• Chemistry 30.04.2011 No Comments
    Molecular Structure of Umbelliferone

    Molecular Structure of Umbelliferone

    And once again the quest for easily synthesizable fluorescent dyes was successful: Umbelliferone. (Notice the similarity of the molecule to Aesculine. It is just missing the glycosidically bound glucose.)This substance is a naturally occurring dye of the courmarin family, but it can also be manufactured by a simple reaction. Only two reactants are needed, Resorcinol and Malic Acid. Sulfuric Acid is added as a hygroscopic catalyst to produce Formylacetic Acid from the Malic Acid in situ.

    The empirical reaction equation is as follows:

    C4H6O5 + C6H6O2 ————> CO + 3 H2O + C9H6O3

    Resorcinol has a molar mass of  110.10 g/mol, Malic Acid 134.09 g/mol.
    This equates to a 1:0.82 weight ratio.
    I used 1 gram of Malic Acid and 0.82 gram of Resorcinol and added a few drops of Sulfuric Acid. The whole mixture was heated with hot air until both educts were solved in the acid and bubbling started.
    After a short while, the solution began to change color to a dark orange. Upon further heating, the color got darker until it was deep red and had the viscosity of honey.

    Umbelliferon in Water

    Umbelliferon in Water

    A drop of the cooled product was added to a 600ml beaker of cold water and observed under ultraviolet light. Instantly, a bright green plume descending from the surface was visible, changing color to a bright blue while getting more diluted.

    Umbelliferon in Water

    Umbelliferon in Water

    A small concentration in water fluoresces blue under UV light and green in sunlight. In ethanol the concentration shows no influence on the color, as it is always a bright yellowish green.

    Umbelliferon in Ethanol

    Umbelliferon in Ethanol

    EDIT: On a second thought, the green color might come from fluorescein that was formed by a side reaction during synthesis of the umbelliferone. I will try to record absorption and emission spectra to figure out which substances are present.

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  • 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 – 370nm.
    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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