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Due to their pivotal role in atmospheric processes, hydrogen abstraction reactions are vital in the study of tropospheric chemistry. In this work, we present an algorithm that generates a large number of chemically sound geometries for the optimization of transition states (TSs) of tropospheric bimolecular H abstraction reactions. The code, which was developed in the early stages with the help of artificial intelligence (AI), automatically detects the active H atoms of the molecule and can be used with the OH, Cl, and NO 3 oxidants. Given the ubiquity of H transfer reactions in various fields, the algorithm was designed in general terms to facilitate easy adaptation to other oxidants, thus allowing for a broader range of applications. As a result of its use, a much greater number of TSs is predicted when compared with previous theoretical studies of six oxidation reactions. In addition to improving our understanding of the H-abstraction process, obtaining an increased number of TSs is also fundamentally important in calculating more accurate rate constants and atmospheric lifetimes for volatile organic compounds. The simplicity and significance of such a tool in the context of environmental chemistry should make it appealing to researchers of all backgrounds. [Display omitted] • An algorithm for transition state sampling of H abstraction reactions is presented. • The Fortran code is provided and is easy to adapt to other oxidants. • The algorithm enhances the calculation of atmospheric oxidation rate constants. [ABSTRACT FROM AUTHOR]

Electronically excited nitrogen atoms and N 2 molecules play a major role in nitrogen-rich atmospheres, specially under extreme conditions. Here we computationally explore several excited states of the N 2 O system and identify two new reactions involving the excited species N 2 (A) and N( 2 D) that can occur without electronic transitions. Their rate coefficients are estimated for the first time, and their implication to atmospheric models are discussed. We infer that the O( 3 P)+N 2 (A) → N( 2 D)+NO(X) channel should account for the total experimental NO production at room temperature. [Display omitted] • We survey many electronic states of NO 2 : 1 3 A", 2 3 A", 3 3 A", 4 3 A", 1 5 A' and 1 5 A". • Rate coefficients are calculated for the O( 3 P)+N 2 (X) → N( 2 D)+NO(X) reaction. • The O( 3 P)+N 2 (A) → N( 4 S)+NO(X) reaction is explored in the quintet states. • Within O( 3 P)+N 2 (A) → N( 4 S/ 2 D)+NO(X) we predict that only N(2D) is formed experimentally. [ABSTRACT FROM AUTHOR]

[Display omitted] • The highest adsorbed amounts of methylene blue and indigo carmine are obtained in less functionalized rGOs. • DFT calculations show that the most favorable rGO-dye interaction geometry is parallel via π-stacking interactions. • MLFM indicates that the elimination of functional groups increases the fraction of molecules that adsorb a parallel orientation. • MLFM revealed that adsorption sites on rGO surface are capable of orienting up to two adsorbate molecules. • The combination of DFT and MLFM fitting provides a comprehensive explanation for the adsorption experimental data. In this work, an alternative theoretical–experimental approach was combined to investigate the influence of the degree of functionalization of reduced graphene oxides (rGO) on the capacity and adsorption mechanisms of two model organic dyes. The experimental adsorption equilibrium data for methylene blue (MB) and indigo carmine (IC) were adjusted and studied using an efficient Multi-Layer Finite Model (MLFM) based on statistical mechanics. Additionally, density functional calculations (DFTB and DFT) were carried out to study the molecular interaction geometry and adsorption energies. With this approach, a greater amount of information about the adsorption process can be obtained in relation to commonly used methodologies for adsorption at a solid–liquid interface. Herein, kinetic and adsorption equilibrium experiments were conducted on rGOs prepared via thermal reduction at different temperatures (300, 700, and 1000 °C) in order to obtain very different contents of oxygenated functional groups. The highest adsorbed amounts are obtained for rGO1000, reaching 208 and 320 mg g−1 for MB and IC, respectively. The MLFM results revealed that the rGO-dye interaction occurs preferentially via π-stacking, and with the formation of up to two adsorption layers. The elimination of functional groups from the surface of rGOs is also revealed to be favorable, decreasing the adsorption energy and increasing the amount and fraction of molecules adsorbed in parallel orientation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ferrihydrite (Fh) shows a superior capacity for amoxicillin-AMX uptake (75 mg g−1). • The Al-for-Fe substitution increases surface OH and decreases AMX adsorption. • Bidentate-binuclear complexation is the main AMX adsorption mechanism on Fh. • Inner-sphere complexation characterizes strong sorption, less mobile adsorbate. • Strong sorption on soils can minimize superficial and groundwater contamination. The fixation of amoxicillin (AMX) by soils is a strategy to minimize the contamination of plants and groundwater by this antibiotic. Ferrihydrite (Fh) is a mineral largely found in the soil, and capable of removing emerging contaminants, such as AMX. To better understand the role of this mineral on AMX retention, nanoparticles containing 0, 10, and 20 mol% of Al, a common substitute for iron in Fh, were synthesized. Ferrihydrites showed AMX adsorption capacity superior (75 mg g−1) to other common soil constituents. The optimum pH for the AMX adsorption by the studied materials (Fh-0 %Al, Fh-10 %Al, and Fh-20 %Al) was pH 4. This condition favors electrostatic attraction (AMX-carboxyl/Fh), though experiments demonstrated this is not the main mechanism of adsorption. Raman and Fourier transform infrared spectroscopies combined with a theoretical approach using the density functional tight-binding method showed the bidentate binuclear complexation of the AMX - COO– group with the Fh particle as the main adsorption mechanism. The Al substitution decreases AMX uptake. The effect was attributed to the increase of surface OH, thus avoiding CH 3 interaction with the Fh surface. The interaction mechanism suggests that a strong AMX fixation on Fh-rich natural soil will occur, preventing water contamination and allowing for further biotic degradation. [ABSTRACT FROM AUTHOR]

