Identification of an iridium(III) complex with anti-bacterial and anti-cancer activity

Application of Mono and Trinuclear Cyclometalated Iridium (III) Complexes in Differential Bacterial Imaging and Antimicrobial Photodynamic Therapy

The application of transition metal complexes for antimicrobial photodynamic therapy (PDT) has emerged as an attractive alternative in mitigating a broad range of bacterial pathogens, including multidrug-resistant pathogens. In view of their photostability, long excited-state lifetimes, and tunable emission properties, transition metal complexes also contribute as bioimaging agents. In the present work, we designed mono and trinuclear cyclometalated iridium (III) complexes to explore their imaging application and antibacterial potential. For this, we used Methicillin-resistant S. aureus (MRSA), the most prevalent of community-associated (CA) multidrug-resistant (MDR) bacteria (CA MDR) and Lactococcus lactis (L. lactis) as Gram-positive while Campylobacter jejuni (C. jejuni) and E. coli as Gram-negative bacteria. In addition to differential bioimaging of these bacteria, we assessed the antibacterial effects of both mono and trinuclear Ir(III) complexes under exposure to 427 nm LED light. The data presented herein strongly suggest better efficacy of trinuclear Ir(III) complex over the mononuclear complex in imparting photoinduced cell death of MRSA. Based on the safety profile of these complexes, we propose that trinuclear cyclometalated iridium(III) complex holds great promise for selective recognition and targeting MDR bacteria with minimal off-target effect.

Evaluation of multi-target iridium(iii)-based metallodrugs in combating antimicrobial resistance and infections caused by Staphylococcus aureus

The rapid emergence and spread of multidrug-resistant bacteria pose a serious challenge to human life and health, necessitating the development of novel antibacterial agents. Herein, to address this challenge, three iridium-based antibacterial agents were prepared and their antimicrobial activity were explored. Importantly, the three complexes all showed robust potency against S. aureus with MIC values in the range of 1.9-7.9 μg mL-1. Notably, the most active complex Ir3 also exhibited relative stability in mammalian fluids and a significant antibacterial effect on clinically isolated drug-resistant bacteria. Mechanism studies further demonstrated that the complex Ir3 can kill S. aureus by disrupting the integrity of the bacterial membrane and inducing ROS production. This multi-target advantage allows Ir3 to not only effectively combat bacterial resistance but also efficiently clear the bacterial biofilm. In addition, when used together, complex Ir3 could enhance the antibacterial potency of some clinical antibiotics against S. aureus. Moreover, both G. mellonella wax worms and mouse infection model demonstrated that Ir3 has low toxicity and robust anti-infective efficacy in vivo. Overall, complex Ir3 can serve as a new antibacterial agent for combating Gram-positive bacterial infections.

Iridium(III)-based minor groove binding complexes as DNA photocleavage agents

Transition metal complexes containing the qtpy ligand (2':4,4'':4',4'''-quaterpyridyl) are known to be DNA intercalators or minor groove binders. In this study, new tricationic iridium(III) complexes of qtpy are reported. Both [Ir(bpy)2(qtpy)]3+1 and [Ir(phen)2(qtpy)]3+2 display good water solubility as chloride salts. The complexes possess high-energy excited states, which are quenched in the presence of duplex DNA and even by the mononucleotides guanosine monophosphate and adenosine monophosphate. Further studies reveal that although the complexes bind to quadruplex DNA, they display a preference for duplex structures, which are bound with an order of magnitude higher affinities than their isostructural dicationic RuII-analogues. Detailed molecular dynamics simulations confirm that the complexes are groove binders through the insertion of, predominantly, the qtpy ligand into the minor groove. Photoirradiation of 1 in the presence of plasmid DNA confirms that this class of complexes can function as synthetic photonucleases by cleaving DNA.

Review on the Applications of Selected Metal-Based Complexes on Infectious Diseases

Fatalities caused by infectious diseases (i.e., diseases caused by parasite, bacteria, and viruses) have become reinstated as a major public health threat globally. Factors such as antimicrobial resistance and viral complications are the key contributors to the death numbers. As a result, new compounds with structural diversity classes are critical for controlling the virulence of pathogens that are multi-drug resistant. Derivatization of bio-active organic molecules with organometallic synthons is a promising strategy for modifying the inherent and enhanced properties of biomolecules. Due to their redox chemistry, bioactivity, and structural diversity, organometallic moieties make excellent candidates for lead structures in drug development. Furthermore, organometallic compounds open an array of potential in therapy that existing organic molecules lack, i.e., their ability to fulfill drug availability and resolve the frequent succumbing of organic molecules to drug resistance. Additionally, metal complexes have the potential towards metal-specific modes of action, preventing bacteria from developing resistance mechanisms. This review's main contribution is to provide a thorough account of the biological efficacy (in vitro and in vitro) of metal-based complexes against infectious diseases. This resource can also be utilized in conjunction with corresponding journals on metal-based complexes investigated against infectious diseases.

