OH-Stretching in Synthetic Hydrogen-Bonded Chains

Abstract

We study hydrogen bond dynamics in stereoselectively synthesized polyalcohols by combining linear and two-dimensional (2D) infrared spectroscopy experiments with simulations. We consider two variants of the polyalcohols: the all-syn and all-anti tetrol, which because of their different stereochemistry of the hydroxyl groups form a linear hydrogen-bonded chain that is stable for tens of picoseconds or a system where hydrogen bonds are formed and broken on a picosecond timescale, respectively. The differences in structure and hydrogen bond dynamics gives rise to significant differences in the linear spectra for the two compounds. Furthermore, we show that the stronger hydrogen bonding for the all-syn variant leads to faster fluctuations of the site frequencies than for the all-anti one, which is reflected in the higher degree of homogeneous broadening in the 2D spectra. Because of the different stereochemistry, the coupling in the all-syn molecule is stronger than for the all-anti one, which leads to a faster delocalization of a local excitation. This explains the previously observed pump-frequency independent vibrational lifetime for the all-syn variant, since the excitation loses the memory of the pump frequency before relaxation. For the all-anti form, the coupling is weak and the excitation remains in the initially excited state, maintaining the memory of the pump frequency.

Multidimensional infrared spectroscopy reveals the vibrational and solvation dynamics of isoniazid

“…In particular, it alters from diagonally-elongated at short waiting times to more circular as the waiting time increases. This effect has been described in detail previously 10,12,13,18,36,37 and is assigned to spectral diffusion associated with the inhomogeneous broadening of the transition. In this case, of a water-solvated C=O bond, the effect is caused, primarily, by the motion of solvent molecules leading to fluctuations in the strength of H-bonds between water and the C=O oscillator.…”

“…The major difference between systems such as N-methylacetamide and simple peptides and INH is the proposed existence of an intramolecular H-bond between the NH 2 group and the carbonyl oxygen. In cases where the effect of such a structure on the spectral diffusion dynamics or linebroadening mechanisms have been reported, an intramolecular H-bond tends to increase the rate of spectral diffusion 37,41 and this has been attributed to the stronger, localised interaction arising as compared to generic solvation H-bonding from mobile water. 39,42 In addition, static components have been observed in the spectral diffusion dynamics of peptide modes involved in such interactions.…”

Lessons from combined experimental and theoretical examination of the FTIR and 2D-IR spectroelectrochemistry of the amide I region of cytochrome c

“…Furthermore, the difference spectrum is varying a lot as a function of population time delay. While a direct comparison between predicted and experimental spectra is tempting, such a comparison is very challenging as the simulations do not take into account occurring thermalization effects 58,59 and relaxation-assisted crosspeaks 60,61 arising during the population time delay. Also, due to a finite pulse duration, the experimental data cannot be obtained without artifacts for zero time-delay.…”

2D IR spectroscopy of high-pressure phases of ice

“…The inclusion of relaxation would be computationally too demanding for a large system such as ice. [87][88][89][90] This also implies that the thermal signal expected to appear after heating due to energy transferred from the OD-vibrations to low frequency vibrations of the lattice is not included either. The thermal signal is expected to be isotropic in nature, dominating the experimental isotropic signal at 1 ps.…”