*2.3. Fraction Folded Population and* ∆*Gfold*

The fraction folded population and folding free energy (∆Gfold) of each residue on the experimental peptides were derived from the Hα chemical shift deviation data (Figures S51 and S52). The residues close to the termini suffered from the end fraying effects [3,21–23]. The residues next to the turn were intrinsically highly folded due to proximity to the turn residues. Therefore, the residues near the center of the strands (positions 2, 3, 9, 10) were used to derive the fraction folded population and ∆Gfold for each peptide (Tables 1 and 2) [3, 11,20,22,23]. Both hydrogen-bonded sites (positions 3 and 10) and non-hydrogen-bonded sites (positions 2 and 9) were included [3,11,20,22,23]. Since the fraction folded population and the folding free energy showed the same trends (i.e., the more negative the folding free energy, the higher the fraction folded population), further discussion will only focus on the fraction folded data.


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**Table 1.** The fraction folded population (%) for the HPTXaaZbb peptides <sup>1</sup>

<sup>1</sup> Average value for residues 2, 3, 9, and 10.

**Table 2.** The folding free energy (∆Gfold, kcal/mol) for the HPTXaaZbb peptides <sup>1</sup> .


<sup>1</sup> Average value for residues 2, 3, 9, and 10.

The fraction folded populations for the peptides were between 35% and 72%, and the standard deviations were within 5% (Table 1). Peptides HPTDapAsp and HPTDapGlu, containing the shortest positively charged residue Dap, exhibited exceptionally high fraction folded populations. In particular, HPTDapGlu exhibited the highest fraction folded population among all the HPTXaaZbb peptides. In contrast, HPTDapAad exhibited the least fraction folded population.

The fraction folded population of the HPTXaaAsp peptides followed the trend HPTDapAsp > HPTDabAsp ~ HPTOrnAsp > HPTLysAsp. Similarly, the fraction folded population

of the HPTXaaGlu peptides followed the trend HPTDapGlu > HPTDabGlu ~ HPTOrnGlu ~ HPTLysGlu. However, the fraction folded population of the HPTXaaAad peptides followed the trend HPTDapAad < HPTDabAad < HPTOrnAad > HPTLysAad. If one disregards HPTDapAad and HPTDabAad, the fraction folded population of the HPTXaaZbb peptides for a given negatively charged residue Zbb9 generally decreased upon increasing the side-chain length of the positively charged residue Xaa4.

The fraction folded population of the HPTDapZbb peptides followed the trend HPT-DapAsp < HPTDapGlu > HPTDapAad. The fraction folded population of the HPTDabZbb peptides followed the trend HPTDabAsp ~ HPTDabGlu < HPTDabAad. Similarly, the fraction folded population of the HPTOrnZbb peptides followed the trend HPTOrnAsp ~ HPTOrnGlu < HPTOrnAad. The fraction folded population of the HPTLysZbb peptides followed the trend HPTLysAsp ~ HPTLysGlu < HPTLysAad. Again, if one disregards HPTDapAad, the fraction folded population of the HPTXaaZbb peptides for a given positively charged residue Xaa4 generally increased with increasing side-chain length of the negatively charged residue Zbb9.
