Self-Assembled Multi-Component Catenanes: The Effect of Multivalency and Cooperativity on Structure and Stability
NORTH CAROLINA UNIV AT CHAPEL HILL OFFICE OF SPONSORED RESEARCH
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Using dynamic combinatorial chemistry DCC, mixtures of dipeptide monomers were combined to probe how the structural elements of a family of self-assembled 2-catenanes affect their equilibrium stability versus competing non-catenated structures. Of particular interest were experiments to target the role of CH-pi interactions, inter-ring hydrogen bonds and Beta-turn types on 2-catenane energetics. The non-variant core of the 2-catenane was shown to only adopt type II and type VIII turns at the Beta-2 and Beta-4 positions, respectively. Monomers were designed to delineate how these factors contribute to 2-catenane equilibrium speciationstability. Dipeptide turn adaptation studies, including three-component dynamic self-assembly experiments, suggested that stability losses are localized to the mutated sites, and that the turn types for the core Beta-2 and Beta-4 positions, type II and type VIII, respectively, cannot be modified. Mutagenesis studies on the core Aib residue involved in a seemingly key CH-pi-CH sandwich reported on how CH-pi interactions and inter-ring hydrogen bonds affect stability. The interacting methyl group of Aib could be replaced with a range of alkyl and aryl substituents with monotonic affects on stability, though polar heteroatoms were disproportionately destabilizing. The importance of a key cross-ring H-bond was also probed by examining an Aib for L-Pro variant. Inductive affects and the effect of CH donor multiplicity on the core proline-pi interaction also demonstrated that electronegative substituents and the number of CH donors can enhance the effectiveness of a CH-pi interaction. These data were interpreted using a cooperative binding model wherein multiple non-covalent interactions create a web of interdependent interactions.
- Physical Chemistry
- Atomic and Molecular Physics and Spectroscopy