Synthesis, characterization, and reactivity of [Ru(bpy)(CH3CN)3(NO2)]PF6, a synthon for [Ru(bpy)(L3)NO2] complexes

Unravelling the kinetics of electro- and photochemical S → O linkage isomerization in Ru(II)-NHC-DMSO complexes utilised for photoinduced substitution reactions

Our recently reported Ru(III)-NHC complexes 1a and 1b were utilized as suitable precursors to prepare new Ru(II)-NHC-(DMSO)2 complexes 2a and 2b. Complexes 2a and 2b reacted with 2,2'-bipyridine to give complexes 3a and 3b, respectively, with substitution of only one of the DMSO ligands. All new complexes were characterized using various spectroscopic techniques and the molecular structures of 2a and 3a were determined using single-crystal X-ray diffraction technique. Complexes 2a, 2b, 3a, and 3b showed the S → O linkage isomerization of the DMSO ligand upon oxidation of the Ru centre from +II to +III, as confirmed by the thermodynamic and kinetic data obtained from cyclic voltammetry experiments. It was observed that in the bisdimethylsulfoxide complexes 2a and 2b, only one DMSO ligand isomerized, which was further corroborated by the computational studies performed to optimize the geometry of the possible linkage isomers of complexes 2a and 3a in +2 and +3 oxidation states, whereas complexes 3a and 3b showed a high preference for the O-bound isomer in the Ru(III) redox state. The role of NHC in stabilizing the mixed isomer in complexes 2a and 2b and preventing the isomerization of both DMSO ligands coordinated to the Ru centre was studied; moreover, NHC provided good solvent compatibility for photochemical S → O isomerization in all the complexes. Taking advantages of the photoinduced linkage isomerization in 2a and 2b, the synthesis of 3a and 3b was revisited and performed using 2a and 2b, respectively, following a photoinduced substitution reaction in the presence of 2,2'-bipyridine. The kinetics of the reversion from the O-bound to S-bound isomer was found to follow the DMSO-assisted intermolecular S → O isomerization pathway.

A half sandwich Ru(II)-p-cymene nitrite complex selectively induces cell death in cisplatin-resistant malignant melanoma cells

The Ru(II)-nitrite complex, Ru4, is explored to release nitric oxide (NO) under acidic conditions and selectively induce a cytotoxic effect towards SK-MEL-28 cisplatin-resistant malignant melanoma cells. These findings suggest that targeting the tumor-associated pHe level could be an effective strategy for the drug function of Ru(II)-nitrite compounds.

Enhancing Control Over Nitric Oxide Photorelease via a Molecular Keypad Lock

Based on Boolean logic, molecular keypad locks secure molecular information, typically with an optical output. Here we investigate a rare example of a molecular keypad lock with a chemical output. To this end, the light-activated release of biologically important nitric oxide from a ruthenium complex is studied, using proton concentration and photon flux as inputs. In a pH-dependent equilibrium, a nitritoruthenium(II) complex is turned into a nitrosylruthenium(II) complex, which releases nitric oxide under irradiation with visible light. The precise prediction of the output nitric oxide concentration as function of the pH and photon flux is achieved with an artificial intelligence approach, namely the adaptive neuro-fuzzy inference system. In this manner an exceptionally high level of control over the output concentration is obtained. Moreover, the provided concept to lock a chemical output as well as the output prediction may be applied to other (photo)release schemes.

Influence of diimine bidentate ligand in the nitrosyl and nitro terpyridine ruthenium complex on the HSA/DNA interaction and antiviral activity

Nitric oxide (NO) acts in different physiological processes, such as blood pressure control, antiparasitic activities, neurotransmission, and antitumor action. Among the exogenous NO donors, ruthenium nitrosyl/nitro complexes are potential candidates for prodrugs, due to their physicochemical properties, such as thermal and physiological pH stability. In this work, we proposed the synthesis and physical characterization of the new nitro terpyridine ruthenium (II) complexes of the type [RuII(L)(NO2)(tpy)]PF6 where tpy = 2,2':6',2″-terpyridine; L = 3,4-diaminobenzoic acid (bdq) or o-phenylenediamine (bd) and evaluation of influence of diimine bidentate ligand NH.NHq-R (R = H or COOH) in the HSA/DNA interaction as well as antiviral activity. The interactions between HSA and new nitro complexes [RuII(L)(NO2)(tpy)]+ were evaluated. The Ka values for the HSA-[RuII(bdq)(NO2)(tpy)]+ is 10 times bigger than HSA-[RuII(bd)(NO2)(tpy)]+. The sites of interaction between HSA and the complexes via synchronous fluorescence suppression indicate that the [RuII(bdq)(NO2)(tpy)]+ is found close to the Trp-241 residue, while the [RuII(bd)(NO2)(tpy)]+ complex is close to Tyr residues. The interaction with fish sperm fs-DNA using direct spectrophotometric titration (Kb) and ethidium bromide replacement (KSV and Kapp) showed weak interaction in the system fs-DNA-[RuII(bdq)(NO)(tpy)]+. Furthermore, fs-DNA-[RuII(bd)(NO2)(tpy)]+ and fs-DNA-[RuII(bd)(NO)(tpy)]3+ system showed higher intercalation constant. Circular dichroism spectra for fs-DNA-[RuII(bd)(NO2)(tpy)]+ and fs-DNA-[RuII(bd)(NO)(tpy)]3+, suggest semi-intercalative accompanied by major groove binding interaction modes. The [RuII(bd)(NO2)(tpy)]+ and [RuII(bd)(NO)(tpy)]3+ inhibit replication of Zika and Chikungunya viruses based in the nitric oxide release under S-nitrosylation reaction with cysteine viral.

