Phenoxazinone Synthase Activity Research Articles

Catecholase and phenoxazinone synthase activities of two structurally characterized mononuclear complexes [Cu(L)(NCS)(ClO4)] and [Zn(L)(NCS)2] [L = N,N-diethyl-2-((phenyl(pyridin-2-yl)methylene)-amino)ethan-1-amine

Synthesis and X-ray structural characterization of a Cu(II) and a Zn(II) mononuclear complexes [Cu(L)(NCS)(ClO4)] (1) [Zn(L)(NCS)2] (2) [L = N,N-diethyl-2-((phenyl(pyridin-2-yl)methylene)-amino)ethan-1-amine] were done. 1 and 2 were crystalized in Pbca and P121/c1 space groups. Metal centres at both the complexes adopted distorted square pyramidal geometries. Both 1 and 2 responded to catecholase and phenoxazinone synthase activities in different solvents. The biomimicking activities were monitored by repetitive UV–Vis scan. Several kinetic parameters for both 1 and 2 were measured. The turn over numbers of 1 were 25.20 (MeOH) and 50.00 (ethylacetate), and for 2, 582.00 (MeOH) for the catecholase activity. For the phenoxazinone synthase activity the turn over numbers were 78.28 (MeOH), 21.17 (MeCN) and 43.06 (ethylacetate) for 1, and 40.00 (MeOH), 11.00 (MeCN) and 4.00 (ethylacetate) for 2.

Triazine-based mononuclear copper(ii) cis-dichloro and dibromo complexes as functional biomimetic model systems for phenoxazinone synthase and catecholase activities

Two new mononuclear Cu(ii) complexes were synthesized and thoroughly characterised. Molecular integrities were determined by SCXRD analysis and their catalytic activities and kinetics for the oxidation of o-aminophenol and catechol were examined.

Novel bioinspired dinuclear Cu(II) ‘paddle wheel’ acetate complex: Catalytic and in vitro biological activity studies

A versatile bioinspired metallocatalyst [Cu2L2(OAc)4] (L = 2-(3-(dimethylamino)propyl)isoindoline-1,3-dione) has been synthesized and found distorted octahedral complex on the basis of various spectroscopic characterization. XRD date shows that it is monoclinic system with space group C 2/c. Non classical intramolecular H-bond stabilise it's dimeric nature. The additional signal appeared at g ca 2.10 in EPR and shifting of irreversible cathodic peak from −0.292 V to −0.910 V in CV confirm it is phenoxazinone synthase activity while base peak at m/z 221.15 obtained from ESI Mass and irreversible cathodic peak shifting from −0.292 to −0.211 V ratify it's catechol oxidase activity. Besides, Michaelis-Menten analysis shows prominent catalytic activity towards 3,5-DTBC and 2-AP (Kcat 12.0726×103 h-1 and 6.6654×103 h-1). In vitro study supported by molecular docking study exposes substantial dose dependent anti-leukemic activity against Hep-G2 cell line (GI50 ˂ 10 µg/mL). Moreover, promising anti-bacterial property was also detected on multi-drug resistant E. coli and B. cereus bacteria (B. cereus OD 0.21 ± 0.016; E. coli OD 0.172 ± 0.013) at 100mM concentration of complex.

A novel mixed azido/phenoxido bridged 1D CuII coordination polymer containing o-vanillin-based compartmental ligand: Synthesis, magnetism, phenoxazinone synthase and catalytic activity in epoxidation of alkenes

A novel 1-D coordination polymer, formulated as [Cu2(L)(N3)3]·H2O (1), has been synthesized by reacting the Schiff base ligand, 2-methoxy-6-((2-(2-hydroxyethylamino)ethylimino) methyl)-phenol (HL), with copper(II) chloride dihydrate in the presence of sodium azide. The X-ray structural analysis shows that compound 1 consists of tetranuclear [Cu2(L)(N3)3]2 units bearing a central double asymmetric μ1,1-N3 bridge and terminal mixed µ1,1-N3/phenoxido bridges that are linked via a double µ1,1,3-N3 bridge forming a 1-D network. The magnetic properties of 1 show the presence of ferromagnetic Cu···Cu interactions through the central double μ1,1-N3 bridge (J1 = 81.7(3) cm−1) coexisting with antiferromagnetic Cu···Cu interactions through the double µ1,1-N3/phenoxido bridge (J2 = –62.3(4)cm−1). Additionally, there is a very weak antiferromagnetic interaction (zJ = –0.12(2) cm−1) through the asymmetric µ1,1,3-N3 bridge connecting the tetranuclear units. Using o-aminophenol (OAP) as a substrate, the phenoxazinone synthase-like catalytic activity of the CuII coordination polymer 1 has been studied. The compound efficiently catalyzes the aerobic oxidation of o-aminophenol in DMF medium with a turnover number Kcat = 31.69 h−1. Moreover, 1 has been used as an active catalyst for the epoxidation of cis-cyclooctene, as a model alkene, with tert-butyl hydroperoxide (TBHP), showing an excellent epoxide yield and selectivity in CHCl3 under reflux conditions. To enlarge the scope of the reaction, the efficacy of the catalytic method has also been investigated in the epoxidation of some other substituted alkenes.

