Fluorescent, phosphorescent, magnetic resonance contrast and radioactive tracer labelling of extracellular vesicles

This review focusses on the significance of fluorescent, phosphorescent labelling and tracking of extracellular vesicles (EVs) for unravelling their biology, pathophysiology, and potential diagnostic and therapeutic uses. Various labeling strategies, such as lipid membrane, surface protein, luminal, nucleic acid, radionuclide, quantum dot labels, and metal complex-based stains, are evaluated for visualizing and characterizing EVs. Direct labelling with fluorescent lipophilic dyes is simple but generally lacks specificity, while surface protein labelling offers selectivity but may affect EV-cell interactions. Luminal and nucleic acid labelling strategies have their own advantages and challenges. Each labelling approach has strengths and weaknesses, which require a suitable probe and technique based on research goals, but new tetranuclear polypyridylruthenium(II) complexes as phosphorescent probes have strong phosphorescence, selective staining, and stability. Future research should prioritize the design of novel fluorescent probes and labelling platforms that can significantly enhance the efficiency, accuracy, and specificity of EV labeling, while preserving their composition and functionality. It is crucial to reduce false positive signals and explore the potential of multimodal imaging techniques to gain comprehensive insights into EVs.

Catalyst self-assembly accelerates bimetallic light-driven electrocatalytic H2 evolution in water

Hydrogen evolution is an important fuel-generating reaction that has been subject to mechanistic debate about the roles of monometallic and bimetallic pathways. The molecular iridium catalysts in this study undergo photoelectrochemical dihydrogen (H2) evolution via a bimolecular mechanism, providing an opportunity to understand the factors that promote bimetallic H-H coupling. Covalently tethered diiridium catalysts evolve H2 from neutral water faster than monometallic catalysts, even at lower overpotential. The unexpected origin of this improvement is non-covalent supramolecular self-assembly into nanoscale aggregates that efficiently harvest light and form H-H bonds. Monometallic catalysts containing long-chain alkane substituents leverage the self-assembly to evolve H2 from neutral water at low overpotential and with rates close to the expected maximum for this light-driven water splitting reaction. Design parameters for holding multiple catalytic sites in close proximity and tuning catalyst microenvironments emerge from this work.

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.

Synthesis, characterization, photophysical, lipophilicity, and in vitro fluorescence studies of mono-, di-, and trinuclear Ru(II) polypyridyl complexes of pyridinyl benzimidazole derivatives

The synthesis, characterization, and photophysical properties of mononuclear ruthenium(II) complexes [Ru(bpy)₂(py-BIm-Bz)](ClO₄)₂ (1) and [Ru(phen)₂(py-BIm-Bz)](ClO₄)₂ (2), dinuclear complexes [(bpy)₂Ru-μ₂-(py-BIm-Xy)-Ru(bpy)₂](ClO₄)₄ (3) and [(phen)₂Ru-μ₂-(py-BIm-Xy)-Ru(phen)₂](ClO₄)₄ (4), and trinuclear complexes [((bpy)₂Ru)₃-μ₃-(py-BIm-Ms)](ClO₄)₆ (5) and [((phen)₂Ru)₃-μ₃-(py-BIm-Ms)](ClO₄)₆ (6) of pyridinyl benzimidazole ligands with 2,2'-bipyridine or 1,10-phenanthroline ancillary ligands as fluorescent imaging probes are reported. The ligand py-BIm-Bz crystallizes with inherent disorder due to the competing π-π interactions between two (2-pyridinyl)benzimidazole moieties aligned in parallel and in the opposite direction. The complex 2 forms non-merohedrally twinned crystal with the twin law matrix [0.259 -0.776 0.741, 0.000 -1.000 0.000, 1.259 -0.776 -0.259] and a batch scale factor (BASF) of 0.05. The electronic absorption spectra of the complexes 1-6 differ typically in the π-π* transitions of the ancillary ligands. The complexes exhibit orange-red fluorescence at 624-634 nm at room temperature with quantum yield (0.096 - 0.117) higher than that of [Ru(bpy)₃]²⁺ and a hypsochromic shift of the emission maxima in frozen acetonitrile (λ_em = 613-628 nm) due to the rigidochromic effect. The excited state lifetime of these complexes are in the range 72-194 ns with the mononuclear complexes exhibiting the highest values. The complexes 1-6 are nontoxic (IC₅₀ > 275 μM) toward both HeLa and Vero cell lines. They are hydrophilic and the logP_o/w values are in the -0.53 to -1.46 range. The confocal microscopic study of cellular localization of the complexes on the HeLa cells co-stained with the nuclear staining DAPI dye shows their localization in the cytoplasm and the nuclear membrane penetration increases with nuclearity.

