Spin-Crossing in the ()-Selective Alkyne Semihydrogenation Mechanism Catalyzed by MoS Clusters: A Density Functional Theory Exploration.

Semihydrogenation of internal alkynes catalyzed by the air-stable imidazolyl amino [MoSCl(ImNH)] cluster selectively affords the ()-alkene under soft conditions in excellent yields. Experimental results suggest a sulfur-based mechanism with the formation of a dithiolene adduct through interaction of the alkyne with the bridging sulfur atoms. However, computational studies indicate that this mechanism is unable to explain the experimental outcome: mild reaction conditions, excellent selectivity toward the ()-isomer, and complete deuteration of the vinylic positions in the presence of CDOD and CHOD.

Fe(II) complexes of pyridine-substituted thiosemicarbazone ligands as catalysts for oxidations with hydrogen peroxide.

The reaction of three [Fe(TSC)] complexes, where TSC is a pyridine-substituted thiosemicarbazone of the HDpT or HBpT families, with HO in acetonitrile solution does not result in the accumulation of the corresponding [Fe(TSC)] complexes. Instead, a mixture of diamagnetic low-spin Fe species is generated. According to the MS spectra, those species result from the sequential addition of up to five oxygen atoms to the complex.

Metal bioaccumulation in spontaneously grown aquatic macrophytes in Fe-rich substrates of a passive treatment plant for acid mine drainage.

Some plants may thrive in polluted environments, accumulating high concentrations of metal/loids in their organs. This study investigates for the first time the bioaccumulation and translocation of metal/loids in Typha domingensis spontaneously grown in extremely Fe-rich substrates (38-44% of FeO) from different components of an acid mine drainage disperse alkaline substrate passive treatment. Most metal/loids were predominantly accumulated in the roots over the aerial parts of the plant, with concentrations of 0.

Metal mobility and bioaccessibility from cyanide leaching heaps in a historical mine site.

Unlike acidic sulfide mine wastes, where metal/loid mobility and bioaccessibility has been widely studied, less attention has been paid to alkaline cyanide heap leaching wastes. Thus, the main goal of this study is to evaluate the mobility and bioaccessibility of metal/loids in Fe-rich (up to 55%) mine wastes resulting from historical cyanide leaching activities. Wastes are mainly composed of oxides/oxyhydroxides (i.

Consequences of sea level rise for high metal(loid) loads in the Ría of Huelva estuary sediments.

Ría of Huelva, located in southwestern Spain, is a highly metal(loid)-contaminated estuary system where sediments are exceeding action limits in an increasing order for Cd, Zn, Pb, Cu, and As. With a predicted sea level rise over the next 50 years, the estuary will be subject to flooding with brackish water or seawater. To evaluate the risk of metal(loid) mobilization under future climate scenarios, different locations along the estuary were sampled at different depths.

Characterization of a Ferryl Flip in Electronically Tuned Nonheme Complexes. Consequences in Hydrogen Atom Transfer Reactivity.

Two oxoiron(IV) isomers ( 2a and 2b) of general formula [Fe (O)( PyNMe )(CH CN)] are obtained by reaction of their iron(II) precursor with NBu IO . The two isomers differ in the position of the oxo ligand, cis and trans to the pyridine donor. The mechanism of isomerization between 2a and 2b has been determined by kinetic and computational analyses uncovering an unprecedented path for interconversion of geometrical oxoiron(IV) isomers.

Stream-pit lake interactions in an abandoned mining area affected by acid drainage (Iberian Pyrite Belt).

Opencast mining of sulfide ore deposits may lead to the formation of anthropogenic acidic lakes with highly polluted waters. In these systems, it is crucial to understand the hydrological connections between surface and groundwater and their contribution to the pollutant load delivered to the downgradient streams. This study characterizes the interactions between surface and groundwater in an acidic pit lake using different geochemical tracers (i.

Geochemical behaviour and transport of technology critical metals (TCMs) by the Tinto River (SW Spain) to the Atlantic Ocean.

This paper addresses the behaviour of several technology critical metals (TCMs), i.e., rare earth elements (REEs), Y, Sc, Ga and Tl, in the Tinto River (SW Spain), quantifying their fluxes to the Atlantic Ocean and unravelling the governing geochemical processes controlling their solubility.

Spin State Tunes Oxygen Atom Transfer towards Fe O Formation in Fe Complexes.

Oxoiron(IV) complexes bearing tetradentate ligands have been extensively studied as models for the active oxidants in non-heme iron-dependent enzymes. These species are commonly generated by oxidation of their ferrous precursors. The mechanisms of these reactions have seldom been investigated.

Distribution and availability of rare earth elements and trace elements in the estuarine waters of the Ría of Huelva (SW Spain).

Metal pollution in estuaries represents a serious environmental challenge, especially in areas affected by industrial and mining activities. This study investigates the metal partitioning and availability of rare earth elements (REE), Y and other trace metals (Ag, Tl, U and Cs) in the Ria of Huelva estuary (SW Spain), strongly affected by mining and industrial activities. A 30 h monitoring campaign was performed collecting periodic water samples and deploying diffusive gradient in thin films (DGTs) devices to determine the main factors controlling metal availability.

Metal partitioning and speciation in a mining-impacted estuary by traditional and passive sampling methods.

