Pulse Radiolysis Technique Research Articles

Chemical Kinetics for the Oxidation of Californium(III) Ions with Select Radiation-Induced Inorganic Radicals (Cl2•- and SO4•-).

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 (Cl2•-) and sulfate (SO4•-) 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 (k) for these radiation-induced processes are k( + Cl2•-) = (8.28 ± 0.61) × 105 M-1 s-1 and k( + SO4•-) = (9.50 ± 0.43) × 108 M-1 s-1 under ambient temperature conditions (22 ± 1 °C).

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 in vitro 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 (IC50) 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. Highlights MeImSe, a derivative of selenoneine protects DNA and lipid from radiation damage MeImSe scavenges all major short- and long-lived oxidants involved in radiation toxicity Rate constants of MeImSe for ROS scavenging determined by pulse radiolysis technique First organoselenium compound reported to scavenge nitrogen dioxide radical MeImSe exhibits GPx-like activity through reductive pathway

Radiolytic degradation of selective actinide extractants from bis-1,2,4-triazine family in cyclohexanone solutions

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 were studied by means of pulse radiolysis technique with spectrophotometric detection. Cyclohexanone was proposed...

Free radical induced degradation and computational studies of hydroxychloroquine in aqueous solution

Hydroxychloroquine (HCQ) is a potential drug molecule for treating malaria. Recently it has also been tried as adjustment in Covid 19 therapy. Interaction of HCQ with free radicals is very important, which controls its stability in the environment where free radicals are generated unintentionally. In this report, we present detailed investigation on the reactions of hydrated electrons (eaq−) and hydroxyl radical (•OH) with HCQ in aqueous solution through electron pulse radiolysis technique and computational studies. The degradation of HCQ was found to be faster in the case of reaction with •OH radicals. However, the degradation could be substantially slowed down in the presence of antioxidants like ascorbic acid and gallic acid. This revealed that the stability of HCQ could be enhanced in an oxidative environment in the presence of these two compounds, which are easily available through food supplements. Various global and local reactivity parameters are also determined to understand the reactivity trend using Hard-Soft Acid-Base (HSAB) principle in the realm of the DFT methods. Computational studies were performed to elucidate the site-specific reactivity trend towards the electrophilic and nucleophilic attack by calculating the condensed Fukui index for various species of HCQ.

Intermediates derived from p-terphenyl in the methyltributylammonium bis[(trifluoromethyl)sulfonyl]imide ionic liquid saturated with carbon dioxide: Pulse radiolysis study

Abstract Radiation-induced processes in ionic liquid (IL) methyltributylammonium bis[(trifluoromethyl)sulfonyl] imide ([MeBu3N][NTf2]) solutions containing p-terphenyl (TP) and saturated with carbon dioxide (CO2) were studied using nanosecond pulse radiolysis technique with UV-vis detection. The transient absorption spectra generated in these solutions were assigned to TP radical anions (TP•−) and triplet excited states (3TP*). Saturation of [MeBu3N][NTf2] solutions with carbon dioxide efficiently takes out presolvated electrons ( e presolv − ) ( {{\rm{e}}_{{\rm{presolv}}}^ - } ) and solvated electrons ( e solv − ) ( {{\rm{e}}_{{\rm{solv}}}^ - } ) . On the other hand CO2 is not a scavenger of excited states of TP (1TP*, 3TP*), which in the reaction with triethylamine (TEA) leads to the formation of TP•−.

Photophysical properties of a β-Carboline Rhenium (I) complex. Solvent effects on excited states and their redox reactivity