Ruthenium Complexes in the Fight against Pathogenic Microorganisms. An Extensive Review

The widespread use of antibiotics has resulted in the emergence of drug-resistant populations of microorganisms. Clearly, one can see the need to develop new, more effective, antimicrobial agents that go beyond the explored 'chemical space'. In this regard, their unique modes of action (e.g., reactive oxygen species (ROS) generation, redox activation, ligand exchange, depletion of substrates involved in vital cellular processes) render metal complexes as promising drug candidates. Several Ru (II/III) complexes have been included in, or are currently undergoing, clinical trials as anticancer agents. Based on the in-depth knowledge of their chemical properties and biological behavior, the interest in developing new ruthenium compounds as antibiotic, antifungal, antiparasitic, or antiviral drugs has risen. This review will discuss the advantages and disadvantages of Ru (II/III) frameworks as antimicrobial agents. Some aspects regarding the relationship between their chemical structure and mechanism of action, cellular localization, and/or metabolism of the ruthenium complexes in bacterial and eukaryotic cells are discussed as well. Regarding the antiviral activity, in light of current events related to the Covid-19 pandemic, the Ru (II/III) compounds used against SARS-CoV-2 (e.g., BOLD-100) are also reviewed herein.

Organometallic ruthenium (η6-p-cymene) complexes interfering with quorum sensing and biofilm formation: an anti-infective approach to combat multidrug-resistance in bacteria

Organometallic ruthenium complexes of flavonoids as antiquorum sensing agents against pathogens likeChromobacterium violaceumATCC 12472,Pseudomonas aeruginosaPAO1 and methicillin-resistantS. aureus(MRSA).

A Novel Ruthenium Based Coordination Compound Against Pathogenic Bacteria

The current epidemic of antibiotic-resistant infections urges to develop alternatives to less-effective antibiotics. To assess anti-bacterial potential, a novel coordinate compound (RU-S4) was synthesized using ruthenium-Schiff base-benzimidazole ligand, where ruthenium chloride was used as the central atom. RU-S4 was characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Antibacterial effect of RU-S4 was studied against Staphylococcus aureus (NCTC 8511), vancomycin-resistant Staphylococcus aureus (VRSA) (CCM 1767), methicillin-resistant Staphylococcus aureus (MRSA) (ST239: SCCmecIIIA), and hospital isolate Staphylococcus epidermidis. The antibacterial activity of RU-S4 was checked by growth curve analysis and the outcome was supported by optical microscopy imaging and fluorescence LIVE/DEAD cell imaging. In vivo (balb/c mice) infection model prepared with VRSA (CCM 1767) and treated with RU-S4. In our experimental conditions, all infected mice were cured. The interaction of coordination compound with bacterial cells were further confirmed by cryo-scanning electron microscope (Cryo-SEM). RU-S4 was completely non-toxic against mammalian cells and in mice and subsequently treated with synthesized RU-S4.

