Red Alga Pigments Stand The Test Of Time

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.