Synthesis and Characterization of Self-Assembled Nanoscopic Metallarectangles Capable of Binding Fullerenes with Size-Selective Responses

Self-Assembled Manganese(I)-Based Selenolato-Bridged Tetranuclear Metallorectangles: Host-Guest Interaction, Anticancer, and CO-Releasing Studies

Supramolecular one-step self-assembly of dimanganese decacarbonyl, diaryl diselenide, and linear dipyridyl ligands (L = pyrazine (pz), 4,4'-bipyridine (bpy), and trans-1,2-bis(4-pyridyl)ethylene (bpe)) has resulted in the formation of selenolato-bridged manganese(I)-based metallorectangles. The synthesis of tetranuclear Mn(I)-based metallorectangles [{(CO)₃Mn(μ-SeR)₂Mn(CO)₃}₂(μ-L)₂] (1-6) was facilitated by the oxidative addition of diaryl diselenide to dimanganese decacarbonyl with the simultaneous coordination of linear bidentate pyridyl linker in an orthogonal fashion. Formation of metallorectangles 1-6 was ascertained using IR, UV-vis, NMR spectroscopic techniques, and elemental analyses. The molecular mass of compounds 2, 4, and 6 were determined by ESI-mass spectrometry. Solid-state structural elucidation of 2, 3, and 6 by single-crystal X-ray diffraction methods revealed a rectangular framework wherein selenolato-bridges and pyridyl ligands define the shorter and longer edges, respectively. Also, the guest binding capability of metallorectangles 3 and 5 with different aromatic guests was studied using UV-vis absorption and emission spectrophotometric titration methods that affirmed strong host-guest binding interactions. The formation of the host-guest complex between metallorectangle 3 and pyrene has been explicitly corroborated by the single-crystal X-ray structure of 3•pyrene. Moreover, select metallorectangles 1-4 and 6 were studied to explore their anticancer activity, while CO-releasing ability of metallorectangle 2 was further appraised using equine heart myoglobin assay.

Coordination-Driven Self-Assembly of Triazole-Based Apoptosis-Inducible Metallomacrocycles

Ru(II)-metallomacrocycles containing 4-pyridyl-1,2,3-triazole moiety were realized by coordination-driven self-assembly. All new compounds were characterized by electrospray ionisation mass spectrometry, elemental analysis, and 1H and 13C NMR spectroscopic techniques. The molecular structure of metallomacrocycle 8 was determined by single-crystal X-ray crystallography. The anticancer activities of metallomacrocycles 5-8 were evaluated by cytotoxicity, cell cycle analysis, and related protein expression. Metallomacrocycle 7 showed the highest cytotoxicity in HepG2 human hepatocellular carcinoma cells. In addition, apoptotic HepG2 cells were analyzed when metallomacrocycle 7 was treated. Our results suggest that metallomacrocycle 7 induces liver cancer cell death by increasing apoptosis and cell cycle arrest and that it has potential use as an agent for the treatment of human hepatocellular carcinoma.

Amide-Functionalized Chalcogen-Bridged Flexible Tetranuclear Rhenacycles: Synthesis, Characterization, Solvent Effect on the Structure, and Guest Binding

The synthesis of flexible rhenium(I)-based amide-functionalized chalcogen-bridged tetranuclear metallacycles of general formula [{(CO)₃Re(μ-ER)₂Re(CO)₃}₂(μ-L)₂] (1-8) was achieved by treating rhenium carbonyl with dialkyl/diaryl chalcogenide (RE-ER; E = S and Se) in the presence of ditopic flexible or semiflexible pyridyl ligand with amide functionality (L = N,N'-bis(4-pyridylcarboxamide)-1,2-ethane (bpce) and N,N'-bis(4-(4-pyridylcarboxamide)phenyl)methane (bpcpm)). Compounds 1-8 were formed by multicomponent self-assembly under one-pot reaction conditions via oxidative addition of dialkyl/diaryl chalcogenide to rhenium carbonyl with pyridyl ligands. The resultant metallacyclophanes were characterized using elemental analyses, infrared, ultraviolet-visible, and NMR spectroscopic techniques. Metallacyclophanes 1-3 and 7 were structurally characterized by single-crystal X-ray diffraction methods. The solvent-induced structural change of flexible tetranuclear metallacyclophane 2 was demonstrated by crystallizing 2 in dichloroethane and dimethylformamide. Molecular recognition capabilities of 2 and 7 were studied with few aromatic compounds containing ethereal linkages.