Ruthenium based antimicrobial theranostics - using nanoscopy to identify therapeutic targets and resistance mechanisms in Staphylococcus aureus

In previous studies we reported that specific dinuclear RuII complexes are particularly active against pathogenic Gram-negative bacteria and, unusually for this class of compounds, appeared to display lowered activity against Gram-positive bacteria. With the aim of identifying resistance mechanisms specific to Gram-positive bacteria, the uptake and antimicrobial activity of the lead complex against Staphylococcus aureus SH1000 and other isolates, including MRSA was investigated. This revealed differential, strain specific, sensitivity to the complex. Exploiting the inherent luminescent properties of the RuII complex, super-resolution STED nanoscopy was used to image its initial interaction with S. aureus and confirm its cellular internalization. Membrane damage assays and transmission electron microscopy confirm that the complex disrupts the bacterial membrane structure before internalization, which ultimately results in a small amount of DNA damage. A known resistance mechanism against cationic antimicrobials in Gram-positive bacteria involves increased expression of the mprF gene as this results in an accumulation of positively charged lysyl-phosphatidylglycerol on the outer leaflet of the cytoplasmic membrane that electrostatically repel cationic species. Consistent with this model, it was found that an mprF deficient strain was particularly susceptible to treatment with the lead complex. More detailed co-staining studies also revealed that the complex was more active in S. aureus strains missing, or with altered, wall teichoic acids.

Synthesis and biological properties of tetranuclear ruthenium complexes containing the bis[4(4′-methyl-2,2′-bipyridyl)]-1,7-heptane ligand

The non-linear polypyridylruthenium(ii) complex (Rubb7-TNL) exhibited good antimicrobial activity, but surprisingly was also highly active against cancer cells. The results suggestRubb7-TNLmay have potential as a new anticancer agent.

Applications of Ruthenium Complex in Tumor Diagnosis and Therapy

Ruthenium complexes are a new generation of metal antitumor drugs that are currently of great interest in multidisciplinary research. In this review article, we introduce the applications of ruthenium complexes in the diagnosis and therapy of tumors. We focus on the actions of ruthenium complexes on DNA, mitochondria, and endoplasmic reticulum of cells, as well as signaling pathways that induce tumor cell apoptosis, autophagy, and inhibition of angiogenesis. Furthermore, we highlight the use of ruthenium complexes as specific tumor cell probes to dynamically monitor the active biological component of the microenvironment and as excellent photosensitizer, catalyst, and bioimaging agents for phototherapies that significantly enhance the diagnosis and therapeutic effect on tumors. Finally, the combinational use of ruthenium complexes with existing clinical antitumor drugs to synergistically treat tumors is discussed.

Kinetic and mechanistic study on the reactions of ruthenium(ii) chlorophenyl terpyridine complexes with nucleobases, oligonucleotides and DNA

In this study, we investigated the ability of Ru(ii) polypyridyl complexes to act as DNA binders. The substitution reactions of three Ru(ii) chlorophenyl terpyridine complexes, i.e. [Ru(Cl-Ph-tpy)(en)Cl]Cl (1), [Ru(Cl-Ph-tpy)(dach)Cl]Cl (2) and [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) (Cl-Ph-tpy = 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine, en = 1,2-diaminoethane, dach = 1,2-diaminocyclohexane, bpy = 2,2'-bipyridine), with a mononucleotide guanosine-5'-monophosphate (5'-GMP) and oligonucleotides such as fully complementary 15-mer and 22-mer duplexes with a centrally located GG-binding site for DNA, and fully complementary 13-mer duplexes with a centrally located GG-binding site for RNA were studied quantitatively by UV-Vis spectroscopy. Duplex RNA reacts faster with complexes 1-3 than duplex DNA, while shorter duplex DNA (15mer GG) reacts faster compared with 22mer GG duplex DNA. The measured enthalpies and entropies of activation (ΔH^≠ > 0, ΔS^≠ < 0) support an associative mechanism for the substitution process. ¹H NMR spectroscopy studies performed on complex 3 demonstrated that after the hydrolysis of the Cl ligand, it is capable to interact with guanine derivatives (i.e., 9-methylguanine (9MeG) and 5'-GMP) through N7, forming monofunctional adducts. The molecular structure of the cationic compound [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) was determined in the solid state by X-ray crystallography. The interactions of 1-3 with calf thymus (CT) and herring testes (HT) DNA were examined by stopped-flow spectroscopy, in which HT DNA was sensibly more reactive than CT DNA. The reactivity towards the formation of Ru-DNA adducts was also revealed by a gel mobility shift assay, showing that complexes 1 and 2 have a stronger DNA unwinding ability compared to complex 3. Overall, the complexes with bidentate aliphatic diamines proved to be superior to those with bpy in terms of capability to bind to the here studied biomolecules.

