Photochemical Degradation of Curcumin: a Mechanism for Aqueous Based Sensing of Fluoride

Abstract

The present work describes the enhanced photochemical degradation of natural dye Curcumin in acetonitrile-water mixture in the presence of fluoride upon irradiation with light. The strong basicity of fluoride modifies the solvent environment around Curcumin molecule leading to alkaline mediated degradation of Curcumin which is further accelerated by irradiation with light. The photochemical degradation of Curcumin is studied using absorption and fluorescence spectroscopy and verified using infrared spectroscopy and fluorescence lifetime studies. The results of the work indicate that the method of Curcumin irradiation can be used as a sensing technique for fluoride detection in a wide range.

Colorful Curry: The Color Changes and Application of Curcumin

“…比较敏感，可发生光解反应而褪色 [4,5] 。 姜黄素易于从植物中提取，且具有丰富的光化学性质 [6] 。因此，本文以姜黄素为实验原料，通过 优化文献方法，由浅入深地设计了一系列不同层次的科普实验，具有如下优点： ( 为进一步探究pH对姜黄素显色的影响，我们采用醋酸-碳酸钠体系调节姜黄素溶液的pH (6.0-11.0)，如图6a所示，随pH增大，姜黄素溶液颜色呈现明显变化。在pH 6.0-7.0范围内溶液呈亮黄色； 在pH 8.0时，溶液变为橙红色，与文献报道吻合 [1] 。这是因为在碱性条件下，烯醇式上的氢会先于酚 羟基上的氢解离，发生电子云偏离，从而引起颜色变化。随着溶液碱性的进一步增强(pH 11.0)，姜 黄素羟基上的质子完全脱去，其溶液变为橙红色。在紫外-可见吸收光谱中(图6b)，随溶液pH的升高 其最大吸收波长逐渐增大，从424 nm增大至461 nm，这是由于姜黄素中酚羟基发生解离，氧负离子 增强整个分子的共轭效应，使其紫外-可见吸收峰红移。 图6 (a) 姜黄素溶液随pH发生颜色变化；(b) 姜黄素溶液在不同pH时的紫外-可见吸收光谱…”