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5-Azidomethyl-2′-deoxyuridine (5-AmdU, 1) has been successfully employed for the metabolic labeling of DNA and fluorescent imaging of live cells. 5-AmdU also demonstrated significant radiosensitization in breast cancer cells via site-specific nitrogen-centered radical (π-aminyl (U-5-CH2–NH•), 2, and σ-iminyl (U-5-CH═N•), 3) formation. This work shows that these nitrogen-centered radicals are not formed via the reduction of the azido group in 6-azidomethyluridine (6-AmU, 4). Radical assignments were performed using electron spin resonance (ESR) in supercooled solutions, pulse radiolysis in aqueous solutions, and theoretical (DFT) calculations. Radiation-produced electron addition to 4leads to the facile N3–loss, forming a stable neutral C-centered allylic radical (U-6-CH2•, 5) through dissociative electron attachment (DEA) via the transient negative ion, TNI (U-6-CH2-N3•–), in agreement with DFT calculations. In contrast, TNI (U-5-CH2–N3•–) of 1, via facile N2loss (DEA) and protonation from the surrounding water, forms radical 2. Subsequently, 2undergoes rapid H-atom abstraction from 1and produces the metastable intermediate α-azidoalkyl radical (U-5-CH•-N3). U-5-CH•-N3converts facilely to radical 3. N3–loss from U-6-CH2–N3•–is thermodynamically controlled, whereas N2loss from U-5-CH2–N3•–is dictated by protonation from the surrounding waters and resonance conjugation of the azidomethyl side chain at C5 with the pyrimidine ring.

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 Cl2•–to form the σ2σ*1adduct radical −P–SCl, which subsequently reacts with DMTP(O–)═S to produce [−P–SS–P−]−. −P–SCl 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–SS–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.

Selective and sensitive detection of Cu(I) is an ongoing challenge due to its important role in biological systems, for example. Herein, we describe a photoluminescent molecular chemosensor integrating two lanthanide ions (Tb3+and Eu3+) and respective tryptophan and naphthalene antennas onto a polypeptide backbone. The latter was structurally inspired from copper-regulating biomacromolecules in Gram-negative bacteria and was found to bind Cu+effectively under pseudobiological conditions (log KCu+= 9.7 ± 0.2). Ion regulated modulation of lanthanide luminescence in terms of intensity and long, millisecond lifetime offers perspectives in terms of ratiometric and time-gated detection of Cu+. The role of the bound ion in determining the photophysical properties is discussed with the aid of additional model compounds.

Substitution of the thymidine moiety in DNA by C5-substituted halogenated thymidine analogues causes significant augmentation of radiation damage in living cells. However, the molecular pathway involved in such radiosensitization process has not been clearly elucidated to date in solution at room temperature. So far, low-energy electrons (LEEs; 0–20 eV) under vacuum condition and solvated electrons (esol–) in solution are shown to produce the σ-type C5-centered pyrimidine base radical through dissociative electron attachment involving carbon–halogen bond breakage. Formation of this σ-type radical and its subsequent reactions are proposed to cause cellular radiosensitization. Here, we report time-resolved measurements at room temperature, showing that a radiation-produced quasi-free electron (eqf–) in solution promptly breaks the C5-halogen bond in halopyrimidines forming the σ-type C5 radical via an excited transient anion radical. These results demonstrate the importance of ultrafast reactions of eqf–, which are extremely important in chemistry, physics, and biology, including tumor radiochemotherapy.

Due to their similar coordination properties, discrimination of Cu+and Ag+by water-soluble luminescent probes is challenging. We have synthesized LCC4Eu, an 18 amino acid cyclic peptide bearing a europium complex, which is able to bind one Cu+or Ag+ion by the side chains of two methionines, a histidine and a 3-(1-naphthyl)-l-alanine. In this system, the naphthyl moiety establishes a cation−π interaction with these cations. It also acts as an antenna for the sensitization of Eu3+luminescence. Interestingly, when excited at 280 nm, LCC4Eubehaves as a turn-on probe for Ag+(+150% Eu emission) and as a turn-off probe for Cu+(−50% Eu3+emission). Shifting the excitation wavelength to 305 nm makes the probe responsive to Ag+(+380% Eu3+emission) but not to Cu+or other physiological cations. Thus, LCC4Euis uniquely capable of discriminating Ag+from Cu+. A detailed spectroscopic characterization based on steady-state and time-resolved measurements clearly demonstrates that Eu3+sensitization relies on electronic energy transfer from the naphthalene triplet state to the Eu3+excited states and that the cation−π interaction lowers the energy of this triplet state by 700 and 2400 cm–1for Ag+and Cu+, respectively. Spectroscopic data point to a modulation of the efficiency of the electronic energy transfer caused by the differential red shift of the naphthalene triplet, deciphering the differential luminescence response of LCC4Eutoward Ag+and Cu+.

