Selectively Addressable Photogenerated Spin Qubit Pairs in DNA Hairpins.

Photoinduced electron transfer can produce radical pairs having two quantum entangled electron spins that can act as spin qubits in quantum information applications. Manipulation of these spin qubits requires selective addressing of each spin using microwave pulses. In this work, photogenerated spin qubit pairs are prepared within chromophore-modified DNA hairpins with varying spin qubit distances, and are probed using transient EPR spectroscopy. By performing pulse-EPR measurements on the shortest hairpin, selective addressing of each spin qubit comprising the pair is demonstrated. Furthermore, these spin qubit pairs have coherence times of more than 4 µs, which provides a comfortable time window for performing complex spin manipulations for quantum information applications. The applicability of these DNA-based photogenerated two-qubit systems is discussed in the context of quantum gate operations, specifically the controlled-NOT gate.

Effect of Infrared Low-Intensity Laser Irradiation on Lipid Peroxidation under Conditions of Experimental Circulatory Hypoxia of Visual Analyzer.

The physiological stress modeled by circulatory hypoxia activates LPO processes in various tissues. In posthypoxic period, the infrared low-intensity laser irradiation significantly decreased the chemiluminescence parameters in blood plasma, normalized the retinal levels of diene and triene conjugates, and decreased MDA in the rat brain attesting to the correcting effect of this irradiation during various types of physiological stresses.

A Semiconducting Conjugated Radical Polymer: Ambipolar Redox Activity and Faraday Effect.

Investigations of magnetism in electronically coupled polyradicals have largely focused on applications in photonic and magnetic devices, wherein radical polymers were found to possess molecularly tunable and cooperative magnetic properties. Radical polymers with nonconjugated insulating backbones have been intensively investigated previously; however the integration of radical species into conducting polymer backbones is at an early stage. We report herein 1,3-bisdiphenylene-2-phenylallyl (BDPA)-based conjugated radical polymers that display ambipolar redox activities and conductivities. Moreover, these radical polymers were demonstrated to be promising magneto-optic (MO) materials with Faraday rotations wherein the sign is modulated by the radical character and display absolute Verdet constants up to (2.80 ± 0.84) × 104 deg T-1 m-1 at 532 nm. These values rival the performance of the present-day commercial inorganic MO materials (e.g., terbium gallium garnet, V = -1.0 × 104 deg T-1 m-1 at 532 nm). The structure property studies detailed herein reveal the promise of multifunctional conjugated radical polymers as responsive MO materials.

Adenine radicals generated in alternating AT duplexes by direct absorption of low-energy UV radiation.

There is increasing evidence that the direct absorption of photons with energies that are lower than the ionization potential of nucleobases may result in oxidative damage to DNA. The present work, which combines nanosecond transient absorption spectroscopy and quantum mechanical calculations, studies this process in alternating adenine-thymine duplexes (AT)n. We show that the one-photon ionization quantum yield of (AT)10 at 266 nm (4.66 eV) is (1.5 ± 0.3) × 10-3. According to our PCM/TD-DFT calculations carried out on model duplexes composed of two base pairs, (AT)1 and (TA)1, simultaneous base pairing and stacking does not induce important changes in the absorption spectra of the adenine radical cation and deprotonated radical. The adenine radicals, thus identified in the time-resolved spectra, disappear with a lifetime of 2.5 ms, giving rise to a reaction product that absorbs at 350 nm. In parallel, the fingerprint of reaction intermediates other than radicals, formed directly from singlet excited states and assigned to AT/TA dimers, is detected at shorter wavelengths. PCM/TD-DFT calculations are carried out to map the pathways leading to such species and to characterize their absorption spectra; we find that, in addition to the path leading to the well-known TA* photoproduct, an AT photo-dimerization path may be operative in duplexes.

DNA Damage Emanating From a Neutral Purine Radical Reveals the Sequence Dependent Convergence of the Direct and Indirect Effects of γ-Radiolysis.

Nucleobase radicals are the major intermediates generated by the direct (e.g., dA•+) and indirect (e.g., dA•) effects of γ-radiolysis. dA• was independently generated in DNA for the first time. The dA•+/dA• equilibrium, and consequently the reactivity in DNA, is significantly shifted toward the radical cation by a flanking dA. Tandem lesions emanating from dA• are the major products when the reactive intermediate is flanked by a 5'-dGT. In contrast, when dA• is flanked by dA, the increased dA•+ pKa results in DNA damage arising from hole transfer. This is the first demonstration that sequence effects lead to the intersection of the direct and indirect effects of ionizing radiation.

