Carbon nanotubes quench singlet oxygen generated by photosynthetic reaction centers

Photosensitizers may convert molecular oxygen into reactive oxygen species (ROS) including, e.g., singlet oxygen (1O2), superoxide anion (O2-•), and hydroxyl radicals (•OH), chemicals with extremely high cyto- and potential genotoxicity. Photodynamic ROS reactions are determinative in medical photodynamic therapy (cancer treatment with externally added photosensitizers) and in reactions damaging the photosynthetic apparatus of plants (via internal pigments). The primary events of photosynthesis take place in the chlorophyll containing reaction center protein complex (RC), where the energy of light is converted into chemical potential. 1O2 is formed by both bacterial bacteriochlorophylls and plant RC triplet chlorophylls in high light and if the quenching of 1O2 is impaired. In plant physiology, reducing the formation of the ROS and thus lessening photooxidative membrane damage (including the RC protein) and increasing the efficiency of the photochemical energy conversion is of special interest. Carbon nanotubes, in artificial systems, are also known to react with singlet oxygen. To investigate the possibility of 1O2 quenching by carbon nanotubes in a biological system, we studied the effect of carbon nanotubes on 1O2 photogenerated by photosynthetic RCs purified from purple bacteria. 1,3-Diphenylisobenzofuran (DPBF), a dye responding to oxidation by 1O2 with absorption decrease at 420nm was used to measure 1O2 concentrations. 1O2 was produced either from a photosensitizer (methylene blue) or from triplet photosynthetic RCs and the antioxidant capacity of carbon nanotubes was assessed. Less 1O2 was detected by DPBF in the presence of carbon nanotubes, suggesting that these are potential quenchers of this ROS. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Detailed cool star flare morphology with CHEOPS and TESS

Context. White-light stellar flares are proxies for some of the most energetic types of flares, but their triggering mechanism is still poorly understood. As they are associated with strong X and UV emission, their study is particularly relevant to estimate the amount of high-energy irradiation onto the atmospheres of exoplanets, especially those in their stars' habitable zone. Aims. We used the high-cadence, high-photometric capabilities of the CHEOPS and TESS space telescopes to study the detailed morphology of white-light flares occurring in a sample of 130 late-K and M stars, and compared our findings with results obtained at a lower cadence. We developed dedicated software for this purpose. Results. Multi-peak flares represent a significant percentage ($\gtrsim 30$\%) of the detected outburst events. Our findings suggest that high-impulse flares are more frequent than suspected from lower-cadence data, so that the most impactful flux levels that hit close-in exoplanets might be more time-limited than expected. We found significant differences in the duration distributions of single-peak and complex flare components, but not in their peak luminosity. A statistical analysis of the flare parameter distributions provides marginal support for their description with a log-normal instead of a power-law function, leaving the door open to several flare formation scenarios. We tentatively confirmed previous results about quasi-periodic pulsations in high-cadence photometry, report the possible detection of a pre-flare dip, and did not find hints of photometric variability due to an undetected flare background. Conclusions. The high-cadence study of stellar hosts might be crucial to evaluate the impact of their flares on close-in exoplanets, as their impulsive phase emission might otherwise be incorrectly estimated. Future telescopes such as PLATO and Ariel will help in this respect.Comment: 28 pages, 25 figures, 4 tables, to be published in Astronomy & Astrophysic

Glancing through the debris disk: Photometric analysis of DE Boo with CHEOPS

DE Boo is a unique system, with an edge-on view through the debris disk around the star. The disk, which is analogous to the Kuiper belt in the Solar System, was reported to extend from 74 to 84 AU from the central star. The high photometric precision of the Characterising Exoplanet Satellite (CHEOPS) provided an exceptional opportunity to observe small variations in the light curve due to transiting material in the disk. This is a unique chance to investigate processes in the debris disk. Photometric observations of DE Boo of a total of four days were carried out with CHEOPS. Photometric variations due to spots on the stellar surface were subtracted from the light curves by applying a two-spot model and a fourth-order polynomial. The photometric observations were accompanied by spectroscopic measurements with the 1m RCC telescope at Piszk\'estet\H{o} and with the SOPHIE spectrograph in order to refine the astrophysical parameters of DE Boo. We present a detailed analysis of the photometric observation of DE Boo. We report the presence of nonperiodic transient features in the residual light curves with a transit duration of 0.3-0.8 days. We calculated the maximum distance of the material responsible for these variations to be 2.47 AU from the central star, much closer than most of the mass of the debris disk. Furthermore, we report the first observation of flaring events in this system. We interpreted the transient features as the result of scattering in an inner debris disk around DE Boo. The processes responsible for these variations were investigated in the context of interactions between planetesimals in the system

1,3,5,7-Tetrakis(tetrazol-5-yl)-adamantane: the smallest tetrahedral tetrazole-functionalized ligand and its complexes formed by reaction with anhydrous M(II)Cl-2 (M = Mn, Cu, Zn, Cd)

