Radiolysis Method Research Articles

Aggregation of Albumins under Reductive Radical Stress.

The reactions of radicals with human serum albumin (HSA) under reductive stress conditions were studied using pulse radiolysis and photochemical methods. It was proved that irradiation of HSA solutions under reductive stress conditions results in the formation of stable protein aggregates. HSA aggregates induced by ionizing radiation are characterized by unique emission, different from the UV emission of non-irradiated solutions. The comparison of transient absorption spectra and the reactivity of hydrated electrons (eaq-) with amino acids or HSA suggests that electron attachment to disulfide bonds is responsible for the transient spectrum recorded in the case of albumin solutions. The reactions of eaq- and CO2•- with HSA lead to the formation of the same products. Recombination of sulfur-centered radicals plays a crucial role in the generation of HSA nanoparticles, which are stabilized by intermolecular disulfide bonds. The process of creating disulfide bridges under the influence of ionizing radiation is a promising method for the synthesis of biocompatible protein nanostructures for medical applications. Our Raman spectroscopy studies indicate strong modification of disulfide bonds and confirm the aggregation of albumins as well. Low-temperature measurements indicate the possibility of electron tunneling through the HSA protein structure to specific CyS-SCy bridges. The current study showed that the efficiency of HSA aggregation depends on two main factors: dose rate (number of pulses per unit time in the case of pulse radiolysis) and the temperature of the irradiated solution.

Effects of acid generator anions on radiation-induced decomposition and dissolution kinetics of chemically amplified resists

Chemically amplified resists (CARs) are widely used in lithography for manufacturing semiconductor devices. To reduce the occurrence of stochastic defects in CARs, increased acid generator concentration is required. In this study, we investigated the effects of acid generator anions on the radiation-induced decomposition of acid generators using electron pulse radiolysis and γ-radiolysis methods. Their effects on the dissolution dynamics of poly(4-hydroxystyrene) (PHS) films were also investigated using contact angle measurement and quartz crystal microbalance methods. Triphenylsulfonium trifluoromethanesulfonate, triphenylsulfonium nonafluoro-1-butanesulfonate, triphenylsulfonium 4-toluenesulfonate, and triphenylsulfonium salicylate, were used as acid generators or photodecomposable quenchers. The anions showed minimal effect on the decomposition of the acid generators and photodecomposable quenchers; however, they influenced the surface free energy, dissolution kinetics of the PHS films, and water penetration into the PHS films. In particular, the effect of salicylate on the dissolution kinetics of PHS films is significant.

Sustainable Development in Dye Waste Managemen : A Comparative Study on the Effectiveness of Adsorption and γ-Radiolysis

Pyrromethene 567 (PM567), a BODIPY class of dye; is widely used in medicine, chemistry, material science, and high-power dye lasers. During its use, PM567 dye waste is generated in ethanol solvent which needs to be treated before its disposal. In our study, we -radiolysis, an advanced oxidation process (AOP), and adsorption, a simple and easy option. Interestingly, -radiolysis were not efficient for dye effluent treatment in organic solvents. This inefficiency was attributed to competing reactions leading to the scavenging of dye-degrading radicals. -dose rate (3.5 kGy) feasible in the system; 62% is the maximum removal efficiency achieved by this method. For a comparison, we also investigated the adsorption efficiency of PM567 dye from ethanol solvent using commercially available adsorbents. Among these, powdered activated carbon (PAC) demonstrated the highest removal efficiency, reaching 95%, much higher than that of -radiolysis method. In line with the pursuit of sustainable development, we synthesized granular activated carbons (AC1, AC2, AC3) from coconut shells, a lignocellulosic biowaste. The characterization of these carbons revealed that AC3, with a higher iodine value and CCl4 activity, possessed a systematic pore structure (SEM analysis), a larger specific surface area (1708 m2 .g-1), and a higher micro-pore volume (0.61 cc.g-1). AC3 hence, emerged as the most effective adsorbent, achieving 95% efficiency comparable to PAC.

