Fruits and flowers are colorful, quite unlike leaves that have shades of green. While green color comes from chlorophyll; shades of orange, yellow, and red come from carotenoids and betalains; purple, blue and yellow come from flavinoids. Together, these compounds that give rise to bright colors are a rich source of vitamins and anti-oxidants, that keep human body healthy and agile. Today carotenoids, flavinoids, betalains, chlorophyll and their derivatives are important dietary supplements.
Discovery of chemicals behind plant pigments
Chlorophyll was first plant pigment that was isolated and named so in 1817 by French pharmacists Joseph Bienaimé Caventou and Pierre Joseph Pelletier. The duo is however remembered more for their work on discovery of Quinine, which they had extracted from Cinchona plant.
Later in 1831, another German chemist Wilhelm Ferdinand Wackenroder had isolated a pigment carotene from carrots. While these substances were extracted, their structures were unknown. Further work on these plant pigments was made possible by Russian botanist Mikhail Tsvet who around 1901-03 a invented the technique called “chromatography”. He used a glass column packed with calcium carbonate to separate colorful plant pigments, and hence named the technique “chroma” for color and “graphein” for writing. Thus began writing of the colors.
Between 1906-14 a German chemist Richard Willstätter separated and purified chlorophyll. He also worked on carotenoids, and could classify these into two types – Carotenes and Xanthophylls. This work on plant pigments earned him 1915 Nobel Prize.
Born in 1872, Willstätter was a prominent German Scientist. In 1934 he announced his retirement as a gesture against increasing antisemitism. Himself a jew, he had to leave Germany in 1939, and he died in Switzerland in 1942.
How did we discover chemistry behind these colorful natural substances
This journey of discovery of chemistry behind carotenoids was completed by a Swiss chemist Paul Karrer. He discovered exact chemical structure of carotenoids in 1926 and it’s role as a precursor compound to Vitamin A. Till that time, role of vitamin A had just been discovered, without knowing that it comes from a plant pigment.
Born in 1889 to a dentist father, Paul started to study chemistry in 1908 at University of Zurich. He was initially trained under Alfred Warner in Zurich (who later got a Nobel Prize in chemistry in 1913), and later with Paul Ehrlich in Frankfurt (who had received a Nobel earlier in 1908). The two mentors, shaped his career. Ehrlich passed away in 1915, and Werner in 1918.
Paul Karrer was eventually appointed to Werner’s chair at a young age of 29, in university of Zurich. He started working on organic chemistry, and isolating various substances, including carbohydrates, amino-acids, tannins and lecithin.
In 1927, Karrer started working on substances that give color to plant products. By next year, he and his team isolated a family of substances or carotenoids. By 1930, it was clear that all these compounds had similar chemical structures. As he discovered the structure of beta-carotene, he could also isolate its derivative – Vitamin A. Karrer went on to discover structures of Riboflavin, and energy generating co-enzymes we know as NAD and NADP. Thus he was awarded a 1937 Nobel Prize for these discoveries, along with WN Howarth, who discovered the structure of Vitamin C.
What do these discoveries mean ?
Discovery of structures of these vitamins, allowed these to be artificially produced. Today we know of more about 500 carotenoids, and can artificially produce beta-carotene as well as vitamin A. Beta-carotene is a precursor of Vitamin A or retinol. This in turn metabolizes to Retinoic acid, which is important for vision, reproductive as well as skin health. Knowing these structures helps us know the pathways of how these molecules work in human bodies. Today retinoids are also a family of useful compounds, that have diverse medicinal uses.
So the molecules, that give plant its colors are not only important nutrients, but are also an important physiological substance in humans. These colors after-all have a lot of substance !!
