Figure 6.

FTIR spectra for the ¹²C-carbonyl (i.e., “native”) FP peptide and a suite of multiply ¹³C-carbonyl enhanced FP peptides in PBS solution. Peptides were suspended at 470 μM in deuterated PBS (pH 7.4), as described in Materials and Methods. (A) FP_A1/G3 is the solid line and native FP is the dashed line. The amide I band is shown for the native FP spectrum, with a dominant peak at 1628 cm⁻¹ and a minor peak at 1696 cm⁻¹ denoting antiparallel β-sheet, and a high-field shoulder at 1643 cm⁻¹ indicating random structure. The FP_A1/G3 spectrum indicates a residual ¹²C amide peak at 1634 cm⁻¹ and a ¹³C amide peak at 1616 cm⁻¹, denoting antiparallel β-sheet. (B) FP_A1/G3/G5/L7 (solid line), native FP (dashed line). The FP_A1/G3/G5/L7 spectrum indicates a residual 12C amide peak at 1644 cm⁻¹ and a ¹³C amide peak at 1610 cm⁻¹, denoting antiparallel β-sheet. (C) FP_G5-A15 (solid line), native FP (dashed line). The FP_G5-A15 spectrum indicates a minimal residual ¹²C amide peak at and a pronounced ¹³C amide peak at 1590 cm^-1, denoting antiparallel β-sheet. (D) FP_G20/A21 (solid line), FP (dashed line). The low-field shoulder at ~1607 and tail at ~1593 cm⁻¹in the FPG20/A21 spectrum indicates random (disordered) and β-sheet structure.