Heterobridged dinuclear, tetranuclear, dinuclear-based 1-d, and heptanuclear-based 1-D complexes of copper(II) derived from a dinucleating ligand: syntheses, structures, magnetochemistry, spectroscopy, and catecholase activity

A very rare fluorescent chemosensor of zinc(II) exhibiting AIEE, ESIPT and TICT: Spectroscopic, crystallographic and theoretical exploration

The basic systems in this study are HL (1; 1:2 condensation product of 2,6-diformyl-4-ethylphenol and o-anisidine) and its ZnII and CdII complexes of composition [ZnII(LH)Cl2]·CH3OH (2) and [CdII(LH)Cl2] (3), all of which are synthesized and characterized by CHN elemental analyses, single crystal X-ray crystallography, powder X-ray diffraction (PXRD) and fourier transform infrared (FT-IR) spectrum. It has been established from the following experimental and theoretical studies that 1 is a fluorescent turn on sensor of ZnII ion and it exhibits all of excited state intramolecular proton transfer (ESIPT), photoinduced electron transfer (PET), twisted intramolecular charge transfer (TICT) and aggregation induced enhanced emission (AIEE): (i) Detailed absorption and emission (steady state / time resolved) studies in various single solvents, in solvent mixtures, with pH variation, with various single metal ions, with mixtures of metal ions, on varying temperature and on varying viscosity; (ii) dynamic light scattering (DLS) and scanning electron microscopy (SEM) in solvent mixtures; (iii) density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations in ground and excites states of 1-3. It is shown that 1 can be efficaciously applied in inkless writing with the "write - erase - write" facility. The mechanisms/reasons of the observed properties have been addressed. The difference in fluorescence of ZnII and CdII complexes, unusual case of crystal structures of probe and complexes with ZnII and CdII, unusual features in the structures of 2 and 3 as well as a structure-property correlation have been discussed.

Enzymatic Substrate Inhibition in Metal Free Catecholase Activity

The catecholase activities were routinely modeled using transition metal complexes as catalyst and in some case basic pH were used as a reaction condition. In this article, the catalytic aerobic oxidation of proxy substrate 3,5-di-tert-butylcatechol (DTBC) in methanol using triethylamine/diethylamine as catalyst was demonstrated as a functional mimic of catecholase activity. The kinetic manifestation of DTBC oxidation was explained as enzymatic substrate inhibition pattern in Michaelis-Menten kinetic model. The mechanistic insight of the aerobic oxidation of DTBC was further validated using various spectroscopic techniques and DFT methods.

Aerial Oxidation of Phenol/Catechol in the Presence of Catalytic Amounts of [(Cl)2Mn(RCOOET)], RCOOET= Ethyl-5-Methyl-1-(((6-Methyl-3-Nitropyridin-2-yl)Amino)Methyl)-1H-Pyrazole-3-Carboxylate

In this work, we report on the catalytic activity of a manganese complex [(Cl)2Mn(RCOOET)], where RCOOET is ethyl-5-methyl-1-(((6-methyl-3-nitropyridin-2-yl)amino)methyl)-1H-pyrazole-3-carboxylate, in the oxidation of phenol or catechol by atmospheric oxygen to form o-quinone. The [(Cl)2Mn(RCOOET)] catalyzes the oxidation of catechol at a rate of 3.74 µmol L−1 min−1 in tetrahydrofuran (THF), in a similar manner to catecholase or tyrosinase.

A metal complex based fluorescent chemodosimeter for selective detection of 2,4-dinitrophenol and picric acid in aqueous medium

The work in this report describes the syntheses, characterization, crystal structures, absorption and emission spectra and DFT calculations of three dizinc(II) compounds of composition [ZnII2L(μ1,1-N3)(N3)2] (1), [Zn2L'(2,4-dinitrophenolate)2] (2) and [Zn2L'(picrate)2]...

