Chiral Influence on Synthetic Molecules

Reported are the studies on chiral influence on synthetic molecules such as azobenzene containing oligomers, benzophenone derivatives, and 1, 4, 5, 8-perylenetetracarboxylic acid diimides. Amino acids and other simple, low-cost chiral inducers were used as readily available sources of asymmetric induction. The design of the folded azobenzene oligomer originated from the concept that the architecture of the meta-substituted aromatic groups would force the molecule to assemble into a helix. The stability of this helical formation would be assisted by both pi-pi stacking and hydrogen bonding. The resulting oligomer exists in two enantiomeric helical forms. It was hypothesized that a small chiral perturbation placed at a specific point at the end of the oligomer would then be amplified throughout the length of the entire molecule creating a preference for one-handed sense of the helix over the other antipode. This theory was proven through the use of circular dichroism (CD) spectra. The chiral oligomers were synthesized in two and four turn variants and the induced chirality increased by more than two times with this increase in length. The oligomer was determined to be right-handed or P sense. This conclusion was reached though interpretation of the CD spectra, computer assisted molecular modeling, calculated CD's, and through collaboration with Christopher M. Hadad's research group.;Benzophenone was envisioned as a ligand in asymmetric catalysis. Benzophenone is a chiral-racemic molecule that exists in two enantiomeric, propeller-like forms. It was proposed that after the benzophenone scaffold was appended with a pair of phosphine atoms it can act as a ligand in transition metal catalysis. The ketone moiety could then be manipulated with a chiral amine to form an imine and then this handed perturbation could be amplified through the molecule. The induced chirality would subsequently transfer to the active site of the metal catalyst. Favorable hydrogen bonding interactions the assist in stabilizing the catalyst in its preferred handed form. A benefit of this ligand would be the modularity granted to the catalyst by changing the identity or handedness of the amino acid used for induction. It was observed via CD that the identity of the amine employed had a great effect on the resulting signal and therefore the chiral environment of the pre-catalyst.;Finally, the self-assembly of several one-dimensional nanostructures comprised of 1, 4, 5, 8-perylenetetracarboxylic acid diimides with various imide groups was studied. The imides were altered from simple alkyl chains or several combinations of protected lysine to form amphiphiles and bola-amphiphiles. Perylene was selected because of its many opto-electronic properties that are frequently exploited in intermolecular charge transfer. It was observed through various analytical techniques that the perylene diimides strongly assembled in numerous solvent conditions with the exception of 2,2,2-trifluoroethanol (TFE).