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Early stages of radiolysis of solutions with 2,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4]triazin-3-yl)pyridine (CyMe4-BTP) and 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4-]triazin-3-yl)-[2,2']bipyridine (CyMe4-BTBP) ligands in cyclohexanone, proposed as a solvent for selective actinide extraction, were studied by means of the pulse radiolysis technique with spectrophotometric detection. Transient UV-vis spectra of excited triplet states of ligands, formed by energy transfer from cyclohexanone excited triplet states to ligands, were recorded for the first time. The influence of typical extraction conditions (the presence of diluted acid and O 2 from air) on the mechanisms of reactions in the system studied was assessed. It was shown that an addition of benzophenone in high concentrations to the system together with its continuous saturation by O 2 could partially protect ligands from radiation damage, caused by the high-energy radiation emitted by the spent nuclear fuel.

We examined the reaction of hydroxyl radicals (HO • ) and sulfate radical anions (SO 4 •- ), 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.

Objective. The aim of this work was to develop and validate a method for remote dosimetric auditing that enables dose-volume histogram parameter comparisons of measured and planned dose in the patient CT volume. Approach . The method is derived by adapting and combining a remote electronic portal imaging (EPID) based auditing method (Virtual Epid based Standard Phantom Audit-VESPA) and a method to estimate 3D in-patient dose distributions from planar dosimetric measurements. The method was tested with a series of error-induced plans including monitor unit and multileaf collimator (MLC) positioning errors. A pilot audit study was conducted with eleven radiotherapy centres. IMRT plans from two clinical trials, a post-prostatectomy (RAVES trial) plan and a head and neck (HPV trial) plan were utilized. Clinically relevant DVH parameters for the planned dose and estimated measured dose were compared. Main results . The method was found to reproduce the induced dose errors within 0.5% and was sensitive to MLC positioning errors as small as 0.5 mm. For the RAVES plan audit all DVH results except one were within 3% and for the HPV plan audit all DVH results were within 3% except three with a maximum difference of 3.2%. Significance . The results from the audit method produce clinically meaningful DVH metrics for the audited plan and could enable an improved understanding of a centre's radiotherapy quality., (© 2023 Institute of Physics and Engineering in Medicine.)

Hydroxyl radicals (HO • ) have long been regarded as a major source of cellular damage. The reaction of HO • with methionine residues (Met) in peptides and proteins is a complex multistep process. Although the reaction mechanism has been intensively studied, some essential parts remain unsolved. In the present study we examined the reaction of HO • generated by ionizing radiation in aqueous solutions under anoxic conditions with two compounds representing the simplest model peptide backbone CH 3 C(O)NHCHXC(O)NHCH 3 , where X = CH 2 CH 2 SCH 3 or CH 2 SCH 3 , i.e., the Met derivative in comparison with the cysteine-methylated derivative. We performed the identification and quantification of transient species by pulse radiolysis and final products by LC-MS and high-resolution MS/MS after γ-radiolysis. The results allowed us to draw for each compound a mechanistic scheme. The fate of the initial one-electron oxidation at the sulfur atom depends on its distance from the peptide backbone and involves transient species of five-membered and/or six-membered ring formations with different heteroatoms present in the backbone as well as quite different rates of deprotonation in forming α-(alkylthio)alkyl radicals.

