Controllable biomolecule release from self-assembled organic nanotubes with asymmetric surfaces: pH and temperature dependence

Abstract

The release behavior of fluorescent dyes, oligo DNAs and spherical proteins from self-assembled organic nanotubes having 7–9 nm inner diameters has been studied in terms of novel nanocontainers with high-axial ratios. Both much smaller inner diameters and asymmetric inner and outer surfaces are characteristic of the nanotubes. The acid-dissociation constant (pK_a) of the amino groups located at the inner surface and the thermal phase transition temperature (T_g–l) of the nanotube were evaluated based on the pH titration and variable-temperature circular dichroism (CD) spectroscopic experiments, respectively. Each guest was slowly released from both open ends of the nanotube under weak alkaline conditions (pH 8.5), as a result of the decrease in electrostatic attraction between the inner surface and the guests. Elevated temperatures above the obtained T_g–l converted the monolayer membrane of the nanotube from a solid state to a fluid one, promoting the remarkably fast release of the guests. The unique release properties of the nanotube as a nanocontainer with two terminal open ends were compared with those of liposomes that posses a closed hollow space covered with fluid bilayer membranes.