Narrow Results

Effective systems for the catalytic oxygenation of hydrocarbons have been developed based on metalloporphyrins containing iron, manganese and ruthenium. These metalloporphyrin catalysts were inspired by studies of the mechanism of the heme oxygenase cytochrome P450 and related enzymes. Oxometalloporphyrins, which have now been spectroscopically characterized, have very high reactivity as oxygen transfer agents. A combination of experimental and computational methods has begun to provide an understanding of the structure and reactivity of these oxometalloporphyrin complexes and the mechanisms of oxygen transfer reactions they catalyze.

Manganese complexes of 5,15-diaryl-β-substituted-porphyrins were prepared and their behaviour as oxidation catalysts was studied. The role of the pyrrolic and meso-substituents on the activity and selectivity of these catalysts was studied to reveal new structure–activity relationships in these porphyrin-based epoxidation catalysts. The beneficial effect of the halogen atoms at the meso-phenyls is still observed with these catalysts but, for the first time, a strong dependence on the selectivity of the epoxide production was found to be dependent on the nature of the non-halogen substituents at the β-pyrrolic positions of the porphyrin.

The groundwater pollution by arsenic in Bangladesh causes a serious problem for millions of people who are exposed to poisoning by this toxic element. In an attempt to evaluate the extent of arsenic poisoning, hair samples of people living in Pabna district were collected. The hair samples were analyzed using Proton Induced X-ray Emission (PIXE) through exciting the atoms of a specimen so that their intensities can be converted into elemental concentrations in the specimen. The elements present in the specimen are identified by the corresponding X-ray energies and their concentrations are deduced from the X-ray intensities. The results from hair samples indicate substantially higher level of arsenic than those demarcated as toxic levels, in people from member families both affected and non-affected by poisoning. We correlate it with exceedingly high arsenic concentration in drinking water far above the permissible limit. The analytical results are compared with the results of arsenic and other elemental analysis of 160 Bangladeshi hair samples with that of 250 Japanese samples. The results show markedly higher levels of arsenic, manganese, iron and lead where the latter three elements show a positive relation with arsenic in the case of Bangladeshi as compared to the samples from Japan. On the other hand, selenium concentrations show very low level in the Bangladeshi samples compared to Japanese, displaying an inverse relationship with arsenic. The mechanism of arsenic in relation to other elements in the human body needs further investigation. The preliminary results call for detailed experimental and epidemiological studies to further characterize these aspects.

In salt farms of Thailand, saline ground water is pumped up and then solar-evaporated to produce salt for commercial purpose. However, when they continue to precipitate salt in the same pools, the product is stained yellow or brown in color. In order to recover only white salt, workers cut trees and create a new pool next to the old one. Due to this practice, year by year, salt-farming area loses vegetation cover and expands barren section of salt damage. In order to understand the changes of in salt grains, salt was collected and measured by PIXE. The result indicates that manganese is clearly responsible for the coloring, and possibly also irons. This information is expected to base the discussion to stop deforestation in the salt-damaged area.

In this paper, we measured the concentrations and spatial distributions of aluminum and manganese with the growing period of a tea leaf. Both elemental concentrations increased with the growing period and showed a rapid increase between five and six months. Aluminum showed clear localization in the epidermis with the growing period. Manganese did not show clear localization like aluminum throughout the growing period. The spatial correlation between aluminum and manganese were not observed.

Glasses of the xMnO·(100–x)[Bi₂O₃·CdO] system with 0<x≤50 mol%, were prepared and studied by means of EPR and magnetic susceptibility measurements. The EPR investigations indicated the compositional domains favorable to isolated manganese ions or to those magnetically clustered. The magnetic measurements evidenced the presence of both Mn²⁺ and Mn³⁺ ions, with their relative content depending on the MnO concentration. The prevalence of the dipolar and respectively the superexchange interactions between the manganese ions can be correlated with the relative content of the Mn²⁺ and Mn³⁺ species.

