The solvation structure of protons in aqueous media is highly relevant to electric properties and to proton transport in liquids and membranes. At ambient temperature, polar liquids display structural fluctuations on femto-to picosecond time scales with a direct impact on proton solvation. We apply two-dimensional infrared (2D-IR) spectroscopy for following proton dynamics in acetonitrile/water mixtures with the Zundel cation H5O2 + prepared in neat acetonitrile as a benchmark. The 2D-IR spectra of the proton transfer mode of H5O2 + demonstrate stochastic large-amplitude motions in the double-minimum proton potential, driven by fluctuating electric fields. In all cases the excess proton is embedded in a water dimer, forming an H5O2 + complex as major solvation species. This observation is rationalized by quantum mechanics/molecular mechanics molecular dynamics simulations including up to 4 water molecules embedded in acetonitrile. The Zundel motif interacts with its closest water neighbor in an H7O3 + unit without persistent proton localization. TOC figure

We study a series of intermolecular hydrogen-bonded 1 : 1 complexes formed by chloroacetic acid with 19 substituted pyridines and one aliphatic amine dissolved in CDCl at low temperature by H andC NMR and FTIR spectroscopy. The hydrogen bond geometries in these complexes vary from molecular (O-HN) to zwitterionic (OH-N) ones, while NMR spectra show the formation of short strong hydrogen bonds in intermediate cases. Analysis of C[double bond, length as m-dash]O stretching and asymmetric CO stretching bands in FTIR spectra reveal the presence of proton tautomerism. On the basis of these data, we construct the overall proton transfer pathway. In addition to that, we also study by use of ab initio molecular dynamics the complex formed by chloroacetic acid with 2-methylpyridine, surrounded by 71 CDCl molecules, revealing a dual-maximum distribution of hydrogen bond geometries in solution. The analysis of the calculated trajectory shows that the proton jumps between molecular and zwitterionic forms are indeed driven by dipole-dipole solvent-solute interactions, but the primary cause of the jumps is the formation/breaking of weak CHO bonds from solvent molecules to oxygen atoms of the carboxylate group.

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Abstract. We study the ultrafast dynamics of OH stretching and bending vibrations of water inside dioleoylphosphatidylcholine (DOPC) reverse micelles in a wide range of hydration. A strong hydration level dependence for the spectral diffusion rates is found and explained by the distinctly different environment for single water molecules bound to the anionic phosphate group. We show that the energy relaxation pathway of the OH stretching vibration at low hydration level involves the OH bending.Phospholipids, building blocks of biological membranes, typically self-assemble into bilayers in aqueous solution. The amphiphilic nature of phospholipids allows the formation of a variety of other structures, including reverse micelles. We recently introduced reverse micelles composed of dioleoylphosphatidylcholine (DOPC), a phospholipid with hydrophobic tails and a hydrophilic head consisting of a phosphate (PO 4 -) unit and a covalently linked choline group (cf. Figure 1). Such systems form when DOPC is dissolved in nonpolar solvents resulting in hydrophilic head groups pointing to the interior. Addition of water leads to hydration of the head groups as well as the buildup of nanoscopic water pools inside the reverse micelles (the water content is characterized by the parameter w 0 =[H 2 O]/[DOPC]). Therefore, reverse micelles allow for detailed studies of the fundamental hydration interactions of phospholipids.

How far ……does the influence of aproton reach in water?X-ray spectroscopy reveals how--layer by layer--the electronic structure of water molecules is altered when hydrating aproton. Ag eneral architectural hierarchy exists in which the proton strongly interacts with the three nearest water molecules to form ahybridized H 7 O 3 + core while the first hydration shell is affected by the electric field of the protonsp ositive charge.F urther solvation shells contain bulk-like water molecules,a sr eported by Ehud Pines,P hilippe Wernet, Michael Odelius,E rik T. J. Nibbering,a nd co-workers in their Research Article (e202211066).