Developing non-radioactive, radical methods to screen for radiolytic stability.

Radiolytically generated radicals cause degradation of nutrients in food, materials in satellites and solar cells, and human health. Radiation effects are studied using gamma radiolysis, a low-throughput, high-cost, and low-accessibility method. We developed a higher-throughput, low-cost, non-radioactive, radical assay that produces radicals similar to those generated in gamma radiolysis and examined monoamide degradation. Our radical assay results correspond to those from gamma irradiation in both monoamide stability and decomposition products, establishing this radical assay as a proof-of-concept screening tool for radiolytic stability.

Recovery of Zn(II) from Simulated Liquid Waste Using Poly(Vinyl Alcohol-Acrylamide) Synthesized by Gamma Radiolysis Method

Recovery of Zn(II) from Simulated Liquid Waste Using Poly(Vinyl Alcohol-Acrylamide) Synthesized by Gamma Radiolysis Method

Unveiling the Intimate Mechanism of the Crocin Antioxidant Properties by Radiolytic Analysis and Molecular Simulations.

The successive steps of the oxidation mechanism of crocin, a major compound of saffron, by the free OH• radical are investigated by pulse radiolysis, steady-state (gamma) radiolysis methods, and molecular simulations. The optical absorption properties of the transient species and their reaction rate constants are determined. The absorption spectrum of the oxidized radical of crocin resulting from the H-abstraction presents a maximum of 678 nm and a band of 441 nm, almost as intense as that of crocin. The spectrum of the covalent dimer of this radical contains an intense band at 441 nm and a weaker band at 330 nm. The final oxidized crocin, issued from radical disproportionation, absorbs weaker with a maximum of 330 nm. The molecular simulation results suggest that the OH• radical is electrostatically attracted by the terminal sugar and is scavenged predominantly by the neighbor methyl site of the polyene chain as in a sugar-driven mechanism. Based on detailed experimental and theoretical investigations, the antioxidant properties of crocin are highlighted.

One-pot gamma radiolysis synthesis of a graphene oxide-supported cobalt oxyhydroxide electrocatalyst for oxygen reduction reaction

In this work, high-performance non-platinum group metal (non-PGM) electrocatalysts for oxygen reduction reaction (ORR) are synthesized from graphene oxide-supported cobalt oxyhydroxide nanoparticles via a one-pot gamma radiolysis method. Investigations are conducted into how cobalt precursor concentration and the amount of gamma radiation affect the electrocatalysts' ability to perform oxygen reduction reactions as well as their physicochemical characteristics. Results show that the electrocatalyst prepared with the 0.1 M cobalt precursor and gamma radiation dose of 25 kGy has an advantage over the other samples in displaying good oxygen reduction activity. The characterization results of the synthesized electrocatalyst obtained through field-emission scanning electron microscopy–energy dispersive spectroscopy and X-ray diffraction combined with Rietveld refinement confirm the presence of nanosized cobalt oxyhydroxide particles that are evenly distributed on the surface of graphene oxide. ORR results show that the electrocatalyst has an onset potential of 0.90 V (vs. the reversible hydrogen electrode or RHE), a half-wave potential of 0.75 V (vs. RHE), a low peroxide yield of 7.08%, and an electron transfer number of 3.86, indicating a four-electron transfer path-way in the ORR process. This work provides an alternative facile means to mass-produce competitive non-PGM ORR electrocatalysts for fuel cell applications.

