Phenylene Ethynylene Foldamers: Cooperative Conformational Transition, Twist Sense Bias, Molecular Recognition Properties, and Solid -State Organization
Prince, Ryan Benjamin
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https://hdl.handle.net/2142/84472
Description
Title
Phenylene Ethynylene Foldamers: Cooperative Conformational Transition, Twist Sense Bias, Molecular Recognition Properties, and Solid -State Organization
Author(s)
Prince, Ryan Benjamin
Issue Date
2000
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, Organic
Language
eng
Abstract
Several series of sequence-specific meta connected phenylene ethynylene oligomers were designed, synthesized, and studied. The oligomers were determined to adopt highly ordered conformations both in solution and the solid-state. The conformational transition from a random coil to helical conformation was quantitatively characterized by fluorescence spectroscopy. From these measurements, it was determined that the stability of the helical conformation is linearly dependent on chain length. The addition of nonpolar methyl groups to the oligomeric backbone was found to stabilize the helical conformation. Circular dichroism spectroscopy was used to show that the attachment of a chiral, polar side chain results in a twist sense bias of the helical conformation. A second series of oligomers containing chiral, nonpolar side chains was also determined to adopt a helically biased conformation in nonpolar solvents. The metal coordination properties of several oligomers substituted with cyano groups were determined by UV-vis, fluorescence spectroscopy, proton NMR spectroscopy, electrospray mass spectrometry and isothermal microtitrational calorimetry. These results showed that the oligomers can be modified to tightly and selectively bind metal ions. The helical conformation was determined to be stabilized by a combination of metal coordination and solvophobic interactions. The solid-state organization of several oligomer series was examined by optical microscopy, differential scanning calorimetry and powder X-ray diffraction. Oligomers that cannot fill the void space of the tubular cavity were determined to adopt a lamellar organization, while those that can, spontaneously organized into a tubular mesophase. The tubular cavity present in the helical conformation was used to reversibly bind a variety of small-molecule guests. The association was determined to be a solvophobically driven process that could me modified by the addition of space-filling methyl groups to the oligomer backbone.
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