Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates.

The activation of dioxygen by FeII(Me3TACN)(S2SiMe2) (1) is reported. Reaction of 1 with O2 at -135 °C in 2-MeTHF generates a thiolate-ligated (peroxo)diiron complex FeIII2(O2)(Me3TACN)2(S2SiMe2)2 (2) that was characterized by UV-vis (λmax = 300, 390, 530, 723 nm), Mössbauer (δ = 0.53, |ΔEQ| = 0.76 mm s-1), resonance Raman (RR) (ν(O-O) = 849 cm-1), and X-ray absorption (XAS) spectroscopies. Complex 2 is distinct from the outer-sphere oxidation product 1ox (UV-vis (λmax = 435, 520, 600 nm), Mössbauer (δ = 0.45, |ΔEQ| = 3.6 mm s-1), and EPR (S = 5/2, g = [6.38, 5.53, 1.99])), obtained by one-electron oxidation of 1. Cleavage of the peroxo O-O bond can be initiated either photochemically or thermally to produce a new species assigned as an FeIV(O) complex, FeIV(O)(Me3TACN)(S2SiMe2) (3), which was identified by UV-vis (λmax = 385, 460, 890 nm), Mössbauer (δ = 0.21, |ΔEQ| = 1.57 mm s-1), RR (ν(FeIV═O) = 735 cm-1), and X-ray absorption spectroscopies, as well as reactivity patterns. Reaction of 3 at low temperature with H atom donors gives a new species, FeIII(OH)(Me3TACN)(S2SiMe2) (4). Complex 4 was independently synthesized from 1 by the stoichiometric addition of a one-electron oxidant and a hydroxide source. This work provides a rare example of dioxygen activation at a mononuclear nonheme iron(II) complex that produces both FeIII-O-O-FeIII and FeIV(O) species in the same reaction with O2. It also demonstrates the feasibility of forming Fe/O2 intermediates with strongly donating sulfur ligands while avoiding immediate sulfur oxidation.

Inactivation of myostatin by photo-oxygenation using catalyst-functionalized peptides.

Inhibition of myostatin is an attractive treatment for muscular dystrophy and other amyotrophic diseases. A myostatin-binding peptide was functionalized by equipped with an on/off switchable photo-oxygenation catalyst. This peptide induces a selective oxygenation of myostatin under near-infrared light, resulting in inactivation of myostatin. This peptide shows several orders of magnitude greater inhibitory effect than the original peptide.

Hydroxyl-Radical Reaction Pathways for the Fast Photochemical Oxidation of Proteins Platform As Revealed by 18O Isotopic Labeling.

Fast photochemical oxidation of protein (FPOP) has become an important mass spectrometry-based protein footprinting approach. Although the hydroxyl radical (•OH) generated by photolysis of hydrogen peroxide (H2O2) is most commonly used, the pathways for its reaction with amino-acid side chains remain unclear. Here, we report a systematic study of •OH oxidative modification of 13 amino acid residues by using 18O isotopic labeling. The results differentiate three classes of residues on the basis of their oxygen uptake preference toward different oxygen sources. Histidine, arginine, tyrosine, and phenylalanine residues preferentially take oxygen from H2O2. Methionine residues competitively take oxygen from H2O2 and dissolved oxygen (O2), whereas the remaining residues take oxygen exclusively from O2. Results reported in this work deepen the understanding of •OH labeling pathway on a FPOP platform, opening new possibilities for tailoring FPOP conditions in addressing many biological questions in a profound way.

Peculiar Effects of Electromagnetic Millimeter Waves on Tumor Development in BALB/c Mice.

The study examined the effects of millimeter electromagnetic waves at a frequency of 130 GHz corresponding to the molecular absorption and radiation spectra of NO and O2 with the total exposition time of 6 h on tumor morphogenesis in 3- and 6-month-old tumor-prone BALB/c mice of both sexes. In experimental mice exposed to electromagnetic radiation, the development of cancer process was slowed down throughout the observation period; moreover, no macroscopic signs of the tumors were revealed. However, in contrast to control mice, experimental animals demonstrated the formation of pathological reactions reflected by hepatic biochemical indices accompanied by the development of dystrophic and microcirculatory alterations in the liver tissue.

Improvements on the Fluorescence Quenching/Deflection Method for Real-time in situ Simultaneous Monitoring of Dissolved Oxygen and Material Movement-induced Beam Deflection in the Vicinity of an Aquatic Plant.

