密度泛函理论的氨基酸近红外非谐振动光谱解析

Analysis of Near-Infrared Anharmonic Vibration Spectra of Amino Acids Using Density Functional Theory

氨基酸作为组成蛋白质的基本结构单元在生物体中起着重要作用。不同的基团组成和手性结构所代表的功能均有差异,因此甄别其基本化学结构和分子振动信息将为构建基础生物分子光谱与结构相关性模型提供重要的理论依据。近红外光谱主要展示各类含氢基团(如O—H、N—H和C—H等)的倍频和合频振动信息;振动信息比较复杂,加上常规红外光谱仪器分辨率限制等原因,导致实验测得的谱带变宽,无法准确对其振动模式进行指认,分析较为困难。理论计算可以对每个振动模式进行独立计算,能够提供更清晰的光谱信息,进而对实验得到的宽谱带进行解析,使其更易甄别和分析不同分子体系的各类基团的结构振动信息。采用非谐振DFT方法对氨基酸(谷氨酸、半胱氨酸、甘氨酸)及由此三种氨基酸组成的多肽(谷胱甘肽)进行结构优化和非谐振振动分析,计算得到四种分子7500~4500 cm-1波段内的高精度NIR光谱,并对它们的谱图进行了详细的振动峰位指认。以振动强度作为标准,将整个近红外波段分为三个光谱区探究分子结构和组成基团对光谱特征的影响,对计算光谱进行了详细的分析并且建立了光谱与结构间的对应关系。该研究为更深的理解氨基酸及多肽的结构性质提供了思路。

Amino acids play an important role in organisms as the basic building blocks of proteins.The functions of amino acids with different group compositions and chiral structures are different,showing an urgent requirement to identify the basic chemical structure and molecular vibration information.This will provide an important theoretical basis for constructing basic biomolecule spectra and structural correlation models.NIR spectrum mainly shows the first overtone and binary combination vibration information of various hydrogen-containing groups(such as O—H,N—H,C—H,etc.).The vibration information is relatively complex,coupled with the resolution limitations of conventional infrared spectroscopy instruments and other reasons,resulting in a spectrum of experimental results.The band becomes wider,and its vibration mode cannot be accurately identified,making analysis more difficult.The theoretical calculation can independently calculate each vibration mode,providing clearer spectral information,and then analyze the wide absorption band obtained experimentally.This makes it easier to identify and analyze the structural vibration information of various groups in different molecular systems.In this work,the DFT calculation method carried out the structure optimization and anharmonic vibration analysis of three amino acids(glutamic acid,cysteine,glycine)and polypeptide(glutathione)composed of these three amino acids.The high-precision NIR spectrum of the four molecules in the band of 7500~4500 cm~(-1)was calculated,and detailed band assignments were made,dividing the entire near-infrared band into three spectral regions dependent on the vibration intensity.Furthermore,the influence of structure and constituent groups on the spectral characteristics was explored,and the corresponding relationships between the spectra and the structure were established.Our research would provide ideas for a deeper understanding of the structural properties of amino acids and peptides.