Radiation-induced Radicals Research Articles

Potential properties of L-Asparagine for ESR dosimetry applications

Radiation-induced free radicals in x-ray irradiated L-asparagine have been investigated by Electron Spin Resonance (ESR) spectroscopy, for dosimetric purposes. Optimal signal-to-noise (S/N) ratio and signal intensity for ESR spectra were found for a microwave power of 2 mW, and modulation amplitude of 1 mT. The dosimetric properties of L-asparagine are characterized by a linear dose-response in the therapeutic dose range, and lowest detectable dose was 0.1 Gy, including a small energy dependence (80 KV-6 MV), dose rate independence over a range of clinical relevance (100–600 cGy/min). The ESR signal stability was also investigated in the period of 6 months at room temperature. No changes in the signal intensity were observed over this period. Therefore, we propose L-asparagine as a potential candidate for electron spin resonance dosimetry of ionizing radiation.

Formation of different types of paramagnetic centers in the alanine dosimeters exposed to alpha and gamma radiation - Study by EPR spectroscopy

EPR spectra of alanine dosimeters irradiated by gamma-rays and by alpha-particles were measured at different microwave power. The spectra were decomposed into three components corresponding to different stable radiation-induced radicals. Different ratio of the components was obtained for gamma- and alpha-irradiated alanine. The observed effect can be used for discrimination of the contribution of alpha- and gamma-radiation in mixed radiation field. That may be useful for control of dose at phantom experiments with neutron boron capture therapy, performed in mixed neutron-gamma field in which alpha-particles are emitted through neutrons capture reaction with boron.

Radiation induced defects in timolol: temperature dependent electron paramagnetic resonance spectroscopy analysis

Ionizing radiation-induced antihypertensive drug timolol in powder form was studied by means of electron paramagnetic resonance (EPR) technique as a function of temperature. The effect of temperature on EPR linewidth, intensity and spectra was investigated. The room temperature EPR spectra of ionizing radiation-induced timolol were recorded in dimethyl sulfoxide solution at a frozen state. The first-order kinetic mechanism rate constant of timolol was calculated. The findings on all EPR experimental data indicated that ionizing radiation-induced stable-free radical species on timolol are characterized by g = 2.0027.

Protective effect of lycopene on oral mucositis and antioxidant capacity of blood plasma in the rat exposed to gamma radiation.

Background:Nowadays, radiotherapy is used effectively for the treatment of head and neck cancers. Mucositis is one of the most important side effects of radiotherapy. Radio-protective agents protect tissues and cells against the adverse effects due to ionizing radiation and cleave radiation-induced free radicals. Lycopene as a potent antioxidant protects cells against oxidative damage by free radical–scavenging. The present study investigated the antioxidant effect of lycopene on oral mucosa of irradiated rats.Methods:In this experimental animal study, 28 rats were placed in four groups as follows: treated with 50 mg /kg of lycopene (L50), solvent+irradiation (SR), 25 mg / kg of lycopene+irradiation (LR25), and 50 mg / kg of lycopene+irradiation (LR50). The rats received lycopene intraperitoneally. On the irradiation day (day 0) and tenth day of radiation, blood samples were taken from the animals for FRAP and TBARS tests.Results:The results showed that the LR50 group did not show mucositis higher than grade 2. There was a significant difference (p<0.05) between SR and the L50 regarding the severity of mucositis. In addition, L50 showed higher antioxidant activity and lower peroxidation than SR.Conclusion:Lycopene reduced the severity of mucositis. Therefore, it can be used as a potential and promising nutritional substance to prevent radiotherapy complications, especially in the treatment of head and neck cancers. However, further research is necessary to confirm these results.

Experimental alternative to investigate the radiation-induced radical chemistry at the molecular level

SynopsisThis project aims to develop an original approach to investigate the damage at the molecular level on biomolecules from the indirect irradiation effects. We will construct a new device to put biomolecules in the gas phase, based on the soft laser desorption from microdroplets directly into vacuum, and this source will be coupled with an irradiation platform.