The photochemical and photophysical properties of a Re(I) tricarbonyl complex, ClRe(CO)3(nHo)2, where nHo = 9H-pyrido[3,4-b] indole (norharmane), were investigated in solution phase by a combination of steady state emission spectroscopy, laser flash photolysis (LFP) and pulse radiolysis (PR) techniques. These results allowed us to identify and study the reactivity of the β-carboline (nHo) Rhenium(I) complex main excited states. The absorption spectrum as well as the steady-state and time-resolved luminescence of the complex exhibits a marked dependence with the solvent properties. These experimentally observed results were corroborated by quantum chemical calculations, TD-DFT. The most important electronic transitions present in the spectrum in all solvents are MLLCTRe(CO)3→nHo1, nHo2 along with a mixture of ILnHo and LLCTCl→nHo transitions. The relationship between the dipole moment and the polarity of the solvent was rationalized in terms of the electron density inside and outside the complex. While the luminescence of the complex is mainly attributed to the emitting 1ILnHo state, in LFP experiments a MLCT excited state was also detected. The species generated in either reductive or oxidative conditions in LFP experiments were compared with those obtained in PR. Also, the quenching rate constant (kq) of the excited state with MV+2 was calculated. The excited state of the complex can efficiently generate singlet oxygen in acetonitrile yielding a ΦΔ = 0.25 ± 0.02. Optoacoustic measurements showed that, after photonic excitation, almost all the absorbed energy by the complex is released to the medium as prompt heat. The investigated photophysical and photochemical properties of ClRe(CO)3(nHo)2 are of significant importance in relation to the use of this β-carboline Rhenium(I) complex in several biomedical fields, such as photodynamic therapy and photoactivated chemotherapy as well as new alternative therapies such as regional hyperthermia.

Dynamics of Ion Pairing in Dilute Aqueous HCl Solutions by Spectroscopic Measurements of Hydroxyl Radical Conversion into Dichloride Radical Anions.

The rate of formation of dichloride anions (Cl2•–) in dilute aqueous solutions of HCl (2–100 mmol·kg–1) was measured by the technique of pulse radiolysis over the temperature range of 288–373 K. The obtained Arrhenius dependence shows a concentration averaged activation energy of 7.3 ± 1.8 kJ·mol–1, being half of that expected from the mechanism assuming the •OHCl– intermediate and supporting the ionic equilibrium-based mechanism, i.e., the formation of Cl2•– in the reaction of •OH with a hydronium–chloride (Cl–·H3O+) contact ion pair. Assuming diffusion-controlled encounter of the hydronium and chloride ions and including the effect of the ionic atmosphere, we showed that the reciprocal of τ, the lifetime of (Cl–·H3O+), follows an Arrhenius dependence with an activation energy of 23 ± 4 kJ·mol–1, independent of the acid concentration. This result indicates that the contact pair is stabilized by hydrogen bonding interaction of the solvent molecules. We also found that at a fixed temperature, τ is noticeably increased in less-concentrated solutions (mHCl < 0.01 m). Since this concentration effect is particularly pronounced at near ambient temperatures, the increasing pair lifetime may result from the solvent cage effect enhanced by the presence of large supramolecular structures (patches) formed by continuously connected four-bonded water molecules.

Fast autooxidation of a bis-histidyl-ligated globin from the anhydrobiotic tardigrade, Ramazzottius varieornatus, by molecular oxygen.

Tardigrades, a phylum of meiofaunal organisms, exhibit extraordinary tolerance to various environmental conditions, including extreme temperatures (-273 to 151°C) and exposure to ionizing radiation. Proteins from anhydrobiotic tardigrades with homology to known proteins from other organisms are new potential targets for structural genomics. Recently, we reported spectroscopic and structural characterization of a hexacoordinated haemoglobin (Kumaglobin [Kgb]) found in an anhydrobiotic tardigrade. In the absence of its exogenous ligand, Kgb displays hexacoordination with distal and proximal histidines. In this work, we analysed binding of the molecular oxygen ligand following reduction of haem in Kgb using a pulse radiolysis technique. Radiolytically generated hydrated electrons (eaq-) reduced the haem iron of Kgb within 20 µs. Subsequently, ferrous haem reacted with O2 to form a ferrous-dioxygen intermediate with a second-order rate constant of 3.0 × 106 M-1 s-1. The intermediate was rapidly (within 0.1 s) autooxidized to the ferric form. Redox potential measurements revealed an E'0 of -400 mV (vs. standard hydrogen electrode) in the ferric/ferrous couple. Our results suggest that Kgb may serve as a physiological generator of O2▪- via redox signalling and/or electron transfer.