Antimicrobial Activity of Manganese(I) Tricarbonyl Complexes Bearing 1,2,3-Triazole Ligands

BACKGROUND

Antimicrobial resistance is one of the most pressing health issues of our time. The increase in the number of antibiotic-resistant bacteria allied to the lack of new antibiotics has contributed to the current crisis. It has been predicted that if this situation is not dealt with, we will be facing 10 million deaths due to multidrug resistant infections per year by 2050, surpassing cancer-related deaths. This alarming scenario has refocused attention into researching alternative drugs to treat multidrug-resistant infections.

AIMS

In this study, the antimicrobial activities of four manganese complexes containing 1,2,3,-triazole and clotrimazole ligands have been evaluated. It is known that azole antibiotics coordinated to manganese tricarbonyl complexes display interesting antimicrobial activities against several microbes. In this work, the effect of the introduction of 1,2,3,-triazole-derived ligands in the [Mn(CO)3(clotrimazole)] fragment has been investigated against one Gram-positive bacterium and five Gram-negative bacteria.

METHODS

The initial antimicrobial activity of the above-mentioned complexes was assessed by determining the minimum inhibitory and bactericidal concentrations using the broth microdilution method. Growth curves in the presence and absence of the complexes were performed to determine the effects of these complexes on the growth of the selected bacteria. A possible impact on cellular viability was determined by conducting the MTS assay on human monocytes.

RESULTS

Three of the Mn complexes investigated (4-6) had good antimicrobial activities against all the bacteria tested, with values ranging from 1.79 to 61.95 µM with minimal toxicity.

CONCLUSIONS

Due to the increased problem of antibiotic resistance and a lack of new antibacterial drugs with no toxicity, these results are exciting and show that these types of complexes can be an avenue to pursue in the future.

Radical scavenging capacity, antibacterial activity, and quantum chemical aspects of the spectrophotometrically investigated iridium (III) complex with benzopyran derivative

A comprehensive aqueous phase spectrophotometric study concerning the trace level determination of iridium (III) by its reaction with benzopyran-derived chromogenic reagent, 6-chloro-3-hydroxy-7-methyl-2-(2′-thienyl)-4-oxo-4H-1-benzopyran (CHMTB), is performed. The complexing reagent instantly forms a yellow complex with Ir (III) at pH 4.63, where metal is bound to the ligand in a ratio of 1:2 as deduced by Job’s continuous variations, mole ratio, and equilibrium shift methods. The complex absorbs maximally at 413–420 nm retaining its stability for up to 4 days. An optimum set of conditions have been set with respect to the parameters governing the formation of the complex. Under the set optimal conditions, the Ir (III)-CHMTB complex coheres to Beer’s law between 0.0 and 1.5 µg Ir (III) mL⁻¹. The attenuation coefficient and Sandell’s sensitivity are, respectively, 1.18×10⁵ L mol⁻¹ cm⁻¹ and 0.00162 μg cm⁻² at 415 nm. The correlation coefficient (r) and standard deviation (SD) were 0.9999 and ± 0.001095, respectively, whereas the detection limit as analyzed was 0.007437 μg ml⁻¹. The interference with respect to analytically important cations and complexing agents has been studied thoroughly. It is found that the majority of the ions/agents do not intervene with the formation of the complex, thus adding to the versatility of the method. The results obtained from the aforesaid studies indicate a simple, fast, convenient, sensitive, and versatile method for microgram analysis of iridium (III) using CHMTB as a binding ligand. Furthermore, the studied complex is subjected to the evaluation of antibacterial and antioxidant capacity by employing the Agar Diffusion assay and DPPH^. radical scavenging method, respectively. The results obtained from the mentioned assays reveal that the investigated complex possesses significant potency as an antibacterial and antioxidant agent. Finally, the computational approach through DFT of the formed complex confirmed the associated electronic properties of the studied complex.

