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Journal of Hazardous Materials Sep 2023Recovery of platinum group metals (PGMs) including palladium (Pd), rhodium (Rh), and ruthenium (Ru) from high-level radioactive liquid waste (HLLW) possesses enormous...
Recovery of platinum group metals (PGMs) including palladium (Pd), rhodium (Rh), and ruthenium (Ru) from high-level radioactive liquid waste (HLLW) possesses enormous environmental and economic benefits. A non-contact photoreduction method was herein developed to selectively recover each PGM from HLLW. Soluble Pd(II), Rh(III), and Ru(III) ions were reduced to insoluble zero-valent metals and separated from simulated HLLW containing neodymium (Nd) as a representative for lanthanides, another main component in HLLW. Detailed investigation on the photoreduction of different PGMs revealed that Pd(II) could be reduced under 254- or 300-nm UV exposure using either ethanol or isopropanol as reductants. Only 300-nm UV light enabled the reduction of Rh(III) in the presence of ethanol or isopropanol. Ru(III) was the most difficult to reduce, which was only realized by 300-nm UV illumination in isopropanol solution. The effects of pH was also studied, suggesting that lower pH favored the separation of Rh(III) but hindered the reduction of Pd(II) and Ru(III). A delicate three-step process was accordingly designed to achieve the selective recovery of each PGM from simulated HLLW. Pd(II) was reduced by 254-nm UV light with the help of ethanol in the first step. Then Rh(III) was reduced by 300-UV light in the second step after the pH was adjusted to 0.5 to suppress the Ru(III) reduction. In the third step, Ru(III) was reduced by 300-nm UV light after isopropanol was added and the pH was adjusted to 3.2. The separation ratios of Pd, Rh, and Ru exceeded 99.8%, 99.9%, and 90.0%, respectively. Meanwhile, all Nd(III) still remained in the simulated HLLW. The separation coefficients between Pd/Rh and Rh/Ru exceeded 56,000 and 75,000, respectively. This work may provide an alternative method to recover PGMs from HLLW, which minimize the secondary radioactive wastes compared with other approaches.
PubMed: 37331059
DOI: 10.1016/j.jhazmat.2023.131852 -
Influence of Ionizing Radiation on Spontaneously Formed Aggregates in Proteins or Enzymes Solutions.Pharmaceutics Apr 2023We have shown that many proteins and enzymes (ovalbumin, β-lactoglobulin, lysozyme, insulin, histone, papain) undergo concentration-dependent reversible aggregation as...
We have shown that many proteins and enzymes (ovalbumin, β-lactoglobulin, lysozyme, insulin, histone, papain) undergo concentration-dependent reversible aggregation as a result of the interaction of the studied biomolecules. Moreover, irradiation of those protein or enzyme solutions under oxidative stress conditions results in the formation of stable soluble protein aggregates. We assume that protein dimers are mainly formed. A pulse radiolysis study has been made to investigate the early stages of protein oxidation by N3• or OH radicals. Reactions of the N3• radical with the studied proteins lead to the generation of aggregates stabilized by covalent bonds between tyrosine residues. The high reactivity of the OH with amino acids contained within proteins is responsible for the formation of various covalent bonds (including C-C or C-O-C) between adjacent protein molecules. In the analysis of the formation of protein aggregates, intramolecular electron transfer from the tyrosine moiety to Trp radical should be taken into account. Steady-state spectroscopic measurements with a detection of emission and absorbance, together with measurements of the dynamic scattering of laser light, made it possible to characterize the obtained aggregates. The identification of protein nanostructures generated by ionizing radiation using spectroscopic methods is difficult due to the spontaneous formation of protein aggregates before irradiation. The commonly used fluorescence detection of dityrosyl cross-linking (DT) as a marker of protein modification under the influence of ionizing radiation requires modification in the case of the tested objects. A precise photochemical lifetime measurement of the excited states of radiation-generated aggregates is useful in characterizing their structure. Resonance light scattering (RLS) has proven to be an extremely sensitive and useful technique to detect protein aggregates.
PubMed: 37242609
DOI: 10.3390/pharmaceutics15051367 -
Heliyon Jul 2022Natural dietary products of health promoting and disease preventive functional relevance are gaining significant prominence. Current investigation was aimed to decipher...
