Pulse radiolysis studies of etoposide and 4′-demethylepipodophyllotoxin in aqueous solution

The reactions of etoposide (VP 16, 4′-demethyl-epipodophyllotoxin ethylidene-β-d-glucoside) and 4′-demethylepipodophyllotoxin (DMEP) with the primary radiolytic products of water, such as e⁻_aq, H and OH/O⁻ radicals, and the secondary radical (SO⁻₄) in aqueous solution were studied by use of the techniques of pulse radiolysis, respectively. The absorption spectra of reaction products with e⁻_aq, H and OH/O⁻ and SO⁻₄ radicals were observed, and the rate constants of them were determined by following the build-up kinetics of radicals produced or the decay of hydrated electron observed at 600 nm, respectively.     

Studies on the reactions of sylvatesmin and lantbeside with oxidizing free radicals

Sylvatesmin (SYL) and lantbeside (LAN) are two lignans, isolated from a Chinese folk medicinal herb, Lancea tibetica. Their abilities of scavenging oxidizing free radical models, OH, SO₄⁻ and N₃, were investigated in aqueous solution by pulse radiolysis techniques. The OH-adduct radicals with small amount of oxidized products were formed by the reaction of SYL or LAN with OH radical. SYL undergoes one-electron oxidation either by SO₄⁻ or N₃ radicals, LAN can only be detected to react with stronger oxidant SO₄⁻ radical anion. No reaction between LAN and N₃ radical was detectable. The relationship of structure with the abilities of scavenging free radicals was discussed. The reaction rate constants were determined by analysis of the build-up trace of the radical products.     

Carbonate radical anion-induced electron transfer in bovine serum albumin

Reaction of native and thermally denatured bovine serum albumin (BSA) with carbonate radical anion (CO₃⁻) has been studied using pulse radiolysis technique. Scavenging of CO₃⁻ by native BSA and consequent electron transfer from tyrosine to tryptophan radical has been observed to occur with almost same rate constant (k∼1.7×10⁸ dm³ mol⁻¹ s⁻¹) at pH 8.8. Effect of structural changes, due to thermal denaturation, on scavenging of CO₃⁻ and the electron transfer process have been studied and discussed in this paper.     

Effect of N+ ion implantation on antioxidase activity in Blakeslea trispora

The effect of N⁺ implantation on the activities of CAT, POD, SOD, T-AOC and the capacities of scavenging O₂⁻ and OH in Blakeslea trispora (−) were studied. Results showed that N⁺ implantation caused different changes of CAT, POD, SOD, T-AOC activities and cell scavenging O₂⁻ and OH capacities. With the implantation dose increasing CAT activity was lower than the control sample, while POD, SOD activities and the scavenging O₂⁻ and OH capacities all decreased at the beginning, and then increased lately. At the dose of 6.0×10¹⁵ N⁺ cm⁻² T-AOC activity was lowest, while at the dose of 1.2×10¹⁵ N⁺ cm⁻² its activity was highest, and this change trend was same to the B. trispora (−) survival rate curve. So we speculated that the changes of these antioxidases activity of B. trispora (−) induced by low-energy N⁺ probably have some relationship with its “saddle shape” survival rate curve.     

Role of reactive intermediates in the radiolytic degradation of Acid Red 1 in aqueous solution

The role of reactive intermediates of water radiolysis (e_aq⁻, H, HO, O₂⁻/HO₂) in decoloration and mineralization of aqueous solutions of Acid Red 1 dye was investigated. The decoloration is highly effective in the reactions of e_aq⁻ and H, and less effective in HO reactions. The O₂⁻/HO₂ pair does not take part in decoloration. For mineralization, which is an oxidative degradation, HO radicals are needed: the efficiency increases with the dissolved oxygen concentration. The reactions of the O₂⁻/HO₂ radical pair slightly increase the rate of mineralization. Iron and copper ions (possible constituents of waste waters) in low concentration do not influence the reactions.     

Radical intermediates generated in the reactions of l-arginine with hydroxyl radical and sulfate radical anion: A pulse radiolysis study

Reactions of l-arginine (Arg) with hydroxyl radical (OH) and sulfate radical anion (SO₄⁻) were kinetically investigated by the pulse radiolysis technique. Hydrogen abstraction from Arg by OH afforded redox chemically oxidizing, neutral, and reducing carbon-centered Arg radicals. Kinetic properties of the radicals indicated that the reducing species might include the δ-C-centered Arg radical and CO₂ radical anion. Similar transient spectra were observed in the SO₄⁻ reaction with Arg, suggesting direct oxidation at the guanidino group is less likely.     

