Radiation-induced Free Radicals Research Articles

Synthesis, molecular modeling, DFT studies, and EPR analysis of 1,4-dihydropyridines as potential calcium channel blockers

1,4-Dihydropyridines (DHPs) are widely recognized as a highly effective class of L-type calcium channel blockers that offer significant therapeutic potential in managing cardiovascular conditions. Furthermore, their ability to target other types of calcium channels makes DHPs attractive candidates for therapeutic applications in neurological and psychiatric disorders. Close examination of the chemical structures of approved DHP-based antihypertensive drugs with a history of over forty years in the market reveals that the C-4 position is the least altered part of this privileged ring system. In the present study, we focused on this position and synthesized two novel compounds (DB1 and DB2) by carrying out chemical modifications on suitable positions of the main scaffold of DA1 (isobutyl 4-(benzo[d][1,3]dioxol-5-yl)-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate) that was previously identified as a DHP-based effective and selective inhibitor of T-type (Cav3.2) over L-type (Cav1.2) calcium channel. Based on whole-cell patch-clamp analysis on Cav1.2 and Cav3.2, DB1 with bromine group on the benzodioxole ring appeared to be a more effective and selective inhibitor of Cav3.2 compared to DB2 with nitro at the same locus. Molecular docking and molecular dynamics (MD) simulations were performed to investigate the binding mode of both DB1 isomers to Cav3.2. Furthermore, density functional theory (DFT) methods were employed to obtain information regarding the stability of the molecules by computing various parameters, such as electric dipole moment, band gap, electronegativity, and global chemical hardness-softness, related to their charge-transfer characteristics. According to DFT studies, DB1 also appeared to be chemically more stable than DB2. Finally, ionizing radiation-induced free radicals of gamma-irradiated DB1 and DB2 in powder form were examined utilizing the electron paramagnetic resonance (EPR) technique and the obtained data demonstrated that radiation sterilization is suitable for the dosage forms including DB1 and DB2.

Radiation-Chemical Oxygen Depletion Depends on Chemical Environment and Dose Rate: Implications for the FLASH Effect

FLASH (dose rates >40 Gy/s) radiation therapy protects normal tissues from radiation damage, compared with conventional radiation therapy (∼Gy/m). Radiation-chemical oxygen depletion (ROD) occurs when oxygen reacts with radiation-induced free radicals, so a possible mechanism for FLASH involves radioprotection by the decreased oxygen as ROD occurs. High ROD rates would favor this mechanism, but prior studies have reported low ROD values (∼0.35 µM/Gy) in chemical environments such as water and protein/nutrient solutions. We proposed that intracellular ROD might be much larger, possibly promoted by its strongly reducing chemical environment. ROD was measured, using precision polarographic sensors, from ∼100 µM to zero in solutions containing intracellular reducing agents ± glycerol (1M), to simulate intracellular reducing and hydroxyl-radical-scavenging capacity. Cs irradiators and a research proton beamline allowed dose rates from 0.0085 to 100 Gy/s. Reducing agents significantly altered ROD values. Most greatly increased ROD but some (eg, ascorbate) actually decreased ROD and additionally imposed an oxygen dependence of ROD at low oxygen concentrations. The highest values of ROD were found at low dose rates, but these montonically decreased with increasing dose rate. ROD was greatly augmented by some intracellular reducing agents but others (eg, ascorbate) effectively reversed this effect. Ascorbate had its greatest effect at low oxygen concentrations. ROD decreased with increasing dose rate in most cases.

Effect of Gamma Irradiation on Fat Content, Fatty Acids, Antioxidants and Oxidative Stability of Almonds, and Electron Paramagnetic Resonance (EPR) Study of Treated Nuts.

