Biological applications of Ru(II) polypyridyl complexes

Silver(I) Complexes with Mefenamic Acid and Nitrogen Heterocyclic Ligands: Synthesis, Characterization, and Biological Evaluation

Four Ag(I) complexes with mefenamato and nitrogen heterocyclic ligands, [Ag(2-apy)(mef)]2 (1), [Ag(3-apy)(mef)] (2), [Ag2(tmpyz)(mef)2] (3), and {[Ag(4,4'-bipy)(mef)]2(CH3CN)1.5(H2O)2}n (4), (mef = mefenamato, 2-apy = 2-aminopyridine, 3-apy = 3-aminopyridine, tmpyz = 2,3,5,6-tetramethylpyrazine, 4,4'-bipy = 4,4'-bipyridine), were synthesized and characterized. The interactions of these complexes with BSA were investigated by fluorescence spectroscopy, which indicated that these complexes quench the fluorescence of BSA by a static mechanism. The fluorescence data also indicated that the complexes showed good affinity for BSA, and one binding site on BSA was suitable for the complexes. The in vitro cytotoxicity of the four complexes against human cancer cell lines (MCF-7, HepG-2, A549, and MDA-MB-468) and one normal cell line (HTR-8) was evaluated by the MTT assay. Complex 1 displayed high cytotoxic activity against A549 cells. Further studies revealed that complex 1 could enhance the intracellular levels of ROS (reactive oxygen species) in A549 cells, cause cell cycle arrest in the G0/G1 phase, and induce apoptosis in A549 cells in a dose-dependent manner.

Synthesis and structural characterizations of three carbonyl(α-diimine)hydrido(triphenylphosphine)ruthenium(II) complexes with derivatives of 1,10-phenanthroline

Three new ruthenium(II) polypyridyl complexes containing α-diimine ligands, namely, carbonylhydrido(1,10-phenanthroline-κ2N,N)bis(triphenylphosphine-κP)ruthenium(II) hexafluorophosphate, [RuH(C12H8N2)(C18H15P)2(CO)]PF6, carbonylhydrido(2,9-dimethyl-1,10-phenanthroline-κ2N,N)bis(triphenylphosphine-κP)ruthenium(II) hexafluorophosphate, and carbonylhydrido(4,7-dimethyl-1,10-phenanthroline-κ2N,N)bis(triphenylphosphine-κP)ruthenium(II) hexafluorophosphate, both [RuH(C14H12N2)(C18H15P)2(CO)]PF6, were synthesized and characterized by spectroscopic and X-ray diffraction methods. In these complexes, the ruthenium(II) ion adopts a distorted octahedral geometry. There are no intermolecular hydrogen bonds in the crystal structures of the analysed complexes and Hirshfeld surface analysis showed that the H...H contacts constitute a high percentage, close to 50%, of the intermolecular interactions.

Development of ruthenium complexes with S-donor ligands for application in synthesis, catalytic acceptorless alcohol dehydrogenation and crossed-aldol condensation

The reaction of [Ru(dmso)4Cl2] with a potassium salt of four xanthate (RO-C(S)S-; R = Me, Et, iPr and tBu) ligands (depicted as Ln; n = 1-4) in hot methanol afforded a group of mixed-ligand complexes of type [Ru(Ln)2(dmso)2]. The crystal structures of all the four complexes have been determined, which show that the xanthate ligands are bound to the metal center forming four-membered chelates and dmso is coordinated through sulfur and they are mutually cis. The relative thermodynamic stability of this cis and the other possible trans-isomers of these complexes has been assessed with the help of DFT calculations, which have revealed that the cis-isomer is the more stable isomer. The coordinated dmso in the [Ru(Ln)2(dmso)2] complexes could be easily displaced by chelating bidentate ligands (depicted as L') to furnish complexes of type [Ru(Ln)2(L')], as demonstrated through isolation of two such complexes, viz. [Ru(L3)2(bpy)] and [Ru(L2)2(phen)] (bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline). The crystal structure of [Ru(L3)2(bpy)] has been determined and the structure of [Ru(L2)2(phen)] has been optimized by the DFT method. The electronic spectra of the four [Ru(Ln)2(dmso)2] complexes and the two derivatives ([Ru(Ln)2(L')]; n = 3, L' = bpy; n = 2, L' = phen), recorded in dichloromethane solutions, show intense absorptions spanning the visible and ultraviolet regions, which have been analyzed by the TDDFT method. The [Ru(Ln)2(dmso)2] complexes are found to serve as efficient catalyst precursors for the acceptorless dehydrogenation of 2-propanol followed by crossed-aldol condensation with substituted benzaldehydes (and related aldehydes), using tert-butoxide as the co-catalyst, producing dibenzylideneacetone derivatives in good yields.

Visible-Light-Responsive Novel Ru(II)-Metallo-Antibiotics with Potential Antibiofilm and Antibacterial Activity

Growing challenges with antibiotic resistance pose immense challenges in combating microbial infections and biofilm prevention on medical devices. Lately, antibacterial photodynamic therapy (aPDT) is now emerging as an alternative therapy to overcome this problem. Herein, we synthesized and characterized four Ru(II)-complexes, viz., [Ru(ph-tpy)(bpy)Cl]PF6 (Ru1), [Ru(ph-tpy)(dpq)Cl]PF6 (Ru2), [Ru(ph-tpy)(dppz)Cl]PF6 (Ru3), and [Ru(ph-tpy)(dppn)Cl]PF6 (Ru4) (where 4'-phenyl-2,2':6',2″-terpyridine = ph-tpy; 2,2'-bipyridine = bpy; dipyrido[3,2-f:2',3'-h]quinoxaline = dpq; dipyrido[3,2-a:2',3'-c]phenazine = dppz; and Benzo[I]dipyrido[3,2-a:2',3'-c]phenazine = dppn), among which Ru2-Ru4 are novel. Octahedral geometry of the complexes with a RuN5Cl core was evident from the crystal structure of Ru2. Ru1-Ru4 showed an MLCT absorption band in the 450-600 nm region, useful for aPDT performances. Further, optimum triplet excited state energy and excellent photostability of Ru1-Ru4 made them good photosensitizers for aPDT. Ru1-Ru4 demonstrated enhanced antimicrobial activity on visible-light exposure (400-700 nm, 10 J cm-2), confirmed using different antibacterial assays. Mechanistic studies revealed that inhibition of bacterial growth was due to the generation of oxidative stress (via NADH oxidation and ROS generation) upon treatment with Ru2-Ru4, resulting in destruction of the bacterial wall. Ru2 performed best killing performance against both Gram-negative (Escherichia coli) and Gram-positive (Bacillus subtilis) bacteria when exposed to light. Ru2-Ru4, when coated on a polydimethylsiloxane (PDMS) disk, showed long-term reusability and durable antibiofilm properties. Molecular docking confirmed the efficient interaction of Ru2-Ru4 with FabH (regulates fatty acid biosynthesis of E. coli) and PgaB (gives structural stability and helps biofilm formation of E. coli), resulting in probable downregulation. In vivo studies with healthy Wistar rats confirmed the biocompatibility of Ru2. This study shows that these lead complexes (Ru2-Ru4) can be used as potent alternative antimicrobial agents in low concentrations toward bacterial eradication with photodynamic therapy (PDT).