Role of the (pseudo)halido ligand in ruthenium(II) p-cymene α-amino acid complexes in speciation, protein reactivity and cytotoxicity

The reactions of the dimeric complexes [RuX2(η6-p-cymene)]2 (X = Br, I, SCN) with L-proline (ProH) and trans-4-hydroxy-L-proline (HypH), in methanol in the presence of NaOH, afforded [RuX(κ2N,O-Pro)(η6-p-cymene)] (X = Br, 1b; I, 1c; SCN, 1d) and [RuX(κ2N,O-Hyp)(η6-p-cymene)] (X = Br, 2b; I, 2c; SCN, 2d), respectively. Alternatively, the one-pot, sequential addition of the appropriate α-amino carboxylate and X- salt to [RuCl2(η6-p-cymene)]2 led to [RuX(κ2N,O-Pro)(η6-p-cymene)] (X = N3, 1e; NO2, 1f; CN 1g) and [Ru(N3)(κ2N,O-Hyp)(η6-p-cymene)] (2e). Complexes [Ru(κ3N,O,O'-O2CCH(NH2)(R)O)(η6-p-cymene)] (R = CH2, 3h; R = CHMe, 4h; R = CH2CH2, 5h) were prepared from the reaction of [RuCl2(η6-p-cymene)]2 with the appropriate α-amino acid and NaOH in refluxing isopropanol. Treatment of the L-serine (SerH2) derivative [RuCl(κ2N,O-SerH)(η6-p-cymene)] (3a) with 1,3,5-triaza-7-phosphaadamantane (PTA) in water at reflux produced [Ru(κ2N,O-Ser)(κP-PTA)(η6-p-cymene)]Cl ([3i]Cl). The products were isolated in good to excellent yields, and were characterized by elemental analysis, IR and multinuclear NMR spectroscopy. The structures of 1f and 2b-e were ascertained by X-ray diffraction studies. The behaviour of the complexes in water and cell culture medium was investigated by multinuclear NMR and UV-Vis spectroscopy, revealing a considerable influence of the monodentate ligand on the aqueous chemistry. Complexes 1d-e, 2d-e, 3h, 4h and [3i]Cl, showing substantial inertness in aqueous media, were assessed for their cytotoxicity towards A2780 and A2780cisR cancer cell lines and the noncancerous HEK 293T cell line. A selection of compounds was also investigated for Ru uptake in A2780 cells and interactions with cytochrome c as a model protein. Combined, these studies provide insights into the previously debated role of the 'leaving' ligand on the biological activity of Ru(II) arene α-amino acid complexes.

1,2,3-Triazolylidene ruthenium(ii)(η6-arene) complexes: synthesis, metallation and reactivity

Three bis(1,2,3-triazolylidene) silver(i) complexes were reacted with [RuCl₂(p-cymene)]₂ and the ruthenium complexes [RCH₂N₂(NMe)C₂Ph]RuCl₂(p-cymene) (R = C₆H₂Me₃4a1, C₆H₂iPr₃4b1, Ph 4c1) were isolated as major products with the minor C(sp²)–H activated products [RCH₂N₂(NMe)C₂C₆H₄]RuCl(p-cymene) (R = C₆H₂Me₃4a2, C₆H₂iPr₃4b2, Ph 4c2) and [(C₆H₄)CH₂N₂(NMe)C₂Ph]RuCl(p-cymene) (4c3).

Searching for new chemotherapies for tropical diseases: ruthenium-clotrimazole complexes display high in vitro activity against Leishmania major and Trypanosoma cruzi and low toxicity toward normal mammalian cells

Eight new ruthenium complexes of clotrimazole (CTZ) with high antiparasitic activity have been synthesized, cis,fac-[Ru(II)Cl(2)(DMSO)(3)(CTZ)] (1), cis,cis,trans-[Ru(II)Cl(2)(DMSO)(2)(CTZ)(2)] (2), Na[Ru(III)Cl(4)(DMSO)(CTZ)] (3), Na[trans-Ru(III)Cl(4)(CTZ)(2)] (4), [Ru(II)(η(6)-p-cymene)Cl(2)(CTZ)] (5), [Ru(II)(η(6)-p-cymene)(bipy)(CTZ)][BF(4)](2) (6), [Ru(II)(η(6)-p-cymene)(en)(CTZ)][BF(4)](2) (7), and [Ru(II)(η(6)-p-cymene)(acac)(CTZ)][BF(4)] (8) (bipy = bipyridine; en = ethlylenediamine; acac = acetylacetonate). The crystal structures of compounds 4-8 are described. Complexes 1-8 are active against promastigotes of Leishmania major and epimastigotes of Trypanosoma cruzi. Most notably, complex 5 increases the activity of CTZ by factors of 110 and 58 against L. major and T. cruzi, with no appreciable toxicity to human osteoblasts, resulting in nanomolar and low micromolar lethal doses and therapeutic indexes of 500 and 75, respectively. In a high-content imaging assay on L. major-infected intraperitoneal mice macrophages, complex 5 showed significant inhibition on the proliferation of intracellular amastigotes (IC(70) = 29 nM), while complex 8 displayed some effect at a higher concentration (IC(40) = 1 μM).