A diphenoxido-bridged dinuclear copper(II) complex, [Cu2L 2(ClO4)2] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)-ethylamino]methyl] phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu2L2(OH)]ClO4 (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm -1. The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu⋯Cu distance from 3.018 Å (avg.) to 2.798 Å (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm-1. Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (kcat = 233.4 h-1) than compound 1 (kcat = 93.6 h-1). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution. © 2012 American Chemical Society.

ASHUTOSH GHOSH

Chemistry

A BISWAS

L K DAS

C DIAZ

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Inorganic Chemistry

A set of tetra- and dinuclear copper(ii) complexes, [Cu4(L1)(μ-O)(OAc)4] (1), [Cu2(L2)2](ClO4)2 (2), [Cu2(L2)2(OAc)2] (3), [Cu2(L2)2(Br)2] (4) and [Cu2(L2)2(Cl)2] (5), were synthesized from two Mannich-base ligands HL1 and HL2, where HL1 = 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol and HL2 = 2-[bis(2-methoxyethyl)aminomethyl]-4-methylphenol. The catalytic efficiency of the complexes for catecholase activity was systematically evaluated by spectrophotometry using 3,5-di-tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) in pure dry acetonitrile (MeCN) and water-MeCN solvent mixtures (10%, 25%, 40% and 50% water). In spite of remarkable rate enhancements by the tetranuclear species in MeCN (kcat = 0.0218 s-1), complex 1 follows a reverse trend in the solvent dependent kinetic study compared to complexes 2-5 with a minimum at 25% water (kcat = 0.0118 s-1) under similar experimental conditions. Theoretical modeling involving the reactions of complexes 1, 3 and 5 provides the counterintuitive rationalization of the apparently dramatic behaviour of these novel catechol models on addition of water to the MeCN solution. More importantly, it vindicates the combination of the contradictory parameters like alcoholysis and hydrolysis as the governing factors for kcat extrema in catalytic pathways. Thus, the reactivity and mechanism of Mannich-base metallocatalysts across water-induced oxidation of catechols is predictable through their nuclearity. © 2017 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

New Journal of Chemistry

Nuclearity dependent solvent contribution to the catechol oxidase activity of novel copper(II) complexes derived from Mannich-base ligand platforms: Synthesis, crystal structure and mechanism

A versatile bioinspired metallocatalyst [Ni2L2(NCS)(Ac)(H2O)0.5(MeOH)0.5]·1.25H2O (HL&nbsp;=&nbsp;2-((E)-(2-(pyridin-2-yl)ethylimino)methyl)-4-chlorophenol) has been synthesized from a Schiff-base ligand and characterized as reported earlier (Sanyal et al., 2016). It portrays catecholase activity as an oxygen dependent enzymatic radical catalysis under completely aerobic conditions (λmax&nbsp;=&nbsp;375&nbsp;nm, ε&nbsp;=&nbsp;1900&nbsp;M−1&nbsp;cm−1) against the model substrate 3,5-di-tert-butylcatechol (3,5-DTBC). Interestingly, Michaelis-Menten analysis of pseudo first-order reaction kinetics establishes that DMF medium provides a better catalytic pathway for catecholase activity (kcat&nbsp;=&nbsp;2.8&nbsp;×&nbsp;10−3&nbsp;s−1) than acetonitrile (9.11&nbsp;×&nbsp;10−4&nbsp;s−1) under excess substrate conditions. Cell viability study, drug uptake assay, reactive oxygen species (ROS) formation, alteration of mitochondrial membrane potential (MMP), apoptosis study and DNA fragmentation demonstrates a significant dose dependent anti-leukemic activity on KG-1A (AML) and K562 (CML) cell lines. Notably, outstanding anti-bacterial property was also observed on multi-drug resistant&nbsp;E. coli&nbsp;and&nbsp;S. aureus&nbsp;bacteria.<h2>Graphical abstract</h2>The biocatalytic promiscuity of a dinickel(II) complex from a&nbsp;<a href="https://www.sciencedirect.com/topics/chemistry/schiff-base">Schiff-base</a>&nbsp;ligand has been explored with special emphasis on catecholase activity and&nbsp;in vitro&nbsp;bioactivity. This “artificial model” of&nbsp;<a href="https://www.sciencedirect.com/topics/chemistry/catechol">catechol</a>&nbsp;<a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/oxidase">oxidase</a>&nbsp;can act as a novel therapeutic agent as demonstrated by its anti-leukemic and&nbsp;<a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/antibacterial-activity">anti-bacterial activity</a>.<figure class="image"><img src="https://ars.els-cdn.com/content/image/1-s2.0-S002016931630500X-fx1.jpg" alt=""></figure>

Inorganica Chimica Acta

Novel bioinspired acetato-bridged dinuclear nickel(II)-Schiff-base complex: Catechol oxidase and in vitro biological activity studies

