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Abstract: We report a suite of coordination‐driven self‐assembled prisms for heterogeneous electrocatalytic oxygen reduction (ORR) differing in the molecular clips linking two porphyrin faces in a cofacial arrangement. ORR activities and selectivities of monomeric CoTPyP along with cofacial prisms Ox‐Co, Oxa‐Co, and Benzo‐Co were probed using cyclic voltammetry and rotating ring‐disk techniques. All species were immobilized as heterogeneous catalysts on glassy carbon electrodes using a Nafion ink method. The selectivities of Ox‐Co, Oxa‐Co, and Benzo‐Co prisms towards H2O as determined by RRDE were 87, 97, and 75 %, respectively. The current density of the Oxa‐Co plateaus at five times that of Pt/C when normalized per Co/Pt. The high synthetic yield (79 %), competitive overpotential (η ≈800 mV) and high selectivity (%H2O ≈97 %) of the Oxa‐Co highlights how self‐assembly can be used to address multi‐electron multi‐proton transformations using polynuclear catalysts. [ABSTRACT FROM AUTHOR]

A reversible Fe3+/Fe2+ redox couple of an azamacrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The FeIII complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E1/2(Fe3+/Fe2+)=317 to −270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe3+/Fe2+ redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 100 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element iron. [ABSTRACT FROM AUTHOR]

The quantum yields of organic fluorophores used as donors in coordination-driven self-assembly often suffer from the heavy atom effect of nearby metal sites. Here, the role of intersystem crossing from a deactivating process to one that delivers emissive triplet states was reversed. A phosphorescent trans bis- N-heterocyclic carbene platinum(II) compound, Pt(dhim)2(C≡C-4-py)2 ( D1; dhim=1,3-dihexyl-2-H-imidazol-2-ylidene), was used along with other linear donors 4,4′-bipyridine ( D2) and 1,4-bis(4-pyridyl ethynyl)benzene ( D3) in self-assembly reactions with Pt(dtbpy)X2 acceptors (dtbpy=4,4′-di-tert-butyl-2,2′-bipyridine) to afford three metallacycles. Photophysical investigations revealed that, although the building blocks used to construct M1 have relatively low quantum yields ( Φ=1.2 and <1 % for D1 and 2, respectively), the metallacycle has a quantum yield of 14 %. This increase reflects a change in radiative rate constant from 3.6×104 s−1 for D1 to 2.1×105 s−1 for M1. [ABSTRACT FROM AUTHOR]

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 CH3NO2/CH2Cl2 (1:1) solvent. Both complexes were isolated with adequate yields as triflate salts and were then characterized using 1H, 13C, and 31P 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. [ABSTRACT FROM AUTHOR]

A suite of three tetraruthenium metallacycles have been obtained from [2+2] self-assemblies between N, N′-Di-(4-pyridyl)-1,4,5,8-naphthalenetetracarbo-xydiimide ( 4) and one of the three dinuclear arene ruthenium clips, (η6- p- iPrC6H4Me)2Ru2( OO∩OO)][OTf]2 ( OO∩OO=oxalate 1, 2,5-dioxydo-1,4-benzoquinonato (dobq) 2, 5,8-dihydroxy-1,4-naphthaquinonato (donq) 3; OTf=triflate). All complexes were isolated in good yield (>85 %) as triflate salts and were fully characterized by using 1H NMR and UV/Vis spectroscopies, and high-resolution electrospray mass spectrometry. A single crystal of the metallarectangle 5 was suitable for X-ray diffraction structural characterization. The biological activities of the metallacycles were determined by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays, establishing their in vitro anticancer properties. Our results show that for the AGC (gastric cancer) cell lines, the cytotoxicity of (donq)-containing SCC 7 exceeds that of cisplatin, which was used as a control. For HCT15 (colon cancer) cell lines, the cytotoxicity is comparable to both cisplatin and doxorubicin. An in vivo hollow fiber model was used to show growth-inhibitory activity against HCT15 and image-based cytometry experiments indicated that 7 induced apoptosis as the mode of cell death. Complex 7 also showed significant antitumor activity for multidrug-resistant HCT15/CLO2 cell lines, for which doxorubicin was ineffective. [ABSTRACT FROM AUTHOR]

The synthesis of six new [2+2] metallarectangles through the coordination-driven self-assembly of octahedral RuII-based acceptors with ambidentate pyridyl-carboxylate donors is described. These molecular rectangles are fully characterized by 1H NMR spectroscopy, high-resolution electrospray mass spectrometry, and single-crystal X-ray diffraction. In each case, despite the possible formation of multiple isomers, based on the relative orientation of the pyridyl and carboxylate groups (head-to-head versus head-to-tail), evidence for the formation of a single preferred ensemble (head-to-tail) was found in the 1H NMR spectra. Furthermore, the cytotoxicities of all of the rectangles were established against A549 (lung), AGS (gastric), HCT-15 (colon), and SK hep 1 (liver) human cancer cell lines. The cytotoxicities of rectangles that contained the 5,8-dihydroxy-1,4-naphthaquinonato bridging moiety between the Ru centers ( 9- 11) were particularly high against AGS cancer cells, with IC50 values that were comparable to that of reference drug cisplatin. [ABSTRACT FROM AUTHOR]