Electron paramagnetic resonance study of gamma induced free radicals in single crystal of 1-[2-(1-ethoxy-carbonyl-3-phenylpropylamino)propionyl]octahydrocylo-penta[b]pyrrole-2-carboxylic acid

The aim of this study was to investigate the structure of the radicals produced by gamma irradiation on single crystals of 1-[2-(1-ethoxy-carbonyl-3-phenyl propyl amino) propionyl]octahydrocylo-penta[b]pyrrole-2-carboxylic acid (C23H32N2O5) by using electron paramagnetic resonance spectroscopy technique. The radiation-induced free radical of single crystals was studied at the temperatures between 120 and 300 K and it has been found that gamma-irradiation produced the CγH2CβH2ĊNH(COOC2H5) radicals. The hyperfine coupling constants and the g value of the free radical was reported as ACβH2CγH2 = 1.37 mT, aN = 1.10 mT and g = 2.0061. The free radical formed in compound was observed to be stable at 300 K during two months of gamma-irradiation. The results were observed as being in good conformity with the existing literature.

Radiation-induced free radicals from different milk powders and its possible use as radiation dosimeters

Abstract Electron paramagnetic resonance spectroscopy (EPR) has been used to assess the free radical signal in different kinds of milk powder. Buffalos, colostrum’s, butter, milk cows, goat, camel and commercial milk before and after γ-ray irradiation. Moreover, un-irradiated milk samples exhibited weak signals, but upon increasing the absorbed doses EPR signal intensities were increased. The useful dose range was from 0.1 to 11 kGy. The results show that the stability of the signal of milk powder in relation to gamma irradiation was in order as follows: buffalo’s buttermilk; camel; cows; commercial milk; goat; buffalo’s; and colostrum milk. This study was recommended to use EPR as a new technique in an evaluation, quality control of dairy products and food irradiation applications. These milk powders undergo the influence of γ-rays can be applied as radiation dosimeters. Moreover, it can be used in food preservation, food irradiation processing, medical sterilization and water treating.

ESR investigation on the potential use of potassium citrate as a dosimeter material

Un-irradiated potassium citrate exhibited a weak ESR singlet at g = 2.0045 ± 0.0003 with peak-to-peak line-width of ΔHpp = 0.16 mT. However, multi-resonance signals spreading over a magnetic field range of ~5 mT were observed in gamma irradiated potassium citrate. A linear function of absorbed radiation dose was found to describe well the dose-response curves of the resonance signals A, B and C in a dose range of 5-5000 Gy. Room temperature fading study showed that radiation-induced radicals in potassium citrate are highly stable but less stable when exposed to the sunlight. Three different radical species were found to describe well experimental room temperature ESR spectrum of irradiated potassium citrate. The resonance signal B can be used in measuring the accidental radiation doses and the radiation doses used in food industry, at least up to a dose of 5 kGy. Further studies were needed in order to increase the sensitivity of potassium citrate at low radiation doses.

Bis[2-(methacryloyloxy)ethyl] phosphate radiografted into track-etched PVDF for uranium (VI) determination by means of cathodic stripping voltammetry

We report the radiation grafting of bis[2-(methacryloyloxy)ethyl] phosphate (B2MP) through electron-beam onto PVDF films and through swift heavy ions (SHI) irradiations into the pores of track-etched PVDF membranes. Radiolytically produced radicals were studied using EPR. To adapt the radiation grafting protocol inside the nanopores of track-etched membranes, the electron-beam irradiated films at varying monomer concentrations, doses and solvent mixtures were first studied. It was found that track-etched membranes, even after 1 h of chemical treatment, do not require a post-etching irradiation to initiate free-radical polymerization of B2MP from remaining radiationinduced radicals. The presence of functional groups inside the nanopores of the membrane were examined using FTIR and XPS. After exposure of B2MP-g-PVDF membranes to a uranyl solution, XPS was also exploited to evidence of O2UO22+ trapping inside the membrane nanoporosity by tracking the presence of U 4f peak. The B2MP-g-PVDF membranes were converted into electrodes by depositing 35 nm of gold on each side through a mask. Detection of ppb concentrations (from 20 to 100 ppb) of uranyl by B2MP-g-PVDF membrane electrodes was demonstrated by means of square wave cathodic stripping voltammetry (SW-CSV). The limit of detection (LOD) was estimated to be 17 ppb (3σ−/ slope).