1,3,5,7-Tetrakis(tetrazol-5-yl)-adamantane (H4L) was probed as a building block for the synthesis of tetrazolato/halido coordination polymers with open-network structures. MCl2 (M = Cu, Cd, Zn, Mn) was reacted with H4L in DMF at 70 degrees C to yield Cu4Cl4L(DMF)(5)]center dot DMF, 1; Cd4Cl4L(DMF)(7)]center dot DMF, 2; Zn3Cl2L(DMF)(4)]center dot 2DMF, 3 and Mn2L(DMF)(2)(MeOH)(4)]center dot DMF center dot 2MeOH center dot 2H(2)O, 4.1 and 2 (Fddd) are nearly isostructural and have zeolitic structures with a {4(3).6(2).8}, gis or gismondine underlying net, where the rote of the tetrahedral nodes is served by the coordination bonded clusters and the adamantane moiety. 3 (P2(1)/n) has a porous structure composed of coordination bonded layers with a (4.8(2)) fes topology joined via trans-{Zn(tetrazolate)(2)(DMF)(4)) pillars with an overall topology of {4.6(2)}{4.6(6).8(3)}, fsc-3,5-Cmce-2. 4 (Pca2(1)) is composed of stacked (Mn2L) hexagonal networks. In 1 and 2 the ligand fulfills a symmetric role of a tetrahedral building block, while in 3 and 4 it fulfills rather a role of an effective trigonal unit. Methanol-exchanged and activated 1 displayed an unusual type IV isotherm with H2 type hysteresis for N-2 sorption with an expected uptake at high P/P-0, but with a smaller S-BET = 505.5 m(2) g(-1) compared to the calculated 1789 m(2) g(-1), which is a possible result of the framework's flexibility. For H-2 sorption 0.79 wt% (1 bar, 77 K) and 0.06 wt% (1 bar, RT) uptake and Q(st) = -7.2 kJ mol(-1) heat of adsorption (77 K) were recorded. Weak antiferromagnetic interactions were found in 1 and 4 with J(1) = -9.60(1), J(2) = -17.2(2), J(3) = -2.28(10) cm(-1) and J = -0.76 cm(-1) respectively. The formation of zeolitic structures in 1 and 2, the concept of structural `imprinting' of rigid building blocks, and design opportunities suggested 4 as a potential hexafunctionalized biadamantane building block

Diamantan-4,9-dikarboxylát založení na UiO-66 analogu: náročnější na rozsáhlé uhlovodíkové strukturní platformy

The first use of a bulky barrel-shaped ligand is demonstrated in HHUD-3, with accessible porosity only feasible for a defect structure. With 35%+ missing linker defects and S-BET = 890 m(2)g(-1) (N-2), HHUD-3 features higher CH4 but lower CO2 and H-2 adsorption than UiO-66.První použití objemného ligandu soudkového typu je demonstrováno v HHUD-3 s akceptovatelnou porozitou použitelnou pouze pro defektní strukturu. S více než 35 % chybějících defektů linkeru a S-BET = 890 m(2)g(-1) (N-2) mají HHUD-3 prvky vyšší CH4, ale nižší CO2 a H-2 adsorpci než UiO-66

Carbon nanotubes quench singlet oxygen generated by photosynthetic reaction centers

Photosensitizers may convert molecular oxygen into reactive oxygen species (ROS) including, e.g., singlet oxygen (O-1(2)), superoxide anion (O-2(-center dot)), and hydroxyl radicals ((OH)-O-center dot), chemicals with extremely high cyto- and potential genotoxicity. Photodynamic ROS reactions are determinative in medical photodynamic therapy (cancer treatment with externally added photosensitizers) and in reactions damaging the photosynthetic apparatus of plants (via internal pigments). The primary events of photosynthesis take place in the chlorophyll containing reaction center protein complex (RC), where the energy of light is converted into chemical potential. O-1(2) is formed by both bacterial bacteriochlorophylls and plant RC triplet chlorophylls in high light and if the quenching of O-1(2) is impaired. In plant physiology, reducing the formation of the ROS and thus lessening photooxidative membrane damage (including the RC protein) and increasing the efficiency of the photochemical energy conversion is of special interest. Carbon nanotubes, in artificial systems, are also known to react with singlet oxygen. To investigate the possibility of O-1(2) quenching by carbon nanotubes in a biological system, we studied the effect of carbon nanotubes on O-1(2) photogenerated by photosynthetic RCs purified from purple bacteria. 1,3-Diphenylisobenzofuran (DPBF), a dye responding to oxidation by O-1(2) with absorption decrease at 420nm was used to measure O-1(2) concentrations. O-1(2) was produced either from a photosensitizer (methylene blue) or from triplet photosynthetic RCs and the antioxidant capacity of carbon nanotubes was assessed. Less O-1(2) was detected by DPBF in the presence of carbon nanotubes, suggesting that these are potential quenchers of this ROS. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei