Electrocatalytic Water Oxidation by Mononuclear Copper Complexes of Bis-amide Ligands with N4 Donor: Experimental and Theoretical Investigation.

The present work describes electrocatalytic water oxidation of three monomeric copper complexes [CuII(L1)] (1), [CuII(L2)(H2O)] (2), and [CuII(L3)] (3) with bis-amide tetradentate ligands: L1 = N,N'-(1,2-phenylene)dipicolinamide, L2 = N,N'-(4,5-dimethyl-1,2-phenylene)bis(pyrazine-2-carboxamide), L3 = N,N'-(1,2-phenylene)bis(pyrazine-2-carboxamide), for the production of molecular oxygen by the oxidation of water at pH 13.0. Ligands and all complexes have been synthesized and characterized by single crystal XRD, analytical, and spectroscopic techniques. X-ray crystallographic data show that the ligand coordinates to copper in a dianionic fashion through deprotonation of two -NH protons. Cyclic voltammetry study shows a reversible copper-centered redox couple with one ligand-based oxidation event. The electrocatalytic water oxidation occurs at an onset potential of 1.16 (overpotential, η ≈ 697 mV), 1.2 (η ≈ 737 mV), and 1.23 V (η ≈ 767 mV) for 1, 2, and 3 respectively. A systematic variation of the ligand scaffold has been found to display a profound effect on the rate of electrocatalytic oxygen evolution. The results of the theoretical (density functional theory) studies show the stepwise ligand-centered oxidation process and the formation of the O-O bond during water oxidation passes through the water nucleophilic attack for all the copper complexes. At pH = 13, the turnover frequencies have been experimentally obtained as 88, 1462, and 10 s-1 (peak current measurements) for complexes 1, 2, and 3, respectively. Production of oxygen gas during controlled potential electrolysis was detected by gas chromatography.

Hydrolytically Stable TiIV-Hydrazone-Based Metallodrugs: Protein Interaction and Anticancer Potential.

In this work, three titanium(IV) [TiIV(L1-3)2] (1-3) complexes have been reported using three different tridentate dibasic ONO donor hydrazone ligands, pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L1), furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L2), and thiophene-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L3) tethered with heterocyclic moieties. Elemental analysis, FT-IR, UV-vis, NMR, HR-ESI-MS, and single-crystal X-ray analysis have been used to characterize H2L1-3 and 1-3. In solid structures of 1-3, two ligand molecules with N2O4 donor sets give distorted octahedral geometries to the metal center. The aqueous stability of 1-3 was investigated and well correlated to their perceived pharmacological results. During the investigation, all three complexes were found to be hydrolytically stable in a 90% DMSO-d6/10% D2O (v/v) medium up to 48 h. Furthermore, the interaction of 1-3 with bovine serum albumin (BSA) was tested using fluorescence and absorption techniques. The complexes showed static quenching with a biomolecular quenching constant of Kq ∼ 1013 proposing a high affinity of complexes for BSA. Finally, the anticancer potential of 1-3 was tested against HeLa, A549, and NIH-3T3 cell lines. Among all, 1 with an IC50 value of 11.6 ± 1.1 µM against HeLa cells was found to be the most cytotoxic in the series. Furthermore, it has been found that the compounds induce an apoptotic mode of cell death, which is confirmed by the live cell confocal microscopy and flow cytometry techniques.

Electrocatalytic water oxidation by heteroleptic ruthenium complexes of 2,6-bis(benzimidazolyl)pyridine Scaffold: a mechanistic investigation.

Three monomeric ruthenium complexes with anionic ligands [RuII(L)(L1)(DMSO)][ClO4] (1), [RuII(L)(L2)(DMSO)] [PF6] (2), and [RuII(L)(L3)(DMSO)][PF6] (3) [L = pyrazine carboxylate, L1 = 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridine, L2 = 4,5-dmbimpy = 2,6-bis(5,6-dimethyl-1H-benzo[d]imidazol-2-yl)pyridine, L3 = 4-Fbimpy = 2,6-bis(5-fluoro-1H-benzo[d]imidazol-2-yl)pyridine, DMSO = dimethyl sulfoxide] as electrocatalysts for water oxidation are reported herein. The single crystal X-ray structure of the complexes reveals the presence of a DMSO molecule, which is supposed to be the labile group undergoing water exchange under the experimental condition of electrocatalysis. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) study shows the appearance of the catalytic wave for water oxidation at Ru(IV/V) oxidation. LSV, CV, and bulk electrolysis technique has been used to study the redox properties of the complexes and their electrocatalytic activity. A systematic variation on the ligand scaffold has been found to display a profound effect on the rate of electrocatalytic oxygen evolution. Electrochemical and theoretical (density functional theory) studies support the O-O bond formation during water oxidation passes through water nucleophilic attack (WNA) for all the ruthenium complexes. At pH 1, the maximum turnover frequency (TOFmax) has been experimentally obtained as 17556.25 s-1, 31648.41 s-1, and 39.69 s-1 for complexes 1, 2, and 3, respectively, from the foot of wave analysis (FOWA). The high value of TOFmax for complex 2 indicates its efficiency as an electrocatalyst for water oxidation in a homogeneous medium.

