Abstract:

The red cabbage leaves are found rich in anthocyanins which have antioxidant activity and can reduce the damage of free radicals on human tissues and improve the regeneration ability of tissues. In this work, the anthocyanin pigments were extracted from red cabbage by solvents. Based on the chemical structure, a combination of the pigment and hydroxylammonium salt was designed as a supramolecular probe by taking advantage of its protonation tautomerism to form pH-responsive chromism. The proton was released through the reaction between formaldehyde and hydroxylammonium salt, and the proton would combine with the anthocyanin which was converted from cyan-green quinone form into a purplish red pyrylium form, thus realizing the color-change function by reaction with formaldehyde. A smart gel was prepared by dissolving the supramolecular probe in agar. Scanning electron microscopy （SEM） was used to analyze the micromorphology of the smart gel. The surface of the smart hydrogel was porous （pore size was 100-300 μm）, and there were intercommunication channels inside the gel. These pore structures were conducive to the migration of color reaction substances. The formaldehyde concentration was then measured and calculated according to the method of CIE to define color difference based on CIELab color space.

Key words: purple cabbage, smart gel, formaldehyde, supramolecular probe