New Bis-Cyclometalated Iridium(III) Complexes with β-Substituted Porphyrin-Arylbipyridine as the Ancillary Ligand: Electrochemical and Photophysical Insights

An efficient synthetic access to new cationic porphyrin-bipyridine iridium(III) bis-cyclometalated complexes was developed. These porphyrins bearing arylbipyridine moieties at β-pyrrolic positions coordinated with iridium(III), and the corresponding Zn(II) porphyrin complexes were spectroscopically, electrochemically, and electronically characterized. The features displayed by the new cyclometalated porphyrin-bipyridine iridium(III) complexes, namely photoinduced electron transfer process (PET), and a remarkable efficiency to generate ¹O₂, allowing us to envisage new challenges and opportunities for their applications in several fields, such as photo(catalysis) and photodynamic therapies.

Inert cationic iridium(III) complexes with phenanthroline-based ligands: application in antimicrobial inactivation of multidrug-resistant bacterial strains

The antimicrobial activity of a new series of heteroleptic iridium(III) complexes of the type [Ir(C^N)₂(N^N)][PF₆] (C^N = deprotonated 2-phenylbenzimidazole-κN, κC; N^N = phen (Ir1), dpq (Ir2), dppz (Ir3), dppn (Ir4), and dppz-idzo (Ir5)) was studied towards two Gram positive (vancomycin-resistant Enterococcus faecium and a methicillin-resistant Staphylococcus aureus) and two Gram negative (Acinetobacter baumanii and Pseudomonas aeruginosa) multidrug-resistant bacterial strains of clinical interest. Although the complexes were inactive towards Gram negative bacteria, their effectiveness against Gram positive strains was remarkable, especially for Ir1 and Ir2, the most bactericidal complexes that were even more active (10 times) than the fluoroquinolone antibiotic norfloxacin and displayed no toxicity in human kidney cells (HEK293). Mechanistic studies revealed that the cell wall and membrane of MRSA S. aureus remained intact on treatment with these compounds and that DNA was not their main target. It is important to note that the complexes were able to induce ROS generation, this being the feature key to their antimicrobial activity.

Metal Peptide Conjugates in Cell and Tissue Imaging and Biosensing

Metal complex luminophores have seen dramatic expansion in application as imaging probes over the past decade. This has been enabled by growing understanding of methods to promote their cell permeation and intracellular targeting. Amongst the successful approaches that have been applied in this regard is peptide-facilitated delivery. Cell-permeating or signal peptides can be readily conjugated to metal complex luminophores and have shown excellent response in carrying such cargo through the cell membrane. In this article, we describe the rationale behind applying metal complexes as probes and sensors in cell imaging and outline the advantages to be gained by applying peptides as the carrier for complex luminophores. We describe some of the progress that has been made in applying peptides in metal complex peptide-driven conjugates as a strategy for cell permeation and targeting of transition metal luminophores. Finally, we provide key examples of their application and outline areas for future progress.

Ru(ii), Ir(iii), Re(i) and Rh(iii) based complexes as next generation anticancer metallopharmaceuticals

Several anticancer drugs such as cisplatin, and its analogues, epirubicin, and doxorubicin are well known for their anticancer activity but the therapeutic value of these drugs comes with certain side effects and they cannot distinguish between normal and cancer cells. Thus, a major challenge for researchers around the world is to develop an anticancer drug with the least toxicity and more target specificity. With the successful reporting of NAMI-A and KP1019, a new path has emerged in the anticancer field. Recently, several Ru(ii) complexes have been reported for their anticancer activity due to their enhanced cellular uptake and selectivity towards cancer cells. Apart from the Ru(ii) complexes, a large amount of research has been carried out with Ir(iii), Re(i), and Rh(iii) based complexes, which exhibited promising anticancer activity. The present review reports various Ru(ii), Ir(iii), Re(i), and Rh(iii) based complexes for their anticancer activity based on their cytotoxicity profiles, biological targets and mechanism of action.

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.

A New Potent Antimicrobial Metalloporphyrin

A series of bis-acryl functionalized porphyrins and their corresponding metalloporphyrins (M=Co, Mn) were synthesized and investigated for their antimicrobial properties through MIC screening and bacteria time-kill kinetic studies. The Mn(III) 4-(bis)methylphenyl-substituted-porphyrins showed superior batericidal activities even in the dark with low hemotoxicity and good cytotoxicity profile.

