Water Confined in Carbon Nanotubes: Magnetic Response and Proton Chemical Shieldings

We study the proton nuclear magnetic resonance of a model system consisting of liquid water confined in carbon nanotubes (CNTs). Chemical shieldings are evaluated from linear response theory, where the electronic structure is derived from density functional theory with plane-wave basis sets and periodic boundary conditions. The shieldings are sampled from trajectories generated via first-principles molecular dynamics simulations at ambient conditions for water confined in (14,0) and (19,0) CNTs with diameters d = 11 and 14.9 Å, respectively. We find that confinement within the CNT leads to a large (ca. −23 ppm) upfield shift relative to bulk liquid water. This shift is a consequence of strongly anisotropic magnetic fields induced in the CNT by an applied magnetic field.