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In this work, the mechanism of dioxygen reduction catalysed by gold nanoparticles (AuNPs) by two electron donors was investigated, i.e. , by sodium ascorbate and hydroethidine, focusing on potential ROS (reactive oxygen species) formation, such as O 2 ˙ - and H 2 O 2 . According to our results, when AuNPs catalyse the reduction of O 2 , ROS are formed only as intermediates on the surface of nanoparticles, and they are unavoidably reduced to water, catalysed by the AuNPs. Thus, the statement on ROS production in the presence of AuNPs often reported in the literature is excessive. The AuNPs can catalyze the oxidation of electron donors in the cell, e.g. , antioxidants causing oxidative stress. Therefore we propose that when explaining damage in the living cells observed in the presence of AuNP, the catalysis of redox reactions by AuNPs must be considered., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Over the past two decades, several distinct solution concepts for rate-independent evolutionary systems driven by non-convex energies have been suggested in an attempt to model properly jump discontinuities in time. Much attention has been paid in this context to the modelling of crack propagation. This paper studies two fully discrete (in time and space) approximation schemes for the rate-independent evolution of a single crack in a two-dimensional linear elastic material. The crack path is assumed to be known in advance, and the evolution of the crack tip along it relies on the Griffith theory. On the time-discrete level, the first scheme is based on local minimization, whereas the second scheme is a regularized version of the first one. The crucial feature of the schemes is their adaptive time-stepping nature, with finer time steps at those points where the evolution of the crack tip might develop a discontinuity. The set of discretization parameters includes the mesh size, crack increment, locality parameter and regularization parameter. In both cases, we explore the interplay between the discretization parameters and derive sufficient conditions on them ensuring the convergence of discrete interpolants to parametrized balanced viscosity solutions of the continuous model. To illustrate the performance of the approximation schemes, we support our theoretical analysis with numerical simulations. This article is part of the theme issue 'Non-smooth variational problems and applications'.

This work shows that S atom substitution in phosphate controls the directionality of hole transfer processes between the base and sugar-phosphate backbone in DNA systems. The investigation combines synthesis, electron spin resonance (ESR) studies in supercooled homogeneous solution, pulse radiolysis in aqueous solution at ambient temperature, and density functional theory (DFT) calculations of in-house synthesized model compound dimethylphosphorothioate (DMTP(O - )═S) and nucleotide (5'- O -methoxyphosphorothioyl-2'-deoxyguanosine (G-P(O - )═S)). ESR investigations show that DMTP(O - )═S reacts with Cl 2 •- to form the σ 2 σ* 1 adduct radical -P-S[Formula: see text]Cl, which subsequently reacts with DMTP(O - )═S to produce [-P-S[Formula: see text]S-P-] - . -P-S[Formula: see text]Cl in G-P(O - )═S undergoes hole transfer to Gua, forming the cation radical (G •+ ) via thermally activated hopping. However, pulse radiolysis measurements show that DMTP(O - )═S forms the thiyl radical (-P-S • ) by one-electron oxidation, which did not produce [-P-S[Formula: see text]S-P-] - . Gua in G-P(O - )═S is oxidized unimolecularly by the -P-S • intermediate in the sub-picosecond range. DFT thermochemical calculations explain the differences in ESR and pulse radiolysis results obtained at different temperatures.

Metal nanoparticles can catalyze reactions involving organic free radicals. From the first studies focused on the catalytic reduction of water by free radicals until today, the catalytic oxidation of organic radicals has not received attention. In this work, we present the results on the catalytic activity of gold nanoparticles in the oxidation of 2-propanol to acetone and acetanilide hydroxylation during water radiolysis. A detailed reaction mechanism of α-hydroxyisopropyl radical oxidation is discussed, explaining the increase in acetone formation by ca. 340% in the presence of gold nanoparticles. In the case of acetanilide hydroxylation in the presence of nanoparticles, a strong effect of oxygen in the reaction mechanism was observed: the increase in the oxygen concentration from 0 to 1.22 mM leads to a 40-fold decrease in hydroxylation product formation. This observation is unexpected since, in the absence of gold nanoparticles, oxygen stimulates hydroxylation reactions. We propose that in the presence of both oxygen and nanoparticles, oxygen attaches first to acetanilide OH-adducts, and then nanoparticles catalyze the oxidation of peroxyl type radicals, which does not lead to the formation of hydroxylation products.

Numerous additives are used in the electrolytes of lithium-ion batteries, especially for the formation of an efficient solid electrolyte interphase at the surface of the electrodes. Understanding the degradation processes of these compounds is thus important; they can be seen through radiolysis. In the case of fluoroethylene carbonate (FEC), picosecond pulse radiolysis experiments evidenced the formation of FEC .- . This radical is stabilized in neat FEC, whereas the ring opens to form more stable radical anions when FEC is a solute in other solvents, as confirmed by quantum chemistry calculations. In neat FEC, pre-solvated electrons primarily undergo attachment rather than solvation. On long timescales, the gases produced (H 2 , CO, and CO 2 ) were quantified. A reaction scheme for both the oxidizing and reducing pathways at stake in irradiated FEC is proposed. This work shows that the nature of the primary species formed in FEC depends on the amount of FEC in the solution., (© 2021 Wiley-VCH GmbH.)

