Ruthenium(II) Polypyridyl-Based Photocages for an Anticancer Phytochemical Diallyl Sulfide: Comparative Dark and Photoreactivity Studies of Caged and Precursor Uncaged Complexes

The spatiotemporal control over the drug's action offered by ruthenium(II) polypyridyl complexes by the selective activation of the prodrug inside the tumor has beaconed toward much-desired selectivity issues in cancer chemotherapy. The photocaging of anticancer bioactive ligands attached synergistically with cytotoxic Ru(II) polypyridyl cores and selective release thereof in cancer cells are a promising modality for more effective drug action. Diallyl sulfide (DAS) naturally found in garlic has anticancer, antioxidant, and anti-inflammatory activities. Herein, we designed two Ru(II) polypyridyl complexes to cage DAS having a thioether-based donor site. For in-depth photocaging studies, we compared the reactivity of the DAS-caged compounds with the uncaged Ru(II)-complexes with the general formula [Ru(ttp)(NN)(L)]+/2+. Here, in the first series, ttp = p-tolyl terpyridine, NN = phen (1,10-phenanthroline), and L = Cl- (1-Cl) and H2O (1-H2O), while for the second series, NN = dpq (pyrazino[2,3-f][1,10]phenanthroline), and L = Cl- (2-Cl) and H2O (2-H2O). The reaction of DAS with 1-H2O and 2-H2O yielded the caged complexes [Ru(ttp)(NN)(DAS)](PF6)2, i.e., 1-DAS and 2-DAS, respectively. The complexes were structurally characterized by X-ray crystallography, and the solution-state characterization was done by 1H NMR and ESI-MS studies. Photoinduced release of DAS from the Ru(II) core was monitored by 1H NMR and UV-vis spectroscopy. When irradiated with a 470 nm blue LED in DMSO, the photosubstitution quantum yields (Φ) of 0.035 and 0.057 were observed for 1-DAS and 2-DAS, respectively. Intriguing solution-state speciation and kinetic behaviors of the uncaged and caged Ru(II)-complexes emerged from 1H NMR studies in the dark, and they are depicted in this work. The caged 1-DAS and 2-DAS complexes remained mostly structurally intact for a reasonably long period in DMSO. The uncaged 1-Cl and 2-Cl complexes, although did not undergo substitution in only DMSO but in the 10% DMSO/H2O mixture, completely converted to the corresponding DMSO-adduct within 16 h. Toward gaining insights into the reactivity with the biological targets, we observed that 1-Cl upon hydrolysis formed an adduct with 5'-GMP, while a small amount of GSSG-adduct was observed when 1-Cl was reacted with GSH in H2O at 323 K. 1-Cl after hydrolysis reacted with l-methionine, although the rate was slightly slower compared with that with DMSO, suggesting varying reaction kinetics with different sulfur-based linkages. Although 1-H2O reacted with sulfoxide and thioether ligands at room temperature, the rate was much faster at higher temperatures obviously, and thiol-based systems needed higher thermal energy for conjugation. Overall, these studies provide insight for thoughtful design of new generation Ru(II) polypyridyl complexes for caging suitable bioactive organic molecules.

In situ ligand exchange-mediated 0D/1D transformation of a polyoxovanadate

The antimonato-polyoxovanadate {Ni^II(en)₃}₃[VIV15SbIII6O₄₂(H₂O)]·ca.15H₂O was utilized as a synthon for the solvothermal in situ generation of the new compound {Ni^II(phen)₃}₂[{Ni^II(en)₂}VIV15SbIII6O₄₂(H₂O)]·19H₂O, a rearrangement induced by ligand metathesis.

Mixed ligand cobalt(II) picolinate complexes: synthesis, characterization, DNA binding and photocleavage

Complexes of the type [Co(pic)(2)(NN)], where pic = picolinate, NN = dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (4) and 4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f][1,10]-phenanthroline-6,13-dione (bipyridyl-glycoluril) (bpg) (6) have been synthesized and characterized by elemental analysis, IR, UV-vis, NMR and ESI-MS spectroscopy and thermogravimetic analysis (TGA). Their physicochemical properties are compared with previously synthesized complexes, where NN = (H(2)O)(2) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (5). The crystal structures of the complexes 4-6 were solved by single-crystal X-ray diffraction. The complexes 4 and 5 crystallize from a mixture of chloroform and methanol in monoclinic and orthorhombic crystal systems, respectively, whereas complex 6 crystallizes from dimethyl sulfoxide (DMSO) in a tetragonal crystal system. The coordination sphere consists of two oxygen atoms and two nitrogen atoms from the two picolinates and two nitrogen atoms from the dpq, dppz or bpg ligand, respectively. Co(ii)/Co(iii) oxidation potentials have been determined by cyclic voltammetry. The DNA binding of complexes 1-5 has been investigated using thermal melting, fluorescence quenching and viscosity measurements, which indicate the partial intercalation of complex 5 with an apparent binding constant (k(app)) of 8.3 × 10(5) M(-1). DNA cleavage studies of complexes 1-5 have been investigated using gel electrophoresis in the presence of H(2)O(2) as an oxidizing agent and also by photoirradiation at 365 nm. The mechanistic investigations suggest that singlet oxygen ((1)O(2)) is the major species involved in the DNA cleavage by these complexes. The structures of complexes 2-6 were optimized with density functional theory (DFT) method (B3LYP/6-31G(d,p)). The low vertical ionization potential values indicate photoredox pathways for the DNA cleavage activity by complexes 4 and 5, which is corroborated by DNA cleavage experiments.