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Materials

Red Alga Pigments Stand The Test Of Time

Boron-containing organic pigments are responsible for the color of a fossilized Jurassic-period red alga

by Celia Henry Arnaud
November 1, 2010 | A version of this story appeared in Volume 88, Issue 44

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Credit: Proc. Natl. Acad. Sci. USA
A polished sample of S. jurassica from France containing pink fossilized pigments.
Credit: Proc. Natl. Acad. Sci. USA
A polished sample of S. jurassica from France containing pink fossilized pigments.

An unusual class of boron-containing organic pigments, dubbed borolithochromes, is responsible for the pink color of a fossilized Jurassic-period red alga, scientists propose (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1007973107). Because the pigments are found only in the algae and not in the surrounding limestone, it is assumed that they were produced by the algae and not by some later transformation in the rock. Klaus Wolkenstein and Heinz Falk of Johannes Kepler University, in Linz, Austria, and Jürgen H. Gross of the University of Heidelberg, in Germany, extracted the pigments from Solenopora jurassica specimens found in Great Britain and France. Mass spectrometric measurements revealed an isotope pattern indicative of a single boron atom in the borolithochromes, identified as C50H36O12B, C51H38O12B, and C52H40O12B. The pigments and their solvolysis products contain deuterium-exchangeable hydrogen atoms, signaling the presence of multiple hydroxyl groups, and UV-visible spectra reveal that the hydroxyl groups are phenolic. On the basis of these data, the researchers suggest that the borolithochromes are boric acid esters with aromatic ligands. The pigments are unlike any known in modern red algae, they note.

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