Department of Chemistry, Visva-Bharati University, Santiniketan, W.B., 731235, India.
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
Anal Bioanal Chem. 2019 Sep;411(23):6203-6212. doi: 10.1007/s00216-019-02012-9. Epub 2019 Jul 12.
Cysteine is a crucial amino acid, found in a huge amount in protein-rich foods. We focused our research to determine the amount of free cysteine consumed highly in foods such as pork, beef, poultry, eggs, dairy, red peppers, soybeans, broccoli, brussels sprouts, oats, and wheat germs. A newly designed carbazole-pyridine-based fluorescent probe (CPI) has been introduced for quantitative estimation of cysteine (Cys) with a "turn on" fluorescence in some popular processed food samples chosen from our daily diet. CPI shows both naked eye and UV-visible color changes upon interaction with cysteine. The binding approach between CPI and Cys at biological pH has been thoroughly explored by UV-visible and fluorescence spectroscopy. From Job's plot analysis, 1:1 stoichiometric reaction between CPI and Cys is observed with a detection limit of 3.8 μM. NMR, ESI mass spectrometry, and time-dependent density functional theory (TD-DFT) study enlightens the formation of more stable product CPI-Cys. The "turn on" response of the probe CPI occurs due to the interruption of intra-molecular charge transfer (ICT) process upon reacting with cysteine. Moreover, CPI is a very stable, cost-effective compound and exhibits excellent real-time selectivity towards Cys over all other comparative biorelevant analytes. Interestingly, our proposed method is much advantageous as it is able to estimate cysteine predominantly by screening out other comparative biocomponents found in different protein-rich foods.
半胱氨酸是一种重要的氨基酸，在富含蛋白质的食物中大量存在。我们的研究重点是确定在猪肉、牛肉、家禽、鸡蛋、奶制品、红辣椒、大豆、西兰花、抱子甘蓝、燕麦和小麦胚芽等高蛋白食物中摄入的游离半胱氨酸的含量。我们设计了一种基于咔唑-吡啶的新型荧光探针（CPI），用于定量估计胱氨酸（Cys），在一些选自我们日常饮食的常见加工食品样品中，该探针具有“开启”荧光。CPI 在与半胱氨酸相互作用时会发生肉眼和紫外-可见颜色变化。通过紫外-可见和荧光光谱法深入研究了 CPI 与 Cys 在生理 pH 值下的结合方式。从 Job 图分析可知，CPI 与 Cys 之间观察到 1:1 的化学计量反应，检测限为 3.8 μM。NMR、ESI 质谱和时间相关密度泛函理论（TD-DFT）研究阐明了更稳定的产物 CPI-Cys 的形成。探针 CPI 的“开启”响应是由于与半胱氨酸反应时中断了分子内电荷转移（ICT）过程。此外，CPI 是一种非常稳定、具有成本效益的化合物，对 Cys 具有出色的实时选择性，优于所有其他相关生物分析物。有趣的是，我们提出的方法具有很大的优势，因为它能够通过筛选不同高蛋白食物中发现的其他比较生物成分，主要估计半胱氨酸。
