Unidimensional 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 and organic chemistry and resulted in, for instance, carbon nanotubes, peptide and rosette nanotubes, as well as surfactant-derived tubular architectures. Here we present a new family of self-assembled organic nanotubes with tunable chemical and physical properties.
The heteroaromatic bicyclic base G∧C, possessing the Watson-Crick donor-donor-acceptor of guanine and acceptor-acceptor-donor of cytosine was recently reported by our group in the context of the self-assembly of helical rosette nanotubes1. Because of the disymmetry of its hydrogen bonding arrays, their spatial arrangement, and the hydrophobic character of the bicyclic system, G∧C undergoes a hierarchical self-assembly process under physiological conditions to form a six-membered supermacrocycle maintained by 18 H-bonds (rosette). 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). The inner space is directly related to the distance separating the H-bonding arrays within the G∧C motif, while the peripheral diameter and its chemistry are dictated by the choice of the functional groups conjugated to this motif. Fig. 1 shows a top view of a self-assembled rosette nanotube generated from the G∧C motif conjugated to benzo-18-crown-6.
The specific molecular recognition of a chiral amino acid in its zwitterionic form by the crown ethers within the nanotubes results in a cooperative transition from racemic to homochiral helical nanotubes. Besides the fundamental significance of this process, this supramolecular strategy offers a rapid approach to modifying the chemical and physical properties of the self-assembled nanotubes simply by decorating their surface with the crown ether molecular guests that offer the desired chemical or physical property. These results along with the ability of these nanotubes to self-replicate will be discussed at the conference.
Figure 1. top view of a self-assembled rosette nanotube generated from the G∧C motif conjugated to benzo-18-crown-6.
(a) Fenniri, H.; Mathivanan, P.; Vidale, K. A.; Sherman, D. M.; Hallenga, K.; Wood, K. V.; Stowell, J. G., Helical Rosette Nanotubes: Design, Self-Assembly, and Characterization. J. Am. Chem. Soc.2001, 123, 3854-3855. (b) Fenniri, H.; Deng, B.-L.; Ribbe, A. E.; Hallenga, K.; Jacob, J.; Thiyagarajan, P., Entropically Driven Self-Assembly of Multichannel Rosette Nanotubes, Proc. Natl. Acad. Sci. USA2002, 99, 6487-6492.
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