Gamma irradiation has been applied as an efficient and inexpensive method for the sterilization of nuts for years. However, along with the benefits of such treatment, negative effects are possible because of the formation of reactive oxygen species with a toxic effect on important biologically active substances. Because of the scarce and contradictory information in the literature about gamma-irradiated almonds, the aim of our work was the examination of the lipid changes, antioxidant activity, and oxidative stability of almonds treated by 10 and 25 kGy gamma rays, as well as changes in intensity of the EPR spectra as an indicator for the stability of radiation-induced free radicals. The results revealed no significant differences in the EPR spectra of almonds treated at 10 and 25 kGy doses, neither in their intensity nor in kinetic behaviour. The EPR signals decayed exponentially over 250 days, with a decreasing of central line by 90%, with satellite lines by about 73%. No significant changes in the fat content, fatty acids composition, and acid value of irradiated almonds were observed. However, the amount of (alpha)tocopherols decreased from 292 to 175 mg/kg, whereas the conjugated dienes and trienes increased, K232 from 1.3 to 3 and K268 from 0.04 to 0.15, respectively, with the increasing of irradiation dose. The same was observed for total polyphenols in defatted almonds (1374 to 1520 mg/100 g), where in vitro antioxidant activity determined by ORAC and HORAC methods increased from 100 to 156 µmol TE/g and from 61 to 86 µmol GAE/g, respectively. The oxidative stability of oil decreased from 6 to 4 h at 120 °C and from 24.6 to 18.6 h at 100 °C (measured by Rancimat equipment). The kinetic parameters characterizing the oxidative stability of oil from 10 kGy irradiated almonds were studied before and after addition of different concentrations of ascorbyl palmitate as a synergist of tocopherols. Its effectiveness was concentration-dependent, and 0.75 mM ensured the same induction period as that of non-irradiated nut oil. Further enrichment with alpha-tocopherol in equimolar ratio with palmitate did not improve the oil stability. In conclusion, gamma irradiation is an appropriate method for the treatment of almonds without significant changes in fat content and fatty acids composition. The decreasing of oxidative stability after higher irradiation could be prevented by the addition of ascorbyl palmitate.

Electron spin resonance (ESR) study on gamma irradiated some modern paper samples

In this work, we use paramagnetic defects induced by gamma radiation in some modern paper samples to determine their main dosimetric properties in the decontamination dose range (0.5–10 kGy) of ancient papers. Electron spin resonance (ESR) spectra of photo paper, cigarette paper, white paper napkin (napkin), cash register receipt, straw paper and white photocopy paper recorded before and after irradiation with gamma rays were reported. Photo paper, cigarette paper and napkin samples displayed the radiation-induced cellulose-like ESR signals well known from the literature on cellulose-containing foods. Cash register receipt, straw paper, and white photocopy paper are another set of samples where different ESR spectra were recorded. The ESR signals of these three paper samples were shown to originate from carbonate mineral filler grains. Inorganic mineral fillers are commonly used in paper manufacturing. The dose-response curves associated with the radiation-induced sharp ESR signals originating from the CaCO3 filler of the cash register receipt (g = 2.0027), the straw paper (g = 1.9995), and the white photocopy paper (g = 1.9996) were found to follow a single exponential saturation function. Despite the observed decreases with time in the signal intensities of cash register receipt and white photocopy paper, detectable ESR signals were obtained even 100 days after irradiation for them and straw paper. The radiation-induced free radicals responsible for the ESR spectrum of straw paper were more stable than those of cash register receipt and white photocopy paper. The results indicate that free radicals induced in mineral CaCO3 filler grains incorporated within papers have the potential to be used for application to retrospective ESR dosimetry in the range of 0.5–10 kGy.

Elite Zingiber extracts as potential free radical scavengers and radioprotectors

ABSTRACT Fresh rhizome extracts of four elite Zingiber species, viz., Zingiber kangleipakense, Zingiber montanum, Zingiber officinale, and Zingiber zerumbet, prepared in 60% aqueous ethanol/60% aqueous methanol solutions were used for assessing their comparative free radical scavenging and radioprotective properties. Various methods, such as ferric ion reducing power assay, DPPH ion scavenging assay, nitric oxide scavenging assay, metal chelating assay, thiyl/sulfur free radical reactivity assay, and hydroxyl ion scavenging assay, were employed for radical scavenging capabilities. Bio-active principles, such as total phenolic, flavonoid, and ascorbic acid contents, were also assessed. Z. officinale showed the highest TPC, TFC, and ascorbic acid content of 650 mg GAE/100 g, 889 mg QE/100 g, and 3.19 mg/100 g, respectively, as well as the greatest efficacy in ferric ion reducing and DPPH scavenging ability having lowest IC50 value of 0.22 mg/mL. Z. montanum showed the lowest IC50 value of 0.91 mg/mL in NO scavenging assay and also exhibited the highest curcumin protection in thiyl free radical scavenging assay. Z. kangleipakense showed the lowest IC50 value of 0.24 mg/mL and 0.25 mg/mL in metal ion chelating assay and hydroxyl radical assay, respectively. 60% aqueous ethanol extracts of Z. officinale and Z. kangleipakense were used for radioprotective assays both for in vitro and in vivo using plasmid pBR322 DNA and bone marrow cells of albino rats, respectively, based on their significant free radical scavenging properties. At the same concentration of 0.25 mg/mL, Z. officinale and Z. kangleipakense showed 71.50% and 56.54% protection, respectively, of DNA from exposure to 6 Gy gamma radiation. Also, Z. officinale and Z. kangleipakense exhibited 51.16% and 38.96% protection from radiation-induced chromosomal damages in rats, respectively, when exposed to 2 Gy. Reduction in the DNA open circular form as well as the chromosomal aberrations in treatments with plant extracts compared to the controls confirmed the radioprotective potentials of the extracts. The results showed that the extracts possessed potential antioxidant compounds having capacities to scavenge radiation-induced free radical species. The accessibility of the extracts in radiation countermeasures can provide immense nutraceutical potentials.