A versatile bioinspired metallocatalyst [Ni 2 L 2 (NCS)(Ac)(H 2 O) 0.5 (MeOH) 0.5 ]·1.25H 2 O (HL = 2-((E)-(2-(pyridin-2-yl)ethylimino)methyl)-4-chlorophenol) has been synthesized from a Schiff-base ligand and characterized as reported earlier (Sanyal et al., 2016). It portrays catecholase activity as an oxygen dependent enzymatic radical catalysis under completely aerobic conditions (λ max = 375 nm, ε = 1900 M −1 cm −1 ) against the model substrate 3,5-di-tert-butylcatechol (3,5-DTBC). Interestingly, Michaelis-Menten analysis of pseudo first-order reaction kinetics establishes that DMF medium provides a better catalytic pathway for catecholase activity (k cat = 2.8 × 10 −3 s −1 ) than acetonitrile (9.11 × 10 −4 s −1 ) under excess substrate conditions. Cell viability study, drug uptake assay, reactive oxygen species (ROS) formation, alteration of mitochondrial membrane potential (MMP), apoptosis study and DNA fragmentation demonstrates a significant dose dependent anti-leukemic activity on KG-1A (AML) and K562 (CML) cell lines. Notably, outstanding anti-bacterial property was also observed on multi-drug resistant E. coli and S. aureus bacteria. © 2016

Two copper(II) complexes, [Cu2L2(μ1,1-N3)2]·2CH2Cl2 (1) and [CuL(μ1,5-dca)]n (dca = dicyanamide) (2) have been synthesized using a tridentate Schiff base ligand, 1-[(3-methylamino-propylimino)-methyl]-naphthalen-2-ol (HL) and azide or dicyanamide as co-ligand. Both complexes are characterized by elemental analysis, IR and UV-Vis spectroscopy and single crystal X-ray diffraction studies. The coordination geometry around the copper center in complex 1 is as an elongated (4 + 1) square pyramid and that in complex 2 is square planar with the tridentate Schiff base ligand in the basal plane. Complex 1 is a centrosymmetric dimer in which metal centers are connected by the double μ-1,1-azido bridges. On the other hand, complex 2 is a 1D zigzag chain in which metal centers are connected by μ1,5-N(CN)2 ligands. The catecholase like activity for both complexes have been studied by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate. Complex 1 shows higher activity (kcat = 40.8 h-1) than that of complex 2 (27.6 h-1) towards such oxidation reaction. © 2015 Elsevier B.V. All rights reserved.

A dinuclear and a 1D zigzag chain of copper(II) complexes with N2O donor Schiff base ligand and psuedohalides (azide and dicyanamide): Studies on catecholase-like activity

An &ldquo;end-off&rdquo; pentadentate compartmental ligand HL has been synthesized by Mannich base condensation using p-cresol and 2-benzyl amino ethanol and structurally characterized. A dinuclear copper(II) complex, namely [Cu2(L)(&micro;-OH)(H2O)(ClO4)2], has been prepared by treating HL with Cu(ClO4)2 . 6H2O in methanolic solution with the aim to investigate its catalytic promiscuity. Single crystal structural analysis reveals that Cu-Cu separation is of 2.9 &Aring;. Catecholase activity of the complex has been investigated in anhydrous DMSO as well as in DMSO-water mixture with progressive increasing quantity of water up to a 1:1 volume ratio in order to assess the bio compatibility of the catalyst using 3,5-DTBC as model substrate. In anhydrous DMSO the catalytic activity reaches its peak and decreases with increasing the water concentration, a feature most likely due to insolubility of 3,5-DTBQ, the product formed in the catalysis, in water. The complex also shows excellent phosphatase-like activity by exploiting the Lewis acidity, the necessary requirement for that activity, under different pH. Thorough investigation reveals that no activity is observed at pH 6 but the activity increases with increasing pH and attains maximum at pH 9. Variable temperature magnetic study shows that the two Cu centers are antiferromagnetically coupled at low temperature with J value Page 1 of 29 RSC Advances RSC Advances Accepted Manuscript Published on 03 June 2015. Downloaded by University of Birmingham on 04/06/2015 08:15:19. View Article Online DOI: 10.1039/C5RA05776K 2 2 &ndash;78.63&plusmn;1.30cm&minus;1. In acetonitrile medium the complex shows very exciting behavior. A new transformed ligand is generated that has been assigned as a Schiff-base ligand, 2,6-bis-[(2- hydroxy-ethylimino)-methyl]-4-methylphenol. The genesis of the new ligand is a consequence of dealkylation from HL followed by oxidation. This oxidation is counterbalanced by reduction of Cu(II) to Cu(I) as it is evidenced from isolation of [Cu(MeCN)4](ClO4) from the mixture followed by X-ray structural characterization of the species.

