Fig. 3. (A) Interplay of pseudoallylic strain (pA^1,2 and pA^1,3) in the reverse turn to induce the β-sheet folding. Note the spatial positioning of the methyl groups between i+1 C^α and i+2 C^α which modulates the folding of the polypeptide in aqueous solution at 25 °C. (B) CD spectrum of the peptides in acetate buffer (pH 3.8). (C) ¹H NMR in acetate buffer (pH 3.8), clearly indicating the enhanced dispersion of the H^N resonance and upfield shifted, distinguishable Leu11 H^δ1/2 in the well-folded peptides. (D) Secondary chemical shifts obtained from the respective random coil control peptides, where the d-residue is substituted with the l-residue. Leu11 H^α shows a negative deviation due to its proximity to the phenyl ring of Tyr2 in the folded analogs. In 1, the secondary chemical shifts were determined by subtracting the H^α chemical shifts from the mean random coil chemical shifts of the respective residues obtained from the random coils of 2 and 3. The ring constrained reverse turn motif, pG, was taken as a reference.19 (E) Summation of the secondary chemical shifts; only the absolute values were considered.