We investigate the oxidation of silver cyanide AgI(CN)2‐in water by the OH radical in order to compare this complex with the free cation Ag+and to measure the influence of the ligands. High-level ab initiocalculations of the model species AgII(CN)2·enable the calibration of molecular simulations and the prediction of the oxidized species: AgII(CN)2(H2O)2·and its absorption spectrum, with an intense band at 292 nm and a weaker one at 390 nm. Pulse radiolysis measurements of the oxidation of AgI(CN)2‐by the OH radical in water yields a transient species with a broad, intense band at 290 nm and a weaker band at 410 nm at short times after the pulse and a blue shift of the spectrum at longer times. The prediction of the simulations, that the oxidized complex AgII(CN)2(H2O)2·is formed, is confirmed by thermochemistry. Our calculations also suggest that the formation of the OH-adduct is possible only in very basic solution and that the blue shift observed at long times after the pulse is due to disproportionation of the oxidized complex. We also perform molecular simulations of the oxidation of free Ag+cations by the OH radical. The results are compared to that of the literature and to the results obtained with the AgI(CN)2‐complex.

The catalytic role of oxide-derived Cu (OD-Cu) in promoting CO2reduction (CO2R) to C2+products has been appreciated for decades. However, the dynamic evolution of the surface oxidation states, together with their real correlation to the binding of reaction intermediates, remains unclear due to technical challenges. Here, we show the time-resolved spectroscopic signatures of key OD-Cu-CO2•–intermediates during catalytic CO2reduction through one electron transfer from nanoseconds to seconds time scale. We generated the initial intermediate CO2•–radicals in the bulk solution and monitored the interfacial reaction kinetics with well-defined OD-Cu (Cu(0), Cu(I), and Cu(II)) nanoparticles. Combined with molecular simulations, transient absorption profiles analysis reveals that Cu(I) induced a faster CO2•–radical coupling reaction than Cu(0), whereas Cu(II) is only reduced to Cu(I) by the CO2•–radical. Furthermore, the newly developed multistep cumulative pulse methodology uncovered the transition in chemical states of mixed OD-Cu during radical coupling reactions. This pulse radiolysis study provides compelling evidence for the beneficial role of subsurface oxides in early time catalytic CO2transformation.

Photoexcitation of sulfite (SO32–) is often used to generate hydrated electrons (eaq–) in processes to degrade perfluoroalkyl and polyfluoroalkyl substances (PFASs). Conventional consensus discourages the utilization of SO32–concentrations exceeding 10 mM for effective defluorination. This has hindered our understanding of SO32–chemistry beyond its electron photogeneration properties. In contrast, the radiation-chemical study presented here, directly producing eaq–through water radiolysis, suggests that SO32–plays a previously overlooked activation role in the defluorination. Quantitative 60Co gamma irradiation experiments indicate that the increased SO32–concentration from 0.1 to 1 M enhances the defluorination rate by a remarkable 15-fold, especially for short-chain perfluoroalkyl sulfonate (PFSA). Furthermore, during the treatment of long-chain PFSA (C8F17–SO3–) with a higher concentration of SO32–, the intermediates of C8H17–SO3–and C3F7–COO–were observed, which are absent without SO32–. These observations highlight that a higher concentration of SO32–facilitates both reaction pathways: chain shortening and H/F exchange. Pulse radiolysis measurements show that elevated SO32–concentrations accelerate the bimolecular reaction between eaq–and PFSA by 2 orders of magnitude. 19F NMR measurements and theoretical simulations reveal the noncovalent interactions between SO32–and F atoms, which exceptionally reduce the C–F bond dissociation energy by nearly 40%. As a result, our study offers a more effective strategy for degrading highly persistent PFSA contaminants.

