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Wednesday, February 28, 2007

Nobel Laureate: Walter Norman Haworth

The Nobel Prize inChemistry 1937.

"for his investigations on carbohydrates and vitamin C"

Sir Norman Haworth won the Nobel Prize in 1937 for his work on the three-dimensional structure of carbohydrates in general and the structure of vitamin C in particular. The presentation speech summarizes his contribution to carbohydrate chemistry.
What has Haworth then accomplished within this domain? The answer may be thus formulated that he has, above all, made clear the chemical structure of vitamin C.

The chemical structure of substances is expressed by the so-called chemical formulas. By chemical analysis the percentage of the different elements - in this case of carbon, hydrogen, and oxygen - which enter into a compound may be ascertained. Further, the weight of the atoms of the different elements, expressed for instance in relation to the atom of hydrogen, has long been known, the hydrogen atom being the lightest of all the elements. It is likewise possible to determine the weight of a particle, or molecule, of a compound, expressed in the same measure. It is hence possible to indicate how many atoms of the different elements are entering into one molecule of the compound. Thus, the gross formula of the compound is obtained. This formula, in the case of vitamin C, is quite simple, considering that it represents a vitamin, viz.: C6H8O6. This formula tells us that one molecule of vitamin C consists of 6 atoms of carbon, 8 of hydrogen, and 6 of oxygen. It also indicates that vitamin C may be conceived as having originated through the elimination of 4 atoms of hydrogen from one molecule of grape-sugar.

But it is possible to advance still further. By ingenious adjustment or speculation, reminding us somewhat of the play of a puzzle, only perhaps a little more intricate, a firm conception has been formed about the order in which the atoms combine. If we conceive an ultra-enlarged model of a molecule, taken at a certain moment - because the atoms are not at a standstill within the molecule - and place a white screen on the one side of the model, while the other is exposed to light, a shadow-figure, also called a projection, of the molecule is obtained on the screen, showing the position of the atoms in their relation to each other. A formula which is intended to reproduce this situation, under the assumption that the atoms were placed on the same plane, is called a structural formula. Such formulas have proved capable of explaining with a high degree of clarity the properties of the compound, and the puzzle thus may be considered as having been solved.

In reality it is, however, hardly correct to suppose that all the atoms within a molecule should be placed on the same plane; if that were the case, even the largest molecules would have the shape of a leaf of paper, which is less than probable. There remains then their dispersion in space, the so-called configuration, which also may be expressed by a formula.

Such a formula for vitamin C has been proposed by Haworth and Hirst, as well as by von Euler and has been subsequently proved to be correct by Haworth.
Haworth's acceptance speech from 1937 contains a number of structures that will be very familiar to biochemistry students. For example, he shows the strucures of α-D-glucopyranose and β-D-glucopyranose.

We recognize these structures today because of the way Haworth drew them to show the three-dimensional configuration. In fact, we now call these figures "Haworth projections" after the man who deciphered the configurations and conformations and developed a way of projecting them on a two-dimensional page.

The final strucure of ascorbic acid (vitamin C) is also presented in Haworth's Nobel Lecture. In this case he choose to show it as a "Fischer projection" rather than the Haworth projection that he is famous for. (See Monday's Molecule #15 for the Haworth projection of vitamin C.)

The relationship between a properly drawn Fischer projection and a Haworth projection is the bane of biochemistry students since it comes up on countless exams. It's probably safe to say that the failure to appreciate Haworth's 1937 Nobel Prize is responsible for lowering the average grade of biochemistry students all over the world by 3-5%.


Paul MacGregor said...

Hi Larry. I am th emoderator from the Bible skeptics conference. Could you please let your students know that I responded to their comments ? Thanks, Paul MacGregor

Steve LaBonne said...

Thanks for this post, Larry. I'm ashamed to confess that if I had thought beforehand about "Nobel Prize for ascorbic acid" I would only have come up with Szent-Gyorgi's name. It's always a good day when I can remove another tiny piece of my ignorance. ;)