Synthesis and characterization of a copper (II) compound with a new N3Py2 core ligand: Influence of methyl substitution on structural parameters and catalytic mimicking activity

A mononuclear copper (II) compound [Cu(L1)](ClO4)21 containing nonheme N3Py2 pentadentate ligand N1,N3-dimethyl-N1-(3-(methyl(pyridin-2-ylmethyl)amino)propyl)-N3-(pyridin-2-ylmethyl)propane-1,3-diamine) have been synthesized and characterized by several methods. A new ligand L1 has been prepared by methylation of secondary -NH of L2 (N1-(pyridin-2-ylmethyl)-N3-(3-((pyridin-2-ylmethyl)amino)propyl)propane-1,3-diamine) at and characterized by NMR spectroscopy. Compound 1 has been characterized by single-crystal X-ray crystallography and spectroscopic techniques. It crystallizes in a centrosymmetric space group P21/n and adopts a distorted square-pyramidal geometry with τ5= 0.13. We also prepared compound [Cu(L2)](ClO4)22, and its structural properties were compared with 1. The geometry of 1 is nearly SP, while compound 2 is intermediate between SP and TBP. We then investigated the applications of 1 and 2 in phenoxazinone synthase and catecholase activity. The results suggest compound 1 was more effective in both activities than 2.

Spectroscopic and electrochemical study of biomimetic catecholase and phenoxazinone synthase activities of in situ complexes bearing pyrazolic ligands

Spectroscopic and electrochemical study of biomimetic catecholase and phenoxazinone synthase activities of in situ complexes bearing pyrazolic ligands

Structure–function correlation of mononuclear nonheme copper(ii) compounds based on a ligand backbone effect and phenoxazinone synthase activity

Mononuclear nonheme Cu(ii) compounds 1 and 2 were synthesized and characterized by elemental analysis, ESI-MS, EPR, and single-crystal X-ray diffractrometry.

Synthesis, characterization, design, molecular docking, anti COVID-19 activity, DFT calculations of novel Schiff base with some transition metal complexes

The elemental analyses, infrared, magnetic measures, UV–Visible, 1H NMR, 13C NMR, and XRD analysis were used to study Co(II), Ni(II), and Cu(II) metal complexes (1–3) with a novel Schiff base (HL). The ligand performances as a mononegative tridentate NNO, according to the spectrum data. In Co(II), Ni(II), and Cu(II) metal complexes, an octahedral structure has been proposed based on magnetic and electronic spectrum data. The thermodynamic properties of the ligand and its complexes are measured via the Coats-Redfern and Horowitz-Metzger procedures. The bond angles, the bond lengths, and quantum chemical factors are shown in the molecular modeling using the DFT approach. The ligand and its complexes have been studied via absorption spectra studies in calf thymus DNA binding and also viscosity calf thymus DNA binding studies. Utilizing o-aminophenol such as a reference material catalyzed by metal complexes, dioxygen stimulation in parameters of phenoxazinone synthase activity is comprehensively examined. By interacting by SARS-CoV-2 main protease, which was obtained from the RCSB pdb database PDB ID: 6 W41, to anticipate the action of HL in contradiction of COVID-19 and its anticancer properties with cancer of prostate protein 3qum, the docking binding sites contacts were evaluated. As a result, future research and clinical studies into HL as a potential COVID-19 illness and prostate cancer therapy drug induced. Vinblastine and colchicine viability tests were used to compare the outcomes of the complexes targeting human tumor cell lines MCF-7 and HepG-2. All complexes' in vitro antioxidant properties were measured by DPPH free radical scavenger tests. Additionally, antibacterial action of the ligand and specific complexes was investigated in vitro in contradiction of Gram + ve bacteria (Staphylococcus aureus) and Gram-ve bacteria Escherichia coli (E. coli) utilizing inhibition zone diameter.