Fucose-containing Abroma augusta mucilage hydrogel as a potential probiotic carrier with prebiotic function.

The mucilaginous polysaccharide from Abroma augusta stem was examined for its physicochemical, thermal, and functional behavior and explored as a carrier for probiotic bacteria. Composed of glucose, galactose, rhamnose, galactouronic acid and fucose, Abroma augusta mucilage (AAM) exhibited shear thinning behavior (following power law equation) and gel like characteristic (showing higher G' value than G″ value). AAM promoted the growth of probiotic strains with positive prebiotic scores of 0.5 ± 0.06 and 0.51 ± 0.05 for Lactobacillus acidophilus and Lactobacillus casei, respectively. Further, probiotic strains were embedded in the AAM matrix followed by freeze-drying with embedding efficiency of >95%. Viscoelastic properties were retained substantially in the rehydrated probiotic-embedded matrix. AAM could protect probiotic bacteria in simulated gastrointestinal conditions, at elevated (80 °C, 20 min) and at low (4 °C, 4 months) temperatures ensuring higher viabilities of embedded probiotic cells. Our findings established potential carrier capabilities of AAM polysaccharides for probiotic bacteria with thickening and prebiotic activity.

Selective cyanide sensing using a Fe(III) complex of pyridoxal-beta alanine Schiff base.

Fluorogenic chemosensors using pyridoxal derivatized ligands as fluorophore is a rapidly growing field of research. Here we report a new Fe(III) complex, [Fe(HBala-pydx)(Bala-pydx)] (H2Bala-pydx is the Schiff base of pyridoxal with beta-alanine), which can serve as a sensitive and selective turn-on fluorescent sensor for the detection of cyanide(CN-) in micromolar concentrations (L.O.D. is 1.134 µM), via the ligand displacement approach, in aqueous-acetonitrile medium. The Fe(III) complex is adequately characterized by analytical and spectroscopic methods along with X-ray crystal structure determination.

Cubane-like tetranuclear Cu(ii) complexes bearing a Cu4O4 core: crystal structure, magnetic properties, DFT calculations and phenoxazinone synthase like activity.

In the present work, two new copper complexes 3a and 3b with a Cu4O4 cubane core are reported. Both complexes are obtained by means of the in situ conversion of the imine functionality of Schiff's base ligands 1a [(E)-4-chloro-2-((thiazol-2-ylimino)methyl)phenol] and 1b [(E)-4-bromo-2-((thiazol-2-ylimino)methyl)phenol] into amino alcohols 2a (4-chloro-2-(hydroxy(thiazol-2-ylamino)methyl)phenol) and 2b (4-bromo-2-(hydroxy(thiazol-2-ylamino)methyl)phenol), respectively. The ligand transformation may be metal assisted and the generated ligands show an interesting mode of coordination in which the alkoxo-O atom binds in a µ3-manner connecting simultaneously three copper centers and forming a Cu4O4 cubane core. The first analysis of single crystal X-ray diffraction studies reveals that both molecules possess a [4 + 2] cubane-type core, and low temperature magnetic measurements show antiferromagnetic behaviour, in agreement with DFT calculations. However, the best fit and DFT calculations point out three pairs of coupling constants, more coherent with a [2 + 2 + 2] situation, in accordance with the fine analysis of structural data. Finally, phenoxazinone synthase activity has been measured for both molecules, finding kcat = 86.3 h-1 for the chloride derivative copper(ii) complex in methanol, whereas the bromide derivative copper(ii) complex displays kcat = 3.4026 × 102 h-1 and 10.289 × 102 h-1 in methanol and DMSO, respectively.