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Carthamin Red Dye

November 29, 2021

Everyone has heard the mantra, "Dress for Success." This idea has been around for millennia. In the ancient world, the higher classes wore clothing dyed with Tyrian purple, also known as royal purple, and now known chemically as 6,6'-dibromoindigo (C16H8Br2N2O2). This dye was harvested as a secretion produced by sea snails in the family Muricidae. It was expensive, since many snails were required and the extraction involved much labor. So close was the relationship between this dye color and status, that eventually only the Roman emperor was permitted to wear Tyrian purple.

Tyrian Purple, 6,6'-dibromoindigo

Chemical structure of (C16H8Br2N2O2), known as Tyrian purple. The IUPAC name of this compound, usually called 6,6'-dibromoindigo, is an impressive 6-bromo-2-(6-bromo-3-hydroxy-1H-indol-2-yl)indol-3-one. The hexadecimal color code, as shown in the color patch, is 66023C. (Created using Inkscape. Click for larger image.)

The use of Tyrian purple is traced as early as 1,570 BC in Phoenicia. The Greek historian, Theopompus (Θεόπομπος, c.380 BC - c.315 BC) reported that Tyrian purple was worth its weight in silver. Aristotle (384 BC - 322 BC) described in his History of Animals the source of Tyrian purple and its process of extraction. Pliny the Elder (23 AD - 79 AD) described the production of Tyrian purple in Book IX of his Natural History. About 2,500 sea snails were need to produce just an ounce of the dye.

Before the advent of chemical synthesis, Nature was our only source of colorants. The following table lists some of the many natural sources of colorants.

Some of the many plants that can be used for dyes[1-2]

Dye Color Plant Common Name (Additional Colors)
Yellow Dyes Honey Locust
Indiangrass (brown, green)
Safflower (red)
Gardenia (red, blue)
Orange Dyes Bloodroot (brown, yellow)
Sassafras (black, green, purple, yellow)
Red Dyes Sumac (yellow, green, brown, black)
Slippery Elm (brown, green, yellow)
Grape (blue-violet)
Purple / Blue Dyes Red Mulberry (brown, yellow, green)
Summer Grape (orange, yellow, black)
Black Locust (black, green, yellow, brown)
Green Dyes Stinging nettle
Goldenrod (yellow, brown)
Gray Dyes Butternut (brown)
Brown Dyes Elderberry (yellow)
Black Dyes Sumac (yellow, red, green, brown)

The first synthetic dye, mauveine, was discovered accidentally by a very young William Henry Perkin (1838-1907) in 1856. Since it was an aniline derivative, it's also known as aniline purple. Interestingly, the chemical structure of mauveine was unknown until 1994.[3] Perkin made the discovery while assisting chemist, August Wilhelm von Hofmann (1818-1892), in research on synthetic quinine, but he made the discovery in his home laboratory independently of Hofmann. This is reminiscent of the home laboratory discovery of xerography by Chester Carlson (1906-1968).

William Henry Perkin (1838-1907) and mauveine color patches

William Henry Perkin (1838-1907) in 1906 is shown on the left, with a photograph of a patch of mauveine dyed silk that he made at the center, and a box on the right that's colored with the acknowledged #8D029B hexadecimal color code for mauveine. (Left image, a 1906 photo of William Henry Perkin from A History of Chemistry (1918) by F. J. Moore. Center image, a portion of a photograph by Henry Rzepa. The left and center images are from Wikimedia Commons. Click for larger image.)

The safflower, Carthamus tinctorius, produces a range of colorants from yellow to red, and it's cultivated mostly for its seeds that are used to make vegetable oil. Dried safflower flowers are a source for the orange-red dye, carthamin, also known as Natural Red 26. Safflower petals are yellow to orange in color until full bloom, and they change to a reddish color upon wilting.

Carthamin has been used worldwide for more than 4500 years and it's the major component of the Japanese textile dye called beni. In a recent study, a team of Japanese scientists from Tohoku University (Sendai, Miyagi, Japan), Toyo Ink SC Holdings Co. (Saitama, Japan), TOYOCHEM Co., Ltd (Tokyo, Japan), and the Tohoku Medical Megabank Organization (Sendai, Miyagi, Japan) has identified the genes coding for the enzyme responsible for the formation of carthamin from a compound known as precarthamin, a water-soluble quinochalcone.[4-5] An explanation was also developed that explains how the red pigmentation of safflower petals forms during flower senescence.[4]

Red-orange safflower and the chemical structure of the red dye, carthamin

(Red-orange safflower and the chemical structure of the red dye, carthamin. Left image via Wikimedia Commons. Right image, ©Toshiyuki Waki et al. Click for larger image.)

Although carthamin dye has been used for more that 4,000 years, it wasn't until the late 19th and early 20th centuries that scientists started to examine its chemical structure.[5] The present study identified the genes for an enzyme that's responsible for the final step of carthamin biosynthesis called "carthamin synthase."[5] Carthamin synthase is similar to peroxidase, an enzyme found in such plants as turnips and radishes. It uses molecular oxygen instead of the hydrogen peroxide of peroxidase as a hydrogen acceptor in its formation of carthamin.[5] Carthamin synthase transforms the safflower yellow to red.[5]

Says study co-author, Toru Nakayama, of Tohoku University,
"In the future, we may be able to produce this useful compound [carthamin] microbially in large amounts using metabolic engineering."[5]


  1. Native Plant Dyes, U.S. Forest Service of the United States Department of Agriculture.
  2. List of colorants derived from natural products, TOYOCHEM CO., LTD.
  3. Otto Meth-Cohn and Mandy Smith, "What did W. H. Perkin actually make when he oxidised aniline to obtain mauveine?" Journal of the Chemical Society, Perkin Transactions, vol. 1 (1994), pp. 5-7, doi:10.1039/P19940000005.
  4. Toshiyuki Waki, Miho Terashita, Naoki Fujita, Keishi Fukuda, Mikiya Kato, Takashi Negishi, Hiromi Uchida, Yuichi Aoki, Seiji Takahashi, and Toru Nakayama, "Identification of the Genes Coding for Carthamin Synthase, Peroxidase Homologs that Catalyze the Final Enzymatic Step of Red Pigmentation in Safflower (Carthamus tinctorius L.)," Plant and Cell Physiology, vol. 122 (August 26, 2021), https://doi.org/10.1093/pcp/pcab122.
  5. Researchers Identify the Biosynthesis of Carthamin, the Historic Red Colorant in Safflowers, Tohoku University Research News. September 2, 2021.

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