Proton controlled synthesis of two dicopper(II) complexes and their magnetic and biomimetic catalytic studies together with probing the binding mode of the substrate to the metal center

This paper describes the synthesis, and structural and spectroscopic characterizations of two doubly bridged dicopper(II) complexes, [Cu₂(μ-H₂L)(μ-OMe)](ClO₄)₄·2H₂O (1) and [Cu₂(μ-L)(μ-OH)](ClO₄)₂ (2), with a binucleating ligand (HL) derived from the Schiff base condensation of DFMP and N,N-dimethyldipropylenetriamine, and their biomimetic catalytic activities were related to CAO and phenoxazinone synthase using 3,5-di-tert-butylcatechol and o-aminophenol (OAPH), respectively, as model substrates. Structural studies reveal that the major differences in these structures appear to be from the distinct roles of the tertiary amine groups of the ligands, which are protonated in 1, whereas it coordinates the metal centers in 2. Magnetic studies disclose that two copper(II) centers are strongly antiferromagnetically coupled with slightly different J values, which is further interpreted and discussed. They exhibited very different biomimetic catalytic activities; whereas 2 is an efficient catalyst, complex 1 showed somewhat lower substrate oxidation. The higher reactivity in 2 is rationalized by the strong involvement of the tertiary amine group of the Schiff base ligand, where the substrate oxidation is favored because of the transfer of protons from the substrate to the tertiary amine group, showing the importance of the functional groups in proximity to the bimetallic active site. Emphasis was also given to probing the binding mode of the substrate using an electronically deficient tetrabromomocatechol (Br₄CatH₂) and the isolated compound [Cu₆(μ-HL)₂(μ-OH)₂(Br₄Cat)₄](NO₃)₂·4H₂O (3) which suggests that monodentate asymmetric binding of 3,5-di-tert-butylcatechol and OAPH occurs during the course of the catalytic reaction.

Exploring the Noncovalent Interactions of the Dinuclear Cu(II) Schiff Base Complex with Bovine Serum Albumin and Cell Viability against the SiHa Cancer Cell Line

In the present study, a dinuclear bis(μ-acetate) dicopper(II) complex [Cu₂L₂(μ_1.1-CH₃COO^-)₂] has been synthesized from a tridentate NNO Schiff Base ligand L (L = 2,4-dibromo-6-((3-(methylamino)propylimino)methyl)phenol) and characterized by elemental, ultraviolet-visible (UV-vis), Fourier transform infrared (FTIR), ¹H NMR, and electrospray ionization-mass spectrometry (ESI-MS) spectroscopic studies. The single-crystal X-ray structure, different noncovalent interactions, Hirshfeld surface analysis, and density functional theory (DFT) studies of the dinuclear complex were determined by crystallographic computational studies. The structural study exposed that the complex consists of the penta-coordinated double μ_1.1-acetato-bridged dinuclear units of Cu(II), and it is a centrosymmetric dimer in which the center of inversion lies at the midpoint of two Cu(II) ions. Hirshfeld surface and DFT studies pointed out the probable potentiality of the crystal in prospective binding with the protein. This was experimentally verified by carrying out the binding interaction studies against bovine serum albumin (BSA) protein using various spectroscopic methods. It was observed that the copper(II) complex could strongly bind to BSA and could quench the intrinsic fluorescence of BSA. Further, the studied complex was appraised for cell viability studies against SiHa cancer cells. It is observed that cell viability increases with time, demonstrating the biocompatible nature of the complex.

Structure, DFT studies and evaluation of catechol oxidase (CO) mimic activity of mononuclear Co(II) complexes derived from aminoalcohols: an experimental and theoretical approach

The impetus to modeling of enzyme mimics comes from their potential to provide insight to the alternate mechanistic pathways of the native enzymes. The present study demonstrates the syntheses and characterization of two different cobalt(II) complexes, [Co(pdm)(Phen)Cl]Cl·H₂O (1) and [Co(pmmH)₂(SCN)₂] (2) with the aminoalcohol ligands such as pyridine-2,6-dimethanol (pdmH₂) or 2-pyridinemonomethanol (pmmH) and their assessment as catechol oxidase (CO) enzyme mimic. Single Crystal X-ray diffraction and powder X-ray diffraction data suggest the octahedral environment around the Co(II) ion and the complexes form extensive 1D or 2D propagating network as a result of non-covalent interactions (O···H and C-H···π). TD-DFT calculations were used to explain the spectral bands obtained during the UV-Vis absorption studies and it is ascertained that the transitions were mainly of the intra-ligand charge transfer (ILCT) type. The catecholase biomimetic catalytic activity of the synthesized complexes has been investigated in detail and the kinetics is also performed. The results obtained show that both the complexes catalyze the aerobic oxidation of catechol to the corresponding o-quinone. The K_cat value for 1 is 106.99 h^‒1 and for 2 is 90.32 h^‒1 in methanol. It may be mentioned here that 1 and 2 are effective catalysts, with the order of activity being 1 > 2. The order of enzymatic activity is well justified by CV and DFT studies.Communicated by Ramaswamy H. Sarma.

