Emil Hermann Fischer

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GERMAN CHEMIST
1852–1919

Emil Hermann Fischer, born October 9, 1852, in Euskirchen, Germany, received the Nobel Prize in chemistry in 1902 for his elucidations of the structure of sugars and the synthesis of purines. His father, a very successful lumber merchant, intended Emil to join the family business upon completion of his secondary school education. Young Fischer showed exceptional abilities as a student in the natural sciences, particularly in physics. In 1859 he dutifully entered his father's business, but showed little aptitude for commerce. In frustration his father enrolled him at the University of Bonn in 1871 to study chemistry, which at least had practical applications.

The following year he transferred to the University of Strasbourg, where he attended the lectures of Adolf von Baeyer. He gave up any remaining interest in physics for a career in organic chemistry. Fischer pursued graduate studies in chemistry under von Baeyer's mentorship, and was awarded a doctorate degree in 1874. In the course of his doctoral research he synthesized the compound phenylhydrazine, which would prove to be invaluable in his studies of carbohydrates (but would also, because of his prolonged exposure to it, leave him with cancer).

In 1875 Fischer followed von Baeyer to the University of Munich, and in 1881 he obtained his first academic post as professor of organic chemistry at the University of Erlangen. This was followed by his being called to the University of Würzburg in 1888, and finally, in 1892, to the University of Berlin, where he remained until his death in 1919. His son Hermann Otto (1888–1960) went on to have a distinguished career in biochemistry.

Fischer's most important scientific work was carried out between 1882 and 1906. Little was known about the naturally occurring sugars when Fischer began his investigations of them in 1884. Four sugars were known at that time: glucose , galactose , fructose, and sorbose, each having the formula C ₆ H ₁₂ O ₆ . It was known that each had a six-carbon chain, and five alcohol groups as well as a carbonyl ( aldehyde or ketone ) functional group attached to the chain.

Fischer saw in the sugars what no one else had seen. In 1874 Dutch chemist Jacobus van't Hoff had proposed that molecules in which a central carbon atom is bonded to four constituent atoms had a tetrahedral geometry in space, and that if a carbon atom were bonded to four different constituents, the molecule could exist in two forms (as stereoisomers) that were mirror images of one another. These two forms would possess distinct right- and left-handedness. Fischer realized that in glucose there were four carbon atoms that met the criteria for exhibiting stereoisomerism. A glucose molecule would exist as one of sixteen possible stereoisomers, each differing only by its orientation in space. Using the methods of chemical synthesis and degradation that were available to him, he was able by 1891 to identify the structures of all isomers of the naturally occurring D -glucose.

To enable representation of these isomers on the flat surface of a page, Fischer developed a notation system (Fischer projections). Fischer projections denoted right- and left-handed isomers. These were called D (dextrorotatory) and L (levorotatory), respectively, and the compound glyceraldehyde (which exists in two forms) was used as a reference.

With the Fischer projections, the constituents on the horizontal lines may be envisioned as coming out of the page, and the vertical constituents, as pointing backward, away from the onlooker. Fischer assumed the D isomer corresponded to the projection in which the OH group was to the right of the CH ₂ OH group. This assignment (which was a guess) was proven correct in 1954 when the orientations in space of the glyceraldehyde stereoisomers were established by x-ray analysis.

Fischer's identification of the stereoisomers of D -glucose (naturally occurring d-glucose was the sugar that Fischer worked with) was important validation of the ideas of van't Hoff.

In 1899 Fischer turned his attention to the study of proteins, wishing to understand their chemical structures. It was known at that time that proteins were composed of amino acids, and thirteen naturally occurring ones were identified. Fischer was able to isolate via the hydrolysis of proteins three additional naturally occurring amino acids: valine, proline, and hydroxyproline. Amino acids exhibit stereoisomerism, and Fischer was able to separate individual forms from mixtures of stereoisomers for several of these compounds.

Another Fischer achievement was the synthesis of small peptides via the condensation of amino acids. Fischer suggested that there was a common linkage that held pairs of amino acids together in all proteins—the peptide bond. He understood that proteins were tremendously complex, owing to the large number of constituents and the fact of stereoisomerism. By 1916 Fischer had synthesized and characterized 100 peptides, but knew they represented a tiny fraction of what was possible.

SEE ALSO Amino Acid ; Carbohydrates ; Isomerism ; VAN'T Hoff, Jacobus .

Martin D. Saltzman

Bibliography

Farber, Eduard (1972). "Emil Fischer." In Dictionary of Scientific Biography, Vol. 5. New York: Scribner.

Fruton, Joseph S. (1990). Contrasts in Scientific Style: Research Groups in the Chemical and Biochemical Sciences. Philadelphia: American Philosophical Society.

Lucier, J. J. (1993). "Emil Fischer." Nobel Laureates in Chemistry, 1901–1992, ed. Laylin K. James. Washington, DC: American Chemical Society; Chemical Heritage Foundation, pp. 8–14.