Dissociation Of Chloride Research Articles

DLPNO-CCSD(T) and DFT study of the acetate-assisted C-H activation of benzaldimine at [RuCl2(p-cymene)]2: the relevance of ligand exchange processes at ruthenium(II) complexes in polar protic media.

To gain mechanistic insights into the acetate-assisted cyclometallations of arylimines promoted by [RuCl2(p-cymene)]2 in polar protic media, DFT geometry optimizations (with M06 and ωB97X-D3 functionals and the cc-pVDZ-PP[Ru] basis set) followed by DLPNO-CCSD(T)/CBS energy evaluations were performed using benzaldimine as a model substrate and methanol as the solvent (with CPCM or SMD models). The calculation results show that coordination of the imine to an acetate ruthenium precursor is followed by anion (chloride or acetate) dissociation as the rate-determining step of the process. H-Bonding of two explicit MeOH to the anion reduces the calculated activation energy to ca. 23 kcal mol-1, in good agreement with the experimental half-life at room temperature. Subsequent AMLA/CMD C-H activation of the intermediate cationic complexes is a faster, reversible process. Alternative reaction pathways involving neutral diacetate ruthenium complexes offer AMLA/CMD transition state structures of lower energy but are precluded due to higher energy barriers for the initial ligand exchange processes at ruthenium. Solvent assistance accelerates the final chloride/acetate exchange processes on the cycloruthenate intermediates, particularly when compression in the condensed phase is taken into consideration. The performance of six DFT functionals (with the aug-pVTZ-PP[Ru] basis set) was assessed using the DLPNO-CCSD(T)/CBS reference energies. Neutral diacetate ruthenium complexes were incorrectly predicted as being kinetically relevant when using hybrid DFT methods (PBE0-D3(BJ), M06-2X or ωB97M-V). Good agreement between the calculated barrier heights and our benchmark energy results was obtained by using double-hybrid DFT methods. PWPB95 with D3(BJ) or D4 dispersion energy corrections was found to be the most accurate (ΔG≠ MUE of ca. 1 kcal mol-1). This study may aid our understanding of and help with further experimental investigations of synthetically useful carboxylate-assisted C-H bond functionalizations involving (N,C)-cyclometallated (p-cymene)Ru(II) intermediate complexes in sustainable polar protic solvents.

Visible Light-Assisted Coordination of a Rh(III)-BODIPY Complex to Guanine.

Most photodynamic therapeutics (PDTs) used in cancer treatment require oxygen to work efficiently to terminate cancer cells. These PDTs do not efficiently treat tumors in hypoxic conditions. Rh(III) polypyridyl complexes have been reported to have a photodynamic therapeutic effect in hypoxic conditions when exposed to UV light. UV light can damage tissue and cannot penetrate deep to reach cancer cells. This work proposes the coordination of a BODIPY fluorophore to a rhodium metal center to form a Rh(III)-BODIPY complex that enhances the reactivity of the rhodium under visible light. This complex formation is facilitated with the BODIPY as the highest occupied molecular orbital (HOMO), while the lowest unoccupied molecular orbital (LUMO) is localized on the Rh(III) metal center. Irradiation of the BODIPY transition at ∼524 nm can cause an indirect electron transfer from the orbital of the BODIPY-centered HOMO to the Rh(III)-centered LUMO, populating the dσ* orbital. In addition, photo binding of the Rh complex covalently coordinated to the N (7) position of guanine in an aqueous solution was also observed by mass spectrometry after chloride dissociation upon irradiation with green visible light (532 nm LED). Calculated thermochemistry values of the Rh complex reaction in methanol, acetonitrile, water, and guanine were determined using DFT calculations. All enthalpic reactions and Gibbs free energies were identified as endothermic and nonspontaneous, respectively. This observation supports the chloride dissociation using 532 nm light. This Rh(III)-BODIPY complex expands the class of visible light-activated Rh(III) photocisplatin analogs that may have potential photodynamic therapeutic activity for the treatment of cancers in hypoxic conditions.

