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Physical Chemistry Chemical Physics :... Jan 2024The kinetics and mechanism of the reaction between OH radicals and ferrous ions in the temperature range 25-300 °C were studied using pulse radiolysis. At temperatures...
The kinetics and mechanism of the reaction between OH radicals and ferrous ions in the temperature range 25-300 °C were studied using pulse radiolysis. At temperatures <150 °C the rate of reaction is essentially independent of temperature, while at temperatures >150 °C the activation energy is 45.8 ± 3.0 kJ mol. The change in activation energy is attributed to a change in the dominant mechanism from hydrogen atom transfer (HAT) to dissociative ligand interchange. The kinetic isotope effect (KIE) was measured by repeating experiments in heavy water. A value of 2.9 was measured at room temperature where HAT is the dominant mechanism. The KIE decreases to zero at temperatures > 150 °C as ligand interchange becomes dominant and the O-H bond is no longer involved in the reaction.
PubMed: 38231479
DOI: 10.1039/d3cp03819j -
Physical Chemistry Chemical Physics :... Jan 2024Technetium is a problematic radioisotope for used nuclear fuel (UNF) and subsequent waste management owing to its high environmental mobility and coextraction in...
Technetium is a problematic radioisotope for used nuclear fuel (UNF) and subsequent waste management owing to its high environmental mobility and coextraction in reprocessing technologies as the pertechnetate anion (TcO). Consequently, several strategies are under development to control the transport of this radioisotope. A proposed approach is to use diaminoguanidine (DAG) for TcO and transuranic ion redox control. Although the initial DAG molecule is ultimately consumed in the redox process, its susceptibility to radiolysis is currently unknown under envisioned UNF reprocessing conditions, which is a critical knowledge gap for evaluating its overall suitability for this role. To this end, we report the impacts of steady-state gamma irradiation on the rate of DAG radiolysis in water, aqueous 2.0 M nitric acid (HNO), and in a biphasic solvent system composed of aqueous 2.0 M HNO in contact with 1.5 M ,-di-(2-ethylhexyl)isobutyramide (DEHiBA) dissolved in -dodecane. Additionally, we report chemical kinetics for the reaction of DAG with key transients arising from electron pulse radiolysis, specifically the hydrated electron (e), hydrogen atom (H˙), and hydroxyl (˙OH) and nitrate (NO˙) radicals. The DAG molecule exhibited significant reactivity with the ˙OH and NO˙ radicals, indicating that oxidation would be the predominant degradation pathway in radiation environments. This is consistent with its role as a reducing agent. Steady-state gamma irradiations demonstrated that DAG is readily degraded within a few hundred kilogray, the rate of which was found to increase upon going from water to HNO containing solutions and solvents systems. This was attributed to a thermal reaction between DAG and the predominant HNO radiolysis product, nitrous acid (HNO), (DAG + HNO) = 5480 ± 85 M s. Although no evidence was found for the radiolysis of DAG altering the radiation chemistry of the contacted DEHiBA/-dodecane phase in the investigated biphasic system, the utility of DAG as a redox control reagent will likely be limited by significant competition with its degradation by HNO.
PubMed: 38224090
DOI: 10.1039/d3cp04987f -
The Journal of Physical Chemistry. A Jan 2024Despite the availability of transuranic elements increasing in recent years, our understanding of their most basic and inherent radiation chemistry is limited and yet...
Despite the availability of transuranic elements increasing in recent years, our understanding of their most basic and inherent radiation chemistry is limited and yet essential for the accurate interpretation of their physical and chemical properties. Here, we explore the transient interactions between trivalent californium ions () and select inorganic radicals arising from the radiolytic decomposition of common anions and functional group constituents, specifically the dichlorine (Cl) and sulfate (SO) radical anions. Chemical kinetics, as measured using integrated electron pulse radiolysis and transient absorption spectroscopy techniques, are presented for the reactions of these two oxidizing radicals with ions. The derived and ionic strength-corrected second-order rate coefficients () for these radiation-induced processes are ( + Cl) = (8.28 ± 0.61) × 10 M s and ( + SO) = (9.50 ± 0.43) × 10 M s under ambient temperature conditions (22 ± 1 °C).