Luminescent Tetrahedral Molecular Cages Containing Ruthenium(II) Chromophores

We have designed linear metalloligands which contain a central photoactive [Ru(N^∧N)₃]²⁺ unit bordered by peripheral metal binding sites. The combination of these metalloligands with Zn(II) and Fe(II) ions leads to heterometallic tetrahedral cages, which were studied by NMR spectroscopy, mass spectrometry, and photophysical methods. Like the parent metalloligands, the cages remain emissive in solution. This approach allows direct incorporation of the favorable properties of ruthenium(II) polypyridyl complexes into larger self-assembled structures.

Synthesis, isomerisation and biological properties of mononuclear ruthenium complexes containing the bis[4(4'-methyl-2,2'-bipyridyl)]-1,7-heptane ligand

A series of mononuclear ruthenium(ii) complexes containing the tetradentate ligand bis[4(4'-methyl-2,2'-bipyridyl)]-1,7-heptane have been synthesised and their biological properties examined. In the synthesis of the [Ru(phen')(bb₇)]²⁺ complexes (where phen' = 1,10-phenanthroline and its 5-nitro-, 4,7-dimethyl- and 3,4,7,8-tetramethyl- derivatives), both the symmetric cis-α and non-symmetric cis-β isomers were formed. However, upon standing for a number of days (or more quickly under harsh conditions) the cis-β isomer converted to the more thermodynamically stable cis-α isomer. The minimum inhibitory concentrations (MIC) and the minimum bactericidal concentrations (MBC) of the ruthenium(ii) complexes were determined against six strains of bacteria: Gram-positive Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA); and the Gram-negative Escherichia coli (E. coli) strains MG1655, APEC, UPEC and Pseudomonas aeruginosa (P. aeruginosa). The results showed that the [Ru(5-NO₂phen)(bb₇)]²⁺ complex had little or no activity against any of the bacterial strains. By contrast, for the other cis-α-[Ru(phen')(bb₇)]²⁺ complexes, the antimicrobial activity increased with the degree of methylation. In particular, the cis-α-[Ru(Me₄phen)(bb₇)]²⁺ complex showed excellent and uniform MIC activity against all bacteria. By contrast, the MBC values for the cis-α-[Ru(Me₄phen)(bb₇)]²⁺ complex varied considerably across the bacteria and even within S. aureus and E. coli strains. In order to gain an understanding of the relative antimicrobial activities, the DNA-binding affinity, cellular accumulation and water-octanol partition coefficients (log P) of the ruthenium complexes were determined. Interestingly, all the [Ru(phen')(bb₇)]²⁺ complexes exhibited stronger DNA binding affinity (K_a ≈ 1 × 10⁷ M^-1) than the well-known DNA-intercalating complex [Ru(phen)₂(dppz)]²⁺ (where dppz = dipyrido[3,2-a:2',3'-c]phenazine).

The Microbiology of Ruthenium Complexes

Ruthenium is seldom mentioned in microbiology texts, due to the fact that this metal has no known, essential roles in biological systems, nor is it generally considered toxic. Since the fortuitous discovery of cisplatin, first as an antimicrobial agent and then later employed widely as an anticancer agent, complexes of other platinum group metals, such as ruthenium, have attracted interest for their medicinal properties. Here, we review at length how ruthenium complexes have been investigated as potential antimicrobial, antiparasitic and chemotherapeutic agents, in addition to their long and well-established roles as biological stains and inhibitors of calcium channels. Ruthenium complexes are also employed in a surprising number of biotechnological roles. It is in the employment of ruthenium complexes as antimicrobial agents and alternatives or adjuvants to more traditional antibiotics, that we expect to see the most striking developments in the future. Such novel contributions from organometallic chemistry are undoubtedly sorely needed to address the antimicrobial resistance crisis and the slow appearance on the market of new antibiotics.