Comparison of Catalytic Properties of the Easily Interconvertible, Water-Soluble [RuHCl(CO)(mtppms-Na)3] and [RuH(H2O)(CO)(mtppms-Na)3][BF4

The effect of the mobile interconversion of [RuHCl(CO)(mtppms-Na)3] 1, and [RuH(H2O)(CO)(mtppms-Na)3]+ 2, was studied in hydrogenation of phenylacetylene and cinnamaldehyde in aqueous–organic biphasic systems, as a function of the chloride concentration and the pH of the aqueous phase. Catalytic activity of the two complexes was also determined in homogeneous organic solvents without any additives. In the biphasic system, the rate of selective hydrogenation of phenylacetylene to styrene was strongly increased upon addition of NaCl, while the reaction of cinnamaldehyde slowed, with no change in product distribution. Both reactions responded with a rate decrease upon increasing the pH of the aqueous phase. It was concluded that hydrogenation of phenylacetylene was catalyzed by 1 with no chloride dissociation, while in the reduction of cinnamaldehyde, the aquo-complex 2 was the active catalytic species. Catalytic cycles were suggested to rationalize these findings.

Role of the Meso Substituent in Defining the Reduction of Uranyl Dipyrrin Complexes.

The uranyl complex UVIO2Cl(LMes) of the redox-active, acyclic dipyrrin-diimine anion LMes- [HLMes = 1,9-di-tert-butyl-imine-5-(mesityl)dipyrrin] is reported, and its redox property is explored and compared with that of the previously reported UVIO2Cl(LF) [HLF = 1,9-di-tert-butyl-imine-5-(pentafluorophenyl)dipyrrin] to understand the influence of the meso substituent. Cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory studies show that the alteration from an electron-withdrawing meso substituent to an electron-donating meso substituent on the dipyrrin ligand significantly modifies the stability of the products formed after reduction. For UVIO2Cl(LMes), the formation of a diamond-shaped, oxo-bridged uranyl(V) dimer, [UVO2(LMes)]2 is seen, whereas in contrast, for UVIO2Cl(LF), only ligand reduction occurs. Computational modeling of these reactions shows that while ligand reduction followed by chloride dissociation occurs in both cases, ligand-to-metal electron transfer is favorable for UVIO2Cl(LMes) only, which subsequently facilitates uranyl(V) dimerization.

Multiple molecular mechanisms are involved in the activation of the kidney sodium-chloride cotransporter by hypokalemia

Low potassium intake activates the kidney sodium-chloride cotransporter (NCC) whose phosphorylation and activity depend on the With-No-Lysine kinase 4 (WNK4) that is inhibited by chloride binding to its kinase domain. Low extracellular potassium activates NCC by decreasing intracellular chloride thereby promoting chloride dissociation from WNK4 where residue L319 of WNK4 participates in chloride coordination. Since the WNK4-L319F mutant is constitutively active and chloride-insensitive invitro, we generated mice harboring this mutation that displayed slightly increased phosphorylated NCC and mild hyperkalemia when on a 129/sv genetic background. On a low potassium diet, upregulation of phosphorylated NCC was observed, suggesting that in addition to chloride sensing by WNK4, other mechanisms participate which may include modulation of WNK4 activity and degradation by phosphorylation of the RRxS motif in regulatory domains present in WNK4 and KLHL3, respectively. Increased levels of WNK4 and kidney-specific WNK1 and phospho-WNK4-RRxS were observed in wild-type and WNK4L319F/L319F mice on a low potassium diet. Decreased extracellular potassium promoted WNK4-RRxS phosphorylation invitro and exvivo as well. These effects might be secondary to intracellular chloride depletion, as reduction of intracellular chloride in HEK293 cells increased phospho-WNK4-RRxS. Phospho-WNK4-RRxS levels were increased in mice lacking the Kir5.1 potassium channel, which presumably have decreased distal convoluted tubule intracellular chloride. Similarly, phospho-KLHL3 was modulated by changes in intracellular chloride in HEK293 cells. Thus, our data suggest that multiple chloride-regulated mechanisms are responsible for NCC upregulation by low extracellular potassium.