Natural dietary products of health promoting and disease preventive functional relevance are gaining significant prominence. Current investigation was aimed to decipher the underlying molecular mechanism responsible for the antimutagenic action contributing to functional relevance of floral honey ('', Karanj honey) derived abscisic acid (ABA) against ethyl methanesulfonate (EMS) induced mutagenesis. Differential expression of proteins under different treatment conditions was ascertained by 2D gel electrophoresis. Selectively up-regulated characterized using MALDI-TOF MS/MS were identified as polyribonucleotide nucleotidyl transferse (PNPase), LPS-assembly lipoprotein (LptE), Outer membrane Usher protein (HtrE), ATP-dependent DNA helicase (RecG), and Phosphomethyl pyrimidine synthase (ThiC). Antimutagenicity exerted by ABA against EMS was ∼78% in wild type MG1655 strain however, in , this activity was found to be ∼60, 10, 9 and 10%, respectively. Proteomic analysis and antimutagenicity studies using single gene knockout strains thus indicated about the possible role of in observed antimutagenicity. Cyclic voltametry as well as competition kinetics through pulse radiolysis confirmed lack of antioxidant capacity in abscisic acid apparently ruling out the possibility of scavenging of electrophilic intermediates generated by ethyl methanesulfonate. It is proposed that ABA is exerting antimutagenicity through its involvement at the cellular level leading to physiological adaptation, strengthening of cell wall proteins and up-regulation of the repair proteins. This study provides a novel dimension to the functional role of abscisic acid from its nutraceutical perspective.
PubMed: 35874072
DOI: 10.1016/j.heliyon.2022.e09945 -
Physical Chemistry Chemical Physics :... Sep 2020The one-electron redox potentials for aqueous metal couples Co and Ni have been investigated by using pulse radiolysis using their reactions with a series of reference...
The one-electron redox potentials for aqueous metal couples Co and Ni have been investigated by using pulse radiolysis using their reactions with a series of reference compounds to establish the most positive upper limits of E. Experiments with Zn were also carried out to confirm the characteristic shape of the expected reduction kinetics. Both formate ions and t-BuOH were employed to scavenge ˙OH radicals and ˙H atoms. Kinetics and fitted first and second order reaction rates have been reported for reactions with methyl viologen, fluorescein, Ru(NH), Co(en), Co(sepulcrate), Ru(bpy), Cr(bpy), and Ni(Me[14]4,11-dieneN). Previous work demonstrated that both Co and Ni can be reduced by CO˙ radicals, giving a negative E limit of -1.9 V vs. SHE. A definite reaction of Ni with fluorescein di-anions provides a new upper limit of the Ni couple as -0.906 V vs. SHE. The reaction of Co with Ru(bpy) has been confirmed, giving E = -1.3 V vs. SHE as a rigorous upper limit of the Co couple. In the case of Co, kinetics were complicated by a self-catalyzed metal clustering phenomenon. Initiation rate constants of this process have also been reported.
PubMed: 32902533
DOI: 10.1039/d0cp03214j -
Radiation Research Dec 2020Radiation chemists have been routinely using high-dose microsecond-pulsed irradiation for almost 60 years, involving many thousands of studies, in the technique of...
Radiation chemists have been routinely using high-dose microsecond-pulsed irradiation for almost 60 years, involving many thousands of studies, in the technique of "pulse radiolysis". This involves dose rates broadly similar to the FLASH regimen now attracting interest in radiotherapy and radiobiology. Using the experience gained from radiation chemistry, two scenarios are examined here that may provide a mechanistic basis for any differential response in normal tissues versus tumors in FLASH radiotherapy. These are: 1. possible depletion of a chemical critical to the response to radiation, and 2. radical-radical reactions as a possible cause of effects occurring mainly with high-intensity pulsed radiation. The evidence for changes in relative levels of so-called "reactive oxygen species" produced after irradiation using FLASH versus conventional irradiation modalities is also examined.
Topics: Humans; Neoplasms; Radiochemistry; Radiotherapy; Radiotherapy Dosage; Reactive Oxygen Species
PubMed: 33348369
DOI: 10.1667/RADE-19-00016 -
The Journal of Physical Chemistry. A Jul 2020A novel method to determine redox potentials without electrolyte is presented. The method is based on a new ability to determine the dissociation constant, °, for ion...
