The bifunctional catalytic role of water clusters in the formation of acid rain

Abstract

State-of-the-art chemical bonding analyses show that water clusters have a bifunctional catalytic role in the formation of HSO in acid rain. The embedded HO monomers mitigate the change in the chemical bonding scenario of the rate-limiting step, reducing thereby the corresponding activation energy in accordance with Hammond's postulate. We expect that the insights given herein will prove useful in the elucidation of the catalytic mechanisms of water in inorganic and organic aqueous chemistry.

Hydrogen‐Bond Weakening through π Systems: Resonance‐Impaired Hydrogen Bonds (RIHB)

“…RAHBs have previously been characterised through quantum chemical topology as interactions that involve the homogenisation of the DIs through the pseudo‐cycle forming the HB structure shown in Figure a . In other words, the number of shared electrons associated with the double bonds decrease, whereas the number of those related to single bonds show the opposite behaviour; this is in agreement with the arrow‐pushing sketches in Figures a and b and a.…”

“…These methods of wave function analyses are based on the first‐order reduced density matrix, ρ 1 ( r 1 , r 1 ′), and on the one‐ and two‐electron density functions, ρ 1 ( r 1 ) and ρ 2 ( r 1 , r 2 ), respectively. We used these approaches because they have provided valuable information about the nature of HB cooperativity and anticooperativity occurring both across σ and π bonds . Thus, our results establish relevant differences between RAHBs and RIHBs, and hence, we expect that they will aid in the understanding of the complicated interplay between HBs and π‐conjugated systems.…”

“…For example, the oxygen–oxygen distance in small water clusters is reduced due to HB cooperativity, and the relative energy of the isomers of the H 2 O hexamer is determined by a balance between the number of HBs in the system and their non‐additive properties . The HB cooperative effects in O−H⋅⋅⋅O−H motifs were recently used to explain the bifunctional catalytic role of (H 2 O) 2 and (H 2 O) 3 in the formation of H 2 SO 4 in acid rain and the hydrolysis of CO 2 in the generation of H 2 CO 3 . Such HB non‐additivity has been related to the flow of charge density from the HB acceptor to the HB donor that occurs throughout σ bonds, for instance, in hydrogen cyanide chains, H−C≡N⋅⋅⋅H−C≡N⋅⋅⋅H−C≡N⋅⋅⋅H−C≡N, which display a significantly enhanced HCN dipole moment, compared with that of the value in vacuo.…”

Interacting Quantum Atoms—A Review

“…One field where the IQA methodology can be particularly useful is in the examination of catalytic processes, given its ability to account for each individual interaction separately. For instance, Rocha-Rinza et al have used IQA to investigate the catalytic effect of additional water molecules in the formation of acid rain [ 124 ]. Another example is the work of Popelier et al who studied the mechanism behind peptide hydrolysis in HIV-1 protease [ 125 ].…”

DFT Performance in the IQA Energy Partition of Small Water Clusters

“…[7,8] Likewise to conceptual DFT, the topological analysis of the electron density in accordance with the Quantum Theory of Atoms in Molecules (QTAIM) has resulted in new insights about molecules and molecular clusters as well as the processes undergone by these systems. [9,10] The charge distribution is not the only scalar field that can be examined in this way. Many other functions, e.g.…”