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, BrHgNO2, 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. Standard enthalpies and Gibbs free energies of hydration were computed. The temperature dependence of ΔrG°(T) was evaluated for the most stable complexes over the temperature range 200-400 K. Thermodynamic data revealed that the highest fraction hydrated at 298 K and 100% relative humidity will be BrHgNO2-H2O at ∼5%.

Theoretical Investigation of the Reaction of Pyrene Formation from Fluoranthene.

This paper has investigated the reaction process concerning pyrene formation from fluoranthene in their electronic ground states. Both aromatic compounds are considered as direct soot precursors. The geometrical parameters, the vibrational frequencies, and the zero-point energies have been calculated using the BMK (Boese-Martin for kinetics) method and the 6-311++G(d,p) basis set. More accurate single-point energies have been obtained using BMK/6-311++G(3df,2p) to retrieve thermodynamic properties (ΔrH°(T) and ΔrG°(T)) over a wide temperature range (298-2500 K). The isomerization reaction of fluoranthene to pyrene is exothermic and spontaneous in standard conditions. The transition states and the possible intermediate species have been located on the singlet potential energy surface in order to determine the reaction mechanism. Two different reaction channels have been investigated and characterized by entrance reaction barriers of about 419 and 771 kJ mol-1 for the first and the second reaction pathways, respectively. The present work demonstrates that the first reaction channel is the most energetically favored pathway at high temperatures. Therefore, the kinetic parameters of the forward and reverse first step reactions have been determined in sooting flame conditions.

Theoretical Study of the Reactions of H Atoms with CH3I and CH2I2.

High level ab initio methods have been used to provide reliable kinetic data for the H + CH3I and H + CH2I2 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. The energetics was then refined using the coupled cluster theory. For the iodinated species, the spin-orbit coupling was calculated using the MRCI approach. The core valence and the scalar relativistic corrections were considered. Thermal rate constants were reported using the canonical transition-state theory (TST) and compared to computed values with the canonical variational transition-state theory (CVT) using the zero curvature tunneling (ZCT) and the small curvature tunneling (SCT) corrections over a wide temperature range (250-2500 K) to show the importance of quantum tunneling effects at low temperatures. They are given by the following expressions for the overall reactions using the CVT/SCT method: kH+CH3I( T) = 1.07 × 10-17 × T2.13 exp(2.68 (kJ mol-1)/ RT) and kH+CH2I2( T) = 5.73 × 10-21 × T2.97 exp(3.15 (kJ mol-1)/ RT). The I-abstraction is predicted to be the major pathway for both H + CH3I and H + CH2I2 reactions. The obtained kinetic parameters for the H + CH3I reaction are in excellent agreement with their experimental counterparts over the temperature range 300-750 K. On the basis of our calculated reaction enthalpies, a new evaluation of the standard enthalpy of formation at 298 K of CH2I and CHI2 has been provided. Obtained values are Δf H°298K (CH2I) = 219.5 kJ mol-1 and Δf H°298K(CHI2) = 296.3 kJ mol-1.

Reactivity of Hydrogen Peroxide with Br and I Atoms.

The reaction mechanisms of Br and I atoms with H2O2 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. Spin-orbit coupling for each halogenated species was also explicitly computed by employing the MRCI level of theory. Thermochemistry for HOBr and HOI has been revised and updated standard enthalpies of formation at 298 K for HOBr and HOI are the following: ΔfH°298K(HOBr) = (-66.2 ± 4.6) kJ mol-1 and ΔfH°298K(HOI) = (-66.8 ± 4.7) kJ mol-1. The rate constants have been estimated using transition state theory (TST), canonical variational transition state theory (CVT), and CVT with small curvature tunneling (CVT/SCT) over a wide temperature range (250-2500 K). For the direct abstraction mechanism, the overall rate constant at 300 K was predicted to be 2.58 × 10-16 and 7.42 × 10-25 cm3 molecule-1s-1 for the Br + H2O2 and I + H2O2 reactions, respectively. The modified Arrhenius parameters have been estimated for the overall reactions: kBr+H2O2(T) = 4.80 × 10-26 T4.31 exp(-5.51 (kJ mol-1)/RT) and kI+H2O2(T) = 3.41 × 10-23 T3.29 exp(-56.32 (kJ mol-1)/RT).

