Synthesis, characterization and structural analysis of complexes from 2,2':6',2''-terpyridine derivatives with transition metals

The synthesis and structural characterization of three families of coordination complexes synthesized from 4'-phenyl-2,2':6',2''-terpyridine (8, Ph-TPY), 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine (9, ClPh-TPY) and 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine (10, MeOPh-TPY) ligands with the divalent metals Co2+, Fe2+, Mn2+ and Ni2+ are reported. The compounds were synthesized from a 1:2 mixture of the metal and ligand, resulting in a series of complexes with the general formula [M(R-TPY)2](ClO4)2 (where M = Co2+, Fe2+, Mn2+ and Ni2+, and R-TPY = Ph-TPY, ClPh-TPY and MeOPh-TPY). The general formula and structural and supramolecular features were determinated by single-crystal X-ray diffraction for bis(4'-phenyl-2,2':6',2''-terpyridine)nickel(II) bis(perchlorate), [Ni(C21H15N3)2](ClO4)2 or [Ni(Ph-TPY)2](ClO4)2, bis[4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine]manganese(II) bis(perchlorate), [Mn(C22H17N3O)2](ClO4)2 or [Mn(MeOPh-TPY)2](ClO4)2, and bis(4'-phenyl-2,2':6',2''-terpyridine)manganese(II) bis(perchlorate), [Mn(C21H15N3)2](ClO4)2 or [Mn(Ph-TPY)2](ClO4)2. In all three cases, the complexes present distorted octahedral coordination polyhedra and the crystal packing is determined mainly by weak C-H...π interactions. All the compounds (except for the Ni derivatives, for which FT-IR, UV-Vis and thermal analysis are reported) were fully characterized by spectroscopic (FT-IR, UV-Vis and NMR spectroscopy) and thermal (TGA-DSC, thermogravimetric analysis-differential scanning calorimetry) methods.

A Redox-Active Tetrazine-Based Pincer Ligand for the Reduction of N-Oxyanions Using a Redox-Inert Metal

The reaction chemistry of the bis-tetrazinyl pyridine ligand (btzp) towards nitrogen oxyanions coordinated to zinc is studied in order to explore the reduction of the NO_x ^- substrates with a redox-active ligand in the absence of redox activity at the metal. Following syntheses and characterization of (btzp)ZnX₂ for X=Cl, NO₃ and NO₂ , featuring O-Zn linkage of both nitrogen oxyanions, it is shown that a silylating agent selectively delivers silyl substituents to tetrazine nitrogens, without reductive deoxygenation of NO_x ^-1 . A new synthesis of the highly hydrogenated H₄ btzp, containing two dihydrotetrazine reductants is described as is the synthesis and characterization of (H₄ btzp)ZnX₂ for X=Cl and NO₃ , both of which show considerable hydrogen bonding potential of the dihydrotetrazine ring NH groups. The (H₄ btzp)ZnCl₂ complex does not bind zinc in the pincer pocket, but instead H₄ btzp becomes a bridge between neighboring atoms through tetrazine nitrogen atoms, forming a polymeric chain. The reaction of AgNO₂ with (H₄ btzp)ZnCl₂ is shown to proceed with fast nitrite deoxygenation, yielding water and free NO. Half of the H₄ btzp reducing equivalents form Ag⁰ and thus the chloride ligand remains coordinated to the zinc metal center to yield (btzp)ZnCl₂ . To compare with AgNO₂ , experiments of (H₄ btzp)ZnCl₂ with NaNO₂ result in salt metathesis between chloride and nitrite, highlighting the importance of a redox-active cation in the reduction of nitrite to NO.

Targeting G-quadruplex structures with Zn(II) terpyridine derivatives: a SAR study

Based on the ability of terpyridines to react with G-quadruplex DNA (G4) structures along with the interest aroused by Zn as an essential metal centre in many biological processes, we have synthesized and characterized six Zn chloride or nitrate complexes containing terpyridine ligands with different 4'-substituents. In addition, we have studied their interaction with G4 and their cytotoxicity. Our experimental results revealed that the leaving group exerts a strong influence on the cytotoxicity, since the complexes bearing chloride were more cytotoxic than their nitrate analogues and an effect of the terpyridine ligand was also observed. The thermal stabilization profiles showed that the greatest stabilization of hybrid G4, Tel22, was observed for the Zn complexes bearing the terpyridine ligand that contained one or two methylated 4-(imidazol-1-yl)phenyl substituents, 3Cl and 3(L)2, respectively, probably due to their extra positive charge. Stability and aquation studies for these complexes were carried out and no ligand release was detected. Complexes 3Cl and 3(L)2 were successfully internalized by SW480 cells and they seemed to be localized mainly in the nucleolus. The highest cytotoxicity, G4 selectivity and G4 affinity determined by fluorescence and ITC experiments, and subcellular localization quantified by ICP-MS measurements, rendered 3Cl a very interesting complex from a biological standpoint.

Raising the bar in anticancer therapy: recent advances in, and perspectives on, telomerase inhibitors

Telomerase is a ribonucleic reverse transcriptase enzyme that uses an integral RNA component as a template to add tandem telomeric DNA repeats, TTAGGG, at the 3' end of the chromosomes. 85-90% of human tumors and their derived cell lines predominantly express high levels of telomerase, therefore contributing to cancer cell development. However, in normal cells, telomerase activity is almost always absent except in germ cells and stem cells. This differential expression has been exploited to develop highly specific and potent cancer therapeutics. In this review, we outline recent advances in the development of telomerase inhibitors as anticancer agents.

Synthesis, Characterization, and Cytotoxicity of the Cobalt (III) Complex with N,N-Diethyl-4-(2,2':6',2''-terpyridin-4'-yl)aniline

A cobalt(III) complex, [Co(L)₂ ](ClO₄ )₃ (1), in which the ligand L was N,N-diethyl-4-(2,2':6',2''-terpyridin-4'-yl)aniline (L), was synthesized and fully characterized. This new cobalt(III) complex 1 exhibited selective cytotoxicity against HeLa, T-24, A549, MGC80-3, HepG2, and SK-OV-3 cells with IC₅₀ values in the micromolar range (0.52 - 4.33 μm), and it exhibited low cytotoxicity against normal HL-7702 cells. The complex 1 was the most potent against the T-24 cells. It was found that 1 could cause the cell cycle arrest in G1 phase, and it exerted its antitumor activity mainly via disruption of mitochondrial function.

Synthesis, characterization, in vitro cytotoxicity, in silico ADMET analysis and interaction studies of 5-dithiocarbamato-1,3,4-thiadiazole-2-thiol and its zinc(ii) complex with human serum albumin: combined spectroscopy and molecular docking investigations

The binding site of new complex Zn(ii) of 5-dithiocarbamato-1,3,4-thiadiazole-2-thiol and HAS.