N–H Chirality in Folded Peptide LK <sub>7</sub> β Is Governed by the C <sub>α</sub> –H Chirality
Xiaohua Hu, Li Fu, Jian Hou, Yuening Zhang, Zhen Zhang, Hongfei Wang
Abstract
Recent chiral sum-frequency generation vibrational spectroscopy (SFG-VS) measurements revealed that two N–H stretching modes in the 3100–3500 cm–1 range in folded peptide LK7β exhibit chiral characteristics. Here, we report the first phase-resolved subwavenumber high-resolution broadband SFG-VS (HR-BB-SFG-VS) measurement of the folded peptide LK7β. The results show that this chiral N–H band consists of four, instead of two, distinctive peaks, and they are with two groups of opposite spectral phases. Moreover, the phases of these N–H peaks completely flip from the l-LK7β to the d-LK7β peptide, suggesting that the chirality of the N–H in the folded peptide LK7β is completely governed by the chirality of the Cα–H of the amino acids. This discovery provides a clue on why proteins in nature are composed of the α-amino acids rather than β- or γ-amino acids and may help us understand how life works.