Irradiation Of Aqueous Solutions Research Articles

Chloroquine degradation in aqueous solution under electron beam irradiation

Abstract Pharmaceutically active compounds are the most widely produced and consumed consumer products that pose a substantial threat to the environment and living organisms owing to their pharmacokinetics, side effects, and contraindications. In this study, the degradation of chloroquine (CQ), a popular antimalarial and recently proposed COVID-19 drug, was investigated under electron beam (EB) irradiation of aqueous solutions. Both the hydroxyl radical and hydrated electron generated in the radiolysis of water contribute to the degradation of CQ in aqueous solution. The overall removal efficiency for 125 mg·L-1 of the CQ solution under EB treatment is reported to be >80% at neutral pH at a maximum irradiation dose of 7 kGy. Removal efficiency is further favored by acidic and slightly alkaline conditions where reactions with hydroxyl radicals and hydrated electrons are favored, respectively. Additionally, increments in the applied dose resulted in the increased removal efficiency for the same concentration of CQ. Conversely, the removal efficiency decreased with increasing concentration of CQ at the same irradiation dose. The initial solution pH, applied irradiation dose, and initial pollutant concentration play an important role in the EB-induced degradation of CQ by influencing the available oxidizing and reducing species. The chemical oxygen demand (COD) and total organic carbon (TOC) were not significantly decreased during the treatment process and indicated the formation of organic byproducts, which were not further degraded under the current experimental conditions.

Effect of irradiated nonionic surfactant on drug-protein binding

In this work, the effect of γ-irradiated surfactants on drug–protein binding has been assessed. Irradiated aqueous solutions of Pluronic F-127, Pluronic L-35, Tween 20, and Tween 80 surfactants were used. Gamma irradiation was carried out for three different doses, to these four surfactants viz., 6, 30, and 36 kGy. Two drugs, Ornidazole (ONZ) and Telmisartan (TMS) were used for the binding study. The effect of four irradiated surfactants in the presence of drug – Bovine serum albumin (BSA) protein was analyzed. The drug solutions in methanol-aqueous media were combined with BSA in the initial step. In the next two succeeding steps, drug–BSA interaction in the presence of unirradiated and irradiated surfactants were carried out. The results of drug-BSA due to addition of irradiated and unirradiated surfactants were compared. The interaction processes were assessed through UV Spectroscopy, DLS, zeta potential, turbidity, and docking studies. Improved binding was observed for both the drugs and four surfactants for irradiated surfactants as determined from the binding constant values using UV spectroscopic studies. The DLS measurements demonstrated no general trend of increase or decrease in micellar size with absorbed dose. The binding and change in the size of micelles were observed to be highly drug and surfactant-specific. Among the four surfactants, irradiated Pluronic F-127 showed higher binding affinity. To the best of our knowledge, this is the first report on the effect of γ-irradiated surfactant on drug–BSA interaction. This can be applied to other drug–protein systems to tune their interaction to the required level. Communicated by Ramaswamy H. Sarma

Superior UVC light-mediated catalytic activity of a novel NiFe2O4@ TiO2 magnetic nanocomposite synthesized with green route using Pulicaria Gnaphalodes plant extract for enhanced photocatalytic degradation of an antibiotic in water solution

In this study, the NiFe2O4@TiO2 magnetic nanocomposite was synthesized by the green synthesis method, which is an efficient and economical method. Pulicaria Gnaphalodes plant extract was used for nanocomposite synthesis because this method is suitable for the biosynthesis of nanocomposites on a large scale, and the nanocomposite produced by plants is more stable. The efficiency of the synthesized nanocomposite was investigated for the photocatalytic degradation of Penicillin G (PNG) under UVC light irradiation in aqueous solutions. The structural characteristics of this nanocomposite were determined by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, and dynamic light scattering. The effect of different parameters including pH, nanocomposite dose, penicillin G concentration and time were studied to reach optimum conditions. About 71% of PNG in optimal conditions (pH = 9, nanocomposite dose = 0.6 g/L, and penicillin G concentration = 10 mg/L) was decomposed. Generally, the NiFe2O4@TiO2 nanocomposite can be used as an efficient catalyst for the degradation of PNG in aqueous solutions.