Corrosion of Iron Covered with Iron Oxide Film by Chlorine and Hydrogen Chloride Gases: A Molecular Dynamics Simulation Study Using the ReaxFF

Flue gas produced by biomass fuel combustion contains various chlorine-containing substances and is an important factor causing biomass boiler corrosion. The corrosion processes of chlorine, hydrogen chloride and water on iron covered with an intact/damaged oxide film were investigated under the high temperature of 1300 K through reactive molecular dynamics simulation. The results show that the diffusion processes of oxygen and chlorine are similar and can be divided into three stages: rapid diffusion, continuous diffusion, and no oxide film (stable). Oxygen diffusion in Fe2O3 into a pure iron layer is the main cause of gas corrosion in iron/iron oxide systems. A complete oxide film can hinder iron corrosion by chlorine and hydrogen chloride. Damage in an oxide film significantly affects oxygen and chlorine diffusion and iron corrosion. However, such influence is gradually reduced. The integrity of a protective film is the key to alleviating corrosion. Water facilitates the dissociation of chlorine and hydrogen chloride, and it reacts with iron at high temperatures to enhance corrosion. This study improves the understanding of the iron oxide/iron corrosion from chlorine-containing gases from a microscopic perspective and is of great significance to metal corrosion protection and biomass combustion technologies.

Data-Driven Langevin Modeling of Nonequilibrium Processes.

Given nonstationary data from molecular dynamics simulations, a Markovian Langevin model is constructed that aims to reproduce the time evolution of the underlying process. While at equilibrium the free energy landscape is sampled, nonequilibrium processes can be associated with a biased energy landscape, which accounts for finite sampling effects and external driving. When the data-driven Langevin equation (dLE) approach [Phys. Rev. Lett. 2015, 115, 050602] is extended to the modeling of nonequilibrium processes, an efficient way to calculate multidimensional Langevin fields is outlined. The dLE is shown to correctly account for various nonequilibrium processes, including the enforced dissociation of sodium chloride in water, the pressure-jump induced nucleation of a liquid of hard spheres, and the conformational dynamics of a helical peptide sampled from nonstationary short trajectories.

Theoretical Investigation of Hydrogen‐Bond‐Assisted Tetradentate N4 Copper(I) Chloride andtrans‐1,2‐Peroxodicopper Complexes

AbstractBiological oxygenation catalyzed by copper‐containing enzymes involves a dicopper O2adduct as the key intermediate. Significant insights were offered by thetrans‐1,2‐peroxodicopper intermediates. To understand the activity of thetrans‐1,2‐peroxodicopper intermediate in the oxygenation, a series of hydrogen‐bond‐assisted CuI(L)−Cl andtrans‐1,2‐peroxodicopper complexes [Cu2−O2]2+were investigated by DFT computations. A reasonable two‐parameter structure‐activity model (R2=0.8611) and a three‐parameter structure‐activity model (R2=0.8773) for chloride dissociation (ΔG1RXN) were established. The critical intramolecular out‐sphere hydrogen bonds assist the formation of stabletrans‐1,2‐peroxodicopper complexes, which overcome the steric hindrances and electrostatic repulsion. An acceptable two‐parameter structure‐activity model (R2=0.7051) for O2binding (ΔG2RXN) was obtained. The fundamental structure‐activity interpretation of the hydrogen bonding interactions provides an insight into the modelling oftrans‐1,2‐peroxodicopper mimics.

Dioxygen Activation by Internally Aromatic Metallacycle: Crystallographic Structure and Mechanistic Investigations.