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H₃L and H₅L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu₄(HL²⁻)₂(N₃)₄]·4CH₃OH·56H₂O (1) and [Cu₄(L³⁻)₂(OH)₂(H₂O)₂] (2), dinuclear [Cu₂(H₃L1²⁻)(N₃)(H₂O)(NO₃)] (3), polynuclear {[Cu₂(H₃L1²⁻)(H₂O)(BF₄)(N₃)]·H₂O}_n (4), heptanuclear [Cu₇(H₃L1²⁻)₂(O)₂(C₆H₅CO₂)₆]·6CH₃OH·44H₂O (5), and decanuclear [Cu₁₀(H₃L1²⁻)₄(O)₂(OH)₂(C₆H₅CO₂)₄] (C₆H₅CO₂)₂·20H₂O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one μ-phenolate oxygen atom from HL²⁻ or H₃L1²⁻, and one μ-1,1-azido (N₃⁻) ion and in 2, 5, and 6 by μ-phenoxide oxygen of L³⁻ or H₃L1²⁻ and μ-O²⁻ or μ₃-O²⁻ ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu₂] units are antiferromagnetically coupled, with J ranging from −177 to −278 cm⁻¹.

Dinuclear Copper(II) Complexes with Schiff Bases Derived from 2-Hydroxy-5-Methylisophthalaldehyde and Histamine or 2-(2-Aminoethyl)pyridine and Their Application as Magnetic and Fluorescent Materials in Thin Film Deposition

Two Cu(II) complexes, 1 and 2, with tridentate Schiff bases derived from 2-hydroxy-5-methylisophthalaldehyde and histamine HL1 or 2-(2-aminoethyl)pyridine HL2, respectively, were obtained and characterized by X-ray crystallography, spectroscopic (UV-vis, fluorescence, IR, and EPR), magnetic, and thermal methods. Despite the fact that the chelate formed by the NNO ligand donors (C26-C25H2-C24H2-N23=C23H-C22-C19Ph(O1)-C2(Ph)-C3H=N3-C4H2-C5H2-C6 fragment) are identical, as well as the synthesis of Cu(II) complexes (Cu:L = 2:1 molar ratio) was performed in the same manner, the structures of the complexes differ significantly. The complex 1, {[Cu2(L1)Cl2]2[CuCl4]}·2MeCN·2H2O, consists of [Cu2(L1)Cl2]+ units in which Cu(II) ions are bridged by the HL1 ligand oxygen and each of these Cu(II) ions is connected with Cu(II) ions of the next dimeric unit via two bridging Cl- ions to form a chain structure. In the dinuclear [Cu2(L2)Cl3]0.5MeCN complex 2, each Cu(II) is asymmetrically bridged by the ligand oxygen and chloride anions, whereas the remaining chloride anions are apically bound to Cu(II) cations. In contrast to the complex 1, the square-pyramidal geometry of the both Cu(II) centers is strongly distorted. The magnetic study revealed that antiferromagnetic interactions in the complex 2 are much stronger than in the complex 1, which was corresponded with magneto-structural examination. Thin layers of the studied Cu(II) complexes were deposited on Si(111) by the spin coating method and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), and fluorescence spectroscopy. The Cu(II) complexes and their thin layers exhibited fluorescence between 489-509 nm and 460-464 nm for the compounds and the layers, respectively. Additionally, DFT calculations were performed to explain the structures and electronic spectral properties of the ligands.

