Kuhn, Richard

(b. Vienna-Döbling, Austria, 3 December 1900; d. Heidelberg, Germany, 31 July 1967)

chemistry.

Kuhn, the son of Richard Clemens and Angelika (Rodler) Kuhn, was taught by his mother until he entered the Döbling Gymnasium at the age of nine, where he remained for eight years until drafted into the army. Four days after his release on 18 November 1918, he entered the University of Vienna. After three semesters he proceeded to the University of Munich, where his experimental genius soon became evident. In 1922 he obtained his Ph.D. under Willstätter and not long afterward received his docentship; he became widely known as Willstätter’s greatest discovery.

In 1926 Kuhn moved to Zurich to become professor of chemistry at the Eidgenössische Technische Hochschule. In 1928 he married Daisy Hartmann; they had two sons and four daughters. In 1929 he was appointed director of the new Chemistry Institute of the Kaiser Wilhelm Institute for Medical Research at Heidelberg and professor at the university, where he remained for the rest of his life, notwithstanding later offers from Berlin, Munich, Vienna, and the United States.

In 1937 Kuhn became director of the entire Kaiser Wilhelm Institute for Medical Research, and in 1946–1948 helped to transform the Kaiser Wilhelm Society for Scientific Research into the Max Planck Society for the Advancement of Science. He was a charter member of the society’s senate and later served as vice-president under Otto Hahn and then Adolf Butenandt. His scientific papers numbered over 700, his students and collaborators over 150, and his distinctions over fifty, including the 1939 Nobel Prize in chemistry.

Kuhn demonstrated his major scientific traits—discipline and precision coupled with imagination and fantasy—in both his 1922 doctoral thesis, “Zur Spezifität von Enzymen imKohlenhydratstoff wechsel” (“On the Specificity of Enzymes in Carbohydrate Metabolism”), and 1925 Habilitation thesis, “Der Wirkungsmechanismus der Amylasen; ein Beitrag zum Konfigurations—Problem der Stärke” (“Mechanism of Action of Amylases”). They dealt with greatly improved enzyme adsorption and elution carrier materials and kinetic enzyme measurements applied to a variety of sugar derivatives (glycosides, oligosaccharides, and polysaccharides). Specificity problems led him inevitably to problems in optical stereochemistry that preoccupied him for the rest of his life. He began research on additions on ethylene bonds; thus, addition of hypochlorous acid to fumaric or maleic acid resulted in chloromalic acid and also in ring closure to form ethylene oxide dicarboxylic acid. This work led in Zurich to studies on inhabited rotation among diphenyls, especially ortho-substituted derivatives. Kuhn showed that benzidine was stretched out on a plane, with the two NH₂—groups about 10 Å apart, instead of angled back and only about 1.5 Å apart. Kuhn, like Pasteur, had early dominating experiences with different forms of isomerism, and, like van’t Hoff, had a remarkable understanding of stereoisomerism.

With further studies on the activation energies of rotation among ortho-substituted diphenyls, Kuhn and his collaborators arrived at quantitative concepts of the spatial needs of particular groups, including the concept of “atropisomerism,” long before the terms “conformation” and “constellation” gained acceptance and applicability not only to substituted compounds but also to totally unsubstituted ones as in trans-cycloocten.

Proceeding to the preparation of diphenylpolyenes containing conjugated double bonds (—CH=CH—)_n added in unbroken order, Kuhn and his collaborators showed that the diphenyls were colorless when n = 1 or 2, but colored for n = 3 to 15. They thereby definitely established the existence of colored hydrocarbons. Research on crocetin, bixin, and most important, carotene (in crystallizable ?, ? and ? forms) demonstrated that Kuhn-type polyenes are found in nature. Work on carotene proved that symmetrical provitamin A yields two molecules of water. Among the synthetic polyenes, it was found that the position of the longest wavelength maximum

.? = K“; n^1/2 K”

helped to determine the structures of natural carotenoids.

Kuhn next attacked water-soluble vitamins. He showed vitamin B₂. isolated and crystallized from milk and named lactoflavin, to be part of Warburg’s yellow enzyme’ and he synthesized and structurally identified the vitamin. He prepared lactoflavin identified the vitamin. He prepared lactoflavin phosphate and, after combining it with the protein carrier of the yellow enzyme, he found it to be enzymatic ally identical with the reversible yellow oxidation enzyme (yellow flavin ? colorless leukoflavin), and that identifiable intermediate stages displayed free radical paramagnet ism and dimerism. Kuhn then identified vitamin B₆ (adermin, phridoxine), p-aminobenzoic acid, and pantothenic acid and synthesized numerous analogues and reversibly competitive inhibitors (“antivitamins”). It was for the his work on carotenids and vitamins that Kuhn was awarded the Noble prize.

From the 1950’s on Kuhn worked on and identified various “resistance” factors effective against infection—nitrogenous oligosaccharides isolated from human milk; brain gangliosides; and potato alkaloidglycoside (demission), active against larvae of potato beetles. Of especial interest was the finding that lactaminyl (sialic acid) oligosaccharides could be split by influneza virus and also by the receptor-destroying enzyme (RDE) of cholera vibrio (?-ketosidas action). Lactaminyl oligosaccharide was recognized as a receptor for influenze virs; therefore the virusinhibiting action of human milk (compared with bovine, which does not contain lactaminyl oligosaccharide) was explained: cells that do not form lactaminyl-oligosaccharide structures on their surfaces show resistance to influenza virus. Some twenty-five papers on the isolation and synthesis of amino-sugar saplit products of N-oligosaccharides followed.

Like Pasteur of France and Virtanen of Finland, Kuhn of Germany and Austria developed over the years intens interest in applications of his academic researches to medicine and agriculture. At the end of World War II Kuhn demostrated experimentally to a U.S, Army colonel’s wife that the she could trun green plants into red plants by adding triphenyltetrazolium chloride to the nutrient medium and so the institute was spared molestation.

BIBLIOGRAPHY

The complete scientific works of Kuhn have not yet been published; the most complete review is in the 63-page supp. to the Mitteilungen aus der Max-Planck-Gesellschaft zur Foerderung der Wissenschaften (1968), which the lists over 100 references to the most important works of Kuhn and his collaborators.

Dean Burk