16887-00-6Relevant articles and documents
A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction
Bi, Eric Y.,Gao, Jinyu,Liu, Jinyong,Palmer, Jacob,Ren, Changxu,Sun, Jiaonan,Wu, Yiying,Yang, Peng,Zhu, Mengqiang
, p. 7891 - 7896 (2021)
Perchlorate (ClO4-) is a pervasive, harmful, and inert anion on both Earth and Mars. Current technologies for ClO4- reduction entail either harsh conditions or multicomponent enzymatic processes. Herein, we report a heterogeneous (L)Mo-Pd/C catalyst directly prepared from Na2MoO4, a bidentate nitrogen ligand (L), and Pd/C to reduce aqueous ClO4- into Cl- with 1 atm of H2 at room temperature. A suite of instrument characterizations and probing reactions suggest that the MoVI precursor and L at the optimal 1:1 ratio are transformed in situ into oligomeric MoIV active sites at the carbon-water interface. For each Mo site, the initial turnover frequency (TOF0) for oxygen atom transfer from ClOx- substrates reached 165 h-1. The turnover number (TON) reached 3840 after a single batch reduction of 100 mM ClO4-. This study provides a water-compatible, efficient, and robust catalyst to degrade and utilize ClO4- for water purification and space exploration.
ELECTROCHEMICAL BEHAVIOR OF SELENIUM AND SELENIUM COMPOUNDS IN SODIUM TETRACHLOROALUMINATE MELTS.
Robinson,Osteryoung
, p. 1454 - 1460 (1978)
The electrochemistry of selenium and various selenium compounds in AlCl//3:NaCl melts has been investigated by a variety of techniques including pulse and cyclic voltammetry, coulometry, and the rotating-disk electrode. It was found that selenium can be reduced, in both acid and basic melts, by a single two-electron step to selenide which exists in the melt as either AlSeCl or AlSeCl//2** minus (or their analogous solvated species Al//2SeCl//5** minus and Al//2SeCl//6**2** minus ) depending upon the acidity. The mechanism for the oxidation of selenium to Se(IV) was found to be dependent upon the melt acidity. In basic melts, selenium was first oxidized by a two-electron step to an Se(II) species and then by a further two-electron step to Se(IV). In acid melts the oxidation is a single quasireversible four-electron step. This work is of interest in the areas of high energy density batteries and fuel cells.
Understanding the roles of strictly conserved tryptophan residues in O 2 producing chlorite dismutases
Blanc, Beatrice,Rodgers, Kenton R.,Lukat-Rodgers, Gudrun S.,Dubois, Jennifer L.
, p. 3156 - 3169 (2013)
The chlorite dismutases (Clds) degrade ClO2- to O2 and Cl- in perchlorate respiring bacteria, and they serve still poorly defined cellular roles in other diverse microbes. These proteins share 3 highly conserved Trp residues, W155, W156, and W227, on the proximal side of the heme. The Cld from Dechloromonas aromatica (DaCld) has been shown to form protein-based radicals in its reactions with ClO2 - and peracetic acid. The roles of the conserved Trp residues in radical generation and in enzymatic function were assessed via spectroscopic and kinetic analysis of their Phe mutants. The W155F mutant was the most dramatically affected, appearing to lose the characteristic pentameric oligomerization state, secondary structure, and heme binding properties of the WT protein. The W156F mutant initially retains many features of the WT protein but over time acquires many of the features of W155F. Conversion to an inactive, heme-free form is accelerated by dilution, suggesting loss of the protein's pentameric state. Hence, both W155 and W156 are important for heme binding and maintenance of the protein's reactive pentameric structure. W227F by contrast retains many properties of the WT protein. Important differences are noted in the transient kinetic reactions with peracetic acid (PAA), where W227F appears to form an [Fe(iv)O]-containing intermediate, which subsequently converts to an uncoupled [Fe(iv)O + AA+] system in a [PAA]-dependent manner. This is in contrast to the peroxidase-like formation of [Fe(iv)O] coupled to a porphyrin π-cation radical in the WT protein, which decays in a [PAA]-independent manner. These observations and the lack of redox protection for the heme in any of the Trp mutants suggests a tendency for protein radical formation in DaCld that is independent of any of these conserved active site residues.