Photo-Induced Atom-Transfer Radical Reactions Using Charge-Transfer Complex between Iodine and Tertiary Amine.

In the presence of charge-transfer complexes between iodine and tertiary amines, the aqueous-medium atom-transfer radical reactions proceeded under visible light irradiation without the typical photocatalysts.

Mechanistic study of photo-oxidation of Bisphenol-A (BPA) with hydrogen peroxide (H2O2) and sodium persulfate (SPS).

The removal of Bisphenol-A (BPA) from contaminated water using advanced oxidation methods such as UV-C assisted oxidation by hydrogen peroxide (H2O2) and sodium persulfate (SPS) has been reported by the authors earlier (Sharma et al., 2015a). In the present study, the authors report the removal of BPA from aqueous solution by the above two methods and its degradation mechanism. UV-C light (254 nm wavelength, 40 W power) was applied to BPA contaminated water at natural pH (pHN) under room temperature conditions. Experiments were carried out with the initial BPA concentration in the range of 0.04 mM-0.31 mM and the oxidant/BPA molar ratio in the range of 294:1-38:1 for UV-C/H2O2 and 31.5-4.06:1 for UV-C/SPS systems. The removal of BPA enhanced with decreasing BPA concentration. The total organic carbon also decreased with the UV-C irradiation time under optimum conditions ([H2O2]0 = 11.76 mM; [SPS]0 = 1.26 mM; temperature (29 ± 3 °C). Competition of BPA for reaction with HO or [Formula: see text] radicals at its higher concentrations results in a decrease in the removal of BPA. The intermediates with smaller and higher molecular weights than that of BPA were found in the treated water. Based on GC-MS and FTIR spectra of the reaction mixture, the formation of hydroxylated by-products testified the HO mediated oxidation pathway in the BPA degradation, while the formation of quinones and phenoxy phenols pointed to the [Formula: see text] dominating pathway through the formation of hydroxycyclohexadienyl (HCHD) and BPA phenoxyl radicals. The main route of BPA degradation is the hydroxylation followed by dehydration, coupling and ring opening reactions.

EFFECT OF MICROWAVE POWER ON SHAPE OF EPR SPECTRA--APPLICATION TO EXAMINATION OF COMPLEX FREE RADICAL SYSTEM IN THERMALLY STERILIZED ACIDUM BORICUM.

Complex free radical system in thermally sterilized acidum boricum (AB) was studied. Acidum boricum was sterilized at temperatures and times given by pharmaceutical norms: 160 degrees C and 120 min, 170 degrees C and 60 min and 180 degrees C and 30 min. The advanced spectroscopic tests were performed. The EPR spectra of free radicals were measured as the first derivatives with microwaves of 9.3 GHz frequency and magnetic modulation of 100 kHz. The Polish X-band electron paramagnetic resonance spectrometer of Radiopan (Poznan) was used. EPR lines were not observed for the nonheated AB. The broad EPR asymmetric lines were obtained for all the heated AB samples. The influence of microwave power in the range of 2.2-70 mW on the shape of EPR spectra of the heated drug samples was tested. The following asymmetry parameters: A1/A2, A1-A2, B1/B2, and B1-B2, were analyzed. The changes of these parameters with microwave power were observed. The strong dependence of shape and its parameters on microwave power proved the complex character of free radical system in thermally sterilized AB. Changes of microwave power during the detection of EPR spectra indicated complex character of free radicals in AB sterilized in hot air under all the tested conditions. Thermolysis, interactions between free radicals and interactions of free radicals with oxygen may be responsible for the complex free radicals system in thermally treated AB. Usefulness of continuous microwave saturation of EPR lines and shape analysis to examine free radicals in thermally sterilized drugs was confirmed.

Density of hydroxyl radicals generated in an aqueous solution by irradiating carbon-ion beam.