Caesium hydride: MS-CASPT2 potential energy curves and A1Σ+→X1Σ+ 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 X1Σ+ and A1Σ+ 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. The anharmonic shape of the A1Σ+ potential and the shape of the pertinent vibrational wave functions have an interesting impact on the final shape of the spectrum and result in the complicated fine structure of individual emission bands.

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. The energetics was then recalculated using the one-component DK-CCSD(T) approach with the relativistic ANO basis sets. The spin-orbit coupling for the iodine containing species was calculated a posteriori using the restricted active space state interaction method in conjunction with the multiconfigurational perturbation theory (CASPT2/RASSI) employing the complete active space (CASSCF) wave function as the reference. The CCSD(T) energies were also corrected for BSSE for molecular complexes and refined with the extrapolation to CBS limit while the DK-CCSD(T) values were refined with the extrapolation to FCI. The exploration of the potential energy surface revealed a two-steps mechanism with a trans and a cis pathway. The rate constants for the direct and complex mechanism were computed as a function of temperature (250-2500 K) using the canonical transition state theory. The three-parameter Arrhenius expressions obtained for the direct and indirect mechanism at the DK-CCSD(T)-cf level of theory is 1.49 × 10(-17) × T(1.77) exp(-47.4 (kJ mol(-1))/RT).

Thermochemistry of Ruthenium Oxyhydroxide Species and Their Impact on Volatile Speciations in Severe Nuclear Accident Conditions.

Literature thermodynamic data of ruthenium oxyhydroxides reveal large uncertainties in some of the standard enthalpies of formation, motivating the use of high-level relativistic correlated quantum chemical methods to reduce the level of discrepancies. Reaction energies leading to the formation of all possible oxyhydroxide species RuOx(OH)y(H2O)z have been calculated for a series of reactions combining DFT (TPSSh-5%HF) geometries and partition functions, CCSD(T) energies extrapolated to the complete basis set limits. The highly accurate ab initio thermodynamic data were used as input data of thermodynamic equilibrium computations to derive the speciation of gaseous ruthenium species in the temperature, pressure and concentration conditions of severe nuclear accidents occurring in pressurized water reactors. At temperatures lower than 1000 K, gaseous ruthenium tetraoxide is the dominating species, between 1000 and 2000 K ruthenium trioxide becomes preponderant, whereas at higher temperatures gaseous ruthenium oxide, dioxide and even Ru in gaseous phase are formed. Although earlier studies predicted the formation of oxyhydroxides in significant quantities, the use of highly accurate ab initio thermodynamic data for ruthenium gaseous species leads to a more reliable inventory of gaseous ruthenium species in which gaseous oxyhydroxide ruthenium molecules are formed only in negligible amounts.

Gas-Phase Reactivity of Cesium-Containing Species by Quantum Chemistry.

Thermodynamics and kinetics of cesium species reactions have been studied by using high-level quantum chemical tools. A systematic theoretical study has been done to find suitable methodology for calculation of reliable thermodynamic properties, allowing us to determine bimolecular rate constants with appropriate kinetic theories of gas-phase reactions. Four different reactions have been studied in this work: CsO + H2 = CsOH + H (R1), Cs + HI = CsI + H (R2), CsI + H2O = CsOH + HI (R3), and CsI + OH = CsOH + I (R4). All reactions involve steam, hydrogen, and iodine in addition of cesium. Most of the reactions are fast and (R3) and (R4) proceed even without energetic barrier. In terms of chemical reactivity in the reactor coolant system (RCS) in the case of severe accident, it can be expected that there will be no kinetic limitations for main cesium species (CsOH and CsI) transported along the RCS. Cs chemical speciation inside the RCS should be governed by the thermodynamics.

Thermodynamic properties of gaseous ruthenium species.

