Fig. 2: The triple-helix stability of X-CMP featuring a weakly trans-amide favoring (Pro < Kcis/trans < 1) or strongly cis-amide preferring (Kcis/trans > 1) peptoid residue X.
From: Cis-trans isomerization of peptoid residues in the collagen triple-helix
a The cis-trans isomerization of the peptide bond for an N-gly model compound Ac-X-OMe, which was used to calculate the Kcis/trans value for residue X. b Chemical structure of X-CMP, a host-guest collagen mimetic peptide with the sequence of (GlyProHyp)7, where the central X-position Pro was substituted. c The CD thermal unfolding curves (top) and their first derivatives (bottom) of the X-CMPs featuring Pro or a weakly trans-favoring N-gly (Kcis/trans < 1) as the guest X unit. As temperature increases, an X-CMP triple-helix will unfold into single chains, shown as a drop in CD signal, where the mid-point of this two-state transition (i.e., the lowest point of the derivative curve) is defined as the melting temperature (Tm, in °C), indicating the thermal stability of the X-CMP. d Triple-helical stabilities of X-CMPs featuring N-gly or amino acid residues with variable Kcis/trans values. e Cis-amide induction caused by hydrogen bonding or n→π*Ar electronic interactions. f The CD thermal unfolding curves (top) and their first derivatives (bottom) of the X-CMPs featuring a series of strongly cis-amide favoring N-glys (Kcis/trans > 1). g The structures and Kcis/trans values for the strongly cis-amide favoring N-glys, as well as the Tm values of their corresponding X-CMPs in PBS solutions (except for N2pic-CMP, which was measured in 1 mM HCl). *: value cited from ref. 31.