The mechanism of high-energy radiation induced degradation of perfluorooctanoate anion (PFOA, C 7 F 15 COO - ) was investigated in aqueous solutions. Identification and quantification of transient species was performed by pulse radiolysis and of final products by gas and ion chromatography, electrochemical method using fluoride ion-selective electrode and ESI-MS after γ-radiolysis. Experimental data were further supported by kinetic simulations and quantum mechanical calculations. Radiation induced degradation of PFOA includes as a primary step one-electron reduction of PFOA by hydrated electrons (e - aq ) resulting in formation of [C 7 F 15 COO - ] ●- . The rate constants of this reaction were found to be in the range 7.7 × 10 7 -1.3 × 10 8  M -1 s -1 for ionic strength of the solutions in the range 0.01-0.1 M and were independent of pH of the solutions. At pH > 11 [C 7 F 15 COO - ] ●- tends to defluorination whereas at lower pH undergoes protonation forming [C 7 F 15 COOH] •- . A sequence of consecutive reactions involving [C 7 F 15 COOH] •- leads to PFOA regeneration what explains a high radiation resistance of PFOA at moderately acidic solutions. A simultaneous presence of oxidizing transient species ( ● OH) in the irradiated system enhanced decomposition of (C 7 F 14 )·COO - as well as [C 7 F 15 COOH] •- . The key steps in this complex radical mechanism are the reactions of both these radical anions with ● OH leading to semi-stable products which further undergo consecutive thermal reactions. On the other hand, direct reactions of PFOA with ● OH and ● H were found to be relatively slow (7 × 10 3 and <4 × 10 7  M -1 s -1 , respectively) and do not play relevant role in PFOA degradation. Collected for the first time results, such as dependence of selected reaction rate constants and selected products radiation chemical yields on pH as well as finding of several semi-stable products, missing in previous studies, indicate incompleteness of published earlier reaction pathways of PFOA degradation. The presented overall mechanism explains experimental results and verifies previously suggested mechanisms found in the literature., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Oxidation of methionine (Met) is an important reaction that plays a key role in protein modifications during oxidative stress and aging. The first steps of Met oxidation involve the creation of very reactive and short-lived transients. Application of complementary time-resolved radiation and photochemical techniques (pulse radiolysis and laser flash photolysis together with time-resolved CIDNP and ESR techniques) allowed comparing in detail the one-electron oxidation mechanisms initiated either by ● OH radicals and other one-electron oxidants or the excited triplet state of the sensitizers e.g., 4-,3-carboxybenzophenones. The main purpose of this review is to present various factors that influence the character of the forming intermediates. They are divided into two parts: those inextricably related to the structures of molecules containing Met and those related to external factors. The former include (i) the protection of terminal amine and carboxyl groups, (ii) the location of Met in the peptide molecule, (iii) the character of neighboring amino acid other than Met, (iv) the character of the peptide chain (open vs cyclic), (v) the number of Met residues in peptide and protein, and (vi) the optical isomerism of Met residues. External factors include the type of the oxidant, pH, and concentration of Met-containing compounds in the reaction environment. Particular attention is given to the neighboring group participation, which is an essential parameter controlling one-electron oxidation of Met. Mechanistic aspects of oxidation processes by various one-electron oxidants in various structural and pH environments are summarized and discussed. The importance of these studies for understanding oxidation of Met in real biological systems is also addressed.

One-electron oxidation of 2-selenouracil (2-SeU) by hydroxyl ( ● OH) and azide ( ● N 3 ) radicals leads to 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 the density functional theory (DFT) method. The transient absorption spectra recorded in the reactions of ● OH with 2-SeU are dominated by an absorption band with an λ max = 440 nm, the intensity of which depends on the concentration of 2-SeU and pH. Based on the combination of conductometric and DFT studies, the transient absorption band observed both at low and high concentrations of 2-SeU was assigned to the dimeric 2c-3e Se-Se-bonded radical in neutral form (2 ● ). The dimeric radical (2 ● ) is formed in the reaction of a selenyl-type radical (6 ● ) with 2-SeU, and both radicals are in equilibrium with K eq = 1.3 × 10 4 M -1 at pH 4 (below the pK a of 2-SeU). Similar equilibrium with K eq = 4.4 × 10 3 M -1 was determined for pH 10 (above the pK a of 2-SeU), which admittedly involves the same radical (6 ● ) but with a dimeric 2c-3e Se-Se bonded radical in anionic form (2 ●- ). In turn, at the lowest concentration of 2-SeU (0.05 mM) and pH 10, the transient absorption spectrum is dominated by an absorption band with an λ max = 390 nm, which was assigned to the ● OH adduct to the double bond at C5 carbon atom (3 ● ) based on DFT calculations. Similar spectral and kinetic features were also observed during the ● N 3 -induced oxidation of 2-SeU. In principle, our results mostly revealed similarities in one-electron oxidation pathways of 2-SeU and 2-thiouracil (2-TU). The major difference concerns the stability of dimeric radicals with a 2c-3e chalcogen-chalcogen bond in favor of 2-SeU.