A novel method to determine redox potentials without electrolyte is presented. The method is based on a new ability to determine the dissociation constant, °, for ion pairs formed between any radical anion and any inert electrolyte counterion. These dissociation constants can be used to determine relative shifts of redox potential as a function of electrolyte concentration, connecting referenced potentials determined with electrochemistry (with 0.1 M electrolyte) to electrolyte-free values. Pulse radiolysis created radical anions enabling determination of equilibrium constants for electron transfer between anions of donor and acceptor molecules as a function of electrolyte concentration in THF. The measurements determined "composite equilibrium constants", , which contain information about the dissociation constant for the electrolyte cations, X, with the radical anions of both the donor, °(D,X) and the acceptor, °(A,X). Dissociation constants were obtained for a selection of radical anions with tetrabutylammonium (TBA). The electrolyte was found to shift the reduction potentials of small molecules 1-methylpyrene and -stilbene by close to +130 mV whereas oligo-fluorenes and polyfluorenes experienced shifts of only (+25 ± 6) mV due to charge delocalization weakening the ion pair. These shifts for reduction of aromatic hydrocarbon molecules are smaller than shifts of +232 and +451 mV seen previously for benzophenone radical anion with TBA and Na respectively where the charge on the radical anion is localized largely on one C═O bond, thus forming a more tightly bound ion pair.
PubMed: 32437607
DOI: 10.1021/acs.jpca.0c02948 -
Molecules (Basel, Switzerland) Dec 2019Oxidative damage to 2-thiouracil (2-TU) by hydroxyl (OH) and azide (N) radicals produces various primary reactive intermediates. Their optical absorption spectra and...
Oxidative damage to 2-thiouracil (2-TU) by hydroxyl (OH) and azide (N) radicals produces various primary reactive intermediates. Their optical absorption spectra and kinetic characteristics were studied by pulse radiolysis with UV-vis spectrophotometric and conductivity detection and by time-dependent density functional theory (TD-DFT) method. The transient absorption spectra recorded in the reactions of OH with 2-TU depend on the concentration of 2-TU, however, only slightly on pH. At low concentrations, they are characterized by a broad absorption band with a weakly pronounced maxima located at λ = 325, 340 and 385 nm, whereas for high concentrations, they are dominated by an absorption band with λ ≈ 425 nm. Based on calculations using TD-DFT method, the transient absorption spectra at low concentration of 2-TU were assigned to the OH-adducts to the double bond at C5 and C6 carbon atoms (3, 4) and 2c-3e bonded OH adduct to sulfur atom (1…OH) and at high concentration of 2-TU also to the dimeric 2c-3e S-S-bonded radical in neutral form (2). The dimeric radical (2) is formed in the reaction of thiyl-type radical (6) with 2-TU and both radicals are in an equilibrium with K = 4.2 × 10 M. Similar equilibrium (with K = 4.3 × 10 M) was found for pH above the pK of 2-TU which involves admittedly the same radical (6) but with the dimeric 2c-3e S-S bonded radical in anionic form (2). In turn, N-induced oxidation of 2-TU occurs via radical cation with maximum spin location on the sulfur atom which subsequently undergoes deprotonation at N1 atom leading again to thiyl-type radical (6). This radical is a direct precursor of dimeric radical (2).
Topics: Density Functional Theory; Electrons; Free Radicals; Hydrogen-Ion Concentration; Hydroxyl Radical; Kinetics; Oxidation-Reduction; Pulse Radiolysis; Radiation, Ionizing; Spectrum Analysis; Thiouracil
PubMed: 31810289
DOI: 10.3390/molecules24234402 -
Chemistry (Weinheim An Der Bergstrasse,... Aug 2020The directionality of the hole-transfer processes between DNA backbone and base was investigated by using phosphorodithioate [P(S )=S] components. ESR spectroscopy in...
The directionality of the hole-transfer processes between DNA backbone and base was investigated by using phosphorodithioate [P(S )=S] components. ESR spectroscopy in homogeneous frozen aqueous solutions and pulse radiolysis in aqueous solution at ambient temperature confirmed initial formation of G -P(S )=S. The ionization potential of G-P(S )=S was calculated to be slightly lower than that of guanine in 5'-dGMP. Subsequent thermally activated hole transfer from G to P(S )=S led to dithiyl radical (P-2S ) formation on the μs timescale. In parallel, ESR spectroscopy, pulse radiolysis, and density functional theory (DFT) calculations confirmed P-2S formation in an abasic phosphorodithioate model compound. ESR investigations at low temperatures and higher G-P(S )=S concentrations showed a bimolecular conversion of P-2S to the σ -σ* -bonded dimer anion radical [-P-2S 2S-P-] [ΔG (150 K, DFT)=-7.2 kcal mol ]. However, [-P-2S 2S-P-] formation was not observed by pulse radiolysis [ΔG° (298 K, DFT)=-1.4 kcal mol ]. Neither P-2S nor [-P-2S 2S-P-] oxidized guanine base; only base-to-backbone hole transfer occurs in phosphorodithioate.
Topics: Anions; DNA; Electron Spin Resonance Spectroscopy; Guanine; Nucleosides; Oxidation-Reduction; Phosphates; Pulse Radiolysis; Water
PubMed: 32059063
DOI: 10.1002/chem.202000247 -
Medical Physics Nov 2023Hydrated electrons, which are short-lived products of radiolysis in water, increase the optical absorption of water, providing a pathway toward near-tissue-equivalent...
BACKGROUND
Hydrated electrons, which are short-lived products of radiolysis in water, increase the optical absorption of water, providing a pathway toward near-tissue-equivalent clinical radiation dosimeters. This has been demonstrated in high-dose-per-pulse radiochemistry research, but, owing to the weak absorption signal, its application in existing low-dose-per-pulse radiotherapy provided by clinical linear accelerators (linacs) has yet to be investigated.
PURPOSE
The aims of this study were to measure the optical absorption associated with hydrated electrons produced by clinical linacs and to assess the suitability of the technique for radiotherapy (⩽ 1 cGy per pulse) applications.
METHODS
40 mW of 660-nm laser light was sent five passes through deionized water contained in a 10 2 cm glass-walled cavity by using four broadband dielectric mirrors, two on each side of the cavity. The light was collected with a biased silicon photodetector. The water cavity was then irradiated by a Varian TrueBeam linac with both photon (10 MV FFF, 6 MV FFF, 6 MV) and electron beams (6 MeV) while monitoring the transmitted laser power for absorption transients. Radiochromic EBT3 film measurements were also performed for comparison.
RESULTS
Examination of the absorbance profiles showed clear absorption changes in the water when radiation pulses were delivered. Both the amplitude and the decay time of the signal appeared consistent with the absorbed dose and the characteristics of the hydrated electrons. By using literature value for the hydrated electron radiation chemical yield (3.0±0.3), we inferred doses of 2.1±0.2 mGy (10 MV FFF), 1.3±0.1 mGy (6 MV FFF), 0.45±0.06 mGy (6 MV) for photons, and 0.47±0.05 mGy (6 MeV) for electrons, which differed from EBT3 film measurements by 0.6%, 0.8%, 10%, and 15.7%, respectively. The half-life of the hydrated electrons in the solution was ∼ 24 s.
CONCLUSIONS
By measuring 660-nm laser light transmitted through a cm-scale, multi-pass water cavity, we observed absorption transients consistent with hydrated electrons generated by clinical linac radiation. The agreement between our inferred dose and EBT3 film measurements suggests this proof-of-concept system represents a viable pathway toward tissue-equivalent dosimeters for clinical radiotherapy applications.
Topics: Electrons; Radiation Dosimeters; Photons; Phantoms, Imaging; Particle Accelerators; Water; Radiotherapy Dosage; Radiometry
PubMed: 37334736
DOI: 10.1002/mp.16555 -
The Journal of Physical Chemistry. A Jul 2021Light-induced blinking, an inherent feature of many forms of super-resolution microscopy, has been linked to transient reduction of the fluorescent cyanine dye used as...
Light-induced blinking, an inherent feature of many forms of super-resolution microscopy, has been linked to transient reduction of the fluorescent cyanine dye used as an imaging agent. There is, however, only scant literature information related to one-electron reduced cyanine dyes, especially in an aqueous environment. Here, we examine a small series of cyanine dyes, possessing disparate π-conjugation lengths, under selective reducing or oxidizing conditions. The experiment allows recording of both differential absorption spectra and decay kinetics of the resultant one-electron reduced or oxidized transient species in water. Relative to the ground state, absorption transitions for the various radicals are weak and somewhat broadened but do allow correlation with the π-conjugation length. In all cases, absorption maxima lie to the blue of the main ground-state transition. Under anaerobic conditions, the transient species decay on the microsecond to millisecond time scale, with the mean lifetime depending on molecular structure, radiation dose, and dye concentration. The experimental absorption spectra recorded for the one-electron reduced radicals and the presumed dimer cation radical compare well to spectra obtained from time-dependent density functional theory calculations. The results allow conclusions to be drawn regarding the plausibility of the reduced species being responsible for light-induced blinking in direct stochastic optical reconstruction microscopy.
PubMed: 34165985
DOI: 10.1021/acs.jpca.1c03776