Predictable electronic tuning of FeII and RuII complexes via choice of azine: correlation of ligand pKa with Epa(MIII/II) of complex

Five new mononuclear ruthenium(II) tris-ligated complexes have been synthesised, varying through the choice of azine in the family of 3-azinyl-4-(4-methylphenyl)-5-phenyl-4H-1,2,4-triazole ligands (Lazine): [Ru(Lpyridine)](PF6)2 (1), [Ru(Lpyridazine)](PF6)2 (2), [Ru(L4-pyrimidine)](PF6)2 (3), [Ru(Lpyrazine)](PF6)2 (4), [Ru(L2-pyrimidine)](PF6)2 (5). Three of them, 1·2MeCN·Et2O, 3·2MeCN·Et2O and 4·2MeCN, have been structurally characterised, confirming the presence of the meridional isomer, as was previously reported for the FeII analogues. Cyclic voltammetry studies, in dry CH3CN vs. Ag/0.01 M AgNO3, show that all five RuII complexes undergo a reversible RuIII/RuII process, with the midpoint potential (Em) increasing from 0.87 to 1.18 V as the azine is changed: pyridine < pyridazine < 2-pyrimidine < 4-pyrimidine < pyrazine. A strong inverse linear correlation (R2 = 0.98) is found between the RuIII/RuII redox potential and the calculated HOMO orbital energies, which is consistent with the expectation that it is easier to oxidise (lower Em) a metal ion with a higher HOMO orbital energy. The same trend was reported earlier for the family of analogous FeII complexes, albeit at lower values of Em in all cases. In addition, the ionisation potentials of the RuII complexes, as well as those of the other group 8 analogues (FeII and OsII), showed a linear relationship with Epa. As the MIII/II redox potentials of a family of complexes has been previously reported to correlate with ligand pKa values, a computational protocol to calculate, in silico, the pKa of the Lazine family of ligands was developed. A strong linear relationship was found between the readily calculated pKa of the Lazine ligand and the Epa of the MII complex, for all three families of complexes (R2 = 0.98).

Exploration of the Pharmacophore for Cytoskeletal Targeting Ruthenium Polypyridyl Complexes

Ruthenium(II) trisdiimine complexes of the formula, [Ru(dip)n (L-L)3-n ]2+ , where n=0-3; dip=4,7-diphenyl-1,10-phenanthroline; L-L=2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) were prepared and tested for cytotoxicity in two cell lines (H358, MCF7). Cellular uptake and subcellular localization were determined by harvesting treated cells and determining the ruthenium concentration in whole or fractionated cells (cytosolic, nuclear, mitochondrial/ ER/Golgi, and cytoskeletal proteins) by Ru ICP-MS. The logP values for the chloride salts of these complexes were measured and the data were analyzed to determine the role of lipophilicity versus structure in the various biological assays. Cellular uptake increased with lipophilicity but shows the biggest jump when the complex contains two or more dip ligands. Significantly, preferential cytoskeletal localization is also correlated with increased cytotoxicity. All of the RPCs promote tubulin polymerization in vitro, but [Ru(dip)2 phen]2+ and [Ru(dip)3 ]2+ show the strongest activity. Analysis of the pellet formed by centrifugation of MTs formed in the presence of [Ru(dip)2 phen]2+ establish a binding stoichiometry of one RPC per tubulin heterodimer. Complexes of the general formula [Ru(dip)2 (L-L)]2+ possess the necessary characteristics to target the cytoskeleton in live cells and increase cytotoxicity, however the nature of the L-L ligand does influence the extent of the effect.

Fluorescent nano- and microparticles for sensing cellular microenvironment: past, present and future applications

The tumor microenvironment (TME) demonstrates distinct hallmarks, including acidosis, hypoxia, reactive oxygen species (ROS) generation, and altered ion fluxes, which are crucial targets for early cancer biomarker detection, tumor diagnosis, and therapeutic strategies. Various imaging and sensing techniques have been developed and employed in both research and clinical settings to visualize and monitor cellular and TME dynamics. Among these, ratiometric fluorescence-based sensors have emerged as powerful analytical tools, providing precise and sensitive insights into TME and enabling real-time detection and tracking of dynamic changes. In this comprehensive review, we discuss the latest advancements in ratiometric fluorescent probes designed for the optical mapping of pH, oxygen, ROS, ions, and biomarkers within the TME. We elucidate their structural designs and sensing mechanisms as well as their applications in in vitro and in vivo detection. Furthermore, we explore integrated sensing platforms that reveal the spatiotemporal behavior of complex tumor cultures, highlighting the potential of high-resolution imaging techniques combined with computational methods. This review aims to provide a solid foundation for understanding the current state of the art and the future potential of fluorescent nano- and microparticles in the field of cellular microenvironment sensing.

Reactivity of non-organometallic ruthenium(II) polypyridyl complexes and their application as catalysts for hydride transfer reactions

Recently, we investigated the substitution behavior of a series of ruthenium(II) complexes of the general formula [RuII(terpy)(N∧N)Cl]Cl, where terpy = 2,2′:6′,2″-terpyridine, N∧N = bidentate ligand, in aqueous solutions. We have shown that the most and least reactive complexes of the series are [RuII(terpy)(en)Cl]Cl (en = ethylenediamine) and [RuII(terpy)(phen)Cl]Cl (phen = 1, 10-phenantroline), respectively, as a result of different electronic effects provided by the bidentate spectator chelates. Polypyridyl amine Ru(II) complex, viz. [Ru(terpy)(en)Cl]Cl and [Ru(terpy)(ampy)Cl]Cl (where ampy = 2-(aminomethyl)pyridine), in which the terpy chelate labilizes the metal center, are able to catalyze the conversion of NAD+ to 1,4-NADH using sodium formate as a source of hydride. We showed that this complex can control the [NAD+]/[NADH] ratio and potentially induce reductive stress in living cells, which is accepted as an effective method to kill cancer cells. Polypyridyl Ru(II) complexes, characterized in terms of the behavior in aqueous solutions, can be used as model systems to monitor heterogeneous multiphase ligand substitution reactions at the solid-liquid interface. Colloidal coordination compounds in the submicron range were synthesized from Ru(II)-aqua derivatives of starting chlorido complexes via the anti-solvent procedure and stabilized by a surfactant shell layer.

