Karrer, Paul (1889-1971) was a Russian-born Swiss chemist acclaimed for his research on plant pigments and the chemical makeup of vitamins. He received the Nobel Prize in chemistry in 1937 for his investigation of carotenoids, flavins, and vitamins A and B2. He shared the prize with the British chemist Sir Walter Norman Haworth, who was then studying vitamin C and carbohydrates.

Karrer was born in Moscow, Russia, where his father was working as a dentist, but both his parents were Swiss, and the family returned to their homeland when Karrer was 3 years old. They first settled in Zurich and then moved to the northern canton of Aargau, where Karrer began his schooling. While he was in secondary school, Karrer became keenly interested in science. He entered the University of Zurich in 1908, where he studied chemistry with Nobel laureate chemist Alfred Werner. After completing his Ph.D. degree in 1911, Karrer remained at the university for another year to work as one of Werner's research assistants.

In 1912, Karrer published his first paper on organic arsenical compounds, which caught the attention of another acclaimed chemist, Paul Ehrlich of Germany. Karrer accepted Erlich's invitation to work as his assistant in Frankfurt-am-Main at the Georg Speyer Haus, a research institute, and stayed there until the outbreak of World War I (1914-1918), at which time he returned to Switzerland and served a tour of duty as a Swiss artillery officer. He then returned to the Georg Speyer Haus and spent the next three years continuing to study the chemical makeup of plant products.

In 1918, Karrer returned to the University of Zurich to take the position of associate professor of chemistry, again working with Werner. After Werner's death the next year, Karrer became a full professor and also director of the Chemical Institute there. He remained at the University of Zurich for the rest of his esteemed career, serving as a researcher and a highly competent teacher and administrator.

Karrer's early research involved the study of complex metal compounds and moved gradually into investigation of the molecules of proteins, peptides, and amino acids. By the late 1920's, his interest was focused on plant pigmentation, specifically the study of anthocyanins, the red and blue pigments found in flowers and berries, and later crocin, the yellow pigment found in flowers. These substances had been discovered in earlier research by others, but Karrer's contribution was to identify their chemical makeup. He also studied the structure of the carotenoids, the pigments that give yellow-to-orange vegetables such as sweet potatoes, squash, and carrots their hue.

The German chemist Richard Kuhn had already isolated beta-carotene and was attempting to determine its molecular structure, but Karrer actually succeeded in doing so first in 1930. After he discovered from this important research that vitamin A is synthesized in the body from carotene, he began to investigate the chemical makeup of vitamins themselves, and by 1931, he became the first to explain the chemical structure of a vitamin.

Karrer's demonstration that vitamin A was nearly identical to half of a carotene molecule, containing a regular, ringlike formation of hydrogen, oxygen, and carbon atoms, was especially significant because vitamins had previously been suspected to be colloids or some other unusual state of matter. This led to his study of other vitamins, particularly those in the B group. He was the first to successfully synthesize vitamins B, E, and others, and he became known as an authority on flavins.

After winning the Nobel Prize in chemistry in 1937, Karrer continued to make important contributions to the field of chemistry, including synthesizing all the carotenoids and conducting research on nicotinamide adenine dinucleotide (NAD), an enzyme involved in energy transmission within cells. Additionally, he made important discoveries about curare, a poisonous resin derived from trees in South America, which is used today in general anesthesia and in treatments for muscle spasms.

Karrer's long and fruitful career resulted in scores of awards, prizes, honorary degrees, and memberships in prestigious chemical and biochemical societies. He was also a prolific writer, having over 1,000 publications to his name. In 1955, he was president of the 14th International Congress on Pure and Applied Chemistry in Zurich.