While preparing the treebark for the extraction of the Aesculin (see previous entry), I noticed that some lichen, growing on the bark, glowed yellow in ultraviolet light. Under normal light it has an orange color. Some research on Wikipedia revealed the lichen as Xanthoria parietina (Xanthus meaning “yellow” in greek, parietina “on walls”). The fluorescent dye contained in the upper layers of the lichen is Parietin.
I collected some of the lichen and tried several solvents (Isopropanol, Acetone and Ethanol) to extract the parietin. All solvents were heated to their respective boiling point to accelerate the process.
The color of the solution differs between the solvents under visible light as well as under ultraviolet light. The Isopropanol-solution is dark green and fluoresces orange while the Acetone- and Ethanol-solutions have a brighter green and glow yellow.
Due to this result I tested the influence of different solvents on the color of Aesculin. Here, the effect was not as distinct as with the parietin solutions, but the brightness of the fluorescence differed.
Solutions in the images from left to right:
- Aesculin in distilled Water
- Aesculin in 75% Isopropanol
- Aesculin in Acetone
- Aesculin in 96% Ethanol
- Parietin in Acetone with 33% Sodium Hydroxide
- Parietin in 75% Isopropanol
- Parietin in Acetone
- Parietin in 96% Ethanol
Interestingly, the effect of the NaOH also depends on the solvent. On the one hand, the color in visible light is either violet/pink (in case of Aceton) or it stays green (in case of Isopropanol). On the other hand, the response to ultraviolet light changes. The Isopropanol solution emits a bright magenta fluorescence when irradiated with 405nm light and a dim orange fluorescence with 350nm – 370nm.
The Acetone solution shows no fluorescence with 350nm – 370nm and almost none with 405nm.
To further concentrate and purify the Aesculin and the Parietin, the Isopropanol solutions are slowly evaporated to crystallize the dyes.
The previous attempt with water solutions failed, due to the many other substances that solved in the water and caused mold to grow.