Chemical Education Today
NCW 2001: Celebrating Chemistry and Art
Biology of the Blues: The Snails behind the Ancient Dyes
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by Carol E. Steinhart
The Snails There is a great deal of information about the ancient blue and purple dyes (1), but very little about the animals they came from. The dye precursors were obtained from marine snails of the family Muricidae. These snails were considered edible, and their shells were used for ornamental and ritual purposes and as construction material for roads (2). The species commonly harvested in the Mediterranean were Bolinus brandaris (Fig. 1A), Hexaplex trunculus (Fig. 1B), and Stramonita haemastoma (Fig. 1C). Many sources refer to them respectively as Murex brandaris, Murex trunculus, and Thais haemastoma. The source of the dye precursors is the hypobranchial gland. Lying in the mantle cavity, it has several roles. Its mucus-like secretion traps particles in the current of sea water that passes through the mantle, and the fanning action of hairlike structures transports the trapped particles to the exhalant region, where they are excreted, enabling the snail to feed in sand and sediment without becoming fouled with silt. The gland also secretes neurotoxic choline esters, which may have a role in the predatory behavior of the snails (2). The Chemistry The dye precursors are found in a clear fluid secreted by the hypobranchial gland. They are derivatives of indole and comprise a set of variations on the indoxylsulfuric acid theme: OSO2OK R N H
X
where X is H or Br, and R is H, SCH3, or SO2CH3. Different species contain different combinations of these. OSO2OK
OH tautomerization
purpurase
R
R N H
X
N H
X O
O R X
N H
H
H R N
Ox
X'
N R' H
X
O O H N
sunlight if R, R' ≠ H Ox
X
N H O
Scheme I
1444
X'
A
B
C
Figure 1. Shells of the snails from which dye precursors were obtained. A: Bolinus brandaris and B: Hexaplex trunculus, courtesy of Paul Monfils; C: Stramonita haemastoma, courtesy of G. Thomas Watters, Ohio State University.
The first reaction in dye production is enzymatic (Scheme I) and requires yet another constituent of the hypobranchial secretion, an aryl sulfatase called purpurase. Subsequent reactions are nonenzymatic (3). The ultimate color of the dye depends on whether X and X⬘ are H or Br. W
Supplemental Material
The full version of this article is available in this issue of JCE Online. Literature Cited 1. A number of articles have appeared in J. Chem. Educ. See Schatz, Paul. 2001, 78, 1442, and references therein. Two excellent bibliographies are Cooksey, C. Bibliography of Tyrian Purple; http://www.chriscooksey.demon.co.uk/tyrian/cjcbiblio.html (originally published in Dyes Hist. Archaeol. 1994, 12, 57–66). Anonymous. http://www.tekhelet.com/pdf/ta02.pdf. Both accessed Aug 2001. A comprehensive source of information is The Royal Purple and the Biblical Blue; Spanier, E., Ed.; Keter: Jerusalem, 1987. For information on dye production, see Cooksey, C. Tyrian Purple; http:// www.chriscooksey.demon.co.uk/tyrian/. Khalaf, S. G. Phoenician Industrial Art & Manufacturing; http:// phoenicia.org/industry.html. Both accessed Aug 2001. 2. Spanier, E.; Karmon, N. In The Royal Purple and the Biblical Blue; Spanier, E., Ed.; Keter: Jerusalem, 1987; pp 179–192. 3. Sterman, B. Tekhelet; http://www.tekhelet.com/pdf/st01.pdf (accessed Aug 2001). Baker, J. T. Endeavour 1974, 33 (118), 11–17. Fouquet, H.; Bielig, H. J. Angew. Chem., Int. Ed. Engl. 1971, 10, 816–817. Koren, Z. C. Isr. J. Chem. 1995, 35, 117–124. Clark, J. J. H.; Cooksey, C. J.; Daniels, M. A. M.; Withnall, R. Endeavour 1993, 17, 191–199. Benkendorff, K.; Bremner, J. B.; Davis, A. R. Molecules 2001, 6, 70–78; http://www.mdpi.org/molecules/papers/ 60100070.pdf (accessed Aug 2001).
Carol E. Steinhart is an Assistant Editor of the Journal of Chemical Education;
[email protected].
Journal of Chemical Education • Vol. 78 No. 11 November 2001 • JChemEd.chem.wisc.edu