Conductometric pulse radiolysis study of the interconversion Cr(III)/Cr(VI) redox reactions in acidic solution: Atmospheric pollution relevance

ABSTRACT Hexavalent chromium (VI) is a potent carcinogen for humans, while trivalent chromium (III) is an important element in glucose metabolism. In atmospheric water droplets, oxidation of Cr(III) to Cr(VI) by free radicals is a major environmental issue. Laboratory simulation studies of the aqueous phase oxidation-reduction of the couple Cr(III)/Cr(VI) by OH• and HO2 •/O2 •− by applying conductometric pulse radiolysis techniques were carried out in the pH range 3.5–5.5 chosen as characteristic values of atmospheric water droplets acidity. A pKa of 3.9 was found for the first hydrolysis of Cr(IV). The bimolecular second-order decay of the Cr(V) transient species shows a strong pH dependency consequence of the change of the coordination sphere of the tetrahedral Cr(VI) to the octahedral Cr(III).

On the Primary Water Radicals' Production in the Presence of Gold Nanoparticles: Electron Pulse Radiolysis Study.

Gold nanoparticles are known to cause a radiosensitizing effect, which is a promising way to improve radiation therapy. However, the radiosensitization mechanism is not yet fully understood. It is currently assumed that gold nanoparticles can influence various physical, chemical, and biological processes. Pulse radiolysis is a powerful tool that can examine one of the proposed effects of gold nanoparticles, such as increased free radical production. In this work, we shed light on the consequence of ionizing radiation interaction with gold nanoparticles by direct measurements of solvated electrons using the pulse radiolysis technique. We found that at a therapeutically relevant gold concentration (<3 mM atomic gold, <600 μg × cm−3), the presence of gold nanoparticles in solution does not induce higher primary radicals’ formation. This result contradicts some hypotheses about free radical formation in the presence of gold nanoparticles under ionizing radiation previously reported in the literature.

A study of light induced surface reactions of sildenafil citrate on hybrid AgCl/Ag nanoparticle dimers by surface enhanced Raman scattering and pulse radiolysis techniques

AgCl/Ag nanoparticle dimers (NPD) are important from photocatalysis point of view as it is reported to show photocatalytic activity in visible region. In this work, AgCl/Ag NPDs were synthesized by controlling the concentration of available chloride ions as well as the capping agent, sildenafil citrate (SC). Transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–vis absorption property was used to probe morphology, lattice structure and optical property of as synthesized AgCl/Ag NPDs. SERS spectrum of SC adsorbed on the AgCl/Ag NPD excited at 632 nm, which is energetically closer to the coupled plasmon peak at 605 nm, showed some unexplained vibrational peaks. The above system was probed further by using pulse radiolysis technique and time-dependent density functional theory (TD-DFT) calculations. The results suggest that a direct electron transfer reaction from AgCl/Ag NPD to SC is involved in appearance of anomalous features in SERS spectrum.

Kinetics and mechanism of the advanced oxidation process of Cr(III) to Cr(VI) by SO4 −˙ free radicals in slightly acidic simulated atmospheric water

Abstract In a previous work, we showed that the oxidation of Cr(III) to Cr(VI) by OH˙ present in the atmospheric water droplets has the potential to threaten the people’s health since non-toxic species is transformed into environmental carcinogens. The same oxidation might be initiated by the SO4 −˙ free radicals. Here, we shed some light on the detailed mechanisms of this oxidation reaction occurring in ambient atmosphere. Steady state irradiation and pulse radiolysis technique were used to generate SO4 −˙. The advanced oxidation process mechanism was investigated at pH 4 and 6 selected as typical values of cloud water acidity. Our findings showed that the oxidation is pseudo-first order with respect to Cr(III) and is pH dependent. In the suggested reaction mechanism, the electron transfer proceeds via an inner sphere mechanism, with formation of the [Cr(III)–SO4 −˙] precursor adduct, followed by an electron transfer inside the adduct, from Cr(III) to SO4 −˙, to form Cr(IV): Cr(III) + SO 4 − · ⇌ [ C r ( III ) – SO 4 − · ] → Cr(IV) + SO 4 2 − . $${\rm{Cr(III)}} + {\rm{S}}{{\rm{O}}_4}^{ - \cdot}[Cr({\rm{III}})-{\rm{S}}{{\rm{O}}_4}^{ -\cdot }] \to {\rm{Cr(IV)}} + {\rm{S}}{{\rm{O}}_4}^{2 - }.$$ At pH 4, the equilibrium constant and the rate constant are 7.52 × 104 M−1 and 2.47 × 104 s−1, respectively. At pH 6 these values become 1.90 × 105 M−1 and 1.41 × 104 s−1, respectively.