Cyclometalated iridium(III) complexes as mitochondria-targeted anticancer and antibacterial agents to induce both autophagy and apoptosis

Mitochondrial damage will hinder the energy production of cells and produce excessive ROS (reactive oxygen species), resulting in cell death through autophagy or apoptosis. In this paper, four cyclometalated iridium(III) complexes (Ir1: [Ir(piq)₂L]PF₆; Ir2: [Ir(bzq)₂L]PF₆; Ir3: [Ir(dfppy)₂L]PF₆; Ir4: [Ir(thpy)₂L]PF₆; piq = 1-phenylisoquinoline; bzq = benzo[h]quinoline; dfppy = 2-(2,4-difluorophenyl)pyridine;thpy = 2-(2-thienyl)pyridine; L = 1,10-phenanthroline-5-amine) were synthesized and characterized. Cytotoxicity tests show that these complexes have excellent cytotoxicity to cancer cells, and mechanism studies indicatethat these complexes can specifically target mitochondria. Complexes Ir1 and Ir2 can damage the function of mitochondria, subsequently increasing intracellular levels of ROS, decreasing MMP (mitochondrial membrane potential), and interfering with ATP energy production, which leads to autophagy and apoptosis. Furthermore, autophagy induced by Ir1 and Ir2 can promote cell death in coordination with apoptosis. Surprisingly, these four complexes also showed moderate antibacterial activity to S. aureusand P. aeruginosa.

Evaluation of the Synthesized Novel Iridium (III) Complexes Against HeLa Cell Lines Through In-Silico, In-Vitro and DNA Nicking

Globally, the pharmaceutical industry is continuously driven in search of new anticancer drugs due to increasing rate of cancer patients. Clinical trials of Cisplatin has been explored, however, usage of Cisplatin as a drug is limited due to its various side effects, hence, alternative to platinum based complex drugs and its analogues are needed. Iridium complexes have been attracted widespread interests by virtue of their pharmacological and photo-physical properties; however the less number of complexes was reported in the literature. In this article, a new series of novel Iridium (III) complexes were synthesized using substituted quinoline Schiff Base (SB) ligands and characterized by spectroscopic techniques. The in- vitro cyto-toxicity assay showed that the Iridium (III) complex activity is equal to standard Cisplatin. In addition, computational docking studies have shown that the prominent binding sites for synthesized complexes against HeLa cell lines, which is comparable with standard Cisplatin drugs and other Ruthenium complexes.

New Antimicrobial Strategies Based on Metal Complexes

Traditional organic antimicrobials mainly act on specific biochemical processes such as replication, transcription and translation. However, the emergence and wide spread of microbial resistance is a growing threat for human beings. Therefore, it is highly necessary to design strategies for the development of new drugs in order to target multiple cellular processes that should improve their efficiency against several microorganisms, including bacteria, viruses or fungi. The present review is focused on recent advances and findings of new antimicrobial strategies based on metal complexes. Recent studies indicate that some metal ions cause different types of damages to microbial cells as a result of membrane degradation, protein dysfunction and oxidative stress. These unique modes of action, combined with the wide range of three-dimensional geometries that metal complexes can adopt, make them suitable for the development of new antimicrobial drugs.

Triazole-based osmium(ii) complexes displaying red/near-IR luminescence: antimicrobial activity and super-resolution imaging

Cellular uptake, luminescence imaging and antimicrobial activity against clinically relevant methicillin-resistant S. aureus (MRSA) bacteria are reported. The osmium(ii) complexes [Os(N^N)3]2+ (N^N = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (1 2+); 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (2 2+); 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (3 2+)) were prepared and isolated as the chloride salts of their meridional and facial isomers. The complexes display prominent spin-forbidden ground state to triplet metal-to-ligand charge transfer (3MLCT) state absorption bands enabling excitation as low as 600 nm for fac/mer-3 2+ and observation of emission in aqueous solution in the deep-red/near-IR regions of the spectrum. Cellular uptake studies within MRSA cells show antimicrobial activity for 1 2+ and 2 2+ with greater toxicity for the meridional isomers in each case and mer-1 2+ showing the greatest potency (32 μg mL-1 in defined minimal media). Super-resolution imaging experiments demonstrate binding of mer- and fac-1 2+ to bacterial DNA with high Pearson's colocalisation coefficients (up to 0.95 using DAPI). Phototoxicity studies showed the complexes exhibited a higher antimicrobial activity upon irradiation with light.

