Rosette nanotubes are a new class of organic nanotubes obtained through the hierarchical self-assembly of low molecular weight synthetic modules in water. Here we demonstrate that these materials can serve as scaffolds for the supramolecular synthesis of multichannel nanotubular architectures and report on the discovery of their entropy-driven self-assembly process.U nidimensional nanotubular objects have captivated the minds of the scientific community over the past decade because of their boundless potential in nanoscale science and technology. The strategies developed to achieve the synthesis of these materials spanned the areas of inorganic (1-5) and organic (6 -12) chemistry and resulted in, for instance, carbon nanotubes (1), peptide (9 -11), and rosette nanotubes (12), as well as surfactant-derived tubular architectures (13)(14)(15)(16)(17)(18)(19)(20). Although inorganic systems benefit from the vast majority of the elements of the periodic table and the rich physical and chemical properties associated with them, organic systems inherited the power of synthetic molecular (21, 22) and supramolecular (23, 24) chemistry. As such, the latter approach offers limitless possibilities in terms of structural, physical, and chemical engineering. Here, we present the design, self-assembly, and characterization of multichannel organic nanotubes in water and the discovery of their apparently entropy-driven self-assembly.
Design and SynthesisThe heteroaromatic bicyclic base GٙC (Scheme 1), possessing the Watson-Crick donor-donor-acceptor of guanine and acceptor-acceptor-donor of cytosine, was recently reported in the context of the self-assembly of helical rosette nanotubes (12). Because of the disymmetry of its hydrogen bonding arrays, their spatial arrangement, and the hydrophobic character of the bicyclic system, GٙC undergoes a hierarchical self-assembly process under physiological conditions to form a six-membered supermacrocycle maintained by 18 H-bonds ( Fig. 1 Upper, thin solid bars). The resulting and substantially more hydrophobic aggregate then undergoes a second level of organization to produce a stack. The architecture thus generated defines an unoccluded central pore running the length of the stack with tunable inner and outer diameters (Fig. 1 Lower). The inner space is directly related to the distance separating the H-bonding arrays within GٙC, whereas the peripheral diameter and its chemistry are dictated by the choice of the functional groups conjugated to this motif.In addition to their demonstrated synthetic accessibility and broad solvent compatibility, crown ethers are a very versatile class of receptors that display size, shape, and charge selectivity toward their guests (25). Furthermore, extensive investigations were carried out to establish their ionophoric properties (25) and incorporate them in artificial channel systems (26, 27), molecular photonic (28 -30), and electronic (31, 32) devices. In the present article, 1 and 2 were synthesized and investigated to establish the rosette nanotubes...