Although the newly developed beam deflection/fluorescence detection system for real-time in situ simultaneous monitoring of dissolved oxygen (DO) and material movements in the vicinity of aquatic plants was not only much more sensitive but also could be carried out much more closely to real time than conventional analytical methods that monitor the concentration changes at a bulk solution, it could not be applied to the photosynthesis process of aquatic plants. Here, improvements are reported to enable application of the system to the photosynthesis process. A white-light LED, which was used as a light source for photosynthesis in our previous paper, was replaced by a red-blue LED with wavelength of about 660 and 450 nm. Also, an interference filter of 589 ± 25 nm was placed in front of a photomultiplier tube (PMT). Furthermore, the LED and its electric power supply were placed outside of the dark room for preventing great temperature increases in the photosynthetic experiments. Experimental results showed the DO-quenched fluorescence could be sensitively monitored in both the respiration and photosynthesis processes, while only in the respiration process before the improvements. It is successfully demonstrated that the DO change and material movement-induced beam deflection in the vicinity of the plants in both the respiration and photosynthesis processes could be real-time in situ monitored with high sensitivity.

Biological effects of mixed-ion beams. Part 1: Effect of irradiation of the CHO-K1 cells with a mixed-ion beam containing the carbon and oxygen ions.

Carbon and oxygen ions were accelerated simultaneously to estimate the effect of irradiation of living cells with the two different ions. This mixed ion beam was used to irradiate the CHO-K1 cells, and a survival test was performed. The type of the effect of the mixed ion beam on the cells was determined with the isobologram method, whereby survival curves for irradiations with individual ion beams were also used. An additive effect of irradiation with the two ions was found.

Sustained molecular oxygen activation by solid iron doped silicon carbide under microwave irradiation: Mechanism and application to norfloxacin degradation.

Sustained molecular oxygen activation by iron doped silicon carbide (Fe/SiC) was investigated under microwave (MW) irradiation. The catalytic performance of Fe/SiC for norfloxacin (NOR) degradation was also studied. Rapid mineralization in neutral solution was observed with a pseudo-first-order rate constant of 0.2239 min-1 under 540 W of MW irradiation for 20 min. Increasing Fe/SiC rod and MW power significantly enhanced the degradation and mineralization rate with higher yield of reactive oxygen species (ROS). Fe shell corrosion and subsequent Fe0/II oxidation by molecular oxygen with MW activation was the key factor for NOR degradation through two-electron-transfer by Fe0 under acidic conditions and single-electron-transfer by FeII under neutral-alkaline solution. Removal rate of NOR was significantly affected by solution pH, showing higher degradation rates at both acidic and alkaline conditions. The highest removal efficiencies and rates at alkaline pH values were ascribed to the contribution of bound FeII species on the Fe shell surface due to the hydroxylation of Fe/SiC. ·OH was the main oxidizing specie for NOR degradation, confirmed by density functional theory (DFT) calculations and radical scavenger tests. DFT calculations were conducted on the reaction/activation energies of the transition/final states of NOR/degradation products, combined with intermediate identification with high performance liquid chromatography coupled with a triple-quadruple mass spectrometer (HPLC-MS/MS), the piperazinyl ring was the most reactive site for ·OH attack, followed by further ring-opening and stepwise oxidation. In this study, Fe/SiC were proved to be an excellent catalyst for the treatment of fluoroquinolone antibiotics with MW activation.

Light-induced structural changes and the site of O=O bond formation in PSII caught by XFEL.

Photosystem II (PSII) is a huge membrane-protein complex consisting of 20 different subunits with a total molecular mass of 350 kDa for a monomer. It catalyses light-driven water oxidation at its catalytic centre, the oxygen-evolving complex (OEC). The structure of PSII has been analysed at 1.9 Å resolution by synchrotron radiation X-rays, which revealed that the OEC is a Mn4CaO5 cluster organized in an asymmetric, 'distorted-chair' form. This structure was further analysed with femtosecond X-ray free electron lasers (XFEL), providing the 'radiation damage-free' structure. The mechanism of O=O bond formation, however, remains obscure owing to the lack of intermediate-state structures. Here we describe the structural changes in PSII induced by two-flash illumination at room temperature at a resolution of 2.35 Å using time-resolved serial femtosecond crystallography with an XFEL provided by the SPring-8 ångström compact free-electron laser. An isomorphous difference Fourier map between the two-flash and dark-adapted states revealed two areas of apparent changes: around the QB/non-haem iron and the Mn4CaO5 cluster. The changes around the QB/non-haem iron region reflected the electron and proton transfers induced by the two-flash illumination. In the region around the OEC, a water molecule located 3.5 Å from the Mn4CaO5 cluster disappeared from the map upon two-flash illumination. This reduced the distance between another water molecule and the oxygen atom O4, suggesting that proton transfer also occurred. Importantly, the two-flash-minus-dark isomorphous difference Fourier map showed an apparent positive peak around O5, a unique µ4-oxo-bridge located in the quasi-centre of Mn1 and Mn4 (refs 4,5). This suggests the insertion of a new oxygen atom (O6) close to O5, providing an O=O distance of 1.5 Å between these two oxygen atoms. This provides a mechanism for the O=O bond formation consistent with that proposed previously.

