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Here, we report the detailed mechanisms of benzophenone (BZP) photosensitized thymine damage and repair by Paternò–Büchi (PB) cycloaddition. It was found that the head-to-head and head-to-tail PB cycloadditions lead to the formation of the C–O bonds in the 3(nπ*) state and the 3(ππ*) state, respectively. The conical intersection occurs before the head-to-tail C–O bonding. Then, the C–C bonds are formed via intersystem crossing (ISC). The C–O bonding is the rate-determining step of PB cycloaddition. For the cycloreversion reactions, the ring-opening processes completely occur in the singlet excited states of oxetanes. The head-to-head oxetane goes through a conical intersection before cycloreversion with a little energy barrier of 1.8 kcal mol−1. The head-to-tail oxetane splits without a barrier. Then, the ISC processes take place to restore thymine. Throughout the ring-closing and ring-opening processes, ISC plays an important role. These findings are in good agreement with the available experimental findings. We hope that this comprehensive work can provide a deeper understanding of photosensitive DNA damage and repair. [ABSTRACT FROM AUTHOR]

The significant role of hydrogen abstraction in chemistry and biology has inspired many theoretical works to link its practical phenomena and mechanistic properties. Here, the photophysical processes and hydrogen abstraction mechanisms of benzophenone (BZP) photosensitized thymine damage were systematically investigated from theoretical principles. It was found that the BZP photosensitizer upon UV irradiation undergoes vertical excitation, internal conversion, vibrational relaxation and intersystem crossing into a triplet excited state. Then the triplet BZP damages thymine by a hydrogen abstraction process. However, the reverse reaction easily occurs due to the lower reaction energy, which causes a low yield of hydrogen abstraction products. We hope this comprehensive work can provide a deeper understanding of photosensitive DNA damage from hydrogen abstraction. [ABSTRACT FROM AUTHOR]

To improve the water-resistance of MgO-based metal–insulator–metal (MIM) capacitors, BeO/MgO/BeO/MgO/BeO (BMBMB) stacked layers with a total thickness of ∼10 nm (2/2/2/2/2 nm) were deposited at 335 °C by atomic layer deposition (ALD) using bis(cyclopentadienyl)magnesium [Mg(Cp)2] and diethyl beryllium (DEB) as Mg and Be precursors, respectively, and O3 as an oxygen source. High-quality MgO and BeO single films were produced under optimized ALD conditions. The bottom electrode was a sputtered 50 nm-thick TiN layer, and a 10/30 nm-thick TiN/Pt layer served as the top electrode. The adoption of BeO layers in the insulator stack enabled excellent water-resistance, while the MgO-based capacitor suffered from severely degraded electrical performance during water exposure. Moreover, the capacitors with BeO layer insertion showed a significantly reduced leakage current density (J) to ∼10−9 A cm−2 at an applied bias of +0.8 V even without further annealing treatment during the aggressive water immersion test. Even with a relatively low k of the inserted BeO layer, the equivalent oxide thickness (EOT) could be further decreased to ∼3.5 nm for the 10 nm-thick BMBMB stacked layer, which was similar to the EOT value of the single MgO film with identical thickness. The chemical composition, interface properties, chemical bonding, and crystallization behaviors were comparatively studied for single and stacked layers. This work demonstrated that the BMBMB thin film stack could be a desirable moisture and leakage current blocking layer in recent electronic devices with nanoscale dimensions. [ABSTRACT FROM AUTHOR]

The reactions of cycloaddition, intramolecular H-shift and concerted elimination of alkenyl peroxy radicals are three kinds of important reactions in the low temperature combustion of alkenes. In this study, the cycloaddition reactions are divided into classes considering endo-cycloaddition, exo-cycloaddition and the size of the transition states; the intramolecular H-shift reactions are divided into classes depending upon the ring size of the transition states and the type of C–H bonds from which the hydrogen atom is transferred; the concerted elimination reactions are divided into classes according to the type of H–CβCαOO bond that is broken. All geometry optimizations are performed at the B3LYP/6-31G(2df,p) level. With the electronic structure calculations being performed using the composite Gaussian-4 (G4) method, high pressure limit rate constants and pressure-dependent rate constants at pressures varying from 0.01 to 100 atm are calculated by using canonical transition state theory and the Rice–Ramsberger–Kassel–Marcus/master equation method, respectively. All rate constants are given in the form of the modified Arrhenius expression. The high pressure limit rate rules and the pressure-dependent rate rules are derived by averaging the rate constants of a representative set of reactions in each class. The results show that the rate rules for these three classes of reactions have a large uncertainty and the impact of the pressure on the rate constants increases as temperature increases. [ABSTRACT FROM AUTHOR]

For the first time, we report the synthesis of Ag nanoparticles (NPs) arranged in a helical structure on a chiral metal–organic framework via a facile process at room temperature. This material can serve as a new type of surface-enhanced Raman scattering sensor for the efficient recognition of d/l-cysteine and d/l-asparagine enantiomers. [ABSTRACT FROM AUTHOR]

The effects of different one-dimensional laminar flames on the prediction of nitrogen oxide (NO X ) emission in Sandia Flame D are numerically investigated using a flamelet method in the present work. In addition to the basic control variables of the mixture fraction and the reaction progress variable for chemistry tabulation in this combustion model, two additional variables of mixture fraction variance and enthalpy loss are added to the control variable space to improve prediction accuracy of the NO X pollutant. The former variable of mixture fraction variance is used for the presumed probability density function integration, and the latter takes into account the non-adiabatic effect. Two flamelet libraries are generated based on the one-dimensional unstretched premixed flame and the one-dimensional counterflow diffusion flame, respectively. An additional transport equation for the mass fraction of nitrogen oxide (NO) is solved for improving prediction accuracy. The unsteady Reynolds-averaged Navier-Stokes (URANS) simulation results are compared and analyzed with experimental data. The simulation results show dependence on the type of laminar flame. In the four-dimensional control variable space, the results with steady unstretched premixed flame indicate great agreement on the predictions of temperature and NO field. The computational method proposed in the present work sheds light on the high-precision combustion numerical simulation of NO X emission., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)