(4-Amino-pyridine-κN 1)(2,2'-bi-pyridine-κ2 N,N')(2,2':6',2''-terpyridine-κ3 N,N',N'')ruthenium(II) bis-(hexa-fluorido-phosphate) unknown solvate.

The title compound, [Ru(C5H6N2)(C10H8N2)(C15H11N3)](PF6)2 solvent, crystallizes in the triclinic space group P with one dicationic Ru complex, two PF6 - anions, and undefined solvent in the asymmetric unit. The cation and anions are linked via N-H⋯F hydrogen bonding. One PF6 - anion is disordered over two positions, with occupancies 0.634 (8) and 0.366 (8). The solvent, which is located in channels in the crystal, is highly disordered. Reflection contributions from the solvent were added to the calculated structure factors using the SQUEEZE routine [Spek (2015) Acta Cryst. C71, 9-18] of the program PLATON, which determined there to be 59 electrons in 264 Å3 treated this way per unit cell. Because the exact identity and amount of solvent were unknown, no solvent was included in the atom list or mol-ecular formula.

Inhibition of cathepsin activity in a cell-based assay by a light-activated ruthenium compound.

Light-activated inhibition of cathepsin activity was demonstrated in a cell-based assay. Inhibitors of cathepsin K, Cbz-Leu-NHCH2 CN (2) and Cbz-Leu-Ser(OBn)-CN (3), were caged within the complexes cis-[Ru(bpy)2 (2)2 ]Cl2 (4) and cis-[Ru(bpy)2 (3)2 ](BF4 )2 (5) (bpy=2,2'-bipyridine) as 1:1 mixtures of Δ and Λ stereoisomers. Complexes 4 and 5 were characterized by (1) H NMR, IR, and UV/Vis spectroscopies and electrospray mass spectrometry. Photochemical experiments confirm that 4 releases two molecules of 2 upon exposure to visible light for 15 min, whereas release of 3 by 5 requires longer irradiation times. IC50 determinations against purified cathepsin K under light and dark conditions with 4 and 5 confirm that inhibition is enhanced from 35- to 88-fold, respectively, upon irradiation with visible light. No apparent toxicity was observed for 4 in the absence or presence of irradiation in bone marrow macrophage (BMM) or PC3 cells, as determined by MTT assays, at concentrations up to 10 µM. Compound 5 is well tolerated at lower concentrations (<1 µM), but does show growth-inhibitory effects at higher concentrations. Confocal microscopy experiments show that 4 decreases intracellular cathepsin activity in osteoclasts with light activation. These results support the further development of caged nitrile-based inhibitors as chemical tools for investigating spatial aspects of proteolysis within living systems.

Cellular toxicity induced by the photorelease of a caged bioactive molecule: design of a potential dual-action Ru(II) complex.

The series [Ru(tpy)(CH3CN)3](2+) (1), cis-[Ru(tpy)(CH3CN)2Cl](+) (2), and [Ru(tpy)(5CNU)3](2+) (3), where tpy = 2,2':6',2″-terpyridine and 5CNU = 5-cyanouracil, was synthesized, and their photochemical properties were investigated for use as potential photodynamic therapy (PDT) agents. When irradiated with visible light, 1-3 exhibit efficient exchange of the axial CH3CN or 5CNU ligand with H2O solvent molecules. Complexes 1-3 also exhibit photoinitiated binding to DNA when irradiated with λirr ≥ 395 nm light, and DNA binding can be accessed for 2 with λirr > 645 nm, well within the PDT window. Since 3 binds DNA and simultaneously releases biologically active 5CNU, it has the potential to be a dual-action therapeutic agent. Indeed, 3 is cytotoxic upon irradiation with visible light, whereas 1 is not under similar experimental conditions. The lack of toxicity imparted by 1 is explained by the exchange of only one CH3CN ligand in the complex under the irradiation conditions used for the cellular studies. Strategies are being sought to increase the quantum yields of ligand exchange and the cellular penetration of these compounds.

Light activation of a cysteine protease inhibitor: caging of a peptidomimetic nitrile with Ru(II)(bpy)2.

A novel method for caging protease inhibitors is described. The complex [Ru(II)(bpy)(2)(1)(2)](PF(6))(2) (2) was prepared from the nitrile-based peptidomimetic inhibitor Ac-Phe-NHCH(2)CN (1). (1)H NMR, UV-vis, and IR spectroscopic and mass spectrometric data confirmed that 2 equiv of inhibitor 1 bind to Ru(II) through the nitrile functional group. Complex 2 shows excellent stability in aqueous solution in the dark and fast release of 1 upon irradiation with visible light. As a result of binding to the Ru(II) center, the nitriles of complex 2 are caged, and 2 does not act as a potent enzyme inhibitor. However, when 2 is irradiated, it releases 1, which inhibits the cysteine proteases papain and cathepsins B, K and L up to 2 times more potently than 1 alone. Ratios of the IC(50) values in the dark versus in the light ranged from 6:1 to 33:1 for inhibition by 2 against isolated enzymes and in human cell lysates, confirming that a high level of photoinduced enzyme inhibition can be obtained using this method.

[Ru(bpy)2(5-cyanouracil)2]2+ as a potential light-activated dual-action therapeutic agent.

The cation cis-[Ru(bpy)(2)(5CNU)(2)](2+) (bpy = 2,2'-bipyridine; 5CNU = 5-cyanouracil) was synthesized and investigated for use as a potential light-activated dual-action therapeutic agent. The complex undergoes efficient photoinduced 5CNU ligand exchange for solvent water molecules, thus simultaneously releasing biologically active 5CNU and generating [Ru(bpy)(2)(H(2)O)(2)](2+). The latter binds covalently to ds-DNA, such that photolysis results in the generation of 3 equiv of potential therapeutic agents from a single molecule.

Effect of electronic structure on the photoinduced ligand exchange of Ru(II) polypyridine complexes.

The series of complexes [Ru(bpy)(2)(L)](2+), where bpy = 2,2'-bipyridine and L = 3,6-dithiaoctane (bete, 1), 1,2-bis(phenylthio)ethane (bpte, 2), ethylenediamine (en, 3), and 1,2-dianilinoethane (dae, 4), were synthesized, and their photochemistry was investigated. Photolysis experiments show that the bisthioether ligands in 1 and 2 are more easily photosubstituted by chloride ions, bpy, and H(2)O than the corresponding diammine complexes in 3 and 4 to generate the bis-substituted products. Electronic structure calculations show that bond elongation in the lowest energy triplet metal-to-ligand charge transfer ((3)MLCT) state compared to the ground state is greater for complexes containing bisthioether ligands than those with coordinated bidentate nitrogen atoms. This elongation in the excited state is attributed to Ru-S π-bonding character of the highest occupied molecular orbitals, which is not present in the diamine complexes. In the Ru→bpy (3)MLCT state, the lower electron density on the metal-centered highest occupied molecular orbital (HOMO) weakens the Ru-S bond and results in the greater photoreactivity of 1 and 2 relative to that of 3 and 4. The more efficient photoinduced ligand exchange of the complexes possessing thioether ligands results in binding of 1 and 2 to DNA upon irradiation.