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Proceedings of the National Academy of... May 2023Protonation reactions involving organometallic complexes are ubiquitous in redox chemistry and often result in the generation of reactive metal hydrides. However, some...
Protonation reactions involving organometallic complexes are ubiquitous in redox chemistry and often result in the generation of reactive metal hydrides. However, some organometallic species supported by η-pentamethylcyclopentadienyl (Cp*) ligands have recently been shown to undergo ligand-centered protonation by direct proton transfer from acids or tautomerization of metal hydrides, resulting in the generation of complexes bearing the uncommon η-pentamethylcyclopentadiene (Cp*H) ligand. Here, time-resolved pulse radiolysis (PR) and stopped-flow spectroscopic studies have been applied to examine the kinetics and atomistic details involved in the elementary electron- and proton-transfer steps leading to complexes ligated by Cp*H, using Cp*Rh(bpy) as a molecular model (where bpy is 2,2'-bipyridyl). Stopped-flow measurements coupled with infrared and UV-visible detection reveal that the sole product of initial protonation of Cp*Rh(bpy) is [Cp*Rh(H)(bpy)], an elusive hydride complex that has been spectroscopically and kinetically characterized here. Tautomerization of the hydride leads to the clean formation of [(Cp*H)Rh(bpy)]. Variable-temperature and isotopic labeling experiments further confirm this assignment, providing experimental activation parameters and mechanistic insight into metal-mediated hydride-to-proton tautomerism. Spectroscopic monitoring of the second proton transfer event reveals that both the hydride and related Cp*H complex can be involved in further reactivity, showing that [(Cp*H)Rh] is not necessarily an off-cycle intermediate, but, instead, depending on the strength of the acid used to drive catalysis, an active participant in hydrogen evolution. Identification of the mechanistic roles of the protonated intermediates in the catalysis studied here could inform design of optimized catalytic systems supported by noninnocent cyclopentadienyl-type ligands.
PubMed: 37186841
DOI: 10.1073/pnas.2217189120 -
Environmental Science & Technology May 2023Advanced reduction processes (ARP) have garnered increasing attention for the treatment of recalcitrant chemical contaminants, most notably per- and polyfluoroalkyl...
Advanced reduction processes (ARP) have garnered increasing attention for the treatment of recalcitrant chemical contaminants, most notably per- and polyfluoroalkyl substances (PFAS). However, the impact of dissolved organic matter (DOM) on the availability of the hydrated electron (e), the key reactive species formed in ARP, is not completely understood. Using electron pulse radiolysis and transient absorption spectroscopy, we measured bimolecular reaction rates constant for e reaction with eight aquatic and terrestrial humic substance and natural organic matter isolates ( ), with the resulting values ranging from (0.51 ± 0.01) to (2.11 ± 0.04) × 10 M s. measurements at varying temperature, pH, and ionic strength indicate that activation energies for diverse DOM isolates are ≈18 kJ mol and that could be expected to vary by less than a factor of 1.5 between pH 5 and 9 or from an ionic strength of 0.02 to 0.12 M. exhibited a significant, positive correlation to % carbonyl carbon for the isolates studied, but relationships to other DOM physicochemical properties were surprisingly more scattered. A 24 h UV/sulfite experiment employing chloroacetate as an e probe revealed that continued e exposure abates DOM chromophores and e scavenging capacity over a several hour time scale. Overall, these results indicate that DOM is an important e scavenger that will reduce the rate of target contaminant degradation in ARP. These impacts are likely greater in waste streams like membrane concentrates, spent ion exchange resins, or regeneration brines that have elevated DOM concentrations.
Topics: Dissolved Organic Matter; Water; Electrons; Water Pollutants, Chemical; Humic Substances
PubMed: 37141499
DOI: 10.1021/acs.est.3c00909 -
Water Science and Technology : a... Apr 2023ClO plays a key role in the UV/chlorine process besides Cl, Cl2 - , and OH. In many experiments, ClO proved to be the main reactant that destroyed the organic pollutants...
ClO plays a key role in the UV/chlorine process besides Cl, Cl2 - , and OH. In many experiments, ClO proved to be the main reactant that destroyed the organic pollutants in advanced oxidation process. About 200 rate constants of ClO reactions were collected from the literature, grouped together according to the chemical structure, and the molecular structure dependencies were evaluated. In most experiments, ClO was produced by the photolytic reaction of HClO/ClO-. For a few compounds, the rate constants were determined by the absolute method, pulse radiolysis. Most values were obtained in steady-state experiments by competitive technique or by complex kinetic calculations after measuring the pollutant degradation in the UV/chlorine process. About 30% of the listed rate constant values were derived in quantum chemical or in structure-reactivity (QSAR) calculations. The values show at least six orders of magnitude variations with the molecular structure. Molecules having electron-rich parts, e.g., phenol/phenolate, amine, or sulfite group have high rate constants in the range of 10-10 mol dm s. ClO is inactive in reactions with saturated molecules, alcohols, or simple aromatic molecules.
