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The synthesis, X-ray molecular structure, physico-chemical characterization and dual antioxidant activity (catalase and superoxide dismutase) of a new polymeric mixed valence Mn(III)Mn(II) complex, containing the ligand H 2 BPClNOL (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)] propylamine) is described. The monomeric unit is composed of a dinuclear Mn(II)Mn(III) moiety, [Mn(III)(μ-HBPClNOL)(μ-BPClNOL)Mn(II)(Cl)](ClO 4 )·2H 2 O, 1 , in which the Mn ions are connected by two different bridging groups provided by two molecules of the ligand H 2 BPClNOL, a phenoxide and an alkoxide group. In the solid state, this mixed valence dinuclear unit is connected to its neighbors through chloro bridges. Magnetic measurements indicated the presence of ferromagnetic [ J = +0.076(13) cm -1 ] and antiferromagnetic [ J = -5.224(13) cm -1 ] interactions. The compound promotes O 2 • - dismutation in aqueous solution (IC 50 = 0.370 μmol dm -3 , k cat = 3.6x10 6 M -1 s -1 ). EPR studies revealed that a high-valent Mn(III)-O-Mn(IV) species is involved in the superoxide dismutation catalytic cycle. Complex 1 shows catalase activity only in the presence of a base, e.g., piperazine or triethylamine. Kinetic studies were carried out in the presence of piperazine and employing two different methods, resulting in k cat values of 0.58 ± 0.03 s -1 (detection of O 2 production employing a Clark electrode) and 2.59 ± 0.12 s -1 (H 2 O 2 consuption recorded via UV-Vis). EPR and ESI-(+)-MS studies indicate that piperazine induces the oxidation of 1 , resulting in the formation of the catalytically active Mn(III)-O-Mn(IV) species.

In our previous studies, heme was bound into honeybee silk to generate materials that could function as nitric oxide sensors or as recoverable heterogeneous biocatalysts. In this study, we sought to increase the heme-binding capacity of the silk protein by firstly redesigning the heme binding site to contain histidine as the coordinating residue and secondly, by adding multiple histidine residues within the core of the coiled coil core region of the modified silk protein. We used detergent and a protein denaturant to confirm the importance of the helical structure of the silk for heme coordination. Aqueous methanol treatment, which was used to stabilize the materials, transformed the low-spin, six-coordinate heme to a five-coordinate high-spin complex, thus providing a vacant site for ligand binding. The optimal aqueous methanol treatment time that simultaneously maintains the helical protein structure and stabilizes the silk material without substantial leaching of heme from the system was determined., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Substituted semicarbazones/thiosemicarbazones and their copper complexes have been prepared and several single crystal structures examined. The copper complexes of these semicarbazone/thiosemicarbazones were prepared and several crystal structures examined. The single crystal X-ray structure of the pyridyl-substituted semicarbazone showed two types of copper complexes, a monomer and a dimer. We also found that the p-nitrophenyl semicarbazone formed a conventional 'magic lantern' acetate-bridged dimer. Electron Paramagnetic Resonance (EPR) of several of the copper complexes was consistent with the results of single crystal X-ray crystallography. The EPR spectra of the p-nitrophenyl semicarbazone copper complex in dimethylsulfoxide (DMSO) showed the presence of two species, confirming the structural information. Since thiosemicarbazones and semicarbazones have been reported to exhibit anticancer activity, we examined the anticancer activity of several of the derivatives reported in the present study and interestingly only the thiosemicarbazone showed activity while the semicarbazones were not active indicating that introduction of sulphur atom alters the biological profile of these thiosemicarbazones., (Copyright © 2016 Elsevier Inc. All rights reserved.)

This study investigated how to control the rate of photoreduction of metastable AuCl2(-) at the solid-solution interface of large ZnO nanoparticles (NPs) (50-100 nm size). Band-gap photoexcitation of electronic charge in ZnO by 370 nm UV light yielded Au NP deposition and the formation of ZnO-Au NP hybrids. Au NP growth was observed to be nonepitaxial, and the patterns of Au photodeposition onto ZnO NPs observed by high-resolution transmission electron microscopy were consistent with reduction of AuCl2(-) at ZnO facet edges and corner sites. Au NP photodeposition was effective in the presence of labile oleylamine ligands attached to the ZnO surface; however, when a strong-binding dodecanethiol ligand coated the surface, photodeposition was quenched. Rates of interfacial electron transfer at the ZnO-solution interface were adjusted by changing the solvent, and these rates were observed to strongly depend on the solvent's permittivity (ε) and viscosity. From measurements of electron transfer from ZnO to the organic dye toluidine blue at the ZnO-solution interface, it was confirmed that low ε solvent mixtures (ε ≈ 9.5) possessed markedly higher rates of photocatalytic interfacial electron transfer (∼3.2 × 10(4) electrons·particle(-1)·s(-1)) compared to solvent mixtures with high ε (ε = 29.9, ∼1.9 × 10(4) electrons·particle(-1)·s(-1)). Dissolved oxygen content in the solvent and the exposure time of ZnO to band-gap, near-UV photoexcitation were also identified as factors that strongly affected Au photodeposition behavior. Production of Au clusters was favored under conditions that caused electron accumulation in the ZnO-Au NP hybrid. Under conditions where electron discharge was rapid (such as in low ε solvents), AuCl2(-) precursor ions photoreduced at ZnO surfaces in less than 5 s, leading to deposition of several small, isolated ∼6 nm Au NP on the ZnO host instead.