Synergy of ruthenium metallo-intercalator, [Ru(dppz)2(PIP)]2+, with PARP inhibitor Olaparib in non-small cell lung cancer cells

Poly(ADP-ribose) polymerase (PARP) are critical DNA repair enzymes that are activated as part of the DNA damage response (DDR). Although inhibitors of PARP (PARPi) have emerged as small molecule drugs and have shown promising therapeutic effects, PARPi used as single agents are clinically limited to patients with mutations in germline breast cancer susceptibility gene (BRCA). Thus, novel PARPi combination strategies may expand their usage and combat drug resistance. In recent years, ruthenium polypyridyl complexes (RPCs) have emerged as promising anti-cancer candidates due to their attractive DNA binding properties and distinct mechanisms of action. Previously, we reported the rational combination of the RPC DNA replication inhibitor [Ru(dppz)₂(PIP)]²⁺ (dppz = dipyrido[3,2-a:2',3'-c]phenazine, PIP = 2-(phenyl)-imidazo[4,5-f][1,10]phenanthroline), "Ru-PIP", with the PARPi Olaparib in breast cancer cells. Here, we expand upon this work and examine the combination of Ru-PIP with Olaparib for synergy in lung cancer cells, including in 3D lung cancer spheroids, to further elucidate mechanisms of synergy and additionally assess toxicity in a zebrafish embryo model. Compared to single agents alone, Ru-PIP and Olaparib synergy was observed in both A549 and H1975 lung cancer cell lines with mild impact on normal lung fibroblast MRC5 cells. Employing the A549 cell line, synergy was confirmed by loss in clonogenic potential and reduced migration properties. Mechanistic studies indicated that synergy is accompanied by increased double-strand break (DSB) DNA damage and reactive oxygen species (ROS) levels which subsequently lead to cell death via apoptosis. Moreover, the identified combination was successfully able to inhibit the growth of A549 lung cancer spheroids and acute zebrafish embryos toxicity studies revealed that this combination showed reduced toxicity compared to single-agent Ru-PIP.

Ruthenium(II) polypyridyl complexes with benzothiophene and benzimidazole derivatives: Synthesis, antitumor activity, solution studies and biospeciation

With the aim to incorporate pharmacophore motifs into the Ru(II)-polypyridyl framework, compounds [Ru(II)(1,10-phenantroline)₂(2-(2-pyridyl)benzo[b]thiophene)](CF₃SO₃)₂ (1) and [Ru(II)(1,10-phenantroline)₂(2-(2-pyridyl)benzimidazole)](CF₃SO₃)₂ (2) were prepared, characterized and tested for their antitumor potential. The solid-state structure of the compounds was confirmed by single-crystal X-ray diffraction analysis. The solution behavior of both complexes was investigated, namely their solubility, stability, and lipophilicity in physiological mimetic conditions, as well as an eventual uptake by passive diffusion. In vitro anticancer activity of the complexes on ovarian and different colon cancer cells and apoptosis induction by the complexes were studied. A slow transformation process was observed for complex 1 in aqueous solution when exposed to sunlight, while complex 2 undergoes deprotonation (pK_a = 7.59). The lipophilicity of this latter complex depends strongly on the pH and ionic strength. In contrast, 1 is rather hydrophilic under various conditions. Complex 1 was highly cytotoxic on Colo-205 human colon (IC₅₀ = 7.87 μM) and A2780 ovarian (IC₅₀ = 2.2 μM) adenocarcinoma cell lines, while 2 displayed moderate anticancer activity (30.9 μM and 18.0 μM, respectively). The complexes induced late apoptosis and necrosis. Only a weak binding of the complexes to human serum albumin, the main transport protein in blood serum, was found. However, a more significant binding to calf thymus DNA was observed in UV-visible titrations and fluorometric dye displacement studies. Detailed analysis of fluorescence lifetime data collected for the latter systems reveals not only the partial intercalation of the complexes, but goes beyond the usual simplified interpretations.

The effect of halogenation of salicylaldehyde on the antiproliferative activities of {Δ/Λ-[Ru(bpy)2(X,Y-sal)]BF4} complexes

Ru(II) polypyridyl complexes are widely used in biological fields, due to their physico-chemical and photophysical properties. In this paper, a series of new chiral Ru(II) polypyridyl complexes (1-5) with the general formula {Δ/Λ-[Ru(bpy)₂(X,Y-sal)]BF₄} (bpy = 2,2'-bipyridyl; X,Y-sal = 5-bromosalicylaldehyde (1), 3,5-dibromosalicylaldehyde (2), 5-chlorosalicylaldehyde (3), 3,5-dichlorosalicylaldehyde (4) and 3-bromo-5-chlorosalicylaldehy (5)) were synthesized and characterized by elemental analysis, FT-IR, and ¹H/¹³C NMR spectroscopy. Also, the structures of complexes 1 and 5 were determined by X-ray crystallography; these results showed that the central Ru atom adopts a distorted octahedral coordination sphere with two bpy and one halogen-substituted salicylaldehyde. DFT and TD-DFT calculations have been performed to explain the excited states of these complexes. The singlet states with higher oscillator strength are correlated with the absorption signals and are mainly described as ¹MLCT from the ruthenium centre to the bpy ligands. The lowest triplet states (T₁) are described as ³MLCT from the ruthenium center to the salicylaldehyde ligand. The theoretical results are in good agreement with the observed unstructured band at around 520 nm for complexes 2, 4 and 5. Biological studies on human cancer cells revealed that dihalogenated ligands endow the Ru(II) complexes with enhanced cytotoxicity compared to monohalogenated ligands. In addition, as far as the type of halogen is concerned, bromine is the halogen that provides the highest cytotoxicity to the synthesized complexes. All complexes induce cell cycle arrest in G0/G1 and apoptosis, but only complexes bearing Br are able to provoke an increase in intracellular ROS levels and mitochondrial dysfunction.

Nuclease-like metalloscissors: Biomimetic candidates for cancer and bacterial and viral infections therapy

Despite the extensive and rapid discovery of modern drugs for treatment of cancer, microbial infections, and viral illnesses; these diseases are still among major global health concerns. To take inspiration from natural nucleases and also the therapeutic potential of metallopeptide antibiotics such as the bleomycin family, artificial metallonucleases with the ability of promoting DNA/RNA cleavage and eventually affecting cellular biological processes can be introduced as a new class of therapeutic candidates. Metal complexes can be considered as one of the main categories of artificial metalloscissors, which can prompt nucleic acid strand scission. Accordingly, biologists, inorganic chemists, and medicinal inorganic chemists worldwide have been designing, synthesizing and evaluating the biological properties of metal complexes as artificial metalloscissors. In this review, we try to highlight the recent studies conducted on the nuclease-like metalloscissors and their potential therapeutic applications. Under the light of the concurrent Covid-19 pandemic, the human need for new therapeutics was highlighted much more than ever before. The nuclease-like metalloscissors with the potential of RNA cleavage of invading viral pathogens hence deserve prime attention.

