Wednesday, August 29, 2007

Nobel Laureate: Paul Karrer


The Nobel Prize in Chemistry 1937.

"for his investigations on carotenoids, flavins and vitamins A and B2"

In 1937, Paul Karrer (1889-1971) shared the Nobel Prize in Chemistry with Walter Norman Haworth. Karrer won the award fro his pioneering work on the structure of carotene [Monday's Molecule #40] and vitamin A (retinol).

Professor W. Palmær, Chairman of the Nobel Committee for Chemistry of the Royal Swedish Academy of Sciences, delivered the presentation speech on on December 10, 1937. Only the part addressed to Karrer is quoted below.
The Royal Academy of Sciences has decided also to award to Professor Paul Karrer in Zurich one half of the Nobel Prize in Chemistry this year in recognition of his researches concerning carotenoids and flavins, and the vitamins A and B2.

Thus these two scientists have both worked on another common field of research, the vitamins. As I have already endeavoured to elucidate at some length the importance of making clear the chemical structure of the vitamins, taking vitamin C as an example, I may be somewhat brief regarding the brilliant discoveries made by Professor Karrer.

The carotenoids form a group of yellowish-red colouring matters, widely dispersed within the vegetable kingdom, which have obtained their name from the carrot in which they were first observed. The French name of the carrot is known to be carotte, while Karotte is one of the German names thereof. Carotenoids occur in various other red or yellow parts of vegetables, such as tomatoes, hips, turnips. The examination of these numerous substances was commenced by Karrer ten years ago, and he has succeeded in making clear their chemical structure. The mother substance is in itself a hydrocarbon of very complicated composition, i.e. a chemical compound consisting only of carbon and hydrogen. Its molecule consists of no less than 40 atoms of carbon and 56 of hydrogen. Other carotenoids also contain oxygen, as is the case, for instance, with astacene, which gives the red colour to boiled crayfish and to the "cardinal of the sea", the lobster. The colour of saffron and of paprica is likewise due to carotenoids.

The splendid research concerning the carotenoids, made by Karrer, received its coronation, when it led to the isolation, the production in a pure form and the determination of the chemical structure of vitamin A. This vitamin, which had been known to exist from its biological effects already since 1906 and the synthesis of which in a pure form had been tried in vain in many laboratories all over the world, was successfully isolated by Karrer in 1931 from cod-liver oil, and it was the first of the vitamins of which the chemical structure was clarified. It forms a growth factor, i.e. a substance necessary for the growth of the body. In 1929 von Euler found the same property existing in the carotine itself, and it has been proved since then that this is dependent on the circumstance that carotine, that is the dyestuff of the carrot, is a substance from which the animal body can in itself produce the vitamin A, which has a somewhat less complicated structure. It is also a medicine, as it prevents the serious disease of the eye called "dry eye" or xerophthalmia. Hence vitamin A has received the name of axerophthol.

Some words now regarding Karrer's researches on flavins and on vitamin B2, which were commenced in 1933. Flavins are natural substances of a light yellow colour which often glisten, or fluoresce to the green. One of them is vitamin B2, also called factoflavin, which was discovered by Warburg and Christian in the yellow respiratory ferment, and which has also been disentangled in regard to its chemical structure by Karrer. It constitutes likewise a growth factor, and Karrer's method of producing this compound has led to a technical production of the substance, which is of great biological importance. It contains, besides carbon, hydrogen and oxygen and also nitrogen.

Karrer has thus succeeded in elucidating completely the nature of two of the vitamins, hitherto considered as so mysterious, and one of them is now produced artificially. A characteristic of this scientist is his open eye to the great and important problems as well as to their kernels, and the independent way in which he attacks the problems and pursues his new departures with the aid of his own methods.

There remain many questions to be studied regarding the way in which the vitamins cooperate in such processes of life as cannot be started without their presence.

A vitamin does certainly not produce the effect alone, however. The lactoflavin, for instance, combines, with the aid of phosphoric acid, with an albuminous substance, and only in this way the yellow respiratory ferment is formed. Its molecule contains about 200 times as many atoms as that of the vitamin itself. The yellow ferment is reckoned as belonging to the catalyzers, i.e. substances capable to accelerate a chemical reaction without undergoing any change themselves. Their action may be compared to that of a lubricating oil on a rusty machine. In this case the oxidation of certain substances present in the body is taking place, thus a kind of combustion, although of course much slower than for instance the burning of wood in a stove. We may perhaps compare the very effect of the vitamin to that of a key. A heavy door may thus resist the strongest blows and knocks, but can easily be opened by the aid of a small key - always provided that the right key is found.

The discoveries, which have now engaged our attention, touch upon the domain of Physiology as well as that of Chemistry, a circumstance which has found its expression in that they have been awarded Nobel Prizes in Medicine as well as in Chemistry. Often it is just within the borderland between two sciences, where efforts have been frequently made to establish demarcatory lines (although mostly in vain), that the important discoveries are to be found. In such cases it is evidently of small avail, generally speaking, to try to decide, even with the aid of the greatest acuteness, to which field of science such discovery should be properly attributed. The principal thing is, however, that the discoveries are recognized, if such be their value, and the classification of the prize awarded is a question of minor importance. In the present case it may be said, nevertheless, that the discoveries which have been awarded a prize in Chemistry are on the whole more chemically accentuated in their character than those which have received the prize in Medicine. In all the cases, however, such discoveries may be said to have "conferred the greatest benefit on mankind" in accordance with the intentions expressed in the will of Alfred Nobel....

Professor Karrer. The Royal Swedish Academy of Sciences has decided to confer upon you and Professor Haworth this year's Nobel Prize in Chemistry. In this way the Academy wishes to express to you her recognition for your brilliant investigations on carotenoids and flavins, as well as on vitamins A and B2. As a result of your work, the structure of a vitamin has for the first time been clarified. The structure of a second vitamin has also been cleared up, thus enabling its technical preparation.

I convey to you the congratulations of the Academy and request you to receive the prize from the hands of his Majesty the King.

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