In this paper the transport properties of water confined inside hydrophobic and hydrophilic nanotubes are compared for different nanotube radii and densities. While for wider nanotubes the nature of the wall plays no relevant role in the water mobility, for small nanotubes the hydrophobic confinement presents a peculiar behavior. As the density is increased the viscosity shows a huge increase associated with a small increase in the diffusion coefficient. This breakdown in the Stokes-Einstein relation for diffusion and viscosity was observed in the hydrophobic, but not in the hydrophilic nanotubes. The mechanism underlying this behavior is explained in terms of the structure of water under confinement. This result indicates that some of the features observed for water inside hydrophobic carbon nanotubes cannot be observed in other nanopores.

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h i g h l i g h t s• The water diffusion near the protein surface is lower than in bulk.• A crossover in the diffusion of the hydration water is observed.• The crossover happens at different temperatures for hydrophilic and hydrophobic sites. g r a p h i c a l a b s t r a c t a b s t r a c t Molecular dynamics simulations were performed to study the water structure and dynamics in the hydration shell of the globular TS-Kappa protein. The results show that for a wide range of temperatures the diffusion coefficient of water near the protein surface is lower than in bulk. A crossover in the diffusion behavior of hydration water is observed at different temperatures for hydrophilic and hydrophobic vicinities. We have found a correlation between the crossover in the hydrophilic case and the protein dynamical transition. An explanation in terms of the competition between water-water water-protein H-bond formation is provided based on H-bond network analysis.

Carboxylated semiconductor and metallic carbon nanotubes under transverse electrical fields are investigated through density functional theory based on first-principles calculations. The external field polarizes the system, resulting in an induced electric dipole moment toward the incident field with the modulus directly dependent on the field strength. The structural and electronic properties of the resulting system due to the orbital hybridization between the nanotube and COOH states are shown to be affected by the applied field. These results open new perspectives for different potential uses, such as to enhance the capacity of the composite to bind and characterize other substances, especially polar molecules, and as mechanisms to monitor the bound substances or control electron injection or detection, by varying the external field through a controlled application.