Copper(II) catalyses the reduction of perchlorate by both formaldehyde and by dihydrogen in aqueous solutions
Shamir, Dror,Meyerstein, Dan,Zilbermann, Israel,Burg, Ariela,Albo, Yael,Shames, Alexander I.,Vainer, Radion,Borojovich, Eitan J.C.,Yardeni, Guy,Kornweitz, Haya,Maimon, Eric
, p. 2905 - 2912 (2018)
During an effort to synthesize the trans-III-copper(II) complex with 1,4,8,11-tetramethyl-pyro-phosphonate-1,4,8,11-tetra-aza-cyclo-tetradecane, using only perchlorate salts, it was noted that the perchlorate is reduced to chloride. Analysis of the reactions leading to this surprising result points out that Cu(H2O)42+ catalyzes the reduction of perchlorate by H2 and by CH2O. These reactions are slow at room temperature and ambient pressures. A plausible mechanism, supported by DFT calculations, is proposed pointing out that the role of CuH+ under mild conditions cannot be ignored.
Configuration Control in the Synthesis of Homo- and Heteroleptic Bis(oxazolinylphenolato/thiazolinylphenolato) Chelate Ligand Complexes of Oxorhenium(V): Isomer Effect on Ancillary Ligand Exchange Dynamics and Implications for Perchlorate Reduction Catalysis
Liu, Jinyong,Wu, Dimao,Su, Xiaoge,Han, Mengwei,Kimura, Susana Y.,Gray, Danielle L.,Shapley, John R.,Abu-Omar, Mahdi M.,Werth, Charles J.,Strathmann, Timothy J.
, p. 2597 - 2611 (2016)
This study develops synthetic strategies for N,N-trans and N,N-cis Re(O)(LO-N)2Cl complexes and investigates the effects of the coordination spheres and ligand structures on ancillary ligand exchange dynamics and catalytic perchlorate reduction activities of the corresponding [Re(O)(LO-N)2]+ cations. The 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) and 2-(2′-hydroxyphenyl)-2-thiazoline (Hhtz) ligands are used to prepare homoleptic N,N-trans and N,N-cis isomers of both Re(O)(hoz)2Cl and Re(O)(htz)2Cl and one heteroleptic N,N-trans Re(O)(hoz)(htz)Cl. Selection of hoz/htz ligands determines the preferred isomeric coordination sphere, and the use of substituted pyridine bases with varying degrees of steric hindrance during complex synthesis controls the rate of isomer interconversion. The five corresponding [Re(O)(LO-N)2]+ cations exhibit a wide range of solvent exchange rates (1.4 to 24,000 s-1 at 25°C) and different LO-N movement patterns, as influenced by the coordination sphere of Re (trans/cis), the noncoordinating heteroatom on LO-N ligands (O/S), and the combination of the two LO-N ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of aqueous ClO4- by H2 when the Re(O)(LO-N)2Cl complexes are immobilized onto Pd/C. Findings from this study provide novel synthetic strategies and mechanistic insights for innovations in catalytic, environmental, and biomedical research.
Production of Sb(IV) chloro complex by flash photolysis of the corresponding Sb(III) and Sb(V) complexes in CH3CN and CHCl3
Shinohara, Nobuyoshi,Ohshima, Masaaki
, p. 1599 - 1604 (2000)
[SbCl6]2- was formed in the flash photolysis of [SbCl6]3- or [SbCl6]- in both solutions of CH3CN and CHCl3 in the presence of an excess of chloride. [SbCl6]2- had absorption maxima at 293, 328, and 390 nm in CH3CN. A similar absorption spectrum of [SbCl6]2- was also obtained in CHCl3. The lifetime of [SbCl6]2- was much shorter in CHCl3 than in CH3CN. [SbCl6]- was easily reduced to [SbCl6]3- upon continuous UV- irradiation in CH3CN as well as in CHCl3. On the other hand, [SbCl6]3- was oxidized to [SbCl6]- in CHCl3 in the presence of oxygen, but was not in CH3CN. The spectrum and the decay rate of [SbCl6]2- were not essentially affected by oxygen in both solutions of CH3CN and CHCl3.