Monomeric and dimeric coordinatively saturated and substitutionally inert Ru(ii) polypyridyl complexes as anticancer drug candidates

Monomeric and dimeric coordinatively saturated and substitutionally inert Ru(ii) polypyridyl complexes with anticancer properties are reviewed.

Biological processing of dinuclear ruthenium complexes in eukaryotic cells

The biological processing - mechanism of cellular uptake, effects on the cytoplasmic and mitochondrial membranes, intracellular sites of localisation and induction of reactive oxygen species - of two dinuclear polypyridylruthenium(ii) complexes has been examined in three eukaryotic cells lines. Flow cytometry was used to determine the uptake of [{Ru(phen)2}2{μ-bb12}](4+) (Rubb12) and [Ru(phen)2(μ-bb7)Ru(tpy)Cl](3+) {Rubb7-Cl, where phen = 1,10-phenanthroline, tpy = 2,2':6',2''-terpyridine and bbn = bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane} in baby hamster kidney (BHK), human embryonic kidney (HEK-293) and liver carcinoma (HepG2) cell lines. The results demonstrated that the major uptake mechanism for Rubb12 and Rubb7-Cl was active transport, although with a significant contribution from carrier-assisted diffusion for Rubb12 and passive diffusion for Rubb7-Cl. Flow cytometry coupled with Annexin V/TO-PRO-3 double-staining was used to compare cell death by membrane damage or apoptosis. Rubb12 induced significant direct membrane damage, particularly with HepG2 cells, while Rubb7-Cl caused considerably less membrane damage but induced greater levels of apoptosis. Confocal microscopy, coupled with JC-1 assays, demonstrated that Rubb12 depolarises the mitochondrial membrane, whereas Rubb7-Cl had a much smaller affect. Cellular localisation experiments indicated that Rubb12 did not accumulate in the mitochondria, whereas significant mitochondrial accumulation was observed for Rubb7-Cl. The effect of Rubb12 and Rubb7-Cl on intracellular superoxide dismutase activity showed that the ruthenium complexes could induce cell death via a reactive oxygen species-mediated pathway. The results of this study demonstrate that Rubb12 predominantly kills eukaryotic cells by damaging the cytoplasmic membrane. As this dinuclear ruthenium complex has been previously shown to exhibit greater toxicity towards bacteria than eukaryotic cells, the results of the present study suggest that metal-based cationic oligomers can achieve selective toxicity against bacteria, despite exhibiting a non-specific membrane damage mechanism of action.

Apoptosis, autophagy, cell cycle arrest, cell invasion and BSA-binding studies in vitro of ruthenium(ii) polypyridyl complexes

Four new ruthenium(ii) polypyridyl complexes were synthesized and characterized. The anticancer activity was investigated by cytotoxicity in vitro, apoptosis, comet assay, ROS, autophagy, cell invasion and western blot analysis.

High catalytic abilities of binuclear rhenium(i) complexes in the photochemical reduction of CO2 with a ruthenium(ii) photosensitiser

Photocatalytic systems for CO₂ reduction using a Ru(ii) photosensitiser and dinuclear Re(i) diimine tricarbonyl complexes (Re(n)Re), in which diimine ligands are connected by alkyl chains of various lengths (–C_nH_2n–: n = 2, 3, 4, 6, 14), as catalysts were investigated.

Cooperative effects in homogenous water oxidation catalysis by mononuclear ruthenium complexes

The homogenous water oxidation catalysis by [Ru(terpy)(bipy)Cl](+) (1) and [Ru(terpy)(Me2bipy)Cl](+) (2) (terpy = 2,2':6',2''-terpyridine, bipy = 2,2'-bipyridine, Me2bipy = 4,4'-dimethyl-2,2'-bipyridine) under the influence of two redox mediators [Ru(bipy)3](2+) (3) and [Ru(phen)2(Me2bipy)](2+) (4) (phen = 1,10-phenanthroline) was investigated using Ce(4+) as sacrificial oxidant. Oxygen evolution experiments revealed that mixtures of both 2-4 and 2-3 produced more molecular oxygen than catalyst 2 alone. In contrast, the combination of mediator 4 and catalyst 1 resulted in a lower catalytic performance of 1. Measurements of the temporal change in the intensity of a UV transition at 261 nm caused by the addition of four equivalents of Ce(4+) to 2 revealed three distinctive regions-suggested to correspond to the stepwise processes: (i) [Ru(IV)=O](2+) → [Ru(V)=O](3+); (ii) [Ru(V)=O](3+) → [Ru(III)-(OOH)](2+); and (iii) [Ru(III)-(OOH)](2+) → [Ru(II)-OH2](2+). UV-Visible spectrophotometric experiments on the 1-4 and 2-4 mixtures, also carried out with four equivalents of Ce(4+), demonstrated a faster [Ru(phen)2(Me2bipy)](3+) → [Ru(phen)2(Me2bipy)](2+) reduction rate in 2-4 than that observed for the 1-4 combination. Cyclic voltammetry data measured for the catalysts and the mixtures revealed a coincidence in the potentials of the Ru(II)/Ru(III) redox process of mediators 3 and 4 and the predicted [Ru(IV)=O](2+)/[Ru(V)=O](3+) potential of catalyst 2. In contrast, the [Ru(IV)=O](2+)/[Ru(V)=O](3+) process for catalyst 1 was found to occur at a higher potential than the Ru(II)/Ru(III) redox process for 4. Both the spectroscopic and electrochemical experiments provide evidence that the interplay between the mediator and the catalyst is an important determinant of the catalytic activity.

Synthesis, characterization and anticancer activity of dinuclear ruthenium(ii) complexes linked by an alkyl chain

Anticancer activity of three novel ruthenium complexes was studied and the cytotoxicity increased with the increase of the amount of methylene in the bridging ligands.

Synthesis, characterisation and antibacterial activity of [(p-cym)RuX(L)]+/2+ (X = Cl, H2O; L = bpmo, bpms) complexes

Simple replacement of Cl⁻ by H₂O in {(p-cym)Ru^II(L)X]ⁿ⁺ (X = Cl or H₂O) complexes enhances antibacterial activity significantly.

RNA and DNA binding of inert oligonuclear ruthenium(ii) complexes in live eukaryotic cells

Oligonuclear polypyridylruthenium(ii) complexes show selectivity for the nucleus of eukaryotic cells with a considerable preference for the RNA-rich nucleolus.

Development of ruthenium(II) complexes as topical antibiotics against methicillin resistant Staphylococcus aureus

A series of ruthenium(II) bis(2,2'-bipyridyl) complexes containing N-phenyl-substituted diazafluorenes (Ru-C1, Ru-C6, Ru-C7 and Ru-F) was synthesized and their potential antibacterial activity against methicillin resistant Staphylococcus aureus (MRSA) was investigated. The Ru-C7 complex showed significant improvement in both minimum inhibitory concentration (MIC, 6.25 μg mL(-1)) and minimum bactericidal concentration (MBC, 25 μg mL(-1)) towards MRSA when compared with those of methicillin (positive control) (MIC = 25 μg mL(-1) and MBC = 100 μg mL(-1)). The Ru-C7 complex possessed much stronger antibacterial effects than the Ru-C6 complex (MIC, 25 μg mL(-1), MBC, >100 μg mL(-1)). Both Ru-C6 and Ru-C7 complexes were also demonstrated to be biologically safe when tested on normal human skin keratinocytes.

Multinuclear ruthenium(ii) complexes as anticancer agents

The dinuclear ruthenium complex with X = H is four-times more cytotoxic than cisplatin against breast cancer cell lines; however, when X = NO₂ the ruthenium complex is less active than cisplatin.

Tri- and tetra-nuclear polypyridyl ruthenium(ii) complexes as antimicrobial agents

Tri- and tetra-nuclear polypyridylruthenium(ii) complexes have been synthesised which exhibit high levels of antimicrobial activity.