The conversion of ribonucleosides to 2'-deoxyribonucleosides is catalyzed by ribonucleoside reductase enzymes in nature. One of the key steps in this complex radical mechanism is the reduction of the 3'-ketodeoxynucleotide by a pair of cysteine residues, providing the electrons via a disulfide radical anion (RSSR •- ) in the active site of the enzyme. In the present study, the bioinspired conversion of ketones to corresponding alcohols was achieved by the intermediacy of disulfide radical anion of cysteine (CysSSCys) •- in water. High concentration of cysteine and pH 10.6 are necessary for high-yielding reactions. The photoinitiated radical chain reaction includes the one-electron reduction of carbonyl moiety by disulfide radical anion, protonation of the resulting ketyl radical anion by water, and H-atom abstraction from CysSH. The (CysSSCys) •- transient species generated by ionizing radiation in aqueous solutions allowed the measurement of kinetic data with ketones by pulse radiolysis. By measuring the rate of the decay of (CysSSCys) •- at λ max = 420 nm at various concentrations of ketones, we found the rate constants of three cyclic ketones to be in the range of 10 4 -10 5 M -1 s -1 at ~22 °C.

Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO • ) play an important role, being the most aggressive towards biomolecules. The reactions of HO • with methionine residues (Met) in peptides and proteins have been intensively studied, but some fundamental aspects remain unsolved. In the present study we examined the biomimetic model made of Ac-Met-OMe, as the simplest model peptide backbone, and of HO • generated by ionizing radiation in aqueous solutions under anoxic conditions. We performed the identification and quantification of transient species by pulse radiolysis and of final products by LC-MS and high-resolution MS/MS after γ-radiolysis. By parallel photochemical experiments, using 3-carboxybenzophenone (CB) triplet with the model peptide, we compared the outcomes in terms of short-lived intermediates and stable product identification. The result is a detailed mechanistic scheme of Met oxidation by HO • , and by CB triplets allowed for assigning transient species to the pathways of products formation.

Introduction: Protective Behavioral Strategies (PBS) are an alcohol-specific cognitive-behavioral strategies that may be employed before, during and/or after drinking, in order to reduce alcohol consumption and related consequences, particularly in the at-risk populations. Previous research on PBS was limited to North American college students. The purpose of this study was to examine the role of PBS use in a sample of Polish adolescents attending Special Educational Centers (SEC)., Method: Data were collected from a nationwide sample of 12-19 year-old (Mean = 15.8; SD = 1.22) students attending SEC in Poland (N = 1585; about 33% female). The self-administered anonymous questionnaires were completed on-site in the SEC. PBS were measured by the authors adaptation of the PBSS-20. Alcohol-related problems were assessed by the Polish adaptation of the measures used in the MINI-KID tool. Alcohol use was measured by a single question on drinking frequency. These two latter variables were measured in the past year timeframe. Hierarchical regression models were used to test the main and interaction effects of employing PBS (total and subscales scores) on alcohol-related problems, after adjusting for demographics (gender, family composition and type of SEC) and alcohol use., Results: The majority (about 94%) of study participants reported employment of some PBS. Regression analyses indicated that PBS use was associated with reduced risk of alcohol use and alcohol-related problems. We found that PBS significantly moderated the relationship between alcohol use and alcohol-related problems, for PBS total scale (F-change (1,1555) = 15.96, p < .001) and one of the PBS subscale: Limiting/Stopping Drinking (F-change (1,1555) = 4.80, p < .029). Findings were discussed within the results of PBS literature and resilience theory framework., Conclusion: The use of PBS helps to reduce alcohol-related problems among adolescents attending SEC. Implementation of tailored interventions that teach PBS among vulnerable adolescents may be an effective way to strengthen adolescent self-protection, reduce risky alcohol use and related negative consequences., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this work, the feasibility of sterilizing a water suspension of poly-3-hexylthiophene nanoparticles (P3HT-NPs) is investigated using ionizing radiation, either γ-rays or high-energy electrons (e-beam). It is found that regardless of the irradiation source, the size, polydispersity, aggregation stability, and morphology of the NPs are not affected by the treatment. Furthermore, the impact of ionizing radiation on the physicochemical properties of NPs at different absorbed radiation doses (10-25 kGy) and dose rates (kGy time -1 ) is evaluated through different spectroscopic techniques. The results indicate that delivering a high dose of radiations (25 kGy) at a high dose rate, that is, kGy s -1 , as achieved by e-beam irradiation, preserves the characteristics of the polymeric NPs. Differently, the same radiation dose but delivered at a lower dose rate, that is, kGy h -1 , as attained by using a γ-source, can modify the physicochemical properties of the polymer. Sterility tests indicate that an absorbed dose of 10 kGy, delivered either with γ-rays or e-beam, is already sufficient for effective sterilization of the colloidal suspension and for reducing the endotoxin content. Finally, NPs irradiated at different doses, exhibit the same cytocompatibility and cell internalization characteristics in human neuroblastoma SH-SY5Y cells of NPs prepared under aseptic conditions., (© 2021 Wiley-VCH GmbH.)