Formation of two centre three electron bond by hydroxyl radical induced reaction of thiocoumarin: evidence from experimental and theoretical studies

Radiation chemical studies of thioesculetin (1), a thioketone derivative of coumarin, were performed by both pulse radiolysis technique and DFT calculations. Hydroxyl (•OH) radical reaction with 1 resulted transients absorbing at 320, 360 and 500 nm. To identify the nature of the transients, the reaction was studied with specific one-electron oxidant (N3•) radical, where 360 nm band was absent. The transient absorption at 500 nm was concentration-dependent. The overall impression for •OH radical reaction was that the transient absorbing at 320, 360 and 500 nm was due to sulphur centred monomer radical, hydroxysulfuranyl and dimer radical of 1 respectively. The equilibrium constant between the monomer to dimer radical was 3.75 × 104 M−1. From the transients’ redox nature, it was observed that 57 and 24% of •OH radical yielded to oxidising and reducing products respectively. Further, the product analysis by HPLC suggested that the dimer radical disproportionate to esculetin and thioesculetin. DFT energy calculation for all the possible transients revealed that dimer radical has the lowest energy. The HOMO of 1 and its monomer radical suggested that the electron density was localised on the sulphur atom. The bond length between the two sulphur atoms in dimer radical was 2.88 Å which was less than the van der Waals distance. Bond order between the two sulphur atoms was 0.55, suggesting that the bond was two centre three electron (2c–3e). From TD-DFT calculation, the electronic transition of dimer radical was at 479 nm which was in close agreement with the experimental value. The nature of the electronic transition was σ → σ* from a 2c − 3e bond.

Kinetics of the reactions of catechins with hypochlorite, peroxynitrite, and amino acid–derived peroxyl‐ radicals

AbstractCatechins, one of the class of flavonoids, are known as very efficient antioxidants. Here we investigated the kinetics of the reactions of three catechins, namely, catechin, epigallocatechin, and epigallocatechin gallate (EGCG) with some oxidants, which are formed in vivo under oxidative stress, hypochlorite, peroxynitrite, and amino acid peroxyl radicals. Stopped‐flow spectrophotometry and pulse radiolysis technique with absorption detection were used to observe the formation of intermediate products of oxidized catechins. We found that catechins react with hypochlorite with the rate constant of the order of 105–106 M−1 s−1 at pH 7.4. Experimental kinetic traces of the reaction of EGCG with valine peroxyl radicals were fitted using chemical simulation, and the rate constant of this reaction was found to be 5 × 105 M−1 s−1. The rate constants of the formation of unstable catechin quinones in the reaction with peroxynitrite were comparable to that of spontaneous peroxynitrite isomerization, which indicates that catechins are oxidized indirectly by peroxynitrite. Biological consequences of these reactions are discussed.

Formation of the Charge-Localized Dimer Radical Cation of 2-Ethyl-9,10-dimethoxyanthracene in Solution Phase.