SummaryMononuclear metal-peroxo species are invoked as the key intermediates in metalloenzymatic or synthetic catalysis. However, either transience or sluggishness reactivity of synthetic analogs of metal-peroxo species impedes our understanding of oxygen activation mechanism. Herein, we designed and characterized a dioxygen-derived mononuclear osmium-peroxo complex, in which the peroxo ligand is stabilized by internally aromatic metallacycle. We demonstrate that the osmium-peroxo species shows catalytic activity toward promoterless alcohol dehydrogenations. Furthermore, computational studies provide a new mechanism for the osmium-peroxo-mediated alcohol oxidation, starting with the concerted double-hydrogen transfer and followed by the generation of osmium-oxo species. Interestingly, the internally aromatic metallacycle also plays a vital role in catalysis, which mediates the hydrogen transfer from osmium center to the distal oxygen atom of Os–OOH moiety, thus facilitating the Os–OOH→Os=O conversion. We expect that these insights will advance the development of aromatic metallacycle toward aerobic oxidation catalysis.

A new organometallic rhodium(I) complex with dpp-bian ligand: Synthesis, structure and redox behaviour

Reaction of [{Rh(COD)}2(μ-Cl)2] with 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian) has afforded a new organometallic complex [Rh(COD)(dpp-bian)Cl] (1). The crystal structure of 1·0.25H2O was determined by X-ray single crystal analysis. The rhodium(I) ion has a distorted square-pyramidal coordination. The RhCl distance (2.5908 (12) Å) is rather long, indicating weak coordination of the chloride. Dissociation of chloride in solution to produce cationic [Rh(COD)(bian)]+ ([1-Cl]+) was confirmed by ESI-MS, 1H NMR, CV and DFT calculations. Cyclic voltammetry of 1 in acetonitrile (CH3CN) showed two reversible one-electron redox waves at E1/2 = −0.36 V and −1.18 V (versus Ag/AgCl) attributable to successive reduction of the dpp-bian ligand in [1-Cl]+. DFT calculations were performed to explain the anomalously long RhCl distance and interpret the reduction sequence of 1.

Imaging the infrared multiphoton excitation and dissociation of propargyl chloride.

Infrared multiphoton excitation is combined with UV excitation and state-resolved probes of Cl(2P3/2), Cl*(2P1/2), and HCl to study the photochemistry of propargyl chloride. The results show evidence both of infrared multiphoton dissociation on the ground electronic state and infrared multiphoton excitation followed by UV dissociation. The results are interpreted with the aid of a full characterization of the stationary points on the ground state using ab initio methods, as well as our recent experimental and theoretical characterization of the UV photochemistry of the molecule. The data suggest elimination of HCl on the ground electronic state produces linear propadienylidene as a coproduct over a roaming-like transition state that accesses the Cl-H-C abstraction geometry. This identification is supported by separate chirped-pulse microwave studies in a quasi-uniform flow also reported here.

ON MECHANISMS OF INCREASING HCL DISSOCIATION DEGREE IN GLOW DISCHARGE PLASMA

The influence of initial compositions of the binary HCl+Ar and HCl+O2 gas mixtures on the hydrogen chloride dissociation kinetics in low temperature gas discharge plasma was investigated. The experiments were carried out under the conditions of direct current glow discharge at constant total gas pressure (100 Pa) and discharge current (25 mA). The data on electro-physical plasma parameters and plasma composition were obtained by modeling procedure based on the simultaneous solution of Boltzmann kinetic equation and the equations of chemical kinetics for neutral and charged species in a steady-state approximation. It was found that an increase in the second component fraction in both gas mixtures results in the sufficient increase in the HCl dissociation degree (aHCl = 23–43% for 0–80% Ar and 23–90% for 0–80% O2), which is associated with different mechanisms. Particularly, in the HCl+Ar gas mixture, an effect of increasing aHCl is provided by an increase in the electron impact dissociation frequency due to the change in electro-physical plasma parameters, such as electron mean energy and electron density. For the HCl+O2 gas mixture, such mechanism is almost negligible because of the weak disturbances in both electron energy distribution and formation/decay balance for charged species in the combination of two molecular electronegative gases. At the same time, the HCl dissociation kinetics in this gas system appears to be strongly dependent on the gas-phase interactions with ground state of oxygen atoms O(3P), metastable atoms O(1D) and OH radicals. It was found that the rates of corresponding processes begin to exceed the HCl electron impact dissociation rate at 20% O2 in HCl+O2.Forcitation:Efremov A.M., Murin D.B., Belyaev S.V. On mechanisms of increasing hcl dissociation degree in glow discharge plasma. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 61-66