The azide radical (N 3 ● ) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N 3 ● reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N 3 ● addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO 4 ●- , CO 3 ●- ) and Tl 2+ ions with the reduction potentials higher, and one radical (SCN) 2 ●- with the reduction potential slightly lower than the reduction potential of N 3 ● were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N 3 ● with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N 3 ● differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N 3 ● is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N 3 ● with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ) ●+ , radicals (7-R-3-MeQ) ● and N 3 ● adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning's aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

The kinetics of intramolecular-contact formation between remote functional groups in peptides with restricted conformational flexibility were examined using designed peptides with variable-length proline bridges. As probes for this motion, free radicals were produced using the • OH-induced oxidation at the C-terminal methionine residue of γ-Glu-(Pro) n -Met peptides ( n = 0-3). The progress of the radicals' motion along the proline bridges was monitored as the radicals underwent reactions along the peptides' backbones. Of particular interest was the reaction between the sulfur atom located in the side chain of the oxidized Met residue and the unprotonated amino group of the glutamic acid moiety. Interactions between them were probed by the radiation-chemical yields (expressed as G values) of the formation of C-centered, α-aminoalkyl radicals (αN) on the Glu residue. These radicals were monitored directly or via their reaction with p -nitroacetophenone (PNAP) to generate the optically detected PNAP •- radical anions. The yields of these αN radicals were found to be linearly dependent on the number of Pro residues. A constant decrease by 0.09 μM J -1 per spacing Pro residue of the radiation-chemical yields of G (αN) was observed. Previous reports support the conclusion that the αN radicals in these cases would have to result from (S∴N) + -bonded cyclic radical cations that arose as a result from direct contact between the ends of the peptides. Furthermore, by analogy with the rate constants for the formation of intramolecularly (S∴S) + -bonded radical cations in Met-(Pro) n -Met peptides ( J. Phys. Chem. B 2016, 120, 9732), the rate constants for the formation of intramolecularly (S∴N) + -bonded radical cations are activated to the same extent for all of the γ-Glu-(Pro) n -Met peptides. Thus, the continuous decrease of G (αN) with the number of Pro residues (from 0 to 3) suggests that the formation of a contact between the S-atom in the C-terminal Met residue and the N-atom of a deprotonated N-terminal amino group of Glu is controlled in peptides with 0 to 3 Pro residues by the relative diffusion of the S •+ and unoxidized N-atom. The overall rate constants of cyclization to form the (S∴N)-bonded radical cations were estimated to be 3.8 × 10 6 , 1.8 × 10 6 , and 8.1 × 10 5 s -1 for peptides with n = 0, 1, and 2 Pro residues, respectively. If activation is the same for all of the peptides, then these rate constants are a direct indication for the end-to-end dynamics along the chain.

Laser flash photolysis and high-resolution mass spectrometry were used to investigate the mechanism of one-electron oxidation of two S -alkylglutathiones using 3-carboxybenzophenone (3CB) as a photosensitizer. This report indicates an unexpected reaction pathway of the α-aminoalkyl radical cation (αN + ) derived from the oxidation of S -alkylglutathiones. Instead of a common hydrolysis reaction of αN + reported earlier for methionine and other sulfur-containing aminoacids and peptides, an intramolecular ring-closure reaction was found for S -alkylglutathiones., Competing Interests: The authors declare no conflict of interest.

Oxidative damage to 2-thiouracil (2-TU) by hydroxyl ( • OH) and azide ( ● N 3 ) 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 max ≈ 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 eq = 4.2 × 10 3 M -1 . Similar equilibrium (with K eq = 4.3 × 10 3 M -1 ) was found for pH above the pK a 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 3 -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 ● ).

