Phonon driven proton transfer in crystals with short strong hydrogen bonds

Abstract

Recent work on understanding why protons migrate with increasing temperature in short, strong hydrogen bonds is extended here to three more organic, crystalline systems. Inelastic neutron scattering and density functional theory based simulations are used to investigate structure, vibrations, and dynamics of these systems as functions of temperature. The mechanism determined in a previous work on urea phosphoric acid of low frequency vibrations stabilizing average crystal structures, in which the potential energy well of the hydrogen bond has its minimum shifted towards the center of the bond, is found to be valid here. The new feature of the N–H⋯O hydrogen bonds studied in this work is that the proton is transferred from the donor atom to the acceptor atom. Molecular dynamics simulations show that in an intermediate temperature regime, in which the proton is not completely transferred, the proton is bistable, jumping from one side of the hydrogen bond to the other. In the case of 3,5-pyridine dicarboxylic acid, which has been studied in most detail, specific phonons are identified, which influence the potential energy surface of the proton in the short, strong hydrogen bond.

Collagen and component polypeptides: Low frequency and amide vibrations

“…In particular, in crystals with short strong hydrogen-bonds, the vibrational analysis based on parameter-free methods revealed the mechanism of the proton transfer as being driven by low frequency phonons, activated by temperature [10,11].…”

Measurement of Proton Tunneling in Short Hydrogen Bonds in Single Crystals of 3,5 Pyridinedicarboxylic Acid Using Nuclear Magnetic Resonance Spectroscopy

“…Incoherent tunneling, via excited vibrational states, dominates the rate of PT at all temperatures since the potential barrier, estimated to be 2000 K [23], is always significantly greater than kT. However, in short HBs, the direct observation of tunneling processes has, to our knowledge, never been reported despite many experimental [24][25][26][27][28] and theoretical [29][30][31][32][33][34][35][36] studies. is an almost perfect model system in which to study PT in a very short HB (Fig.…”

Diffusion inélastique des neutrons et simulations atomistiques

“…Une autre limitation des méthodes TFD qui doit être soulignée réside dans l'étude de matériaux amorphes ou partiellement cristallins [36]. Pour ces matériaux, le bruit résultant de la résolution numérique de l'équation de Schroedinger peut devenir comparable aux différences d'énergies entre des minima locaux de la SEP.…”

“…Dans le cas du 3,5-pyridine acide dicarboxylique [13] (cf Figure 8) les méthodes DR et DM ont toutes deux été utilisées pour étudier l'influence des vibrations du réseau cristallin dans la migration du proton le long de la liaison hydrogène N-H. . .O à température croissante.…”