Topics: Chlorides; Chlorine; Phenol; Oxidation-Reduction; Water Purification; Water Pollutants, Chemical; Kinetics; Ultraviolet Rays
PubMed: 37119164
DOI: 10.2166/wst.2023.114 -
The Journal of Physical Chemistry. B May 2023The octadentate hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO) has been identified as a promising candidate for both chelation and -element separation...
The octadentate hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO) has been identified as a promising candidate for both chelation and -element separation technologies, two applications that require optimal performance in radiation environments. However, the radiation robustness of HOPO is currently unknown. Here, we employ a combination of time-resolved (electron pulse) and steady-state (alpha self-radiolysis) irradiation techniques to elucidate the basic chemistry of HOPO and its -element complexes in aqueous radiation environments. Chemical kinetics were measured for the reaction of HOPO and its Nd(III) ion complex ([Nd(HOPO)]) with key aqueous radiation-induced radical transients (e, H atom, and OH and NO radicals). The reaction of HOPO with the e is believed to proceed via reduction of the hydroxypyridinone moiety, while transient adduct spectra indicate that reactions with the H atom and OH and NO radicals proceeded by addition to HOPO's hydroxypyridinone rings, potentially allowing for the generation of an extensive suite of addition products. Complementary steady-state Am(III)-HOPO complex ([Am(HOPO)]) irradiations showed the gradual release of Am(III) ions with increasing alpha dose up to 100 kGy, although complete ligand destruction was not observed.
PubMed: 37084416
DOI: 10.1021/acs.jpcb.3c01469 -
The Journal of Physical Chemistry. B Mar 2023Radiation chemistry of hydrated metal ions plays a significant role in the field of nuclear energy, especially regarding water radiolysis in coolant water in nuclear...
Radiation chemistry of hydrated metal ions plays a significant role in the field of nuclear energy, especially regarding water radiolysis in coolant water in nuclear reactors. This work reports new experimental data on the reactivity of Ni species under critical conditions of temperature and pressure. The reaction rates of hydrated nickel ions with water radiolysis products (e, OH, H, and HO) have been investigated for a 25-300 °C temperature range and 200 bar pressure using electron pulse radiolysis/transient absorption. Extensive experiments with the Ni species in various salts and pH up to 300 °C were performed. Kinetic decay traces of short-lived monovalent nickel ions were fitted to extract the rate constants versus temperature up to 300 °C. A blue shift of the absorption spectrum of the monovalent nickel ion with increasing temperature was demonstrated, which may indicate a change in the average coordination number. The Arrhenius parameters for the reactions of Ni with e and Ni with OH, H, and HO were obtained. All measured rate constants increased with temperature and followed Arrhenius behavior.
PubMed: 36926873
DOI: 10.1021/acs.jpcb.3c00046 -
Journal of the American Chemical Society Mar 2023High-energy radiation that is compatible with renewable energy sources enables direct H production from water for fuels; however, the challenge is to convert it as...
High-energy radiation that is compatible with renewable energy sources enables direct H production from water for fuels; however, the challenge is to convert it as efficiently as possible, and the existing strategies have limited success. Herein, we report the use of Zr/Hf-based nanoscale UiO-66 metal-organic frameworks as highly effective and stable radiation sensitizers for purified and natural water splitting under γ-ray irradiation. Scavenging and pulse radiolysis experiments with Monte Carlo simulations show that the combination of 3D arrays of ultrasmall metal-oxo clusters and high porosity affords unprecedented effective scattering between secondary electrons and confined water, generating increased precursors of solvated electrons and excited states of water, which are the main species responsible for H production enhancement. The use of a small quantity (<80 mmol/L) of UiO-66-Hf-OH can achieve a γ-rays-to-hydrogen conversion efficiency exceeding 10% that significantly outperforms Zr-/Hf-oxide nanoparticles and the existing radiolytic H promoters. Our work highlights the feasibility and merit of MOF-assisted radiolytic water splitting and promises a competitive method for creating a green H economy.
PubMed: 36812014
DOI: 10.1021/jacs.3c00547 -
The Journal of Physical Chemistry. B Feb 20235-Azidomethyl-2'-deoxyuridine (5-AmdU, ) has been successfully employed for the metabolic labeling of DNA and fluorescent imaging of live cells. 5-AmdU also demonstrated...
