Doctor of Philosophy
James A. Wisner
The design and characterization of linear oligomers that self-assemble into double helical structures has been a subject of interest to chemists since the elucidation of the double helix structure of DNA in 1953. Transition metal templates have been widely used in the construction of artificial double helical complexes from linear multidentate ligands. The use of other non-covalent interactions as the driving force in the self-assembly of these types of complexes is less common. Aromatic stacking interactions, anion templates, and salt-bridges have all been applied in this context. The great majority of these investigations have been concerned with the dimerization of identical linear oligomers to form homoduplex products. There are very few examples of artificial double helices that form from complementary strands to give heteroduplexes. Notably, Yashima, Furusho and coworkers have demonstrated that two complementary molecules may interact via amidinium-carboxylate salt bridges in a sequence dependent manner resembling the hybridization of ss-DNA. Our group has reported the formation of a double helical complex based on self-complementary molecular strands containing alternating hydrogen bond donors and acceptors but its association constant was very low. In this thesis, we attempt to design and synthesize complementary hydrogen bonded AAAA-DDD double helices with high association constants and further develop supramolecular polymers based on them.
The first non-coplanar DDD molecule including three thiazine dioxide subunits and AAA component including two pyridine and one 3,5-lutidine subunits can form the double helical structure. The DDD component insoluble in chloroform resulted in that high association constant is not figured out. However, DDD analogue based on indole and thiazine dioxide subunits can be dissolved in chloroform and the AAA-DDD binding property in solution was investigated.
Electron- withdrawing groups on DDD component increase the stabilities of AAA-DDD complexes and electron-donating groups on AAA component also improve the stabilities of AAA-DDD complexes. Substituent groups on DDD or AAA molecules not only change their electronic distributions but also their original conformations. Therefore, substituent effect is not simply equal to electronic effect.
Two DDD and AAA components were linked with an aliphatic chain respectively. The main-chain AA-BB supramolecular polymer is formed from the 1:1 mixture of bisAAA and bisDDD. BisAAA and bisDDD follow the ring-chain supramolecular polymerization mechanism. Relative to the same length linkers in bisAAA and bisDDD, the largely different length of linkers led to the lower critical polymerization concentration.
Wang, Hong-Bo, "Double Helical Hydrogen-Bonded AAA-DDD Complexes and Supramolecular Polymers" (2011). Electronic Thesis and Dissertation Repository. 211.