To Dye For

I enjoyed “The New Naturals” (C&EN, Feb. 10, page 10). But no story about the search for nonsynthetic colors, preservatives, and flavors would be complete without some mention of the colorful history of dyes, among them the legendary red (cochineal) dye that was once one of the world’s most precious commodities.

Interested readers can learn more about this centuries-long tale of “greed and subterfuge” from the wonderful book “A Perfect Red” by Amy Butler Greenfield. Enjoy!

David W. Pratt
Vergennes, Vt.

In “The New Naturals” the phycocyanobilin configurational stereochemistry is written as 4(E),10(E),15(E) instead of the correct all-Z. It is an understandable mistake, because the stereochemistry is incorrectly drawn in many popular and early scientific sources. However, phycocyanobilin’s biological precursor is natural (all-Z) biliverdin, and phycocyanobilin has the same stereochemistry, which turns out to be important in its role as a photosensory pigment. Light activation involves a change from Z to E at one of the stereocenters, which induces a conformational change in the protein to which it is bound.

David A. Lightner
Reno, Nev.