The density of hydroxyl radicals (·OH) produced in aqueous samples by exposure to X-ray or carbon-ion beams was investigated. The generation of ·OH was detected by the electron paramagnetic resonance (EPR) spin-trapping technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent. When the concentration of DMPO is in excess of the generated ·OH, the production of DMPO-OH (spin-trapped ·OH) should be saturated. Reaction mixtures containing several concentrations (0.5-1685 mM) of DMPO were then irradiated by a 32 Gy 290 MeV carbon-ion beam (C290-beam) or X-ray. C290-beam irradiation was performed at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, National Institute of Radiological Sciences, Chiba, Japan), applying different linear energy transfers (LET) (20-169 keV/µm). The amount of DMPO-OH in the irradiated samples was detected by EPR spectroscopy. The generation of DMPO-OH increased with the concentration of initial DMPO, displayed a shoulder around 3.3 mM DMPO, and reached a plateau. This plateau suggests that the generated ·OH were completely trapped. Another linear increase in DMPO-OH measured in solutions with higher DMPO concentrations suggested very dense ·OH generation (>1.7 M). Generation of ·OH is expected to be localized on the track of the radiation beam, because the maximum concentration of measured DMPO-OH was 40 µM. These results suggested that both sparse (≈3.3 mM) and dense (>1.7 M) ·OH generation occurred in the irradiated samples. The percentage of dense ·OH generation increased with increasing LET. Different types of dense ·OH generation may be expected for X-ray and C290-beams.

A Visible-Light-Mediated Radical Smiles Rearrangement and its Application to the Synthesis of a Difluoro-Substituted Spirocyclic ORL-1 Antagonist.

A visible-light-mediated radical Smiles rearrangement has been developed to address the challenging synthesis of the gem-difluoro group present in an opioid receptor-like 1 (ORL-1) antagonist that is currently in development for the treatment of depression and/or obesity. This method enables the direct and efficient introduction of the difluoroethanol motif into a range of aryl and heteroaryl systems, representing a new disconnection for the synthesis of this versatile moiety. When applied to the target compound, the photochemical step could be conducted on 15 g scale using industrially relevant [Ru(bpy)3Cl2] catalyst loadings of 0.01 mol %. This transformation is part of an overall five-step route to the antagonist that compares favorably to the current synthetic sequence and demonstrates, in this specific case, a clear strategic benefit of photocatalysis.

Visible-light-promoted iminyl-radical formation from acyl oximes: a unified approach to pyridines, quinolines, and phenanthridines.

A unified strategy involving visible-light-induced iminyl-radical formation has been established for the construction of pyridines, quinolines, and phenanthridines from acyl oximes. With fac-[Ir(ppy)3 ] as a photoredox catalyst, the acyl oximes were converted by 1 e(-) reduction into iminyl radical intermediates, which then underwent intramolecular homolytic aromatic substitution (HAS) to give the N-containing arenes. These reactions proceeded with a broad range of substrates at room temperature in high yield. This strategy of visible-light-induced iminyl-radical formation was successfully applied to a five-step concise synthesis of benzo[c]phenanthridine alkaloids.

Highly efficient exciplex formation via radical ion pair recombination in X-irradiated alkane solutions for luminophores with short fluorescence lifetimes.

X-irradiation of alkane solutions of N,N-dimethylaniline with various organic luminophores produces characteristic emission bands ascribed to the corresponding exciplexes. In contrast to optical generation, which requires diffusion-controlled quenching of excited states, an additional channel of exciplex formation via irreversible recombination of radical ion pairs is operative here, which produces exciplexes in solution with high efficiency even for p-terphenyl and diphenylacetylene having fluorescence decay times of 0.95 ns and 8 ps, respectively. The exciplex emission band is sensitive to an external magnetic field and exerts a very large observed magnetic field effect of up to 20%, the maximum possible value under the conditions of the described experiment.

Pressure effects on the radical-radical recombination reaction of photochromic bridged imidazole dimers.

The bridged imidazole dimers are some of the attractive fast photochromic compounds which have potential applications to the ophthalmic lenses, real-time hologram and molecular machines. The strategy for expanding their photochromic properties such as the colour variation and tuning the decolouration rates has been vigorously investigated, but the insight into the structural changes along the photochromic reactions has not been demonstrated in detail. Here, we demonstrated the pressure dependence of the radical-radical recombination reaction of the bridged imidazole dimers. The radical-radical interaction can be controlled by applying high pressure. Our results give fundamental information about the molecular dynamics of the bridged imidazole dimers, leading to the development of new functional photochromic machines and pressure-sensitive photochromic materials.

[Free-radical reactions in Daphnia after low doses of γ-irradiation in vivo].

A violation of free-radical reactions has been found by the method of free-radical copolymerization in the two groups of Daphnia magna exposed to 100 and 1000 mGy of gamma-rays and their non-exposed first generation progeny. The method is based on a quantitative radiometric registration of the polymerization process that develops in the cells of a multicellular organism in tissue in proportion to the existing number of free radicals. The fact of the increased level of free radicals may be indicative of the hereditary transgenerational effect and the cause of lower survival of Daphnia in both generations. However, the effect of a reduced survival rate does not persist in the second generation, which can be explained by the effect of radiation on the embryos of the first generation after acute irradiation of parents.

