短寡肽中结合的亮氨酸在氯化过程中形成有臭味的醛、腈和 N-氯代亚胺。
Formation of odorous aldehydes, nitriles and N-chloroaldimines from combined leucine in short oligopeptides during chlorination.
机构信息
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China.
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai, 200092, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China.
出版信息
Water Res. 2020 Jun 15;177:115803. doi: 10.1016/j.watres.2020.115803. Epub 2020 Apr 7.
Previous studies have focused on investigating the formation of odorous by-products during the chlorination of free amino acids (AAs). However, studies on the formation of odorous by-products during the chlorination of combined AAs, which are much more abundant in natural waters than free AAs, are very limited. In this study, the generation of odorous aldehyde, nitrile and N-chloroaldimine from short oligopeptides containing combined Leucine (Leu) (a typical precursor of odorous by-products), including glycylleucine (Gly-Leu), leucylglycine (Leu-Gly), and trileucine (Leu-Leu-Leu), was investigated. The reaction mechanisms were then proposed based on Acquity UPLC-qTOF mass spectrometer measurement and kinetic studies modelled with Kintecus. The results indicated that a series of sequential reactions, including substitution, dehydrohalogenation, β-elimination, hydrolysis and decarboxylation reactions, occurred during the chlorination of short oligopeptides. The chlorination of Gly-Leu and Leu-Leu-Leu formed free Leu, which continued to react with chlorine, producing isovaleraldehyde, isovaleronitrile and N-chloroisovaleraldimine. Compared with Gly-Leu, Leu-Leu-Leu produced less free Leu, and therefore, a smaller amount of Leu-derived odorous by-products was generated. Leu-Gly produced free Gly, which was not a precursor of odorous by-products. Thus, neither isovaleraldehyde nor N-chloroisovaleraldimine was formed. Notably, isovaleronitriles can be formed directly from a β-elimination reaction during chlorination of Leu-Gly and Leu-Leu-Leu, and thus high yields of isovaleronitriles were observed after chlorination. The yields of odorous by-products during chlorination of short oligopeptides increased with increasing Cl/N ratios (the molar ratio of chlorine to nitrogen in the AAs) and reached their maximum at Cl/N = 2.4, except the yield of isovaleraldehyde formed from Gly-Leu reached its maximum at Cl/N = 1.6. UV and UV/HO pre-treatments decreased odorous by-product formation during subsequent chlorination through non-peptide bond breaking of short oligopeptides. This study facilitates the identification of the causes of off-flavour problems in drinking water and the development of ways to control these problems.
先前的研究主要集中在研究游离氨基酸（AAs）氯化过程中产生的恶臭副产物的形成。然而，与天然水中更丰富的游离氨基酸相比，关于结合氨基酸氯化过程中产生恶臭副产物的研究非常有限。在这项研究中，研究了含有结合亮氨酸（Leu）（恶臭副产物的典型前体）的短寡肽，包括甘氨酰亮氨酸（Gly-Leu）、亮氨酰甘氨酸（Leu-Gly）和三亮氨酸（Leu-Leu-Leu），生成恶臭醛、腈和 N-氯亚胺。然后根据 Acquity UPLC-qTOF 质谱仪测量和 Kintecus 建模的动力学研究提出了反应机制。结果表明，在短寡肽的氯化过程中发生了一系列连续反应，包括取代、脱卤化氢、β-消除、水解和脱羧反应。甘氨酰亮氨酸（Gly-Leu）和三亮氨酸（Leu-Leu-Leu）的氯化形成游离亮氨酸，游离亮氨酸继续与氯气反应，生成异戊醛、异戊腈和 N-氯异戊亚胺。与甘氨酰亮氨酸（Gly-Leu）相比，三亮氨酸（Leu-Leu-Leu）产生的游离亮氨酸较少，因此生成的亮氨酸衍生恶臭副产物较少。亮氨酰甘氨酸（Leu-Gly）生成游离甘氨酸，不是恶臭副产物的前体。因此，既没有形成异戊醛，也没有形成 N-氯异戊亚胺。值得注意的是，异戊腈可以直接通过 Leu-Gly 和 Leu-Leu-Leu 氯化过程中的β-消除反应形成，因此氯化后观察到异戊腈的高收率。短寡肽氯化过程中恶臭副产物的产率随 Cl/N 比（AA 中氯与氮的摩尔比）的增加而增加，在 Cl/N = 2.4 时达到最大值，除了甘氨酰亮氨酸（Gly-Leu）形成的异戊醛在 Cl/N = 1.6 时达到最大值。UV 和 UV/HO 预处理通过打破短寡肽的非肽键，降低后续氯化过程中恶臭副产物的形成。本研究有助于确定饮用水异味问题的原因，并开发控制这些问题的方法。
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