Pulse Radiolytic Study of the Interaction of SO−·4 with Deoxynucleosides. Possible Implications for Direct Energy Deposition

Summary

Using the technique of pulse radiolysis it has been demonstrated that the interaction of SO^?·₄ with deoxynucleosides (k ～ < 2 × 10⁸–2·3 × 10⁹ dm³ mol^?1 s^?1) in aqueous solution at pH 7·0 results in the formation of the corresponding one-electron oxidized radicals which either deprotonate or hydrate to yield OH adducts. Based upon the ease of oxidation of the deoxynucleosides, dG, dA, dC, dT, by SO^?·₄, the apparent redox potentials are in the order dG ? dA ≈ dC > dT. With the exception of deoxyuridine, the deoxynucleoside radicals produced on interaction with SO^?·₄ have been shown to have oxidizing properties based upon the interactions with tetranitromethane and the nitroxyls, TMPN and NPPN. The deoxynucleoside radicals (dG, dA and dC) do not interact with oxygen (k < 10⁶ dm³ mol^?1 s^?1) in contrast to the interaction observed with the thymidine radical (k = 2·5 × 10⁷ dm³ mol^?1 s^?1). The implications of these findings are presented in terms of the properties of the discussed radicals as relating to those of potential DNA base radicals (positive centres) produced by direct energy deposition within DNA. The use of SO^?·₄ to mimic, to some extent, the effects of direct energy deposition in DNA may assist in our understanding of the resulting molecular processes relevant to radiobiological studies.     

Ultraviolet Difference Spectral Studies in the γ-radiolysis of DNA and Model Compounds. II. Oxygen and Temperature Dependence in Adenine Radiation Chemistry

Summary

Ultraviolet difference spectra between γ-irradiated and unirradiated aqueous solutions of oxygenated adenine reveal spectral maxima at 224, 286 and 360 nm, and suggest the existence of multiple radiation products. The presence of long-wavelength absorbing products implies the extension of the conjugation of the adenine ring. The product absorbing at 360 nm appears only in the presence of oxygen, with its yield dependent on both oxygen concentration and temperature. The absorbance peak at 360 nm in the UV difference spectra appears to demonstrate simple first-order decay kinetics, with a half-life of 50 min at 3°C. At temperatures below 23°C relative yields of the radiation products are approximately constant, suggesting a common mechanism. Higher temperatures apparently induce a mechanistic alteration. Since the temperature during and subsequent to irradiation, as well as the oxygen concentration of the solution, affects the absolute yields and distribution of the radiation products, great care must be exercised in controlling these variables.     

Standardization of 99mTc and 99Mo by the use of a 4πβ−4πγ counter

Technetium-99m is widely used for many diagnostic investigations in nuclear medicine, thus the standardization of this nuclide is important. In classical 4πβ?γ coincidence counting of ^99mTc, the steep slope of the efficiency function and the large extrapolation range may cause a large measurement uncertainty. In order to overcome these difficulties, we apply the 4πβ+4πγ sum counting technique for the standardization. Furthermore, we adopt both the 4πβ?4πγ coincidence counting method and the 4πβ+4πγ sum counting technique for the standardization of its parent nuclide ⁹⁹Mo. High efficiencies for both nuclides were easily achieved by the use of our 4πβ?4πγ counter. All the results were consistent with the reference value obtained by the conventional method obtained by NMIJ.     

Chemical Reactions by Pulsed Ultrasound: Memory Effects in the Formation of NO−3 and NO−2 in Aerated Water

Summary

The formation of nitrate and nitrite in the sonolysis of aerated water was studied using pulses of 300 kHz ultrasound. At very low on/off ratios, the yield decreases with decreasing pulse duration. At a pulse length of 3 × 10^?3s, the yield is zero. This time is identified as the ‘activation’ time τ₁ of small gas bubbles formed by cavitation. At larger on/off ratios, a pulse is more effective the shorter the time interval between the pulses. This memory effect is described by a ‘deactivation’ time τ₂ of the system, which amounts to about 6 × 10^?2s. At large on/off ratios (1:3 and 1:1) the yield never becomes zero. It first decreases with decreasing pulse length (increasing modulation frequency) and increases again for very short pulses. The results are also discussed with respect to the use of pulsed ultrasound in diagnostic applications.     

SO·−4-induced Oxidation of 1,3,6-trimethyluracil and 1,3,5-trimethyluracil (1,3-dimethylthymine) by Potassium Peroxodisulphate in Aqueous Solution: An Interesting Contrast

