What molecule am I?
Lawsone (2-hydroxy-1,4-naphthoquinone; aka hennotannic acid) is a dye found in the leaves of the henna plant (Lawsonia inermis). Solid lawsone is yellow; but when it or powdered henna leaves are dispersed in water or other aqueous materials to form a paste, it becomes a deep reddish-brown.
Henna has been used for thousands of years to dye skin and hair. A paste is prepared from powdered henna leaves, water, and often 鈥渟ticky鈥� materials such as sugar to make it stay on the skin. The paste must be stored for 2鈥�6 days to allow the lawsone to leach from the powder. After the paste is applied, it must stay on the skin for 4 h to overnight to create the dark color the individual wants. Then the paste is removed with a nonaqueous liquid鈥攏ot water, which interferes with stain development.
Lawsone has also been investigated for reasons other than henna use. In 1949, Harold E. Zaugg at Abbott Research Laboratories (then in North Chicago, IL) reported that the 1 produces an adduct that can be further cyclized to a ketal. Zaugg鈥檚 objective was to develop compounds for use in antimalarial studies; however, neither product was active to the malaria parasite Plasmodium lophurae.
Two much more recent studies had better outcomes for lawsone. In 2022, Alfonso T. Garc铆a-Sosa at the University of Tartu (Estonia); Anne Robert and Michel Baltas at Laboratoire de Chimie de Coordination du CNRS-UPR 8241 (Toulouse, France); and collaborators at these and other institutions described anti-infectious agents synthesized via the under microwave radiation. Many of the compounds exhibited moderate-to-good activity against the pathogens Plasmodium falciparum, Leishmania donovani, and Mycobacterium tuberculosis.
And last November, Patrick A. Ward at Savannah River National Laboratory (Aiken, SC), Joseph A. Teprovich, Jr., at California State University Northridge, and colleagues at both institutions reported that (LPDs) have excitation-independent emission with well-defined electronic transitions and a high quantum yield of 37%. The researchers also prepared a water-soluble LPD derivative and demonstrated its feasibility as a fluorescence microscopy dye to image breast cancer cells.
1. CAS Reg. No. 937-53-1; now called benzylideneacetone.
Lawsone聽hazard information*
| Hazard class** | GHS code and hazard statement | |
|---|---|---|
| Acute toxicity, oral, category 4 | H302鈥擧armful if swallowed |  |
| Skin corrosion/irritation, category 2 | H315鈥擟auses skin irritation | |
| Serious eye damage/eye irritation, category 2A | H319鈥擟auses serious eye irritation | |
| Specific target organ toxicity, single exposure, respiratory tract irritation, category 3 | H335鈥擬ay cause respiratory irritation | |
*Compilation of multiple safety data sheets.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. .
MOTW update
Methanol1 was the Molecule of the Week for March 11, 2013. The simplest alcohol, it is a widely used solvent, motor fuel, ethanol denaturant, and especially a feedstock for manufacturing other chemicals.
Methanol is toxic: During Prohibition, many people died from drinking methanol-laced liquor; and this type of poisoning is still widespread today. Recently, Douglas J. Lanska at the University of Wisconsin鈥揗adison and others reported that . The principal culprits are formaldehyde and formic acid, which are produced by the action of liver enzymes on methanol. These metabolites can cause eye and brain damage and metabolic acidosis.
1. CAS Reg. No. 503612-47-3.
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Lawsone聽fast facts
| CAS Reg. No. | 83-72-7 |
| SciFindern name | 1,4-Naphthalenedione, 2-hydroxy- |
| Empirical formula | C10H6O3 |
| Molar mass | 174.15 g/mol |
| Appearance | Yellow crystals or powder |
| Melting point | 195 掳C (dec.) |
| Water solubility | 1.8 g/L |
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