Mahanty Susobhan, Rathinasamy Krishnan, Suresh Devarajan
School of Biotechnology, National Institute of Technology Calicut, Calicut, Kerala, India.
Department of Chemistry, School of Chemical and Biotechnology, SASTRA Deemed University, Tamil Nadu, 613 401, Thanjavur, India.
J Fluoresc. 2022 Jan;32(1):247-256. doi: 10.1007/s10895-021-02836-8. Epub 2021 Nov 3.
Purpurin (1,2,4-trihydroxy-9,10-anthraquinone) is a natural red dye obtained from the red madder plant that is widely used in food and dyeing industries. The present study investigated the characteristics of purpurin and its application as a pH-sensitive probe to detect the pH of solutions and intracellular pH of mammalian and bacterial cells. Purpurin exhibited high pH-sensitive behavior, low analytes interference, high stability with pKa of 4.6 and visible colorimetric change. H NMR and FTIR studies indicated protonation of phenolic hydroxyl group under acidic condition with hypsochromic shift in the absorption and fluorescence spectra relative to that of basic condition. Cell culture studies using HeLa cells revealed that purpurin is well tolerated by the cells and the fluorescent imaging result indicated excellent cell permeability with possible use of the dye to detect the pH fluctuations in living cells under various physiological conditions such as apoptosis. Microbiological studies indicated that the dye could be used for visualization of bacteria under acidic condition.
紫红素（1,2,4-三羟基-9,10-蒽醌）是一种从红色茜草植物中提取的天然红色染料，广泛应用于食品和印染行业。本研究考察了紫红素的特性及其作为pH敏感探针检测溶液pH值以及哺乳动物细胞和细菌细胞内pH值的应用。紫红素表现出高pH敏感行为、低分析物干扰、高稳定性，其pKa为4.6且有可见的比色变化。1H NMR和FTIR研究表明，在酸性条件下酚羟基发生质子化，相对于碱性条件，吸收光谱和荧光光谱发生蓝移。使用HeLa细胞进行的细胞培养研究表明，细胞对紫红素耐受性良好，荧光成像结果表明该染料具有出色的细胞通透性，有可能用于检测各种生理条件（如细胞凋亡）下活细胞内的pH波动。微生物学研究表明，该染料可用于在酸性条件下对细菌进行可视化。