Radiochromic and radiofluorogenic solid state polymer dosimeter; a third signal: Electron Paramagnetic Resonance (EPR)

A solid-state polymeric dosimeter has been developed. The solid-state dye-doped polymeric dosimeter comprises the photo-curable polymer materials Poly(ethylene glycol)-diacrylate (PEGDA) and 2-Hydroxyethyl-methacrylate (HEMA) and the radiochromic leuco-dye 4,4′,4″- Triamino-triphenyl –acetonitrile. Using a photo-curable polymer blend facilitates a tight control of the polymerization process and hence the properties of the solid-state dosimeter. The radiation sensitive leuco-dye responds to ionising radiation by forming a stable free radical – a triphenylmethyl dye. This free radical has strong colour, and is fluorescent because it is dissolved in the solid polymeric material. Both physical properties can be measured optically. The free radical, however, provides a third signal as it is paramagnetic and hence can be detected by means of Electron Paramagnetic Resonance (EPR) spectroscopy. The EPR signal makes it possible to measure the radiation-induced free radical signal free from optical artefacts of the polymer material. Results from irradiations using a low-dose-rate cobalt-60 gamma irradiator shows an EPR signal measured using a Bruker EMX EPR spectrometer for the solid polymeric dosimeter, whose peak-to-peak amplitude is linear with the dose in the medical dose range and saturates for higher doses (100 Gy).

ESR spectroscopic investigation of gamma-irradiated lithium trifluoromethanesulfonate

ABSTRACTThe effect of gamma radiation on lithium trifluoromethanesulfonate (LiTf) was investigated in detail using electron spin resonance (ESR) spectroscopy. The experimental spectra consisted of complex overlapped signals. Simulations of both the 1st- and 10th-day ESR spectra gave valuable information about the spectroscopic and structural features of radiation-induced radicals. More information about the qualitative and quantitative features of the radicals were gathered from the microwave power, storage time and dosimetric feature findings. In the light of the information obtained, four radicals were accepted to be produced after irradiation of LiTf.

Antipsychotic drugs scavenge radiation-induced hydroxyl radicals and intracellular ROS formation, and protect apoptosis in human lymphoma U937 cells

Antioxidant activity has been reported for some atypical antipsychotic drugs; however, the detailed mechanism is not well known. Here, we investigated the effects of atypical antipsychotic drugs on •OH radical formation, intracellular reactive oxygen species (ROS), and apoptosis induced by ionising radiation. The reaction rate constants with •OH radicals were determined for five antipsychotic drugs as follows, in descending order: olanzapine, aripiprazole, clozapine, haloperidol, and risperidone. Experiments with aminophenyl fluorescein, a fluorescent dye, showed that olanzapine and clozapine could scavenge intracellular ROS. However, experiments with hydroxyphenyl fluorescein showed that only olanzapine inhibited ROS generation. X-irradiation-induced apoptosis in human lymphoma U937 cells was inhibited by clozapine at relatively low concentrations and by olanzapine at higher concentrations. Clozapine inhibited caspase-8 and caspase-3 activation and prevented loss of mitochondrial membrane potential. In contrast, olanzapine inhibited X-irradiation-induced p-JNK activation. Although the atypical antipsychotic drugs used here have relatively high reaction rate constants with •OH radicals in aqueous solutions, inhibition of intracellular ROS was not due to •OH radical scavenging. In addition, suppression of X-irradiation-induced apoptosis was not directly linked with intracellular ROS scavenging. When apoptosis signalling pathways were studied, clozapine-mediated inhibition of apoptosis was dependent on caspase-3 and caspase-8. In contrast, olanzapine inhibited apoptosis via down regulation of X-irradiation-induced p-JNK. These results suggested that both olanzapine and clozapine have antioxidative and antiapoptotic activities via distinct pathways, and provide useful information for better understanding of drug characteristics.

Study of radiation-induced stable radicals in synthetic octacalcium phosphate by pulsed EPR

Study of radiation-induced stable radicals in synthetic octacalcium phosphate by pulsed EPR

Evaluation of the radioprotective effects of thymoquinone on dynamic thiol-disulphide homeostasis during total-body irradiation in rats.