Although dimer radical ions of aromatic molecules in the liquid-solution phase have been intensely studied, the understanding of charge-localized dimers, in which the extra charge is localized in a single monomer unit instead of being shared between two monomer units, is still elusive. In this study, the formation of a charge-localized dimer radical cation of 2-ethyl-9,10-dimethoxyanthracene (DMA), (DMA)2 .+ is investigated by transient absorption (TA) and time-resolved resonance Raman (TR3 ) spectroscopic methods combined with a pulse radiolysis technique. Visible- and near-IR TA signals in highly concentrated DMA solutions supported the formation of non-covalent (DMA)2 .+ by association of DMA and DMA.+ . TR3 spectra obtained from 30 ns to 300 μs time delays showed that the major bands are quite similar to those of DMA except for small transient bands, even at 30 ns time delay, suggesting that the positive charge of non-covalent (DMA)2 .+ is localized in a single monomer unit. From DFT calculations for (DMA)2 .+ , our TR3 spectra showed the best agreement with the calculated Raman spectrum of charge-localized edge-to-face T-shaped (DMA)2 .+ , termed DT.+ , although the charge-delocalized asymmetric π-stacked face-to-face (DMA)2 .+ , termed DF3.+ , is the most stable structure of (DMA)2 .+ according to the energetics from DFT calculations. The calculated potential energy curves for the association between DMA.+ and DMA showed that DT.+ is likely to be efficiently formed and contribute significantly to the TR3 spectra as a result of the permanent charge-induced Coulombic interactions and a dynamic equilibrium between charge localized and delocalized structures.

Pulse Radiolysis Studies for Mechanism in Biochemical Redox Reactions.

Pulse radiolysis is a powerful method for generating highly reduced or oxidized species and free radicals. Combined with fast time-resolved spectroscopic measurement, we can monitor the reactions of intermediate species on time scales ranging from picoseconds to seconds. The application of pulse radiolysis to water generates hydrated electrons (eaq-) and specific radicals, rendering this technique useful for investigating a number of biological redox processes. The first pulse radiolysis redox investigations explored in this review involved intramolecular electron transfer processes in protein with multiple electron-accepting sites. Pulse radiolysis enabled direct monitoring of the internal electron transfer rates and the distribution of electrons within proteins. Structural information from X-ray data has allowed analysis of the rate constants and their activation parameters in relation to the mechanisms with current theoretical treatments. The second set of pulse radiolysis redox investigations explored here concerned the intermediates of enzyme reactions after redox reactions. Pulse radiolysis allowed the extremely rapid donation of electrons to a redox center in a protein. It makes it possible to observe the unstable intermediates after the reduction and the following subsequent steps. For example, the intermediates generated through the one-electron reduction of oxygenated hemoproteins, such as cytochrome P450 and nitric oxide synthase, were characterized. Interestingly, ligand exchange can occur upon the reduction of heme iron, in which different amino acid residues bind to heme in the ferrous and ferric states, respectively. We directly observed the ligand-switching intermediates of bacterial CooA, a CO sensor, and bacterial iron response regulator protein. These ligand exchange processes are physiologically important for regulating the electrode potential and effective formation of superoxide anion or HO•. The third set of pulse radiolysis redox investigations explored in this review concerns free-radical processes in biological systems. Free radicals are produced in cells and organisms in a variety of processes. The cell has developed special and very effective machinery for controlling and detoxifying reactive radicals. Radiation-generated radicals allow studies of the reactions between specific radicals and solutes, often revealing the mechanisms underlying the initial and subsequent reactions. The crucial contribution was made using pulse radiolysis techniques and knowledge of the identities, properties, and reactions of radicals. These radicals include superoxide (O2•-), nitric monoxide (NO•), ascorbate, urate, and protein radicals. This review focuses on the reactions of these radicals and their physiological functions.

Effect of phenyl moiety on the formation of radicals and radical cations of thioamides in n-butyl chloride: a pulse radiolysis study