Coordination-Driven Self-Assembly Using Ditopic Pyridyl-Pyrazolyl Donor and p-Cymene Ru(II) Acceptors: [2]Catenane Synthesis and Anticancer Activities

Coordination-driven self-assembly of m-bis[3-(4-pyridyl)pyrazolyl]xylene (L) and [(p-cymene)₂Ru₂(OO∩OO)₂(OTf)₂] (A₁) (OO∩OO = 6,11-dioxido-5,12-naphthacenedione) in methanol resulted in a mixture of [2]catenane 1 and macrocycle 2, and self-assembly in nitromethane resulted in pure macrocycle 2, whereas the coordination-driven self-assembly of L and similar acceptors [(p-cymene)₂Ru₂(OO∩OO)₂(OTf)₂] [OO∩OO = 5,8-dioxido-1,4-naphthoquinonnato (A₂); 2,5-dioxido-1,4-benzoquinonato (A₃); oxalato (A₄)] resulted in the formations of monomeric macrocycles 3-5, respectively. All self-assembled macrocycles were obtained in excellent yields (>90%) as triflate salts and were fully characterized by multinuclear NMR, elemental analysis, and electrospray ionization mass spectrometry (ESI-MS). The structures of [2]catenane 1 and macrocycles 5 were confirmed by single-crystal X-ray diffraction analysis. The X-ray structure of 1 confirmed an edge-to-face interaction between the tetracene moiety in parallel-displaced π-π stacks (3.5 Å), and CH···π (2.5 Å) stabilizes the [2]catenane topology. Macrocycles 2-5 were assessed for anticancer activities using human cancer cell lines of different origins, and the macrocycle 3 was found to exhibit the best inhibitory effect and to do so in a dose-dependent manner. Further examination with the Tali apoptosis assay suggested the growth inhibitory effect of 3 involved the induction of the programmed cell death, and this suggestion was supported by observations of PARP and caspase 3 cleavage after treating cells with 3. In addition, exposure to 3 increased the expression of Bax and repressed the expression of Bcl-2, thus indicating the involvement of macrocycle 3 upstream of Bax and Bcl-2 in the apoptotic signaling pathway. Macrocycle 3 also tended to repress metastasis as evidenced by changes in the transcriptional expressions E- and N-cadherin (markers of metastasis). Furthermore, a stability assay demonstrated macrocycle 3 remained stable at high concentration.

Coordination-Driven Self-Assembly and Anticancer Potency Studies of Ruthenium-Cobalt-Based Heterometallic Rectangles

Three new cobalt-ruthenium heterometallic molecular rectangles, 1-3, were synthesized through the coordination-driven self-assembly of a new cobalt sandwich donor, (η⁵ -Cp)Co[C₄ -trans-Ph₂ (4-Py)₂ ] (L; Cp: cyclopentyl; Py: pyridine), and one of three dinuclear precursors, [(p-cymene)₂ Ru₂ (OO∩OO)₂ Cl₂ ] [OO∩OO: oxalato (A₁ ), 5,8-dioxido-1,4-naphthoquinone (A₂ ), or 6,11-dioxido-5,12-naphthacenedione (A₃ )]. All of the self-assembled architectures were isolated in very good yield (92-94 %) and were fully characterized by spectroscopic analysis; the molecular structures of 2 and 3 were determined by single-crystal X-ray diffraction analysis. The anticancer activities of bimetallic rectangles 1-3 were evaluated with a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, an autophagy assay, and Western blotting. Rectangles 1-3 showed higher cytotoxicity than doxorubicin in AGS human gastric carcinoma cells. In addition, the autophagic activities and apoptotic cell death ratios were increased in AGS cells by treatment with 1-3; the rectangles induced autophagosome formation by promoting LC3-I to LC3-II conversion and apoptotic cell death by increasing caspase-3/7 activity. Our results suggest that rectangles 1-3 induce gastric cancer cell death by modulating autophagy and apoptosis and that they have potential use as agents for the treatment of human gastric cancer.

