Investigation of the Correlations between Amino Acids, Amino Acid Mixtures and Dipeptides by Terahertz Spectroscopy
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Investigation of the Correlations between Amino Acids, Amino Acid Mixtures and Dipeptides by Terahertz Spectroscopy Yujing Bian 1 & Xun Zhang 1 & Zhenqi Zhu 1 & Xiaodong Wu 1 & Xiang Li 2 & Bin Yang 1 Received: 21 April 2020 / Accepted: 17 November 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Terahertz (THz) spectroscopy is regarded as a professional technology to probe collective molecular vibrational modes and intensity of bio–molecules, which is potential to analyze amino acids and short peptides. In this study, THz spectroscopy is utilized to investigate the correlations of glycine (Gly), Serine (Ser), amino acid mixtures of Gly/Ser, and dipeptides (GS and SG) in the frequency range of 0.3–2.5 THz. The results manifest that the collective molecular vibrational intensity of Ser is larger than Gly, implying that the hydroxyl methyl group (–CH2–OH) on the side chain of Ser exhibits larger motions than that of –H in Gly. Additionally, the THz spectra of amino acid mixtures of Gly/Ser fit the linear addition of the individual amino acid absorption spectrum. Herein, the THz spectra of dipeptide GS and its isomer SG are distinguished according to the different collective molecular vibrations produced by the terminal groups on the carbon skeleton. Compared to physical amino acid mixtures of Gly/Ser, the dipeptides exhibit diverse THz spectra, indicating that the different collective vibrational modes are caused by peptide bonds and terminal groups. These solid evidences confirm that THz spectroscopy can be availably used to analyze the correlations of amino acids, amino acid mixtures, and dipeptides, as well as to identify dipeptide and its isomer from molecular level. Keywords THz spectroscopy . Amino acid . Mixture . Dipeptides . Collective molecular vibration
* Bin Yang [email protected]
1
College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Zhejiang 310018 Hangzhou, China
2
School of Materials Science and Engineering, Zhejiang Sci-Tech University, Zhejiang 310018 Hangzhou, China
Journal of Infrared, Millimeter, and Terahertz Waves
1 Introduction Amino acids, as a kind of vital bio–molecules, are considered to be the constitutional unit of protein [1]. Eighteen kinds of α–amino acids are used to make silk fibroin, each of them can be distinguished by the side chains of “R” groups by traditional methods [2, 3]. Peptides are linked by peptide bonds, which are constructed by dehydration condensation of carboxyl (–COOH) and amino (–NH2) groups of amino acids [4]. Owing to the motions of the side chains, peptides possess the unique configuration, including diverse secondary structures (an intermediate level of protein structure) such as α–helixes, β–sheets and β–turns [5]. Silk fibroin is discriminated by the number and sequential orders of amino acids, where the peptides are folded into well– defined three–dimensional (3D) structures. A stable 3D conformation is mainly maintained by intermolecular and intramolec
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