Theoretical insights into the HO-induced oxidation of chlorpyrifos pesticide: Mechanism, kinetics, ecotoxicity, and cholinesterase inhibition of degradants.

The oxidation of the common pesticide chlorpyrifos (CPF) initiated by HO radical and the risks of its degradation products were studied in the gaseous and aqueous phases via computational approaches. Oxidation mechanisms were investigated, including H-, Cl-, CH- abstraction, HO-addition, and single electron transfer. In both phases, HO-addition at the C of the pyridyl ring is the most energetically favorable and spontaneous reaction, followed by H-abstraction reactions at methylene groups (i.

Cyclo[]carbons and catenanes from different perspectives: disentangling the molecular thread.

All-carbon atomic rings, cyclo[]carbons, have recently attracted vivid attention of experimentalists and theoreticians. Among them, cyclo[18]carbon is the most studied system. In this paper, we summarize and review various properties of cyclo[]carbons, emphasising the aspects of their aromaticity/antiaromaticity.

New insight into environmental oxidation of phosmet insecticide initiated by HO˙ radicals in gas and water - a theoretical study.

Phosmet is an organophosphorus insecticide widely used in agriculture to control a range of insects; recently, it was banned by the European Union in 2022 due to its harmful effects. However, its environmental degradation and fate have not yet been evident. Thus, phosmet oxidation by HO˙ radicals was theoretically studied in this work using the DFT approach at the M06-2X/6-311++G(3df,3pd)//M06-2X/6-31+G(d,p) level of theory.

Hydroxyl radical-initiated decomposition of metazachlor herbicide in the gaseous and aqueous phases: Mechanism, kinetics, and toxicity evaluation.

The oxidation of widely-used herbicide metazachlor (MTZ) by hydroxyl radical (HO) in the gas and the aqueous phases was investigated in terms of mechanistic and kinetic behaviors using the M06-2X/6-311++G (3df, 3pd)//M06-2X/6-31 + G (d,p) level of theory over the temperature range 250-400 K. The formal hydrogen transfer, HO-addition, and single electron transfer mechanisms were considered. The overall rate constants in the gas phase range from 8.

Together, Not Separately, OH and O Oxidize Hg to Hg in the Atmosphere.

Mercury, a highly toxic metal, is emitted to the atmosphere mostly as gaseous Hg. Atmospheric Hg enters ecosystems largely through uptake by vegetation, while Hg largely enters ecosystems in oceans and in rainfall. Consequently, the redox chemistry of atmospheric mercury strongly influences its fate and its global biogeochemical cycling.

Improved Mechanistic Model of the Atmospheric Redox Chemistry of Mercury.

We present a new chemical mechanism for Hg/Hg/Hg atmospheric cycling, including recent laboratory and computational data, and implement it in the GEOS-Chem global atmospheric chemistry model for comparison to observations. Our mechanism includes the oxidation of Hg by Br and OH, subsequent oxidation of Hg by ozone and radicals, respeciation of Hg in aerosols and cloud droplets, and speciated Hg photolysis in the gas and aqueous phases. The tropospheric Hg lifetime against deposition in the model is 5.

Theoretical Study of the Monohydration of Mercury Compounds of Atmospheric Interest.

The structures, vibrational frequencies, and model IR spectra of the monohydrates of oxygenated mercury compounds (BrHgO, BrHgOH, BrHgOOH, BrHgNO, BrHgONO, and HgOH) have been theoretically studied using the ωB97X-D/aug-cc-pVTZ level of theory. The ground state potential energy surface exhibits several stable structures of these monohydrates. The thermodynamic properties of the hydration reactions have been calculated at different levels of theory including DFT and coupled-cluster calculations DK-CCSD(T) with the ANO-RCC-Large basis sets.

On the work function of the surface Mo(0 0 1) and its temperature dependence: an ab initio molecular dynamics study.

Ab initio molecular dynamics simulations in NVT ensemble have been performed to investigate the finite temperature structure of the Mo(0 0 1) surface and its effect on work function (ϕ). In accord with previous experimental and theoretical work, our simulations predict that a termination with a stable reconstruction pattern is formed at T  =  123 K. This pattern vanishes when temperature is increased to 423 K or 623 K and a disordered surface phase is formed whose time average corresponds to a bulk-like termination.

