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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1 000~2 502nm波长范围内的近红外光谱,分辨率8cm-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1 000~2 502nm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1 600~1 800nm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1 050~1 200nm主要由C—H基团的二级倍频构成;第2特征光谱区为1 300~1 500nm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1 600~1 850nm和第4特征光谱区2 000~2 502nm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。
The aim of this study is to study the molecular structure of 20 kinds of amino acids and their correlations with their near infrared spectra and to lay a theoretical foundation for the popularization and application of amino acid near infrared spectroscopy in animal science, food and medicine. The Shimadzu Fourier transform infrared spectrometer IRPrestige-21 and its near-infrared attachment FlexIRTM Near-Infrared Fiber Optics module were used to acquire the near-infrared spectra of 20 amino acid reference materials in the wavelength range from 1 000 to 2 502 nm with a resolution of 8 cm -1 , Each sample scanning 3 times, each scan 50 times, take the average value of the amino acid standard near-infrared spectroscopy. According to the difference of amino acid side chain groups, the correlation between the structure of each amino acid in aliphatic amino acids, aromatic amino acids and heterocyclic amino acids and their near infrared spectra were compared respectively. Studies have shown that 20 kinds of amino acids in the 1 000 ~ 2 502 nm region has a very significant near-infrared absorption and significant differences. The near infrared spectra of aliphatic amino acids with larger molecular weight are more affected by the side chain groups, while the glycine near infrared spectra are more affected by the carboxyl and amino groups. The difference between the two aromatic amino acids near infrared spectra mainly comes from the benzene ring , -OH groups on tyrosine benzene ring reduce the symmetry of benzene molecules, resulting in more vibration absorption peaks; heterocyclic amino acids due to the composition of the heterocyclic groups on their side chains, the near infrared spectroscopy in the 1 600 ~ 1 800nm larger regional differences. In summary, there are four characteristic spectral regions of the 20 kinds of amino acids: the first characteristic spectral region is from 1 050 to 1 200 nm and the second characteristic spectral region is from 1 300 to 1 500 nm Mainly composed of the combined frequency of C-H groups. Due to the different molecular structure of the side chain groups, the characteristics are quite different in the third characteristic spectrum region from 1 600 to 1 850 nm and the fourth characteristic spectrum region from 2 000 to 2 502 nm Absorption peak. Therefore, the four NIR spectral regions can be used to quantitatively and qualitatively analyze the amino acids to improve the prediction accuracy of amino acid near infrared spectroscopy models.