The reaction of hydroxyl radical (HO • ) with DNA produces many primary reactive species and many lesions as final products. In this study, we have examined the optical spectra of intermediate species derived from the reaction of HO • with a variety of single- and double-stranded oligodeoxynucleotides and ct-DNA in the range of 1 μs to 1 ms by pulse radiolysis using an Intensified Charged Coupled Device (ICCD) camera. Moreover, we applied our published analytical protocol based on an LC-MS/MS system with isotopomeric internal standards to enable accurate and precise measurements of purine lesion formation. In particular, the simultaneous measurement of the four purine 5',8-cyclo-2'-deoxynucleosides (cPu) and two 8-oxo-7,8-dihydro-2'-deoxypurine (8-oxo-Pu) was obtained upon reaction of genetic material with HO • radicals generated either by γ-radiolysis or Fenton-type reactions. Our results contributed to the debate in the literature regarding absolute level of lesions, method of HO • radical generation, 5' R /5' S diastereomeric ratio in cPu, and relative abundance between cPu and 8-oxo-Pu.

Radiosensitizing properties of substituted uridines are of great importance for radiotherapy. Very recently, we confirmed 5-iodo-4-thio-2'-deoxyuridine (ISdU) as an efficient agent, increasing the extent of tumor cell killing with ionizing radiation. To our surprise, a similar derivative of 4-thio-2'-deoxyuridine, 5-bromo-4-thio-2'-deoxyuridine (BrSdU), does not show radiosensitizing properties at all. In order to explain this remarkable difference, we carried out a radiolytic (stationary and pulse) and quantum chemical studies, which allowed the pathways to all radioproducts to be rationalized. In contrast to ISdU solutions, where radiolysis leads to 4-thio-2'-deoxyuridine and its dimer, no dissociative electron attachment (DEA) products were observed for BrSdU. This observation seems to explain the lack of radiosensitizing properties of BrSdU since the efficient formation of the uridine-5-yl radical, induced by electron attachment to the modified nucleoside, is suggested to be an indispensable attribute of radiosensitizing uridines. A larger activation barrier for DEA in BrSdU, as compared to ISdU, is probably responsible for the closure of DEA channel in the former system. Indeed, besides DEA, the XSdU anions may undergo competitive protonation, which makes the release of X - kinetically forbidden.

The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH 3 , -OCH 3 , and -N(CH 3 ) 2 ) or electron-withdrawing (R = -OCF 3 ) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH 3 ), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O 2 ) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ •- ) are characterized by two absorption maxima located at λ max = 470-490 nm and λ max = 510-540 nm, with the respective molar absorption coefficients ε 470-490 = 8500-13 100 M -1 cm -1 and ε 510-540 = 6100-10 300 M -1 cm -1 , depending on the substituent (R). All 4R-SQ •- decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) × 10 6 s -1 . In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH • ), which are characterized by weak absorption bands with λ max = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ •+ ) are characterized by a strong absorption with λ max = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN •+ ) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) × 10 5 s -1 measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (ρ = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ •+ in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) × 10 4 s -1 and, in principle, is not affected by the presence of O 2 , suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ •- ) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ •+ ).