Spectroscopic characterization of Cu(II), Ni(II), Co(II) complexes, and nano copper complex bearing a new S, O, N-donor chelating ligand. 3D modeling studies, antimicrobial, antitumor, and catalytic activities

A new tridentate hydrazone ligand (HL), its Co(II), Ni(II), Cu(II) complexes (in 1:1, 1:2 molar ratios of metal to ligand), and the mixed-ligand Co(II), Ni(II), Cu(II) complexes of the ligand HL, with 8-HQ in 1:1:1 (M:L:8-HQ) stoichiometry, in addition to a nano Cu(II) complex have been synthesized and characterized using physical, analytical and spectral methods. Octahedral geometry was assigned for all investigated complexes except Cu(II) complex 1 which exhibited square planar arrangement. The TGA results suggested the thermal stability of the current complexes. The XRD data indicated that the particles of Cu(II) complex 2 were situated in nano-scale range. Furthemore, the SEM and TEM images of the nano Cu(II) complex 2 showed spherical and sheet-shaped particles with an average size of 48 nm. The geometries of the metal complexes were optimized with respect to the energy taking the 6-311G(p,d) basis set in Gaussian 09 W program in gaseous phase by DFT. The data obtained revealed that all metal complexes are more reactive than the free ligand HL, and the Cu(II) complex 1 has the highest chemical reactivity. The antimicrobial activity study illustrated enhancement in activity of the free ligand upon complex formation., and the Cu(II) complex 1 may be considered as promising antibacterial agent, and as promising antifungal agent. The results of antitumor activity study revealed an inhibition of HepG-2 cell growth for the ligand HL, with enhancement in activity upon complexation, and the Cu(II) complex 1 exhibited the highest cytotoxic activity. The phenoxazinone synthase activity study indicated the ability of both Cu(II) complexes 1 and 2 to catalyze the oxidative dehydrogenation of 2-aminophenol (OAPH) to 2-aminophenoxazine-3-one (APX) under atmospheric conditions and at room temperature.

Mononuclear iron(III) complexes derived from tridentate ligands containing non‐innocent phenolato donors: Self‐activated nuclease, protease, and phenoxazinone synthase activity studies

The tridentate ligands HPhimpH, OCH3PhimpH, CH3PhimpH, tBuPhimpH, and NO2PhimpH have been synthesized and characterized. These tridentate ligands having non‐innocent phenolato function, Npy and Nim donors upon deprotonation bind to iron(III) center resulting in a series of novel iron complexes, namely, [Fe(HPhimp)2](ClO4) (1), [Fe(OCH3Phimp)2](ClO4) (2), [Fe(CH3Phimp)2](ClO4) (3), [Fe(tBuPhimp)2](ClO4) (4), and [Fe(NO2Phimp)2](ClO4) (5). Complexes were characterized by elemental analysis, IR, and UV–visible, and electrospray ionization mass spectral (ESI–MS) studies. Molecular structure of complex 2 was determined by single‐crystal X‐ray diffraction study. Electrochemical studies depicted Fe(III)/Fe(II) couple in the range of −0.50 to −0.65 V versus Ag/AgCl. Theoretical calculation using density functional theory (DFT) was also performed to optimize the geometrical and structural parameters. Time‐dependent DFT (TD‐DFT) was also optimized to observe the electronic properties, and data obtained were found to be consistent with experimentally observed values. Representative complex 4 exhibited nuclease and protease activities in the absence of external agents. Complex 4 was found to cleave the DNA and protein via self‐activated mechanism. Complexes 1–5 were utilized to optimize oxidation of o‐aminophenol in methanol. Complexes were found to be efficient in the oxidation of o‐aminophenol. Kinetic experiments were also explored to gain better insight into the oxidation process.