The review of thermodynamic data of ruthenium oxides reveals large uncertainties in some of the standard enthalpies of formation, motivating the use of high-level relativistic correlated quantum chemical methods to reduce the level of discrepancies. The reaction energies leading to the formation of ruthenium oxides RuO, RuO2, RuO3, and RuO4 have been calculated for a series of reactions. The combination of different quantum chemical methods has been investigated [DFT, CASSCF, MRCI, CASPT2, CCSD(T)] in order to predict the geometrical parameters, the energetics including electronic correlation and spin-orbit coupling. The most suitable method for ruthenium compounds is the use of TPSSh-5%HF for geometry optimization, followed by CCSD(T) with complete basis set (CBS) extrapolations for the calculation of the total electronic energies. SO-CASSCF seems to be accurate enough to estimate spin-orbit coupling contributions to the ground-state electronic energies. This methodology yields very accurate standard enthalpies of formations of all species, which are either in excellent agreement with the most reliable experimental data or provide an improved estimate for the others. These new data will be implemented in the thermodynamical databases that are used by the ASTEC code (accident source term evaluation code) to build models of ruthenium chemistry behavior in severe nuclear accident conditions. The paper also discusses the nature of the chemical bonds both from molecular orbital and topological view points.

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. Calculated reaction enthalpies at 0 K are -108.2 and -5.1 kJ mol(-1) for the H- and I-abstraction pathways, respectively; the strongly exothermic H-abstraction pathway is energetically favored over the modestly exothermic I-abstraction one. The overall rate constant at 298 K based on our ab initio calculations is 4.90 × 10(-11) cm(3) molecule(-1) s(-1), with the I-abstraction pathway being the major channel over the temperature range of 250-2000 K. The CHI3 atmospheric lifetime with respect to the removal reaction with OH radical is predicted to be about 6 h, very short compared to that of other halomethanes.

Oxidation of metazachlor herbicide by ozone in the gas and aqueous phases: mechanistic, kinetics, and ecotoxicity studies.

The atmospheric and aqueous ozonolysis of metazachlor (MTZ) is investigated using high-level quantum chemical and kinetic calculations (M06-2X/6-311 + + G(3df,3pd)//M06-2X/6-31 + G(d,p) level of theory). The ozone (O3)-initiated degradation pathways of MTZ under three different mechanisms, namely cycloaddition, oxygen-addition, and single electron transfer (SET), are explored in the temperature range of 283-333 K and 1 atm pressure. As a result, the cycloaddition reaction at the C16C18 double bond of the benzene ring of MTZ is found to be the most dominant channel in the atmosphere with the standard Gibbs free energy of reaction (ΔrG0g) of - 129.13 kJ mol-1 and the highest branching ratio of 95.18%. In the aqueous phase, the main reaction channel turns into the SET mechanism, which owns the lowest Gibbs free energy of activation (ΔG#aq) of 73.8 kJ mol-1 and contributes 87.8% to the ktotal. Over the temperature range of 283-333 K, the total rate constant (ktotal) significantly increases from 8.42 to 5.82 × 101 M-1 s-1 in the atmosphere and from 4.10 × 102 to 2.40 × 104 M-1 s-1 in the aqueous environment. Remarkably, the ecotoxicity assessment shows that MTZ may be harmful to fish and chronically harmful to daphnia. In contrast, its main ozonolysis products exhibit no acute or chronic toxicity or mutagenic effects.

Adsorption dynamics of Cd2+(aq) on microwave-synthetized pristine biochar from cocoa pod husk: Green, experimental, and DFT approaches.

Biochar obtained via microwave-assisted pyrolysis (MAP) at 720 W and 15 min from cocoa pod husk (CPH) is an efficient adsorbent of Cd2+(aq). Biochar of residual biomass of CPH (BCCPH) possesses favorable physicochemical and morphological properties, featuring a modest surface area yet a suitable porous structure. Adsorption, predominantly governed by physisorption, is influenced by the oxygen-containing active sites (-COOR, -C(R)O, and -CH2OR; R = H, alkyl). CdCO3 formation occurs during adsorption. Experimental data were well-fitted into various kinetic models for a broad understanding of the sorption process. Langmuir model indicates a maximum adsorption capacity of 14.694 mg/g. The thermodynamic study confirms the spontaneous and endothermic sorption. Studies at the molecular level have revealed that the Cd2+ ion tends to bind to surface aromatic carbon atoms. This sustainable approach produces BCCPH via MAP as a solution for waste transformation into water-cleaning materials.

