Related compounds Formula C10H6O3 | Molar mass 174.15 g/mol Appearance Yellow solid | |
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Juglone, also called 5-hydroxy-1,4-naphthalenedione (IUPAC) is an organic compound with the molecular formula C10H6O3. In the food industry, juglone is also known as C.I. Natural Brown 7 and C.I. 75500. It is insoluble in benzene but soluble in dioxane, from which it crystallizes as yellow needles. It is an isomer of lawsone, which is the staining compound in the henna leaf.
Contents
Juglone occurs naturally in the leaves, roots, husks, fruit (the epicarp), and bark of plants in the Juglandaceae family, particularly the black walnut (Juglans nigra), and is toxic or growth-stunting to many types of plants. It is sometimes used as an herbicide, as a dye for cloth and inks, and as a coloring agent for foods and cosmetics.
History
The harmful effects of walnut trees on other plants have been observed for at least two millennia. The ancient civilizations of Greece and Rome used the walnut for its cytotoxic properties as did residents of the American South for easily gathering fish when they threw cut husks into the water with the fish. However, juglone was not isolated until the 1850s. Two men, A. Vogel Jr. and C. Reischauer, were able to isolate the compound from the walnut tree in 1851. The compound was known as nucin at that time. Juglone was then synthesized and characterized for the first time in 1887 by A. Bernthsen and A. Semper. It was not until 1928 the compound was identified and confirmed to be toxic to other plants by E.F. Davis.
The use of walnut tree has historically been used within the field of traditional medicine. In America during the early 1900s, doctors prescribed juglone for the treatment of various skin diseases.
Synthesis
Juglone is derived by oxidation of 1,5-dihydroxynaphthalene. It can be also be obtained by oxidations of 5,8-dihydroxy-1-tetralone with silver oxide (Ag2O), manganese dioxide (MnO2), or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).
Extraction
Juglone has been extracted from the husk of walnut fruit of which it contains 2-4% by fresh weight.
Biological effects
Juglone is an example of allelopathic compound, a substance that is produced by a plant to stunt the growth of another. Landscapers have long known that gardening underneath or near black walnut trees can be difficult. Juglone exerts its effect by inhibiting certain enzymes needed for metabolic function. A number of plants and trees are resistant to juglone including some species of maple (Acer), birch (Betula), and beech (Fagus).
It is highly toxic to many insect herbivores. Some of them, however, are capable of detoxification of juglone (and related naphthoquinones) to non-toxic 1,4,5-trihydroxynaphthalene. It has also shown anthelmintic (expelling parasitic worms) activity on mature and immature Hymenolepis nana in mice. Napthoquinonic compounds also exhibit antimicrobial activity.
Uses
Juglone is occasionally used as a herbicide. Traditionally, juglone has been used as a natural dye for clothing and fabrics, particularly wool, and as ink. Because of its tendency to create dark orange-brown stains, juglone has also found use as a coloring agent for foods and cosmetics, such as hair dyes.
Juglone is currently being studied for its anticancer properties. One of the potential pathways through which juglone achieves its anticancer properties is through the formation of the semiquinone radical; the semiquinone radical causes superoxide anion radicals to form which can lead to apoptosis when present in large concentrations. This conversion from juglone to semiquinone radical that causes the superoxide anion radical to form takes place in the mitochondria as well as the cytosol.
Spectral data
The spectral data for juglone confirms its bicyclic structure which contains a hydroxyl group as well as two carbonyl groups. The IR for juglone shows peaks at 3400 cm-1, 1662 cm-1, and 1641 cm-1 which are characteristic of the hydroxyl and carbonyl groups. The 13C NMR shows 10 peaks indicating the correct number of unique carbon atoms in the molecule as well as peaks at 160.6 ppm, 183.2 ppm, and 189.3 ppm for the carbon attached to the hydroxyl group and the two carbons part of the two carbonyl groups.