Silva Gustavo Thalmer M, Silva Karen Magno, Silva Cassio P, Gonçalves Josué M, Quina Frank H
Instituto de Química, Universidade de São Paulo, Av. Lineu Prestes 748, Cidade Universitária, São Paulo 05508-000, Brazil.
Instituto Federal de Educação, Ciência e Tecnologia de São Paulo, Campus São Paulo, 01109-010 São Paulo, Brazil.
ACS Omega. 2020 Oct 5;5(41):26592-26600. doi: 10.1021/acsomega.0c03354. eCollection 2020 Oct 20.
Flavylium cations are synthetic analogues of anthocyanins, the natural plant pigments that are responsible for the majority of the red, blue, and purple colors of flowers, fruits, and leaves. Unlike anthocyanins, the properties and reactivity of flavylium cations can be manipulated by the nature and position of substituents on the flavylium cation chromophore. Currently, the most promising strategies for stabilizing the color of anthocyanins and flavylium cations appear to be to intercalate and/or adsorb them on solid surfaces and/or in confined spaces. We report here that hybrid pigments with improved thermal stability, fluorescence, and attractive colors are produced by the cation-exchange-mediated adsorption of flavylium cations (FL) on two synthetic clays, the mica-montmorillonite SYn-1, and the laponite SYnL-1. Compared to the FL/SYn-1 hybrid pigments, the FL/SYnL-1 pigments exhibited improved thermal stability as judged by color retention, better preferential adsorption of the cationic form of FL1 at neutral to mildly basic pH (pH 7-8), and lower susceptibility to color changes at pH 10. Although both clays adsorb the cationic form on their external surfaces, SYnL-1 gave more evidence of adsorption in the interlayer regions of the clay. This interlayer adsorption appears to be the contributing factor to the better properties of the FL/SYnL-1 hybrid pigments, pointing to this clay to be a promising inorganic matrix for the development of brightly colored, thermally more stable hybrid pigments based on cationic analogues of natural plant pigments.
黄酮阳离子是花青素的合成类似物，花青素是天然植物色素，是花朵、果实和叶子中大部分红色、蓝色和紫色的来源。与花青素不同，黄酮阳离子的性质和反应活性可以通过黄酮阳离子发色团上取代基的性质和位置来控制。目前，稳定花青素和黄酮阳离子颜色最有前景的策略似乎是将它们插入和/或吸附在固体表面和/或受限空间中。我们在此报告，通过黄酮阳离子（FL）在两种合成粘土（云母蒙脱石SYn-1和锂皂石SYnL-1）上的阳离子交换介导吸附，可产生具有改善的热稳定性、荧光和诱人颜色的混合颜料。与FL/SYn-1混合颜料相比，通过颜色保留判断，FL/SYnL-1颜料表现出更好的热稳定性，在中性至弱碱性pH（pH 7-8）下对FL1阳离子形式具有更好的优先吸附性，在pH 10时颜色变化的敏感性更低。尽管两种粘土都在其外表面吸附阳离子形式，但SYnL-1在粘土的层间区域有更多吸附证据。这种层间吸附似乎是FL/SYnL-1混合颜料具有更好性能的促成因素，表明这种粘土是开发基于天然植物色素阳离子类似物的颜色鲜艳、热稳定性更高的混合颜料的有前景的无机基质。