PubMed: 38215218
DOI: 10.1021/acs.jpca.3c07404 -
International Journal of Molecular... Dec 2023In the retina, retinoids involved in vision are under constant threat of oxidation, and their oxidation products exhibit deleterious properties. Using pulse radiolysis,...
In the retina, retinoids involved in vision are under constant threat of oxidation, and their oxidation products exhibit deleterious properties. Using pulse radiolysis, this study determined that the bimolecular rate constants of scavenging cation radicals of retinoids by taurine are smaller than 2 × 10 Ms whereas lutein scavenges cation radicals of all three retinoids with the bimolecular rate constants approach the diffusion-controlled limits, while zeaxanthin is only 1.4-1.6-fold less effective. Despite that lutein exhibits greater scavenging rate constants of retinoid cation radicals than other antioxidants, the greater concentrations of ascorbate in the retina suggest that ascorbate may be the main protectant of all visual cycle retinoids from oxidative degradation, while α-tocopherol may play a substantial role in the protection of retinaldehyde but is relatively inefficient in the protection of retinol or retinyl palmitate. While the protection of retinoids by lutein and zeaxanthin appears inefficient in the retinal periphery, it can be quite substantial in the macula. Although the determined rate constants of scavenging the cation radicals of retinol and retinaldehyde by dopa-melanin are relatively small, the high concentration of melanin in the RPE melanosomes suggests they can be scavenged if they are in proximity to melanin-containing pigment granules.
Topics: Retinoids; Vitamin A; Melanins; Retinaldehyde; Lutein; Zeaxanthins; Taurine; Cations
PubMed: 38203675
DOI: 10.3390/ijms25010506 -
Free Radical Research Jan 2024Bis(1-methylimidazol-2-yl) diselenide (MeImSe), a derivative of selenoneine, has been examined for bimolecular rate constants for scavenging of various radiolytically...
Bis(1-methylimidazol-2-yl) diselenide and its evaluation as a chemical radio-protector: role of kinetic rate constants for ROS scavenging and glutathione peroxidase like activity.
Bis(1-methylimidazol-2-yl) diselenide (MeImSe), a derivative of selenoneine, has been examined for bimolecular rate constants for scavenging of various radiolytically and non-radiolytically generated reactive oxygen species (ROS). Further, its potential to show glutathione peroxidase (GPx)-like activity and to protect models of DNA and lipid against radiation induced strand breakage and lipid peroxidation, respectively were studied. The results confirmed that MeImSe scavenged all major short-lived (hydroxyl radical) and long-lived (peroxyl radical, carbonate radical, nitrogen dioxide radical, hypochlorite and hydrogen peroxide) oxidants involved in the radiation toxicity either directly or through GPx-like catalytic mechanism. The rate constants of MeImSe for these oxidants were found to be comparable to analogous sulfur and selenium-based compounds. The enzyme kinetics study established that MeImSe took part in the GPx cycle through the reductive pathway. Further, MeImSe inhibited the radiation induced DNA strand cleavage and lipid peroxidation with half maximal inhibitory concentration (IC) of ∼ 60 μM and ∼100 μM, respectively. Interestingly, MeImSe treatment in the above concentration range (>100 μM) did not show any significant toxicity in normal human lung fibroblast (WI26) cells. The balance between efficacy and toxicity of MeImSe as a chemical radioprotector was attributed to the formation of less reactive intermediates during its oxidation/reduction reactions as evidenced from NMR studies.HighlightsMeImSe, a derivative of selenoneine protects DNA and lipid from radiation damageMeImSe scavenges all major short- and long-lived oxidants involved in radiation toxicityRate constants of MeImSe for ROS scavenging determined by pulse radiolysis techniqueFirst organoselenium compound reported to scavenge nitrogen dioxide radicalMeImSe exhibits GPx-like activity through reductive pathway.
