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Design and development of novel, low-cost and efficient electrocatalysts for oxygen evolution reaction (OER) in alkaline media is crucial for lowering the reaction overpotential and thus decreasing the energy input during the water electrolysis process. Herein, we present the synthesis of new 14-membered bis-thiosemicarbazide and bis-isothiosemicarbazide macrocycles and their nickel(II) complexes characterized by spectroscopic techniques ( 1 H and 13 C NMR, IR, UV-vis), electrospray ionization mass spectrometry, single crystal X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and cyclic voltammetry. Finally, the activity of nickel(II) complexes towards OER is reported. NiIILSEt delivered a current density of 10 mA cm -2 at the lowest overpotential of 350 mV with the lowest Tafel slope of 93 mV dec -1 . The high performance of NiIILSEt might be attributed to its high surface area and thus abundant active sites with the observed low charge-transfer resistance enabling the effective current flow through the electrocatalyst. Square-planar coordination geometry and increment in Ni oxidation state are believed to favor its OER performance. Beside high activity towards OER, NiIILSEt demonstrated excellent long-term stability with continuous operation, advocating its possible application in commercial systems.

Quite recently we discovered that copper(II) complexes with isomeric morpholine-thiosemicarbazone hybrid ligands show good cytotoxicity in cancer cells and that the molecular target responsible for this activity might be tubulin. In order to obtain better lead drug candidates, we opted to exploit the power of coordination chemistry to (i) assemble structures with globular shape to better fit the colchicine pocket and (ii) vary the metal ion. We report the synthesis and full characterization of bis-ligand cobalt(III) and iron(III) complexes with 6-morpholinomethyl-2-formylpyridine 4 N -(4-hydroxy-3,5-dimethylphenyl)-3-thiosemicarbazone (HL1), 6-morpholinomethyl-2-acetylpyridine 4 N -(4-hydroxy-3,5-dimethylphenyl)-3-thiosemicarbazone (HL2), and 6-morpholinomethyl-2-formylpyridine 4 N -phenyl-3-thiosemicarbazone (HL3), and mono -ligand nickel(II), zinc(II) and palladium(II) complexes with HL1, namely [Co III (HL 1 )(L 1 )](NO 3 ) 2 (1), [Co III (HL 2 )(L 2 )](NO 3 ) 2 (2), [Co III (HL 3 )(L 3 )](NO 3 ) 2 (3), [Fe III (L 2 ) 2 ]NO 3 (4), [Fe III (HL 3 )(L 3 )](NO 3 ) 2 (5), [Ni II (L 1 )]Cl (6), [Zn(L 1 )Cl] (7) and [Pd II (HL 1 )Cl]Cl (8). We discuss the effect of the metal identity and metal complex stoichiometry on in vitro cytotoxicity and antitubulin activity. The high antiproliferative activity of complex 4 correlated well with inhibition of tubulin polymerization. Insights into the mechanism of antiproliferative activity were supported by experimental results and molecular docking calculations.

The development of copper(II) thiosemicarbazone complexes as potential anticancer agents, possessing dual functionality as inhibitors of R2 ribonucleotide reductase (RNR) and tubulin polymerization by binding at the colchicine site, presents a promising avenue for enhancing therapeutic effectiveness. Herein, we describe the syntheses and physicochemical characterization of four isomeric proligands H 2 L 3 - H 2 L 6 , with the methylmorpholine substituent at pertinent positions of the pyridine ring, along with their corresponding Cu(II) complexes 3 - 6 . Evidently, the position of the morpholine moiety and the copper(II) complex formation have marked effects on the in vitro antiproliferative activity in human uterine sarcoma MES-SA cells and the multidrug-resistant derivative MES-SA/Dx5 cells. Activity correlated strongly with quenching of the tyrosyl radical (Y • ) of mouse R2 RNR protein, inhibition of RNR activity in the cancer cells, and inhibition of tubulin polymerization. Insights into the mechanism of antiproliferative activity, supported by experimental results and molecular modeling calculations, are presented.

