Modelling the reaction OH-+ CO2→ HCO-3in the gas phase and in aqueous solution: a combined density functional continuum approach

Investigations on mechanisms, kinetics, and ecotoxicity in OH-initiated degradation of 1,2,4,5-tetramethylbenzene in the environment

As one of the volatile organic compounds (VOCs) in the environment, 1,2,4,5-tetramethylbenzene (1,2,4,5-TeMB) present in oily wastewater, and it can occur substitution, abstraction, and addition reactions with OH radicals in the atmosphere and wastewater. Electrostatic potential (ESP) and average local ionization energy (ALIE) prediction indicate that H atoms from CH₃ group and the benzene ring are the most active sites in 1,2,4,5-TeMB. The result shows that potential energy surfaces (PESs) in the gas and aqueous phase are similar, and the relevant barriers in the latter one are higher. The dominant channel is H abstraction from the benzene ring, and the subdominant one is OH radical addition to the benzene ring. Furthermore, subsequent reactions of dominant products with O₂, NO₂, NO, and OH radicals in the atmosphere are studied, as well. The total reaction rate constant is calculated to be 2.36×10^-10 cm³ molecule^-1 s^-1 at 1 atm and 298 K in the atmosphere, which agrees well with the experimental data. While the total rate constant in the aqueous phase is much lower than that in the gas phase. Ecologic toxicity analysis shows that 1,2,4,5-TeMB is very toxic to fish, daphnia, and green algae; and OH-initiated degradation in the environment will reduce its toxicity.

Solvation effects on the vibrational modes in hydrated bicarbonate clusters

Harmonic analysis and ab initio molecular dynamics simulations reveal the solvation effects on the vibrational modes of HCO₃⁻(H₂O)_n.

Examining the structural evolution of bicarbonate–water clusters: insights from photoelectron spectroscopy, basin-hopping structural search, and comparison with available IR spectral studies

Combining NIPES, theoretical calculations and available IR spectra allows us to identify the minimum energy structures that best fit the experiments.

CO(2) incorporation in hydroxide and hydroperoxide containing water clusters--a unifying mechanism for hydrolysis and protolysis

The reactions of CO2 with anionic water clusters containing hydroxide, OH(-)(H2O)n, and hydroperoxide, HO2(-)(H2O)n, have been studied in the isolated state using a mass spectrometric technique. The OH(-)(H2O)n clusters were found to react faster for n = 2,3, while for n >3 the HO2(-)(H2O)n clusters are more reactive. Insights from quantum chemical calculations revealed a common mechanism in which the decisive bicarbonate-forming step starts from a pre-reaction complex where OH(-) and CO2 are separated by one water molecule. Proton transfer from the water molecule to OH(-) then effectively moves the hydroxide ion motif next to the CO2 molecule. A new covalent bond is formed between CO2 and the emerging OH(-) in concert with the proton transfer. For larger clusters, successive proton transfers from H2O molecules to neighbouring OH(-) are required to effectively bring about the formation of the pre-reaction complex, upon which bicarbonate formation is accomplished according to the concerted mechanism. In this manner, a general mechanism is suggested, also applicable to bulk water and thereby to CO2 uptake in oceans. Furthermore, this mechanism avoids the intermediate H2CO3 by combining the CO2 hydrolysis step and the protolysis step into one. The general mechanistic picture is consistent with low enthalpy barriers and that the limiting factors are largely of entropic nature.

Ab Initio Molecular Dynamics Study of Carbon Dioxide and Bicarbonate Hydration and the Nucleophilic Attack of Hydroxide on CO2

We apply ab initio molecular dynamics (AIMD) to study the hydration structures of the carbon dioxide molecule and the bicarbonate and carbonate anions in liquid water. We also compute the free energy change associated with the nucleophilic attack of the hydroxide ion on carbon dioxide. CO2 behaves like a hydrophobic species and exhibits weak interactions with water molecules. The bicarbonate and carbonate ions are strongly hydrated and coordinate to an average of 6.9 and 8.7 water molecules, respectively. The energetics for the reaction in the gas phase are investigated using density functional theory and second-order Møller-Plesset perturbation theory (MP2) in conjunction with high-quality basis sets. Using umbrella sampling techniques, we compute the standard state, aqueous phase free energy difference associated with the reaction CO2+OH--->HCO3- after correcting AIMD energies with MP2 results. Our predictions are in good agreement with experiments. The hydration structures along the reaction coordinate, which give rise to a predicted 9.7 kcal/mol standard state free energy barrier, are further analyzed.