Mechanism of Chemical and Electrochemical N2 Splitting by a Rhenium Pincer Complex.

A comprehensive mechanistic study of N2 activation and splitting into terminal nitride ligands upon reduction of the rhenium dichloride complex [ReCl2(PNP)] is presented (PNP– = N(CH2CH2PtBu2)2–). Low-temperature studies using chemical reductants enabled full characterization of the N2-bridged intermediate [{(PNP)ClRe}2(N2)] and kinetic analysis of the N–N bond scission process. Controlled potential electrolysis at room temperature also resulted in formation of the nitride product [Re(N)Cl(PNP)]. This first example of molecular electrochemical N2 splitting into nitride complexes enabled the use of cyclic voltammetry (CV) methods to establish the mechanism of reductive N2 activation to form the N2-bridged intermediate. CV data was acquired under Ar and N2, and with varying chloride concentration, rhenium concentration, and N2 pressure. A series of kinetic models was vetted against the CV data using digital simulations, leading to the assignment of an ECCEC mechanism (where “E” is an electrochemical step and “C” is a chemical step) for N2 activation that proceeds via initial reduction to ReII, N2 binding, chloride dissociation, and further reduction to ReI before formation of the N2-bridged, dinuclear intermediate by comproportionation with the ReIII precursor. Experimental kinetic data for all individual steps could be obtained. The mechanism is supported by density functional theory computations, which provide further insight into the electronic structure requirements for N2 splitting in the tetragonal frameworks enforced by rigid pincer ligands.

Ligand Control of Supramolecular Chloride Photorelease.

Supramolecular assembly is shown to provide control over excited-state chloride release. Two dicationic chromophores were designed with a ligand that recognizes halide ions in CH2Cl2 and a luminescent excited state whose dipole was directed toward, 12+, or away, 22+, from an associated chloride ion. The dipole orientation had little influence on the ground-state equilibrium constant, Keq ∼ 4 × 106 M-1, but induced a profound change in the excited-state equilibrium. Light excitation of [12+,Cl-]+ resulted in time-dependent shifts in the photoluminescence spectra with the appearance of biexponential kinetics consistent with the photorelease of Cl-. Remarkably, the excited-state equilibrium constant was lowered by a factor of 20 and resulted in nearly 45% dissociation of chloride. In contrast, light excitation of [22+,Cl-]+ revealed a 45-fold increase in the excited-state equilibrium constant. The data show that rational design and supramolecular assembly enables the detection and photorelease of chloride ions with the potential for future applications in biology and chemistry.

Modifying the steric and electronic character within Re(I)-phenanthroline complexes for electrocatalytic CO 2 reduction

