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    Protein-water coupling tunes the anharmonicity of amide I modes in the interfacial membrane-bound proteins

    Year: 2022

    Journal: J. Chem. Phys., Volume 156, MAR 14

    Authors: Tan, Junjun; Ni, Zijian; Ye, Shuji

    Organizations: National Key Research and Development Program of China [2017YFA0303500, 2018YFA0208702]; National Natural Science Foundation of China [21925302, 21633007, 21873090, 21903081]; Anhui Initiative in Quantum Information Technologies [AHY090000]

    The diagonal anharmonicity of an amide I mode of protein backbones plays a critical role in a protein's vibrational dynamics and energy transfer. However, this anharmonicity of long-chain peptides and proteins in H2O environment is still lacking. Here, we investigate the anharmonicity of the amide I band of proteins at the lipid membrane/H2O interface using a surface-sensitive pump-probe setup in which a femtosecond infrared pump is followed by a femtosecond broadband sum frequency generation vibrational spectroscopy probe. It is found that the anharmonicity of the amide I mode in ideal alpha-helical and beta-sheet structures at hydrophobic environments is 3-4 cm(-1), indicating that the amide I mode in ideal alpha-helical and beta-sheet structures is delocalized over eight peptide bonds. The anharmonicity increases as the bandwidth of the amide I mode increases due to the exposure of peptide bonds to H2O. More H2O exposure amounts lead to a larger anharmonicity. The amide I mode of the peptides with large H2O exposure amounts is localized in one to two peptide bonds. Our finding reveals that the coupling between the amide I mode and the H2O bending mode does not facilitate the delocalization of the amide I mode along the peptide chain, highlighting the impact of H2O on energy transfer and structural dynamics of proteins. Published under an exclusive license by AIP Publishing.
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