Characterization,stability, and origin of natural radiation-induced defects in the biogenic calcite of Belemnitella americana from the Upper Cretaceous: An electron paramagnetic resonance study

The rostrum of Belemnitella americana (Morton) from the Marshalltown formation (Kmt, Upper Cretaceous) of the Chesapeake and Delaware Canal was investigated by electron paramagnetic resonance (EPR) spectroscopy. The rostrum composed of biogenic calcite possessed inorganic radical centers CO₂⁻, SO₂⁻, and SO₃⁻ with isotropic resonances with g values of 2.0007, 2.0057, and 2.0031, respectively. SO₃⁻ was found to also display an axially symmetric resonance typical of that seen in calcite of geologic origin with g_⊥=2.0036 and g_∥=2.0021. Mn²⁺ signals of orthorhombic symmetry and very narrow line width (∼0.1 mT) were also noted (|D|=9.3 mT (∼0.009 cm⁻¹), |E|=3.1 mT (∼0.003 cm⁻¹)). Isochronal annealing studies reveal that these inorganic radical species reside in energy traps that are significantly deeper than previously determined as revealed by their annealing temperatures: SO₂⁻ (isotropic), T^*∼340 °C; SO₃⁻ (isotropic), T^*∼230 °C; SO₃⁻ (axial), T^*∼190 °C. These data suggest that these spin centers may be used to extend the upper limit for dating purposes to times on the order of 1 Ma for SO₃⁻ (axial) and 200–300 Ma for SO₃⁻ (isotropic). Spin–spin and spin–lattice relaxation studies employing progressive microwave saturation were determined for all sulfur-based radical species and found to be consistent with the supposition of the isotropic signals existing in environments that are conducive to dynamic averaging of the g-anisotropy.     

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.     

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.     

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.     

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.     

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.     

Comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures

In a recent paper (Radiation Physics and Chemistry, 2005, vol. 74, pp. 210) it was suggested that the anomalous increase of molecular hydrogen radiolysis yields observed in high-temperature water is explained by a high activation energy for the reaction H+H₂O→H₂+OH. In this comment we present thermodynamic arguments to demonstrate that this reaction cannot be as fast as suggested. A best estimate for the rate constant is 2.2×10³ M⁻¹ s⁻¹ at 300 °C. Central to this argument is an estimate of the OH radical hydration free energy vs. temperature, ΔG_hyd(OH)=0.0278t−18.4 kJ/mole (t in °C, equidensity standard states), which is based on analogy with the hydration free energy of water and of hydrogen peroxide.     

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.     

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.     

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.     

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.     

Pulse radiolysis of aqueous diphenyloxide

Pulse radiolysis of aqueous diphenyloxide (DPO) has been performed under various experimental conditions. The OH radicals react with DPO on various positions of the molecule with a rate constant, k=2.1×10¹⁰ l mol⁻¹ s⁻¹. The major reaction step appears to be a cleavage of the C–O bond of DPO resulting into C₆H₄OH (λ=285 nm) and C₆H₅O(λ=325 nm) radicals in addition to DPO–OH adducts. They disappear according to a second-order reaction. In the presence of air or in a gas mixture of N₂O:O₂=4:1 the DPO–OH adducts are scavenged by oxygen, resulting into peroxyl radicals, which are long-lived species. For the reaction of e_aq⁻ with DPO a rate constant, k=2×10¹⁰ l mol⁻¹ s⁻¹ was found.     

Raman spectroscopic study of CuO–V2O5–P2O5–CaO glass system

In order to evidence the structural changes induced by CuO and V₂O₅ in the phosphate glass network and their modifier or former role, x(CuO·V₂O₅)(100 − x)[P₂O₅·CaO] glass system was prepared and investigated using Raman spectroscopy (0 ≤ x ≤ 40 mol%).Raman spectra of the studied glasses present the specific bands of the phosphate glasses at low concentration of transition metal (TM) ions, but at higher concentration (x > 7 mol%) a strong depolymerization of the phosphate network appears; non-bridging oxygen atoms are involved in VOP and CuOP bonds and new short units are formed. For a high concentration of V₂O₅ (x > 10 mol%) the Raman bands of V₂O₅ prevail in the spectra; this fact suggests that vanadium oxide imposes its structural units in the network acting thus as a network glass former.2D correlation analysis was also applied for the concentration-dependent Raman spectra in order to verify the assignments of the vibration modes and to find correlations in the changes induced by TM ions content. 2D correlation maps indicate a good correlation between the bands at ∼705 cm⁻¹ assigned to POP stretching vibration and at ∼1175 cm⁻¹ assigned to PO₂ groups which suggest the depolymerization of the phosphate network. The correlation between the 1270 cm⁻¹ and 930 cm⁻¹ bands also suggests that V₂O₅ oxide is responsible for PO bonds breaking and POV formation.     