Dinuclear polypyridylruthenium(II) complexes: flow cytometry studies of their accumulation in bacteria and the effect on the bacterial membrane

OBJECTIVES

To determine the energy dependency of and the contribution of the membrane potential to the cellular accumulation of the dinuclear complexes [{Ru(phen)2}2{μ-bbn}](4+) (Rubbn) and the mononuclear complexes [Ru(Me4phen)3](2+) and [Ru(phen)2(bb7)](2+) in Staphylococcus aureus and Escherichia coli, and to examine their effect on the bacterial membrane.

METHODS

The accumulation of the ruthenium complexes in bacteria was determined using flow cytometry at a range of temperatures. The cellular accumulation of the ruthenium complexes was also determined in cells that had been incubated with the metal complexes in the presence or absence of metabolic stimulators or inhibitors and/or commercial dyes to determine the membrane potential or membrane permeability.

RESULTS

The accumulation of ruthenium complexes in the two bacterial strains was shown to increase with increasing incubation temperature, with the relative increase in accumulation greater with E. coli, particularly for Rubb12 and Rubb16. No decrease in accumulation was observed for Rubb12 in ATP-inhibited cells. While carbonyl cyanide m-chlorophenyl hydrazone (CCCP) did depolarize the cell membrane, no reduction in the accumulation of Rubb12 was observed; however, all ruthenium complexes, when incubated with S. aureus at concentrations twice their MIC, depolarized the membrane to a similar extent to CCCP. Except for the mononuclear complex [Ru(Me4phen)3](2+), incubation of any of the other ruthenium complexes allowed a greater quantity of the membrane-impermeable dye TO-PRO-3 to be taken up by S. aureus.

CONCLUSIONS

The results indicate that the potential new antimicrobial Rubbn complexes enter the cell in an energy-independent manner, depolarize the cell membrane and significantly permeabilize the cellular membrane.

Ruthenium(II) polypyridyl complexes and DNA--from structural probes to cellular imaging and therapeutics

In the last few decades, coordination complexes based on d(6) metal centres and polypyridyl ligand architectures been developed as structure- and site-specific reversible DNA binding agents. Due to their attractive photophysical properties, much of this research has focused on complexes based on ruthenium(II) centres and, more recently, attention has turned to the use of these complexes in biological contexts. As the rules that govern the cellular uptake and cellular localisation of such systems are determined they are finding numerous applications ranging from imaging to therapeutics. This review illustrates how the interdisciplinary nature of this research-which takes in synthetic chemistry, biophysical and in cellulo studies-makes this an exciting area in which an array of further applications are likely to emerge.

Mechanism of cytotoxicity and cellular uptake of lipophilic inert dinuclear polypyridylruthenium(II) complexes

The accumulation, uptake mechanism, cytotoxicity, cellular localisation of-and mode of cell death induced by-dinuclear ruthenium(II) complexes ΔΔ/ΛΛ-[{Ru(phen)(2) }(2) {μ-bb(n) }](4+) (Rubb(n)), where phen is 1,10-phenanthroline, bb(n) is bis[4(4'-methyl-2,2'-bipyridyl)]-1,n-alkane (n=2, 5, 7, 10, 12 or 16), and the corresponding mononuclear complexes containing the bb(n) ligands, were studied in L1210 murine leukaemia cells. Cytotoxicity increased with linker chain length, and the ΔΔ-Rubb(16) complex displayed the highest cytotoxicity of the series, with an IC(50) value of 5 μM, similar to that of carboplatin in the L1210 murine leukaemia cell line. Confocal microscopy and flow cytometry studies indicated that the complexes accumulate in the mitochondria of L1210 cells, with the magnitude of cellular uptake and accumulation increasing with linking chain length in the bb(n) bridge of the metal complex. ΔΔ-Rubb(16) entered the L1210 cells by passive diffusion (with a minor contribution from protein-mediated active transport), inducing cell death via apoptosis. Additionally, metal-complex uptake in leukaemia cells was approximately 16-times that observed in healthy B cells highlighting that the bb(n) series of complexes may have potential as selective anticancer drugs.