Copper(II) complexes with a benzimidazole functionalized Schiff base: Synthesis, crystal structures, and role of ancillary ions in phenoxazinone synthase activity

This research study reports the synthesis, structural characterization and phenoxazinone synthase‐like activity of two structurally similar copper(II) complexes developed with a benzimidazole functionalized Schiff base (L). The ligand, L, was designed and synthesized in high yield by the reaction of p‐methoxy benzaldehyde with o‐phenylenediamine. The reaction of L with CuCl2 and Cu(NO3)2 leads to the formation of two isostructural complexes, [Cu(L)2Cl2]2 (1) and [Cu(L)2(NO3)2]2 (2). Single crystal X‐ray structural study reveals that both the Cu(II) centre in 1 and 2 adopts a square planar geometry. An attempt has also been made to understand the role of coordinated co‐ligands on the catalytic oxidation of 2‐aminophenol (2‐AP) to 2‐amino‐3H‐phenoxazine‐3‐one (2‐APX) in methanol. The presence of coordinated nitrate to Cu(II) ions imparts a more labile character to complex 2, and the catalytic efficiency (kcat/KM) for complex 2 (1.50 × 107) was determined almost double compared with that of complex 1 (8.78 × 106). Electro‐chemical and electrospray ionization mass spectrometry studies of 1 and 2 with 2‐AP suggests that the square planar geometries of the Cu(II) centres remain the driving force to develop enzyme‐substrate adducts and excellent catalytic performance of the complexes. Electrochemical and EPR spectral analysis of the reaction mixture confirm the presence of active 2‐AP−/2‐AP•− redox species in the course of catalytic oxidation and suggest the radical driven oxidative coupling of 2‐AP in an aerobic environment. Temperature‐dependent kinetic measurements were carried out to evaluate the activation parameters (Ea, ΔH‡, ΔS‡), which favours the higher rate of catalytic oxidation of 2‐AP for complex 2 than complex 1.

Design, synthesis, structural, spectral, and redox properties and phenoxazinone synthase activity of tripodal pentacoordinate Mn(II) complexes with impressive turnover numbers.

Catechol oxidase (CO) and phenoxazinone synthase (PHS) are two enzymes of immense significance due to their capability to oxidize catechols and o-aminophenols to o-quinones and phenoxazinones, respectively. In this connection two mononuclear manganese complexes with the molecular framework [MnII(Ln)Cl]Cl {L1: tris((1H-benzo[d]imidazol-2-yl)methyl)amine; n = 1 and L2: tris(N-methylbenzimidazol-2-ylmethyl)amine; n = 2} have been designed to be potential catalysts for OAPH (o-aminophenol) oxidation. Both the ligands and their corresponding metal complexes have been successfully synthesized and thoroughly characterized by different spectroscopic and analytical techniques such as FT-IR, 1H NMR, UV-vis spectroscopy, EPR spectroscopy and ESI mass spectroscopy. The molecular structures of [MnII(L1)Cl]Cl (1) and [MnII(L2)Cl]Cl (2) have been revealed by a single-crystal X-ray diffraction study. The spectral properties and redox behaviour of both the complexes were examined. Under ambient conditions, 1 and 2 show excellent phenoxazinone synthase activity as both are very susceptible to oxidize o-aminophenol to phenoxazinone. The kinetic parameters for both complexes have been determined by analyzing the experimental spectroscopic data. The turnover numbers (kcat value) of these two complexes are extremely high, 440 h-1 and 234 h-1 for 1 and 2, respectively. The present report offers a thorough overview of information involving the role of the metal ions and their extent of phenoxazinone synthase mimicking activity. The oxidation of o-aminophenol to 2-amino-3H-phenoxazine-3-one (APX) by catalytic oxidation of oxygen (O2) by the reaction with transition metal complexes has been an important study for the last few decades. The current study evidently showed better performance of our synthesized Mn(II) complexes than all the predecessors. The plausible mechanism has been reiterated based on the experimental data via ESI-MS spectra and considering the concepts from the previously reported mechanisms involved in the formation of hydrogen peroxide (H2O2) as an intermediate substrate is fairly indicating the involvement of molecular oxygen in the catalytic cycle.

Joining of Trinuclear Heterometallic CuII2-MII (M = Mn, Cd) Nodes by Nicotinate to Form 1D Chains: Magnetic Properties and Catalytic Activities.

