Dielectric Response in Bisquaric Acid Crystal:  Possible Generation of Protonic Soliton in a Quasi-One-Dimensional Hydrogen-Bonded System

Abstract

We investigated the proton dynamics of crystalline bisquaric acid (H 2 BSQ) in terms of the temperature and frequency dependence of its permittivity. It was found that the dielectric response of the H 2 BSQ crystal exhibited two-step changes. With raising temperature, the dielectric permittivity increased slightly at 40 K. Whereas the temperature dependence of the permittivity at this temperature showed a large isotope effect, there was no frequency dependence of the permittivity. However, the permittivity increased largely at 290 K and showed distinct frequency dependence, although there was no-isotope effect on its characteristic temperature dependence. It was concluded that such a dielectric response of the H 2 BSQ crystal was derived from the migration of protonic soliton coupled with the polarity inversion along the quasi-one-dimensional hydrogenbonded chain.

Nano breathers and molecular dynamics simulations in hydrogen-bonded chains

“…The gain in (14) shows the interesting dependence of on the coupling parameters J 1 , J 2 and the applied electric field. Equation (14) determines the stability and instability of a plane wave with wavenumber q in discrete HB chains.…”

“…Most of the papers that mention HB chains or proton channels assume that such channels will transport fast and sufficiently for bioenergetic purposes [2,11]. Recently, extensive theoretical investigations [12][13][14][15][16] and also some experimental evidence [17] predicted that solitons may give some answers to the fundamental question of the transmission of energy in biological macromolecules. The proton dynamics in HB chains is often modeled by a characteristic non-linear substrate potential with two degenerate equilibrium positions.…”

Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism

“…Moreover, the transition temperature rises to 274 K upon deuterium substitution of the H‐bonded hydrogen atoms (the Supporting Information, Figure S14). This isotope effect stems from a decrease in the zero‐point energy of deuterium, which is heavier than hydrogen 7b. 9b, 13, 28 This reveals that the proton (deuteron) order–disorder transition in the H‐bonds plays a major role in the phase transition mechanism.…”

“…The soliton model for proton transfer (the ADZ model) was first proposed by Antonchenko, Davydov, and Zolotaryuk to describe collective proton transport in ice 1a. 30 This protonic soliton mechanism has been proposed to explain the dielectric response observed in 1D H‐bonded chain systems of bisquaric acid and dabcoHX (dabco=1,4‐diazabicyclo[2.2.2]octane, X − =Br − , I − , and BF 4 − ) 7b. 31 In strongly H‐bonded 1D solids of 3‐hydroxyenone derivatives, their IR spectra exhibit a low‐lying weak band around 1800 cm −1 , called the S band, which becomes sharper with decreasing temperature, in addition to a broad OH stretching mode around 2500 cm −1 7.…”

“…Sugawara and Mochida et al. have found three proton dynamics phenomena resulting from the controlled dimensionality of the H‐bonded π‐conjugated electron system and the intervention of water molecules in the H‐bonds: A protonic soliton7b and proton relay10 in which the proton moves over a barrier as a classic particle and a proton tunneling 11. Furthermore, PCET is not restricted to biological systems but also occurs in molecular materials 2a.…”