Richard Willstätter decoded the colours of flowers

Person: Richard Willstätter
Lived: 1872–1942
Field: Organic chemistry
From: German

The story

Richard Willstätter had already made his name with chlorophyll, the green pigment of leaves, when he turned to the reds, purples and blues of flowers and fruit. These pigments, now called anthocyanins, were even harder to study. He began the work in Zurich in winter, using dried cornflowers because they were available commercially. It turned out to be a poor choice: the dried flowers contained only about one per cent of pigment or less.

In 1912 Willstätter moved to Berlin to direct the new Kaiser Wilhelm Institute for Chemistry in Dahlem. There he took a gardener's approach to the problem. He planted fields of double cornflowers, asters, chrysanthemums, pansies and dahlias around the institute and his home, and he found that the fresh flowers contained far more pigment. Blue-black pansies yielded up to a third of their dry weight.

Between 1913 and 1916 he published eighteen papers on anthocyanins. He showed that the many shades of red and blue in flowers and fruits, including cornflowers, roses, poppies, cherries, cranberries, plums and elderberries, come mainly from three closely related compounds, cyanidin, pelargonidin and delphinidin, linked to sugar units. He also showed that the colour depends strongly on the acidity or alkalinity of the flower, so that the shade of a pigment shifts with conditions in the plant. These discoveries explained, for the first time, the chemistry behind much of the colour of the natural world.

The work was cut short by the First World War. In its first year most of his co-workers went into military service, and the flowers grown for the laboratory were sent to military hospitals instead. Willstätter was bitterly disappointed and could not bring himself to return to the subject after the war. In 1915 he was awarded the Nobel Prize in Chemistry for his research on plant pigments, especially chlorophyll, and his anthocyanin studies were part of the work it honoured.

His studies became the foundation on which the chemist Robert Robinson built further work on flower pigments. The names cyanidin, pelargonidin and delphinidin are still in everyday use, and anthocyanins are studied today in many foods, from red cabbage to grapes.

Why it matters

Anthocyanin chemistry now underpins work on natural food colourings, plant breeding for new flower colours and research into the health effects of colourful fruits and vegetables.

About Richard Willstätter

Nobel-winning chemist who unravelled chlorophyll and the colours of flowers, refused to convert, resigned his chair in protest at antisemitism and died a refugee in Switzerland.

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Richard Willstätter

1872–1942 · Organic chemistry

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