Use of Cotton Textiles Coated by Ir(III) Tetrazole Complexes within Ceramic Silica Nanophases for Photo-Induced Self-Marker and Antibacterial Application

This study was aimed at the production and characterization of coated cotton textiles with luminescent ceramic nanophases doped with cationic Ir(III) tetrazole complexes. We confirmed that SiO₂ nanoparticles (NPs) do not affect the phosphorescent properties of the complexes that maintain their emission (610 and 490 nm). For the first time we transferred the luminescence feature from nanosol to textile surface, highlighting the advantages of using nanosilica as an encapsulating and stabilizing matrix. The optimized Ir@SiO₂ suspensions were homogenously applied onto the cotton surface by dip-pad-dry-cure technique, as proved by the 2p-fluorescence microscope analysis. Once we verified the self-marker properties of the Ir(III) complex, we observed an excellent washing fastness of the coating with a very limited release. SiO₂ in the washing water was quantified at maximum around 1.5 wt% and Ir below the inductively coupled plasma optical emission spectrometry (ICP-OES) detection limit of 1 ppm. A Franz cell test was used to evaluate any possible ex-vivo uptake of Ir@SiO₂ nanoparticles across human skin tissues, showing that epidermis and dermis stop over 99% of Ir, implying a reduced impact on human health. The light-induced antimicrobial potential of the Ir@SiO₂ were assessed toward both Gram(−) and Gram(+) bacteria. The results encouraged further developments of such functional textiles coated by self-markers and antibacterial active nanophases.

Recent Studies on the Antimicrobial Activity of Transition Metal Complexes of Groups 6–12

Antimicrobial resistance is an increasingly serious threat to global public health that requires innovative solutions to counteract new resistance mechanisms emerging and spreading globally in infectious pathogens. Classic organic antibiotics are rapidly exhausting the structural variations available for an effective antimicrobial drug and new compounds emerging from the industrial pharmaceutical pipeline will likely have a short-term and limited impact before the pathogens can adapt. Inorganic and organometallic complexes offer the opportunity to discover and develop new active antimicrobial agents by exploiting their wide range of three-dimensional geometries and virtually infinite design possibilities that can affect their substitution kinetics, charge, lipophilicity, biological targets and modes of action. This review describes recent studies on the antimicrobial activity of transition metal complexes of groups 6–12. It focuses on the effectiveness of the metal complexes in relation to the rich structural chemical variations of the same. The aim is to provide a short vade mecum for the readers interested in the subject that can complement other reviews.

Potent Inhibition of Thioredoxin Reductase by the Rh Derivatives of Anticancer M(arene/Cp*)(NHC)Cl2 Complexes

Metal complexes provide a versatile platform to develop novel anticancer pharmacophores, and they form stable compounds with N-heterocyclic carbene (NHC) ligands, some of which have been shown to inhibit the cancer-related selenoenzyme thioredoxin reductase (TrxR). To expand a library of isostructural NHC complexes, we report here the preparation of Rh^III- and Ir^III(Cp*)(NHC)Cl₂ (Cp* = η⁵-pentamethylcyclopentadienyl) compounds and comparison of their properties to the Ru^II- and Os^II(cym) analogues (cym = η⁶-p-cymene). Like the Ru^II- and Os^II(cym) complexes, the Rh^III- and Ir^III(Cp*) derivatives exhibit cytotoxic activity with half maximal inhibitory concentration (IC₅₀) values in the low micromolar range against a set of four human cancer cell lines. In studies on the uptake and localization of the compounds in cancer cells by X-ray fluorescence microscopy, the Ru and Os derivatives were shown to accumulate in the cytoplasmic region of treated cells. In an attempt to tie the localization of the compounds to the inhibition of the tentative target TrxR, it was surprisingly found that only the Rh complexes showed significant inhibitory activity at IC₅₀ values of ∼1 μM, independent of the substituents on the NHC ligand. This indicates that, although TrxR may be a potential target for anticancer metal complexes, it is unlikely the main target or the sole target for the Ru, Os, and Ir compounds described here, and other targets should be considered. In contrast, Rh(Cp*)(NHC)Cl₂ complexes may be a scaffold for the development of TrxR inhibitors.

Metal Complexes, an Untapped Source of Antibiotic Potential?

With the widespread rise of antimicrobial resistance, most traditional sources for new drug compounds have been explored intensively for new classes of antibiotics. Meanwhile, metal complexes have long had only a niche presence in the medicinal chemistry landscape, despite some compounds, such as the anticancer drug cisplatin, having had a profound impact and still being used extensively in cancer treatments today. Indeed, metal complexes have been largely ignored for antibiotic development. This is surprising as metal compounds have access to unique modes of action and exist in a wider range of three-dimensional geometries than purely organic compounds. These properties make them interesting starting points for the development of new drugs. In this perspective article, , the encouraging work that has been done on antimicrobial metal complexes, mainly over the last decade, is highlighted. Promising metal complexes, their activity profiles, and possible modes of action are discussed and issues that remain to be addressed are emphasized.

