Shobhraj Haldar

Exploring the catalytic activity of new water soluble dinuclear copper(II) complexes towards the glycoside hydrolysis

Two water soluble dinuclear copper(II) complexes of a new dinucleating ligand, H3phpda [H3phpda = N,N′-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine-N,N′-dipropionic acid] have been synthesized and characterized for the investigation of catalytic hydrolysis of glycosides. In methanol, the reaction of stoichiometric amounts of Cu(OAc)2·H2O and the ligand H3phpda in the presence of NaOH, produced a new water soluble dinuclear copper(II) complex, [Cu2(phpda)(μ-OAc)] (1). Similarly, the reaction of stoichiometric amounts of Cu(ClO4)2·6H2O and the ligand H3phpda in the presence of NaOH, in methanol, afforded a new water soluble dinuclear copper(II) complex, [Cu2(phpda) (H2O)2](ClO4) (2). Characterizations of the complexes have been performed using various analytical techniques including DFT calculation. The DFT optimized structure of complex 1 shows that two copper(II) centers are in a distorted square pyramidal geometry with Cu⋯Cu separation of 3.677 A. On the other hand, the DFT optimized structure of complex 2 reveals that one copper(II) center adopts a five-coordinate distorted square pyramidal geometry and the other copper(II) center is in a distorted square planar geometry with Cu⋯Cu separation of 3.553 A. Further, the mass spectroscopic analyses of complexes 1 and 2 reconfirm their dimeric nature, even in solution. Glycosidase-like activity of complexes 1 and 2 has been evaluated in aqueous solution at pH ∼ 10.5 by UV-vis spectrophotometric techniques using p-nitrophenyl-α-D-glucopyranoside and p-nitrophenyl-β-D-glucopyranoside as the model substrates. Both complexes are active in catalyzing the hydrolysis of glycosides. DFT calculation has been performed to find the Fukui functions at the metal centers in complexes 1 and 2 to predict the possible metal sites involved in the binding process with substrates during the catalytic hydrolysis reactions.

Inorganic Phosphate and Arsenate within New Tetranuclear Copper and Zinc Complexes: Syntheses, Crystal Structures, Magnetic, Electrochemical, and Thermal Studies

Three, PO43–/HPO42– and AsO43–-incorporated, new tetranuclear complexes of copper(II) and zinc(II) ions have been synthesized and fully characterized. In methanol–water, reactions of H3cpdp (H3cpdp = N,N′-Bis[2-carboxybenzomethyl]-N,N′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) with copper(II) chloride in the presence of either NaOH/Na2HPO4·2H2O or KOH/Na2HAsO4·7H2O lead to the isolation of the tetranuclear complexes Na3[Cu4(cpdp)2(μ4-PO4)](OH)2·14H2O (1) and K2[Cu4(cpdp)2(μ4-AsO4)](OH)·162/3H2O (2), respectively. Similarly, the reaction of H3cpdp with zinc(II) chloride in the presence of NaOH/Na2HPO4·2H2O yields a tetranuclear complex, Na(H3O)2[Zn4(cpdp)2(μ4-HPO4)]Cl3·121/2H2O (3). All complexes are characterized by single-crystal X-ray diffraction and other analytical techniques, such as Fourier transform infrared and UV−vis spectroscopy, thermogravimetric and electrochemical studies. The solid-state molecular framework of each complex contains two monocationic [M2(cpdp)]+ (M = Cu, Zn) units, which are exclusively coordinated to either phosphate/hydrogen phosphate or arsenate groups in a unique mode. All three complexes exhibit a μ4:η1:η1:η1:η1 bridging mode of the PO43–/HPO42–/AsO43– groups, with each bridging among four metal ions. The thermal properties of all three complexes have been investigated by thermogravimetric analysis. Low-temperature magnetic studies of complexes 1 and 2 disclose moderate antiferromagnetic interactions mediated among the copper centers through alkoxide and phosphate/arsenate bridges. Electrochemical studies of complexes 1 and 2 in dimethylformamide using cyclic voltammetry reveal the presence of a fairly assessable one-electron metal-based irreversible reduction and one quasireversible oxidation couple.

Structure and properties of a novel staircase-like decanuclear [CuII10] cluster supported by carbonate and carboxylate bridges

This article describes a novel staircase-like decanuclear copper(II) cluster [CuII10(cpdp)4(CO3)4(CH3OH)2]·3.33CH3OH·7.83H2O (1) (H3cpdp = N,N′-bis[2-carboxybenzomethyl]-N,N′-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol) composed of a pair of [CuII5] pentamers. In methanol, the reaction of H3cpdp with Cu(NO3)2·3H2O in the presence of K2CO3 leads to the isolation of complex 1. This complex has been characterized by various analytical techniques including single crystal X-ray crystallography. Structural analysis reveals that the two [CuII5] pentameric units are bridged together exclusively by two μ2:η2:η1 carbonate groups. Complex 1 shows a rare μ3:η2:η1:η1 bridging coordination mode of four benzoate groups of cpdp3− ligands with each bridging among three copper(II) ions. Complex 1 also represents the first example of a carbonate-coordinated decanuclear copper(II) cluster with any class of bridging or non-bridging ligand. Thermal, magnetic, EPR and electrochemical properties of this complex have been discussed. Variable temperature magnetic measurement discloses the antiferromagnetic interactions among the copper(II) ions. Electrochemical investigation of 1 in methanol solution using cyclic voltammetry reveals the presence of one metal-based quasi-reversible reduction at 870 mV (ΔEp = 190 mV).

A phenoxo–azido assorted Schiff base copper(II) bridged dimer in trace level fluorescence sensing of a pesticide: a DFT supported phenomenon

Abstract A binuclear phenoxo- and azido-bridged copper(II) Schiff base complex has been synthesized along with its mononuclear copper-Schiff base analog. The compounds have been characterized by IR spectroscopy and CHN elemental analysis. The single-crystal structure and variable temperature magnetic properties of the binuclear compound have been studied from the X-ray crystallographic data and superconducting quantum interference device magnetometry, respectively. The synthesized crystalline binuclear complex has interesting spectral features that allow it to act as a spectral sensor toward an organophosphorus pesticide which is a potential environmental toxicant coming to the environment as agricultural waste. Although both the mononuclear and binuclear complexes are suitable as sensors for the organophosphorus, the binuclear complex being crystalline is suitable for attaining structural and mechanistic details of the interaction. Density functional theory calculations and ESI MS analysis of the interactions with the binuclear complex suggest that the binding of organophosphorus substrate with 2 occurs through one copper center.