Anticancer activity of ruthenium(II) plumbagin complexes with polypyridyl as ancillary ligands via inhibiting energy metabolism and GADD45A-mediated cell cycle arrest

To study the antitumor activity and action mechanism of Ru(II) polypyridyl plumbagin (PLN) complexes, four complexes [Ru(PLN)(DMSO)₂]Cl (Ru1), [Ru(bpy)₂(PLN)](PF₆) (bpy is bipyridine) (Ru2), [Ru(phen)₂(PLN)](PF₆) (phen is 1,10-phenanthroline) (Ru3), and [Ru(DIP)₂(PLN)](PF₆) (DIP is 4,7-diphenyl-1,10-phenanthroline) (Ru4) were obtained and fully characterized. Lipophilicity, cellular uptake and cytotoxicity of these Ru(II) complexes are in the order of: Ru1<Ru2<Ru3<Ru4. The ancillary polypyridyl ligands affected the bioactivity and action mechanisms of these Ru(II) complexes. Ru3 and Ru4 inhibited energy metabolism by severely impairing mitochondrial respiration and glycolysis processes. Moreover, Ru3 and Ru4 induced DNA damage and the increased expression of GADD45A, which led to cell cycle arrest in G0/G1 phase in MGC-803 cells, while the inactivation of GADD45A attenuated these effects; however, Ru3 or Ru4-induced GADD45A did not affect cell apoptosis. Further studies revealed that Ru3 and Ru4 induced ROS-dependent and caspase-dependent apoptotic cell death by mitochondrial dysfunction, and Ru4 displayed higher potency than Ru3. The in vivo results in MGC-803 xenograft nude mice model also confirmed that Ru4 obviously inhibited tumor growth. Ru4 is a promising candidate to be developed as a chemotherapeutic agent.

Evaluation of the anticancer activities with various ligand substituents in Co(II/III)-picolyl phenolate derivatives: synthesis, characterization, DFT, DNA cleavage, and molecular docking studies

The reactions between 2-(pyridine-2-ylmethoxy)-benzaldehyde (L) and various primary amines furnish tridentate (L1 to L3) and tetradentate (L4) chelating ligands. The choice of different primary amines in the condensation reaction incorporates the chiral carbon atom in L2 and L3. A series of mononuclear cobalt(II) complexes, [CoII(L1)(Cl)2] (1), [CoII(L2)(Cl)2]·CH3CN (2), [CoII(L3)(Cl)2] (3), and [CoIII(L4)(N3)2] (4) are synthesized in the pure crystalline state from the resulting solution of cobalt(II) chloride and/or azide and respective ligand. The new ligands and cobalt complexes are characterized using spectral (UV-Vis, 1H-NMR, IR, and HRMS), cyclovoltammetric, and DFT studies. The structure of L1, L2, and all four cobalt complexes are determined by single X-ray crystallography. Cytotoxic activity of the compounds is evaluated using three different tissues of origin e.g., U-937 (histiocytic lymphoma), HEK293T (embryonic kidney), and A549 (lung carcinoma). The cobalt complexes are more active than the corresponding ligands against U-937 and HEK293T. The MTT assay demonstrates that the cobalt compounds are more effective anticancer agents against U-937 cancer cells than HEK293T and A549. The toxicity order, 1 (7.2 ± 0.3 μM) > 3 (11.4 ± 0.6 μM) > 2 (12 ± 0.1 μM) > 4 (29 ± 1 μM) is observed against U-937 cancer cells. All the compounds induce cell death through an apoptosis mechanism and all are ineffective against PBMCs. The mechanism of activity against U937 cancer cells involves caspase-3 activation and two different mitogen-activated protein kinases attesting the programmed cell death. Among the compounds, complexes 1, 2, and 3 show DNA cleavage activity both in oxidizing (H2O2) and reducing (GSH) environments. The mechanistic study reveals that singlet oxygen (1O2) is the major species involved in DNA cleavage. The absolute chemical hardness values of the ligands and 4 are relatively higher than 1, 2, and 3, which tacitly support the DNA cleavage experiment. The docking result indicates that the compounds under investigation strongly interact with DNA base pairs through a variety of interactions which attests successfully to the experimental results. A structure-activity relationship has been drawn to correlate the variation of antitumor activity with ligand conformations.

Development of a ruthenium–aquo complex for utilization in synthesis and catalysis for selective hydration of nitriles and alkynes

A ruthenium(ii)–aquo complex serves as a precursor for the synthesis of new ternary complexes and also as an efficient catalyst for selective hydration of aryl nitriles to aryl amides and aryl alkynes to aryl aldehydes.

Photoactivable Ruthenium-Based Coordination Polymer Nanoparticles for Light-Induced Chemotherapy

Green light photoactive Ru-based coordination polymer nanoparticles (CPNs), with chemical formula [[Ru(biqbpy)]_1.5(bis)](PF₆)₃ (biqbpy = 6,6'-bis[N-(isoquinolyl)-1-amino]-2,2'-bipyridine; bis = bis(imidazol-1-yl)-hexane), were obtained through polymerization of the trans-[Ru(biqbpy)(dmso)Cl]Cl complex (Complex 1) and bis bridging ligands. The as-synthesized CPNs (50 ± 12 nm diameter) showed high colloidal and chemical stability in physiological solutions. The axial bis(imidazole) ligands coordinated to the ruthenium center were photosubstituted by water upon light irradiation in aqueous medium to generate the aqueous substituted and active ruthenium complexes. The UV-Vis spectral variations observed for the suspension upon irradiation corroborated the photoactivation of the CPNs, while High Performance Liquid Chromatography (HPLC) of irradiated particles in physiological media allowed for the first time precisely quantifying the amount of photoreleased complex from the polymeric material. In vitro studies with A431 and A549 cancer cell lines revealed an 11-fold increased uptake for the nanoparticles compared to the monomeric complex [Ru(biqbpy)(N-methylimidazole)₂](PF₆)₂ (Complex 2). After irradiation (520 nm, 39.3 J/cm²), the CPNs yielded up to a two-fold increase in cytotoxicity compared to the same CPNs kept in the dark, indicating a selective effect by light irradiation. Meanwhile, the absence of ¹O₂ production from both nanostructured and monomeric prodrugs concluded that light-induced cell death is not caused by a photodynamic effect but rather by photoactivated chemotherapy.