We have synthesized and characterized a series of fac-[Re(R2phen)(CO)3Cl] complexes (R2phen = 2,9-disubstituted-1,10-phenanthroline) that function as electrocatalysts for the reduction of CO2 to CO. The 2,9-disubstituted phenanthroline ligands contain proton (phen), methyl (2,9-Me2phen), trimethylphenyl (Mes2phen), or trimethoxyphenyl ((2,4,6-tmp)2phen and (3,4,5-tmp)2phen) groups as steric and electronic modifiers to provide insight into factors impacting catalytic activity. Cyclic voltammograms (CVs) recorded in CO2-saturated CH3CN or DMF solutions reveal that following two-electron reduction and chloride dissociation to form the active [Re(R2phen)(CO)3]− intermediate, current enhancement indicative of CO2 reduction to CO was observed and confirmed by controlled potential electrolysis (CPE). Using current enhancement values (icat/ip, where icat and ip are the current response under CO2 and N2, respectively) to estimate catalytic activity, it was observed that catalysts with more cathodic ReI/0 potentials displayed greater activity, in accord with an electronic effect driving catalysis. Interestingly, the trimethoxyphenyl-substituted complexes Re((2,4,6-tmp)2phen) and Re((3,4,5-tmp)2phen) showed different degrees of activity in DMF (icat/ip = 14.8 and 6.0, respectively) and CH3CN (icat/ip = 8.5 and 7.7, respectively). These results suggest that while electronics dominate the observed catalytic activity within this fac-[Re(R2phen)(CO)3Cl] architecture, factors such as sterics and solvent play an important role as well.

Neutral and Cationic Bis-Chelate Monoorganosilicon(IV) Complexes of 1-Hydroxy-2-pyridinone

A series of spirocyclic monoorganosilicon compounds of the form RSi(OPO)2Cl (R = phenyl (1), p-tolyl (2), benzyl (3), Me (4), tBu (5), thexyl (6); OPO = 1-oxo-2-pyridinone) was synthesized and characterized by 1H, 13C, and 29Si NMR spectroscopy, X-ray crystallography, and elemental analysis. In the solid state, complexes 1–3 are neutral and possess cis-OPO ligands in an octahedral arrangement and complexes 4–6 are cationic and possess effectively trans-OPO ligands in nearly ideal square-pyramidal geometries along the Berry pseudorotation coordinate. In 4–6, chloride dissociation is attributed to the additive effect of multiple intermolecular C–H···Cl interactions in their crystals. In DMSO-d6 solution, compounds 1–6 form cationic hexacoordinate DMSO adducts with trans-OPO ligands, all of which undergo dynamic isomerization with energy barriers of ∼18–19 kcal/mol. Compounds with better leaving groups, (p-tolyl)Si(OPO)2X (X = I (7), X = triflate (8)), exhibit solution NMR spectra identical with those of 2, ...

Synthesis, characterization and solution behavior of a systematic series of pentapyridyl-supported RuII complexes: comparison to bimetallic analogs.

A series of RuII complexes stabilized with the pentapyridyl ligand Py5Me2 (Py5Me2 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine) and with an axial X ligand (X = Cl-, H2O, N3-, MeCN) were prepared and characterized in the solid state and in non-aqueous solution. The cyclic voltammograms of these complexes in MeCN reflect a reversible substitution of the axial X ligand with MeCN. Irreversible ligand substitution of [(Py5Me2)RuN3]+ is also observed in propylene carbonate, but only at oxidizing potentials that decompose the azide ligand. The monometallic chloride and azide species are compared with analogous Ru2 metal-metal bonded complexes, which have been reported to undergo irreversible chloride dissociation upon reduction.

Cytotoxicity of spherical gold nanoparticles synthesised using aqueous extracts of aerial roots of Rhaphidophora aurea (Linden ex Andre) intertwined over Lawsonia inermis and Areca catechu on MCF‐7 cell line

A facile synthesis of gold nanoparticles (GNPs) using the aqueous extracts of the aerial roots of Rhaphidophora aurea (Linden ex Andre) intertwined over Lawsonia inermis and Areca catechu was carried out under different conditions, namely room temperature, higher temperature, sonication, solar irradiation and pH variation. The surface plasmon resonance (SPR) band at 536 and 575 nm obtained in UV-visible spectrum revealed the formation of AuNP's. The sharp SPR band of the synthesised nanogold indicates the formation of spherical-shaped and uniform-sized nanoparticles. The TEM analysis revealed spherical nanogold particles of size 35 and 10 nm for MM and MP extracts. The secondary metabolites present in the aqueous extract are suggested to be responsible for the reduction of metal ions to metal nanoparticles as evidenced from results of FTIR analysis. Rapid synthesis of GNPs by sunlight is the production of microscopic grains of gold due to the dissociation of gold chloride. This may induce the reaction between secondary metabolites and gold chloride solutions and results in GNPs. The cytotoxic activity of the synthesised nanogold studied against human breast cancer cells (MCF-7) by 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide assay showed significant activity at higher concentration.

