Ruthenium(II) arene complexes containing four- and five-membered monoanionic O,O-chelate rings

Screening the biological properties of transition metal carbamates reveals gold(I) and silver(I) complexes as potent cytotoxic and antimicrobial agents

We report a screening study aimed to assess for the first time the air- and water-stability and the biological potential of simple metal-carbamates. These molecular metallic species are based on elements belonging to the groups 4-5, 7-9 and 11, and tin, and are easily available from inexpensive reagents. Complexes [Ag(O₂CNEt₂)] (13-Ag) and [Au(O₂CNMe₂)(PPh₃)] (14-Au) resulted substantially stable in aqueous media and exhibited a potent in vitro cytotoxicity. Especially 13-Ag revealed a significant selectivity against the A549 lung adenocarcinoma and the A2780 ovarian cancer cell lines with respect to the noncancerous HEK293 cell line. Generation of ROS (reactive oxygen species) and mitochondrial membrane depolarization were recognized for 13-Ag and 14-Au; notwithstanding, the cell death mechanism is different in the two cases: apoptosis and cell cycle arrest in G0/G1 phase for 13-Ag; necroptosis and cell cycle arrest in S phase for 14-Au. Both 13-Ag and 14-Au are endowed with antibacterial activity, which is relatively stronger for 13-Ag towards Gram negative and for 14-Au towards Gram positive strains, respectively.

Pyridylphosphinate metal complexes: synthesis, structural characterisation and biological activity

For the first time, a series of 25 pseudo-octahedral pyridylphosphinate metal complexes (Ru, Os, Rh, Ir) has been synthesised and assessed in biological systems. Each metal complex incorporates a pyridylphosphinate ligand, a monodentate halide and a capping η(6)-bound aromatic ligand. Solid- and solution-state analyses of two complexes reveal a structural preference for one of a possible two diastereomers. The metal chlorides hydrolyse rapidly in D2O to form a 1 : 1 equilibrium ratio between the aqua and chloride adducts. The pKa of the aqua adduct depends upon the pyridyl substituent and the metal but has little dependence upon the phosphinate R' group. Toxicity was measured in vitro against non-small cell lung carcinoma H460 cells, with the most potent complexes reporting IC50 values around 50 μM. Binding studies with selected amino acids and nucleobases provide a rationale for the variation in toxicity observed within the series. Finally, an investigation into the ability of the chelating amino acid l-His to displace the phosphinate O-metal bond shows the potential for phosphinate complexes to act as prodrugs that can be activated in the intracellular environment.

Nanoparticles of chitosan conjugated to organo-ruthenium complexes

The synthesis of nanoparticles of conjugates of caffeic acid-modified chitosan with ruthenium arene complexes is described.

Arene-Ru(II) complexes of curcumin exert antitumor activity via proteasome inhibition and apoptosis induction

Organometallic ruthenium(II) complexes of general formula [(η(6)-arene)Ru(curcuminato)Cl], with arene being p-iPrC6 H4Me (1), C6H6 (2), and C6Me6 (3), were synthesized, characterized, and evaluated for their antitumor effects. Specifically, we explored their ability to regulate the proteasome, a validated pharmacological target in cancer treatment. Ruthenium complexes inhibited isolated proteasomes to various extents, with the biological activity of these complexes depending on the nature of the bound arene; in particular, [(η(6)-arene)Ru(curcuminato)Cl] 2 suppressed proteasomal activities more potently than 1, 3, or free curcumin. Each complex also inhibited proteasomes in cultured colon cancer cells and consequently triggered apoptosis, with the [(η(6)-benzene)Ru(curcuminato)Cl] complex 2 being the most active. The influence on the oxidative status of HCT116 cells and the DNA binding ability of the [(η(6)-arene)Ru(curcuminato)Cl] complexes were studied. Complex 2 showed the highest antioxidant capacity; moreover, complexes 1 and 2 were shown to bind isolated DNA with higher affinity (up to threefold) than free curcumin. Collectively, our results demonstrate that the complexation of curcumin with ruthenium(II) is a promising starting point for the development of curcumin-based anticancer drugs.

Ruthenium complexes containing bis-benzimidazole derivatives as a new class of apoptosis inducers

A series of ruthenium complexes containing bis-benzimidazole derivatives have been synthesized and identified as able to target mitochondria and induce caspase-dependent apoptosis in cancer cells through superoxide overproduction.