Exploring a new dinuclear Fe(iii) complex for the fixation of atmospheric CO2 and optical recognition of nano-molar levels of Zn2+ ions

A dinuclear Fe(iii) complex (F1) of an imine derivative (L1) derived from 3-ethoxy-2-hydroxy-benzaldehyde and hydrazine, structurally characterised via single crystal X-ray studies, is employed for the catalytic conversion of epoxides to cyclic carbonates utilizing carbon dioxide. In addition, F1 is employed for the selective optical recognition of nano-molar levels of Zn²⁺ (42.23 nM) via a metal displacement approach. The Job plot reveals interactions between F1 and Zn²⁺ at a 1 : 3 molar ratio with an association constant of 7.71 × 10⁴ M⁻¹. Studies on the catecholase-like activity of F1 reveal a k_cat value of 4.42 × 10³ h⁻¹.

A new Fe(iii) complex (F1), structurally characterised using single crystal X-ray studies, was explored for CO₂ fixation, Zn²⁺ recognition and catecholase activity.

A novel Cu(II) distorted cubane complex containing Cu4O4 core as the first tetranuclear catalyst for temperature dependent oxidation of 3,5-di-tert-butyl catechol and in interaction with DNA & protein (BSA)

The tri-dentate Schiff base ligand 3-(2-hydroxyethylimino)-1-phenylbut-1-en-1-ol (L) produced the tetra-nuclear Cu(II) distorted cubane complex which contain Cu₄O₄ core, upon reaction with Cu(II)acetate.H₂O. The complex was structurally characterized by X-ray crystallography and found that, in this tetrameric and tetra-nuclear distorted cubane structure, each two-fold deprotonated Schiff base ligand coordinated to a Cu(II) center with their alcoholic oxygens and imine nitrogens and formed six and five-membered chelate rings. At the same time, each ligand bridged to a neighboring Cu(II) atom by its alcoholic oxygen, thus the metal centers became penta-coordinated. The copper(II) complex with μ-ɳ²-hydroxo bridges and Cu….Cu distance about 3 Å was structurally similar to the active site of natural catechol oxidase enzyme and exhibited excellent catecholase activity in aerobic oxidation of 3,5-di-tert-butyl catechol to its o-quinone. The kinetics and mechanism of the oxidation of 3, 5-DTBCH₂ catalyzed by [CuL]₄ complex, were studied at four different temperatures from 283 to 313K by UV-Vis spectroscopy. Interaction of [CuL]₄ complex with FS-DNA was investigated by UV-Vis and fluorescence spectroscopy, viscosity measurements, cyclic voltammetry (CV), circular dichroism (CD) and agarose gel electrophoresis. The main mode of binding of the complexes with DNA was intercalation. The interaction between [CuL]₄ complex and bovine serum albumin (BSA) was studied by UV-Vis, fluorescence and synchronous fluorescence spectroscopic techniques. The results indicated a high binding affinity of the complex to BSA. In vitro anticancer activity of the complex was evaluated against A549, Jurkat and Ragi cell lines by MTT assay. The complex was remarkably active against the cell lines and can be a good candidate for an anticancer drug. Theoretical docking studies were performed to further investigate the DNA and BSA binding interactions.

Exploring solvent dependent catecholase activity in transition metal complexes: an experimental and theoretical approach

Four coordination compounds are designed with pyridinemethanol ligands, characterized with spectral, magnetic and X-ray analyses, and assessed for catecholase activity in various solvents.

Exploring catecholase activity in dinuclear Mn(ii) and Cu(ii) complexes: an experimental and theoretical approach

Two dinuclear Mn(ii) and Cu(ii) complexes were prepared, characterised and assessed for non-covalent interactions and catecholase oxidase properties. The catecholase activity of2is further corroborated by theoretical calculations using DFT.

Designing antiferromagnetically coupled mono-, di- and tri-bridged copper(ii)-based catecholase models by varying the ‘Auxiliary Parts’ of the ligand and anionic co-ligand

The role of the auxiliary part of ligands towards the architecture of copper(ii)-based catecholase models were unveiled with the help of DFT study.