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-, CH3- 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.e., at H19/H21 in the gas phase and H22/H28 in water). In contrast, other abstractions and electron transfer reactions are unfavorable. However, regarding the kinetics, the significant contribution to the oxidation of CPF is made from H-abstraction channels, mostly at the hydrogens of the methylene groups. CPF can be decomposed in a short time (5-8 h) in the gas phase, and it is more persistent in natural water with a lifetime between 24 days and 66 years, depending on the temperature and HO● concentration. Subsequent oxidation of the essential radical products with other oxidizing reagents, i.e., HO●, NO2●, NO●, and 3O2, gave primary neutral products P1-P15. Acute and chronic toxicity calculations estimate very toxic levels for CPF and two degradation products, P7w and P12w, in aquatic systems. The neurotoxicity of these products was investigated by docking and molecular dynamics. P7w and P12w show the most significant binding scores with acetylcholinesterases, while P8w and P13w are with butyrylcholinesterase enzyme. Finally, molecular dynamics illustrate stable interactions between CPF degradants and cholinesterase enzyme over a 100 ns time frame and determine P7w as the riskiest degradant to the neural developmental system.

Atmospheric reactivity of CH2ICl with OH radicals: high-level OVOS CCSD(T) calculations for the X-abstraction pathways (X = H, Cl, or I).

Reactants, weak molecular complexes, transition states, and products for the H-, Cl-, and I-abstraction channels in the reaction of OH radicals with chloroiodomethane CH(2)ICl as well as the energy profiles at 0 K have been determined using high-level all-electron ab initio methods. The results showed that all-electron DK-CCSD(T)/ANO-RCC approach performed very well in predicting the reactivity of iodine. In terms of activation enthalpy at 0 K, the energy profile for the Cl-abstraction showed that this reaction pathway is not energetically favorable in contrast to the two other channels (H- and I-abstractions), which are competitive. The H-abstraction was strongly exothermic (-87 kJ mol(-1)), while the I-abstraction was modestly endothermic (11.8 kJ mol(-1)). On the basis of our calculations including the following corrections to the potential energies: basis set saturation, valence and core-valence electron correlation, relativistic effects, spin-adaptation, vibration contributions, and tunneling corrections, rate constants were predicted using canonical transition state theory over the temperature range 250-500 K for each abstraction pathway. The overall rate constant at 298 K was estimated to be 4.29 × 10(-14) and 5.44 × 10(-14) cm(3) molecule(-1) s(-1) for complex and direct abstraction mechanisms, respectively. In addition, the overall rate constant computed at 277 K was used in the estimation of the atmospheric lifetime for CH(2)ICl. On the basis of our theoretical calculations, the atmospheric lifetime for the OH removal process is predicted to be close to 1 year. In terms of atmospheric lifetime, the OH reaction is not competitive with the Cl reaction and photolysis processes.

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 8.40 × 1010 to 8.31 × 109 M-1 s-1 at the temperature from 250 to 400 K, respectively, while the ones in the aqueous phase are close to diffusion-controlled rates, with diffusion-corrected rate constants being 1.31 × 109 to 1.27 × 109 M-1 s-1. The formal hydrogen transfer mechanism is the most dominant in the gas phase, whereas the HO•-addition is the most favorable in the aqueous phase. The H-abstraction at two methyl groups and the HO•-addition to C11 and C12 atoms (pyrazole ring), C16 and C18 atoms (benzyl ring) are significant. The short lifetime in the environment, equal to only 4.16 h, requires more attention to this herbicide compound, whereas its lifetime in the aqueous condition varies sharply from half second to several thousand days depending on the HO• concentration. The ecotoxicity estimation of MTZ and its principal transformation products to aquatic organisms suggests that they are harmful or toxic substances. Moreover, the MTZ is a developmental toxicant and mutagenicity-positive, while its decomposed products are developmental toxicants with no mutagenic toxicity. Their bioaccumulation in aquatic organisms is negligible.

