Hydrogen bond

About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.

Quantum nature of the hydrogen bond

Abstract: Hydrogen bonds are weak, generally intermolecular bonds, which hold much of soft matter together as well as the condensed phases of water, network liquids, and many ferroelectric crystals. The small mass of hydrogen means that they are inherently quantum mechanical in nature, and effects such as zero-point motion and tunneling must be considered, though all too often these effects are not considered. As a prominent example, a clear picture for the impact of quantum nuclear effects on the strength of hydrogen bonds and consequently the structure of hydrogen bonded systems is still absent. Here, we report ab initio path integral molecular dynamics studies on the quantum nature of the hydrogen bond. Through a systematic examination of a wide range of hydrogen bonded systems we show that quantum nuclear effects weaken weak hydrogen bonds but strengthen relatively strong ones. This simple correlation arises from a competition between anharmonic intermolecular bond bending and intramolecular bond stretching. A simple rule of thumb is provided that enables predictions to be made for hydrogen bonded materials in general with merely classical knowledge (such as hydrogen bond strength or hydrogen bond length). Our work rationalizes the influence of quantum nuclear effects, which can result in either weakening or strengthening of the hydrogen bonds, and the corresponding structures, across a broad range of hydrogen bonded materials. Furthermore, it highlights the need to allow flexible molecules when anharmonic potentials are used in force field-based studies of quantum nuclear effects.

Ultrafast hydrogen bond strengthening of the photoexcited fluorenone in alcohols for facilitating the fluorescence quenching.

Abstract: The time-dependent density functional theory (TDDFT) method was performed to investigate the excited-state hydrogen-bonding dynamics of fluorenone (FN) in hydrogen donating methanol (MeOH) solvent. The infrared spectra of the hydrogen-bonded FN-MeOH complex in both the ground state and the electronically excited states are calculated using the TDDFT method, since the ultrafast hydrogen-bonding dynamics can be investigated by monitoring the vibrational absorption spectra of some hydrogen-bonded groups in different electronic states. We demonstrated that the intermolecular hydrogen bond C=O...H-O between fluorenone and methanol molecules is significantly strengthened in the electronically excited-state upon photoexcitation of the hydrogen-bonded FM-MeOH complex. The hydrogen bond strengthening in electronically excited states can be used to explain well all the spectral features of fluorenone chromophore in alcoholic solvents. Furthermore, the radiationless deactivation via internal conversion (IC) can be facilitated by the hydrogen bond strengthening in the excited state. At the same time, quantum yields of the excited-state deactivation via fluorescence are correspondingly decreased. Therefore, the total fluorescence of fluorenone in polar protic solvents can be drastically quenched by hydrogen bonding.

Covalency of the Hydrogen Bond in Ice: A Direct X-Ray Measurement

Abstract: Periodic intensity variations in the measured Compton profile anisotropies of ordinary ice $\mathrm{I}h$ correspond to distances of 1.72 and 2.85 \AA{}, which are close to the hydrogen bond length and the nearest-neighbor O-O distance, respectively. We interpret this result as direct evidence for the substantial covalent nature of the hydrogen bond. Very good quantitative agreement between the data and a fully quantum mechanical bonding model for ice $\mathrm{I}h$ and the disagreement with a purely electrostatic (classical) bonding model support this interpretation and demonstrate how exquisitely sensitive Compton scattering is to the phase of the electronic wave function.

Structures and Energies of Hydrogen-Bonded DNA Base Pairs. A Nonempirical Study with Inclusion of Electron Correlation

Abstract: Hydrogen bonding of DNA bases was investigated by reliable nonempirical ab initio calculations. Gradient optimization was carried out on 30 DNA base pairs using the Hartree−Fock (HF) approximation and the 6-31G** basis set of atomic orbitals. The optimizations were performed within Cs symmetry. However, the harmonic vibrational analysis indicates that 13 of the studied base pairs are intrinsically nonplanar. Interaction energies of base pairs were then evaluated at the planar optimized geometries with inclusion of the electron correlation energy using the second-order Moller−Plesset (MP2) method. The stabilization energies of the studied base pairs range from −24 to −9 kcal/mol, and the calculated gas phase interaction enthalpies agree well (within 2 kcal/mol) with the available experimental values. The binding energies and molecular structures of the base pairs are not determined solely by the hydrogen bonds, but they are also strongly influenced by the polarity of the monomers and by a wide variety of s...

On the Accuracy of DFT for Describing Hydrogen Bonds: Dependence on the Bond Directionality

Abstract: A set of representative hydrogen bonded dimers has been studied employing density functional theory (DFT) in the Perdew, Burke, and Ernzerhof (PBE) generalized gradient approximation. Our results for hydrogen bond (hb) strengths and geometry parameters show good agreement with those obtained by Moller−Plesset (MP2) or Coupled-Cluster (CC) methods. We observe that the reliability of DFT-PBE for the description of hbs is closely connected to the bond directionality (i.e. the angle between D−H and H···A where D and A are the donor and the acceptor atoms or regions, respectively, in the hb interaction): with increasing deviation from a linear D−H···A arrangement the accuracy of the DFT-PBE decreases.