Increased photocatalytic activity in Ru(II),Rh(III) supramolecular bimetallic complexes with terminal ligand substitution

Three new Ru(II),Rh(III) supramolecular bimetallic complexes of the design [(Ph2phen)2Ru(dpp)RhCl2(R2-bpy)](PF6)3 (R=CH3 (Ru-Rh(Me2bpy)), H (Ru-Rh(bpy)), or COOCH3 (Ru-Rh(dmeb)); Ph2phen=4,7-diphenyl-1,10-phenanthroline; dpp=2,3-bis(2-pyridyl)pyrazine; dmeb=4,4′-dimethyl ester-2,2′-bipyridine; bpy=2,2′-bipyridine; Me2bpy=4,4′-dimethyl-2,2′-bipyridine) have been synthesized and analyzed to determine the impact that the polypyridyl terminal ligand (TL) coordinated to the cis-dihalide rhodium(III) metal center has on the photocatalytic activity for water reduction. The bimetallic complexes demonstrate that a correlation exists between the σ-donating ability of the substituted bipyridine ligand, the rate of chloride dissociation upon electrochemical reduction and the activity towards photocatalytic hydrogen production. The weaker σ-donating –COOCH3 substituent in Ru-Rh(dmeb) increases the rate constant for Cl− dissociation (k−Cl=0.7s−1) and the amount of H2 produced photocatalytically (37±4μmol H2, 63±7 turnovers after 20h; turnovers=mol H2/mol photocatalyst) when compared to –H and –CH3 substituted complexes Ru-Rh(bpy) (k−Cl=0.2s−1, 21±2μmol H2, 35±3 turnovers) and Ru-Rh(Me2bpy) (k−Cl=0.2s−1, 18±2μmol H2, 30±4 turnovers), respectively. Varied catalytic activity with respect to the σ-donor capacity of the Rh-TL is attributed to the relative ease of ligand dissociation and the ability to afford rapid electron collection at the Rh metal center.

New type of highly selective microcapsules for the removal of mercury from surface polluted waters

Abstract A new class of particulate material for the selective removal of mercury from polluted aqueous streams has been developed. The material consists in core–shell microcapsules containing a highly selective extractant agent for mercury. For this purpose, trioctylmethylammonium chloride (TOMAC) has been encapsulated within a poly(styrene-co-divinylbenzene) – P(St-DVB) – shell by suspension-like polymerisation technique. This process gave rise to a high product yield with an encapsulation efficiency of 95%. Microcapsules presented an average particle size lower than 40 μm and a TOMAC content of 37.70 wt.%. Different equilibrium experiments for mercury uptake were conducted at pH = 1 and natural pH, using synthetic solutions and natural waters from the mining district of Almaden (Spain). A mathematical model that takes into account the dissociation of mercuric chloride in solution was proposed and the solid equilibrium parameters were obtained. A good fitting between the experimental data and the model was achieved, obtaining a maximum useful capacity of 1.009 ± 0.018 eq kg−1 with a value of equilibrium constant of the monovalent specie ( HgCl 3 - ) two orders of magnitude smaller than those of the divalent HgCl 4 2 - . The mercury uptake was favoured at acid pH and low chloride concentration. Finally, it was demonstrated that using this material is possible to remove more than 92% and 99% of the metal content from the natural waters containing mercury in ng L−1 levels at natural and acid pH, respectively. The use of this new type of extractive microcapsules allows to get mercury removal levels in surface polluted waters that satisfy the mercury standard for aquatic life proposed by the USEPA (12 ng L−1) without additional pretreatments for the adjustment of the pH value.