Intramolecular electron transfer from biopterin to FeII-O2 complex in nitric oxide synthases occurs at very different rates between bacterial and mammalian enzymes: Direct observation of a catalytically active intermediate

Nitric oxide synthase (NOS) is a cytochrome P450-type mono‑oxygenase that catalyzes the oxidation of L-arginine to nitric oxide. We previously observed that intramolecular electron transfer from biopterin to Fe2+-O2 in Deinococcus radiodurans NOS (DrNOS) using pulse radiolysis. However, the rate of electron transfer in DrNOS (2.2 × 103 s−1) contrasts with a reported corresponding rate (11 s−1) in a mammalian NOS determined using rapid freeze-quench (RFQ) EPR. We applied pulse radiolysis to Bacillus subtilis NOS (bsNOS) and to rat neural NOS oxygenase domain NOS (mNOS). Concurrently, RFQ EPR was used to trap a pterin radical during single-turnover enzyme reactions of the enzymes. By using the pulse radiolysis method, hydrated electrons (eaq−) reduced the heme iron of NOS enzymes. Subsequently, ferrous heme reacted with O2 to form a Fe2+-O2 intermediate. In the presence of pterin, the intermediate of bsNOS was found to convert to other intermediate in the time range of milliseconds. A similar process was determined to have occurred after pulse radiolysis of the pterin-bound mNOS, though the rate was much slower. The intermediates of all of the NOS enzymes further converted to the original ferric form in the time range of seconds. When using the RFQ method, pterin radicals were formed very rapidly in both DrNOS and bsNOS in the time range of milliseconds. In contrast, the pterin radical in mNOS was observed to form slowly, at a rate of ∼20 s−1.

Spontaneous and Ionizing Radiation-Induced Aggregation of Human Serum Albumin: Dityrosine as a Fluorescent Probe.

The use of spectroscopic techniques has shown that human serum albumin (HSA) undergoes reversible self-aggregation through protein–protein interactions. It ensures the subsequent overlapping of electron clouds along with the stiffening of the conformation of the interpenetrating network of amino acids of adjacent HSA molecules. The HSA oxidation process related to the transfer of one electron was investigated by pulse radiolysis and photochemical methods. It has been shown that the irradiation of HSA solutions under oxidative stress conditions results in the formation of stable protein aggregates. The HSA aggregates induced by ionizing radiation are characterized by specific fluorescence compared to the emission of non-irradiated solutions. We assume that HSA dimers are mainly responsible for the new emission. Dityrosine produced by the intermolecular recombination of protein tyrosine radicals as a result of radiolysis of an aqueous solution of the protein is the main cause of HSA aggregation by cross-linking. Analysis of the oxidation process of HSA confirmed that the reaction of mild oxidants (, , ) with albumin leads to the formation of covalent bonds between tyrosine residues. In the case of •OH radicals and partly, , species other than DT are formed. The light emission of this species is similar to the emission of self-associated HSA.

Multiplex Chemical Labeling of Amino Acids for Protein Footprinting Structure Assessment.

Protein footprinting with mass spectrometry is an established structural biology technique for mapping solvent accessibility and assessing molecular-level interactions of proteins. In hydroxyl radical protein footprinting (HRPF), hydroxyl (OH) radicals generated by water radiolysis or other methods covalently label protein side chains. Because of the wide dynamic range of OH reactivity, not all side chains are easily detected in a single experiment. Novel reagent development and the use of radical chain reactions for labeling, including trifluoromethyl radicals, is a potential approach to normalize the labeling across a diverse set of residues. HRPF in the presence of a trifluoromethylation reagent under the right conditions could provide a "one-pot" reaction for multiplex labeling of protein side chains. Toward this goal, we have systematically evaluated amino acid labeling with the recently investigated Langlois' reagent (LR) activated by X-ray-mediated water radiolysis, followed by three different mass spectrometry methods. We compared the reactivity of CF3 and OH radical labeling for all 20 protein side chains in a competition-free environment. We found that all 20 amino acids exhibited CF3 or OH labeling in LR. Our investigations provide the evidence and knowledge set to perfect hydroxyl radical-activated trifluoromethyl chemistry as "one-pot" reaction for multiplex labeling of protein side chains to achieve higher resolution in HRPF.