Hydrolytic behaviour and chloride ion binding capability of [Ru(η6-p-cym)(H2O)3]2+: a solution equilibrium study

Hydrolysis of an organometallic cation, [Ru(η(6)-p-cym)(H(2)O)(3)](2+) (p-cym = 1-isopropyl-4-methylbenzene), in the presence of 0.20 M KNO(3) or KCl as supporting electrolyte was studied in detail with the combined use of pH-potentiometry, (1)H-NMR, UV-VIS and ESI-TOF-MS. Stoichiometry and stability constants of chlorido, hydroxido and mixed chlorido-hydroxido complexes formed in aqueous solution have been determined. At pH < 4.0 where hydrolysis of [Ru(η(6)-p-cym)(H(2)O)(3)](2+) is negligible with increasing chloride ion concentration two chlorido complexes, [Ru(η(6)-p-cym)(H(2)O)(2)Cl](+) and [{Ru(η(6)-p-cym)}(2)(μ(2)-Cl)(3)](+), are detectable. At pH > 5.0, in chloride ion free samples the exclusive formation of [{Ru(η(6)-p-cym)}(2)(μ(2)-OH)(3)](+) is found. However, if chloride ion is present (in the range 0-3.50 M) novel mixed chlorido-hydroxido species, [{Ru(η(6)-p-cym)}(2)(μ(2)-OH)(2)(μ(2)-Cl)](+) and [{Ru(η(6)-p-cym)}(2)(μ(2)-OH)(μ(2)-Cl)(2)](+) can also be identified at pH > 4.0. The results obtained in this study may help in rationalizing the solution behaviour of half-sandwich [Ru(η(6)-p-cym)(XY)Z] type complexes which, after dissociation of both the monodentate Z and the chelating XY, are capable of yielding the free aqua species [Ru(η(6)-p-cym)(H(2)O)(3)](2+). Our results demonstrate that different chloride ion concentrations can influence the speciation in the acidic pH range but at biologically relevant conditions (pH = 7.4, c(Cl(-)) = 0.16 M) and at c(M) = 1 μM [{Ru(η(6)-p-cym)}(2)(μ(2)-OH)(3)](+) is predominant in the absence of any coordinating ligands.

Complex formation between Ru(η(6)-p-cym)(H2O)3]2+ and (O,O) donor ligands with biological relevance in aqueous solution

The interaction between [Ru(η(6)-p-cym)(H(2)O)(3)](2+) and (O,O) type chelators with different basicity of the donor atoms was studied using combined pH-potentiometric, (1)H-NMR and ESI-TOF-MS techniques. The studied nine ligands are building blocks of reported complexes with antitumor activity or may model (O,O) donor serum components capable of interacting with the administered half-sandwich ruthenium(II) type drug. Composition and stability constants of the [Ru(η(6)-p-cym)(O,O)Y] type species (Y: H(2)O or OH(-)) were determined (T = 25.0 °C; I = 0.20 M (KCl)) and the metal ion binding strengths of the ligands are discussed. It was found that ligands with two low basicity O donors (oxalic and cyclobutane-1,1-dicarboxylic acid) bind the metal ion at acidic conditions but are not able to prevent the hydrolysis at physiologically relevant conditions. Ligands with one low and one high basicity O donor (lactic and salicylic acid) are weak binders for Ru(η(6)-p-cym)(H(2)O)(3)](2+). Pyrone or pyridinone based ligands are capable of binding the metal ion over a wide pH range and no hydrolysis product is detectable at pH = 7.4. The obtained speciation models may help in the rationalization of the biological activity of such complexes and provide a deeper insight into the solution behaviour of half-sandwich Ru(II) complexes with potential anticancer activity.

Medicinal organometallic chemistry: designing metal arene complexes as anticancer agents

The field of medicinal inorganic chemistry is rapidly advancing. In particular organometallic complexes have much potential as therapeutic and diagnostic agents. The carbon-bound and other ligands allow the thermodynamic and kinetic reactivity of the metal ion to be controlled and also provide a scaffold for functionalization. The establishment of structure-activity relationships and elucidation of the speciation of complexes under conditions relevant to drug testing and formulation are crucial for the further development of promising medicinal applications of organometallic complexes. Specific examples involving the design of ruthenium and osmium arene complexes as anticancer agents are discussed.