Two in One: A Dinuclear Ru(II) Complex for Deep-Red Light-Emitting Electrochemical Cells and as an Electrochemiluminescence Probe for Organophosphorus Pesticides

The emissive properties of two Ru(II) complexes, [Ru(dmbipy)₂L₁][PF₆]₂ (1) and [Ru₂(dmbipy)₄L₂][PF₆]₄ (2), (where L₁ and L₂ are π-extended phenanthroline-based ligands and dmbipy = 4,4'-dimethyl-2,2'-bipyridine) have been explored for dual applications, namely, deep-red light-emitting electrochemical cells (LECs) and electrochemiluminescence (ECL) sensors for the detection of organophosphorus pesticides (OPs) that include chlorpyrifos (CPS). A simple single-layer deep-red LEC device comprising 2 is reported that outperforms both its mononuclear derivative 1 and all previously reported dinuclear LECs, with a maximum brightness of 524 cd/m², an external quantum efficiency of 0.62%, and a turn-on voltage of 3.2 V. Optoelectronic studies reveal that the ECL response of 2 is improved when compared to its mononuclear counterpart 1 and benchmark [Ru(bipy)₃]²⁺ (3). Modified glassy carbon electrodes coated with 2 are highly sensitive deep-red ECL sensors that facilitate the detection of CPS directly from river water and fruit samples without any complex pretreatment steps, operating over a broad logarithmic concentration range, with a low detection limit.

Cytotoxicity evaluation and DNA interaction of RuII-bipy complexes containing coumarin-based ligands

Although there are various treatment options for cancer, this disease still has caused an increasing number of deaths, demanding more efficient, selective and less harmful drugs. Several classes of ruthenium compounds have been investigated as metallodrugs for cancer, mainly after the entry of imidazolH [trans-RuCl4-(DMSO-S)(imidazole)] (NAMI-A) and indazolH [trans-RuCl4-(Indazol)2] (KP1019) in clinical trials. In this sense, RuII complexes with general formula [Ru(L1-3)(bipy)2]PF6 (1-3) (L1 = ethyl 3-(6-methyl-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L2 = ethyl 3-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-3-oxopropanoate, L3 = ethyl 3-(8-methoxy-2-oxo-2H-chromen-3-yl)-3-oxopropanoate and bipy = bipyridine) have been synthesized. The crystal structure of 2 revealed that the RuII atom lies on a distorted octahedral geometry with the deprotonated ligand (L2-) coordinated through β-ketoester group oxygen atoms. In vitro cytotoxic activity of the compounds was evaluated against 4T1 (murine mammary carcinoma) and B16-F10 (murine metastatic melanoma) tumor cells, and the non-tumor cell line BHK-21 (baby hamster kidney). Coordination with RuII resulted in expressive enhancement of cytotoxic activity. The precursors were inactive below 100 μM and the final RuII complexes (1-3) showed IC50 ranging from 2.0 to 12.8 μM; 2 being the most potent compound. DNA interaction studies revealed a greater capacity of the complexes to interact with DNA than the ligands, where, 2 exhibited the highest Kb constant of 2.2 × 104 M-1. Fluorescence investigation demonstrated that 1-3 are capable of quenching the fluorescence emission of the EtdBr-DNA complex up to 40%. Molecular docking showed that the interaction of 1-3 between the DNA base pairs from the coumarin portion was with scores of 67.28, 68.62 and 64.88, respectively, and 75.45 for ellipticine, suggesting an intercalative mode of binding. Our findings show that the RuII complexes are eligible for continuing to be investigated as potential antitumor compounds.

Evaluation of the Anticancer and DNA-Binding Characteristics of Dichloro(diimine)zinc(II) Complexes

Several metal diimine complexes have been reported to possess anticancer properties. To evaluate the anticancer properties of tetrahedral zinc(II) diimine complexes, six complexes were synthesized with the general formula M(N^N)Cl2 {where M = Zn, Pt and N^N = 2,2’-biquinoline (1), 2,2’-dipyridylketone (2) and 4-((pyridine-2-ylmethylene)amino)phenol (3)}. In general, the intrinsic DNA-binding constants for the different compounds exhibited values within close proximity; the changes in the viscosity of the CT-DNA upon binding to the compounds suggest intercalation-binding mode. Molecular docking study predicted that complexes containing the highly planar ligand 2,2’-biquinoline are capable to establish π–π interactions with nucleobases of the DNA; the other four complexes engaged in donor–acceptor interactions with DNA nucleobases. The six complexes and two reference drugs (cisplatin and sunitinib) were tested against two cancer cell lines (COLO 205 and RCC-PR) and one normal cell line (LLC-MK2), highlighting the better performance of the zinc(II) complexes compared to their platinum(II) analogues. Moreover, zinc(II) complexes have higher selectivity index values than the reference drugs, with promising anticancer properties.

Multifunctional bacteria-derived tags for advancing immunoassay analytical performance with dual-channel switching and antibodies bioactivity sustaining

Constructing multifunctional immunochromatographic assays (ICA) carriers with multiple signals and retaining bioactivity of monoclonal antibodies (mAbs) are conducive to the sensitive and accurate point-of-care testing (POCT). To fulfill this pressing need, a microorganism-based microsphere mediated dual-modal ICA (DICA) was developed for sensitive and reliable detection of zearalenone (ZEN). As the key to the biosensor, a superb biotag with an intact coccus morphology was designed based on Staphylococcus aureus biosynthesized quantum dots incorporating Ru(bpy)₃²⁺ (SAQDsRu), in which SA offered a specific recognition capacity for Fc region of mAbs, QDs endowed a naked-eye discernible colorimetric signal on the SA, and robust fluorescence signal that remedied for the insufficient brightness of QDs was derived from Ru(bpy)₃²⁺. The characterization of SAQDsRu-labeled mAb (SAQDsRu-mAb) probe demonstrated strong luminescence, excellent stability and high affinity with ZEN (affinity constant was approximately 1.723 × 10⁹ M^-1), which can significantly improve the detection sensitivity. Impressively, a portable sensing system was developed by the integration of SAQDsRu-DICA with a smartphone-based readout. After optimization, this DICA indicated a limit of detection reaching down to 0.008 ng/mL (colorimetric mode) and 0.0058 ng/mL (fluorescent mode), which were much lower than that of conventional gold nanoparticles-based ICA (0.1029 ng/mL), possessing favorable specificity and repeatability (relative standard deviation (RSD) < 10%). Moreover, the feasibility of the immunoassay was further assessed by measuring ZEN in real samples with satisfactory recoveries, and the results are good consistent with liquid chromatography tandem mass spectrometry (LC-MS/MS).

