| Abstract
| - We have investigated temperature effect on control of a peptide helix sense through the noncovalentchiral domino effect (NCDE: Inai, Y. et al., J. Am. Chem. Soc.2003, 125, 8151−8162). Nonapeptide(1: Inai, Y.; Komori, H. Biomacromolecules2004, 5, 1231−1240), which alone prefers a right-handedhelix, maintained a screw-sense balance or a small imbalance at room temperature in the presence ofBoc-d-amino acid. Cooling of the solution induced a left-handed helix more clearly. Conversely, heatingfrom room temperature recovered the original right-handed sense. This helix−helix transition wasessentially reversible in cooling−heating cycles. An increase in the Boc-d-amino acid concentrationelevated temperature for switching CD signs based on the conformational transition. A similar thermal-driven inversion of helix sense was observed for 1 at other initial concentrations, suggesting that thisbehavior is insensitive to some peptide aggregation. NMR study provided direct evidence for the domino-type control of helix sense, in which Boc-Leu-OH is mainly located at the N-terminal segment. In addition,a left-handed helix induced by the d-isomer was shown to participate in equilibrium with a right-handedhelix, whereas the right-handed helix was predominant in the presence of l-isomer. Consequently, wehere have proposed a model for controlling a peptide helix sense (or its screw-sense bias) throughtemperature tuning of the external chiral interaction specific to the N-terminal sequence.
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