Date of Award
Doctor of Philosophy (PhD)
Robin L. McCarley
This work demonstrates the use of pyrrole-terminated dendrimers (PTD)s for the oxidation-state-dependant encapsulation and release of various guest molecules. In order to achieve the goals of this research, a two-step approach was taken. The first portion of this doctoral work involved synthesis of low-generation (small number of peripheral groups) PTDs having a simple structure (DAB-Py x, X = 4, 8, 16) and studying the intramolecular oligomerization of the terminal pyrrole groups by well-known electrochemical methods. After the proof-of-concept study with low-generation PTDs, the next step involving more complex, high-generation PTDs (DAB(COCyPy)x, Y = 3 or 5, X = 32 or 64) was carried out. The larger, more complex PTDs were synthesized, and intramolecularly oligomerized; these oligomeric PTDs were investigated for their ability to effectively trap guest molecules. The PTDs that were used in the oligomerization proof-of-concept study were synthesized by direct conversion of the dendrimer 1° amine termini to a pyrrole ring. PTD synthesis by this method was limited to dendrimers having 16 pyrrole groups (DAB-Py16). Of the all DAB-Pyx, only DAB-Py16 was found to result in an intromolecularly oligomerized monolayer when oxidized by electrochemical means. The difficulty in synthesizing high-generation PTDs and the fact that only the DAB-Py16 was capable of oligomerization indicates that high generation dendrimers exhibit a peripheral crowding (close end groups). This peripheral crowding concept was studied by monitoring the hydrogen bonding between the amide groups terminating various dendrimers. Results from this study reveal that as dendrimer generation increases there is an increase in the hydrogen bonding between the end groups, thus an increase in end group proximity. A PTD system used to encapsulate guest molecules was synthesized by first converting the 1° amine of an amino acid to a pyrrole ring, and then attaching the resulting "pyrrole acid" (N-pyrrolyl(alkane)carboxyic acid) to a dendrimer. The pyrrole groups of the resulting DAB(COCxPy) 32, X = 3, 5 can be intramolecularly oligomerized. Molecular modeling studies indicate that the PTD structure is altered by changing the oxidation state of the peripheral oligo(pyrroles). The structural changes induced by the oxidation state of the oligo(pyrroles) was used to direct the encapsulation/release of guests within the PTD.
Noble, Charles Oakley IV, "Pyrrole -Terminated Dendrimers for Use in Polymerizable Monolayers and Guest Encapsulation Systems." (2001). LSU Historical Dissertations and Theses. 357.