Redox-Active Cerium Fluoride Nanoparticles Selectively Modulate Cellular Response against X-ray Irradiation In Vitro.

Ionizing radiation-induced damage in cancer and normal cells leads to apoptosis and cell death, through the intracellular oxidative stress, DNA damage and disorders of their metabolism. Irradiation doses that do not lead to the death of tumor cells can result in the emergence of radioresistant clones of these cells due to the rearrangement of metabolism and the emergence of new mutations, including those in the genes responsible for DNA repair. The search for the substances capable of modulating the functioning of the tumor cell repair system is an urgent task. Here we analyzed the effect of cerium(III) fluoride nanoparticles (CeF3 NPs) on normal (human mesenchymal stem cells-hMSC) and cancer (MCF-7 line) human cells after X-ray radiation. CeF3 NPs effectively prevent the formation of hydrogen peroxide and hydroxyl radicals in an irradiated aqueous solution, showing pronounced antioxidant properties. CeF3 NPs are able to protect hMSC from radiation-induced proliferation arrest, increasing their viability and mitochondrial membrane potential, and, conversely, inducing the cell death of MCF-7 cancer cells, causing radiation-induced mitochondrial hyperpolarization. CeF3 NPs provided a significant decrease in the number of double-strand breaks (DSBs) in hMSC, while in MCF-7 cells the number of γ-H2AX foci dramatically increased in the presence of CeF3 4 h after irradiation. In the presence of CeF3 NPs, there was a tendency to modulate the expression of most analyzed genes associated with the development of intracellular oxidative stress, cell redox status and the DNA-repair system after X-ray irradiation. Cerium-containing nanoparticles are capable of providing selective protection of hMSC from radiation-induced injuries and are considered as a platform for the development of promising clinical radioprotectors.

UV Irradiation of Polyethylene Terephthalate and Polypropylene and Detection of Formed Microplastic Particles Down to 1 μm.

The degradation of plastics upon UVC irradiation in aqueous solution and the formation of microplastic (MP) particles were investigated. Polypropylene (PP) and recycled and virgin polyethylene terephthalate (PET) were irradiated with a UV lamp emitting light at 254 nm. Irradiation was performed for 15 and 30 min, respectively, at an intensity of about 0.3 W cm-2 . The formation of MP was studied by Raman spectroscopy. The results showed that MP particles were formed after irradiation and that their number was significantly higher in the recycled PET than in the virgin material. The number of PP MP formed was lower compared to PET and was not significantly different after 15 and 30 min. In addition, ethanol was used as an alternative solvent to investigate how its chemical properties and interactions with UVC irradiation affect the degradation of PET and PP plastics. The use of ethanol and recycled PET resulted in a lower number of MP particles at both irradiation times. When ethanol was used after 30 min of irradiation, significantly more PP MP formed. The different chemical structures of PET and PP combined with the different solvent properties of water and ethanol contribute to the differences in their susceptibility to UVC degradation.

Localized Crystallization of Calcium Phosphates by Light-Induced Processes.

Medical treatment options for bones and teeth can be significantly enhanced by taking control over the crystallization of biomaterials like hydroxyapatite in the healing process. Light-induced techniques are particularly interesting for this approach as they offer tremendous accuracy in spatial resolution. However, in the field of calcium phosphates, light-induced crystallization has not been investigated so far. Here, proof of principle is established to successfully induce carbonate-hydroxyapatite precipitation by light irradiation. Phosphoric acid is released by a photolabile molecule exclusively after irradiation, combining with calcium ions to form a calcium phosphate in the crystallization medium. 4-Nitrophenylphosphate (4NPP) is established as the photolabile molecule and the system is optimized and fully characterized. A calcium phosphate is crystallized exclusively by irradiation in aqueous solution and identified as carbonate apatite. Control over the localization and stabilization of the carbonate apatite is achieved by a pulsed laser, triggering precipitation in calcium and 4NPP-containing gel matrices. The results of this communication open up a wide range of new opportunities, both in the field of chemistry for more sophisticated reaction control in localized crystallization processes and in the field of medicine for enhanced treatment of calcium phosphate containing biomaterials.