Spot Scanning and Passive Scattering Proton Therapy: Relative Biological Effectiveness and Oxygen Enhancement Ratio in Cultured Cells.

PURPOSE: To determine the relative biological effectiveness (RBE), oxygen enhancement ratio (OER), and contribution of the indirect effect of spot scanning proton beams, passive scattering proton beams, or both in cultured cells in comparison with clinically used photons. METHODS AND MATERIALS: The RBE of passive scattering proton beams at the center of the spread-out Bragg peak (SOBP) was determined from dose-survival curves in 4 cell lines using 6-MV X rays as controls. Survival of 2 cell lines after spot scanning and passive scattering proton irradiation was then compared. Biological effects at the distal end region of the SOBP were also investigated. The OER of passive scattering proton beams and 6 MX X rays were investigated in 2 cell lines. The RBE and OER values were estimated at a 10% cell survival level. The maximum degree of protection of radiation effects by dimethyl sulfoxide was determined to estimate the contribution of the indirect effect against DNA damage. All experiments comparing protons and X rays were made under the same biological conditions. RESULTS: The RBE values of passive scattering proton beams in the 4 cell lines examined were 1.01 to 1.22 (average, 1.14) and were almost identical to those of spot scanning beams. Biological effects increased at the distal end of the SOBP. In the 2 cell lines examined, the OER was 2.74 (95% confidence interval, 2.56-2.80) and 3.08 (2.84-3.11), respectively, for X rays, and 2.39 (2.38-2.43) and 2.72 (2.69-2.75), respectively, for protons (P<.05 for both cells between X rays and protons). The maximum degree of protection was significantly higher for X rays than for proton beams (P<.05). CONCLUSIONS: The RBE values of spot scanning and passive scattering proton beams were almost identical. The OER was lower for protons than for X rays. The lower contribution of the indirect effect may partly account for the lower OER of protons.

Solar photochemical and thermochemical splitting of water.

Artificial photosynthesis to carry out both the oxidation and the reduction of water has emerged to be an exciting area of research. It has been possible to photochemically generate oxygen by using a scheme similar to the Z-scheme, by using suitable catalysts in place of water-oxidation catalyst in the Z-scheme in natural photosynthesis. The best oxidation catalysts are found to be Co and Mn oxides with the e(1) g configuration. The more important aspects investigated pertain to the visible-light-induced generation of hydrogen by using semiconductor heterostructures of the type ZnO/Pt/Cd1-xZnxS and dye-sensitized semiconductors. In the case of heterostructures, good yields of H2 have been obtained. Modifications of the heterostructures, wherein Pt is replaced by NiO, and the oxide is substituted with different anions are discussed. MoS2 and MoSe2 in the 1T form yield high quantities of H2 when sensitized by Eosin Y. Two-step thermochemical splitting of H2O using metal oxide redox pairs provides a strategy to produce H2 and CO. Performance of the Ln0.5A0.5MnO3 (Ln = rare earth ion, A = Ca, Sr) family of perovskites is found to be promising in this context. The best results to date are found with Y0.5Sr0.5MnO3.

Abundant molecular oxygen in the coma of comet 67P/Churyumov-Gerasimenko.

The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov-Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet's formation, which is unexpected given the low upper limits from remote sensing observations. Current Solar System formation models do not predict conditions that would allow this to occur.

One-pot green synthesis of oxygen-rich nitrogen-doped graphene quantum dots and their potential application in pH-sensitive photoluminescence and detection of mercury(II) ions.