Theoretical Study of the Reactions of H Atoms with CHI and CHI.

High level ab initio methods have been used to provide reliable kinetic data for the H + CHI and H + CHI gas-phase reactions. The (H, I)-abstraction and I-substitution reaction pathways were identified. The structures were determined on the potential energy surface at the MP2/aug-cc-pVTZ level of theory.

Reactivity of Hydrogen Peroxide with Br and I Atoms.

The reaction mechanisms of Br and I atoms with HO have been investigated using DFT and high-level ab initio calculations. The H-abstraction and OH-abstraction channels were highlighted. The geometries of the stationary points were optimized at the B3LYP/aug-cc-pVTZ level of theory, and the energetics were recalculated with the coupled cluster theory.

MS-CASPT2 study of the ground and low lying states of CsH.

Correlated ab initio methods [CASPT2 and R-CCSD(T)] in conjunction with the ANO-RCC basis sets in large contraction were used to calculate potential energy curves (PECs) of the ground and excited electronic states of CsH (doublets and quartets) with the inclusion of the scalar relativistic effects and spin-orbit interaction. The ground XΣ state is a rather fragile van der Waals molecular ion. The binding energy of this XΣ state provided by both computational methods is estimated to be 0.

Caesium hydride: MS-CASPT2 potential energy curves and AΣ→XΣ absorption/emission spectroscopy.

Correlated ab initio methods (CASPT2 and CCSD(T)) in conjunction with the ANO-RCC basis sets were used to calculate potential energy curves (PECs) of the ground, valence, and Rydberg electronic states of CsH with the inclusion of the scalar relativistic effects. The spectroscopic constants of bound states were calculated from the PECs and compared with previous theoretical and/or available experimental data. Absorption and emission spectra arising from the transition between XΣ and AΣ states were modelled using vibrational and rotational energy levels and corresponding nuclear wave functions obtained via the direct numerical integration of one-dimensional rovibrational Schrödinger equation in the CASPT2/ANO-RCC electronic potentials.

A Density Functional Theory and ab Initio Investigation of the Oxidation Reaction of CO by IO Radicals.

To get an insight into the possible reactivity between iodine oxides and CO, a first step was to study the thermochemical properties and kinetic parameters of the reaction between IO and CO using theoretical chemistry tools. All stationary points involved were optimized using the Becke's three-parameter hybrid exchange functional coupled with the Lee-Yang-Parr nonlocal correlation functional (B3LYP) and the Møller-Plesset second-order perturbation theory (MP2). Single-point energy calculations were performed using the coupled cluster theory with the iterative inclusion of singles and doubles and the perturbative estimation for triple excitations (CCSD(T)) and the aug-cc-pVnZ (n = T, Q, and 5) basis sets on geometries previously optimized at the aug-cc-pVTZ level.

Reactivity of CHI3 with OH radicals: X-abstraction reaction pathways (X = H, I), atmospheric chemistry, and nuclear safety.

The X-abstraction (X = H, I) pathways in the reaction of CHI3 with OH radical, a possible iodoform removal process relevant to the Earth's atmosphere and conditions prevailing in the case of a nuclear accident, have been studied applying highly correlated ab initio quantum chemistry methods and canonical transition-state theory to obtain reaction energy profiles and rate constants. Geometry optimizations of reactants, products, molecular complexes, and transition states determined at the MP2/cc-pVTZ level of theory have been followed by DK-CCSD(T)/ANO-RCC single-point energy calculations. Further improvement of electronic energies has been achieved by applying spin-orbit coupling, corrections toward full configuration interaction, vibration contributions, and tunneling corrections.

Microhydration of caesium compounds: Cs, CsOH, CsI and Cs₂I₂ complexes with one to three H₂O molecules of nuclear safety interest.

Structure and thermodynamic properties (standard enthalpies of formation and Gibbs free energies) of hydrated caesium species of nuclear safety interest, Cs, CsOH, CsI and its dimer Cs₂I₂, with one up to three water molecules, are calculated to assess their possible existence in severe accident occurring to a pressurized water reactor. The calculations were performed using the coupled cluster theory including single, double and non-iterative triple substitutions (CCSD(T)) in conjunction with the basis sets (ANO-RCC) developed for scalar relativistic calculations. The second-order spin-free Douglas-Kroll-Hess Hamiltonian was used to account for the scalar relativistic effects.