Hydroxyl Radical vs. One-Electron Oxidation Reactivities in an Alternating GC Double-Stranded Oligonucleotide: A New Type Electron Hole Stabilization.

We examined the reaction of hydroxyl radicals (HO•) and sulfate radical anions (SO4•-), 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.

Fabrication of Sn(IV)porphyrin-Imbedded Silica Aerogel Composite

Optoelectronic functional composite materials with porous structures are of great importance in various fields. A hybrid composite (SnP@SiA) composed of (trans-dihydroxo)(5,10,15,20-tetraphenylporphyrinato)tin(IV) (SnP) in silica aerogel (SiA) was successfully fabricated through the reaction of SnP with silanol groups of SiA in the presence of hexamethyldisilazane (HMDS). SnP@SiA was then characterized using various instrumental techniques. The zeta potential for SnP@SiA (−11.62 mV) was found to be less negative than that for SiA (−18.26 mV), indicating that the surface of SnP@SiA is covered by hydrophobic species such as SnP and trimethylsilyl groups. The Brunauer–Emmett–Teller (BET) surface area, pore volume, and average pore size of SnP@SiA are 697.07 m2/g, 1.69 cm3/g, and 8.45 nm, respectively, making it a suitable composite for catalytic applications. SnP@SiA, a photocatalyst with high porosity and a large surface area, yields promising performance in the photodegradation of acid orange 7 (AO7) under visible light irradiation in aqueous solution. This hybrid composite exhibited the desirable properties of aerogels along with the photoelectronic features of porphyrins. Therefore, this porphyrin-imbedded mesoporous material has valuable potential in various applications such as photocatalysis, light energy conversion, biochemical sensors, and gas storage.

Neutral polymer-pseudo polyelectrolyte transition of a post irradiated polymer dissolved in water

The purpose of this study is to study the conformation transition of a post irradiated polymer dissolved in water. In fact, polyvinylpyrrolidone (PVP) in powder(Mw = 1.300.000 g/mol), is irradiated with various doses, D, ranged from 0.3 to 50 kGy of 60Co-gamma. The irradiated polymer, PVP*, is dissolved in water to obtain post irradiated solutions of different concentration. After the stabilization of the obtained solutions (48 h), refractometry and viscosity measurements, are used to characterize the post irradiated aqueous solutions at 25 °C. The specific volume of PVP* dissolved in water was determined according modified Lorentz-Lorenz and Gaston-Dale equations, showing two dependence on the dose, D. For D ≤ Dc = 20 kGy, the specific volume increases and for D ≥ Dc, the specific volume decreases. The reduced viscosity of PVP*(Mw = 1.300.000 g/mol) aqueous solution permits to delimit the dilute and semi dilute regimes concentration and deduce the overlapping concentration, C*PVP*(D), which found to be insensitive to the dose value. For D < Dc, the intrinsic viscosity PVP* dissolved in water is determined according a modified Huggins equation and so the irradiated polymer behaves as neutral polymer. However, when D = DC the intrinsic viscosity values calculated according modified Fuoss and Fedors equations are very close and the irradiated polymer behaves as a polyelectrolyte in water. For D > Dc, the modified Fedors equation describes perfectly the evolution of the reduced viscosity versus irradiated polymer concentration. So, PVP* behaves as a polyelectrolyte in water and a neutral polymer – pseudo polyelectrolyte transition occurs under gamma irradiation effect. The irradiated polymer molar mass, MwPVP∗(D), was determined by comparing its intrinsic viscosity to these established according the Mark Howink Shakurada equation. MwPVP∗(D) decreases by increasing the dose value, which confirm the scission the polymer chain under gamma irradiation effect.