RSC Advances

Solvent dependent ligand transformation in a dinuclear copper(ii) complex of a compartmental Mannich-base ligand: synthesis, characterization, bio-relevant catalytic promiscuity and magnetic study

Two new reduced Schiff base ligands, [HL1 = 4-{2-[(pyridin-2-ylmethyl)-amino]-ethylimino}-pentan-2-one and HL2 = 4-[2-(1-pyridin-2-yl-ethylamino)-ethylimino]-pentan-2-one] have been prepared by reduction of the corresponding tetradentate unsymmetrical Schiff bases derived from 1:1: 1 condensation of 1,2-ethanediamine, acetylacetone and pyridine-2-carboxaldehyde/2-acetyl pyridine. Four complexes, [Ni(L1)]ClO4 (1), [Cu(L1)]ClO4 (2), [Ni(L2)]ClO4 (3), and [Cu(L2)]ClO4 (4) with these two reduced Schiff base ligands have been synthesized and structurally characterized by X-ray crystallography. The mono-negative ligands L1 and L2 are chelated in all four complexes through the four donor atoms to form square planar nickel(II) and copper(II) complexes. Structures of 3 and 4 reveal that enantiomeric pairs are crystallized together with opposite chirality in the nitrogen and carbon atoms. The two CuII complexes (2 and 4) exhibit both irreversible reductive (CuII/CuI; Epc, -1.00 and -1.04 V) and oxidative (CuII/CuIII; Epa, +1.22 and +1.17 V, respectively) responses in cyclic voltammetry. The electrochemically generated CuI species for both the complexes are unstable and undergo disproportionation. © 2009 Elsevier Ltd. All rights reserved.

Polyhedron

Nickel(II) and copper(II) complexes of unsymmetrical tetradentate reduced Schiff base ligands

A linear trinuclear Ni-Schiff base complex [Ni 3 (salpen) 2(PhCH 2COO) 2(EtOH)] has been synthesized by combining Ni(ClO 4) 2 · 6H 2O, phenyl acetic acid (C 6H 5CH 2COOH), and the Schiff base ligand, N,N′-bis(salicylidene)-1,3- pentanediamine (H 2salpen). This complex is self-assembled through hydrogen bonding and C-H-π interaction in the solid state to generate a sheet-like architecture, while in organic solvent (CH 2Cl 2), it forms vesicles with a mean diameter of 290 nm and fused vesicles, depending upon the concentration of the solution. These vesicles act as an excellent carrier of dye molecules in CH 2Cl 2. The morphology of the complex has been determined by scanning electron microscopy and transmission electron microscopy experiments, and the encapsulation of dye has been examined by confocal microscopic image and electronic absorption spectra. © 2009 American Chemical Society.

Solvent-assisted formation of vesicles by a self-assembling Ni 3-schiff base complex

Four side-off compartmental ligands L1 –L4 [L1 = N,N¢-ethylenebis(3-formyl-5-methyl-salicylaldimine), L2 = N,N¢-1-methylethylenebis(3-formyl-5-methylsalicylaldimine), L3 = N,N¢-1,1-dimethylethylenebis(3-formyl-5-methylsalicylaldimine) and L4 = N,N¢-cyclohexenebis(3-formyl-5- methylsalicylaldimine)] having two binding sites, N2O2 and O4, have been chosen to synthesize mononuclear and dinuclear manganese(III) complexes with the aim to study their catecholase activity using 3,5-di-tert-butylcatechol (3,5-DTBC) as substrate in the presence of molecular oxygen. In all cases only mononuclear manganese complexes (1–4) were obtained, with manganese coordination taking place at the N2O2 binding site only, irrespective of the amount of manganese salt used. All these complexes have been characterized by routine physico-chemical techniques. Complex MnL2 Cl·4H2O (2) has further been structurally characterized by X-ray single crystal structure analysis. Four dinuclear manganese complexes, 5–8, were obtained after condensing the two pending formyl groups on each ligand (L1 –L4 ) with aniline followed by reaction with MnCl2 to put the second Mn atom onto another N2O2 site. The catalytic activity of all complexes 1–8 has been investigated following the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) with molecular oxygen in two different solvents, methanol and acetonitrile. The study reveals that the catalytic activity is influenced by the solvent and to a significant extent by the backbone of the diamine and the behavior seems to be related mainly to steric rather than electronic factors. Experimental data suggest that a correlation, the lower the E1/2 value the higher the catalytic activity, can be drawn between E1/2 and V max of the complexes in a particular solvent. The EPR measurements suggest that the catalytic property of the complexes is related to the metal center(s) participation rather than to a radical mechanism.

Dalton Transactions

Mono- and dinuclear manganese(III) complexes showing efficient catechol oxidase activity: syntheses, characterization and spectroscopic studies

Mechanistic insight on the catecholase activity of dinuclear copper complexes with distant metal centers

A rational design by hydrothermal methods of a tetrazolate-bridged bimetallic spin-canted antiferromagnet. Synthesis, X-ray structure and magnetic properties of [CoNi(pmtz)4] (Hpmtz− = 5-(pyrimidyl)tetrazole)

Insertion of a hydroxido bridge into a diphenoxido dinuclear copper(II) complex: Drastic change of the magnetic property from strong antiferromagnetic to ferromagnetic and enhancement in the catecholase activity

Journal	Inorganic Chemistry
Publisher	-
ISSN	0020-1669
Open Access	No