Single water solvation dynamics in the 4-aminobenzonitrile–water cluster cation revealed by picosecond time-resolved infrared spectroscopy

Abstract

The dynamics of a solvent is important for many chemical and biological processes. Here, the migration dynamics of a single water molecule is triggered by the photoionization of the 4-aminobenzonitrile-water (4ABN-W) cluster and monitored in real time by picosecond time-resolved IR (ps TRIR) spectroscopy. In the neutral cluster, water is hydrogen-bonded to the CN group. When this CN-bound cluster is selectively ionized with an excess energy of 1238 cm À1, water migrates with a lifetime of t = 17 ps from the CN to the NH 2 group, forming a more stable 4ABN + -W(NH) isomer with a yield of unity. By decreasing the ionization excess energy, the yield of the CN -NH 2 reaction is reduced. The relatively slow migration in comparison to the ionization-induced solvent dynamics in the related acetanilide-water cluster cation (t = 5 ps) is discussed in terms of the internal excess energy after photoionization and the shape of the potential energy surface.

Probing Solvation Dynamics around Aromatic and Biological Molecules at the Single-Molecular Level

“…In addition, such experiments are highly requested in order to test and validate the computational approaches used to analyze experimental observations in the solution phase. Here, we review the first applications of a recently developed experimental technique, which has been able to directly probe for the first time the dynamics of individual single solvent molecules in real time: picosecond time-resolved infrared (ps-TRIR) spectroscopy of size- and isomer-selected aromatic clusters generated in molecular beams. − …”

“…This is mainly due to the substantial experimental difficulties arising from the challenging laser technology required for such time-resolved studies. These involve widely tunable multicolor high-power picosecond lasers, which became available only recently, and their coupling to a molecular beam setup for spectroscopic pump–probe experiments. , In this work, we utilize picosecond time-resolved three-color tunable UV–UV′–IR pump–probe spectroscopy to monitor the dynamics of aromatic clusters produced in molecular beams. − ,, …”

Deciphering environment effects in peptide bond solvation dynamics by experiment and theory

“…One possibility to overcome these limitations is the generation of size-and isomer-selected (micro-)hydrated peptides in the gas phase and study the dynamics of a single or several selected solvent molecules with time-resolved pumpprobe techniques, such as time-resolved photoelectron spectroscopy [26][27][28][29] or the recently developed picosecond time-resolved infrared (ps-TRIR) spectroscopy 25,30 . The latter one has successfully been applied to monitor in real time the ionizationinduced π →H site-switching dynamics of rare gas ligands attached to the phenol molecule [30][31][32][33][34] and the water migration dynamics in the 4-aminobenzonitrile-water 35 and trans-acetanilidewater (AA + − W) 36 cluster cations. Combined with theoretical simulations, such experiments provide a detailed atomistic picture of the dynamics of individual solvent molecules.…”

Real-time observation of photoionization-induced water migration dynamics in 4-methylformanilide–water by picosecond time-resolved infrared spectroscopy and ab initio molecular dynamics simulations

“…19 To circumvent the problem of inhomogeneous water molecules, we have been working on hydration dynamics at a single solvent molecular level by probing solvated clusters in the gas phase using time-resolved infrared (TRIR) spectroscopy and advanced ab initio molecular dynamics (MD) simulations. [20][21][22][23][24][25] This approach offers size-and isomer-selectivity as well as full control over solvation structure and energy in the cluster.…”

“…The dynamics is typically initiated by UV laser excitation / photoionization of the clusters, and migration of the water molecule is monitored by changes in the TRIR spectra at the picosecond (ps) time scale. This technique of UV-UV ( ′ ) -IR ps time-resolved IR (ps-TRIR) spectroscopy combined with mass spectrometry has been successfully applied to a variety of monohydrated clusters, including the single water CO → NH migration around the peptide linkage in trans-acetanilide (tAA) 20,21 and trans-formanilide (tFA), 24 the CN → NH migration around 4-aminobenzonitrile, 22 and the NH → OH migration in 5-hydroxyindole. 25 Surprisingly, the lifetimes of these single water migrations vary over four orders of magnitude, ranging from 4 ps to 53 ns.…”