Ionic liquids with reversible photo-induced conductivity regulation in aqueous solution

Stimulus-responsive ionic liquids have gained significant attention for their applications in various areas. Herein, three kinds of azobenzimidazole ionic liquids with reversible photo-induced conductivity regulation were designed and synthesized. The change of electrical conductivity under UV/visible light irradiation in aqueous solution was studied, and the effect of chemical structure and concentration of ionic liquids containing azobenzene to the regulation of photoresponse conductivity were discussed. The results showed that exposing the ionic liquid aqueous solution to ultraviolet light significantly increased its conductivity. Ionic liquids with longer alkyl chains exhibited an even greater increase in conductivity, up to 75.5%. Then under the irradiation of visible light, the electrical conductivity of the solution returned to its initial value. Further exploration of the mechanism of the reversible photo-induced conductivity regulation of azobenzene ionic liquids aqueous solution indicated that this may attributed to the formation/dissociation of ionic liquids aggregates in aqueous solution induced by the isomerization of azobenzene under UV/visible light irradiation and resulted the reversible conductivity regulation. This work provides a way for the molecular designing and performance regulation of photo-responsive ionic liquid and were expected to be applied in devices with photoconductive switching and micro photocontrol properties.

Goethite Mineral Dissolution to Probe the Chemistry of Radiolytic Water in Liquid-Phase Transmission Electron Microscopy.

Liquid-Phase Transmission Electron Microscopy (LP-TEM) enables in situ observations of the dynamic behavior of materials in liquids at high spatial and temporal resolution. During LP-TEM, incident electrons decompose water molecules into highly reactive species. Consequently, the chemistry of the irradiated aqueous solution is strongly altered, impacting the reactions to be observed. However, the short lifetime of these reactive species prevent their direct study. Here, the morphological changes of goethite during its dissolution are used as a marker system to evaluate the influence of radiation on the changes in solution chemistry. At low electron flux density, the morphological changes are equivalent to those observed under bulk acidic conditions, but the rate of dissolution is higher. On the contrary, at higher electron fluxes, the morphological evolution does not correspond to a unique acidic dissolution process. Combined with kinetic simulations of the steady state concentrations of generated reactive species in the aqueous medium, the results provide a unique insight into the redox and acidity interplay during radiation induced chemical changes in LP-TEM. The results not only reveal beam-induced radiation chemistry via a nanoparticle indicator, but also open up new perspectives in the study of the dissolution process in industrial or natural settings.

Visible-Light-Responsive Nano CuO/ZnO Photocatalyst for Chan–Lam Coupling Reaction and Aerobic C(sp3)–H Bond Oxidation

AbstractWhen it comes to heterogeneous photocatalysts, semiconductors are the best candidate with a high potential to respond in visible-light regions. In this study, semiconductor p-n heterojunction, nano CuO/ZnO, was synthesized via a simple, sustainable, and low-cost approach. Photocatalytic activity of the synthesized material with a 2.02 eV band gap was investigated in the Chan–Lam coupling reaction and C(sp3)–H bond oxidation of alkyl aromatic compounds under visible-light irradiation in aqueous solution. In the case of the Chan–Lam coupling reaction, various derivatives of aniline and arylboronic acid successfully took part in the reaction, delivering the desired products in 57–89% yields. In addition, nano CuO/ZnO photocatalyst showed high efficiency in the C(sp3)–H bond oxidation of alkyl aromatic compounds under air as a green oxidant. Noticeably, the photocatalyst showed high performance in the large-scale synthesis of desired products and maintained activity after several uses.