EPR of gamma irradiation induced radicals in NaHCO3, CsHCO3 and Na2CO3

In this study gamma irradiated NaHCO₃, CsHCO₃ and Na₂CO₃ were investigated at room temperature. The radicals induced by gamma irradiation in NaHCO₃ were found to be CO⁻₃, HCO₃ and CO⁻₂; in CsHCO₃ the species were attributed to HCO₃; and in Na₂CO₃ to CO⁻₃ and CO⁻₂ radicals. The hyperfine parameters for the hydrogen in HCO₃, and the ¹³C nucleus in CO⁻₂ radical have been determined. The results were compared with literature data for similar compounds and the EPR properties of the CO⁻₂ radical were discussed.     

Pulse and γ-radiolysis studies on aqueous solution of 1,1′-dimethyl-2-selenourea

One-electron oxidation of 1,1′-dimethyl-2-selenourea (DMSeU) by hydroxyl radicals, one-electron-specific oxidants, was studied using pulse radiolysis technique in aqueous solution. Hydroxyl (OH) radicals and one-electron oxidants, N₃, X₂⁻ (X=Cl, Br, and I) react with DMSeU to form a transient having an absorption spectrum with λ_max at 430 nm. By following the absorbance at 430 nm as a function of solute concentration and in analogy with similar sulfur and selenium compounds, this transient is assigned to dimer radical cation. The dimer radical cations of DMSeU react with oxygen with bimolecular rate constant of 1.0±0.3×10⁸ M⁻¹ s⁻¹. Steady-state γ-radiolysis studies on aqueous solution of DMSeU under hydroxyl radical-induced oxidation condition indicated formation of elemental selenium as one of the by-products, which has been stabilized by the addition of poly vinyl alcohol (PVA), and characterized by dynamic light scattering technique.     

Pulse radiolysis studies of mangiferin: A C-glycosyl xanthone isolated from Mangifera indica

Pulse radiolysis technique has been employed to study the reaction of different oxidizing and reducing radicals with mangiferin. The reaction of OH radical showed the formation of transient species absorbing in 380–390 and 470–480 nm region. The reaction with specific one-electron oxidants (N₃, CCl₃O₂) also showed the formation of similar transient absorption bands and is assigned to phenoxyl radicals. The pK_a values of the transient species have been determined to be 6.3 and 11.9. One-electron oxidation potential of mangiferin at pH 9 has been found to be 0.62 V vs. NHE. The reaction of e_aq⁻ showed the formation of transient species with λ_max at 340 nm, which is assigned to the ketyl anion radical formed on addition of e_aq⁻ at carbonyl site. Reactions of one-electron oxidised mangiferin radicals with ascorbic acid have also been studied.     

Hydroxyl radical,sulfate radical and nitrate radical reactivity towards crown ethers in aqueous solutions

Reaction rate constants of crown ethers (12-crown-4, 15-crown-5, 18-crown-6) and their analogs 1,4-dioxane (6C2) with some important oxidative radicals, hydroxyl radical (OH), sulfate radical (SO₄^?) and nitrate radical (NO₃), were determined in various aqueous solutions by pulse radiolysis and laser photolysis techniques. The reaction rate constants for 6C2 and crown ethers with OH and SO₄^? increase with the number of hydrogen atoms in the ethers, indicating that the hydrogen-atom abstraction is a dominant reaction between crown ethers and these two radicals. The presence of cations in solution has negligible effect on the rate constants of crown ether towards OH and SO₄^?. However, for the NO₃, the rate constants are not proportional to the number of hydrogen atoms in ethers, and 12-crown-4 (12C4) is the most reactive compared with other crown ethers. Except 12C4 and 6C2, the cations in the aqueous solution affect the reactivities of 15-crown-5 (15C5) and 18-crown-6 (18C6). The cations with high binding stability for crown ether would improve the reactivity of 15C5. For the studied crown ethers, the reaction rate constants of these oxidative radicals have the order OH>SO₄^?>NO₃. Furthermore, the formation of radicals after the reaction of crown ethers with sulfate radical could be observed in the range of 260–280 nm using laser photolysis and pulse radiolysis. This is the first report on the kinetic behavior of crown ethers with NO₃, and it would be helpful for the understanding of stability of crown ethers in the processing of spent nuclear fuel.     

Practical use of chemical probes for reactive oxygen species produced in biological systems by γ-irradiation

Application of chemical probes, for detection of reactive oxygen species (ROS), was tested during γ-irradiation. The ethanol/α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) and 3,3′-diaminobenzidine (DAB) were structurally stable enough to detect OH and H₂O₂, increasingly generated by γ-irradiation up to 1000 Gy. Interestingly, the production rate of H₂O₂, but not OH, during γ-irradiation, was significantly different between in vitro systems of lettuce and spinach. These results suggest that 4-POBN and DAB could be utilized as a semi-quantitative probe to quantify OH and H₂O₂, produced by γ-irradiation up to 1000 Gy.     

