Oligomers of the achiral amino acid residue α-aminoisobutyric acid (Aib) are known to be strong promoters of 310 helical conformations in solution and the solid state. Due to the lack of chirality of this residue, homooligomers of Aib form racemic (50/50) mixtures of left- and right-handed helices. The addition of a single chiral center at the C-terminus provides left- and right-handed diastereomers. We have been examining the ability of chiral C-termial groups to bias the handedness of Aib oligomers in solution and the solid state using 1H NMR spectroscopy (solution) and single crystal X-ray studies (solid state), as a function of chiral biasing unit and peptide length. X-ray studies offer configurational details of helical pitch and Φ, ψ angles, as well as diastereotopic excess. Interestingly, C-terminal chiral units do not all bias in the same helical direction (P/M) for the same configuration (R/S) of chirally-biasing unit. 1H NMR studies and X-ray results will be discussed.

1H NMR and X-ray characterization of diastereotopic excess of chirally-biased Aib oligomeric peptides

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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