Hexagonally-Packed Helical Oligo(m-Phenylene Ethynylene) Nanotubules via Structural Modification and Guest Templation
Mio, Matthew John
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https://hdl.handle.net/2142/84027
Description
Title
Hexagonally-Packed Helical Oligo(m-Phenylene Ethynylene) Nanotubules via Structural Modification and Guest Templation
Author(s)
Mio, Matthew John
Issue Date
2001
Doctoral Committee Chair(s)
Moore, Jeffrey S.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Polymer
Language
eng
Abstract
Various sequence-specific oligo(m-phenylene ethynylene) foldamers were designed, synthesized and studied. The foldamers were examined with the intention of translating previously reported solution-phase concepts into the solid-state realm. Specifically, the employment of the highly ordered helical conformation available to these foldamers in the building of well-defined solid-state nanostructures was explored. In addition, research expanded upon the general structural diversity of these oligomers, the forces responsible for the folding event, and possible applications for these systems. A review of the field of foldamers is presented, detailing the current literature concerning non-biological oligomers that use noncovalent interactions to collapse into solution-phase and solid-state secondary structures. The helical conformation of a set of ortho-capped oligomers was qualitatively characterized in solution by UV-vis, fluorescence, and 1H NMR spectroscopy, as well as in the solid state by wide- and small-angle X-ray powder diffraction (WARD and SAXD). Terpene guest binding was also examined using circular dichroism (CD) spectroscopy. The addition of endo-phenoxy methylene tert-butyl esters and carboxylic acids to the seven and ten positions of a symmetrically-capped hexadecamer was found to slightly destabilize the solution helical conformation. In the solid-state, on the other hand, the observation of an uncharacteristic long-spacing led to the discovery of a hexagonal packing motif, as opposed to the fully-extended lamellar structure seen previously. A systematic study of the endo-hydrogen and endo-methyl series was performed using a solvent evaporation sample preparation technique, WAXD, and SAXD. The observation of chain length dependent and independent long spacings for these two series, respectively, fits the two models of lamellae and hexagonally-packed helices. An alternative route to the hexagonal phase, through templation via internal side chain and cationic or small molecule guest was also elucidated. A survey of four minor projects is also provided: the characterization of the chain length dependent solution-phase binding of a rodlike guest to a foldamer, the effect of pressure on foldamer conformation when suspended in a polymer matrix, a thorough examination and comparison of foldamer solid-state morphology, and an extension of known solution-phase foldamer binding of terpenes to a multiple site domain.
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