In the present work, four new heterometallic coordination complexes, {[(CuL)2Mn(nic)(H2O)2](ClO4)(0.5H2O)}n (1), {[(CuL)2Cd(nic)(H2O)2](ClO4)(H2O)}n (2), [(CuL)2Mn(nic)2]·2CH3OH (3), and [(CuL)2Cd(nic)2]·2CH3OH (4) (where H2L = N,N'-bis(α-methylsalicylidene)-1,3-propanediamine and nic = nicotinate ion), have been synthesized and characterized by single-crystal X-ray crystallography. In complexes 1 and 2, the nicotinate ion acts as a bifunctional linker (N,O donor) and joins the linear trinuclear nodes to form 1D polymeric chains. However, in complexes 3 and 4, the nicotinate ion uses only the oxygen atoms of the carboxylic acid (O donor) to bind to the metal centers, forming discrete linear trinuclear units, while the pyridyl nitrogen (N donor atom) remains free. The dc magnetic susceptibility measurements show that the CuII and MnII ions are antiferromagnetically coupled in both 1 and 3, with exchange coupling constants (JMn-Cu) of -20.57 ± 0.08 and -9.38 ± 0.08 cm-1, respectively. Among the four complexes, 1 and 3 show catechol oxidase and phenoxazinone synthase like catalytic activities. The turnover numbers (kcat) of complexes 1 and 3 for catecholase activity are 1121 and 720 h-1, respectively, at an optimum pH of 8.0 and for phenoxazinone synthase activity are 429 and 398 h-1, respectively, at an optimum pH of 9.7. The higher kcat values of 1 for both reactions are attributable to a water molecule coordinated to the central MnII atom that facilitates the substrate-catalyst binding. An ESI-mass spectral analysis indicates that trinuclear heterometallic species, e.g., [(CuL)2Mn(nic)(H2O)]+ for 1 and [(CuL)2Mn(nic)]+ for 3, are the active species that bind to the substrate, and on that basis, probable mechanisms through the formation of radical intermediates have been proposed.

Influence of structural and thermal factors on phenoxazinone synthase activities catalysed by coordinatively saturated cobalt(III) octahedral complexes bearing diazene–disulfonamide N⌃N⌃N chelators

There are increasing efforts towards the development of new synthetic models that can mimic phenoxazinone synthase activity due to the important applications of several biomolecules bearing the phenoxazinone chromophore. However, deliberate studies of systematically varied coordination species for the knowledge of underlying molecular determinants of catalytic outcomes using fully characterized mimicking models are scarce. In this report, two new dianionic and synthetically obtained diazene–disulfonamide N⌃N⌃N chelators of the form RSO2–NH–Ph–N=N–Ph–NHSO2R (R = methyl for 1 and tolyl for 2) are coordinatively self-assembled around cobalt(III) centres in the presence or absence of co-ligands (acetate, bipyridine, 4-dimethylaminopyridine and/or water) to obtain four new and structurally analysed complexes [Co12][Et3NH], Co1·OAc·bpy, Co1·OAc·bpy and Co2·dmap·w, which are all found to be octahedral cobalt(III) polyhedra, distorted to varying extents, by using Continuous Shape Measurement calculations. Based on structural and thermal factors, it is observed that the trends of the phenoxazinone synthase mimicking activities by these complexes correlate with their inherent abilities to generate vacant coordination space for substrate–metal ion interactions. Finally, it is also observed that coordinative steric strains control catalytic trends among the complexes at low temperatures while susceptibility to thermal dissociations is the determinant at higher temperatures.

Synthesis, spectral, magnetic, DFT calculations, antimicrobial studies and phenoxazinone synthase biomimetic catalytic activity of new binary and ternary Cu(II), Ni(II) and Co(II) complexes of a tridentate ONO hydrazone ligand

New mononuclear copper(II), nickel(II) and cobalt(II) hydrazone complexes of 2-cyano-N′-((4-oxo-4H-chromen-3-yl)methylene)acetohydrazide have been synthesized. Structure identification of the prepared complexes was carried out by physicochemical and spectroscopic techniques including elemental analyses, infrared, electronic, mass and electron spin resonance spectra, thermal analysis, conductivity and magnetic susceptibility measurements, powder x-ray diffraction and transmission electron microscope. The isolated binary complexes are neutral mononuclear complexes (with 1:1 and 1:2; M:L stoichiometries) and ternary complexes (with 1:1:1; M:L:L′ stoichiometry). The analytical and spectroscopic techniques illustrated the monoanionic tridentate behavior of the hydrazone ligand with γ-pyrone oxygen, enolic oxygen and azomethine nitrogen coordinating sites. The metal complexes displayed square planar, tetrahedral and octahedral geometries. Density Functional Theory calculations were carried out for the chelating agent and its copper(II) chelates. The phenoxazinone synthase activity of the binary copper(II) complexes was studied and discussed. The antimicrobial activity of the hydrazone ligand and its complexes was evaluated toward some sorts of Gram–positive bacteria, Gram–negative bacteria, yeast and fungus.