Topics: Humans; Antioxidants; Reactive Oxygen Species; Glutathione Peroxidase; Nitrogen Dioxide; Organoselenium Compounds; Lipid Peroxidation; DNA; Oxidants; Lipids; Oxidation-Reduction; Histidine
PubMed: 38165076
DOI: 10.1080/10715762.2023.2299341 -
The Journal of Chemical Physics Dec 2023Homogeneous solar fuels photocatalytic systems often require several additives in solution with the catalyst to operate, such as a photosensitizer (PS), Brønsted...
Homogeneous solar fuels photocatalytic systems often require several additives in solution with the catalyst to operate, such as a photosensitizer (PS), Brønsted acid/base, and a sacrificial electron donor (SED). Tertiary amines, in particular triethylamine (TEA) and triethanolamine (TEOA), are ubiquitously deployed in photocatalysis applications as SEDs and are capable of reductively quenching the PS's excited state. Upon oxidation, TEA and TEOA form TEA•+ and TEOA•+ radical cations, respectively, which decay by proton transfer to generate redox non-innocent transient radicals, TEA• and TEOA•, respectively, with redox potentials that allow them to participate in an additional electron transfer step, thus resulting in net one-photon/two-electron donation. However, the properties of the TEA• and TEOA• radicals are not well understood, including their reducing powers and kinetics of electron transfer to catalysts. Herein, we have used both pulse radiolysis and laser flash photolysis to generate TEA• and TEOA• radicals in CH3CN, and combined with UV/Vis transient absorption and time-resolved mid-infrared spectroscopies, we have probed the kinetics of reduction of the well-established CO2 reduction photocatalyst, fac-ReCl(bpy)(CO)3 (bpy = 2,2'-bipyridine), by these radicals [kTEA• = (4.4 ± 0.3) × 109 M-1 s-1 and kTEOA• = (9.3 ± 0.6) × 107 M-1 s-1]. The ∼50× smaller rate constant for TEOA• indicates, that in contrast to a previous assumption, TEA• is a more potent reductant than TEOA• (by ∼0.2 V, as estimated using the Marcus cross relation). This knowledge will aid in the design of photocatalytic systems involving SEDs. We also show that TEA can be a useful radiolytic solvent radical scavenger for pulse radiolysis experiments in CH3CN, effectively converting unwanted oxidizing radicals into useful reducing equivalents in the form of TEA• radicals.
PubMed: 38146832
DOI: 10.1063/5.0180065 -
IUCrData Jun 2023The study of the oxidation of various proteins necessitates scrutiny of the amino acid sequence. Since me-thio-nine (Met) and tyrosine (Tyr) are easily oxidized,...
The study of the oxidation of various proteins necessitates scrutiny of the amino acid sequence. Since me-thio-nine (Met) and tyrosine (Tyr) are easily oxidized, peptides that contain these amino acids are frequently studied using a variety of oxidation methods, including, but not limited to, pulse radiolysis, electrochemical oxidation, and laser flash photolysis. To date, the oxidation of the Met-Tyr dipeptide is not fully understood. Several investigators have proposed a mechanism of intra-molecular electron transfer between the sulfide radical of Met and the Tyr residue. Our elucidation of the structure and absolute configuration of l-Met-l-Tyr monohydrate, CHNOS·HO (systematic name: (2)-2-{[(2)-2-amino-4-methyl-sulfanyl-butano-yl]amino}-3-(4-hy-droxy-phen-yl)propanoic acid monohydrate) is presented herein and provides information about the zwitterionic nature of the dipeptide. We suspect that the zwitterionic state of the dipeptide and its inter-action within the solvent medium may play a major role in the oxidation of the dipeptide. In the crystal, all the potential donor atoms inter-act strong N-H⋯O, C-H⋯O, O-H⋯S, and O-H⋯O hydrogen bonds.
