Nochebuena Jorge, Cuautli Cristina, Ireta Joel
Departamento de Química, División de Ciencias Básicas e Ingeniería, Universidad Autónoma Metropolitana-Iztapalapa, A.P. 55-534, Ciudad de México 09340, Mexico.
Phys Chem Chem Phys. 2017 Jun 14;19(23):15256-15263. doi: 10.1039/c7cp01695f.
The origin of non-additivity in hydrogen bonds (H-bonds), usually termed as H-bond cooperativity, is investigated in H-bonded linear chains. It is shown that H-bond cooperativity originates solely from classical electrostatics. The latter is corroborated by comparing the H-bond cooperativity in infinitely-long H-bonded hydrogen cyanide, 4-pyridone and formamide chains, assessed using density functional theory (DFT), against the strengthening of the dipole-dipole interaction upon the formation of an infinite chain of effective point-dipoles. It is found that the magnitude of these effective point-dipoles is a consequence of mutual polarization and additional effects beyond a polarizable point-dipole model. Nevertheless, the effective point-dipoles are fully determined once a single H-bond is formed, indicating that quantum effects involved in H-bonding are circumscribed to nearest-neighbor interactions only; i.e. in a linear chain of H-bonds, quantum effects do not contribute to the H-bond non-additivity. This finding is verified by estimating cooperativity along the dissociation path of H-bonds in the infinite chains, using two empirical parameters that account for polarizability, together with DFT association energies and molecular dipoles of solely monomers and dimers.
在氢键线性链中研究了氢键（H键）非加和性的起源，通常称为H键协同性。结果表明，H键协同性仅源于经典静电作用。通过比较使用密度泛函理论（DFT）评估的无限长氢键连接的氰化氢、4-吡啶酮和甲酰胺链中的H键协同性，与有效点偶极子无限链形成时偶极-偶极相互作用的增强情况，证实了后者。研究发现，这些有效点偶极子的大小是相互极化以及可极化点偶极子模型之外的其他效应的结果。然而，一旦形成单个H键，有效点偶极子就完全确定了，这表明氢键中涉及的量子效应仅局限于最近邻相互作用；即，在氢键线性链中，量子效应不会导致H键非加和性。通过使用两个考虑极化率的经验参数以及仅单体和二聚体的DFT缔合能和分子偶极，沿着无限链中氢键的解离路径估计协同性，验证了这一发现。