Polypyridyl Ruthenium(II) Complexes with Red-Shifted Absorption: New Promises in Photodynamic Therapy

In the field of cancer photodynamic therapy (PDT) research, development of metal-based PDT drugs that can be used under red light exposure is the "holy grail" to achieve. This highlight highlighted few current literatures on polypyridyl-based Ru(II) complexes with significantly red-shifted absorption to achieve in-vitro and in-vivo PDT effect in 540-600 nm light. The enormous potential of judicial ligand choice and in-silico optimization to achieve the red light, metal-based PDT drugs are discussed.

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds

We describe a synthetic strategy for the preparation of bis-heteroleptic polypyridyl Ru(II) complexes of the type [Ru(L1)₂(L2)]²⁺ (L1 and L2 = diimine ligands) from well-defined Ru(II) precursors. For this purpose, a series of six neutral, anionic, and cationic cis-locked Ru(II)-DMSO complexes (2–7) of the general formula [Y] fac-[RuX(DMSO–S)₃(O–O)]ⁿ (where O–O is a symmetrical chelating anion: oxalate (ox), malonate (mal), acetylacetonate (acac); X = DMSO–O or Cl^–; n = −1/0/+1 depending on the nature and charge of X and O–O; when present, Y = K⁺ or PF₆^–) were efficiently prepared from the well-known cis-[RuCl₂(DMSO)₄] (1). When treated with diimine chelating ligands (L1 = bpy, phen, dpphen), the compounds 2–7 afforded the target [Ru(L1)₂(O–O)]^0/+ complex together with the undesired (and unexpected) [Ru(L1)₃]²⁺ species. Nevertheless, we found that the formation of [Ru(L1)₃]²⁺can be minimized by carefully adjusting the reaction conditions: in particular, high selectivity toward [Ru(L1)₂(O–O)]^0/+ and almost complete conversion of the precursor was obtained within minutes, also on a 100–200 mg scale, when the reactions were performed in absolute ethanol at 150 °C in a microwave reactor. Depending on the nature of L1 and concentration, with the oxalate and malonate precursors, the neutral product [Ru(L1)₂(O–O)] can precipitate spontaneously from the final mixture, in pure form and acceptable-to-good yields. When spontaneous precipitation of the disubstituted product does not occur, purification from [Ru(L1)₃]²⁺ can be rather easily accomplished by column chromatography or solvent extraction. By comparison, under the same conditions, compound 1 is much less selective, thus demonstrating that locking the geometry of the precursor through the introduction of O–O in the coordination sphere of Ru is a valid strategic approach. By virtue of its proton-sensitive nature, facile and quantitative replacement of O–O in [Ru(L1)₂(O–O)]^0/+ by L2, selectively affording [Ru(L1)₂(L2)]²⁺, was accomplished in refluxing ethanol in the presence of a slight excess of trifluoroacetic acid or HPF₆.

cis-Locked Ru(II)-DMSO complexes bearing a symmetrical chelating anion, such as [K] fac-[RuCl(DMSO−S)₃(η²-mal)] (2), are suitable precursors for the two-step selective preparation of bis-heteroleptic polypyridyl compounds of the type [Ru(L1)₂(L2)]²⁺ (L1 and L2 = diimine ligands).

Dual utility of a single diphosphine-ruthenium complex: a precursor for new complexes and, a pre-catalyst for transfer-hydrogenation and Oppenauer oxidation

The diphosphine-ruthenium complex, [Ru(dppbz)(CO)₂Cl₂] (dppbz = 1,2-bis(diphenylphosphino)benzene), where the two carbonyls are mutually cis and the two chlorides are trans, has been found to serve as an efficient precursor for the synthesis of new complexes. In [Ru(dppbz)(CO)₂Cl₂] one of the two carbonyls undergoes facile displacement by neutral monodentate ligands (L) to afford complexes of the type [Ru(dppbz)(CO)(L)Cl₂] (L = acetonitrile, 4-picoline and dimethyl sulfoxide). Both the carbonyls in [Ru(dppbz)(CO)₂Cl₂] are displaced on reaction with another equivalent of dppbz to afford [Ru(dppbz)₂Cl₂]. The two carbonyls and the two chlorides in [Ru(dppbz)(CO)₂Cl₂] could be displaced together by chelating mono-anionic bidentate ligands, viz. anions derived from 8-hydroxyquinoline (Hq) and 2-picolinic acid (Hpic) via loss of a proton, to afford the mixed-tris complexes [Ru(dppbz)(q)₂] and [Ru(dppbz)(pic)₂], respectively. The molecular structures of four selected complexes, viz. [Ru(dppbz)(CO)(dmso)Cl₂], [Ru(dppbz)₂Cl₂], [Ru(dppbz)(q)₂] and [Ru(dppbz)(pic)₂], have been determined by X-ray crystallography. In dichloromethane solution, all the complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on the complexes shows redox responses within 0.71 to -1.24 V vs. SCE. [Ru(dppbz)(CO)₂Cl₂] has been found to serve as an excellent pre-catalyst for catalytic transfer-hydrogenation and Oppenauer oxidation.

Exploring the potential of highly charged Ru(II)- and heteronuclear Ru(II)/Cu(II)-polypyridyl complexes as antimicrobial agents

The antimicrobial potential of two ruthenium(II) polypyridyl complexes, [Ru(phen)₂L1]²⁺ and [Ru(phen)₂L2]²⁺ (phen = 1,10-phenanthroline) containing the 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridilophane (L1) and the 4,4'-bis-[methylen-(1,4,7,10-tetraazacyclododecane)]-2,2' bipyridine (L2) units, is herein investigated. These peculiar polyamine frameworks afford the formation of highly charged species in solution, influence the DNA-binding and cleavage properties of compounds, but they do not undermine their singlet oxygen sensitizing capacities, thus making these complexes attractive ¹O₂ generators in aqueous solution. L1 and L2 also permit to stably host Fenton -active Cu²⁺ ion/s, leading to the formation of mixed Ru²⁺/Cu²⁺ forms capable to further strengthen the oxidative damages to biological targets. Herein, following a characterization of the Cu²⁺ binding ability by [Ru(phen)₂L2]²⁺, the water-octanol distribution coefficients, the DNA binding, cleavage and ¹O₂ sensitizing properties of [Ru(phen)₂L2]²⁺ and [Cu₂Ru(phen)₂L2]⁶⁺ were analysed and compared with those of [Ru(phen)₂L1]²⁺ and [CuRu(phen)₂L1]⁴⁺. The antimicrobial activity of all compounds was evaluated against B. subtilis, chosen as a model for gram-positive bacteria, both under dark and upon light-activation. Our results unveil a notable phototoxicity of [Ru(phen)₂L2]²⁺ and [Cu₂Ru(phen)₂L2]⁶⁺, with MIC (minimal inhibitory concentrations) values of 3.12 μM. This study highlights that the structural characteristics of polyamine ligands gathered on highly charged Ru(II)-polypyridyl complexes are versatile tools that can be exploited to achieve enhanced antibacterial strategies.

