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. Author manuscript; available in PMC: 2023 May 23.
Published in final edited form as: Free Radic Biol Med. 2019 Dec 26;148:96–107. doi: 10.1016/j.freeradbiomed.2019.12.030

Table 3.

Summary of circular dichroism data for polyproline II helix model peptides.

λmax, nm C4 3JαN, Hz [θ]228, deg cm2 dmol−1 [θ] at λmax, deg cm2 dmol−1
PPII-P4 230 - 3000 ± 170 3070 ± 250
PPII-C4-SH 232 7.2 −390 ± 260 90 ± 180
PPII-C4-SO2− 231 6.2 340 ± 120 1290 ± 180

CD data were collected at pH 4 in an aqueous solution of 5 mM phosphate buffer with 25 mM NaCl at 25 °C. Polyproline II helix is indicated by the magnitude of the local maximum around 228 nm. The intensity ([θ]228) and wavelength (λmax) of this local maximum CD signal are used to determine PPII helix propensity. The 3JαN (vicinal coupling constant between the amide (HN) and alpha (Hα) hydrogens of the same residue) of Cys-SO2− indicates a more compact conformation in ϕ than that of Cys-SH, which is consistent with a greater PPII propensity for Cys-SO2−.