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A theoretical mechanistic study of the formation of imidazo[1,2-a]pyrazine-3,6-diones derived from alpha-amino acids using pyrolysis and silica-catalyzed process is presented. The cyclocondensation of N-acylated diketopiperazincs into bicyclic amidines is endothermic for Gly and exothermic for [alpha]-aminoisobutic acid.

A numerical model that describes the transport of mobile ionic species in metal–insulator–semiconductor (MIS) and photovoltaic (PV) devices subject to temperature and voltage stress is presented. The finite element method (FEM) is used to solve the Nernst–Planck equation while imposing Poisson's equation self‐consistently as a restriction for the electrostatic potential. This allows the contribution of the ionic species to the potential to be taken into account. Using a variational formulation eases the implementation of diverse boundary conditions, including the incorporation of segregation kinetics at the device interfaces. Segregation across the dielectric–semiconductor interface is relevant to modeling the electronic device degradation in systems where contamination reaches the semiconductor. The model in closed systems with no‐flux boundary conditions is validated first. In the limiting case of low contamination levels with respect to the gate bias, the FEM solution matches analytically derived approximations. Then, the implementation is broadened to include an open boundary at the dielectric–semiconductor interface to account for leakage of ions. The predicted time dependence of the flatband voltage in Na‐contaminated MIS test structures agrees well with measurements. The model successfully captures the role of long‐range ion transport at concentrations of relevance to electronic and PV device instability and neuromorphic computing. [ABSTRACT FROM AUTHOR]

The noncovalent bonding between nucleobases (NBs) and Stone–Wales (SW) defect‐containing closed‐end single‐walled carbon nanotubes (SWNTs) was theoretically studied in the framework of density function theory using a dispersion‐corrected functional PBE‐G06/DNP. The models employed in this study were armchair nanotube (ANT) (5,5) and zigzag nanotube (ZNT) (10,0), which incorporated SW defects in different orientations. In one of them, the (7,7) junction is tilted with respect to SWNT axis (ANT‐t and ZNT‐t), whereas in ANT‐p and ZNT‐p models the (7,7) junction is parallel and perpendicular to the axis, respectively. The binding energies for uracil, thymine, cytosine, 5‐methylcytosine, adenine, and guanine interacting with the defect‐containing nanotube models were compared to the values previously obtained with the same calculation technique for the case of defect‐free SWNTs, both in the gas phase (vacuum) and in aqueous medium. For most models, the interaction strength tends to be higher for purine than for pyrimidine complexes, with a clear exception of the systems including ZNT‐p, both in vacuum and in aqueous medium. As it could be expected, the binding strength in the latter case is lower as compared to that in vacuum, roughly by 2–4 kcal/mol, due to the implicit inclusion of a medium (i.e., water) via the conductor‐like screening model model. The closest contacts between NBs and SWNT models, frontier orbital distribution, and highest‐occupied molecular orbital–lowest‐unoccupied molecular orbital gap energies are analyzed as well. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A new reactivity indicator termed general-purpose reactivity indicator was used to predict the regioselectivity in the reaction of hydrogen addition onto azahydro[60]fullerene [C.sub.59][H.sub.n+1]N (n = 0-4) systems. The newly developed reactivity indicator was found to be most efficient to predict the reactivity in the aza[60]fullerene derivatives compared to traditional indicators.

The density functional theory calculations results for new stable structures of the [Au.sub.32.sup.Z] (Z = +1, O, -1) clusters is presented. The results suggest that disordered structures for the [Au.sub.32] clusters could be detected at room temperature as well as lower temperature.