Combinatorial Approach to Materials Fabrication from Higher Hierarchies of Rosette Nanotubes
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Combinatorial Approach to Materials Fabrication from Higher Hierarchies of Rosette Nanotubes Grigory Tikhomirov1, and Hicham Fenniri2 Chemistry, National Institute for Nanotechnology, 11121-82 Ave, Apt. 740, Edmonton, T6G 0T4, Canada 2 Chemistry, University of Alberta, Edmonton, T6G 2M9, Canada 1
ABSTRACT The self-assembly of six self-complimentary Guanine – Cytosine hybrid heterocycles bearing hydrophobic substituents has been studied using combinatorial approach in eight solvents under different conditions. The parameters that were varied include: the structure of the selfassembling module, its concentration, the solvent, temperature, and time of self-assembly. Scanning electron microscopy (SEM) was used as a screening tool. A wide variety of interesting morphologies was found. The most interesting structures were studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray powder diffraction (XRD). INTRODUCTION The top down approach to materials fabrication offers good control over the resulting morphology, but it has an inherent size limit below which design and construction of fine (nanometer and subnanometer) functional features is impractical [1, 2]. A bottom up approach, realized mostly through self-assembly of small molecular building blocks, allows for preparation of large nanostructures, albeit with limited control over higher order aggregation [1, 2]. Here we report a systematic approach to control not only lower, but also higher degrees of assembly from the subnanoscale to the macroscale. Combinatorial chemistry has been used extensively and successfully in drug discovery. It allows for faster and more efficient screening of bioactive molecules with desired properties. The combinatorial parameters varied here are usually substituents on the target molecule that can be introduced using organic synthesis. The number of positions varied determines the dimension of the combinatorial matrix. In this work, we have developed a multi-dimensional matrix covering (a) nature of the self-assembling modules (b) nature of the solvent in which self-assembly takes place, (c) concentration, and (d) sample ageing. EXPERIMENT DLS measurements. DLS experiments were performed on a Malvern Zetasizer Nano S working at a 90º scattering angle at 25ºC. The instrument is equipped with a 40 mW He–Ne laser (λ = 633 nm) and an avalanche photodiode detector. Size distributions were calculated using an inverse Laplace transform algorithm, and the hydrodynamic radii were calculated using the Stokes–Einstein equation. All samples were filtered through 0.2 µm nonsterile PVFD membranes (Whatman filters) prior to measurement.
AFM imaging. RNT samples were prepared by dissolving compound 1 in methanol, chloroform or hexane, sonicating, heating to the boiling point, then allowing the solution to age for 2 h at room temperature. Samples for AFM imaging were prepared in a class 10000 clean room by spin coating 25 µL (Cookson G3-8 Desk-Top Precision Spin Coating Sys
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