Antioxidant activity of curcumin protects against the radiation-induced micronuclei formation in cultured human peripheral blood lymphocytes exposed to various doses of γ-Radiation

Purpose Ionizing radiations trigger the formation of free radicals that damage DNA and cause cell death. DNA damage may be simply evaluated by micronucleus assay and the pharmacophores that impede free radicals could effectively reduce the DNA damage initiated by irradiation. Therefore, it was desired to determine the capacity of curcumin to alleviate micronuclei formation in human peripheral blood lymphocytes (HPBLs) exposed to 0–4 Gy of γ-radiation. Materials and methods HPBLs were exposed to 3 Gy after 30 minutes of 0.125, 0.25, 0.5, 1, 2, 5, 10, 20 or 50 µg/mL curcumin treatment or with 0.5 μg/mL curcumin 30 minutes early to 0, 0.5, 1, 2, 3 or 4 Gy 60Co γ-irradiation. Cytokinesis of HPBLs was blocked by cytochalasin B and micronuclei scored. The ability of curcumin to suppress free radical induction in vitro was determined by standard methods. Results HPBLs treated with different concentrations of curcumin before 3 Gy irradiation alleviated the micronuclei formation depending on curcumin concentration and the lowest micronuclei were detected at 0.5 µg/mL curcumin when compared to 3 Gy irradiation alone. Increasing curcumin concentration caused a gradual rise in micronuclei, and the significant increases were detected at 10–50 µg/mL curcumin than 3 Gy irradiation alone. Irradiation of HPBLs to different doses of γ-rays caused a significant rise in micronuclei depending on radiation dose, whereas HPBLs treated with 0.5 µg/mL curcumin 30 minutes before irradiation to different doses of γ-rays significantly reduced frequencies of HPBLs with one, two, or more micronuclei. Curcumin treatment inhibited the formation of hydroxyl (OH), 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 2,2′-diphenyl-1-picrylhydrazyl (DPPH), and (nitric oxide) NO free radicals in a concentration-related way. Conclusions Curcumin when treated at a dose of 0.5 μg/mL attenuated micronuclei formation after γ-irradiation by inhibiting the formation of radiation-induced free radicals.

Polymerization Reactions and Modifications of Polymers by Ionizing Radiation.

Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on materials, photons or high energy electrons, in both cases ions and electrons are produced. The interactions between electrons and monomers takes place within less than a nanosecond. Depending on the dose rate (dose is defined as the absorbed radiation energy per unit mass), the kinetic chain length of the propagation can be controlled, hence allowing for some control over the degree of polymerization. When polymers are submitted to high-energy radiation in the bulk, contrasting behaviors are observed with a dominant effect of cross-linking or chain scission, depending on the chemical nature and physical characteristics of the material. Polymers in solution are subject to indirect effects resulting from the radiolysis of the medium. Likewise, for radiation-induced polymerization, depending on the dose rate, the free radicals generated on polymer chains can undergo various reactions, such as inter/intramolecular combination or inter/intramolecular disproportionation, b-scission. These reactions lead to structural or functional polymer modifications. In the presence of oxygen, playing on irradiation dose-rates, one can favor crosslinking reactions or promotes degradations through oxidations. The competition between the crosslinking reactions of C-centered free radicals and their reactions with oxygen is described through fundamental mechanism formalisms. The fundamentals of polymerization reactions are herein presented to meet industrial needs for various polymer materials produced or degraded by irradiation. Notably, the medical and industrial applications of polymers are endless and thus it is vital to investigate the effects of sterilization dose and dose rate on various polymers and copolymers with different molecular structures and morphologies. The presence or absence of various functional groups, degree of crystallinity, irradiation temperature, etc. all greatly affect the radiation chemistry of the irradiated polymers. Over the past decade, grafting new chemical functionalities on solid polymers by radiation-induced polymerization (also called RIG for Radiation-Induced Grafting) has been widely exploited to develop innovative materials in coherence with actual societal expectations. These novel materials respond not only to health emergencies but also to carbon-free energy needs (e.g., hydrogen fuel cells, piezoelectricity, etc.) and environmental concerns with the development of numerous specific adsorbents of chemical hazards and pollutants. The modification of polymers through RIG is durable as it covalently bonds the functional monomers. As radiation penetration depths can be varied, this technique can be used to modify polymer surface or bulk. The many parameters influencing RIG that control the yield of the grafting process are discussed in this review. These include monomer reactivity, irradiation dose, solvent, presence of inhibitor of homopolymerization, grafting temperature, etc. Today, the general knowledge of RIG can be applied to any solid polymer and may predict, to some extent, the grafting location. A special focus is on how ionizing radiation sources (ion and electron beams, UVs) may be chosen or mixed to combine both solid polymer nanostructuration and RIG. LLET ionizing radiation has also been extensively used to synthesize hydrogel and nanogel for drug delivery systems and other advanced applications. In particular, nanogels can either be produced by radiation-induced polymerization and simultaneous crosslinking of hydrophilic monomers in “nanocompartments”, i.e., within the aqueous phase of inverse micelles, or by intramolecular crosslinking of suitable water-soluble polymers. The radiolytically produced oxidizing species from water, •OH radicals, can easily abstract H-atoms from the backbone of the dissolved polymers (or can add to the unsaturated bonds) leading to the formation of C-centered radicals. These C-centered free radicals can undergo two main competitive reactions; intramolecular and intermolecular crosslinking. When produced by electron beam irradiation, higher temperatures, dose rates within the pulse, and pulse repetition rates favour intramolecular crosslinking over intermolecular crosslinking, thus enabling a better control of particle size and size distribution. For other water-soluble biopolymers such as polysaccharides, proteins, DNA and RNA, the abstraction of H atoms or the addition to the unsaturation by •OH can lead to the direct scission of the backbone, double, or single strand breaks of these polymers.

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.

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.

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.

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).

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.

Effect of $$\gamma $$ γ -irradiation on the thermal properties of UHMWPE/MWCNTs nanocomposites: a comparative study of incorporating unmodified and $$\gamma $$ γ -ray-modified MWCNTs

The efficacy of defective sites in MWCNTs as free radical scavengers was investigated on the basis of thermal analysis of ultra-high molecular weight polyethylene (UHMWPE)/MWCNTs and UHMWPE/\(\gamma \)-MWCNTs nanocomposites. Homogenized composites of polyethylene (PE) with MWCNTs and \(\gamma \)-MWCNTs (0.5% by weight) were prepared by the ball milling process for 2 h at a speed of 200 rpm. Thereafter, micron-sized sheets were prepared (by hot pressing) and subjected to \(\gamma \)-dose ranging from 25 to 150 kGy. To investigate the thermal properties and thermal stability, differential scanning calorimetric (DSC) and thermo-gravimetric analysis (TGA) measurements were performed in an inert atmosphere. The results showed that peak melting temperature (\(T_{\mathrm{m}})\) and lamellae thickness (\(L_{\mathrm{c}})\) remained unaltered for UHMWPE/MWCNTs composites; however, for UHMWPE/\(\gamma \)-MWCNTs composites the values varied from 138 to \(141^{\!\circ }\hbox {C}\). This behaviour was attributed to chain scission close to crystalline lamellae due to radiation-induced free radicals, thus reducing the percentage of inter-phase contents within the polymer matrix and enhancing the percentage crystallinity for composites. Furthermore, TGA revealed the higher thermal stability of composites as compared with pristine ones and significant increase in residues percentage for composites, i.e., from \(\sim \) 3 to 7%. These results confirmed the importance of defective sites within the MWCNTs as free radical quenchers, and stopping the chain scission, particularly close to crystalline lamellae, thus preventing loss of the important interphase region of UHMWPE.

