Four new dinuclear CuII complexes were synthesised from two Mannich-base ligands namely 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL1) and 2-[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL2): [Cu2(L1)(OH)](ClO4)2·CH3OH (1), [Cu2(L2)2](ClO4)2·H2O (2), [Cu2(L2)2(NO3)2] (3) and [Cu2(L2)2(OAc)2]·H2O (4) and well characterised. X-ray diffraction analysis of the complexes reveals a Cu⋯Cu distance of 2.9183(13), 2.9604(6), 3.0278(4) and 3.0569(11) Å, respectively. In 1 the metal coordination geometry is intermediate between trigonal bipyramidal (TBP) and square pyramidal (SP) (τ = 0.488), in 2 the geometry is TBP (0.828 and 0.639) and in 3 and 4 is SP (τ = 0.188 and 0.083, respectively). Spectrophotometric investigations to evaluate the catecholase activity of complexes against 3,5-di-tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) in three different solvents (acetonitrile, methanol and DMSO) under completely aerobic conditions reveal that complexes 1-4 are able to oxidise 3,5-DTBC in all the solvents, while TCC can be oxidised only in acetonitrile (kcat = 0.0002-0.02 s-1). Intensive DFT calculations prove an ionic pathway for 1-3 while a unique neutral catalytic cycle for 4. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016.

R SANYAL

P KUNDU

G ZHIGULIN

B GHOSH

S K CHATTOPADHYAY

E ZANGRANDO

D DAS

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

New Journal of Chemistry

A library of 15 dicopper complexes as synthetic analogues of catechol oxidase has been synthesized with the aim to determine the relationship between the electrochemical behavior of the dicopper(II) species in the absence as well as in the presence of 3,5-di-tert-butylcatechol (3,5-DTBC) as model substrate and the catalytic activity, kcat, in DMSO medium. The complexes have been characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis in some cases. Fifteen “end-off” compart- mental ligands have been designed as 1 + 2 Schiff-base condensation product of 2,6-diformyl-4-R-phenol (R = Me, t Bu, and Cl) and five different amines, N-(2-aminoethyl)- piperazine, N-(2-aminoethyl)pyrrolidine, N-(2-aminoethyl)- morpholine, N-(3-aminopropyl)morpholine, and N-(2-aminoethyl)piperidine. Interestingly, in case of the combination of 2,6- diformyl-4-methylphenol and N-(2-aminoethyl)morpholine/N-(3-aminopropyl)morpholine/N-(2-aminoethyl)piperidine 1 + 1 condensation becomes the reality and the ligands are denoted as L21−3 . On reaction of copper(II) nitrate with L21−3 in situ complexes 3, 12, and 13 are formed having general formula Cu2(L21−3 )2(NO3)2. The remaining 12 ligands obtained as 1 + 2 condensation products are denoted as L11−12, which produce complexes having general formula Cu2(L11−12)(NO3)2. Catecholase activity of all 15 complexes has been investigated in DMSO medium using 3,5-DTBC as model substrate. Treatment on the basis of Michaelis−Menten model has been applied for kinetic study, and thereby turnover number, kcat, values have been evaluated. Cyclic voltametric (CV) and differential pulse voltametric (DPV) studies of the complexes in the presence as well as in the absence of 3,5-DTBC have been thoroughly investigated in DMSO medium. From those studies it is evident that oxidation of 3,5-DTBC catalyzed by dicopper(II) complexes proceed via two steps: first, semibenzoquinone followed by benzoquinone with concomitant reduction of CuII to CuI . Our study reveals that apparently there is nearly no linear relationship between kcat and E° values of the complexes. However, a detailed density functional theory (DFT) calculation sheds light on this subject. A very good correlation prevails in terms of the energetics associated with the CuII to CuI reduction process and kcat values, as revealed from the combined theoretical and experimental approach.

Inorganic Chemistry

Relation between the Catalytic Efficiency of the Synthetic Analogues of Catechol Oxidase with Their Electrochemical Property in the Free State and Substrate-Bound State

Four new dicopper(II) complexes of phenol based compartmental ligands, namely [Cu2(L1 H)2(H2O)2(NO3)2] (NO3)2 (1), [Cu2(L2 )(OH)(H2O)(NO3)](NO3) (2), [Cu2(L3 )2(H2O)(NO3)](NO3) (3) and [Cu2(L4 )(H2O)2(NO3)] (NO3)2 (4) [where L1 = 2-formyl-4-methyl-6-(4-(aminomethyl)-piperidine)iminomethyl-phenolato, L2 = 2,6-bis(2-amino-2-methyl-1-propanol)iminomethyl-4-methyl-phenolato, L3 = 2-formyl-4-methyl- 6-(ben- zylamine)iminomethyl-phenolato and L4 = 2,6-bis(2-aminoethylpyridine)iminomethyl-4-methyl-pheno- lato] have been synthesized and structurally characterized. The single crystal X-ray analyses reveal that all four complexes are dinuclear in nature; complexes 2 and 4 comprise of one respective ligand, whereas 1 and 3 are contain two respective ligands, and the Cu–Cu separation in each case is ca. 3.0 Å. All four complexes are soluble in dichloromethane (DCM), methanol, acetonitrile (ACN), dimethylsulfoxide (DMSO), water–methanol (50:50, v/v), and this property has been exploited to access the solvent effect on the catecholase activity of the complexes towards the aerobic oxidation of 3,5-DTBC to 3,5-DTBQ. A UV–Vis spectral study in the different solvents, followed by a kinetic investigation, suggests that the change in spectral behavior follows a similar trend, being dependent on the coordinating ability of the solvent, irrespective of the complex used. The commonly known physical parameters of the solvents, like the dielectric constant, dipole moment, polarity, etc., do not seem to be a key factor in controlling the cat- echolase activity. However, protic solvents are observed to be a better choice than aprotic solvents for the oxidation of 3,5-DTBC.