Nanoalloys have been investigated for a wide range of applications, however, our atomistic understanding of the physical-chemistry properties is still far from complete as quantum-size effects play an important role for particles with about 1 nm diameter. In this work, we employed density functional theory calculations to investigate the structural, energetic and electronic properties of 55-atom A 55- n B n nanoalloys, where A , B = Al, Cu, Zn, and Ag. For structure generation, we combined clustering algorithm techniques with design principles, which yields a wide range of conformations. From the analyses of the excess energy results, we found that the CuAl, CuAg, CuZn, and AlAg systems are the most energetically favorable, in particular, the Al 42 Cu 13 and Al 42 Ag 13 compositions (onion-like and core–shell structures, respectively). Through Spearman's correlation analysis, we found that the structural properties (number of under coordinated atoms, effective coordination number, average bond lengths, and chemical order parameter) are the most important descriptors correlated with the energy stability of the nanoalloys (excess energy). Several properties such as the particle volume, binding energy, and average bond length show a linear dependence as a function of composition. [ABSTRACT FROM AUTHOR]

This work describes a facile synthesis of 5,6‐dimethyl‐2‐(pyridin‐2‐yl)‐1‐[(pyridin‐2‐yl)methyl]‐1H‐benzimidazole (dppb) and the preparation of a dinuclear copper(II) complex bearing this ligand in a ring‐like conformation of formula [Cu(dppb)(acn)ClO4]2(ClO4)2·4acn (1), where acn represents acetonitrile. The crystal structure of the complex was determined by single‐crystal X‐ray diffraction experiment, which showed that dppb acts as a bridge in 1 due to its bidentate–monodentate μ‐κ2NN′:κN″coordination mode, and the coordination sphere of each metal center is completed by one acn molecule and one perchlorate ion. The structure of dinuclear copper(II) complex is symmetric and the two square–pyramidal copper(II) centers are separated by 5.381(1) Å. The geometry optimization, electronic structure, and vibrational spectrum of the [Cu(dppb)(acn)ClO4]22+ cation were calculated using the density functional theory method. The geometrical parameters obtained theoretically were remarkably similar to those observed in the crystal structure of 1 and the calculated vibrational frequencies are in satisfactory coherence with experimental data. In solution, the prepared complex can bind to DNA (Kb = 1.43 × 105 M−1) and inhibit the growth of a human chronic myelogenous leukemia cell line (K562) in a concentration‐dependent manner; importantly, it is almost four times more active than the corresponding free benzimidazole. [ABSTRACT FROM AUTHOR]