Self-assembled organic nanotubes with tunable stability, dimensions, and hierarchy
Abstract
Discrete nanoscale tubular architectures currently receive a great deal of attention because of their potential roles in the construction of devices, sensors, artificial channel systems, and biomedical engineering. Our research group has developed a general approach for the self-assembly of organic nanotubes from low molecular weight synthetic modules featuring the guanine-cytosine (GΛC) base. HRN's are biologically-inspired architectures with properties predetermined by the self-assembling modules. Through the synthetic modification of the modules, we have demonstrated that it is possible to tailor the chemical and physical properties of the resulting HRN's. Extensive studies by circular dichroism spectroscopy, transmission electron microscopy, and atomic force microscopy have confirmed that HRN's with amino acid side chains are chiral, have diameters of approximately 3.5 nm, and lengths varying from a few nanometers to several hundred micrometers. Recent studies have shown that titanium surfaces coated with arginine and lysine rich HRN's mimic environments that bone cells recognize. As a result of a structural modification to the lysine module, the amide analog module was found to self-assemble into nanotubules (NT's) with dimensions roughly 10 times larger than the outer diameter of amino acid functionalized HRN's. Due to the structural variation featured in the amide analog, the hydrogen-bonding pattern of the guanine face was inaccessible, which prevented the formation of rosettes. We proposed that the modules self-assembled into 2-dimenional sheets which stack to form the walls of the NT's. The dimensions, biomimetic and supramolecular nature of these novel tubular archutectures implicate potential uses in drug delivery and biomedical engineering. Covalently linked twin-base modules were synthesized because they were anticipated to increase the stability of HRN's due to three novel features of the system design: the covalent linker, which pre-organized the two GAC components, the number of hydrogen bonds per module (12 instead of six) and decreased pendant density which minimizes pendant repulsion on the nanotube's surface. The improved twin-base design gave rise to HRN's which can withstand a wide range of pH (1-14) and accommodate large pendant groups (i.e. dendrimers, biologically active peptides) opening the route to new rosette nanotubes and rosette nanotube-hybrid materials.
Degree
Ph.D.
Advisors
Fenniri, Purdue University.
Subject Area
Organic chemistry
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