Developments in Platinum-Group Metals as Dual Antibacterial and Anticancer Agents

Platinum-group (PG) complexes have been used as antibacterial and anticancer agents since the discovery of cisplatin. The science world still requires improvement on these complexes because of multidrug and antineoplastic resistances. This review observes discoverers and history of these platinum-group metals (PGMs), as well as their beneficial applications. The focus of this study was biological applications of PGMs in relation to human health. Sandwich and half-sandwich PGM coordination compounds and their metal nanoparticles give improved results for biological activities by enhancing efficient delivery of both antibacterial and anticancer drugs, as well as luminescent bioimaging (biomarkers) for biological identifications.

Biological activity and photocatalytic properties of a naphthyl-imidazo phenanthroline (HNAIP) ligand and its [Ir(ppy)2(HNAIP)]Cl and [Rh(ppy)2(HNAIP)]Cl complexes

The synthesized 2-(hydroxy-1-naphtyl)imidazo-[4,5-f][1,10]phenanthroline (HNAIP) ligand and its new iridium ([Ir(ppy)₂(HNAIP)]Cl) and rhodium ([Rh(ppy)₂(HNAIP)]Cl) complexes, being ppy = 2-phenylpiridinate, show cytotoxic effects in SW480 (colon adenocarcinoma) and A549 (epithelial lung adenocarcinoma) cells. They all are cytotoxic in the tested cell lines. HNAIP and [Rh(ppy)₂(HNAIP)]⁺ are the most cytotoxic, whereas [Ir(ppy)₂(HNAIP)]⁺ displays negligible cytotoxicity towards A549 cells and moderate activity towards SW480. The interaction of all three compounds with Bovine Serum Albumin (BSA), l-glutathione reduced (GSH), nicotinamide adenine dinucleotide (NADH) and DNA was studied to explain the differences found in terms of cytotoxicity. None of them are able to interact with BSA, thus excluding bioavailability due to plasma protein interaction as the possible differentiating factor in their biological activity. By contrast, small differences have been observed regarding DNA interaction. In addition, taking advantage of the emission properties of these molecules, they have been visualized in the cytoplasmic region of A549 cells. Inductively coupled plasma mass spectrometry (ICP-MS) experiments show, in turn, that the internalization ability follow the sequence [Rh(ppy)₂(HNAIP)]⁺ > [Ir(ppy)₂(HNAIP)]⁺ > cisplatin. Therefore, it seems clear that the cellular uptake by tumour cells is the key factor affecting the different cytotoxicity of the metal complexes and that this cellular uptake is influenced by the hydrophobicity of the studied complexes. On the other hand, preliminary catalytic experiments performed on the photo-oxidation of GSH and some amino acids such as l-methionine (Met), l-cysteine (Cys) and l-tryptophan (Trp) provide evidence for the photocatalytic activity of the Ir(III) complex in this type of reactions.

Iridium(III) Complexes Targeting Apoptotic Cell Death in Cancer Cells

Targeting apoptosis is a principal strategy in the design of anticancer drugs. In recent years, non-platinum-based scaffolds have been exploited as viable candidates for the exploitation of anticancer agents with potentially lower toxicity than the widely used cisplatin analogues. This review highlights the latest advances in developing iridium(III) complexes as anticancer agents that act particularly via targeting apoptotic cell death in cancer cells.

Synthesis, Characterisation and In Vitro Permeation, Dissolution and Cytotoxic Evaluation of Ruthenium(II)-Liganded Sulpiride and Amino Alcohol

Sulpiride (SPR) is a selective antagonist of central dopamine receptors but has limited clinical use due to its poor pharmacokinetics. The aim of this study was to investigate how metal ligation to SPR may improve its solubility, intestinal permeability and prolong its half-life. The synthesis and characterisation of ternary metal complexes [Ru(p -cymene)(L)(SPR)]PF6 (L1 = (R)-(+)-2-amino-3-phenyl-1-propanol, L2 = ethanolamine, L3 = (S)-(+)-2-amino-1-propanol, L4 = 3-amino-1-propanol, L5 = (S)-(+)-2-pyrrolidinemethanol) are described in this work. The stability constant of the [Ru(p -cymene)(SPR)] complex was determined using Job's method. The obtained value revealed higher stability of the metal complex in the physiological pH than in an acidic environment such as the stomach. The ternary metal complexes were characterised by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), 1H and 13C nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), thermal analyses, Ultraviolet-Visible (UV-Vis). Solubility studies showed higher aqueous solubility for complexed SPR than the free drug. Dissolution profiles of SPR from the metal complexes exhibited slower dissolution rate of the drug. Permeation studies through the pig's intestine revealed enhanced membrane permeation of the complexed drug. In vitro methyl thiazolyl tetrazolium (MTT) assay showed no noticeable toxic effects of the ternary metal complexes on Caco-2 cell line.