Non covalent bonds in some bromo-substituted aromatic anions

Four bromo-substituted derivatives of naphthalene and anthracene were studied by means of Dissociative Electron Attachment Spectroscopy. Long-lived molecular anions with lifetimes ranging from 25 to 144 μs were observed in all molecules under investigation. In all cases molecular anion fragmentation is poor: only the Brˉ, [M-Br]ˉ and (with very small intensity) [M-H]ˉ species were observed, except for the case of 9,10-Br2-anthracene. It was shown that the presence of long-lived molecular anions in 1-Br- and 2-Br-naphthalene (τa=26 μs and τa=25 μs, respectively) does not contradict the fact that their dissociation rates measured by the pulse radiolysis method are fairly large (1.0 ×1010 s−1 and 1.8 ×1010 s−1, respectively). Scanning the potential energy surface of anions in the process of positioning a bromine anion around a polarized aromatic radical revealed the presence of a series of local minima separated by potential barriers. It is inferred that the most energetically favorable structures of the 1-Br- and 2-Br-naphthalene anions should be interpreted as complexes of the bromide anion bound to the polarized aromatic radical by non-covalent Br--H bonds. Similar local minima were found in the 9-Br- and 9,10-Br2-anthracene anions, but the energies of these structures are significantly higher than those of the “standard” anionic structures with a C-Br bond length of ~1.93 Å. The EAas obtained with DFT CAM-B3LYP/6–311 +G(d,p) calculations are in acceptable agreement with the estimates made within the framework of the simple Arrhenius model from the lifetimes of molecular anions.

Radiolysis Studies of Oxidation and Nitration of Tyrosine and Some Other Biological Targets by Peroxynitrite-Derived Radicals.

The widespread interest in free radicals in biology extends far beyond the effects of ionizing radiation, with recent attention largely focusing on reactions of free radicals derived from peroxynitrite (i.e., hydroxyl, nitrogen dioxide, and carbonate radicals). These radicals can easily be generated individually by reactions of radiolytically-produced radicals in aqueous solutions and their reactions can be monitored either in real time or by analysis of products. This review first describes the general principles of selective radical generation by radiolysis, the yields of individual species, the advantages and limitations of either pulsed or continuous radiolysis, and the quantitation of oxidizing power of radicals by electrode potentials. Some key reactions of peroxynitrite-derived radicals with potential biological targets are then discussed, including the characterization of reactions of tyrosine with a model alkoxyl radical, reactions of tyrosyl radicals with nitric oxide, and routes to nitrotyrosine formation. This is followed by a brief outline of studies involving the reactions of peroxynitrite-derived radicals with lipoic acid/dihydrolipoic acid, hydrogen sulphide, and the metal chelator desferrioxamine. For biological diagnostic probes such as ‘spin traps’ to be used with confidence, their reactivities with radical species have to be characterized, and the application of radiolysis methods in this context is also illustrated.

Non-covalent anion structures in dissociative electron attachment to some brominated biphenyls.

The present work combines experiment and theory to reveal the behavior of bromo-substituted-biphenyls after an electron attachment. We experimentally determine anion lifetimes using an electron attachment-magnetic sector mass spectrometer instrument. Branching ratios of dissociative electron attachment fragments on longer timescales are determined using the electron attachment-quadrupole mass spectrometer instrument. In all cases, fragmentation is low: Only the Br- and [M-Br]- ions are detected, and [M-H]- is observed only in the case of 4-Br-biphenyl and parent anion lifetimes as long as 165 µs are observed. Such lifetimes are contradictory to the dissociation rates of 2- and 4-bromobiphenyl, as measured by the pulse radiolysis method to be 3.2 × 1010 and >5 × 1010s-1, respectively. The discrepancy is plausibly explained by our calculation of the potential energy surface of the dissociating anion. Isolated in vacuum, the bromide anion can orbit the polarized aromatic radical at a long distance. A series of local minima on the potential energy surface allows for a roaming mechanism prolonging the detection time of such weakly bound complex anions. The present results illuminate the behavior recently observed in a series of bromo-substituted compounds of biological as well as technological relevance.

Selectively Targeting Tumor Hypoxia With the Hypoxia-Activated Prodrug CP-506.