Ionizing radiation–induced free radicals cause functional and structural harmful effects. Thiol, an important antioxidant, plays a major role in the eradication of reactive oxygen molecules. Thiol/disulphide homeostasis is a marker of oxidative stress. The objective of this study was to assess the potential radioprotective effects of thymoquinone (TQ) on the dynamic thiol/disulphide homeostasis of rats receiving total-body irradiation (IR). Twenty-two rats were divided into three groups to test the radioprotective effectiveness of TQ. The sham control group did not receive TQ or IR. The IR group received only total-body IR. The TQ + IR group received IR plus TQ. Following IR, blood samples were taken. The thiol/disulphide homeostasis parameters were analysed by a newly established method. In the IR group, native thiol and the native thiol/total thiol ratio were significantly decreased (P = 0.003 and P = 0.003, respectively), whereas the disulphide/native thiol and disulphide/total thiol ratios were significantly increased when compared with those of the sham control group (P = 0.003 and P = 0.003, respectively). In the TQ + IR group, the mean disulphide, native thiol and total thiol levels and the disulphide/native thiol, disulphide/total thiol and native thiol/total thiol ratios were not found to be significantly different when compared with those of the sham control group (P > 0.05 for all). Thiol/disulphide homeostasis was found to be disturbed after IR exposure. The results showed that TQ had antioxidant effects and reduced the IR-induced oxidative stress, which was demonstrated through the dynamic thiol/disulphide homeostasis. Thus, the use of TQ before radiation treatment helped protect the rats from oxidant side effects.

Enhanced oxidation stability of highly cross-linked ultrahigh molecular weight polyethylene by tea polyphenols for total joint implants

Despite being currently state-of-the-art to prevent the oxidation of irradiated ultrahigh molecular weight polyethylene (UHMWPE) bearings, vitamin E (VE) poses concerns in the loss of cross-linking efficiency and is limited to be used at very low concentrations. It thus emphasizes the urgent demand for more efficient stabilizers. In this study, oxidation stability of highly cross-linked UHMWPE was demonstrated to be enhanced by tea polyphenols, such as lipid-soluble tea polyphenols (lsPPT), epigallocatechin gallate (EGCG), and lipid-soluble epigallocatechin gallate (lsEGCG). These antioxidants were blended with UHMWPE granules and consolidated by compression molding prior to E-beam irradiation. The presence of tea polyphenols substantially prolonged oxidation induction time of the irradiated UHMWPE before and after accelerated aging. Especially, lsEGCG was significantly superior to VE in terms of stabilizing capacity. Explained by the hydrogen donation mechanism, tea polyphenols with multiple phenolic hydroxyls could scavenge more radiation-induced free radicals than VE with only one phenolic hydroxyl, which was verified by the electron spin resonance spectra. Intriguingly, tea polyphenols showed less inhibitive effect on the cross-link density of irradiated UHMWPE than VE. Besides, there is no significant difference in crystallinity, mechanical performance as well as in vitro biocompatibility between the irradiated UHMWPE stabilized by tea polyphenols and VE. These findings highlight tea polyphenols, especially lsEGCG, are promising alternatives to extend the life span of UHMWPE implants.

EPR measurement of environmental radiation using human fingernails

Abstract In this research work, human fingernails were utilized to estimate the radiation dose using EPR measurements of radiation-induced radicals. The limiting factors in this research were the presence of mechanical induced EPR signals due to the mechanical stress during the preparation of the samples. The mechanically induced signals overlap with the radiation-induced signal, which considerably can overestimate the dose. Thus, different treatment methods of fingernails were used to reduce the mechanical induced signals. The results demonstrate that the mechanical and radiation induced signals have apparently different microwave power saturation behavior. Also, mechanical induced signal shows a fading evolution vs. time and reaches to a constant value. Chemical treatment using the different reagents showed that the minimum mechanical induced signal was obtained using the dithiothreitol reagent. The dose response curves of the treated samples with dithiothreitol for 30 min demonstrated a more linearity, and closer curves in comparison to those treated in 5 min. Therefore, to find out an unknown absorbed dose in a fingernail sample using a calibration curve, it could be recommended to use the mentioned chemical treatment procedure to reduce the uncertainty.

