Local nuclear dynamics of protons in a molecular water pipe.

Atoms in molecules that are self-assembled exhibit unique local dynamical features. In the presence of self-assembly, the vibrational contributions to thermodynamic potentials, and in consequence, the chemical reactivity, are completely different from their counterparts in bulk materials. Of all the assemblies, water channels or single-file water wires have attracted a lot of attention due to their biological relevance. In our recent work, we focused our attention on the serendipitous discovery that an exact 2:1 ratio of water and 2,2,6,6-tetramethylpiperidine (TMP) self-assembles into a 3D structure that exhibits molecular water channels. Overall, the long tube-like rods mirror the internal structure of the compound and can be described as a pseudo-tetragonal arrangement of TMP molecules that host, in the middle, a channel filled with water molecules, the whole assembly held together by hydrogen bonding interactions. A high degree of local disorder in the water–TMP complex structure and relatively isotropic atomic displacement parameters of hydrogen atoms in water channels let us suggest water transport in the channels via proton transfer with a Grotthuss-type mechanism. Motivated by this, we propose to concurrently employ incident neutron energy-dependent transmission (NT) and NCS on Vesuvio to investigate the interplay between the local structure and dynamics in TMP/H2O and TMP/D2O systems at 10K and 100K.