The active site of mammalian purple acid phosphatases (PAPs) have a dinuclear iron site in two accessible oxidation states (Fe(III)2 and Fe(III)Fe(II)), and the heterovalent is the active form, involved in the regulation of phosphate and phosphorylated metabolite levels in a wide range of organisms. Therefore, two sites with different coordination geometries to stabilize the heterovalent active form and, in addition, with hydrogen bond donors to enable the fixation of the substrate and release of the product, are believed to be required for catalytically competent model systems. Two ligands and their dinuclear iron complexes have been studied in detail. The solid-state structures and properties, studied by X-ray crystallography, magnetism, and Mössbauer spectroscopy, and the solution structural and electronic properties, investigated by mass spectrometry, electronic, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and Mössbauer spectroscopies and electrochemistry, are discussed in detail in order to understand the structures and relative stabilities in solution. In particular, with one of the ligands, a heterovalent Fe(III)Fe(II) species has been produced by chemical oxidation of the Fe(II)2 precursor. The phosphatase reactivities of the complexes, in particular, also of the heterovalent complex, are reported. These studies include pH-dependent as well as substrate concentration dependent studies, leading to pH profiles, catalytic efficiencies and turnover numbers, and indicate that the heterovalent diiron complex discussed here is an accurate PAP model system.

Three synthetic analogues of westiallamide, H3L(wa), have previously been synthesized (H3L(1-3)) that have a common backbone (derived from l-valine) with H3L(wa) but differ in their heterocyclic rings (imidazole, oxazole, thiazole, and oxazoline). Herein we explore in detail through high-resolution pulsed electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopy in conjunction with density functional theory (DFT) the geometric and electronic structures of the mono- and dinuclear Cu(II) complexes of these cyclic pseudo hexapeptides. Orientation-selective hyperfine sublevel correlation, electron nuclear double resonance, and three-pulse electron spin echo envelope modulation spectroscopy of [Cu(II)(H2L(1))(MeOH)2](+) reveal delocalization of the unpaired electron spin onto the ligating and distal nitrogens of the coordinated heterocyclic rings and that they are magnetically inequivalent. DFT calculations confirm this and show similar spin densities on the distal heteroatoms in the heterocyclic rings coordinated to the Cu(II) ion in the other cyclic pseudo hexapeptide [Cu(II)(H2L(2,3,wa))(MeOH)2](+) complexes. The magnetic inequivalencies in [Cu(II)(H2L(1))(MeOH)2](+) arise from different orientations of the heterocyclic rings coordinated to the Cu(II) ion, and the delocalization of the unpaired electron onto the distal heteroatoms within these N-methylimidazole rings depends upon their location with respect to the Cu(II) d(x(2)-y(2)) orbital. A systematic study of DFT functionals and basis sets was undertaken to examine the ability to reproduce the experimentally determined spin Hamiltonian parameters. Inclusion of spin-orbit coupling (SOC) using MAG-ReSpect or ORCA with a BHLYP/IGLO-II Wachters setup with SOC corrections and ∼38% Hartree-Fock exchange gave the best predictions of the g and A((63)Cu) matrices. DFT calculations of the (14)N hyperfine and quadrupole parameters for the distal nitrogens of the coordinated heterocyclic rings in [Cu(II)(H2L(1))(MeOH)2](+) with the B1LYP functional and the SVP basis set were in excellent agreement with the experimental data, though other choices of functional and basis set also provided reasonable values. MCD, EPR, mass spectrometry, and DFT showed that preparation of the dinuclear Cu(II) complex in a 1:1 MeOH/glycerol mixture (necessary for MCD) resulted in the exchange of the bridging methoxide ligand for glycerol with a corresponding decrease in the magnitude of the exchange coupling.