Title
Helical Oligopeptides of a Quaternized Amino Acid with Tunable Chiral-Induction Ability and an Anomalous pH Response
Author
Joonil Cho, Yasuhiro Ishida, Takuzo Aida
Year
2017
Journal
Chemistry - A European Journal
Abstract
A series of octamer (8mer) and hexadecamer (16mer) oligopeptides of 4-aminopiperidine-4-carboxylic acid (Api) with L-leucine as a chiral auxiliary at their N- or C-termini were synthesized. Using circular dichroism spectroscopy, the conformational profiles of the peptides were systematically studied, which revealed that the α-helix formation ability of the peptides is determined by the combination of parameters including peptide length, state of the piperidine groups in the Api units, and position of the chiral auxiliary. When the piperidines are at the free-base state, the peptides show low propensity to form helical structures. However, the protonation and acylation of the piperidines enhance the formation of helical structures, where the order in helix formation ability is: protonated > acylated > free-base. In terms of peptide length, the 16mers generally show higher helix-formation ability than the corresponding 8mers, and one of the 16mers shows helicity at a highest level for the oligopeptides with similar length. It was also found that the sensitivity of the helical structure toward the state of the piperidines changes drastically, depending on the chiral auxiliary position; the N-terminal chiral peptides are more sensitive than the C-terminal chiral ones.
Instrument
J-820
Keywords
Circular dichroism, Secondary structure, Thermal stability, Chemical stability, Biochemistry