Structural changes in the series of boron-carbon mixed clusters C(x)B(10-x)- (x = 3-10) upon substitution of boron by carbon.

We report a theoretical investigation on the ten-atom boron-carbon mixed clusters C(x)B(10-x)(-) (x = 3-10), revealing a molecular wheel to monocyclic ring and linear species structural change as a function of x upon increasing the number of carbon atoms in the studied series. The unbiased searches for the global minimum structures of the clusters with x ranging from 3 to 9 were conducted using the Coalescence Kick program for different spin multiplicities. Subsequent geometry optimizations with follow-up frequency calculations at the hybrid density functional B3LYP∕6-311+G(d) level of theory along with the single point coupled-cluster calculations (UCCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(d) and RCCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(d)) revealed that the C3B7(-) and C4B6(-) clusters possess planar distorted wheel-type structures with a single inner boron atom, similar to the recently reported CB9(-) and C2B8(-).

On the way to the highest coordination number in the planar metal-centred aromatic Ta©B10- cluster: evolution of the structures of TaB(n)- (n = 3-8).

The structures and chemical bonding of TaB(n)(-) (n = 3-8) clusters are investigated systematically to elucidate the formation of the planar metal-centred aromatic borometallic cluster, Ta©B10(-) (the © sign is used to designate the central position of the doped atom in monocyclic structures in M©B(n)-type planar clusters), which was found previously to have the highest coordination number for a metal atom in a planar geometry. Photoelectron spectroscopy is combined with ab initio calculations to determine the global minima of the TaB(n)(-) clusters. We find that from TaB3(-) to TaB5(-) the boron atoms nucleate around the central Ta atom to form fan-like structures.

Photoelectron spectroscopy and ab initio study of boron-carbon mixed clusters: CB9- and C2B8-.

We performed a joint photoelectron spectroscopy and ab initio study of two carbon-doped boron clusters, CB(9)(-) and C(2)B(8)(-). Unbiased computational searches revealed similar global minimum structures for both clusters. The comparison of the experimentally observed and theoretically calculated vertical detachment energies revealed that only the global minimum structure is responsible for the experimental spectra of CB(9)(-), whereas the two lowest-lying isomers of C(2)B(8)(-) contribute to the experimental spectra.

Ab initio calculations of molecular properties of low-lying electronic states of 2-cyclopenten-1-one--link with biological activity.

Geometries, vibrational frequencies, vertical and adiabatic excitation energies, dipole moments and dipole polarizabilities of the ground and the three lowest electronic excited states, S₁(n, π*), T₁(n, π*), and T₂(π, π*) of the 2-cyclopenten-1-one molecule (2CP) were calculated at the CCSD and CCSD(T) levels of approximation. Our results indicate that two triplets T₁(n, π*) and T₂(π, π*) are lying very close each to other, while the singlet S₁(n, π*) is well above them. There are dramatic changes in dipole moments for (n, π*) excited states in respect to the ground state.

Toward more efficient CCSD(T) calculations of intermolecular interactions in model hydrogen-bonded and stacked dimers.

Interaction energies of the model H-bonded complexes, the formamide and formamidine dimers, as well as the stacked formaldehyde and ethylene dimers are calculated by the coupled cluster CCSD(T) method. These systems serve as a model for H-bonded and stacking interactions, typical in molecules participating in biological systems. We use the optimized virtual orbital space (OVOS) technique, by which the dimension of the space of virtual orbitals in coupled cluster CCSD(T) calculations can be significantly reduced.

On the ground and some low-lying excited states of ScB: a multiconfigurational study.

The electronic structure of a series of low-lying excited triplet and quintet states of scandium boride (ScB) was examined using multireference configuration interaction (including Davidson's correction for quadruple excitations) and single-reference coupled cluster (CC) methods with averaged natural orbital (ANO) basis sets. The CC approach was used only for the lowest quintet state. The authors have analyzed eight low-lying triplets 3Sigma-(2), 3Sigma+, 3Pi(3), and 3Delta(2) dissociating to Sc(2D)/B(2P) atoms and eight low-lying quintet states 5Sigma-, 5Sigma+, 5Pi(2), 5Phi, and 5Delta(3) dissociating to Sc(4F)/B(2P) atoms.