Nitrogen doping has been a powerful method to modulate the properties of carbon materials for various applications, and N-doped graphene quantum dots (GQDs) have gained remarkable interest because of their unique chemical, electronic, and optical properties. Herein, we introduce a facile one-pot solid-phase synthesis strategy for N-doped GQDs using citric acid (CA) as the carbon source and 3,4-dihydroxy-L-phenylalanine (L-DOPA) as the N source. The as-prepared N-GQDs with oxygen-rich functional groups are uniform with an average diameter of 12.5 nm. Because of the introduction of nitrogen atoms, N-GQDs exhibit excitation-wavelength-independent fluorescence with the maximum emission at 445 nm, and a high quantum yield of 18% is achieved at an excitation wavelength of 346 nm. Furthermore, a highly efficient fluorosensor based on the as-prepared N-GQDs was developed for the detection of Hg(2+) because of the effective quenching effect of metal ions via nonradiative electron transfer. This fluorosensor exhibits high sensitivity toward Hg(2+) with a detection limit of 8.6 nM. The selectivity experiments reveal that the fluorescent sensor is specific for Hg(2+). Most importantly, the practical use of the sensor based on N-GQDs for Hg(2+) detection was successfully demonstrated in river-water samples.

Near infrared radiation protects against oxygen-glucose deprivation-induced neurotoxicity by down-regulating neuronal nitric oxide synthase (nNOS) activity in vitro.

Near infrared radiation (NIR) has been shown to be neuroprotective against neurological diseases including stroke and brain trauma, but the underlying mechanisms remain poorly understood. In the current study we aimed to investigate the hypothesis that NIR may protect neurons by attenuating oxygen-glucose deprivation (OGD)-induced nitric oxide (NO) production and modulating cell survival/death signaling. Primary mouse cortical neurons were subjected to 4 h OGD and NIR was applied at 2 h reoxygenation. OGD significantly increased NO level in primary neurons compared to normal control, which was significantly ameliorated by NIR at 5 and 30 min post-NIR. Neither OGD nor NIR significantly changed neuronal nitric oxide synthase (nNOS) mRNA or total protein levels compared to control groups. However, OGD significantly increased nNOS activity compared to normal control, and this effect was significantly diminished by NIR. Moreover, NIR significantly ameliorated the neuronal death induced by S-Nitroso-N-acetyl-DL-penicillamine (SNAP), a NO donor. Finally, NIR significantly rescued OGD-induced suppression of p-Akt and Bcl-2 expression, and attenuated OGD-induced upregulation of Bax, BAD and caspase-3 activation. These results suggest NIR may protect against OGD at least partially through reducing NO production by down-regulating nNOS activity, and modulating cell survival/death signaling.

Photogeneration of reactive transient species upon irradiation of natural water samples: Formation quantum yields in different spectral intervals, and implications for the photochemistry of surface waters.

Chromophoric dissolved organic matter (CDOM) in surface waters is a photochemical source of several transient species such as CDOM triplet states ((3)CDOM*), singlet oxygen ((1)O2) and the hydroxyl radical (OH). By irradiation of lake water samples, it is shown here that the quantum yields for the formation of these transients by CDOM vary depending on the irradiation wavelength range, in the order UVB > UVA > blue. A possible explanation is that radiation at longer wavelengths is preferentially absorbed by the larger CDOM fractions, which show lesser photoactivity compared to smaller CDOM moieties. The quantum yield variations in different spectral ranges were definitely more marked for (3)CDOM* and OH compared to (1)O2. The decrease of the quantum yields with increasing wavelength has important implications for the photochemistry of surface waters, because long-wavelength radiation penetrates deeper in water columns compared to short-wavelength radiation. The average steady-state concentrations of the transients ((3)CDOM*, (1)O2 and OH) were modelled in water columns of different depths, based on the experimentally determined wavelength trends of the formation quantum yields. Important differences were found between such modelling results and those obtained in a wavelength-independent quantum yield scenario.

Evaluation of carotenoids and reactive oxygen species in human skin after UV irradiation: a critical comparison between in vivo and ex vivo investigations.

UV irradiation is one of the most harmful exogenous factors for the human skin. In addition to the development of erythema, free radicals, that is reactive oxygen species (ROS), are induced under its influence and promote the development of oxidative stress in the skin. Several techniques are available for determining the effect of UV irradiation. Resonance Raman spectroscopy (RRS) measures the reduction of the carotenoid concentration, while electron paramagnetic resonance (EPR) spectroscopy enables the analysis of the production of free radicals. Depending on the method, the skin parameters are analysed in vivo or ex vivo. This study provides a critical comparison between in vivo and ex vivo investigations on the ROS formation and carotenoid depletion caused by UV irradiation in human skin. The oxygen content of tissue was also determined. It was shown that the antioxidant status measured in the skin samples in vivo and ex vivo was different. The depletion in the carotenoid concentration in vivo exceeded the value determined ex vivo by a factor of about 1.5, and the radical formation after UV irradiation was significantly greater in vivo by a factor of 3.5 than that measured in excised human skin, which can be explained by the lack of oxygen ex vivo.