Hypoxia-activated prodrugs (HAP) are a promising class of antineoplastic agents that can selectively eliminate hypoxic tumor cells. This study evaluates the hypoxia-selectivity and antitumor activity of CP-506, a DNA alkylating HAP with favorable pharmacologic properties. Stoichiometry of reduction, one-electron affinity, and back-oxidation rate of CP-506 were characterized by fast-reaction radiolytic methods with observed parameters fulfilling requirements for oxygen-sensitive bioactivation. Net reduction, metabolism, and cytotoxicity of CP-506 were maximally inhibited at oxygen concentrations above 1 μmol/L (0.1% O2). CP-506 demonstrated cytotoxicity selectively in hypoxic 2D and 3D cell cultures with normoxic/anoxic IC50 ratios up to 203. Complete resistance to aerobic (two-electron) metabolism by aldo-keto reductase 1C3 was confirmed through gain-of-function studies while retention of hypoxic (one-electron) bioactivation by various diflavin oxidoreductases was also demonstrated. In vivo, the antitumor effects of CP-506 were selective for hypoxic tumor cells and causally related to tumor oxygenation. CP-506 effectively decreased the hypoxic fraction and inhibited growth of a wide range of hypoxic xenografts. A multivariate regression analysis revealed baseline tumor hypoxia and in vitro sensitivity to CP-506 were significantly correlated with treatment response. Our results demonstrate that CP-506 selectively targets hypoxic tumor cells and has broad antitumor activity. Our data indicate that tumor hypoxia and cellular sensitivity to CP-506 are strong determinants of the antitumor effects of CP-506.

Study on radical dianions of carboxylates used as ligands of metal oxide nanocluster resists

Metal oxide nanocluster resists have recently attracted considerable attention for use in extreme ultraviolet lithography. In this study, radiation-induced reactions of carboxylic acids used as the ligands of metal oxide nanocluster resists were investigated using a pulse radiolysis method. Upon the irradiation of the aqueous solutions of calboxylic acids with an electron beam, radical dianions of carboxylates were generated under the basic condition. From the comparison between pulse radiolyses under acidic and basic conditions, the kinetics of the radical dianions was clarified. For aromatic carboxylates, anion radicals of carboxylic acids were generated through the reaction of their dianions with H2O. For unsaturated carboxylates, their radicals were generated through the reaction of their radical dianions with H2O. The carboxylic anions and vinyl groups were protonated for dianions of aromatic and unsaturated carboxylates, respectively. The proton dynamics control is important for the stable performance of metal oxide nanocluster resists.

Homology modeling and molecular docking study of biogenic Muga silk nanoparticles as putative drug-binding system.

The recent emergence of natural biopolymers as drug delivery vehicles is attributed to their biodegradability and less systemic toxicity. Muga silk nanoparticles were prepared using microwave radiolysis method and were characterized by Fourier transform infrared spectroscopy, circular dichroism, X-ray diffraction and transmission electron microscopy. To find the applicability in the drug delivery system of these nanoparticle and to know the binding site(s), a computational study was carried out. The structure of the Muga protein is predicted using homology modeling, which is further used for molecular docking. The in silico molecular docking between the Muga silk nanoparticles and three United States Food and Drug Administration-approved model drugs of doxorubicin, remdesivir and dexamethasone was performed. The binding capabilities and binding energy of the Muga silk proteins with these drugs are determined. The basic idea of the active site and the residues involved in the binding of the drugs/ligands is also studied. Doxorubicin showed the highest binding affinity of -8.7kcal/mol and that of the remdesivir and dexamethasone are found to be -7.2 and -7.9 kcal/mol, respectively. Such high binding affinity(ies) would help for slow drug release kinetics and the other two drugs can be loaded when the requirement is for sustained drug release. The data were also validated using the UV-vis. spectroscopy.