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. Three different mechanisms were considered, including formal hydrogen transfer (FHT), radical adduct formation (RAF), and single electron transfer (SET). The mechanisms, kinetics, and lifetime were studied in the gas and aqueous phases, in addition to its ecotoxicity evaluation. The results show that FHT reactions were dominant in the gas phase, while RAF was more favourable in the aqueous phase at 298 K, while SET was negligible. The branching ratio indicated that H-abstractions at the methyl and the methylene groups were the most predominant, while the most favourable HO˙-addition was observed at the phosphorus atom of the dithiophosphate group. The overall rate constant values varied from 1.2 × 109 (at 283 K) to 1.40 × 109 M-1 s-1 (at 323 K) in the aqueous phase and from 6.29 × 1010 (at 253 K) to 1.32 × 1010 M-1 s-1 (at 323 K) in the gas phase. The atmospheric lifetime of phosmet is about 6 hours at 287 K, while it can persist from a few seconds to several years depending on the temperature and [HO˙] concentration in the aqueous environment. The QSAR-based ecotoxicity evaluation indicates that phosmet and its degradation products are all dangerous to aquatic organisms, although the products are less toxic than phosmet. However, they are generally developmental toxicants and mutagenicity-negative compounds.

Theoretical study of H-abstraction reactions from CH3Cl and CH3Br molecules by ClO and BrO radicals.

The rate constants of the H-abstraction reactions from CH(3)Cl and CH(3)Br molecules by ClO and BrO radicals have been estimated over the temperature range of 300-2500 K using four different levels of theory. Calculations of optimized geometrical parameters and vibrational frequencies are performed using B3LYP and MP2 methods combined with the cc-pVTZ basis set. Single-point energy calculations have been carried out with the highly correlated ab initio coupled cluster method in the space of single, double, and triple (perturbatively) electron excitations CCSD(T) using the cc-pVTZ and cc-pVQZ basis sets. Canonical transition-state theory combined with an Eckart tunneling correction has been used to predict the rate constants as a function of temperature. In order to choose the appropriate levels of theory with chlorine- and bromine-containing species, the reference reaction Cl ((2)P(3/2)) + CH(3)Cl → HCl + CH(2)Cl (R(ref)) was first theoretically studied because its kinetic parameters are well-established from numerous experiments, evaluation data, and theoretical studies. The kinetic parameters of the reaction R(ref) have been determined accurately using the CCSD(T)/cc-pVQZ//MP2/cc-pVTZ level of theory. This level of theory has been used for the rate constant estimation of the reactions ClO + CH(3)Cl (R(1)), ClO + CH(3)Br (R(2)), BrO + CH(3)Cl (R(3)), and BrO + CH(3)Br (R(4)). Six-parameter Arrhenius expressions have been obtained by fitting to the computed rate constants of these four reactions (including cis and trans pathways) over the temperature range of 300-2500 K.

Thermochemical data and additivity group values for ten species of o-xylene low-temperature oxidation mechanism.