2,5-Diformylfuran production by photocatalytic selective oxidation of 5-hydroxymethylfurfural in water using MoS2/CdIn2S4 flower-like heterojunctions

The selective oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF) is an important reaction for renewable biomass building blocks. Compared with thermal catalytic processes, photocatalytic production of DFF from HMF has attracted tremendous attention. Herein, the MoS 2 /CdIn 2 S 4 (MC) flower-like heterojunctions were prepared and considered as photocatalysts for selective oxidation of HMF into DFF under visible-light irradiation in aqueous solution. Results demonstrated MoS 2 in MC heterojunction could promote the separation of photoexcited electron-hole pairs, while the amount of MoS 2 dropping was proved influenced on the photocatalytic performance. 80.93% of DFF selectivity was realized when using 12.5% MC as photocatalyst. In addition, the MC catalyst also showed great potential in transformation of other biomass derived benzyl- and furyl-alcohols. The catalytic mechanism suggested that · O 2 - was the decisive active radical for HMF oxidation. Therefore, the MC heterojunction could be applied in photocatalytic conversion of biomass to valuable chemicals under ambient condition.

Photocatalytic Activity of CoO/ZnO Nanocrystalline for Dye Wastewater Treatment under UV Light

CoO nanocrystal is well-known photocatalyst for overall water splitting. However it suffers from a very short lifetime of only 1 h. The poor stability is derived from carrier recombination-induced thermal oxidation. This research will provide information about synthesis of CoO/ZnO nanocrystalline that can potentially enhance photocatalysts. CoO has been synthesized first under hydrothermal method, followed by calcination process. Thereafter, CoO has been used to produce CoO/ZnO under precipitation method. The samples were characterized using XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), and UV-VIS (UV–Visible Spectroscopy) to analyze their composition, chemical functional group, optical absorption, and band gap. The XRD spectrum showed that CoO/ZnO had cubic spinel and hexagonal phase structure with crystallite size of 69.0, 46.4, 32.8, and 32,4 nm. The bands in obtained FTIR spectrum at 586.36, 671.23, and 410-429 cm−1 were correlated with vibrations of the Co3+ in octahedral hole, the Co2+ in tetrahedral hole, and Zn-O, respectively. The band gap energy of CoO, CoO/ZnO with variation of 1:1 and 1:3 were 4.39, 4.14, and 3.65 eV, respectively. The photocatalytic activities of CoO/ZnO were confirmed by methylene blue dyes photodegradation of 663 nm under UV light irradiation in aqueous solution. The 22.4% methylene blue can be removed within 3 h. Overall, these findings reveal the potential of CoO/ZnO for practical application.

Influence of Laser Irradiation on the Mechanism of Viscous Flow of Aqueous Sodium Chloride Solution

The effect of 632.8-nm radiation of a helium–neon laser on the viscosity of an aqueous sodium chloride solution has been studied. It has been shown that irradiation changes the nature and numerical values of the concentration dependence of viscosity. The concentration dependences of the viscous-flow activation energy for unirradiated and irradiated aqueous sodium chloride solutions have been determined. The influence of irradiation on the parameters of the power-law dependence of the solution viscosity on concentration has been analyzed, and the temperature dependences of these parameters have been determined. It has been concluded that laser irradiation alters the structural organization of the aqueous system and reduces

Enhanced activation of peroxymonosulfate by a floating Cu0-MoS2/C3N4 photocatalyst under visible-light assistance for tetracyclines degradation and Escherichia coli inactivation