Polyhedron

Dinuclear copper(II) complexes: Solvent dependent catecholase activity

Radical Pathway in Catecholase Activity with Zinc-Based Model Complexes of Compartmental Ligands

Five dinuclear copper(II) complexes, [Cu2L1(N3)2·2H2O] (1), [Cu2L2(N3)2·2H2O] (2), [Cu2L3(N3)2·2H2O] (3), [Cu2L4(N3)2·2H2O] (4) and [Cu2L5(N3)2·2H2O] (5) of Robson type macrocyclic Schiff-base ligands derived from [2 + 2] condensation of 4-methyl-2,6-diformylphenol with 1,3-diaminopropane (H2L1), 1,2-diaminoethane (H2L2), 1,2-diaminopropane (H2L3), 1,2-diamino-2-methylpropane (H2L4) and 1,2- diaminocyclohexane (H2L5), respectively have been synthesized and characterized. Catecholase activity of those complexes using 3,5-di-tert-butylcatechol as substrate has been investigated in two solvents, methanol and acetonitrile. The role of the solvent and of the steric properties of the macrocyclic ligand of these complexes on their catecholase activity has been examined thoroughly. Acetonitrile is observed to be a better solvent than methanol as far as their catalytic activity is concerned. However, methanol reveals to be a better choice to identify the enzyme–substrate adduct. The investigation also prompted that chelate ring size does affect on the catalytic efficiency: 6-membered ring (as in H2L1) exhibits better activity than its 5-membered counterpart (as in H2L2). The activity of the 5-membered counter parts also depend upon the steric factor. Moreover, the catalytic activity of the complexes is enhanced to a signifi- cant extent by increasing the bulkiness of the substituents on the backbone of macrocyclic H2L2 ligands.

Journal of Molecular Catalysis A: Chemical

Catechol oxidase activity of dinuclear copper(II) complexes of Robson type macrocyclic ligands: Syntheses, X-ray crystal structure, spectroscopic characterization of the adducts and kinetic studies

A series of dinuclear copper(II) complexes has been synthesized with the aim to investigate their applicability as potential structure and function models for the active site of catechol oxidase enzyme. They have been characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis: [Cu2(H2L22 )(OH)(H2O)(NO3)](NO3)3 &middot; 2H2O (1), [Cu(HL14 )(H2O)(NO3)]2(NO3)2 &middot; 2H2O (2), [Cu(L11 )(H2O)(NO3)]2 (3), [Cu2(L23 )(OH)(H2O)2](NO3)2, (4) and [Cu2(L21 )(N3)3] (5) [L1 ) 2-formyl-4-methyl-6R-iminomethyl-phenolato and L2 ) 2,6-bis(R-iminomethyl)-4-methyl-phenolato; for L11 and L21 , R ) N-propylmorpholine; for L22 , R ) N-ethylpiperazine; for L23 , R ) N-ethylpyrrolidine, and for L14 , R ) N-ethylmorpholine]. Dinuclear 1 and 4 possess two &ldquo;end-off&rdquo; compartmental ligands with exogenous &mu;-hydroxido and endogenous &mu;-phenoxido groups leading to intermetallic distances of 2.9794(15) and 2.9435(9) &Aring;, respectively; 2 and 3 are formed by two tridentate compartmental ligands where the copper centers are connected by endogenous phenoxido bridges with Cu-Cu separations of 3.0213(13) and 3.0152(15) &Aring;, respectively; 5 is built by an end-off compartmental ligand having exogenous &mu;-azido and endogenous &mu;-phenoxido groups with a Cu-Cu distance of 3.133(2) &Aring; (mean of two independent molecules). The catecholase activity of all of the complexes has been investigated in acetonitrile and methanol medium by UV-vis spectrophotometric study using 3,5-di-tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) as substrates. In acetonitrile medium, the conversion of 3,5-DTBC to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) catalyzed by 1-5 is observed to proceed via the formation of two enzyme-substrate adducts, ES1 and ES2, detected spectroscopically for the first time. In methanol medium no such enzyme-substrate adduct has been detected, and the 3,5-DTBC to 3,5-DTBQ conversion is observed to be catalyzed by 1-5 very efficiently. The substrate TCC forms an adduct with 2-5 without performing further oxidation to TCQ due to the high reduction potential of TCC (in comparison with 3,5-DTBC). But most interestingly, 1 is observed to be effective even in TCC oxidation, a process never reported earlier. Kinetic experiments have been performed to determine initial rate of reactions (3,5-DTBC as substrate, in methanol medium) and the activity sequence is 1 &gt; 5 &gt; 2 ) 4 &gt; 3. A treatment on the basis of Michaelis-Menten model has been applied for kinetic study, suggesting that all five complexes exhibit very high turnover number, especially 1, which exhibits turnover number or Kcat of 3.24 &times; 104 (h-1 ), which is &sim;3.5 times higher than the most efficient catalyst reported to date for catecholase activity in methanol medium.

Catechol Oxidase Activity of a Series of New Dinuclear Copper(II) Complexes with 3,5-DTBC and TCC as Substrates: Syntheses, X-ray Crystal Structures, Spectroscopic Characterization of the Adducts and Kinetic Studies

Journal	Data powered by TypesetNew Journal of Chemistry
Publisher	Data powered by TypesetRoyal Society of Chemistry
ISSN	1144-0546