Selective cytotoxicity of green synthesized silver nanoparticles against the MCF-7 tumor cell line and their enhanced antioxidant and antimicrobial properties

Introduction

Silver nanoparticles (AgNPs) are of great interest due to their unique and controllable characteristics. Different synthesis methods have been proposed to produce these nanoparticles, which often require elevated temperatures/pressures or toxic solvents. Thus, green synthesis could be a replacement option as a simple, economically viable and environmentally friendly alternative approach for the synthesis of silver nanoparticles.

Methods

Here, the potential of the walnut green husk was investigated in the production of silver nanoparticles. An aqueous solution extracted from walnut green husk was used as a reducing agent as well as a stabilizing agent. Then, the synthesized nanoparticles were characterized with respect of their anticancer, antioxidant, and antimicrobial properties.

Results

Results showed that the synthesized nanoparticles possessed an average size of 31.4 nm with a Zeta potential of -33.8 mV, indicating high stability. A significant improvement in the cytotoxicity and antioxidant characteristics of the green synthesized Ag nanoparticles against a cancerous cell line was observed in comparison with the walnut green husk extract and a commercial silver nanoparticle (CSN). This could be due to a synergistic effect of the synthesized silver nanoparticles and their biological coating. AgNPs and the extract exhibited 70% and 40% cytotoxicity against MCF-7 cancerous cells, respectively, while CSN caused 56% cell death (at the concentration of 60 µg/mL). It was observed that AgNPs were much less cytotoxic when tested against a noncancerous cell line (L-929) in comparison with the control material (CSN). The free radical scavenging analysis demonstrated profound anti-oxidant activity for the synthesized nanoparticles in comparison with the extract and CSN. It was also detected that the synthesized AgNPs possess antibacterial activity against nosocomial and standard strains of both Gram-positive and Gram-negative bacteria (minimum inhibitory concentration =5-30 µg/mL).

Conclusion

These findings imply that the synthesized nanoparticles using green nanotechnology could be an ideal strategy to combat cancer and infectious diseases.

Recent Advances on Octahedral Polypyridyl Ruthenium(II) Complexes as Antimicrobial Agents

Recent developments of therapeutic agents based on transition metals have attracted a great deal of attention. Metal drugs have advantages over other small molecule drugs, and it was demonstrated that, in a number of studies, they played an important role in pharmaceutical chemical research and clinical chemotherapy of cancers. It is worthwhile mentioning that octahedral polypyridyl ruthenium(II) complexes have shown remarkable applications in chemical biology and medicinal chemistry over the last decade. However, only very recently has there been comprehensive interest in their antimicrobial properties due to metal-related toxic concerns or neglected potential roles in microbiological systems. Our review will highlight the recent developments in octahedral polypyridyl ruthenium(III) complexes that have exhibited significant antimicrobial activities and will discuss the relationship between the chemical structure and biological process of ruthenium complexes, in both bacterial and fungal cells.

Cobalt Complex with Thiazole-Based Ligand as New Pseudomonas aeruginosa Quorum Quencher, Biofilm Inhibitor and Virulence Attenuator

Pseudomonas aeruginosa is one of the most dreaded human pathogens, because of its intrinsic resistance to a number of commonly used antibiotics and ability to form sessile communities (biofilms). Innovative treatment strategies are required and that can rely on the attenuation of the pathogenicity and virulence traits. The interruption of the mechanisms of intercellular communication in bacteria (quorum sensing) is one of such promising strategies. A cobalt coordination compound (Co(HL)₂) synthesized from (E)-2-(2-(pyridin-2-ylmethylene)hydrazinyl)-4-(p-tolyl)thiazole (HL) is reported herein for the first time to inhibit P. aeruginosa 3-oxo-C12-HSL-dependent QS system (LasI/LasR system) and underling phenotypes (biofilm formation and virulence factors). Its interactions with a possible target, the transcriptional activator protein complex LasR-3-oxo-C12-HSL, was studied by molecular modeling with the coordination compound ligand having stronger predicted interactions than those of co-crystallized ligand 3-oxo-C12-HSL, as well as known-binder furvina. Transition metal group 9 coordination compounds may be explored in antipathogenic/antibacterial drug design.