Oxidative dimerisation of 2-aminophenol by a copper(II) complex: Synthesis, non-covalent interactions and bio-mimics of phenoxazinone synthase activity

This research study aims to overview the synthesis, structural characterization, long range crystalline architectures and bio-inspired oxidative catalysis of a mononuclear copper(II) complex, [Cu(Phen)2(H2O)](NO3)2 (1);[phen = 1,10-phenanthroline]. Single crystal X-ray diffraction study reveals that copper complex crystallizes in C2/c space group and Cu(II) centre exists in a highly distorted trigonalbipyramidal geometry. A close look at supramolecular architecture for this copper(II) complex indicates that oxygen atoms of nitrate ions and H atoms from phenanthroline ligand lead to intermolecular H-bonded 3D crystalline architecture in solid state. Noteworthy O ⋯ π interactions are also operative in between nitrate-O and centroids of ligands to provide additional stability in 3D architecture. Hirshfeld surface analysis further corresponds to the active participation of intermolecular H⋯O bonding and anion ⋯ π interactions. This copper complex has been tested as a bio-inspired catalyst towards oxidative coupling of 2-AP in methanol medium and the catalytic efficiency, kcat/KM(h−1) is found excellent, 1.007 × 107, towards the aerobic oxidation of 2-aminophenol (2-AP). The copper(II) complex in presence of 2-AP exhibits two new additional peaks at −0.13 and 0.49 V which correspond to AP−/AP•− and AP•−/IQ redox couple and suggests the generation of radical as a driving force for the oxidative coupling of 2-AP. Electrospray ionization mass spectrometry of the reaction mixture suggests that the course of oxidative cyclisation proceeds through enzyme-substrate adduct formation during this course of catalysis.

Coordination environment variations in multinuclear trigonal bipyramid Co(II) complexes bearing tetradentate sulfonamide N-donors and phenoxazinone synthase activities

Most documented investigations deploying transition metal complexes as phenoxazinone synthase models only report one or two complexes, which limits understanding of structure-property correlations between varying compositions as well as the coordination environments of the active site changes and the biomimetic activities. In efforts to systematically investigate changes in the vicinity of cobalt(II), five new complexes of two tripod N,N′,N″-(nitrilotris(ethane-2,1-diyl))tris(benzenesulfonamide) ligand derivatives (1 and 2) were self-assembled with incorporation of Na+, K+ or Cs+ as bridging counter cations. All the complexes were structurally analysed and found to possess distorted trigonal bipyramid cobalt(II) centres such that an easily displaceable water molecule always occupy one of the axial positions. While ligand 1 forms (Na[Co1.w]E)n as a 1D coordination polymer, ligand 2 forms the dimeric complexes (Na[Co2.w]M)2, (Na[Co2.w])2, (K[Co2.w]A)2 and (Cs[Co2.w]M2,w2)2. Continuous Shape Measurement (CShM) calculations were carried out to analyse distortions of the obtained trigonal bipyramid geometries. The high turnover numbers of 584 h−1 for (Na[Co2.w])2, 564 h−1 for (Cs[Co2.w]M2.w2)2, 543 h−1 for (K[Co2.w]A)2 and 446 h−1 for (Na[Co2.w]M)2 represent attractive level of phenoxazinone mimicking capacity relative to literature data for mononuclear cobalt(II) complexes. It was concluded that the release of free cobalt(II) anions [Co1.w]− or [Co2.w]− via dissociations of the multinuclear complexes is necessary for the phenoxazinone synthase mimicking activities to occur and that the incorporated group I metal ions possess no influence on the observed mimicking activities. The trigonal bipyramid coordination environments of the anionic chelates [Co1.w]− or [Co2.w]− yielded better outcomes than their previously reported vacant octahedral (vOC-5, C4v) complex analogues.

Trinuclear copper and mononuclear nickel complexes of oxime containing Schiff bases: Single crystal X-ray structure, catecholase and phenoxazinone synthase activity, catalytic study for the homocoupling of benzyl amines

Here we report the synthesis and characterisation of one trinuclear copper complex, [Cu3L3O]ClO4 (1), and one nickel complex, [Ni(L′H)2(dmso)2](ClO4)2) (2), with the Schiff base ligands (3Z)-3-((Z)-(1-(thiophen-2-yl)ethylidene)hydrazono)butan-2-one oxime (LH) and 1-(pyridin-2-yl)ethylidene)hydrazono)butan-2-one oxime (ĹH). Single crystal X-ray structures have been described for the ligand LH and the complexes 1 and 2. 1 shows high catecholase activity (kcat = 8.14 × 102 h−1 in MeOH) using 3,5-di-tert-butylcatechol as the substrate in methanol medium. 2 shows phenoxazinone synthase activity with a moderate value of kcat = 63.11 h−1 in dimethyl sulfoxide. This is the first report for phenox-azinone synthase activity by a nickel complex containing a ligand with oxime functionality. 1 has also been tested as a catalyst for the synthesis of benzylimine and substituted benzylimines from the corresponding amines. Substrates with electron withdrawing halo-substituted benzylamines undergo quantitative conversions to the corresponding benzylimines, whereas electron donating groups on the aromatic ring yielded lower conversions.

Schiff base triggering synthesis of copper(II) complex and its catalytic fate towards mimics of phenoxazinone synthase activity

This research article reports the synthesis, structural characterization and phenoxazinone synthase activity of a new phenoxido-bridged dicopper(II)-Schiff base complex, [Cu2(L)3]ClO4(1), [HL = (Z)-2-methoxy-6-(((2-methoxyphenyl)imino) methyl)phenol]. X-ray structure of the Cu(II) complex reveals that each of the two Cu(II) centres in 1 adopts different coordination geometries (distorted octahedral and distorted square planar) and phenoxido bridges couple two Cu(II) centres to form a dinuclear copper complex with Cu⋯Cu distance 3.182 Å. The dicopper(II) complex catalyzes the aerobic oxidation of 2-aminophenol (2-AP) to aminophenoxazinone species in acetonitrile with good turnover number, 78.14 h−1. Electro-chemical and electrospray ionization mass spectrometry analysis of 1 in presence of 2-AP ensure the involvement and key role of the copper(II) centres in formation of enzyme-substrate adduct. Subsequently, electron paramagnetic resonance study confirms the generation of radical species in the course of catalysis. Finally, density functional theoretical calculations well reproduce the experimental geometrical parameters and spectroscopic behaviours of 1 and decisively argue in favour of the proposed catalytic pathways.

Aerobic oxidation of alcohol by model complexes relevant to metal site galactose oxidase: role of copper(I) intermediate, evidence for the generation of end-on copper(II)–OOH species and catalytic promiscuity for oxidation of benzyl alcohol, catechol and o-aminophenol

Tridentate ligands having meridional NNO donor centres were designed and synthesized mimicking the copper coordination in the metal site of galactose oxidase enzyme. Mononuclear copper complexes [Cu(L1)Cl] (1) (L1H = (E)-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), [Cu(L2)Cl] (2) (L2H = (E)-4-methyl-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), [Cu(L3)Cl] (3) (L3H = (E)-1-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)naphthalen-2-ol), [Cu(L4)Cl] (4) (L4H = (E)-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), [Cu(L5)Cl] (5) (L5H = (E)-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), and [Cu(L6)Cl] (6) (L6H = (E)-2,4-di-tert-butyl-6-(((pyridin-2-ylmethyl)imino)methyl)phenol) were synthesized and characterized. Molecular structure of complex 3 was determined by single crystal X-ray crystallography. Phenoxyl radical complexes were generated in solution via chemical oxidation using ceric ammonium nitrate (CAN), and the radical complexes were characterized by UV–Vis–NIR spectrophotometer. DFT calculations were performed at B3LYP level to optimize the ground-state molecular geometry of the complexes. To understand the electronic properties and absorption spectra of the complexes, TD-DFT calculations were executed for phenoxyl radical complexes considering triplet as well as singlet spin states. Alcohol oxidation was examined utilizing complexes 1–6 as catalyst, and importance of stabilization of Cu(I) intermediate was scrutinized and generation of Cu(II)–OOH was examined. Catalytic promiscuity for catechol oxidase and phenoxazinone synthase activity by complexes (1–5) was investigated. Theoretical calculations and ESI–MS spectral studies were performed during oxidation chemistry of benzyl alcohol, catechol and o-amino phenol to support the proposed mechanism.