complementary to thermal transition metal catalyzed reactions. The vast majority of photoredox processes capitalizes on precious metal ruthenium(II) or iridium(III) complexes that serve as single-electron reductants or oxidants in their photoexcited states. As a low-cost alternative, organic dyes are also frequently used but in general suffer from lower photostability. Copper-based photocatalysts are rapidly emerging, offering not only economic and ecological advantages but also otherwise inaccessible inner-sphere mechanisms, which have been successfully applied to challenging transformations. Moreover, the combination of conventional photocatalysts with copper(I) or copper(II) salts has emerged as an efficient dual catalytic system for cross-coupling reactions.
Journal Article