20种氨基酸近红外光谱及其分子结构的相关性

摘要

The objective of the research was to study the correlations between near infrared spectra and molecular structures of 20 standard amino acids.It was to establish the theoretical foundation for widely use of the amino acids near infrared spectra in ani-mal science,food and medicine.Measurement of the near infrared spectra was performed using a Shimadzu Fourier transform in-frared spectrophotometer IRPrestige-2 1 ,with FlexIRTM Near-Infrared Fiber Optics module.The spectrometric data acquisitions were performed by Shimadzu IRsolution 1.50 system.The spectrometric room temperature was 25 ℃ and humidity was 38%. Spectra of 20 amino acid standard substances were collected by reflectance mode from 1 000 to 2 502 nm in 8 cm-1 increment. Each sample was scanned in three times,each scan was 50 cycles,and the average value of three times scan result was used for each sample.Based on the differences of amino acids side chains,the correlations between near infrared spectra and molecular structures were compared in the fat family amino acids,aromatic amino acids and heterocycle amino acids.The result shows that all 20 standard amino acids have very specific absorption line patterns.It is distinctly different in these absorption line patterns. Near-infrared spectra of high molecular weight fat family amino acids are affected by side chains.Near-infrared spectra of glycine are affected by carboxyl and amino.The differences of near-infrared spectra between two aromatic amino acids are in benzene ring.—OH groups on benzene ring of tyrosine lower the symmetry of benzene molecule.It leads to the emergence of more vibra-tion absorption.Near-infrared spectra of heterocycle amino acids are distinctly different in 1 000~2 502 nm because of side chains.In conclusion,there are four different characteristic spectral regions.The first one is 1 050~1 200 nm spectral region which is composed mainly of second-order frequency doubling of C—H group.The second is 1 300~1 500 nm spectral region which is composed mainly of combination tune of C—H group.Due to side chains of amino acid have different molecular struc- ture,they yield a complete set of near infrared fingerprint spectra between 1 600~1 850 and 2 000~2 502 nm.In another words,these four characteristic regions of near infrared spectra can be used to build the model of qualitative analysis and quanti-tative analysis for amino acid,and improves the accuracy and reliability of model.%旨在研究20种氨基酸的分子结构与其近红外光谱的相关性,为氨基酸近红外光谱在动物科学、食品和医药等方面的推广应用奠定一定的理论基础。应用岛津傅里叶变换红外光谱仪 IRPrestige-21及其近红外附件 FlexIRTM Near-Infrared Fiber Optics module,采集20种氨基酸标准物质在1000~2502 nm波长范围内的近红外光谱,分辨率8 cm-1,每个样品扫描3次,每次扫描50遍,取其平均值为氨基酸标准品的近红外光谱。根据氨基酸侧链基团的不同,分别比较脂肪族氨基酸、芳香族氨基酸和杂环氨基酸中各氨基酸分子结构与其近红外光谱的相关性。研究表明,20种氨基酸在1000~2502 nm区域有非常明显的近红外光谱吸收且差异显著。分子量较大的脂肪族氨基酸其近红外光谱受侧链基团的影响较大,而甘氨酸近红外光谱受羧基和氨基的影响较大；两种芳香族氨基酸近红外光谱的差异主要来自于苯环,酪氨酸苯环上的—OH 基团降低了苯分子的对称性,导致更多振动吸收峰的出现；杂环氨基酸因其侧链上杂环分子基团构成不同,其近红外光谱在1600~1800 nm区域差异较大。综上,20种氨基酸主要存在4个特征光谱区：第1特征光谱区为1050~1200 nm主要由C—H 基团的二级倍频构成；第2特征光谱区为1300~1500 nm主要由C—H基团的组合频构成；因侧链基团分子构成不同,在第3特征光谱区1600~1850 nm和第4特征光谱区2000~2502 nm表现出差异较大的特征吸收峰。因此,可以利用此4个近红外光谱特征区域对氨基酸进行定量和定性分析,提高氨基酸近红外光谱模型预测的准确性。