Mono- and dinuclear zinc complexes bearing identical bis(thiosemicarbazone) ligand that exhibit alkaline phosphatase-like catalytic reactivity

Mono- and dinuclear zinc(II) complexes bearing bis(thiosemicarbazone) (bTSC) ligand were employed in the cleavage of phosphoester bonds. Comparative kinetic studies combined with theory suggested that the P-O bond cleavage is much accelerated by dinuclear zinc(II) complex in the presence of base. Based on the DFT-optimized structures of the proposed intermediates, it is plausible that (1) the removal of sulfur atoms of bTSC ligand from the zinc center provides two vacant sites for the binding of water (or hydroxide ion) and phosphoester and (2) the H-bonding between water (or hydroxide ion) and phosphoester, through several water molecules, may also assist the P-O bond cleavage and facilitate the nucleophilic attack. The kinetic and catalytic studies on the hydrolysis of phosphoester by dinuclear zinc complex showed a much-enhanced reactivity under basic reaction conditions, reaching over 95% conversion yield within 4 h. The currently presented compounds are arguably one of the faster synthetic Zn-based model performing phosphatase-like activity presented so far.

Factors that determine thione(thiol)-disulfide interconversion in a bis(thiosemicarbazone) copper(ii) complex

Solvent-, acidity-, and redox-responsive thione(thiol)-disulfide interconversion were achieved by a dinuclear copper(ii) complex bearing a bis(thiosemicarbazone) (bTSC) ligand. The role of copper(ii) ion coordination was rationalized by parallel comparison with a bare bTSC ligand and zinc(ii) bTSC complexes under identical reaction conditions.

Partial conversion of thioamide into nitrile in a copper(II) complex of 2,6-diacetylpyridine bis(thiosemicarbazone), a drug prototype for Alzheimer's disease

This work reports the crystal structure of [(Z)-2-((E)-1-{6-[1-({[amino(sulfanidyl-κS)methylidene]amino}imino-κN)ethyl]pyridin-2-yl-κN}ethylidene)-1-cyanohydrazinido-κN(1)]copper(II), [Cu(C11H11N7S)], the first description of a copper(II) complex of 2,6-diacetylpyridine bis(thiosemicarbazone) showing partial conversion of a thioamide group to a nitrile group. The asymmetric ligand coordinates to the metal centre in an N,N',N'',S-tetradentate manner via the pyridine N atom, an imine N atom, the hydrazinide N atom and the sulfanidyl S atom, displaying a square-planar geometry. Ligand coordination results in two five-membered chelate rings and one six-membered chelate ring, and in crystal packing based on N-H···N hydrogen bonds of the cyanohydrazinide and hydrazinecarbothioamidate arms of the ligand. The correlation between the partial conversion upon metal complexation, H2S release and possible effects on the activity of bis(thiosemicarbazone)s as drug prototypes for Alzheimer's disease is also discussed.

Iron and Cobalt Complexes of 2,6-Diacetylpyridine-bis(R-thiosemicarbazone) (R=H, phenyl) Showing Unprecedented Ligand Deviation from Planarity

The syntheses, characterization, and single-crystal X-ray crystal structures are reported for four complexes of iron and cobalt with the pentadentate ligands, 2,6-diacetylpyridinebis(thiosemicarbazone) (H(2)L(1)) and 2,6-diacetylpyridinebis-(phenylthiosemicarbazone) (H(2)L(2)), including a cobalt dimer displaying a deviation from planarity which is unprecedented for this class of ligands and allows the ligand to occupy five positions of a pseudo-octahedral coordination sphere. This dimer reacts with KCN to produce a mononuclear complex of relevance to the active site of cobalt nitrile hydratase.

Pentadentate thiosemicarbazones as versatile chelating systems. A comparative structural study of their metallic complexes

We have prepared some transition and post-transition metal complexes derived from the pentadentate thiosemicarbazone ligand bis(4-N-ethylthiosemicarbazone)-2,6-diacetylpyridine H(2)L(Et), by both chemical and electrochemical procedures. The complexes have been synthesised and fully characterised, including the crystal structures for the ligand H(2)L(Et) and its manganese, cadmium and lead complexes. We have also performed multinuclear (109)Ag, (113)Cd, (119)Sn and (207)Pb studies for silver, cadmium, tin and lead compounds, respectively. Moreover we present here a comparative study on the different structures found for pentadentate thiosemicarbazonate complexes, trying to check the influence of different factors, such as experimental procedure, size of metal, structure of the ligand, and metal oxidation state, on the final structure of the complex formed. Our aim is gaining a better insight into the coordination trends of pentadentate thiosemicarbazone ligands.