5-Azidomethyl-2'-deoxyuridine (5-AmdU, ) has been successfully employed for the metabolic labeling of DNA and fluorescent imaging of live cells. 5-AmdU also demonstrated significant radiosensitization in breast cancer cells via site-specific nitrogen-centered radical (π-aminyl (U-5-CH-NH), , and σ-iminyl (U-5-CH═N), ) formation. This work shows that these nitrogen-centered radicals are not formed via the reduction of the azido group in 6-azidomethyluridine (6-AmU, ). Radical assignments were performed using electron spin resonance (ESR) in supercooled solutions, pulse radiolysis in aqueous solutions, and theoretical (DFT) calculations. Radiation-produced electron addition to leads to the facile N loss, forming a stable neutral C-centered allylic radical (U-6-CH, ) through dissociative electron attachment (DEA) via the transient negative ion, TNI (U-6-CH-N), in agreement with DFT calculations. In contrast, TNI (U-5-CH-N) of , via facile N loss (DEA) and protonation from the surrounding water, forms radical . Subsequently, undergoes rapid H-atom abstraction from and produces the metastable intermediate α-azidoalkyl radical (U-5-CH-N). U-5-CH-N converts facilely to radical . N loss from U-6-CH-N is thermodynamically controlled, whereas N loss from U-5-CH-N is dictated by protonation from the surrounding waters and resonance conjugation of the azidomethyl side chain at C5 with the pyrimidine ring.
Topics: Nitrogen; Nucleosides; Azides; Electrons; Electron Spin Resonance Spectroscopy; Water; Free Radicals
PubMed: 36780335
DOI: 10.1021/acs.jpcb.2c08257 -
Radiation Physics and Chemistry... May 2023Hydroxychloroquine (HCQ) is a potential drug molecule for treating malaria. Recently it has also been tried as adjustment in Covid 19 therapy. Interaction of HCQ with...
Hydroxychloroquine (HCQ) is a potential drug molecule for treating malaria. Recently it has also been tried as adjustment in Covid 19 therapy. Interaction of HCQ with free radicals is very important, which controls its stability in the environment where free radicals are generated unintentionally. In this report, we present detailed investigation on the reactions of hydrated electrons (e ) and hydroxyl radical (OH) with HCQ in aqueous solution through electron pulse radiolysis technique and computational studies. The degradation of HCQ was found to be faster in the case of reaction with OH radicals. However, the degradation could be substantially slowed down in the presence of antioxidants like ascorbic acid and gallic acid. This revealed that the stability of HCQ could be enhanced in an oxidative environment in the presence of these two compounds, which are easily available through food supplements. Various global and local reactivity parameters are also determined to understand the reactivity trend using Hard-Soft Acid-Base (HSAB) principle in the realm of the DFT methods. Computational studies were performed to elucidate the site-specific reactivity trend towards the electrophilic and nucleophilic attack by calculating the condensed Fukui index for various species of HCQ.
PubMed: 36685709
DOI: 10.1016/j.radphyschem.2023.110785 -
Dalton Transactions (Cambridge, England... Jan 2023Herein, using generated solvated electrons in the reaction media, a highly time-efficient, one-pot green approach has been employed to synthesize palladium (Pd)...
Herein, using generated solvated electrons in the reaction media, a highly time-efficient, one-pot green approach has been employed to synthesize palladium (Pd) nanoparticles (NPs) coated with a molecular assembly of α-cyclodextrin (α-CD). The appearance of a shoulder peak at 280 nm in the UV-Vis absorption spectra indicated the formation of Pd NPs, which was further confirmed from their cubic phase XRD pattern. The nanomorphology varied considerably as a function of the dose rate, wherein sphere-shaped NPs (average size ∼ 7.6 nm) were formed in the case of high dose rate electron-beam assisted synthesis, while nanoflakes self-assembled to form nanoflower-shaped morphologies in a γ-ray mediated approach involving a low dose rate. The formation kinetics of NPs was investigated by pulse radiolysis which revealed the formation of Pd-based transients by the solvated electron-induced reaction. Importantly, no interference of α-CD was observed in the kinetics of the transient species, rather it played the role of a morphology directing agent in addition to a biocompatible stabilizing agent. The catalytic studies revealed that the morphology of the NPs has a significant effect on the reduction efficiency of 4-nitrophenol to 4-aminophenol. Another important highlight of this work is the demonstration of the morphology-dependent anticancer efficacy of Pd NPs against lung and brain cancer cells. Notably, flower-shaped Pd NPs exhibited significantly higher cancer cell killing as compared to spherical NPs, while being less toxic towards normal lung fibroblasts. Nonetheless, these findings show the promising potential of Pd NPs in anticancer treatment.
Topics: Metal Nanoparticles; Palladium; Electrons; Cyclodextrins; Catalysis
PubMed: 36602081
DOI: 10.1039/d2dt03219h -
Chemphyschem : a European Journal of... Mar 2023Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single-cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation...
Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single-cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady-state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.
PubMed: 36470592
DOI: 10.1002/cphc.202200749