Electron-beam decomposition of carbon tetrachloride in air/nitrogen
Hirota,Arai,Hashimoto
, p. 2719 - 2724 (2000)
Carbon tetrachloride (CCl4, approximately 10, 50, and 100 ppm) in air and nitrogen was irradiated with electron beams in both the presence and absence of water. The absorbed doses ranged from 1.2 to 18.0 kGys. An absorbed dose of 18 kGy led to approximately 90% decomposition of CCl4 at a concentration of 10 ppm in dry air. The presence of water lowered the decomposition rate in air by 20%, but not in nitrogen. Negative oxygen ions (O2/-) formed upon the irradiation of wet air played a role in the oxidation of CCl4. Water molecules became negative cluster ions (O2/-(H2O)n) with negative oxygen ions, which depressed the oxidation.
Pseudophase Ion-Exchange Model Applied to Kinetics in Aqueous Micelles under Extreme Conditions: A Simple Modification
Ferreira, Ligia Catarina Mello,Zucco, Cesar,Zanette, Dino,Nome, Faruk
, p. 9058 - 9061 (1992)
The dehydrochlorination of 1,1-diphenyl-2,2,2-trichloroethane (DTE) with hydroxide ion was studied in the presence of hexadecyltrimethylammonium hydroxide (CTAOH) micelles at 25.0 deg C, under conditions where the pseudophase ion-exchange model (PPIE) normally fails (high sodium hydroxide and salt concentrations).A simple modification of the model, which includes the variable degree of dissociation concept and the contribution of the counterion in the aqueous phase to the interfacial counterion concentration, allows the application of the PPIE model to all ranges of counterion concentrations in the presence and absence of added salts.
Kinetics and Mechanism of the Chlorine Dioxide-Tetrathionate Reaction
Horvath, Attila K.,Nagypal, Istvan,Epstein, Irving R.
, p. 10063 - 10068 (2003)
The chlorine-dioxide-tetrathionate reaction was studied spectrophotometrically in the pH range 4.55-5.55 at 25.0 ± 0.2 °C and 0.5 M ionic strength adjusted with sodium acetate as a buffer component. The stoichiometry was found to be S4O6 2- + 4°ClO2 + 5H2O → 4SO42- + ClO3- + 3Cl- + 10H+with small deviations at high excess of chlorine dioxide with no chloride ion initially present. The initial presence of chloride not only affects the stoichiometry but also accelerates the reaction. A 14-step mechanism, including four known and two newly proposed intermediates, is suggested to describe the observed behavior of the system.
First Micelle-Free Photoredox Catalytic Access to Hydrated Electrons for Syntheses and Remediations with a Visible LED or even Sunlight
Naumann, Robert,Goez, Martin
, p. 17557 - 17567 (2018)
Hydrated electrons are super-reductants, yet can be generated with visible light when two photons are pooled, most efficiently through storing the energy of the first photon in a radical pair formed by the reduction of an excited catalyst by a sacrificial donor. All previous such systems for producing synthetically useable amounts of hydrated electrons with an LED in the visible range had to resort to compartmentalization by SDS micelles to curb the performance-limiting recombination of the pair. To overcome micelle-imposed constraints on sustainability and applications, we have instead attached carboxylate groups to a ruthenium (tris)bipyridyl catalyst such that its pentaanionic radical strongly repels the dianionic radical of the bioavailable donor urate. We have explored the influence of the Coulombic interactions on the electron generation by a time-resolved study from microseconds to hours, including for comparison the unsubstituted complex, which forms a monocationic radical, with and without SDS micelles. The new homogeneous electron source is best with regard to stability and total electron output; it has a broader synthetic scope because it does not entail micellar shielding of less hydrophilic compounds, which particularly facilitates cross-couplings; and it tolerates supramolecular containers as carriers of water-insoluble substrates or products. As an application in the field, we demonstrate the solar remediation of a recalcitrant chloro-organic bulk chemical.
