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Steric hindrance, ligand ejection and associated photocytotoxic properties of ruthenium(II) polypyridyl complexes.

ABSTRACT: Two ruthenium(II) polypyridyl complexes were prepared with the {Ru(phen)₂}²⁺ moiety and a third sterically non-hindering bidentate ligand, namely 2,2'-dipyridylamine (dpa) and N-benzyl-2,2'-dipyridylamine (Bndpa). Hence, complexes [Ru(phen)₂(dpa)](PF₆)₂ (1) and [Ru(phen)₂(Bndpa)](PF₆)₂ (2) were characterized and their photochemical behaviour in solution (acetonitrile and water) was subsequently investigated. Compounds 1 and 2, which do not exhibit notably distorted octahedral coordination environments, contrarily to the homoleptic "parent" compound [Ru(phen)₃](PF₆)₂, experience two-step photoejection of the dpa and Bndpa ligand upon irradiation (1050-430 nm) for several hours. DNA-binding studies revealed that compounds 1 and 2 affect the biomolecule differently upon irradiation; while 2 solely modifies its electrophoretic mobility, complex 1 is also capable of cleaving it. In vitro cytotoxicity studies with two cancer-cell lines, namely A549 (lung adenocarcinoma) and A375 (melanoma), showed that both 1 and 2 are not toxic in the dark, while only 1 is significantly cytotoxic if irradiated, 2 remaining non-toxic under these conditions. Light irradiation of the complex cation [Ru(phen)₂(dpa)]²⁺ leads to the generation of transient Ru species that is present in the solution medium for several hours, and that is significantly cytotoxic, ultimately producing non-toxic free dpa and [Ru(phen)(OH₂)₂]²⁺.

SUBMITTER: Herrera-Ramirez P

PROVIDER: S-EPMC10149480 | biostudies-literature | 2023 Jun

REPOSITORIES: biostudies-literature

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Steric hindrance, ligand ejection and associated photocytotoxic properties of ruthenium(II) polypyridyl complexes.

Herrera-Ramírez Piedad P Berger Sarah Alina SA Josa Dana D Aguilà David D Caballero Ana B AB Fontova Pere P Soto-Cerrato Vanessa V Martínez Manuel M Gamez Patrick P

Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry 20230415 4

Two ruthenium(II) polypyridyl complexes were prepared with the {Ru(phen)2}2+ moiety and a third sterically non-hindering bidentate ligand, namely 2,2'-dipyridylamine (dpa) and N-benzyl-2,2'-dipyridylamine (Bndpa). Hence, complexes [Ru(phen)2(dpa)](PF6)2 (1) and [Ru(phen)2(Bndpa)](PF6)2 (2) were characterized and their photochemical behaviour in solution (acetonitrile and water) was subsequently investigated. ...[more]

PMID: 37059909

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Project description:The photophysical and photobiological properties of a new class of cyclometalated ruthenium(II) compounds incorporating π-extended benzo[ h]imidazo[4,5- f]quinoline (IBQ) cyclometalating ligands (C^N) bearing thienyl rings ( n = 1-4, compounds 1-4) were investigated. Their octanol-water partition coefficients (log Po/w) were positive and increased with n. Their absorption and emission energies were red-shifted substantially compared to the analogous Ru(II) diimine (N^N) complexes. They displayed C^N-based intraligand (IL) fluorescence and triplet excited-state absorption that shifted to longer wavelengths with increasing n and N^N-based metal-to-ligand charge transfer (MLCT) phosphorescence that was independent of n. Their photoluminescence lifetimes (τem) ranged from 4-10 ns for 1IL states and 12-18 ns for 3MLCT states. Transient absorption lifetimes (τTA) were 5-8 μs with 355 nm excitation, ascribed to 3IL states that became inaccessible for 1-3 with 532 nm excitation (1-3, τTA = 16-17 ns); the 3IL of 4 only was accessible by lower energy excitation, τTA = 3.8 μs. Complex 4 was nontoxic (EC50 > 300 μM) to SK-MEL-28 melanoma cells and CCD1064-Sk normal skin fibroblasts in the dark, while 3 was selectively cytotoxic to melanoma (EC50= 5.1 μM) only. Compounds 1 and 2 were selective for melanoma cells in the dark, with submicromolar potencies (EC50 = 350-500 nM) and selectivity factors (SFs) around 50. The photocytotoxicities of compounds 1-4 toward melanoma cells were similar, but only compounds 3 and 4 displayed significant phototherapeutic indices (PIs; 3, 43; 4, >1100). The larger cytotoxicities for compounds 1 and 2 were attributed to increased cellular uptake and nuclear accumulation, and possibly related to the DNA-aggregating properties of all four compounds as demonstrated by cell-free gel mobility-shift assays. Together, these results demonstrate a new class of thiophene-containing Ru(II) cyclometalated compounds that contain both highly selective chemotherapeutic agents and extremely potent photocytotoxic agents.

Project description:Ruthenium polypyridyl complexes are good candidates for photoactivated chemotherapy (PACT) provided that they are stable in the dark but efficiently photosubstitute one of their ligands. Here the use of the natural amino acid l-proline as a protecting ligand for ruthenium-based PACT compounds is investigated in the series of complexes Λ-[Ru(bpy)2(l-prol)]PF6 ([1a]PF6; bpy = 2,2'-bipyridine and l-prol = l-proline), Λ-[Ru(bpy)(dmbpy)(l-prol)]PF6 ([2a]PF6 and [2b]PF6; dmbpy = 6,6'-dimethyl-2,2'-bipyridine), and Λ-[Ru(dmbpy)2(l-prol)]PF6 ([3a]PF6). The synthesis of the tris-heteroleptic complex bearing the dissymmetric proline ligand yielded only two of the four possible regioisomers, called [2a]PF6 and [2b]PF6. Both isomers were isolated and characterized by a combination of spectroscopy and density functional theory calculations. The photoreactivity of all four complexes [1a]PF6, [2a]PF6, [2b]PF6, and [3a]PF6 was studied in water (H2O) and acetonitrile (MeCN) using UV-vis spectroscopy, circular dichroism spectroscopy, mass spectrometry, and 1H NMR spectroscopy. In H2O, upon visible-light irradiation in the presence of oxygen, no photosubstitution took place, but the amine of complex [1a]PF6 was photooxidized to an imine. Contrary to expectations, enhancing the steric strain by the addition of two ([2b]PF6) or four ([3a]PF6) methyl substituents did not lead, in phosphate-buffered saline (PBS), to ligand photosubstitution. However, it prevented photoxidation, probably as a consequence of the electron-donating effect of the methyl substituents. In addition, whereas [2b]PF6 was photostable in PBS, [2a]PF6 quantitatively isomerized to [2b]PF6 upon light irradiation. In pure MeCN, [2a]PF6 and [3a]PF6 showed non-selective photosubstitution of both the l-proline and dmbpy ligands, whereas the non-strained complex [1a]PF6 was photostable. Finally, in H2O-MeCN mixtures, [3a]PF6 showed selective photosubstitution of l-proline, thus demonstrating the active role played by the solvent on the photoreactivity of this series of complexes. The role of the solvent polarity and coordination properties on the photochemical properties of polypyridyl complexes is discussed.

Dataset Information

Steric hindrance, ligand ejection and associated photocytotoxic properties of ruthenium(II) polypyridyl complexes.

Publications

Steric hindrance, ligand ejection and associated photocytotoxic properties of ruthenium(II) polypyridyl complexes.

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