Piperidine-conjugated polyfunctional star-shaped PLLA as a novel bio-based antioxidant additive for bioplastics

Antioxidant-conjugated star-shaped PLLA (star-PLLA-PPD) were originally proposed as a novel polyfunctional free radical stabilizing additive for bioplastics. By a simple ring opening polymerization of l-lactide (L-LA) on a poly-functional core molecule (i.e., pentaerylthritol) using tin (II)-2-ethylhexanoate (SnOct2) as a catalyst, the 4-arms star-shaped PLLA was successfully prepared and confirmed by FT-IR and 1H-NMR. Percent conversion of L-LA to 4-arms star-PLLA was 78.50% and the weight and number average molecular weights determined by GPC were 34726 Da and 27286 Da, respectively (PDI = 1.27). Piperidine (PPD) was then conjugated onto 4-arms star-PLLA to obtain star-PLLA-PPD. As observed by SEM and DSC, the star-PLLA-PPD exhibited excellent compatibilizer as well as nucleating agent for PLA. A model study on free radical scavenging ability of the star-PLLA-PPD in PLA blends was carried out under radiation-induced free radical process. Irradiation doses of 10 kGy and 25 kGy were used because they are generally used for food and medical device sterilization, respectively. Free radical scavenging ability was demonstrated using EPR spectroscopy. The star-PLLA-PPD efficiently scavenges the free radicals in PLA matrix upon irradiation. The star-PLLA-PPD additive could retard the degradation of PLA under irradiation as observed by protecting molecular weight reduction when compared with the neat PLA. The migration of star-PLLA-PPD is significant lower than PPD. A novel star-PLLA-PPD additive would be a good model of polyfunctional bio-based antioxidant additive for bioplastics especially for food packaging and biomedical materials.

Irradiation free radicals in freshwater crayfish Astacus leptodactylus Esch investigated by EPR spectroscopy

The free radicals of irradiated crayfish Astaculs leptodactylus cuticle were studied by X-band electron paramagnetic resonance. The kinetic behaviour as well as the thermal stability of the radiation-induced free radicals in crayfish cuticle were investigated by means of both isothermal and isochronal annealing. Both short, presumable juvenile and long, mature exemplars of freshwater crayfish were investigated. Only the long exemplars cuticle displayed the presence of Mn2+ ions, very similar to those reported for Mn2+ ions in calcite. The 200°C isothermal annealing studies attested the existence of a multitude of radical species, some of them being generated during the first minutes of thermal treatment and then partially of totally vanishing. Regardless these peculiarities, the EPR spectrum of 15 kGy irradiated cuticle showed remarkable time stability, its amplitude decreasing with about 18% after more than 16 months of storage at room temperature. The implications of these observations regarding the diversity of irradiation free radicals as well as their suitability to identify gamma radiation decontamination treatment are discussed.

POSSIBLE NATURE OF THE RADIATION-INDUCED SIGNAL IN NAILS: HIGH-FIELD EPR, CONFIRMING CHEMICAL SYNTHESIS, AND QUANTUM CHEMICAL CALCULATIONS.

Exposure of finger- and toe-nails to ionizing radiation generates an Electron Paramagnetic Resonance (EPR) signal whose intensity is dose dependent and stable at room temperature for several days. The dependency of the radiation-induced signal (RIS) on the received dose may be used as the basis for retrospective dosimetry of an individual's fortuitous exposure to ionizing radiation. Two radiation-induced signals, a quasi-stable (RIS2) and stable signal (RIS5), have been identified in nails irradiated up to a dose of 50 Gy. Using X-band EPR, both RIS signals exhibit a singlet line shape with a line width around 1.0 mT and an apparent g-value of 2.0044. In this work, we seek information on the exact chemical nature of the radiation-induced free radicals underlying the signal. This knowledge may provide insights into the reason for the discrepancy in the stabilities of the two RIS signals and help develop strategies for stabilizing the radicals in nails or devising methods for restoring the radicals after decay. In this work an analysis of high field (94 GHz and 240 GHz) EPR spectra of the RIS using quantum chemical calculations, the oxidation-reduction properties and the pH dependence of the signal intensities are used to show that spectroscopic and chemical properties of the RIS are consistent with a semiquinone-type radical underlying the RIS. It has been suggested that semiquinone radicals formed on trace amounts of melanin in nails are the basis for the RIS signals. However, based on the quantum chemical calculations and chemical properties of the RIS, it is likely that the radicals underlying this signal are generated from the radiolysis of L-3,4-dihydroxyphenylalanine (DOPA) amino acids in the keratin proteins. These DOPA amino acids are likely formed from the exogenous oxidation of tyrosine in keratin by the oxygen from the air prior to irradiation. We show that these DOPA amino acids can work as radical traps, capturing the highly reactive and unstable sulfur-based radicals and/or alkyl radicals generated during the radiation event and are converted to the more stable o-semiquinone anion-radicals. From this understanding of the oxidation-reduction properties of the RIS, it may be possible to regenerate the unstable RIS2 following its decay through treatment of nail clippings. However, the treatment used to recover the RIS2 also has the ability to recover an interfering, mechanically-induced signal (MIS) formed when the nail is clipped. Therefore, to use the recovered (regenerated) RIS2 to increase the detection limits and precision of the RIS measurements and, therefore, the dose estimates calculated from the RIS signal amplitudes, will require the application of methods to differentiate the RIS2 from the recovered MIS signal.