The Discovery of an Iridium(III) Dimer Complex as a Potent Antibacterial Agent against Non-Replicating Mycobacterium smegmatis

Novel agents are urgently needed to rapidly kill drug-resistant Mycobacterium tuberculosis. Noble metal complexes, particularly polypyridyl iridium complexes serving as therapeutic agents, have attracted considerable interest recently, due to their significant cytotoxic or antimicrobial activities. Here, we reported an polypyridyl iridium dimer complex [Ir(ppy)₂Cl]₂ (3), with ppy = phenylpyridine, which was found to be active against both exponential growing and non-replicating M. smegmatis, with minimum inhibitory concentration values of 2 μg/mL, and exhibited rapid bactericidal kinetics, killing pathogens within 30–60 min. Moreover, 3 was demonstrated to generate a large amount of reactive oxygen species and to be effective in drug-resistant strains. Taken together, the selectively active iridium(III) dimer complex showed promise for use as a novel drug candidate for the treatment of M. tuberculosis infection.

Iridium(iii) complexes as reaction based chemosensors for medical diagnostics

This frontier article introduces recent developments and applications of iridium(iii) complexes as luminescent probes for ions and biomolecules.

Antipseudomonal activity enhancement of luminescent iridium(iii) dipyridylamine complexes under visible blue light

Cyclometallated iridium(iii) dipyridylamine complexes present antibacterial activity against P. aeruginosa, a highly resistant pathogenic bacterium. This activity is increased when the complex is conjugated to biotin, a bacterial nutrient, and a MIC of 4 μM (4 μg mL^-1) has been observed. The irradiation of P. aeruginosa cultures with blue LED light potentiates the anti-bacterial activities of these iridium(iii) complexes when they are conjugated to a glycoside.

Methylation of Ir(iii)-tetrazolato complexes: an effective route to modulate the emission outputs and to switch to antimicrobial properties

Two neutral cyclometalated Ir(iii)-tetrazolato complexes that differ by variations of the substituents on either the phenylpyridine or the tetrazolate ligand have been converted into the corresponding methylated and cationic analogues. NMR (¹H and ¹³C) characterization of the Ir(iii) complexes provided the results in agreement with the chemo- and regioselective character of methylation at the N-3 position of the Ir(iii)-coordinated tetrazolato ring. This evidence was further corroborated by the analysis of the molecular structures of the cationic complexes obtained by X-ray diffraction. In view of the photophysical properties, the addition of a methyl moiety to neutral Ir(iii) tetrazolates, which behave as sky-blue or orange phosphors, caused a systematic red shift of their phosphorescence output. The transformation of neutral Ir(iii) tetrazolates into cationic Ir(iii)-tetrazole complexes was screened for any eventual antimicrobial activity in vitro against Gram negative (E. coli) and Gram positive (D. radiodurans) microorganisms. While both kinds of complexes were not active against E. coli, the conversion of the neutral Ir(iii) tetrazolates into the corresponding methylated and cationic Ir(iii)tetrazole derivatives determined the turn-on of a good to excellent antimicrobial activity toward Gram positive Deinococcus radiodurans, a non-pathogenic bacterium that is listed as one of the toughest microorganisms in light of its outstanding resistance to radiation and oxidative stress.

Discovery of an Octahedral Silicon Complex as a Potent Antifungal Agent

Octahedral transition metal complexes have been shown to have tremendous applications in chemical biology and medicinal chemistry. Meanwhile, structural transition metals can be replaced by inert octahedral silicon in a proof-of-principle study. We here introduce the first example of octahedral silicon complexes, which can very well serve as an efficient antimicrobial agent. The typical silicon arenediolate complex 1 {[(phen)₂Si(OO)](PF₆)₂, with phen = 1,10-phenanthroline, OO = 9,10-phenanthrenediolate} exhibited significant inhibition towards the growth of Cryptococcus neoformans with MIC and MFC values of 4.5 and 11.3 μM, respectively. Moreover, it was fungicidal against both proliferative and quiescent Cryptococcus cells. This work may set the stage for the development of novel antifungal drugs based upon hexacoodinate silicon scaffolds.

Twist it! The acid-dependent isomerization of homoleptic carbenic iridium(iii) complexes

An acid mediated isomerization technique allows the conversion of meridional homoleptic carbenic iridium(iii) complexes into their facial counterparts.

A theoretical study on the mechanistic highlights behind the Brønsted-acid dependent mer–fac isomerization of homoleptic carbenic iridium complexes for PhOLEDs

The strongly acid-dependent mer–fac isomerization reaction of homoleptic carbenic iridium complexes used in PhOLEDs has been investigated quantum chemically.

Highly potent extranuclear-targeted luminescent iridium(iii) antitumor agents containing benzimidazole-based ligands with a handle for functionalization

This discovery could open the door to a new large family of multifunctional bioconjugated drugs.