Photo-electrochemical Property of Microwave Synthesized Muga Silk Nanoparticles/ZnO/ITO/PET Structure

Muga silk nanoparticles (MSNP) in the size range of 28–142 nm were synthesized via microwave-assisted radiolysis method. Interestingly, these nanoparticles acquire cuboidal shape and exhibit photoresponsive property, under white light illumination of power 56 mW/cm2 in a photo-electrochemical cell, when fabricated in MSNP/ZnO/ITO/PET flexible device structure. The device was found to be active under visible light illumination and gives photoresponsivity of 0.119 µA/W with the rise/decay time of 0.9/0.6 s, respectively. Such photoresponse of MSNP could serve as an optoelectric biomolecule, which would find its application for next-generation wearable and implantable optoelectronic devices.

Secondary structural analysis of non-mulberry silk fibroin nanoparticles synthesized by using microwave and acetone method

The 3D structure analysis for Muga silk protein was predicted through homology modeling and Ramachandran plot with the determination of quality index for Stereo/packing and 3D quality index. Silk Nanoparticles were synthesized using conventional desolvation and microwave-assisted radiolysis method from Muga silk fibroin. The secondary structure evolution due to two different synthesis methods was investigated using FTIR and Circular Dichroism (CD) spectroscopy. The microwave synthesized nanoparticles showed enhanced β-sheet content than desolvation synthesized nanoparticles. The conformational changes of Muga silk fibroin protein to nanoparticle followed an ordered transition from random coil to α-helix then from α-helix to β-turn and from β-turn to β-sheets where α-helix and β-turn are the intermediate forms before getting stabilized to the metastable β-sheets structure. The thermodynamics involved in secondary structure evolution was studied from CD analysis and activation energy involved in the formation of the secondary structure was determined. Communicated by Ramaswamy H. Sarma

Spectroscopic analysis of Muga silk nanoparticles synthesized by microwave method.

Muga silk nanoparticles (MSNP) were synthesized using a microwave-assisted radiolysis method. The effect of microwave on the Muga protein secondary structures was analyzed. The evolution of the secondary structure from random coils to the β-sheets was determined by using FTIR, circular dichroism and X-ray diffraction techniques. The results showed that Muga silk fibroin protein contained the primary structure in silk-I state. When the protein was irradiated with microwave, nanoparticle synthesis was possible having silk-II state imparting crystallinity. The silk nanoparticles were characterized by a particle size analyzer and found to be of ~240nm in size. The optical properties of these nanoparticles were studied by UV-vis. spectroscopy and photoluminescence. For studying thermal properties, differential scanning calorimetry was performed that revealed early glass transition, which could be attributed to the presence of water and proteins. It also revealed that nanoparticles are thermally stable. Such studies are important for understanding more about the MSNP and would be beneficial for their further wide applications.

Reactions of radicals with PERK kinase inhibitor and its analogue under oxidative and reductive stress conditions. Pulse radiolysis study

The scavenging of primary free radicals generated during radiolysis of water (eaq−,•OH, •H) and CO2•‒ (reducing radical) or N3• (oxidizing radical) by PERK inhibitor, AMD (3-acetyl-6-methylheptane-2,4-dione) and APD (3-acetyl-2,4-pentanedione) has been studied with details. AMD is a low molecular weight inhibitor of the PERK-dependent antiproliferative signaling pathway and constitutes the foundation of an innovative therapeutic strategy in the treatment of cancer diseases. The applied compounds exist in the three different forms depending on pH of aqueous solution: ketone, enol and enolate form. The effect of pH on the absorption spectra of AMD and APD has been studied and the value of pKa for the keto – enol equilibrium (conversion of the ketone to enol) and pKa for the enol – enolate form were calculated. Redox processes studied by pulse radiolysis method were more effective at neutral or alkaline pH than in an acidic solution. The influence of human serum albumin (HSA) on the oxidation and reduction process of examined compounds was studied. The kinetics of radicals reaction with tested compounds has been compared for neat buffer solution and systems containing HSA. The results indicate competitive electron scavenging by studied scavengers and protein.