Lawsone (2-hydroxy-1,4-naphthoquinone), also known as hennotannic acid, is a red-orange

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...

present in the leaves of the

henna Henna is a dye prepared from the plant ''Lawsonia inermis'', also known as the henna tree, the mignonette tree, and the Egyptian privet, the sole species of the genus ''Lawsonia''. ''Henna'' can also refer to the temporary body art resulting fr ...

plant (''

Lawsonia inermis ''Lawsonia inermis'', also known as hina, the henna tree, the mignonette tree, and the Egyptian privet, is a flowering plant and one of the only two species of the genus ''Lawsonia'', with the other being '' Lawsonia odorata''. The species is n ...

''), for which it is named, as well as in the flower of

water hyacinth ''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.Eichhornia crassipes ''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive species, invasive outside its native range ...

''). Humans have used henna extracts containing lawsone as hair and skin

dyes A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

for more than 5,000 years. Lawsone reacts chemically with the protein

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

in skin and hair via

Michael addition In organic chemistry, the Michael reaction or Michael addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a carbon ...

, resulting in a strong permanent stain that lasts until the skin or hair is shed. The darker colored ink is due to more lawsone-keratin interactions occurring, which evidently break down as the concentration of lawsone decreases and the tattoo fades. Lawsone strongly absorbs

UV light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

, and aqueous extracts can be effective

sunless tanning Sunless tanning, also known as UV filled tanning, self tanning, spray tanning (when applied topically), or fake tanning, refers to the effect of a suntan without exposure to the Sun. Sunless tanning involves the use of oral agents (carotenids) ...

and

sunscreen Sunscreen, also known as sunblock or sun cream, is a photoprotective topical product for the skin that mainly absorbs, or to a much lesser extent reflects, some of the sun's ultraviolet (UV) radiation and thus helps protect against sunburn and ...

s. Lawsone is a 1,4-naphthoquinone derivative. Lawsone isolation from ''Lawsonia Inermis'' can be difficult due to its easily biodegradable nature. Isolation involves four steps: # extraction with an extraction solution, usually NaOH # column filtration using a macroporous adsorption resin # a rinse with ethanol to remove impurities, and finally # freeze the product to isolate the lawsone powder, usually a yellow colored dust. During the rinse, the lawsone will be the bottom as it has such a high density and the chlorophyll molecules will all be on the top of the mixture. Lawsone is hypothesized to undergo a reaction similar to Strecker synthesis in reactions with amino acids.Jelly, R.; Lewis, S. W.;Lennard, C.; Lim, K. F.; Almog, J. Lawsone: a novel reagent for the detection of latent fingermarks on paper surfaces. Chem.Commun. 2008, 3513-3515 Recent research has been conducted on lawsone's potential applications in the forensic science field. Since lawsone shows many similarities with

ninhydrin Ninhydrin (2,2-dihydroxyindane-1,3-dione) is an organic compound with the formula C6H4(CO)2C(OH)2. It is used to detect ammonia and amines. Upon reaction with these amines, ninhydrin gets converted into deep blue or purple derivatives, which are ...

, the current reagent for latent fingerprint development, studies have been conducted to see if lawsone can be used in this field. As of now the research is inconclusive, but optimistic. Lawsone non-specifically targets primary amino acids, and displays photoluminescence with forensic light sources. It has a characteristic purple/brown coloration as opposed to the purple/blue associated with ninhydrin. Lawsone shows promise as a reagent for fingerprint detection because of its photoluminescence maximized at 640 nm, which is high enough that it avoids background interference common for ninhydrin.

Related compounds

The naphthoquinones

lawsone methyl ether Lawsone (2-hydroxy-1,4-naphthoquinone), also known as hennotannic acid, is a red-orange dye present in the leaves of the henna plant (''Lawsonia inermis''), for which it is named, as well as in the flower of water hyacinth (''Eichhornia crassipes ...

and methylene-3,3'-bilawsone are some of the active compounds in ''

Impatiens balsamina ''Impatiens balsamina'', commonly known as balsam, garden balsam, rose balsam, touch-me-not or spotted snapweed, is a species of plant native to India and Myanmar. It is an annual plant growing to 20–75 cm tall, with a thick, but soft ste ...

'' leaves.

Juglone 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 i ...

is a structural isomer used as a brown dye.

References

{{Reflist Natural dyes 1,4-Naphthoquinones Hydroxyarenes