Orthometalated N-(Benzophenoxazine)-o-aminophenol: Phenolato versus Phenoxyl States

The molecular and electronic structures of the orthometalated ruthenium(III) and osmium(III) complexes of N-(benzophenoxazine)-o-aminophenol (^OXLH₂) that exhibits versatile redox activities are reported. The redox chemistry of ^OXLH₂ is remarkably different from that of N-(aryl)-o-aminophenol (^APLH₂). The study established that ^OXLH₂ is redox noninnocent and is a precursor of a phenoxyl radical. One of the C-H bonds of ^OXLH₂ is activated by ions, and ^OXLH₂ reveals three different redox states as dianionic phenolato (^OXL^2-), monoanionic phenoxyl radical (^OXL^•-), and zwitterionic phenoxium cation (^OXL^±) states. The reaction of ^OXLH₂ with [Ru^II(PPh₃)₃Cl₂] in boiling toluene in air affords an orthometalated ^OXL^2- complex of ruthenium(III), trans-[(^OXL^2-)Ru^III(PPh₃)₂(Cl)] (1), whereas the similar reaction with [Os^II(PPh₃)₃Br₂] yields an orthometalated ^OXL^•- complex, cis-[(^OXL^•-)Os^III(PPh₃)Br₂] (2). 1 and 2 exhibit ligand-based reversible redox waves due to ^OXL^•-/^OXL^2-, ^OXL^±/^OXL^•-, and M^III/M^II couples. The 1 ⁺ ion is a ^OXL^•- complex of ruthenium(III). 2 ^- exhibits temperature-dependent valence tautomerism due to [Os^II(^OXL^•-) ↔ Os^III(^OXL^2-)] equilibrium. 2 ^2- is a ^OXL^2- complex of osmium(II), while 1 ²⁺ and 2 ⁺ are ^OXL^± complexes of metal(III). 2 is an oxidant and effective catalyst for oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone, and the turnover number is 119.7 h^-1. The UV-vis-NIR absorption spectrum of 1 displays an NIR band at 800 nm due to an intra-ligand-charge-transfer transition, which is absent in 2 incorporating a ^OXL^•- radical. The molecular and electronic structures of 1 and 2 and their oxidized and reduced analogues were confirmed by single-crystal X-ray crystallography, variable-temperature electron paramagnetic resonance spectroscopy, spectroelectrochemical measurements, and density functional theory calculations.

Effect of temperature and ligand protonation on the electronic ground state in Cu(ii) polymers having unusual secondary interactions: a magnetic and catechol oxidase study

Two new polymeric Cu(ii) compounds with significant catecholase activity are described.

Oxygen Delivery as a Limiting Factor in Modelling Dicopper(II) Oxidase Reactivity

Deprotonation of ligand-appended alkoxyl groups in mononuclear copper(II) complexes of N,O ligands L₁ and L₂ , gave dinuclear complexes sharing symmetrical Cu₂ O₂ cores. Molecular structures of these mono- and binuclear complexes have been characterized by XRD, and their electronic structures by UV/Vis, ¹ H NMR, EPR and DFT; moreover, catalytic performance as models of catechol oxidase was studied. The binuclear complexes with anti-ferromagnetically coupled copper(II) centers are moderately active in quinone formation from 3,5-di-tert-butyl-catechol under the established conditions of oxygen saturation, but are strongly activated when additional dioxygen is administered during catalytic turnover. This unforeseen and unprecedented effect is attributed to increased maximum reaction rates v_max , whereas the substrate affinity K_M remains unaffected. Oxygen administration is capable of (partially) removing limitations to turnover caused by product inhibition. Because product inhibition is generally accepted to be a major limitation of catechol oxidase models, we think that our observations will be applicable more widely.

Syntheses, crystal structures, magnetochemistry and catechol oxidase activity of a tetracopper(ii) compound and a new type of dicopper(ii)-based 1D coordination polymer

One phenoxo–hydroxo bridged tetranuclear cluster and one phenoxo-µ_1,1-azido-µ_1,3-azido bridged one-dimensional coordination polymer of copper(ii) derived from a Schiff base ligand are described.

Aminoalcohols and benzoates-friends or foes? Tuning nuclearity of Cu(ii) complexes, studies of their structures, magnetism, and catecholase-like activities as well as performing DFT and TDDFT studies

The Cu(ii) complexes of varying nuclearity are synthesized, characterized and assessed for catecholase activities.

C i -Symmetry, [2 × 2] grid, square copper complex with the N4,N5-bis(4-fluorophenyl)-1H-imidazole-4,5-dicarboxamide ligand: structure, catecholase activity, magnetic properties and DFT calculations

An antiferromagnetically coupled tetranuclear copper complex of a dinucleating bis amide ligand displays catecholase activity.