Ru(II)-diimine complexes and cytochrome P450 working hand-in-hand

With a growing interest in utilizing visible light to drive biocatalytic processes, several light-harvesting units and approaches have been employed to harness the synthetic potential of heme monooxygenases and carry out selective oxyfunctionalization of a wide range of substrates. While the fields of cytochrome P450 and Ru(II) photochemistry have separately been prolific, it is not until the turn of the 21st century that they converged. Non-covalent and subsequently covalently attached Ru(II) complexes were used to promote rapid intramolecular electron transfer in bacterial P450 enzymes. Photocatalytic activity with Ru(II)-modified P450 enzymes was achieved under reductive conditions with a judicious choice of a sacrificial electron donor. The initial concept of Ru(II)-modified P450 enzymes was further improved using protein engineering, photosensitizer functionalization and was successfully applied to other P450 enzymes. In this review, we wish to present the recent contributions from our group and others in utilizing Ru(II) complexes coupled with P450 enzymes in the broad context of photobiocatalysis, protein assemblies and chemoenzymatic reactions. The merging of chemical catalysts with the synthetic potential of P450 enzymes has led to the development of several chemoenzymatic approaches. Moreover, strained Ru(II) compounds have been shown to selectively inhibit P450 enzymes by releasing aromatic heterocycle containing molecules upon visible light excitation taking advantage of the rapid ligand loss feature in those complexes.

Inorganic reaction mechanisms. A personal journey

This review covers highlights of the work performed in the van Eldik group on inorganic reaction mechanisms over the past two decades in the form of a personal journey. Topics that are covered include, from NO to HNO chemistry, peroxide activation in model porphyrin and enzymatic systems, the wonder-world of Ru^III(edta) chemistry, redox chemistry of Ru(iii) complexes, Ru(ii) polypyridyl complexes and their application, relevant physicochemical properties and reaction mechanisms in ionic liquids, and mechanistic insight from computational chemistry. In each of these sections, typical examples of mechanistic studies are presented in reference to related work reported in the literature.

Synthesis, Characterization, Cytotoxic Activity, and Metabolic Studies of Ruthenium(II) Polypyridyl Complexes Containing Flavonoid Ligands

Four novel monocationic Ru(II) polypyridyl complexes were synthesized with the general formula [Ru(DIP)₂flv]X, where DIP is 4,7-diphenyl-1,10-phenanthroline, flv stands for the flavonoid ligand (5-hydroxyflavone in [Ru(DIP)₂(5-OHF)](PF₆), genistein in [Ru(DIP)₂(gen)](PF₆), chrysin in [Ru(DIP)₂(chr)](OTf), and morin in [Ru(DIP)₂(mor)](OTf)), and X is the counterion, PF₆^-, and OTf ̅ (triflate, CF₃SO₃̅), respectively. Following the chemical characterization of the complexes by ¹H and ¹³C NMR, mass spectrometry, and elemental analysis, their cytotoxicity was tested against several cancer cell lines. The most promising complex, [Ru(DIP)₂(gen)](PF₆), was further investigated for its biological activity. Metabolic studies revealed that this complex severely impaired mitochondrial respiration and glycolysis processes, contrary to its precursor, Ru(DIP)₂Cl₂, which showed a prominent effect only on the mitochondrial respiration. In addition, its preferential accumulation in MDA-MB-435S cells (a human melanoma cell line previously described as mammary gland/breast; derived from metastatic site: pleural effusion), which are used for the study of metastasis, explained the better activity in this cell line compared to MCF-7 (human, ductal carcinoma).

Examination of abiotic cofactor assembly in photosynthetic biomimetics: site-specific stereoselectivity in the conjugation of a ruthenium(II) tris(bipyridine) photosensitizer to a multi-heme protein

To understand design principles for assembling photosynthetic biohybrids that incorporate precisely-controlled sites for electron injection into redox enzyme cofactor arrays, we investigated the influence of chirality in assembly of the photosensitizer ruthenium(II)bis(2,2'-bipyridine)(4-bromomethyl-4'-methyl-2,2'-bipyridine), Ru(bpy)2(Br-bpy), when covalently conjugated to cysteine residues introduced by site-directed mutagenesis in the triheme periplasmic cytochrome A (PpcA) as a model biohybrid system. For two investigated conjugates that show ultrafast electron transfer, A23C-Ru and K29C-Ru, analysis by circular dichroism spectroscopy, CD, demonstrated site-specific chiral discrimination as a factor emerging from the close association between [Ru(bpy)3]2+ and heme cofactors. CD analysis showed the A23C-Ru and K29C-Ru conjugates to have distinct, but opposite, stereoselectivity for the Λ and Δ-Ru(bpy)2(Br-bpy) enantiomers, with enantiomeric excesses of 33.1% and 65.6%, respectively. In contrast, Ru(bpy)2(Br-bpy) conjugation to a protein site with high flexibility, represented by the E39C-Ru construct, exhibited a nearly negligible chiral selectivity, measured by an enantiomeric excess of 4.2% for the Λ enantiomer. Molecular dynamics simulations showed that site-specific stereoselectivity reflects steric constraints at the conjugating sites and that a high degree of chiral selectivity correlates to reduced structural disorder for [Ru(bpy)3]2+ in the linked assembly. This work identifies chiral discrimination as means to achieve site-specific, precise geometric positioning of introduced photosensitizers relative to the heme cofactors in manner that mimics the tuning of cofactors in photosynthesis.

Nucleobase Derivatives as Building Blocks to Form Ru(II)-Based Complexes with High Cytotoxicity

Two new Ru(II)-based complexes containing 2-thiouracil derivatives, known as 2-thiouracil (2TU) and 6-methyl-2-thiouracil (6m2TU), were synthesized using cis,trans-[RuCl₂(PPh₃)₂(bipy)] as a precursor. The obtained compounds with a general formula trans-[Ru(2TU)(PPh₃)₂(bipy)]PF₆ (1) and trans-[Ru(6m2TU)(PPh₃)₂(bipy)]PF₆ (2) were characterized by analytical techniques such as NMR, UV-vis, and IR spectroscopies, elementary analysis, mass spectrometry, and single-crystal X-ray diffraction. Moreover, the investigation of the complexes-DNA interaction were carried out using spectrophotometric titrations and showed that the complexes present a weak interaction with this biomolecule. The compounds were evaluated against HL-60, K-562, HepG2, and B16-F10 cancer cells and against noncancer cells (PBMCs). The results of the biological assay revealed that complex 2 is more promising than complex 1. Finally, the present study suggests that complexes 1 and 2 causes cell death by apoptosis, significantly increasing the percentage of apoptotic HL-60 cells, in which the compounds altered the cell cycle, reducing the cells in G₁/G₀, G₂/M, and S phases.