Anticancer potency studies of coordination driven self-assembled arene–Ru-based metalla-bowls

New tetranuclear cationic metalla-bowls 5–7 with the general formula [Ru4(p-cymene)4(N∩N)2(OO∩OO)2]4+ (N∩N=2,6-bis(N-(4-pyridyl carbamoyl)pyridine, OO∩OO=2,5-dihydroxy-1,4-benzoquinonato (5), OO∩OO=5,8-dioxydo-1,4-naphthaquinonato (6), OO∩OO=hoxonato (7)) were prepared by the reaction of the respective dinuclear ruthenium complexes 2–4 with a bispyridine amide donor ligand 1 in methanol in the presence of AgO3SCF3.These new molecular metalla-bowls were fully characterized by analytical techniques including elemental analysis as well as 1H and 13C NMR and HR-ESI-MS spectroscopy. The structure of metalla-bowl 6 was determined from X-ray crystal diffraction data. A UV/visible study was also carried out for the entire suite of new complexes. As with recent studies of similar arene–Ru complexes, the inhibition of cell growth by metalla-bowls was established against SK-hep-1 (liver cancer), AGS (gastric cancer), and HCT-15 (colorectal cancer) human cancer cell lines. Inhibition of cell growth by 6 was found to be considerably stronger against all cancer cell lines than the anticancer drugs, doxorubicin and cisplatin. In particular, in colorectal cancer cells, expression of the cancer suppressor genes APC and p53 was increased following exposure to 6.

Self-assembled supramolecular hetero-bimetallacycles for anticancer potency by intracellular release

Two new tetracationic hetero-bimetallacycles, compounds 4 and 5, have been constructed from an N,N'-bis(4-(pyridin-4-ylethynyl)phenyl)pyridine-2,6-dicarboxamide ligand (1), and cis-blocked complexes [M(dppf)(OTf)2 ] (dppf=1,1'-bis(diphenylphosphino)ferrocene; OTf=trifluoromethanesulfonate; M=Pd (2), Pt (3)) in CH3 NO2 /CH2 Cl2 (1:1) solvent. Both complexes were isolated with adequate yields as triflate salts and were then characterized using (1) H, (13) C, and (31) P NMR spectroscopy, elemental analysis, UV/Vis spectroscopy, and high-resolution electrospray mass spectrometry (HR-ESMS). The molecular structure of 4 was determined by molecular mechanics force-field calculations. The cytotoxic effect of both new complexes were analyzed against T98G (brain tumor), KB (head and neck cancer), SNU-80 (thyroid cancer), and HEK-293 non-malignant cell lines. The cytotoxicity of complexes 4 and 5 were found to be considerably more effective against cancer cells than reference drug cisplatin. Annexin-V/PI staining, caspase-3/7 activity, and the reduction in mitochondrial membrane potential justify a significant level of apoptosis in complex-treated cells.

Supramolecular architectures with pyridine-amide based ligands: discrete molecular assemblies and their applications

This perspective offers an overview on the recent progress achieved in the design of discrete molecular assemblies utilizing assorted pyridine-amide based ligands.

A new arene–Ru based supramolecular coordination complex for efficient binding and selective sensing of green fluorescent protein

A new synthesized arene di-ruthenium based metallacycle binds to the enhanced green fluorescent protein (EGFP) variant of GFP with high binding affinity and selectivity.