Fluorescence detection of hydroxyl radicals

The hydroxyl radical (OH), a product of water radiolysis, reacts to hydroxylate aromatic organic compounds. In some cases, these hydroxylated products are fluorescent. Examples include the benzoate, coumarin, and phenoxazinone systems. For representative members of these systems, we have determined both the rate constants for reaction with OH and the yields of the fluorescent products. The rate constants all fall in the range 2×10⁹ to 2×10¹⁰ L mol⁻¹ s⁻¹, and the yields 5–11% per OH. These results suggest that it may prove feasible to construct a probe consisting of two groups both of which must react with OH to become fluorescent. The efficient process of fluorescence resonance energy transfer implies that such a probe might be able to detect OH clusters, which are generally assumed to be a characteristic feature of energy deposition by ionizing radiation.     

The effect of high-energy radiation on aqueous solution of Acid Red 1 textile dye

The effect of high-energy radiation on Acid Red 1 (AR1) azo-dye solution was investigated by UV–Vis spectroscopy and chemical oxygen demand (COD) measurements. Doses in the order of 10 kGy cause complete decolouration of the 10⁻³–10⁻⁴ mol dm⁻³ solutions; however, for complete mineralization doses higher by 1–2 order of magnitude are needed. Hydrated electrons and H atom are more effective in fading reaction, while the OH radicals have higher efficiency in mineralization. The HO₂^•/O₂^•− radical–radical anion pair is rather inefficient in fading reaction.     

Oxidation of naringenin by gamma-radiation

The reaction of OH with naringenin (4′,5,7-trihydroxyflavanone) in the presence of air induced the formation of the hydroxylation product eriodictyol (3′,4′,5,7-tetrahydroxyflavanone). Its yield was dependent on pH. The initial degradation yield of naringenin was G_i(-Nar)=(2.5±0.2)×10⁻⁷ mol dm⁻³ J⁻¹. For the reaction with OH, a rate constant k (OH+naringenin)=(7.2±0.7)×10⁹ M⁻¹ s⁻¹ was determined. In the presence of N₂O and NaN₃/N₂O, no eriodyctiol was formed. Apigenin (4′,5,7-trihydroxyflavon) was detected as decay product of the naringenin phenoxyl radicals. In Ar-saturated solutions, naringenin exhibited a pronounced radiation resistance, G(-naringenin) ∼0.3×10⁻⁷ mol dm⁻³ J⁻¹.     

Distribution of species in Na2O–CaO–B2O3 glasses as probed by FTIR

The article presents a simple method that can be used to get the concentration of various species in mixed-modifier borate glasses. By using the fraction of four coordinated boron in xCaO (30 − x)Na₂O70B₂O₃ (0 ≤ x ≤ 27.5 mol%) and xCaO(40 − x)Na₂O60B₂O₃ glasses (10 ≤ x ≤ 40 mol%), the concentration of BO₄⁻ and asymmetric BO₃ units related to each modifier oxide could be determined. CaO has a greater tendency to form asymmetric BO₃ units in the first glass series, while Na₂O has the ability to form BO₄ units to a greater extent. In xCaO(40 − x)Na₂O60B₂O₃ glasses, BO₄⁻ and asymmetric BO₃ units are formed at the same rate from Na₂O and CaO. The fraction of four coordinated boron, can be predicted by treating the studied glasses as if they are mixtures of Na₂O–B₂O₃ and CaO–B₂O₃ matrices. The change in N₄ is due to change in the relative concentration of these matrices.     

A combined experimental and model analysis on the effect of pH and O2(aq) on γ-radiolytically produced H2 and H2O2

The effects of pH and dissolved O₂ on the γ-radiolysis of water were studied at an absorbed dose rate of 2.5 Gy s⁻¹. Argon- or air-saturated water with no headspace was irradiated and the aqueous samples were analyzed for molecular radiolysis products (H₂ and H₂O₂) as a function of irradiation time. The experimental results were compared with computer simulation results using a comprehensive water-radiolysis kinetic model, consisting of the primary radiolysis production, subsequent reactions and related acid–base equilibria. Both the experimental and computer model results were discussed based on the steady-state kinetic analysis of smaller reaction sets consisting of key production and removal reactions. While the main production path for a water decomposition product is the primary radiolysis, the main removal path varies. For H₂O₂ the main removal path is the reactions with e_aq⁻ and OH, whereas for H₂ it is the reaction with OH. As a result, the presence of a dissolved species, or a change in chemical environment, affects the concentrations of H₂O₂ and H₂ through interaction with radicals e_aq⁻ and OH. Over a wide range of conditions, there exist quantitative but simple relationships between the radical and the molecular product concentrations. The experimental and model analyses show that dissolved oxygen increases the steady-state concentrations of H₂O₂ and H₂ by reacting with OH and e_aq^–, and the impact of oxygen is more noticeable at pH below 8. The steady-state concentrations of water decomposition products are nearly independent of pH in the range 5–8. However, raising pH above the pKa value of the acid–base equilibrium of H (⇆e_aq⁻+H⁺) significantly increases [H₂O₂] and [H₂] at the expenses of [OH] and [e_aq^–]. At pH >10, the radiolytical production of O₂ becomes significant, but at a finite rate. This considerably increases the time for the irradiated system to reach a steady state, and is responsible for different impacts on [H₂O₂] and [H₂] due to radically produced O₂, compared to impacts due to initially dissolved O₂. Model sensitivity analysis has shown that at higher pHs (pH >10) transient species such as O₂⁻ and O₃⁻ play a major role in determining the steady-state concentration of molecular products H₂ and H₂O₂. Further validation of the water radiolysis model, particularly at higher pHs, is also discussed.     

The sulphate radical is not involved in aqueous radiation oxidation processes

The H₂O₂/persulphate systems are of enormous environmental and commercial importance with the sulphate radical (SO₄⁻) being assumed as the oxidizing/bleaching species. We show that under normal conditions (air-saturated) no SO₄⁻ is produced and, most likely, a much longer-lived species, the adduct of O₂ and the persulphate radical, is formed.     

Formation of π-excimer or π-exciplex in electrogenerated chemiluminescence involving perylene molecule revealed using a dual-electrolysis stopped-flow method

Electrogenerated chemiluminescence (ECL) reactions involving the perylene cation radical (PE⁺) and perylene anion radical (PE⁻) in acetonitrile have been observed using a dual-electrolysis stopped-flow method. In this method, ECL emission from the systems composed of different kinds of ion radicals can be easily observed by mixing both the electrolyzed solutions directly. Therefore, the ECL spectra were observed systematically in the reactions of PE⁺ and PE⁻ with different ion radicals. Consequently, emission definitely from the singlet state of PE was observed in the reactions between PE⁺ and the 9,10-diphenylanthracene anion radical (DPA⁻), PE⁻ and DPA⁺, and PE⁻ and the thianthrene cation radical (TH⁺). In contrast, emission at long wavelength was obtained in the reaction between PE⁺ and the pyrene anion radical (PY⁻) as well as the reaction between PE⁺ and PE⁻. From this result, for the molecular interactions involving PE and PY, the presence of the π complexing interaction to form the π-excimer and the π-exciplex was strongly suggested in the ECL-emitting reactions. The present approach was thus found to be effective to reveal the molecular aspects of the excited states formed in solution.     

Kinetic behavior of the reaction between hydroxyl radical and the SV40 minichromosome

Aqueous solutions containing the minichromosomal form of the virus SV40 and the radical scavenger DMSO were subjected to γ-irradiation, and the resulting formation of single-strand breaks (SSB) was quantified. Under the irradiation conditions, most SSBs were produced as a consequence of hydroxyl radical (OH) reactions. By controlling the competition between DMSO and the viral DNA substrate for OH, we are able to estimate the rate coefficient for the reaction of OH with the SV40 minichromosome. The results cannot be described adequately by homogeneous competition kinetics, but it is possible to describe the rate coefficient for the reaction as a function of the scavenging capacity of the solution. The experimentally determined rate coefficient lies in the range 1×10⁹–2×10⁹ L mol⁻¹ s⁻¹ at 10⁷ s⁻¹, and increases with increasing scavenging capacity.     

Electrochemical oxidation of xanthosine

The electrochemical oxidation of xanthosine in aqueous solution at pH 2.0 at the pyrolytic graphite electrode has been studied. The primary electrochemical oxidation reaction is an irreversible 1 e⁻, 1 H⁺ reaction giving the C(8) free radical. In order to account for the ultimate products formed, the latter primary radical reacts with xanthosine to give at least one N free radical and with water to give an 8-hydroxylated free radical. The C(8) and N radicals couple to give a xanthosylxanthosine dimer which rapidly loses one ribosyl residue to give a xanthosylxanthine dimer. The 8-hydroxylated radical reacts with the C(8) and N radicals to give two isomeric hydroxylated xanthosylxanthosines. The 8-hydroxylated radical can also undergo further electrochemical oxidation (1 e⁻, 1 H⁺) to 9-β-D-ribofuranosyluric acid which is immediately oxidized (2 e⁻, 2 H⁺) to a very reactive quinonoid. Attack by water on the quinonoid gives two isomeric tertiary alcohol intermediates which have been isolated and characterized by their UV and mass spectra and by their reaction with water to give a diol. The latter diol decomposes to 5-hydroxyhydantoin-5-carboxamide-3-riboside.