Nanotubules from a Self-Assembling Small Molecule
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1057-II20-26
Nanotubules from a Self-Assembling Small Molecule Ross S. Johnson1,2, Jesus G. Moralez3, and Hicham Fenniri1,2 1 National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, T6G 2M9, Canada 2 Chemistry, University of Alberta, Edmonton, T6G 2G2, Canada 3 Experimental Station, DuPont Central Research and Development, Wilmington, DE, 198800328
ABSTRACT Control over the dimensions of nanostructured materials is of critical importance for proper utilization in devices. There has been a number of systems reported that utilize amphiphilic molecules that organize themselves into nanotubes or tubules, as well as various polymers that can assemble into tubular nanoscale structures. The organization of these components into nanotubes is mainly driven by hydrophobic effects of the substituents in particular solvents, which contain polar and apolar portions. While studying a modification to a previously reported GC module that normally forms rosette nanotubes (RNTs) with diameters in the 4nm range, we discovered that a small modification led to the formation of nanotubes with diameters 10 times of that expected. These structures were studied by SEM, TEM, and AFM in an attempt to uncover the mechanism of their formation. It was determined that these chiral organic molecules first self-assemble into sheet-like structures, but due to an inherent curvature of the sheet, they roll into large nanotubules. This new type of self-assembled nanotube may have applications in host-guest chemistry and as templates for other nanoparticles and materials. INTRODUCTION Nanoscale tubular structures continue to attract interest in materials science and nanotechnology due to their prospective technological applications.1 The ability to modify both the size and properties of nanoscale architectures is crucial for their incorporation into devices. Our group utilizes the hydrogen bonding array of a guanine/cytosine (G∧C) heterocycle to form 6-membered macrocycles called rosettes, which then stack to form nanotubes with pre-defined dimensions (Figure 1a-c).2,3 While studying a modification to a previously reported G∧C module that normally forms RNTs with diameters in the 3-4nm range, it was discovered that a small modification led to the formation of nanotubules with diameters approximately 10 times of that expected. Herein we describe the characterization of these self-assembled tubules, and propose a mechanism of their formation. RESULTS The G∧C heterocycle of compound 2 was synthesized according to previously published procedures.2 Functionalization was achieved by oxidation of the exocyclic allyl group to a carboxylic acid, followed by a peptide coupling to obtain the amide derivative 2. We expected compound 2 to either form RNTs with dimensions and properties similar to 1 (Figure 1a-d), or to fail to self-assemble as a result of its chemical and physical properties. Stock solutions of 2 in
MeOH (1mg/ml, 1.4 X 10-4 M) were prepared, aged for 3 weeks, and placed on carbon coated TEM grids. Surprisingly, SEM images of 2
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