o-Xylene could be a good candidate to represent the family of aromatic hydrocarbons in a surrogate fuel. This study uses computational chemistry to calculate standard enthalpies of formation at 298 K, Δ(f)H°(298 K), standard entropies at 298 K, S°(298 K), and standard heat capacities C(p)°(T) over the temperature range 300 K to 1500 K for ten target species present in the low-temperature oxidation mechanism of o-xylene: o-xylene (1), 2-methylbenzyl radical (2), 2-methylbenzylperoxy radical (3), 2-methylbenzyl hydroperoxide (4), 2-(hydroperoxymethyl)benzyl radical (5), 2-(hydroperoxymethyl)benzaldehyde (6), 1-ethyl-2-methylbenzene (7), 2,3-dimethylphenol (8), 2-hydroxybenzaldehyde (9), and 3-hydroxybenzaldehyde (10). Δ(f)H°(298 K) values are weighted averages across the values calculated using five isodesmic reactions and five composite calculation methods: CBS-QB3, G3B3, G3MP2, G3, and G4. The uncertainty in Δ(f)H°(298 K) is also evaluated. S°(298 K) and C(p)°(T) values are calculated at B3LYP/6-311G(d,p) level of theory from molecular properties and statistical thermodynamics through evaluation of translational, rotational, vibrational, and electronic partition functions. S°(298 K) and C(p)°(300 K) values are evaluated using the rigid-rotor-harmonic-oscillator model. C(p)°(T) values at T ≥ 400 K are calculated by treating separately internal rotation contributions and translational, external rotational, vibrational, and electronic contributions. The thermochemical properties of six target species are used to develop six new additivity groups taking into account the interaction between two substituents in ortho (ORT/CH2OOH/ME, ORT/ET/ME, ORT/CHO/OH, ORT/CHO/CH2OOH) or meta (MET/CHO/OH) positions, and the interaction between three substituents (ME/ME/OH123) located one beside the other (positions numbered 1, 2, 3) for two- or three-substituted benzenic species. Two other additivity groups are also developed using the thermochemical properties of benzenic species taken from the literature: the C/CB/H2/OO and the CB/CO groups. These groups extend the capacities of the group additivity method to deal with substituted benzenic species.

Application of a multilayer physical model for the critical analysis of the adsorption of nicotinamide and propranolol on magnetic-activated carbon.

The paper describes a theoretical analysis of the adsorption of nicotinamide and propranolol onto a magnetic-activated carbon (MAC). For a better evaluation of the adsorption mechanism, adsorption isotherms expressing the variation of the adsorption capacity as function of adsorbate concentration were determined at different temperatures ranging from 20 to 45 °C. For both the analytes, experimental tests reveal that adsorption capacity increases with temperature. An advanced multi-layer model derived from the statistical physics is set for the interpretation of the entire adsorption data set. The modelling results show that the propranolol molecules change their adsorption orientation from a mixed (parallel and non-parallel) orientation to a multimolecular process. For nicotinamide, the aggregation of molecules is practically absent, except for the data at lower temperatures. The model allows stating that the adsorption of both the pharmaceutical compounds occurs via the formation of one or two layers on MAC adsorbent, the propranolol showing a higher tendency to form multiple layers. Finally, adsorption energy is estimated suggesting that the adsorption is endothermic and physical interactions are the responsible of the adsorption of both the compounds onto MAC adsorbent.

New insights into the competition between antioxidant activities and pro-oxidant risks of rosmarinic acid.

Direct and indirect antioxidant activities of rosmarinic acid (RA) based on HOO˙/CH3OO˙ radical scavenging and Fe(iii)/Fe(ii) ion chelation were theoretically studied using density functional theory at the M05-2X/6-311++G(2df,2p) level of theory. First, four antioxidant mechanisms including hydrogen atom transfer (HAT), radical adduct formation (RAF), proton loss (PL) and single electron transfer (SET) were investigated in water and pentyl ethanoate (PEA) phases. Regarding the free radical scavenging mechanism, HAT plays a decisive role with overall rate coefficients of 1.84 × 103 M-1 s-1 (HOO˙) and 4.49 × 103 M-1 s-1 (CH3OO˙) in water. In contrast to PL, RAF and especially SET processes, the HAT reaction in PEA is slightly more favorable than that in water. Second, the [Fe(iii)(H2O)6]3+ and [Fe(ii)(H2O)6]2+ ion chelating processes in an aqueous phase are both favorable and spontaneous especially at the O5, site-1, and site-2 positions with large negative Δr G 0 values and great formation constant K f. Finally, the pro-oxidant risk of RA- was also considered via the Fe(iii)-to-Fe(ii) complex reduction process, which may initiate Fenton-like reactions forming reactive HO˙ radicals. As a result, RA- does not enhance the reduction process when ascorbate anions are present as reducing agents, whereas the pro-oxidant risk becomes remarkable when superoxide anions are found. The results encourage further attempts to verify the speculation using more powerful research implementations of the antioxidant activities of rosmarinic acid in relationship with its possible pro-oxidant risks.