PubMed: 37936870
DOI: 10.1107/S2414314623005515 -
Nature Communications Nov 2023Time-resolved identification of surface-bound intermediates on metallic nanocatalysts is imperative to develop an accurate understanding of the elementary steps of CO...
Time-resolved identification of surface-bound intermediates on metallic nanocatalysts is imperative to develop an accurate understanding of the elementary steps of CO reduction. Direct observation on initial electron transfer to CO to form surface-bound CO radicals is lacking due to the technical challenges. Here, we use picosecond pulse radiolysis to generate CO via aqueous electron attachment and observe the stabilization processes toward well-defined nanoscale metallic sites. The time-resolved method combined with molecular simulations identifies surface-bound intermediates with characteristic transient absorption bands and distinct kinetics from nanosecond to the second timescale for three typical metallic nanocatalysts: Cu, Au, and Ni. The interfacial interactions are further investigated by varying the important factors, such as catalyst size and the presence of cation in the electrolyte. This work highlights fundamental ultrafast spectroscopy to clarify the critical initial step in the CO catalytic reduction mechanism.
PubMed: 37932333
DOI: 10.1038/s41467-023-42936-6 -
Biomolecules Oct 2023We examined the reaction of hydroxyl radicals (HO) and sulfate radical anions (SO), which is generated by ionizing radiation in aqueous solutions under anoxic...
We examined the reaction of hydroxyl radicals (HO) and sulfate radical anions (SO), which is generated by ionizing radiation in aqueous solutions under anoxic conditions, with an alternating GC doubled-stranded oligodeoxynucleotide (ds-ODN), i.e., the palindromic 5'-d(GCGCGC)-3'. In particular, the optical spectra of the intermediate species and associated kinetic data in the range of ns to ms were obtained via pulse radiolysis. Computational studies by means of density functional theory (DFT) for structural and time-dependent DFT for spectroscopic features were performed on 5'-d(GCGC)-3'. Comprehensively, our results suggest the addition of HO to the G:C pair moiety, affording the [8-HO-G:C] detectable adduct. The previous reported spectra of one-electron oxidation of a variety of ds-ODN were assigned to [G(-H):C] after deprotonation. Regarding 5'-d(GCGCGC)-3' ds-ODN, the spectrum at 800 ns has a completely different spectral shape and kinetic behavior. By means of calculations, we assigned the species to [G:C/C:G], in which the electron hole is predicted to be delocalized on the two stacked base pairs. This transient species was further hydrated to afford the [8-HO-G:C] detectable adduct. These remarkable findings suggest that the double-stranded alternating GC sequences allow for a new type of electron hole stabilization via delocalization over the whole sequence or part of it.
Topics: Oligonucleotides; Hydroxyl Radical; Electrons; Free Radicals; Oxidation-Reduction; Oligodeoxyribonucleotides
PubMed: 37892175
DOI: 10.3390/biom13101493 -
The Journal of Physical Chemistry. A Sep 2023Formal reduction potentials of highly oxidizing and short-lived radical cations of substituted biphenyls generated by pulse radiolysis in 1,2-dichloroethane (DCE) were...
Formal reduction potentials of highly oxidizing and short-lived radical cations of substituted biphenyls generated by pulse radiolysis in 1,2-dichloroethane (DCE) were measured using a redox equilibrium ladder method. The effect of halide ion-radical interactions on reduction potentials of biphenyls was examined by utilizing the ability of DCE to release Cl in the vicinity of the radical cation. The Hammett correlation of measured potentials across a range of over 700 mV shows saturation at high Hammett sigma values. This effect has been explained by both ion-pairing and hemicolligation interactions between biphenyl radical cations and Cl and appears to modulate reduction potentials by as much as 400 mV. This finding offers a convenient way to manipulate the energetics of electron transfer involving organic redox species.
PubMed: 37721794
DOI: 10.1021/acs.jpca.3c03817