• Chemistry 25.04.2011 No Comments
    Molecular Structure of Parietin

    Molecular Structure of Parietin

    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.

    Aesculine & Parietin Solutions in visible Light

    Aesculine & Parietin Solutions in visible Light

    Aesculin & Parietin Solutions in ultraviolet Light

    Aesculin & Parietin Solutions in ultraviolet Light

    Solutions in the images from left to right:

    1. Aesculin in distilled Water
    2. Aesculin in 75% Isopropanol
    3. Aesculin in Acetone
    4. Aesculin in 96% Ethanol
    5. Parietin in Acetone with 33% Sodium Hydroxide
    6. Parietin in 75% Isopropanol
    7. Parietin in Acetone
    8. Parietin in 96% Ethanol
    Parietin in Isopropanol with NaOH

    Parietin in Isopropanol + NaOH (405nm)

    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 Р370nm.
    The Acetone solution shows no fluorescence with 350nm – 370nm and almost none with 405nm.

    Aesculin & Parietin Solution

    Aesculin & Parietin Solution

    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.

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  • Chemistry 29.03.2011 No Comments
    Molecular Structure of Aesculin

    Molecular Structure of Aesculin

    While searching for easily obtainable fluorescent dyes I stumbled upon the Wikipedia entry for Aesculin. This is a naturally occurring substance which exhibits a blue fluorescence under ultraviolet light (360 nm). Its main source are the bark and leaves of horse chestnut trees (Aesculus hippocastanum).

    To extract the Aesculin from the tree bark a larger piece of it was broken down into small chips and put in warm/hot water.
    Under normal light no change will be visible, but under ultraviolet light, the water will get blue almost instantaneously.

    Afterwards, the solution needs to be filtered several times.

    Filtered Aesculin Solution

    Filtered Aesculin Solution under UV Light

    The next step is to dry the solution until the Aesculin remains as a powder.
    Actually crystallisation from a boiling solution might produce a much higher yield, because the solubility in boiling water is 74g/l, as opposed to only 1.7g/l in cold water. The resulting sesquihydrate forms white needle crystals.

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