This study deals with the metal partitioning and bioavailability of metal/loids in the estuary Ria of Huelva (SW Spain) which is strongly affected by historical mining and industrial activities. To address this issue, traditional (i.e.

Salen‑manganese complexes for controlling ROS damage: Neuroprotective effects, antioxidant activity and kinetic studies.

A new manganese(III) complex [MnL(DCA)(HO)](HO)1 [HL is the chelating ligand N,N'-bis(2-hydroxy-3-methoxybenzylidene)-1,2-diaminopropane, and DCA is dicyanamide], has been prepared and characterized by different analytical and spectroscopic techniques. The tetragonally elongated octahedral geometry for the manganese coordination sphere was revealed by X-ray diffraction studies for 1. The antioxidant behavior of this complex and other manganese(III)-salen type complexes was tested through superoxide dismutase and catalase probes, and through the study of their neuroprotective effects in SH-SY5Y neuroblastoma cells.

Trace metal mobility in sub-seabed sediments by CO seepage under high-pressure conditions.

Carbon capture and storage (CCS) is the third contributor to cumulative carbon emission reductions required by the second half of this century. Although this is a promising technology for reducing atmospheric CO, it is only affordable if the confinement of the gas is guaranteed for hundreds of years. Hence, it is of paramount importance to figure out and predict the chemical and biological effects associated with potential CO leakage, to provide decision makers with a good basis for choosing technology and potential storage sites.

Intraspecific variation in the response of the estuarine European isopod Cyathura carinata (Krøyer, 1847) to ocean acidification.

In the present study the model isopod, Cyathura carinata were exposed to four pH treatments (control: 7.9; 7.5, 7, 6.

Causes and impacts of a mine water spill from an acidic pit lake (Iberian Pyrite Belt).

In May 2017, a spill from La Zarza pit lake (SW Spain) resulted in the release of approximately 270,000 m of extremely acidic waters to the Odiel River. Around 780 × 10 kg of Fe, 170 × 10 kg of Al, 2.15 × 10 kg of As and high amounts of other trace metals and metalloids were spilled.

Pitfalls in the ABTS Peroxidase Activity Test: Interference of Photochemical Processes.

ABTS (2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid) oxidation to form its radical cation in the presence of HO is frequently used as a test for determining the peroxidase activity of enzyme mimics. Detailed studies using salen-type Mn(III) complexes show that photochemical processes involving HO, ABTS, and the complex itself can lead to erroneous results. The capability of the complexes to act as OH scavengers can be also relevant when the mechanism of their biological activity is considered.

Coordination Chemistry of Cu Complexes of Small N-Alkylated Tetra-azacyclophanes with SOD Activity.

A new tetraaza-pyridinophane macrocycle (L1) N-alkylated with two isopropyl and one methyl groups symmetrically disposed has been prepared and its behavior compared with those of the unsubstituted pyridinophane (L3) and the related compound with three methyl groups (L2). The protonation studies show that, first, a proton binds to the central methylated amine group of L1, while, second protonation leads to a reorganization of the protons that are at this stage attached to the lateral isopropylated amines. The X-ray structure of [HL1] agrees with the UV-vis and NMR studies as well as with the results of DFT calculations.

Metal fractionation in marine sediments acidified by enrichment of CO: A risk assessment.

Carbon-capture and storage is considered to be a potential mitigation option for climate change. However, accidental leaks of CO can occur, resulting in changes in ocean chemistry such as acidification and metal mobilization. Laboratory experiments were performed to provide data on the effects of CO-related acidification on the chemical fractionation of metal(loid)s in marine-contaminated sediments using sequential extraction procedures.

Acid-Triggered O-O Bond Heterolysis of a Nonheme Fe (OOH) Species for the Stereospecific Hydroxylation of Strong C-H Bonds.

A novel hydroperoxoiron(III) species [Fe (OOH)(MeCN)(PyNMe )] (3) has been generated by reaction of its ferrous precursor [Fe (CF SO ) (PyNMe )] (1) with hydrogen peroxide at low temperatures. This species has been characterized by several spectroscopic techniques and cryospray mass spectrometry. Similar to most of the previously described low-spin hydroperoxoiron(III) compounds, 3 behaves as a sluggish oxidant and it is not kinetically competent for breaking weak C-H bonds.

Pb complexes of small-cavity azamacrocyclic ligands: thermodynamic and kinetic studies.

The synthesis, acid-base behavior and Pb coordination chemistry of the new aza-scorpiand like ligand 5-[2-(N-2-fluorenyl)ethylamino]-2,5,8-triaza[9]-2,6-pyridinophane (L1) have been studied by potentiometry, NMR and spectrofluorimetric titrations, and the results are compared with those obtained for the related compounds L2, lacking the fluorenyl group, and L3, the macrocycle lacking the pendant arm. The crystal structures obtained for complexes [PbL1][PbL1Cl](NO)Cl·4HO (1) and [PbL3](ClO) (2) reveal that the metal ion is located over the plane defined by the nitrogen atoms of the macrocyclic core due to its inability to accommodate the large Pb ion in the macrocyclic cavity. For L1, the secondary amino group of the pendant arm is implicated in the coordination of the metal ion, although the stereoactive lone pair of Pb prevents the closed conformation associated with the coordination of metal ions in aza-scorpiand derivatives.