Title page for ETD etd-11042003-103320


Type of Document Master's Thesis
Author Huang, Feihe
Author's Email Address fehuang@vt.edu
URN etd-11042003-103320
Title Pseudorotaxanes and Supramolecular Polypseudorotaxanes Based on the Dibenzo-24-Crown-8/Paraquat Recognition Motif
Degree Master of Science
Department Chemistry
Advisory Committee
Advisor Name Title
Gibson, Harry W. Committee Chair
Gandour, Richard D. Committee Member
Tanko, James M. Committee Member
Keywords
  • Ion Pairs
  • Association Constant
  • X-ray Crystal Structure
  • Dibenzo-24-Crown-8
  • Polypseudorotaxane
  • Paraquat
  • Cooperative Complexation
  • Crown Ethers
  • Pseudorotaxane
Date of Defense 2003-08-28
Availability unrestricted
Abstract
The research presented in this thesis focused on pseudorotaxanes and supramolecular polymers based on a new recognition motif, the dibenzo-24-crown-8/paraquat recognition motif.

Main kinds of pseudorotaxanes and rotaxanes and various protocols used for the study of them were discussed first.

By preparation and characterization of a series of pesudorotaxanes based on DB24C8 and paraquat derivatives, it was found that these complexes were stabilized by N+...O interactions, C-H...O hydrogen bonding, and face-to-face p-stacking interactions. Because methyl protons of paraquat are involved in hydrogen bonding to the host, the substitution of any methyl hydrogen on paraquat causes apparent association constant of the pseudorotaxane to decrease.

The concentration dependence of apparent association constants, Ka,exp, of fast exchange host-guest systems was studied for the first time by using complexes based on viologens and crown ethers as examples. While the bis(hexafluorophosphate) salts of paraquat derivatives are predominantly ion paired in acetone (and other low dielectric constant solvents presumably) the complex based on dibenzo-24-crown-8 and paraquat is not ion paired in solution, resulting in concentration dependence of Ka,exp. However, four complexes of two different bis(m-phenylene)-32-crown-10 (BMP32C10) derivatives and bis(p-phenylene)-34-crown-10 (BPP3C10) with viologens are ion paired in solution, as shown by the fact that Ka,exp is not concentration dependent for these systems involving hosts with freer access to bound guests. X-ray crystal structures support these soluton-based assessments in that there is clearly ion pairing of the cationic guest and its PF6- counterions in the solid states of the latter four examples, but not in the former. The complexes based on the new dibenzo-24-crown-8/paraquat recognition motif are thus different from the complexes based on two old recognition motifs: the BPP34C10/BMP32C10-paraquat and DB24C8-ammonium motives.

In order to compare these recognition motives further, the selectivity between two hosts, DB24C8 and BPP34C10, and two guests, dimethyl paraquat and dibenzyl ammnonium salt, was discussed. By individual and competitive complexation studies, it was demonstrated that DB24C8 is a better host than BPP34C10 for paraquat, and that paraquat is a better guest than dibenzyl ammonium salt for DB24C8.

Finally the DB24C8-paraquat recognition motif was successfully applied in the preparation the first star-shaped supramolecular polymer based on a tetraparaquat guest and a DB24C8 functionalized polystyrene oligomer. A model system based on this guest and DB24C8 was also studied for comparison. It was found that the complexation in these two systems is cooperative, as are most biological complexations of multitopic species.

Due to the ready availability of DB24C8 and paraquat derivatives, the new recognition motif should prove to be very valuable for self-assembly of other more sophisticated supramolecular systems.

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  Abstract.pdf 106.32 Kb 00:00:29 00:00:15 00:00:13 00:00:06 < 00:00:01
  Acknowledgements.pdf 84.42 Kb 00:00:23 00:00:12 00:00:10 00:00:05 < 00:00:01
  Chapter-I.pdf 609.00 Kb 00:02:49 00:01:26 00:01:16 00:00:38 00:00:03
  Chapter-II.pdf 118.31 Kb 00:00:32 00:00:16 00:00:14 00:00:07 < 00:00:01
  Chapter-III.pdf 983.48 Kb 00:04:33 00:02:20 00:02:02 00:01:01 00:00:05
  Chapter-IV.pdf 1.23 Mb 00:05:41 00:02:55 00:02:33 00:01:16 00:00:06
  Chapter-V.pdf 469.86 Kb 00:02:10 00:01:07 00:00:58 00:00:29 00:00:02
  Chapter-VI.pdf 295.57 Kb 00:01:22 00:00:42 00:00:36 00:00:18 00:00:01
  Chapter-VII.pdf 87.40 Kb 00:00:24 00:00:12 00:00:10 00:00:05 < 00:00:01
  cover.pdf 82.41 Kb 00:00:22 00:00:11 00:00:10 00:00:05 < 00:00:01
  Table-of-Contents.pdf 160.99 Kb 00:00:44 00:00:22 00:00:20 00:00:10 < 00:00:01
  Table-of-Figures.pdf 251.25 Kb 00:01:09 00:00:35 00:00:31 00:00:15 00:00:01
  Table-of-Schemes.pdf 86.10 Kb 00:00:23 00:00:12 00:00:10 00:00:05 < 00:00:01
  Table-of-Tables.pdf 102.65 Kb 00:00:28 00:00:14 00:00:12 00:00:06 < 00:00:01
  Vita.pdf 53.91 Kb 00:00:14 00:00:07 00:00:06 00:00:03 < 00:00:01

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