The objective of this work was to study the influence of titanium variations on the API 5L-X70 steel weld metal properties. The relationship between microstructure and toughness of the weld deposit was studied by means of full metallographic, longitudinal tensile and Charpy-V notch tests on the specimens cut transversely to the weld beads. The best combination of microstructure and impact properties was obtained in the range of 0.02-0.05% titanium. By further increasing of titanium content, the microstructure was changed from a mixture of acicular ferrite, grain-boundary ferrite, Widmanstätten ferrite to a mixture of acicular ferrite, grain-boundary ferrite, bainite and ferrite with M/A microconstituent. Therefore, the mode of fracture also changed from dimpled ductile to quasi-cleavage. Titanium-base inclusions improve impact toughness by increasing the formation of acicular ferrite in the microstructure. The amount of manganese in inclusions was decreased with addition of titanium to the weld metal.

The technique of X-ray photoelectron spectroscopy has been used to investigate the chemical reactivity at the metal/CuO interfaces. Thin films of the metallic overlayer (0.5 nm, 1.0 nm and 2.0 nm thickness) were deposited on copper oxide substrates at room temperature. In situ characterization of the interfaces has been performed. The 2p core level regions of the metals have been investigated. The spectral features show considerable reactivity at the interfaces. The core level peaks of the metal are observed to be shifted to the high BE energy side with the appearance of satellites. The spectral data confirm the formation of the metallic oxide at the interface. The satellite structure in the copper region is observed to disappear and the spectral features are found to approach those of elemental copper. The room temperature deposition of the metal on copper oxide therefore results in the reduction of copper oxide to elemental copper followed by the oxidation of the metal. The interface is found to consist of a mixture of metal oxide and elemental copper. The 2.0 nm samples were annealed. These samples show the diffusion of copper oxide through the overlayer. The metal reacts with this diffusing oxide to form metallic oxide. The interface is found to consist of a mixture of unreacted metal, the metal oxide, and elemental copper. The amount of the unreacted metal varied between 0% and 40% and can be controlled by the processing conditions. The investigation shows room temperature chemical reactivity at the metal/CuO interface and provides a new method of preparing sub-nano-oxide films.

A series of (Fe${}_{2.2}$Mn${}_{0.8}$Cu${}_x{)}_{1-\delta }$O₄ ($x=0$, 0.2, 0.5, and 0.8) was synthesized for elemental mercury capture. The as-synthesized adsorbents were characterized by Brunauer–Emmett–Teller (BET), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental results show that (Fe${}_{2.2}$Mn${}_{0.8}$Cu${}_{0.5}{)}_{1-\delta }$O₄ catalyst adsorbent exhibits the best elemental mercury capture capacity with the increase in mercury removal efficiency by 20% as compared to the (Fe${}_{2.2}$Mn${}_{0.8}{)}_{1-\delta }$O₄ adsorbent. The XPS results indicate Cu dopant can provide the lattice oxygen on the adsorbent surface due to the transformation from Cu${}^{2+}$ cations to Cu${}^{+}$ cations, which increases the active sites for elemental mercury adsorption. The Mn${}^{4+}$ cations on the adsorbent surface may oxidize the adsorbed mercury to mercury oxidization. Meanwhile, the Mn${}^{3+}$ cations formed are also oxidized to the Mn${}^{4+}$ cations by the gaseous oxygen phase in the reactor gas. However, the large Cu content may block the collision between Mn${}^{4+}$ cations and adsorbed mercury, and thus decrease the oxidization capability of adsorbent surface for mercury. Therefore, the Cu dopant with the suitable content may be a potential modified method for the adsorbent to further increase the elemental mercury capture.

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New Mn12 single-molecule nanomagnets [Mn₁₂O₁₂(O₂CCHCl₂)(H₂O)₄]·2CH₂Cl₂·H₂O and [Mn₁₂O₁₂(O₂CCHCl₂)(H₂O)₄]·2CH₃C₆H₅·4H₂O and novel Mn18 complexes [M₁₈O₁₄(O₂CR)₁₈(hmp)₄(hmpH)₂(H₂O)₂](R=Me, Et) have been synthesized and characterized by single crystal X-ray crystallography and dc- and ac-magnetic susceptibility measurements. Mn12 complexes show characteristic SMM properties, such as temperature-dependent out-of-phase ac-susceptibility. Mn18 does not show relaxation behaviors down to 2.0 K, but reveals magnetic anisotropy in reduced magnetization experiment.