The formation of radical cations and radicals of thioamides (R) $$\mathbf{(NH_{2})}$$ CS, where R represents $$\hbox {CH}_{3}$$ in thioacetamide (TA) and $$\hbox {C}_{6}\hbox {H}_{5}$$ in thiobenzamide (TBA) in n-butyl chloride has been studied using pulse radiolysis technique. The radical cations of TA and TBA are observed in n-butyl chloride, and on their subsequent deprotonation, respective radicals are generated. In this study on thioamide solutions in n-butyl chloride, the transient species formed at $$1.2\,\upmu \hbox {s}$$ after the electron pulse exhibiting absorption maxima in 400 nm region are attributed to their radical cations. In the presence of 0.1 M ethanol ( $$\hbox {C}_{2}\hbox {H}_{5}\hbox {OH}$$ ), a radical cation scavenger, the absorbance values at corresponding peaks are reduced substantially, revealing the formation of their respective radical cations. Moreover, at a later time, the generation of radical species takes place through deprotonation of radical cations and also through direct reactions during electron pulse irradiation. The mechanisms for the formation of radical cations and radicals of these two thioamides under pulse radiolysis have been revisited in butyl chloride medium wherein the charge transfer reactions are more prominent. Results of quantum chemical calculation support the mechanistic explanation and provide information on the reactivity of parent molecules, and the charge distribution on radical cations and radicals species of thioamides.

Radiation-induced debromonation of 1,2-dibromotetrafluoroethane (Halon2402) in alcohols followed by Br2•− formation – A pulse radiolysis study

Pulse radiolysis technique was used to investigate early stages of radiation-induced reactions in alcohols (methanol and 2-propanol) containing a halogenated compound, Halon2402, and it was found that repetition of irradiation leads to accumulation of a transient species having absorption around 360 nm, which is attributed to dibromine radical anion (Br2•−). The alcohols containing bromide anion (Br−) were also investigated because it is reported debromonation occurs during the radiation-induced degradation, revealing that at first Br− is oxidized into bromine atom (Br•) by alkoxy radicals of the solvent alcohols, and then, Br2•− is formed by its reaction with another Br−. Since not only Br− but also acid (H+) is produced during the degradation, influence of acid was also investigated, showing that acid is essential in the oxidation of Br− into Br• in the alcohols. In addition, deuteration of the solvent alcohols resulted in significant increase in the amount of Br2•− production, implying it is alkoxy radicals of the solvent alcohols that oxidize Br− into Br•. Difference in the Br− oxidation between methanol and 2-propanol was also discussed in relevance to difference in redox potentials of the transient species.

Free radical induced redox reactions of 2,4,6-triaminopyrimidine: A pulse radiolysis study

Kinetics and mechanism of reactions of 2,4,6-triaminopyrimidine (TAP) with some free radicals have been studied using pulse radiolysis technique. TAP has been found to react with hydrated electron (3.1 × 108 M−1 s−1), hydroxyl radical (4.0 × 109 M−1 s−1), trichloromethyl peroxyl radical (1.1 × 108 M−1 s−1), and sulfate radical (4.5 × 109 M−1 s−1). Density functional calculations have been performed to assign absorption maxima of transients produced on oxidation of TAP as: TAP•+ radical cation (~ 430, ~ 600, ~ 720 nm), TAP(C5)• radical (~ 300, ~ 320 nm), aminyl TAP(NH)• radical (~ 300, ~ 340, ~ 440 and ~ 520 nm) and TAP-OH• radical adduct (640 nm). Almost 72% of TAP transients produced with hydroxyl radical have been found to be oxidizing in nature, which react with tyrosine (8.0 × 107 M−1 s−1), glutathione (1.2 × 108 M−1 s−1) and bovine serum albumin protein (7.8 × 108 M−1 s−1).

Radiation chemists look at damage in redox proteins induced by X-rays.

The three-dimensional structure of proteins, especially as determined by X-ray crystallography, is critical to the understanding of their function. However, the X-ray exposure may lead to damage that must be recognized and understood to interpret the crystallographic results. This is especially relevant for proteins with transition metal ions that can be oxidized or reduced. The detailed study of proteins in aqueous solution by the technique of pulse radiolysis has provided a wealth of information on the production and fate of radicals that are the same as those produced by X-ray exposure. The results reviewed here illustrate how the products of the interaction of radiation with water or with solutes added to the crystallization medium, and with proteins themselves, are formed, and about their fate. Of particular focus is how electrons are produced and transferred through the polypeptide matrix to redox centers such as metal ions or to specific amino acid residues, for example, disulfides, and how the hydroxyl radicals formed may be converted to reducing equivalents or scavenged.