[Influence of extremely low frequency magnetic field on total protein and -sh groups concentrations in liver homogenates]. / Wplyw pola magnetycznego ekstremalnie niskiej czestotliwosci na zawartosc bialka calkowitego oraz grup-SH w homogenatach watroby.

BACKGROUND: Free radicals are atoms, molecules or their fragments, whose excess leads to the development of oxidative stress, the cause of many neoplastic, neurodegenerative and inflammatory diseases, as well as aging of organisms. Industrial pollution, tobacco smoke, ionizing radiation, ultrasound and magnetic fields are the major exogenous sources of free radicals. The low frequency mag- netic field is commonly applied in physiotherapy. The aim of the present study was to evaluate the effect of extremely low frequency magnetic field (1L.F-MF) on the concentration ofsullhydryl groups (-SH) and proteins in liver tissues of experimental animals de- pending on the time of exposure to the field. MATERIAL AND METHODS: Twenty one Sprague-D)awley male rats, aged 3-4 months were randomly divided into 3 experimental groups (each containing 7 animals): controls (group I), the rats exposed to IEI.F-MF of 40 Hz, 7 mT (this kind of the ELF-MF is mostly used in magnetotherapy), 30 min/day for 2 weeks (group II) and the rats exposed to 40 Hz, 7 mT for 60 min/day for 2 weeks (group III). The concentrations of proteins and sulfhydryl groups in the liver tissues were determined after exposure to magnetic fields. RESULTS: Exposure to low magnetic field: 40 Hz, 7 mT for 30 min/day and 60 min/day for 2 weeks caused a significant increase in the concentration of-SH groups and total protein levels in the liver tissues. CONCLUSIONS: The study results suggest that exposure to magnetic fields leads to the development of adaptive mechanisms to maintain the balance in the body oxidation-reduction and in the case of the studied parameters does not depend on the time of exposure.

Computational model of radiation oxygen effect with Monte Carlo simulation: effects of antioxidants and peroxyl radicals.

PURPOSE: Oxygen plays a crucial role in radiation biology. Antioxidants and peroxyl radicals affect the oxygen effect greatly. This study aims to establish a computational model of the oxygen effect and explore the effect attributed to antioxidants and peroxyl radicals. MATERIALS AND METHODS: Oxygen-related reactions are added to our track-structure Monte Carlo code NASIC, including oxygen fixation, chemical repair by antioxidants and damage migration from base-derived peroxyl radicals. Then the code is used to simulate the DNA damage under various oxygen, antioxidant and damage migration rate conditions. The oxygen enhancement ratio(OER) is calculated quantifying by the number of double-strand breaks for each condition. The roles of antioxidants and peroxyl radicals are examined by manipulating the relevant parameters. RESULTS AND CONCLUSIONS: Our results indicate that antioxidants are capable of rapidly restoring DNA radicals through chemical reactions, which compete with natural and oxygen fixation processes. Additionally, antioxidants can react with peroxyl radicals derived from bases, thereby preventing the damage from migrating to DNA strands. By quantitatively accounting for the impact of peroxyl radicals and antioxidants on the OER curves, our study establishes a more precise and comprehensive model of the radiation oxygen effect.

The role of the PCM in reducing oxidative stress induced by radical initiated photoencapsulation of chondrocytes in poly(ethylene glycol) hydrogels.

OBJECTIVE: The objectives for this study were to determine whether radical initiated photopolymerizations typically employed for cell encapsulations lead to oxidative stress incurred by chondrocytes and whether the development of a pericellular matrix (PCM) decreases this oxidative stress and has longer-term benefits on chondrocyte function. METHODS: Freshly isolated bovine chondrocytes were encapsulated in poly(ethylene glycol) (PEG) hydrogels devoid of a PCM or with a PCM, confirmed by immunocytochemistry (IC), and cultured for up to 2 weeks. Reactive oxygen species (ROS) production and damage to cell membrane by lipid peroxidation were accomplished using carboxy-2,7-difluorodihydrofluorescein diacetate (carboxy-H(2)DFFDA) and by malondialdehyde (MDA) content, respectively. Gene expression and proteoglycan synthesis were analyzed using reverse transcription (RT)-quantitative PCR (qPCR) and (35)SO(4) incorporation, respectively. RESULTS: The photopolymerization reaction, which alone generates radicals and extracellular ROS, led to oxidative stress in chondrocytes evidenced by increased intracellular ROS and lipid peroxidation. The presence of a PCM decreased intracellular ROS and abrogated membrane lipid peroxidation, improved aggrecan, collagen II and collagen VI expression, and enhanced proteoglycan synthesis. CONCLUSIONS: The development of the PCM prior to photoencapsulation in PEG hydrogels reduces oxidative stress and improves chondrocyte anabolic activity. Our data suggest this reduction occurs by decreased ROS diffusion into the cell and decreased membrane damage. Our findings suggest that minimizing oxidative stress, such as through the presence of a PCM, may have long-term beneficial effects on tissue elaboration when employing photopolymerizations to encapsulate chondrocytes for cartilage tissue engineering applications.