Efficient immobilization of 9,10-anthraquinonyl moiety at solid interfaces through 2-(bromomethyl)anthraquinone one-electron cleavage

We report here a new and very efficient method for the coverage of different carbon materials with 9,10-anthraquinone attached via a methylene linker. The method is based on one-electron reduction of 2-(bromomethyl)anthraquinone (AQ-CH₂-Br) to a free radical AQ–CH₂ which was readily achieved using propylene carbonate (PC) as solvent containing tetrabutylammonium iodide. This way, the radical AQ–CH₂ adds to the abovementioned carbons forming very stable and dense covalently bound anhraquinonyl methane layers (Г ≈ 2 × 10^− 9 mol cm^− 2). The grafting could be performed by constant potential electrolyses (q < 0.5 × 10^− 3 C mm^− 2).     

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.     

Reduction reactions of bovine serum albumin and lysozyme by CO- .2 radical in polyvinyl alcohol solution: a pulse radiolysis study

Pulse radiolytic reduction of bovine serum albumin (BSA) and lysozyme by CO^⨪₂ radical in presence of polyvinyl alcohol (PVA) has been studied. At pH 6.8 in presence of 2% (w/v) PVA, reduction of BSA and lysozyme (both at 1×10⁻⁴ mol dm⁻³) give an additional transient peak at 390 nm along with the usual 420 nm peak. The bimolecular rate constants for the reaction of CO^⨪₂ radical at pH 6.8±0.2 with BSA are 2.7×10⁸ and 7.13×10⁸ dm³ mol⁻¹ s⁻¹ at 420 nm and 390 nm respectively. The same for lysozyme are 3.2×10⁸ and 5.6×10⁸ dm³ mol⁻¹ s⁻¹ at 420 nm and 390 nm, respectively. Dimethyl disulfide also gives 390 nm and 420 nm peaks in this system upon reduction with CO^⨪₂ radical. The 390 nm peak is ascribed to the sulfenium radical (RSS(H)R). Studies on the variation of pH suggests the protonation of RSSR^⨪ radical (420 nm) to form RSS(H)R radical (390 nm) in this viscous media. The decay of RSS(H)R radical occurs via formation of RS radical and RS(H)S(H)R, the final product being RSH in both cases.     

An FT-IR study of the isomerization of 1-butoxy radicals under atmospheric conditions

Relative rate-studies of the reactions of 1-butoxy radicals have been carried out using a 47 L static reactor with detection of end products by FT-IR spectroscopy. Experiments were performed at 700 torr total pressure and over the temperature range 253–295 K. The chemistry of 1-butoxy is characterized by a competition between reaction with oxygen CH₃CH₂CH₂CH₂O + O₂ → n-C₃H₇CHO + HO₂ (R2), which yields butanal and isomerization CH₃CH₂CH₂CH₂O → CH₂CH₂CH₂CH₂OH (R3), to form a hydroxylated carbonyl-product. A reference spectrum attributed to the product of 1-butoxy isomerization was obtained and used to determine the competition between 1-butoxy isomerization versus reaction with oxygen. The results indicate that isomerization is the dominant fate of 1-butoxy radicals at ambient temperature and pressure and that its importance decreases with decreasing temperature. The rate-coefficient ratio k₃/k₂ (molecule cm⁻³) = 5.5 × 10²³ exp[(−25.1 ± 0.9 kJmol⁻¹)/RT] was obtained. This agrees with other estimates based on methods without monitoring of the isomerization product.     

Pulse radiolysis studies on reactions of α-hydroxyalkyl radicals with nicotinamide and 6-methyl nicotinic acid

Reactions of α-hydroxyalkyl radicals derived from 2-propanol, ethanol and methanol with nicotinamide (NICAM) and 6-methyl nicotinic acid (6-MNA) were studied at various pHs using pulse radiolysis technique. It is found that α-hydroxyalkyl radicals react with NICAM and 6-MNA at pHs when nitrogen is in the protonated state. In these reactions, radical adducts of NICAM/6-MNA with α-hydroxyalkyl radicals are formed which have absorption maxima at about 340–350 nm which subsequently decay to give pyridinyl type of radicals of NICAM and 6-MNA having λ_max at 410 nm. Rate constants for the reactions of (CH₃)₂COH, CH₃CHOH and CH₂OH radicals with NICAM and 6-MNA were found to have linear dependence on reduction potentials of corresponding α-hydroxyalkyl radicals. Adducts formed in the reactions of CH₃CHOH and CH₂OH radicals with both NICAM and 6-MNA decayed slowly compared to the decay of adduct formed in reactions with (CH₃)₂COH radicals.     

Photoredox reactions of Cr(III) mixed-ligand complexes

Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O₂ and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C₂O₄^? radicals. The species undergo fast redox reactions dependent on the presence of O₂ and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to Cr^III. Then geminate recombination regenerates substrate, whereas competitive release of the C₂O₄^? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C₂O₄^? and pda^3?; the intermediate releases also e_aq^?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda.