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Anthocyanin is known as a safe coloring material although its poor stability often limits more extended use. In this study, we tried the enhancement of the photostability of the anthocyanin by the incorporation into the pore of HMS type mesoporous silica containing various metal ions. The anthocyanin was adsorbed on the HMS by pouring a highly concentrated anthocyanin solution to the dried HMS, urging the incorporation of the dye into the mesopore by a capillary condensation. Improved stability of the anthocyanin against visible irradiation was achieved by the adsorption onto the HMS containing Fe 3+ , although other metal ions in the HMS showed less effect on the stabilization. From the UV–vis spectroscopy, the Fe 3+ species effective for the stabilization of the anthocyanin was found to be the tetrahedral one highly dispersed in the silica framework. The decrease in the absorptivity of the anthocyanin on the Fe-HMS compared to other metal-containing HMS suggested that the Fe-HMS promoted the aggregate formation of the anthocyanin molecules. The highly dispersed Fe 3+ species had an ability to gather the anthocyanin molecule close to itself, resulting in tight incorporation of the dye inside the mesopore. The incorporation and aggregate formation of the anthocyanin was expected to contribute to the improvement of the stability against irradiation. [ABSTRACT FROM AUTHOR]

Naturally occurring dyes are expected as an environmentally- and eco-friendly colorant. The limitation of the usage by their low stability can partially be solved by the incorporation into inorganic host materials. However, the stability of the dye-inorganic host composites has still been insufficient. In this study, further stability enhancement of the dye composite is tried by adding several phenolic compounds as a radical scavenging stabilizer. The photostability and thermal stability of β-carotene incorporated in the organoclay interlayer is successfully improved especially when the stabilizer molecules can be efficiently intercalated together with the β-carotene. For rather slow rate of degradation, the phenolic compounds having hindered structure showed higher stabilization effect, whereas for the fast degradation, non-hindered phenols showed high efficiency. The difference in the effectiveness as a stabilizer can be explained both by the stability of the intermediate phenoxy radical species and by the steric hindrance. As a stabilizer of environmentally friendly dye composite materials, naturally occurring gallic acid and vanillic acid are the most preferrable compounds for the present composites. [Display omitted] • Effect of stabilizers on β-carotene stability in the clay interlayer was examined. • Several hindered phenol compounds were used as candidates for the stabilizers. • Photostability and thermal stability were both improved by the stabilizers. • Hydrophobicity and hindered structure were key properties for effective stabilizers. • Type of optimal stabilizer depended on the degradation rate of β-carotene. [ABSTRACT FROM AUTHOR]