With nitric acid (HNO3) being at the core of nuclear technology through actinides separation and extraction processes, achieving a complete characterization of the complex processes involving concentrated HNO3solutions under ionizing radiation equates bringing efficiency and safety into their operation. In this work, the three mechanisms contributing to the formation of nitrate radicals (NO3•) in concentrated nitric acid were investigated by measuring the radiolytic yield of NO3•in HNO3solutions (0.5–23.5 M) at room (22.5 °C) and elevated (80 °C) temperatures on time scales spanning from picosecond to microsecond by pulse radiolysis measurements. We conclude that the formation yield of NO3•, just after the 7 ps electron pulse, is due to the direct effect and to the ultrafast electron transfer reaction between NO3–and the water cation radical, H2O•+. The absolute formation yield of NO3•radicals due to the direct effect, GNO3•dir, is found to be (3.4 ± 0.1) × 10–7mol·J–1, irrespective of the concentration and temperature. On longer time scales, >1 ns, an additional contribution to NO3•formation from the reaction between •OH radicals and undissociated HNO3is observed. The rate constant of this reaction, which is activation-controlled, was determined to be (5.3 ± 0.2) × 107M–1·s–1for 22.5 °C, reaching a value of (1.1 ± 0.2) × 108M–1·s–1at 80 °C.

In the present work, the impact of the rhodium deposition on the thermal stability of ceria-based catalysts was studied. The samples were prepared by an incipient wetness impregnation of the support with aqueous solution of rhodium nitrate. The loading of Rh was 0.1 and 1 wt.%. The textural characteristics of the samples were examined by a low-temperature nitrogen adsorption. It was shown that the addition of rhodium intensifies the process of ceria agglomeration, which leads to the lower values of specific surface area along with increased average pore diameter after the aging at 1000 °C. Stability of the catalysts was investigated by means of a prompt thermal aging procedure. The high-loaded catalyst (1 wt.% Rh/CeO2) was more active than the 0.1 wt.% Rh/CeO2 sample, while the stability of both the catalysts was excellent. It should be emphasized that the alumina-based reference samples with the similar rhodium loading were significantly less active and poorly stable.

Cobalt nanoparticles (NPs) have been prepared by hydrogenation of the organometallic complex [Co(η3-C8H13)(η4-C8H12)] in 1-heptanol in the absence of any other stabilizer and then transformed into Co3O4NPs using mild oxidative reaction conditions. After deposition onto glassy carbon rotating disk electrodes, the electrocatalytic performance of the Co3O4NPs in water oxidation has been tested in 1M NaOH. The activity has been benchmarked with that of state-of-the-art Co3O4NPs through electrochemically-active surface area (ECSA) and specific current density measurements. Furthermore, the covalent grafting of photosensitive polypyridyl-based RuIIcomplexes onto the surface of Co3O4NPs afforded hybrid nanostructured materials able to photo-oxidize water into O2, while steady-state and time-resolved spectroscopic measurements gave some further insight into kinetics and pertinent reaction steps following excitation. These first-row transition metal oxide hybrid nanocatalysts display better catalytic performance than simple mixtures of non-grafted photosensitizers and Co3O4NPs, thus evidencing the advantage of the direct coupling between the two entities for the photo-induced water oxidation reaction.

The decay kinetics of the hydrated electron (eaq–) in aerosol OT (AOT)-based ternary microemulsions with pool sizes ranging from 0.34 to 4.85 nm were studied using picosecond pulse radiolysis coupled with transient absorption UV–vis spectroscopy. Electron transfer from oil to water and the subsequent solvation occurred within a time resolution of 7 ps. The decay kinetics of eaq–were accurately modeled using a double-exponential decay model, revealing the occurrence of two types of reactions, i.e., the recombination reaction at the water–oil interface and the radical–radical reactions in the water pools. The apparent lifetimes of both types of decays decreased significantly as the size of water pools decreased, indicating the influence of nanoconfinement effects. Moreover, the importance of the water–oil interface increased with decreasing water content, regardless of the presence or absence of NO3–as an electron scavenger in the water pools. Our findings provide a comprehensive understanding on the kinetics of the radiation reaction in AOT-based microemulsions.