Chlorido-, aqua-, 9-ethylguanine- and 9-ethyladenine-adducts of cytotoxic ruthenium arene complexes containing O,O-chelating ligands

The synthesis and X-ray structures of a half-sandwich Ru(II)p-cymene beta-diketonato complex as chlorido-, aqua-, 9-ethylguanine- and 9-ethyladenine-adducts are reported. Structural features which contribute to stabilisation of adducts through non-covalent, weak interactions are discussed. The X-ray crystal structure of the cytotoxic complex [(eta(6)-p-cym)Ru(Ph(2)acac)Cl] (1), where Ph(2)acac=1,3-diphenyl-1,3-propanedionate and p-cym=para-cymene, shows that the phenyl rings of the acac-type ligand form a hydrophobic face, conferring lipophilic character on the complex. The structure of the aqua adduct [(eta(6)-p-cym)Ru(Ph(2)acac)H(2)O]CF(3)SO(3).H(2)O.Et(2)O (4.H(2)O.Et(2)O), a possible activated species, possesses a comparatively short Ru-OH(2) bond. In the structure of [(eta(6)-p-cym)Ru(Ph(2)acac)9EtG-N7]CF(3)SO(3).2tol (5.2tol), where tol=toluene and 9EtG=9-ethylguanine, a comparatively long Ru-N7 bond is observed in addition to weak G CH8cdots, three dots, centeredO (Ph(2)acac) H-bonds. The crystal structure of [(eta(6)-p-cym)Ru(acac)9EtA-N7]PF(6) (6), where acac=acetylacetonate and 9EtA=9-ethyladenine, a rare example of a ruthenium complex containing monodentate adenine, shows a strong H-bonding interaction between N6Hcdots, three dots, centeredO(acac), which may contribute to the selectivity of {(eta(6)-p-cym)Ru(acac)}(+) towards adenine bases.

Bifunctional Amine-Tethered Ruthenium(II) Arene Complexes Form Monofunctional Adducts on DNA

The tethered RuII half-sandwich complexes [eta(6):eta(1)-C(6)H(5)(CH(2))(n)NH(2))RuCl(2)] 1 (n = 3) and 2 (n = 2) have been synthesized as potential bifunctional anticancer complexes, and their X-ray crystal structures have been determined. They hydrolyze rapidly in aqueous solution to give predominantly mono-aqua mono-chlorido species. Mono-9EtG adducts, where 9EtG = 9-ethylguanine, form rapidly, but the second 9EtG binds more slowly and more weakly. In the X-ray crystal structure of the di-9EtG adduct [(eta(6):eta(1)-C(6)H(5)(CH(2))(3)NH(2))Ru(9EtG)2](CF(3)SO(3))(2).H(2)O (8.H(2)O), one of the Ru-N7 bonds is significantly longer than the other (2.1588(18) vs 2.101(2) A). The bound guanine bases adopt a head-to-head configuration, stabilized by tether NH2 hydrogen bonding to C6O of 9EtG. The X-ray crystal structure of the dinitrato complex [(eta(6):eta(1)-C(6)H(5)(CH(2))(3)NH(2))Ru(NO(3))(2)] (3) showed both nitrates to be bound to ruthenium. This complex readily rutheniated calf thymus DNA but failed to produce stop sites on pSP73KB plasmid DNA during DNA transcription by an RNA polymerase. This suggested that only monofunctional DNA adducts formed, as did interstrand cross-linking assays. Also, the unwinding angle induced in negatively supercoiled DNA (9 +/- 1 degrees) was less than that induced by cisplatin (13 degrees). These findings may explain why complexes such as 1 and 2 exhibited low cytotoxicities (IC(50) values >100 microM) toward A2780 human ovarian cancer cells.