Single-field slice-imaging with a movable repeller: photodissociation of N2O from a hot nozzle.

We present a new photo-fragment imaging spectrometer, which employs a movable repeller in a single field imaging geometry. This innovation offers two principal advantages. First, the optimal fields for velocity mapping can easily be achieved even using a large molecular beam diameter (5 mm); the velocity resolution (better than 1%) is sufficient to easily resolve photo-electron recoil in (2 + 1) resonant enhanced multiphoton ionization of N2 photoproducts from N2O or from molecular beam cooled N2. Second, rapid changes between spatial imaging, velocity mapping, and slice imaging are straightforward. We demonstrate this technique's utility in a re-investigation of the photodissociation of N2O. Using a hot nozzle, we observe slice images that strongly depend on nozzle temperature. Our data indicate that in our hot nozzle expansion, only pure bending vibrations--(0, v2, 0)--are populated, as vibrational excitation in pure stretching or bend-stretch combination modes are quenched via collisional near-resonant V-V energy transfer to the nearly degenerate bending states. We derive vibrationally state resolved absolute absorption cross-sections for (0, v2 ≤ 7, 0). These results agree well with previous work at lower values of v2, both experimental and theoretical. The dissociation energy of N2O with respect to the O((1)D) + N2¹Σ(g)⁺ asymptote was determined to be 3.65 ± 0.02 eV.

Luminescence and photosensitivity of gadolinium labeled hematoporphyrin monomethyl ether.

Photodynamic therapy for deep-lying lesions needs an appropriate imaging modality, precise evaluation of tissue oxygen and an effective photosensitizer. Gadolinium based metalloporphyrins Gd(III)-HMME is proposed in this study as a potential multifunctional theranostic agent, as photosensitizer, ratiometric oxygen sensor and MRI contrast agent. The time resolved spectroscopy revealed the luminescence peak of Gd(III)-HMME at 710 and 779 nm with a lifetime of 64 µs in oxygen-free methanol to be phosphorescent. This phosphorescence is strongly dependent on dissolved oxygen concentration. Its intensity in oxygen saturated methanol solution is 21% of that in deoxygenated solution. The singlet oxygen quantum yields ΦΔ of HMME and Gd(III)-HMME in air saturated methanol solution were determined to be 0.79 and 0.40 respectively using comparative spectra method. These phenomena indicate that the oxygen sensibility and production of singlet oxygen of Gd(III)-HMME can fulfill the requirement of PDT treatment.

New insights into the catalytic active-site structure of multicopper oxidases.

Structural models determined by X-ray crystallography play a central role in understanding the catalytic mechanism of enzymes. However, X-ray radiation generates hydrated electrons that can cause significant damage to the active sites of metalloenzymes. In the present study, crystal structures of the multicopper oxidases (MCOs) CueO from Escherichia coli and laccase from a metagenome were determined. Diffraction data were obtained from a single crystal under low to high X-ray dose conditions. At low levels of X-ray exposure, unambiguous electron density for an O atom was observed inside the trinuclear copper centre (TNC) in both MCOs. The gradual reduction of copper by hydrated electrons monitored by measurement of the Cu K-edge X-ray absorption spectra led to the disappearance of the electron density for the O atom. In addition, the size of the copper triangle was enlarged by a two-step shift in the location of the type III coppers owing to reduction. Further, binding of O2 to the TNC after its full reduction was observed in the case of the laccase. Based on these novel structural findings, the diverse resting structures of the MCOs and their four-electron O2-reduction process are discussed.

[measurement of optical density in infrared absorption maxima of oxygen molecules based on their photochemical activity upon direct laser excitation].

Generation of singlet oxygen upon excitation of oxygen molecules by infrared diode lasers has been studied in organic media (carbon tetrachloride and acetone) saturated by air under normal pressure and temperature. A new approach to analysis of the experimental data has been developed taking into account a degree of overlapping of the spectral bands of oxygen and laser radiation. Optical density, molar absorption coefficient and the cross section of light absorption were determined for the main absorption maxima of O2 at 765 and 1273 nm. The results are compared with the data of previous studies. A significance of the obtained results for elucidation of photophysics and photochemistry of oxygen molecules and investigation of biological action of laser radiation is discussed.