Manganese complexes as catalase and superoxide dismutase mimics: structure and reactivity relationships

Macrocycle (H2L1) was prepared by a Schiff base condensation reaction of 2,6-diformylpyridine and 1,3-diamino-2-propanol in the presence of Ba(II) as template ion. Seven-coordinate Mn(II) complexes were prepared by transmetallation reactions of the initial [Ba(H2L1)(μ1,2-ClO4)]2(ClO4)2 complex. Two mononuclear, ring-contracted complexes were obtained when methanol or ethanol were used as solvents in transmetallation reactions. For both complexes, X-ray analysis showed that the H2L1 macrocycle undergoes a ring-contraction via addition of methanol or ethanol across one imine bond, followed by a nucleophilic addition of the secondary amine across an adjacent imine bond resulting in a six-membered, hexahydropyrimidine ring sitting in a chair conformation. The ring-contraction process reduces the size of the cavity in the macrocycle to accommodate one Mn(II) ion in the macrocycle. The macrocyclic tetraimine ligand (H2L1) gave access to the polynuclear, ring-expanded assemblies, [Mn4(H2L*)Cl4][MnCl4] and [Mn4(H2L*)(N3)4](ClO4)2, when acetonitrile was used as a solvent. The macrocycle (H2L1) undergoes rearrangement from a 20-membered to a 40-membered tetranuclear Mn(II) complex. Manganese complexes of acyclic ligands, derived from 2,6-diformylpyridine and several aminoalcohols and aminophenols, were prepared and structurally characterised by X-ray crystallography. Most of the complexes are seven-coordinate with approximate pentagonal bipyramidal geometry, however, some five, six and seven-coordinate complexes were identified. Asymmetric and symmetric tripodal Schiff base ligands and their manganese complexes were also prepared and characterised. Additionally, N-alkylated benzimidazole 2,6-bis(1-butyl-1H-benzo[d]imidazol-2-yl)pyridine and its Mn(II) complexes were prepared and characterised. The potential application of the complexes has been tested in two main areas: (a) as new catalase mimics and (b) as new superoxide dismutase (SOD) mimics. The trinuclear, acyclic complex, [Mn3(L9)2(OAc)2(MeOH)2] 2MeOH, derived from 2,6-diformylpyridine and 2-aminophenol, was found to be the most efficient catalase mimic of the tested complexes with approximately 500 molecules of H2O2 broken down per second for each complex during the fastest rate of activity. Catalase testing showed that an increase of the arm size of the tripodal complexes produced an increase in activity overall for the complexes. Most of the complexes tested for catalase activity showed an induction period prior to the activity being observed. This may be due to a rearrangement occurring before catalase activity is observed. The tripodal complex, [Mn(L18)](ClO4)2 is the only complex to show a catalase activity without added base, but with a long induction period. The results that are presented indicate that the axial ligands have an effect on both the rate of catalase activity and the observed induction period. The SOD results indicated that the complex, [Mn(H2L6)Cl(H2O)]Cl H2O, derived from 2,6-diformylpyridine and 1 aminopropan-2-ol, shows the highest SOD activity amongst the complexes prepared, with a rate of 2.05x106 M-1s-1 and the IC50 value of 0.78 μM. Most of the complexes showed SOD activity with a rate around 105-106 M-1s-1. The SOD results showed that the axial ligands have an effect on SOD activity; strongly bound ligands such as thiocyanate and azide generally result in lower SOD activity. Most of the complexes showed both SOD and catalase activity. Ring-contracted complexes, [Mn(H3L2)(NCS)2] and [Mn(H3L3)(NCS)2], show high rates of superoxide dismutase activity but possess limited catalase activity

Re-investigating the structures of [Cu(NO3)2(en)2] and [Cu(NO3)2(pn)2]: tales of twinning and a reversible phase change

Re-investigating the structures of [Cu(NO3)2(en)2] and [Cu(NO3)2(pn)2]: tales of twinning and a reversible phase chang

A new NiCe complex derived from ortho-vanillin: Structural characterization and luminescence properties

In this study, a new heteronuclear NiCe complex [NiL2Ce(NO3)2(OAc)(H2O)(X)]·1.25H2O (where L = ortovanillinato; X: H2O or CH3OH) was prepared and characterized by analytical and spectroscopic methods. Molecular structure of the complex was further characterised by single crystal X-ray diffraction study. In the structure of the complex, there are two geometrical isomers with only water as coordinated solvent at the Ni(II) centre, and two others with part water and part methanol at this site. In the structure of the complex, a NiL2 moiety is bound to the Ce(III) ion via two phenolic and two methoxy oxygen atoms of two ligands L. The coordination sphere of the Ce(III) ion is completed by the coordination of oxygen atoms of two bidentate nitrate anions, an acetate which bridges the two metal ions, and a water ligand. Hirshfeld surface analysis was performed to investigate the intermolecular contacts and their percentage contributions within the crystal packing. The complex molecules are linked by hydrogen bond contacts. The complex shows an emission band at 656 nm when excited at 317 nm with large stokes shift. The complex exhibits a reversible redox potential at –0.36 V due to the cerium-based oxidation/reduction process

Two seven-coordinate Mn(II) complexes derived from pentadentate ligands: Structural characterization and investigation of photophysical properties