A new family of pyrrole substituted metallophthalocyanine complexes, namely cobalt(II), iron(II), manganese(III), nickel(II) and zinc(II) tetrakis-4-(pyrrol-1-yl)phenoxy phthalocyanines (noted as M(TPhPyrPc), where M is the metallic cation) have been synthesized and fully characterized. In particular, the UV-visible spectra of the iron and nickel complexes showed extensive aggregation even at low concentrations. The cyclic voltammetry of the cobalt, iron and manganese complexes showed three to four redox couples assigned to metal and ring based processes. Spectroelectrochemistry of the manganese derivative confirmed that the synthesized complex is Mn^III(TPhPyrPc^-2) and that the reduction of Mn^II(TPhPyrPc^-2) to be centred on the ring and rather than on the metal, forming the Mn^II(TPhPyrPc^-4) species. Also, the electrochemical polymerization of these newly synthesized pyrrole-substituted phthalocyanines has been demonstrated in the case of the cobalt complex and the electrocatalytic activity of the obtained film has been tested towards the oxidation of L-cysteine.

Novel chiral systems for the catalytic asymmetric oxidation and cyclopropanation of olefins based on metalloporphyrins containing iron, ruthenium and manganese, have been recently introduced. High catalyst turnover numbers and sometimes high enantiomeric excess were observed. New catalytic reactions with metalloporphyrins have recently been reported; these are the olefination of aldehydes and cyclotrimerization of terminal alkynes. Dendrimers and polymers containing metalloporphyrins, have also been found to be efficient catalysts for oxidation and carbene transfer.

The Mn complexated corrole [T(4-NO₂P)Corr]Mn(py) (3) has been prepared (py = pyridine) where [T(4-NO₂P)Corr] is the trianion of the electron-poor 5,10,15-tris(4-nitrophenyl)corrole (1). The preparation of 3 includes a new synthetic method to form the corrole ligand 1 in a two-step synthesis. The Mn(III) complex gives a parallel mode EPR signal centered around g = 8.2 with six distinct hyperfine lines (A_|| = 139 × 10^-4cm^-1). Electrochemically 3 undergoes one reversible oxidation (E_1/2 = 0.12 V vs Fc) and two reversible reductions (E_1/2 = -1.45, -1.61 V). The oxidation is metal-centered and the product has been characterized by EPR spectroscopy as an S = 3/2Mn(IV) species with no indication for oxidation of the macrocycle. The reductions of complex 3 are ligand based, and at the potential of the second reduction step a stable nitrogen centered radical with g = 2.0055 is generated. Chemical oxidation of 3 by iodosobenzene yields a Mn(IV) complex and epoxidation of cis-stilbene is not catalyzed by the Mn complex.

A α,ω-dimethyldipyrrin with and without a meso-situated phenyl substituent has been investigated as the substrate in the oxidation reaction with the Mn^II/O₂ system. While for the meso-phenyldipyrrin, the expected, though impure and sensitive diformyl derivative is formed, the reaction of the meso unsubstituted dipyrrin leads to a novel tripyrrolic species, the α-(vinylpyrrolyl)dipyrrin, as the only isolable product. The new tripyrrole displays positive solvatochromic behavior and has been investigated with respect to this property.

This work reports the use of metallo tetra-amino phthalocyanines (MTAPc, M = Co and Mn) polymer thin films on gold and glassy carbon electrode surfaces for the detection and monitoring of hydrogen peroxide (H₂O₂). The polymer-modified electrodes were characterized using electrochemical and microscopic-based methods. Atomic force microscopy (AFM) was used to study the bare and polymer-modified ITO surfaces. The electrocatalytic reduction of H₂O₂ with glassy carbon polymer-modified electrodes gave higher current densities compared to their gold counterparts. The electroanalytical properties of H₂O₂ were obtained using a real-time calibration curve of the amperometric determination in pH 7.4 aqueous solution. The limits of detection (LoD) of the polymer-modified electrodes towards electroreduction of H₂O₂ were of the order of 10^–7 M, with high sensitivity ranging from 6.0–15.4 mA.mM^-1.cm^-2.