Three new thiosemicarbazones (TSCs) HL 1 - HL 3 as triapine analogues bearing a redox-active phenolic moiety at the terminal nitrogen atom were prepared. Reactions of HL 1 - HL 3 with CuCl 2 ·2H 2 O in anoxic methanol afforded three copper(II) complexes, namely, Cu(HL 1 )Cl 2 ( 1 ), [ Cu(L 2 )Cl] ( 2' ), and Cu(HL 3 )Cl 2 ( 3 ), in good yields. Solution speciation studies revealed that the metal-free ligands are stable as HL 1 - HL 3 at pH 7.4, while being air-sensitive in the basic pH range. In dimethyl sulfoxide they exist as a mixture of E and Z isomers. A mechanism of the E/Z isomerization with an inversion at the nitrogen atom of the Schiff base imine bond is proposed. The monocationic complexes [Cu(L 1 - 3 )] + are the most abundant species in aqueous solutions at pH 7.4. Electrochemical and spectroelectrochemical studies of 1 , 2' , and 3 confirmed their redox activity in both the cathodic and the anodic region of potentials. The one-electron reduction was identified as metal-centered by electron paramagnetic resonance spectroelectrochemistry. An electrochemical oxidation pointed out the ligand-centered oxidation, while chemical oxidations of HL 1 and HL 2 as well as 1 and 2' afforded several two-electron and four-electron oxidation products, which were isolated and comprehensively characterized. Complexes 1 and 2' showed an antiproliferative activity in Colo205 and Colo320 cancer cell lines with half-maximal inhibitory concentration values in the low micromolar concentration range, while 3 with the most closely related ligand to triapine displayed the best selectivity for cancer cells versus normal fibroblast cells (MRC-5). HL 1 and 1 in the presence of 1,4-dithiothreitol are as potent inhibitors of mR2 ribonucleotide reductase as triapine.

Thiosemicarbazones continue to attract the interest of researchers as potential anticancer drugs. For example, 3-aminopyridine-2-carboxaldehyde thiosemicarbazone, or triapine, is the most well-known representative of this class of compounds that has entered multiple phase I and II clinical trials. Two new triapine derivatives HL 1 and HL 2 were prepared by condensation reactions of 2-pyridinamidrazone and S-methylisothiosemicarbazidium chloride with 3- N -( tert -butyloxycarbonyl) amino-pyridine-2-carboxaldehyde, followed by a Boc-deprotection procedure. Subsequent reaction of HL 1 and HL 2 with CuCl 2 ·2H 2 O in 1:1 molar ratio in methanol produced the complexes [Cu II (HL 1 )Cl 2 ]·H 2 O ( 1·H 2 O ) and [Cu II (HL 2 )Cl 2 ] ( 2 ). The reaction of HL 2 with Fe(NO 3 ) 3 ∙9H 2 O in 2:1 molar ratio in the presence of triethylamine afforded the complex [Fe III (L 2 ) 2 ]NO 3 ∙0.75H 2 O ( 3∙0.75H 2 O ), in which the isothiosemicarbazone acts as a tridentate monoanionic ligand. The crystal structures of HL 1 , HL 2 and metal complexes 1 and 2 were determined by single crystal X-ray diffraction. The UV-Vis and EPR spectroelectrochemical measurements revealed that complexes 1 and 2 underwent irreversible reduction of Cu(II) with subsequent ligand release, while 3 showed an almost reversible electrochemical reduction in dimethyl sulfoxide (DMSO). Aqueous solution behaviour of HL 1 and 1, as well as of HL 2 and its complex 2 , was monitored as well. Complexes 1 - 3 were tested against ovarian carcinoma cells, as well as noncancerous embryonic kidney cells, in comparison to respective free ligands, triapine and cisplatin. While the free ligands HL 1 and HL 2 were devoid of antiproliferative activity, their respective metal complexes showed remarkable antiproliferative activity in a micromolar concentration range. The activity was not related to the inhibition of ribonucleotide reductase (RNR) R2 protein, but rather to cancer cell homeostasis disturbance-leading to the disruption of cancer cell signalling.