The ability of gold nanoparticles (AuNPs) to catalyze reactions involving radicals is poorly studied. However, AuNPs are used in applications where chemical reactions involving transient radicals occur. Herein, we investigate AuNPs' catalytic effect on 2-propanol oxidation and acetanilide hydroxylation in aqueous solutions under ionizing radiation at room temperature. In both cases, the presence of AuNPs led to selective oxidation of organic radicals, significantly changing the products' composition and ratio. Based on these observations, we stress how AuNPs' catalytic activity can affect the correctness of reactive oxygen species concentration determination utilizing organic dyes. We also provide a discussion on the role of AuNPs' catalytic activity in the radiosensitization effect actively studied for radiotherapy.

Imogolite nanotubes are potentially promising co-photocatalysts because they are predicted to have curvature-induced, efficient electron-hole pair separation. This prediction has however not yet been experimentally proven. Here, we investigated the behavior upon irradiation of these inorganic nanotubes as a function of their water content to understand the fate of the generated electrons and holes. Two types of aluminosilicate nanotubes were studied: one was hydrophilic on its external and internal surfaces (IMO-OH) and the other had a hydrophobic internal cavity due to Si-CH 3 bonds (IMO-CH 3 ), with the external surface remaining hydrophilic. Picosecond pulse radiolysis experiments demonstrated that the electrons are efficiently driven outward. For imogolite samples with very few external water molecules (around 1% of the total mass), quasi-free electrons were formed. They were able to attach to a water molecule, generating a water radical anion, which ultimately led to dihydrogen. When more external water molecules were present, solvated electrons, precursors of dihydrogen, were formed. In contrast, holes moved towards the internal surface of the tubes. They mainly led to the formation of dihydrogen and of methane in irradiated IMO-CH 3 . The attachment of the quasi-free electron to water was a very efficient process and accounted for the high dihydrogen production at low relative humidity values. When the water content increased, electron solvation dominated over attachment to water molecules. Electron solvation led to dihydrogen production, albeit to a lesser extent than quasi-free electrons. Our experiments demonstrated the spontaneous curvature-induced charge separation in these inorganic nanotubes, making them very interesting potential co-photocatalysts.

Gold nanoparticles are known to cause a radiosensitizing effect, which is a promising way to improve radiation therapy. However, the radiosensitization mechanism is not yet fully understood. It is currently assumed that gold nanoparticles can influence various physical, chemical, and biological processes. Pulse radiolysis is a powerful tool that can examine one of the proposed effects of gold nanoparticles, such as increased free radical production. In this work, we shed light on the consequence of ionizing radiation interaction with gold nanoparticles by direct measurements of solvated electrons using the pulse radiolysis technique. We found that at a therapeutically relevant gold concentration (<3 mM atomic gold, <600 μg × cm -3 ), the presence of gold nanoparticles in solution does not induce higher primary radicals' formation. This result indicates that energy absorption by gold nanoparticles and related effects such as higher ionization of surrounding media and • OH radicals overproduction are not the reason for the radiosensitizing effect reported in the literature.

Invited for the cover of this issue are the groups of Roman Dembinski, Mehran Mostafavi, and Amitava Adhikary at the Polish Academy of Sciences, Université Paris-Saclay, and Oakland University. The image depicts a doughnut as a way of illustrating the hole transfer process. Read the full text of the article at 10.1002/chem.202000247., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The directionality of the hole-transfer processes between DNA backbone and base was investigated by using phosphorodithioate [P(S - )=S] components. ESR spectroscopy in homogeneous frozen aqueous solutions and pulse radiolysis in aqueous solution at ambient temperature confirmed initial formation of G .+ -P(S - )=S. The ionization potential of G-P(S - )=S was calculated to be slightly lower than that of guanine in 5'-dGMP. Subsequent thermally activated hole transfer from G .+ to P(S - )=S led to dithiyl radical (P-2S . ) formation on the μs timescale. In parallel, ESR spectroscopy, pulse radiolysis, and density functional theory (DFT) calculations confirmed P-2S . formation in an abasic phosphorodithioate model compound. ESR investigations at low temperatures and higher G-P(S - )=S concentrations showed a bimolecular conversion of P-2S . to the σ 2 -σ* 1 -bonded dimer anion radical [-P-2S - . 2S-P-] - [ΔG (150 K, DFT)=-7.2 kcal mol -1 ]. However, [-P-2S - . 2S-P-] - formation was not observed by pulse radiolysis [ΔG° (298 K, DFT)=-1.4 kcal mol -1 ]. Neither P-2S . nor [-P-2S - . 2S-P-] - oxidized guanine base; only base-to-backbone hole transfer occurs in phosphorodithioate., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The Maggi-Rubinowicz method (MRM) is a useful tool to compute diffraction patterns from opaque planar objects. We adapted the MRM to planar rectangles. In the first part of this study, differences between diffraction patterns, both the intensity and the phase distributions, from a tilted rectangle and from the square having the same orthogonal projection on the observation plane, have been analyzed. In the second part, we compared results obtained with the MRM to those obtained with angular spectrum theory (AST) coupled to fast Fourier transform (FFT). The main novelty of this work is the fact that MRM is particularly well suited for evaluating anti-aliasing procedures applied to AST-FFT calculations.

Magnetotactic bacteria are ubiquitous and can be found in both freshwater and marine environments. Due to intracellular chains of magnetic single domain particles, they behave like swimming compass needles. In external magnetic fields like the Earth's magnetic field, a torque is acting on the chain. This will cause the bacterium to be rotated and aligned with the external field. The swimming direction of magnetotactic bacteria can be controlled with external magnetic fields, which makes it convenient to study them under a light microscope. Usually, a special set of coils arranged around a light microscope is used to control the swimming magnetotactic bacteria. Here, we present a simple mechanical system with a permanent magnet, which produces a rotating magnetic field of nearly constant amplitude in the focal plane of a light microscope. The device is placed beside the light microscope and easily adaptable to almost any microscope and thus convenient for field experiments. To describe the trajectories qualitatively, a theoretical model of the trajectories is presented. This device can be used to control the swimming direction of magnetotactic bacteria and also for studying their magnetic and hydrodynamic properties.

A regularized algorithm that has the potential to improve the quality of Raman lidar data processing is presented. Compared to the conventional scheme, the proposed algorithm has the advantage, which results from the fact that it is based on a well-posed procedure. That is, the profile of the aerosol backscatter coefficient is computed directly, using the explicit relationships, without numerical differentiation. Thereafter, the profile of the lidar ratio is retrieved as a regularized solution of a first-kind Volterra integral equation. Once these two steps have been completed, the profile of the aerosol extinction coefficient is computed by a straightforward multiplication. The numerical simulations demonstrated that the proposed algorithm provides good accuracy and resolution of aerosol profile retrievals. The error analysis showed that the retrieved profiles are continuous functions of the measurement errors and of the a priori information uncertainties.

We present what we believe to be the first results of a light-scattering analysis on several Chebyshev particles characterized by higher orders. Chebyshev particles of comparatively lower orders were used in the past to study the effects of nonspherical but concave geometries in remote sensing applications. We will show that, based on the developed methodology, accurate results can also be obtained for particles of higher orders exhibiting a more pronounced surface waviness. The achieved results demonstrate that higher-order Chebyshev particles can be used to estimate the influence of a weak surface roughness on the light-scattering behavior of the underlying smooth scatterer. The effects obtained correspond with the results of other approaches and with the theoretical expectations of a weak surface roughness. In contrast to what is known for regular particles, there can be observed an essential difference between the phase functions of the underlying spherical scatterer and the corresponding higher-order Chebyshev particle if a higher absorptivity of the scattering medium is considered. This paper demonstrates additionally that Chebyshev polynomials can be simply combined with smooth geometries other than spheres.

An intercomparison of aerosol backscatter lidar algorithms was performed in 2001 within the framework of the European Aerosol Research Lidar Network to Establish an Aerosol Climatology (EARLINET). The objective of this research was to test the correctness of the algorithms and the influence of the lidar ratio used by the various lidar teams involved in the EARLINET for calculation of backscatter-coefficient profiles from the lidar signals. The exercise consisted of processing synthetic lidar signals of various degrees of difficulty. One of these profiles contained height-dependent lidar ratios to test the vertical influence of those profiles on the various retrieval algorithms. Furthermore, a realistic incomplete overlap of laser beam and receiver field of view was introduced to remind the teams to take great care in the nearest range to the lidar. The intercomparison was performed in three stages with increasing knowledge on the input parameters. First, only the lidar signals were distributed; this is the most realistic stage. Afterward the lidar ratio profiles and the reference values at calibration height were provided. The unknown height-dependent lidar ratio had the largest influence on the retrieval, whereas the unknown reference value was of minor importance. These results show the necessity of making additional independent measurements, which can provide us with a suitable approximation of the lidar ratio. The final stage proves in general, that the data evaluation schemes of the different groups of lidar systems work well.

A model system for studying double-strand-break (DSB)-induced genetic recombination in vivo based on the ets1 segCDelta strain of bacteriophage T4 was developed. The ets1, a 66-bp DNA fragment of phage T2L containing the cleavage site for the T4 SegC site-specific endonuclease, was inserted into the proximal part of the T4 rIIB gene. Under segC(+) conditions, the ets1 behaves as a recombination hotspot. Crosses of the ets1 against rII markers located to the left and to the right of ets1 gave similar results, thus demonstrating the equal and symmetrical initiation of recombination by either part of the broken chromosome. Frequency/distance relationships were studied in a series of two- and three-factor crosses with other rIIB and rIIA mutants (all segC(+)) separated from ets1 by 12-2100 bp. The observed relationships were readily interpretable in terms of the modified splice/patch coupling model. The advantages of this localized or focused recombination over that distributed along the chromosome, as a model for studying the recombination-replication pathway in T4 in vivo, are discussed.