We study the Dirac operators on the half-line. If the potential is square summable, we prove existence of the wave operators.

Abstract:: In this article, we consider two orthogonal systems: Sturm–Liouville operators and Krein systems. For Krein systems, we study the behavior of generalized polynomials at the infinity for spectral parameters in the upper half-plain. That makes it possible to establish the presence of absolutely continuous component of the associated measure. For Sturm–Liouville operator on the half-line with bounded potential q, we prove that essential support of absolutely continuous component of the spectral measure is [m,∞) if and q ′∈L 2(R +). That holds for all boundary conditions at zero. This result partially solves one open problem stated recently by S. Molchanov, M. Novitskii, and B. Vainberg. We consider also some other classes of potentials.

In one of his works, M.G. Krein discovered an analogy between polynomials orthogonal on the unit circle and generalized eigenfunctions of certain differential systems. We used some ideas of this paper to obtain new results in spectral analysis of Sturm–Liouville operators.

The excess electron in solution is a highly reactive radical involved in various radiation-induced reactions. Its solvation state critically determines the subsequent pathway and rate of transfer. For instance, water plays a dominating role in the electron-induced dealkylation of n-tributyl phosphate in actinide extraction processing. However, the underlying electron solvation processes in such systems are lacking. Herein, we directly observed the solvation dynamics of electrons in H-bonded water and n-tributyl phosphate (TBP) binary solutions with a mole fraction of water (Xw) varying from 0.05 to 0.51 under ambient conditions. Following the evolution of the absorption spectrum of trapped electrons (not fully solvated) with picosecond resolution, we show that electrons statistically distributed would undergo preferential solvation within water molecules extracted in TBP. We determine the time scale of excess electron full solvation from the deconvoluted transient absorption–kinetical data. The process of solvent reorganization accelerates by increasing the water molar fraction, and the rate of this process is 2 orders of magnitude slower compared to bulk water. We assigned the solvation process to hydrogen network reorientation induced by a negative charge of the excess electron that strongly depends on the local water environment. Our findings suggest that water significantly stabilizes the electron in a deeper potential than the pure TBP case. In its new state, the electron is likely to inhibit the dealkylation of extractants in actinide separation.

Nucleation and growth of crystallites are induced by the shockwave of a single laser nanosecond pulse in highly supersaturated solutions of potassium nitrate (saltpeter). The kinetics of the turbidity resulting from the light scattering by the growing crystals is observed by time-resolved optical spectroscopy. With an optical path of 10 mm, we first focused on the early part of the growth under various conditions, but it is limited by the detection system to a few percent of the total growth. Remarkably, in this domain and for all supersaturated concentrations studied, the turbidity increases proportionally with time. This zero-order process with an accretion rate constant (k= 4.7 × 107L mol–1s–1) implies that the nuclei and growing crystals’ concentration remain constant. This concentration is determined from the final diameter of crystals that are observed to have a bipyramidal shape by transmission electron microscopy (TEM). Moreover, the number of accretion sites per crystal must be constant in this time range and they are identified as the apexes. In complement, the kinetics detected with shorter optical paths permits us to observe larger parts of the total growth (up to 35% with 1 mm of optical path). In this case, after the linear part, the turbidity increase is markedly accelerated, indicating that the number of accretion sites per crystal increases rapidly with the crystal size and that the edges and facet sites also fix the molecules. The complete analysis by a homogeneous kinetics model of the signals obtained under various conditions concludes to an anisotropic growth of the crystals with another accretion rate constant (k′ = 100 L mol–1s–1) that is much lower on these edges and facet sites than on the apexes. However, this contribution becomes predominant only when the crystals develop to a larger size.

We propose a setup to observe soliton ratchet effects using discrete cavity solitons in a 1D array of coupled waveguide optical resonators. The net motion of solitons can be generated by an adiabatic shaking of the holding beam with zero average inclination angle. The resulting soliton velocity can be controlled by different parameters of the holding beam.

These notes contain an introduction to the theory of continuous analogs of polynomials orthogonal on the unit circle. We provide new results as well as simplified proofs for theorems that are already in the literature.