<p>Two mononuclear Mn(II) complexes derived from pentadentate ligands were prepared and characterized. Molecular structures of the complexes were determined by X-ray diffraction studies. Mn(II) ions in both structures are seven-coordinate with approximate pentagonal bipyramidal geometry where the pyridinediimine unit and phenolic or alcoholic oxygen atoms (N₃O₂) of the ligand are located at the pentagonal plane and two exogenous ligands at the axial positions. In the structure of [Mn(HL₂)Cl(CH₃OH)]·2(CH₃OH), methanol solvates link complex molecules into a 1D hydrogen-bonded chain. Emission spectra of the complexes show only one emission band in the 595–625 nm range upon excitation in the 585–615 nm range.</p

Synthesis, characterization and non-linear optical properties of two mononuclear Cu(II) complexes of 2,6-bis(1-butylbenzimidazol-2-yl)pyridine

<p>Two copper(II) complexes, [Cu(L)(N₃)₂]·MeOH and [Cu(L)(NCS)₂]·MeOH, were prepared and characterized by spectroscopic, analytical, and quantum chemical studies, where L is 2,6-bis(1-butylbenzimidazol-2-yl)pyridine. X-ray quality crystals of [Cu(L)(N₃)₂]·MeOH were obtained by slow evaporation of MeOH solution of the complex. Molecular structure of [Cu(L)(N₃)₂]·MeOH was determined by X-ray crystallography. The asymmetric unit contains one [Cu(L)(N₃)₂] and one MeOH molecule. Cu(II) in [Cu(L)(N₃)₂]·MeOH is five-coordinate, bonded to five nitrogens (three from L and two from two azide anions). Coordination geometry around Cu(II) center is distorted square-pyramidal with <i>τ</i> value of 0.065. Optimized geometries, IR spectra, and non-linear optical properties of the complexes were obtained by computational studies based on density functional theory (DFT) with M062X method. NLO properties of these complexes were investigated computationally and both complexes exhibit better NLO properties than urea.</p

Two Cu(II) complexes from an N-alkylated benzimidazole: synthesis, structural characterization, and biological properties

<div><p>Two mononuclear copper(II) complexes, [Cu(L)Cl₂](CH₃OH)₂ and [Cu(L)(NO₃)₂], were prepared and characterized by spectroscopic and analytic methods, where L is 2,6-bis(1-butyl-1<i>H</i>-benzo[<i>d</i>]imidazol-2-yl)pyridine. Molecular structures of the complexes were determined by X-ray diffraction. The X-ray data revealed that the complexes are mononuclear and coordination geometry around Cu(II) is distorted square pyramidal. The complexes were screened for their <i>in vitro</i> antibacterial and antifungal activities. The complexes show moderate antifungal activities against <i>Saccharomyces cerevisiae</i>, <i>Candida utilis,</i> and <i>Candida albicans</i>. Moreover, the complexes inhibit the development of <i>Escherichia coli</i> and <i>Klebsiella pneumoniae</i>.</p></div

SI files for "A new NiCe complex derived from ortho-vanillin: Structural characterization and luminescence properties"

These are the SI files for "A new NiCe complex derived from ortho-vanillin: Structural characterization and luminescence properties".Abstract for associated article:In this study, a new heteronuclear NiCe complex [NiL2Ce(NO3)2(OAc)(H2O)(X)]·1.25H2O (where L = ortovanillinato; X: H2O or CH3OH) was prepared and characterized by analytical and spectroscopic methods. Molecular structure of the complex was further characterised by single crystal X-ray diffraction study. In the structure of the complex, there are two geometrical isomers with only water as coordinated solvent at the Ni(II) centre, and two others with part water and part methanol at this site. In the structure of the complex, a NiL2 moiety is bound to the Ce(III) ion via two phenolic and two methoxy oxygen atoms of two ligands L. The coordination sphere of the Ce(III) ion is completed by the coordination of oxygen atoms of two bidentate nitrate anions, an acetate which bridges the two metal ions, and a water ligand. Hirshfeld surface analysis was performed to investigate the intermolecular contacts and their percentage contributions within the crystal packing. The complex molecules are linked by hydrogen bond contacts. The complex shows an emission band at 656 nm when excited at 317 nm with large stokes shift. The complex exhibits a reversible redox potential at –0.36 V due to the cerium-based oxidation/reduction process.</div

New 1,2,3-triazoles and their oxime derivatives: AChE/BChE enzyme inhibitory and DNA binding properties

1,2,3-Triazole compounds (1a–3a) and their oxime derivatives (1b–3b) were synthesized. The structures of these synthesized compounds were characterized using common spectroscopic methods. Crystal structures of the compounds 3, 2b and 3b were determined by single crystal X-ray diffraction studies. The acetylcholinesteras (AChE) and butyrylcholinesterase (BChE) cholinesterase inhibitor (ChEI) and DNA/calf serum albumin (BSA) binding properties of the compounds were examined. DNA binding studies have shown that compounds interact with DNA through 1,2,3-triazole and oxime groups. When the binding constant Kb values were compared, it was revealed that compound 3b (Kb = 4.6 × 105 M−1) with oxime in its structure binds more strongly than the others. In addition, in vitro BSA binding studies showed that compounds 1b and 3b exhibited higher binding affinity. These results confirm that the quenching is due to the formation of a compound resulting from the static quenching mechanism, rather than being initiated by a dynamic mechanism. Likewise, when the enzyme activity of the compounds was examined, the compounds exhibited high inhibitory activity against AChE. The highest activity was observed for compounds 2b and 3b (8.6 ± 0.05 and 4.8 ± 0.052 µM). It was observed that the compounds were not selective with respect to BChE. Communicated by Ramaswamy H. Sarma</p