Triazole appending ruthenium(ii) polypyridine complex for selective sensing of phosphate anions through C–H–anion interaction and copper(ii) ions via cancer cells

Selective fluorescence enhancement by H₂PO₄⁻/H₂P₂O₇²⁻ anions and maximum fluorescence quenching by Cu²⁺ ions were attained upon treatment with different types of anions and cations, respectively.

Disruption of microtubule function in cultured human cells by a cytotoxic ruthenium(ii) polypyridyl complex

Treatment of malignant and non-malignant cultured human cell lines with a cytotoxic IC₅₀ dose of ∼2 μM tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(ii) chloride (RPC2) retards or arrests microtubule motion as tracked by visualizing fluorescently-tagged microtubule plus end-tracking proteins. Immunofluorescent microscopic images of the microtubules in fixed cells show substantial changes to cellular microtubule network and to overall cell morphology upon treatment with RPC2. Flow cytometry with MCF7 and H358 cells reveals only minor elevations of the number of cells in G₂/M phase, suggesting that the observed cytotoxicity is not tied to mitotic arrest. In vitro studies with purified tubulin reveal that RPC2 acts to promote tubulin polymerization and when imaged by electron microscopy, these microtubules look normal in appearance. Isothermal titration calorimetry measurements show an associative binding constant of 4.8 × 10⁶ M^-1 for RPC2 to preformed microtubules and support a 1 : 1 RPC2 to tubulin dimer stoichiometry. Competition experiments show RPC2 does not compete for the taxane binding site. Consistent with this tight binding, over 80% of the ruthenium in treated cells is co-localized with the cytoskeletal proteins. These data support RPC2 acting as an in vivo microtubule stabilizing agent and sharing many similarities with cells treated with paclitaxel.

Neutral iridium(iii) complexes bearing BODIPY-substituted N-heterocyclic carbene (NHC) ligands: synthesis, photophysics, in vitro theranostic photodynamic therapy, and antimicrobial activity

The synthesis, photophysics, and photobiological activities of a series of novel neutral heteroleptic cyclometalated iridium(iii) complexes incorporating boron dipyrromethene (BODIPY) substituted N-heterocyclic carbene (NHC) ligands (Ir1-Ir5) are reported. The effect of the substitution position of BODIPY on the NHC ligands, either on C4 of the phenyl ring (Ir1-Ir3) or C5 of the benzimidazole unit (Ir4 and Ir5), and its linker type (single or triple bond) on the photophysical properties was studied. Ir1-Ir5 exhibited BODIPY-localized intense 1IL (intraligand transition)/1MLCT (metal-to-ligand charge transfer) absorption at 530-543 nm and 1,3IL/1,3CT (charge transfer) emission at 582-610 nm. The nanosecond transient absorption results revealed that the lowest triplet excited states of these complexes were the BODIPY-localized 3π,π* states. Complexes Ir4 and Ir5 exhibited blue-shifted 1IL absorption and 1,3IL/1,3CT emission bands compared to the corresponding absorption and emission bands in complexes Ir1 and Ir3. However, replacing the methyl substituents on N3 of benzimidazole in complexes Ir1 and Ir4 with oligoether substituents in Ir3 and Ir5, respectively, did not impact the energies of the low-energy absorption and emission bands in the corresponding complexes. Water-soluble complexes Ir3 and Ir5 have been explored as photosensitizers for in vitro photodynamic therapy (PDT) effects toward human SKMEL28 melanoma cells. Ir3 showed no dark cytotoxicity (EC50 > 300 μM) but good photocytotoxic activity (9.66 ± 0.28 μM), whereas Ir5 exhibited a higher dark cytotoxicity (20.2 ± 1.26 μM) and excellent photocytotoxicity (0.15 ± 0.01 μM). The phototherapeutic indices with visible light (400-700 nm) activation were >31 for Ir3 and 135 for Ir5. Ir3 and Ir5 displayed 1O2 quantum yields of 38% and 22% in CH3CN, respectively, upon 450 nm excitation. Ir5 was more effective at generating reactive oxygen species (ROS) in vitro. Ir5 was also active against Staphylococcus aureus upon visible light activation, with a phototherapeutic index of >15 and EC50 value of 6.67 μM. These photobiological activities demonstrated that these neutral Ir(iii) complexes are promising in vitro PDT reagents, and substitution at C5 on the benzimidazole group of the NHC ligand was superior to C4 substitution on the phenyl ring.

Alternative Technologies That Facilitate Access to Discrete Metal Complexes

Organometallic complexes: these two words jump to the mind of the chemist and are directly associated with their utility in catalysis or as a pharmaceutical. Nevertheless, to be able to use them, it is necessary to synthesize them, and it is not always a small matter. Typically, synthesis is via solution chemistry, using a round-bottom flask and a magnetic or mechanical stirrer. This review takes stock of alternative technologies currently available in laboratories that facilitate the synthesis of such complexes. We highlight five such technologies: mechanochemistry, also known as solvent-free chemistry, uses a mortar and pestle or a ball mill; microwave activation can drastically reduce reaction times; ultrasonic activation promotes chemical reactions because of cavitation phenomena; photochemistry, which uses light radiation to initiate reactions; and continuous flow chemistry, which is increasingly used to simplify scale-up. While facilitating the synthesis of organometallic compounds, these enabling technologies also allow access to compounds that cannot be obtained in any other way. This shows how the paradigm is changing and evolving toward new technologies, without necessarily abandoning the round-bottom flask. A bright future is ahead of the organometallic chemist, thanks to these novel technologies.

Development of Natural Product-Conjugated Metal Complexes as Cancer Therapies

Platinum-based drugs have revolutionized cancer care, but are unfortunately associated with various adverse effects. Meanwhile, natural product scaffolds exhibit multifarious bioactivities and serve as an attractive resource for cancer therapy development. Thus, the conjugation of natural product scaffolds to metal complexes becomes an attractive strategy to reduce the severe side effects arising from the use of metal bearing drugs. This review aims to highlight the recent examples of natural product-conjugated metal complexes as cancer therapies with enhanced selectivity and efficacy. We discuss the mechanisms and features of different conjugate complexes and present an outlook and perspective for the future of this field.