Photolysis of recombinant human insulin in the solid state: formation of a dithiohemiacetal product at the C-terminal disulfide bond.

PURPOSE: Exposure of protein pharmaceuticals to light can result in chemical and physical modifications, potentially leading to loss of potency, aggregation, and/or immunogenicity. To correlate these potential consequences with molecular changes, the nature of photoproducts and their mechanisms of formation must be characterized. The present study focuses on the photochemical degradation of insulin in the solid state. METHODS: Solid insulin was characterized by solid-state NMR, polarized optical microscopy and scanning electron microscopy; various insulin preparations were exposed to UV light prior to product analysis by mass spectrometry. RESULTS: UV-exposure of solid human insulin results in photodissociation of the C-terminal intrachain disulfide bond, leading to formation of a CysS(•) thiyl radical pair which ultimately disproportionates into thiol and thioaldehyde species. The high reactivity of the thioaldehyde and proximity to the thiol allow the formation of a dithiohemiacetal structure. Dithiohemiacetal is formed during the UV-exposure of both crystalline and amorphous insulin. CONCLUSIONS: Dithiohemiacetals represent novel structures generated through the photochemical modification of disulfide bonds. This is the first time that such structure is identified during the photolysis of a protein in the solid state.

Carbon-centered radicals in γ-irradiated bone substituting biomaterials based on hydroxyapatite.

Gamma irradiated synthetic hydroxyapatite, bone substituting materials NanoBone(®) and HA Biocer were examined using EPR spectroscopy and compared with powdered human compact bone. In every case, radiation-induced carbon centered radicals were recorded, but their molecular structures and concentrations differed. In compact bone and synthetic hydroxyapatite the main signal assigned to the CO(2) (-) anion radical was stable, whereas the signal due to the CO(3) (3-) radical dominated in NanoBone(®) and HA Biocer just after irradiation. However, after a few days of storage of these samples, also a CO(2) (-) signal was recorded. The EPR study of irradiated compact bone and the synthetic graft materials suggest that their microscopic structures are different. In FT-IR spectra of NanoBone(®), HA Biocer and synthetic hydroxyapatite the HPO(4) (2-) and CO(3) (2-) in B-site groups are detected, whereas in compact bone signals due to collagen dominate.

X-Ray Diffraction and Multifrequency EPR Study of Radiation-Induced Room Temperature Stable Radicals in Octacalcium Phosphate.

Octacalcium phosphate (OCP) {Ca8H2(PO4)6×5H2O] has attracted increasing attention over the last decade as a transient intermediate to the biogenic apatite for bone engineering and in studies involving the processes of pathological calcification. In this work, OCP powders obtained by hydrolysis of dicalcium phosphate dehydrate were subjected to X- and γ-ray irradiation and studied by means of stationary and pulsed electron paramagnetic resonance at 9, 36 and 94 GHz microwave frequencies. Several types of paramagnetic centers were observed in the investigated samples. Their spectroscopic parameters (components of the g and hyperfine tensors) were determined. Based on the extracted parameters, the induced centers were ascribed to H0, CO33-, CO2- and nitrogen-centered (presumably NO32-) radicals. The spectroscopic parameters of the nitrogen-centered stable radical in OCP powders were found to be markedly different from those in hydroxyapatite. According to X-ray diffraction data, γ-ray irradiation allowed the phase composition of calcium phosphates to change; all minor phases with the exception of OCP and hydroxyapatite disappeared, while the OCP crystal lattice parameters changed after irradiation. The obtained results could be used for the tracing of mineralization processes from their initiation to completion of the final product, identification of the OCP phase, and to follow the influence of radiation processes on phase composition of calcium phosphates.