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The first small-molecule X-ray structure of fucoxanthin, a long-standing crystallographic challenge
What is it about?
Fucoxanthin is the orange-brown pigment responsible for the colour of brown algae and diatoms. It is one of the most complex carotenoids in nature, containing an allene, an epoxide, a ketone, and a long polyene chain within a single molecule. Although its chemical connectivity has been known since the 1960s, no one had ever seen its isolated crystal structure. In 1979, a young G. M. Sheldrick attempted to do so. We grew extremely fragile diethyl ether solvate needles that lost solvent within minutes. We then mounted them under ether vapour at 100 K and determined the first small-molecule structure at SPring-8.
Why is it important?
This work demonstrates the ability of modern crystal growth and synchrotron methods to solve the problem of highly unstable, weakly diffracting crystals. Dedicated to the memory of Professor George M. Sheldrick (1942–2025), it turns his initial partial solution into a completed story and establishes a benchmark for the entire allenic xanthophyll family.