Impact of disorder on formation of free radicals by gamma-irradiation: Multi-frequency EPR studies of trehalose polymorphs

Electron paramagnetic resonance (EPR) studies of the radiation-induced radicals in two anhydrous trehalose polymorphs, beta-crystalline (TREc) and glassy (TREg), were conducted with the aim to resolve whether different types of free radicals are induced in a differently disordered environment. A multifrequency approach (9.5 GHz, 94 GHz, and 244 GHz) was applied to improve the g-tensor resolution of the complex EPR spectra. In addition, the thermal stability of the EPR spectra and the respective decay kinetics were analyzed in a series of thermal annealing studies in the temperature interval from 333 K to 363 K. It was found that in the crystalline matrix the transformation process of the induced radicals is more complex than in the glassy host matrix. Qualitative decomposition of the experimental spectra, assuming four contributing species, reproduced characteristic EPR spectral features in both matrices. These were interpreted as carbon-centered radicals while the possibility of the formation of alkoxy radicals due to the abstraction of a hydrogen atom could be ruled out. Only in one case, the tentative assignment of the EPR spectral components revealed the formation of the same radical species in both TREc and TREg. Furthermore, by thermal annealing TREg lost one of the radical species, whereas in TREc all 4 radical species pertained irrespective of the treatment. The results presented here, therefore, provide experimental evidence that the extent of disorder present in the material strongly affects the type and stability of radicals induced by ionizing radiation.

EPR parameters of L-α-alanine radicals in aqueous solution: a first-principles study

ABSTRACTEPR (electron paramagnetic resonance) response for a wide range of possible alanine radicals has been analysed employing quantum chemical methods. The strong correlation between geometry and EPR parameter structure of these radicals has been shown in this research work. Significant solvent effect on EPR parameters has been shown employing both explicit and implicit solvent models. In a relatively good agreement with the experiment, stable conformation of these radicals in acidic and basic conditions was determined, and a new conformation was suggested based on possible proton transfer in the intermediate pH range. The employed methodology along with experimental results may be used for the characterisation of different radiation-induced amino acid radicals.

Experimental and theoretical research on γ-irradiated 7-methoxy-4-methylcoumarin powder through EPR and DFT methods

ABSTRACTIn this paper, the effects of gamma irradiation on 7-Methoxy-4-methylcoumarin (7M4MC) molecule, an essential coumarin derivative, which has an inherent variety of biological activities, therapeutic properties and industrial usage were examined. For this purpose, the sample was irradiated with 60Co-gamma ray source for about 100 kGy total doses. Theoretical calculations were performed using GAUSSIAN03 program for the possible radicals that were modeled from two stable conformations with lowest energies. In order to get well-resolved spectra and to determine the radical identity experimentally, EPR spectra of the irradiated 7M4MC sample were recorded at several spectrometer conditions. By considering the molecular structure and EPR spectra, alkyl-type radical was assumed to be formed by gamma irradiation. To support the estimations, simulations were done using theoretical EPR parameters as an initial value. The experimental spectra were well matched with the sum of simulated spectra obtained from two same type modeled radicals of two different conformations. As a result of experimental estimations and theoretical calculations, radiation-induced radicals were identified as two neutral alkyl radicals, , originated from two stable conformations.

Retrospective dosimetry using fingernail electron paramagnetic resonance response

Abstract Human fingernails were used to estimate the radiation dose via electron paramagnetic resonance measurements of radiation-induced radicals. The limiting factors in this research were mechanically induced electron paramagnetic resonance signals due to the mechanical stress during the preparation of the samples. Therefore, different treatment methods of fingernails were used to reduce the mechanically induced signals. The results demonstrate that the mechanically induced and radiation-induced signals have apparently different microwave power saturation behaviors. In addition, the mechanically induced signal shows a fading evolution over time and reaches a constant value. Chemical treatment using the different reagents showed that the minimum mechanically induced signal was obtained using the dithiothreitol reagent. The dose–response curves of the samples treated with dithiothreitol for 30 minutes demonstrated a greater linearity than those of samples treated for 5 minutes. Therefore, to find an unknown absorbed dose in a fingernail sample using a calibration curve, we recommend adopting the mentioned chemical treatment procedure to reduce the uncertainty.