Summary

In order to mimic the direct effect of ionizing radiation on DNA, deoxygenated aqueous solutions of potassium peroxodisulphate, tert-butanol and 1,3,6-trimethyluracil (1,3,6-Me₃U) or 1,3-dimethylthymine (1,3-Me₂T) were irradiated with ⁶⁰Co γ rays; the sulphate radical formed by the reaction of the solvated electron with peroxodisulphate oxidizes these pyrimidines. In the case of 1,3,6-Me₃U, a chain reaction results in the formation of sulphuric acid, the glycols (two thirds) and 1,3,6-trimethylisobarbituric acid (one third). Typically, at 5 × 10^?4 mol dm^?3 1,3,6-Me₃U, 4 × 10^?2 mol dm^?3 S₂O^2?₈ and 10^?2 mol dm^?3 tert-BuOH with a dose-rate of 2·2 × 10^?3 Gys^?1, G(H⁺) is 220 × 10^?7 mol J^?1. We believe that the sulphate radical adds to the 1,3,6-Me₃U and the adduct rapidly loses the sulphate dianion, giving rise to the 1,3,6-Me₃U radical cation. This reacts with water, yielding a proton and the reducing 1,3,6-Me₃U C(5)-OH,C(6)-yl radical, which reacts with peroxodisulphate and so propagates the chain. In this oxidation process a carbocation is formed which can either react with water yielding the glycols, or deprotonate yielding the 1,3,6-trimethylisobarbituric acid. The 1,3-Me₂T system behaves differently. No chain reaction of any significance is induced. In the presence of oxygen an allyl-type radical can be trapped, as shown by the subsequent formation of 1,3-dimethyl-5-formyluracil (G = 2·1 × 10^?7 mol J^?1) and 1,3-dimethyl-5-hydroxymethyluracil (G = 0·2 × 10^?7 mol J^?1). As the corresponding products are not observed in the 1,3,6-Me₃U system, it is concluded that in contrast to the 1,3,6-Me₃U radical cation, the 1,3-Me₂T radical cation efficiently deprotonates (at C⁵-methyl), apart from also being able to react with water. In basic solution, OH^? adds to the 1,3-Me₂T radical cation, thereby suppressing the formation of the allyl-type radical. Quantum-chemical model calculations on uracil, thymine and 6-methyluracil show why 1,3-Me₂T and 1,3,6-Me₃U should differ in their behaviour. The C(5)-methyl substituted radical cation should differ from the C(6)-methyl substituted cation in the following respects: (1) the tendency to undergo deprotonation should be greater for the methyl group substituted at C(5) than at C(6); (2) the reactivity regarding water addition (to form the OH-adduct radical) should be greater in the case of the C(6)-methyl compound than for the thymine compound; and (3) the selectivity in favour of addition at C(5) versus C(6) should be greater in the case of the C(6)-methyl compound than in the substituted thymine.     

Initial research of screening for the differentially expressed proteins in beagles irradiated with 4.5 Gy60 CO γ-rays by two-dimensional gel electrophoresis and mass spectrometry

Objective To explore the mechanisms of cytokines on acute radiation disease in irradiated beagles.Methods The sera of beagles irradiated with 4.5 Gy γ-rays with cytokines treatment was collected at different time points post irradiation.The two-dimensional gel electrophoresis(2-DE)was used to isolate and compare the differentially expressed proteins in sera.HD-MS was used to analyze the differentially expressed proteins with significance,and the amino acid sequences should be determined. Results High resolution 2-DE gel map was obtained.There were six differentially expressed proteins in sera of irradiated beagles at different time points.Four protein spots were successfully identified by MS.A significant spot was identified as serum amyloid A(SAA)by HD-MS,with relative molecular mass of 13 077 and isoelectfie point of 6.26.Expression of SAA was not found 1 d pre-irradiation and 36 d postirradiation,but increased slightly 1 d(0.2166)and significantly 14 d post-irradiation(0.4577). Conclusions The expression of serum amyloid A was consistent with the process of acute radiation injury,which might indicate the turnover of the disease.     

Initial research of screening for the differentially expressed proteins in beagles irradiated with 4.5 Gy60 CO γ-rays by two-dimensional gel electrophoresis and mass spectrometry

Objective To explore the mechanisms of cytokines on acute radiation disease in irradiated beagles.Methods The sera of beagles irradiated with 4.5 Gy γ-rays with cytokines treatment was collected at different time points post irradiation.The two-dimensional gel electrophoresis(2-DE)was used to isolate and compare the differentially expressed proteins in sera.HD-MS was used to analyze the differentially expressed proteins with significance,and the amino acid sequences should be determined. Results High resolution 2-DE gel map was obtained.There were six differentially expressed proteins in sera of irradiated beagles at different time points.Four protein spots were successfully identified by MS.A significant spot was identified as serum amyloid A(SAA)by HD-MS,with relative molecular mass of 13 077 and isoelectfie point of 6.26.Expression of SAA was not found 1 d pre-irradiation and 36 d postirradiation,but increased slightly 1 d(0.2166)and significantly 14 d post-irradiation(0.4577). Conclusions The expression of serum amyloid A was consistent with the process of acute radiation injury,which might indicate the turnover of the disease.     

Commentary on the article of Wang H,Li J,Huang Z,Wang F,Zhang Y,Chang J,Rao Y (2020) Assessment of the role played by n-propanol in distinction of ethanol source in postmortem blood with the assistance of ethyl glucuronide and ethyl sulfate. Forensic Toxicol 38:195–202. https://doi.org/10.1007/s11419-019-00507-9

Forensic Toxicology -