Gamma and ion-beam irradiation of DNA: Free radical mechanisms, electron effects, and radiation chemical track structure

The focus of our laboratory's investigation is to study the direct-type DNA damage mechanisms resulting from γ-ray and ion-beam radiation-induced free radical processes in DNA which lead to molecular damage important to cellular survival. This work compares the results of low LET (γ-) and high LET (ion-beam) radiation to develop a chemical track structure model for ion-beam radiation damage to DNA. Recent studies on protonation states of cytosine cation radicals in the N1-substituted cytosine derivatives in their ground state and 5-methylcytosine cation radicals in ground as well as in excited state are described. Our results exhibit a radical signature of excitations in 5-methylcytosine cation radical. Moreover, our recent theoretical studies elucidate the role of electron-induced reactions (low energy electrons (LEE), presolvated electrons (epre−), and aqueous (or, solvated) electrons (eaq−)). Finally DFT calculations of the ionization potentials of various sugar radicals show the relative reactivity of these species.

Comparison of the Effects of Melatonin, Tymoquinone and Amifostine on Peripheral Blood Cells During Total Body Irradiation in Rats

Ionizing radiation-induced free radicals causes functional and structural harmful effects through the cell membranes. Melatonin, a well-known powerful antioxidant, can play a role in the prevention of oxidative damage. It also has the ability to protect the genetic material of hematopoietic cells of mice from damaging effects of acute total body irradiation. The objective of this study was to assess the potential radioprotective effects of Melatonin, Thymoquinone (TQ) and Amifostine in peripheral blood cells of rats received total body irradiation. Thirty-eight adult Sprague-Dawley rats were divided into 5 groups. Group 1 (n=6) received no melatonin, amifostine, thymoquinone or irradiation (sham control group). Group 2 (n=8) received only total body irradiation (IR) of 6 Gy. Group 3 (n=8) received irradiation and melatonin (10 mg/kg, i.p., 30 min before IR), Group 4 (n=8) received irradiation plus amifostin (200 mg/kg 30 min. before IR) and Group 5 (n=8) received irradiation plus thymoquinone (10 mg/kg, i.p, 30 min before IR). One and a half hour following IR, blood samples were taken. Leukocytes, thrombocytes and erythrocytes counts were measured in all groups. Statistical analysis was performed using the SPSS (Statistical Package for Social Science; Windows version 16.0) packed program. The statistical comparison of results has been performed by using paired samples Student’s t-test. In preventing irradiation induced leukopenia and thrombocytopenia, Thymoquinone and Amifostine were as effective as melatonin. Tymoquinone and amifostine protected leukocyte and thrombocyte count against irradiation. There was no significant difference in erythrocyte count (Table).Poster Viewing Abstracts 3353; Table 1Leucocyte and Thrombocyte and Erythrocyte Counts in All GroupsGroupsLeucocyte (x103/uL)Thrombocyte (x103/uL)Erythrocyte (106/uL)Sham control (1)10,77±1,42*525,140±86,08†8,398±0,115Irradiation (2)7,93±0,91261,160±45,507,928±0,760Melatonin plus irradiation (3)10,37±1,58*516,420±128,41#9,682±0,160Amifostine plus irradiation (4)10,15±3,52*444,660±71,36†8,630±0,133Timoquinone plus irradiation (5)12,58±2,14*470,600±88,72#9,338±0,207* p<0.05; with respect to irradiation, by Student’s t-test. †p = 0.001; with respect to irradiation, by Student’s t-test. # p<0.01; with respect to irradiation, by Student’s t-test. Open table in a new tab * p<0.05; with respect to irradiation, by Student’s t-test. †p = 0.001; with respect to irradiation, by Student’s t-test. # p<0.01; with respect to irradiation, by Student’s t-test. Our results suggest that Melatonin, TQ and Amifostine administration prior to radiation prevents radiation damage on peripheral blood cells. This radioprotection is achieved by their ability as a scavenger for free radicals generated by ionizing radiation acts probably as a growth factor, especially for granulocytes in bone marrow as Melatonin.