Areneruthenium(II) 4-Acyl-5-pyrazolonate Derivatives: Coordination Chemistry, Redox Properties, and Reactivity

Areneruthenium(II) molecular complexes of the formula [Ru(arene)(Q)Cl], containing diverse 4-acyl-5-pyrazolonate ligands Q with arene = cymene or benzene, have been synthesized by the interaction of HQ and [Ru(arene)Cl(micro-Cl)]2 dimers in methanol in the presence of sodium methoxide. The dinuclear compound [{Ru(cymene)Cl}2Q4Q] (H2Q4Q = bis(4-(1-phenyl-3-methyl-5-pyrazolone)dioxohexane), existing in the RRuSRu (meso form), has been prepared similarly. [Ru(cymene)(Q)Cl] reacts with sodium azide in acetone, affording [Ru(cymene)(Q)N3] derivatives, where Cl- has been replaced by N3-. The reactivity of [Ru(cymene)(Q)Cl] has also been explored toward monodentate donor ligands L (L = triphenylphosphine, 1-methylimidazole, or 1-methyl-2-mercaptoimidazole) and exo-bidentate ditopic donor ligands L-L (L-L = 4,4'-bipyridine or bis(diphenylphosphino)propane) in the presence of silver salts AgX (X = SO3CF3 or ClO4), new ionic mononuclear complexes of the formula [Ru(cymene)(Q)L]X, and ionic dinuclear complexes of the formula [{Ru(cymene)(Q)}2L-L]X2 being obtained. The solid-state structures of a number of complexes were confirmed by X-ray crystallographic studies. Their redox properties have been investigated by cyclic voltammetry and controlled potential electrolysis, which, on the basis of their measured RuII/III reversible oxidation potentials, have allowed the ordering of the bidentate acylpyrazolonate ligands according to their electron-donor character and are indicative of a small dependence of the HOMO energy upon the change of the monodentate ligand. This is accounted for by DFT calculations, which show a relevant contribution of acylpyrazolonate ligand orbitals to the HOMOs, whereas that from the monodentate ligand is minor.

Half-sandwich RuII-[9]aneS3 complexes with dicarboxylate ligands: synthesis, characterization and chemical behavior

With the aim of further developing the structure-activity relationship in biologically active half-sandwich Ru(ii)-[9]aneS(3) complexes ([9]aneS(3)=1,4,7-trithiacyclononane), a series of new mono- and dinuclear complexes bearing the chelating dicarboxylate ligands oxalate (ox), malonate (mal) and methylmalonate (mmal), have been synthesized and studied. Treatment of the precursor [Ru([9]aneS(3))(dmso)(3)][CF(3)SO(3)](2) (7) with equivalent amounts of K(2)(dicarb) afforded the corresponding neutral complexes with the general formula [Ru([9]aneS(3))(dmso-S)(eta(2)-dicarb)] (where dicarb=ox (1), mal (2) and mmal (3)), while using half an equivalent of K(2)(ox), the symmetric dimer [{Ru([9]aneS(3))(dmso-S)}(2)(mu-eta(4)-ox)][CF(3)SO(3)](2) (4) was isolated. The reaction of with the oxalato complex fac-[Ru(dmso-S)(3)(dmso-O)(eta(2)-ox)] (9) yielded two asymmetric dimers, namely [{Ru([9]aneS(3))(dmso-S)}(mu-eta(4)-ox){fac-Ru(dmso-S)(3)(CF(3)SO(3))}][CF(3)SO(3)] (5) and [{Ru([9]aneS(3))(dmso-S)}(mu-eta(4)-ox){fac-Ru(dmso-S)(3)(dmso-O)}][CF(3)SO(3)](2) (6), depending on the reaction conditions. All new complexes were structurally characterized, both in solution (by NMR spectroscopy) and in the solid state (by X-ray crystallography). The chemical behavior of the complexes in aqueous solution was studied by UV-Vis and NMR spectroscopy in view of their potential antitumor activity: the monomers partially release a dmso ligand to yield the monofunctional aqua adduct [Ru([9]aneS(3))(eta(2)-dicarb)(H(2)O)], while the dimers rapidly open up the oxalato bridge to give two mononuclear fragments. Splitting of the asymmetric dimers 5 and 6 occurs selectively and the ox moiety remains bonded to the fac-Ru(dmso-S)(3) fragment. A detailed comparison of the structural and chemical features of 1-6 with those of similar dicarboxylate complexes possessing the fac-Ru(dmso-S)(3) fragment in place of Ru([9]aneS(3)) allows us to draw a number of general conclusions on the binding preferences of dicarb ligands on the octahedral Ru(II) center.