The monitoring of Advanced Oxidation/Reduction Processes (AO/RPs) for the evaluation of the yield and mechanisms of decomposition of perfluorinated compounds (PFCs) is often a more difficult task than their determination in the environmental, biological or food samples with complex matrices. This is mostly due to the formation of hundreds, or even thousands, of both intermediate and final products. The considered AO/RPs, involving free radical reactions, include photolytic and photocatalytic processes, Fenton reactions, sonolysis, ozonation, application of ionizing radiation and several wet oxidation processes. The main attention is paid to the most commonly occurring PFCs in the environment, namely PFOA and PFOS. The most powerful and widely exploited method for this purpose is without a doubt LC/MS/MS, which allows the identification and trace quantitation of all species with detectability and resolution power depending on the particular instrumental configurations. The GC/MS is often employed for the monitoring of volatile fluorocarbons, confirming the formation of radicals in the processes of C‒C and C‒S bonds cleavage. For the direct monitoring of radicals participating in the reactions of PFCs decomposition, the molecular spectrophotometry is employed, especially electron paramagnetic resonance (EPR). The UV/Vis spectrophotometry as a detection method is of special importance in the evaluation of kinetics of radical reactions with the use of pulse radiolysis methods. The most commonly employed for the determination of the yield of mineralization of PFCs is ion-chromatography, but there is also potentiometry with ion-selective electrode and the measurements of general parameters such as Total Organic Carbon and Total Organic Fluoride. The presented review is based on about 100 original papers published in both analytical and environmental journals., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The oxidation processes of l-Met-(Pro) n -l-Met peptides that contain two Met residues located on the N and C termini and separated by a defined number (n = 0-4) of proline residues were investigated in aqueous solutions using laser flash photolysis. The use of such peptides allowed for distance control between the sulfur atoms located in the side chains of the Met residues. Interactions between side chains of the Met residues were probed by the observation of transients with σ*-type 2c-3e (S∴S) + , (S∴N) + , and (S∴O) + bonds as well as of α-(alkylthio)alkyl radicals (αS). This approach enabled the monitoring, in real time, of the efficiency and kinetics of interactions between amino acid chains. Such knowledge is important, inter alia, for long-distance electron-transfer (ET) processes because amino acid side chains can serve as relay stations. The yields of these transients (measured as quantum yields (Φ)) were found to be dependent on the number of Pro residues, however, not dependent in a simple way on the average distance S-S > between sulfur atoms in Met residues. A decrease in the yield of the (S∴S) + species with the number of Pro residues occurred at the expense of an increase in the yields of intramolecular three electron-bonded (S∴O) + /(S∴N) + radical cations and αS radicals. These observations were rationalized by the fact that the time required for adequate overlap of the bonding orbitals is a key factor effecting the yield of the (S∴S) + species. The time, however, can be controlled not only by the average distance S-S > but also by the specific geometrical and conformational properties of the peptide molecules.

Important biological consequences are related to the reaction of HO • radicals with methionine (Met). Several fundamental aspects remain to be defined when Met is an amino acid residue incorporated in the interior of peptides and proteins. The present study focuses on Gly-Met-Gly, the simplest peptide where Met is not a terminal residue. The reactions of HO • with Gly-Met-Gly and its N-acetyl derivative were studied by pulse radiolysis technique. The transient absorption spectra were resolved into contributions from specific components of radical intermediates. Moreover, a detailed product analysis is provided for the first time for Met-containing peptides in radiolytic studies to support the mechanistic proposal. By parallel radiolytical and electrochemical reactions and consequent product identification, the formation of sulfoxide attributed to the direct HO • radical attack on the sulfide functionality of the Met residue could be excluded, with the in situ generated hydrogen peroxide responsible for this oxidation. LC-MS and high resolution MS/MS were powerful analytical tools to envisage the structures of five products, thus allowing to complete the mechanistic picture of the overall Met-containing peptide reactivity.

The radiolysis of deoxygenated aqueous solution containing trimeric oligonucleotides labelled with iodinated pyrimidines and Tris-HCl as the hydroxyl radical scavenger leads to electron attachment to the halogenated bases that mainly results in single strand breaks. The iodinated trimers are 2-fold more sensitive to solvated electrons than the brominated oligonucleotides, which is explained by the barrier-free dissociation of the iodinated base anions. The present study fills the literature gap concerning the chemistry triggered by ionizing radiation in the iodinated pyrimidines incorporated into DNA.

The most important contributions of radiation chemistry to some selected technological issues related to water-cooled reactors, reprocessing of spent nuclear fuel and high-level radioactive wastes, and fuel evolution during final radioactive waste disposal are highlighted. Chemical reactions occurring at the operating temperatures and pressures of reactors and involving primary transients and stable products from water radiolysis are presented and discussed in terms of the kinetic parameters and radiation chemical yields. The knowledge of these parameters is essential since they serve as input data to the models of water radiolysis in the primary loop of light water reactors and super critical water reactors. Selected features of water radiolysis in heterogeneous systems, such as aqueous nanoparticle suspensions and slurries, ceramic oxides surfaces, nanoporous, and cement-based materials, are discussed. They are of particular concern in the primary cooling loops in nuclear reactors and long-term storage of nuclear waste in geological repositories. This also includes radiation-induced processes related to corrosion of cladding materials and copper-coated iron canisters, dissolution of spent nuclear fuel, and changes of bentonite clays properties. Radiation-induced processes affecting stability of solvents and solvent extraction ligands as well oxidation states of actinide metal ions during recycling of the spent nuclear fuel are also briefly summarized.