Corroles that carry either two or three ortho-pyridyl groups at the meso-carbon atoms form stable manganese(III) complexes, from which corresponding water-soluble derivatives are obtained via N-alkylation. These syntheses and the spectroscopic features are disclosed, together with the molecular structure of the manganese(III) corrole that carries three ortho-pyridylium groups. All the manganese(III) corroles may be transformed to stable (nitrido)manganese(V) complexes, whose NMR spectra provide invaluable structural information regarding the identity and number of atropoisomers.

Three manganese biscorrole dyads were synthesized, physicochemically characterized and investigated as to their electrochemistry and spectroelectrochemistry in nonaqueous media. Each dyad contained the same two corroles linked in a face-to-face arrangement via one of the three different linking groups, 9,9-dimethylxanthene, anthracene or diphenylether, the exact nature of which determined the distance and possible interaction between the two metallomacrocycles. The initial compounds contained Mn(III) in their air stable form and were shown to exhibit two major redox processes, one being a Mn(III)/Mn(IV) conversion and the other being either Mn(III)/Mn(II) or reduction at the conjugated macrocycle to give a Mn(III) corrole π-anion radical when the solvent was pyridine. The potentials and reversibility of each electron transfer reaction were shown to depend upon the solvent (pyridine, CH₂Cl₂, or PhCN), type of spacer separating the two macrocycles and/or the presence or absence of axial ligation. The site of each electron transfer was assigned on the basis of spectroscopic and electrochemical data and by comparison with reactions and properties of the monocorrole (Mes₂PhCor)Mn which was characterized in a previous publication and also examined in the current study under the same solution conditions as the newly investigated dyads. Some electrode reactions of the dyads were followed by coupled chemical reactions and these were also elucidated in the present study.

Oxidation of olefins with tert-butyl hydroperoxide (TBHP), tetra-n-butylammonium periodate (TBAP) and potassium peroxomonosulfate (Oxone) in the presence of MCM-41 immobilized meso-tetra-4-carboxyphenylporphyrinatomanganese(III) acetate has been studied. The results of this study show better catalytic performance of the heterogonous catalyst using TBHP as oxidant in comparison with Oxone and TBAP in oxidation of the used olefins with the exception of cyclooctene. However, different order of reactivity of various olefins has been observed in the presence of Oxone and TBHP. In spite of the absence of good electron-withdrawing groups at the periphery of porphyrin ligand, the catalyst was recovered and reused (at least four times) without detectable catalyst leaching or a significant loss of the catalytic efficiency. All results have been obtained in the absence of using excess molar ratios of olefin to the oxidant, commonly employed as a strategy to overcome the instability of metalloporphyrins in oxidative conditions.

The electronic and structural features of (oxo)manganese(V) corroles (Mn(V)-oxo(cor)) in different oxidation states and their oxygen atom transfer (OAT) reactivity towards dimethyl sulfide (DMS) have been investigated by density functional theory (DFT) calculations. Three Mn(V)-oxo corroles with different β-substituents (Br(1), H(2), CH₃(3)) were choosen as model complexes. The results revealed that Mn(V)-oxo corrole bearing electron-withdrawing substituent (Br) is more reactive than those having electron-donating substituents. Moreover, the conceptual DFT descriptor ω for Mn(V)-oxo corrole in one-electron oxidized state is always larger than the neutral or one-electron reduced state. These calculations for the transition state involved in OAT reaction also indicated that the radical cation formed after one-electron oxidation, Mn(V)-oxo(cor^+•), is the most reactive specie, while the neutral [Mn(V)-oxo(cor)] in the triplet states are more reactive than those in the singlet states.