Solvation Dynamics of a Single Water Molecule Probed by Infrared Spectra—Theory Meets Experiment

Abstract

The dynamics and energetics of water at interfaces or in biological systems plays a fundamental role in all solvation and biological phenomena in aqueous solution. In particular, the migration of water molecules is the first step that controls the overall process in the time domain. Experimentally, the dynamics of individual water molecules is nearly impossible to follow in solution, because signals from molecules in heterogeneous environments overlap. Although molecular dynamics simulations do not have this restriction, there is a lack of experimental data to validate the calculated dynamics. Here, we demonstrate a new strategy, in which the calculated dynamics are verified by measured time-resolved infrared spectra. The coexistence of fast and slow migrations of water molecules around a CONH peptide linkage is revealed for a model system representative of a hydrate peptide.

Stepwise Microhydration of Aromatic Amide Cations: Formation of Water Solvation Network Revealed by Infrared Spectra of Formanilide+–(H2O)n Clusters (n ≤ 5)

“…Similar to n = 1, ionization of the CO-bound isomer of n = 2 will cause a drastic reorganization of the hydration structure, which thus is an interesting target for time-resolved experiments. 30,46 Interest- The Journal of Physical Chemistry B Article ingly, no experimental and theoretical data have been reported so far for the neutral n = 3 cluster, 36,60,62,63 while the corresponding cation cluster can readily be observed, and its two isomers I and II have linear and branched hydration structures attached to the NH group. The largest neutral cluster observed, t-FA−(H 2 O) 4 , occurs as a single very stable isomer, with a (H 2 O) 4 solvent chain bridging the gap from the NH donor to the CO acceptor group.…”

“…41 38 for which the H 2 O migration time was measured in real time as 5 ps by time-resolved pump−probe IR spectroscopy, 30 in good agreement with recent MD simulations. 46 The dynamical CO → NH isomerization process triggered by ionization of t-FA−H 2 O(CO) gives rise to broad features with unclear assignments in its ZEKE spectrum. 41 Finally, 1 + 1 REMPI of t-FA−(H 2 O) 4 with a cyclic structure 60 produces a hot cation cluster and thus triggers a ring opening reaction of the H-bonded (H 2 O) 4 network, which has been rationalized by entropic rather than energetic arguments.…”

Photoionization-induced π ↔ H site switching dynamics in phenol+–Rg (Rg = Ar, Kr) dimers probed by picosecond time-resolved infrared spectroscopy

“…In addition, the lowest frequency intramolecular vibration of PhOH + is 177 cm À1 , 46 i.e. This behavior is different for (acidic) aromatic dimers with polyatomic solvent molecules (S = H 2 O, CH 4 ), 1,2,45,[47][48][49][50][51] because then even in the dimers (n = 1) bath modes are available for IVR, which quench the back reaction. Thus, the excess energy is distributed predominantly among the intermolecular modes.…”

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

“…The ps TRIR spectra clearly contain many important details of this fundamental water migration process from the CO to the NH site of this linkage, including the two competing reaction pathways and their rate constants, the occurrence of transient intermediates, the reaction yield and its relation to intracluster vibrational energy redistribution (IVR). 27,34 This migration reaction and the resulting TRIR spectra were subsequently analysed and visualized by ''on-the-fly'' molecular dynamics (MD) simulations. 34 The important aspect of this combined experimental and computational approach is that the MD simulations could precisely be calibrated by the accurate reproduction of the measured TRIR spectra.…”

“…27,34 As both reactions are water migrations around simple benzene derivatives, there is not a substantial difference in the length of the reaction paths. Then, the speed of the water migration in 4ABN + -W should be slower than that in AA + -W. The difference of the reaction rate may be related to the different internal energies of the cluster cations.…”