Transition metal-based photocatalysts have recently attracted much attention in photo-induced Peroxymonosulfate (PMS) activation systems. Herein, a novel floating catalyst Cu0-MoS2/C3N4-expanded graphite (Cu-MSCN-EG) was prepared by a chemical reduction method and applied as a PMS activator to remove tetracyclines (TCs) and inactivate Escherichia coli under visible light irradiation in aqueous solution. Over 99.0 % of TCs and Escherichia coli could be removed and inactivated within 1 h in Vis/PMS/Cu-MSCN-EG system. Compared to the MoS2/C3N4-EG system, the loading of zero-valent copper in the Vis/PMS/Cu-MSCN-EG system increased the reaction rate by 278 %. Raman spectroscopy and density functional theory (DFT) calculations indicated that ·OH and 1O2 were generated via two different adsorption patterns between PMS and copper (≡Cu+-OSO3-–OH and ≡Cu+–OH-OSO3-). With the light assistance, the photo-induced electrons reduced the copper leaching and enhanced the generation of ·SO4- and ·O2–, leading to a high recyclability and mineralization rate. Overall, this study provides a new insight into the fabrication of copper-based PMS activator with high efficiency and durability for contaminants degradation and pathogen inactivation.

Triarylboron-Doped Acenethiophenes as Organic Sonosensitizers for Highly Efficient Sonodynamic Therapy with Low Phototoxicity.

The development of efficient organic sonosensitizers is crucial for sonodynamic therapy (SDT) in the field of cancer treatment. Herein, a new strategy for the development of efficient organic sonosensitizers based on triarylboron-doped acenethiophene scaffolds is presented. The attachment of boron to the linear acenethiophenes lowers the lowest unoccupied molecular orbital (LUMO) energy, resulting in redshifted absorptions and emissions. After encapsulation with the amphiphilic polymer DSPE-mPEG2000 , it is found that the nanostructured BAnTh-NPs and BTeTh-NPs (nanoparticles of BAnThand BTeTh) shows efficient hydroxyl radical (• OH) generation under ultrasound (US) irradiation in aqueous solution with almost no phototoxicity, which can overcome the shortcomings of O2 -dependent SDT and avoid the potential cutaneous phototoxicity issue. In vitro and in vivo therapeutic results validate that boron-doped acenethiophenes as sonosensitizers enable high SDT efficiency with low phototoxicity and good biocompatibility, indicating that boron-functionalization of acenes is a promising strategy toward organic sonosensitizers for SDT.

Au Quantum Clusters and Plasmonic Quantum Nanoparticles Synthesized under Femtosecond-Pulse Laser Irradiation in Aqueous Solution and in ZIF-8 for Catalytic Reduction of 4-Nitrophenol

Au Quantum Clusters and Plasmonic Quantum Nanoparticles Synthesized under Femtosecond-Pulse Laser Irradiation in Aqueous Solution and in ZIF-8 for Catalytic Reduction of 4-Nitrophenol

Design of TiO2/Ag3BiO3 n-n heterojunction for enhanced degradation of tetracycline hydrochloride under visible-light irradiation

Pharmaceutical residual contaminants in aquatic ecosystems have caused severe risks to human health. Affordable, eco-friendly and effective photocatalysts to deal with these pollutants has become a hot topic in the scientific community. In this research, Ag3BiO3 nanoparticles were embedded on TiO2 to form n-n heterojunction through a facile hydrothermal method. According to scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), brunauer emmett teller (BET), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) tests, the successful construction of TiO2/Ag3BiO3 heterojunction is proved. TiO2/Ag3BiO3 heterojunctions were employed as photocatalysts to remove tetracycline hydrochloride (TCH) under visible light irradiation in aqueous solution. Optimum TCH photodegradation efficiency was observed for TiO2/Ag3BiO3 (10%), 15.4 times superior to that of TiO2. The enhanced TCH photodegradation efficiency of TiO2/Ag3BiO3 results from improved light absorption capacity and the reduction of recombination of photogenerated charge carriers via generation of n-n heterojunctions. The mechanism of increasing the photodegradation efficiency of TCH was determined by employing reactive species quenching experiments. TiO2/Ag3BiO3 (10%) also exhibited an acceptable stability.

Evaluation of Hydroxyl Radical Reactivity by Thioether Group Proximity in Model Peptide Backbone: Methionine versus S-Methyl-Cysteine

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 CH3C(O)NHCHXC(O)NHCH3, where X = CH2CH2SCH3 or CH2SCH3, 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.