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HOME > PAST ISSUE > July-August 2007 > Article Detail

MARGINALIA

Legally Sweet

Conflict over the essences of sweeteners and olive oils brings chemistry into the courtroom

Roald Hoffmann

The Same and Not the Same

I've written a book by this title. In chemistry, small differences matter. The compound d-carvone smells like caraway or dill; its mirror image smells like spearmint. Chlorine gas, Cl2, is nasty stuff biologically; chloride ions are necessary in our bodies. HOH is water; HOCl is hypochlorous acid, whose sodium salt is common bleach; HOC2H5 is ethanol. The difference between pseudoephedrine, a decongestant, and methamphetamine, an addictive drug, consists of just two atoms—easily, all too easily, taken away from the decongestant molecule.

A chemical transformation leading to minor changes in chemical structure often, not always, results in a major change in chemical properties. And it really doesn't matter what the starting point of a synthesis is; the biological properties of a molecule are determined by the molecule itself—the atoms in it and the way they are bonded to one another, its flexibility and shape.

Supersweet%20guanidinoacetic%20acidsClick to Enlarge ImageNeither the exceeding sweetness of aspartame nor that of sucralose is related to the sweetness of sucrose; they are consequences of the arrangements of atoms in these molecules and how the molecules bind to the sweet-receptor proteins in our taste buds. Incidentally, these are hardly the most potent sweeteners. The world record is now held by members of an interesting chemical family, the guanidinoacetic acids. Some of these are 200,000 times as sweet as sucrose.

A seemingly different but related concern is worked out, sideways, on the Splenda Web site. Some people are upset by the proliferation of organic chlorine compounds in our environment—the insecticide DDT and industrial chlorofluorocarbons and PCBs are chief sources of worry. Sucralose is, of course, a chlorinated organic. Its manufacturer tries to deal with this concern preemptively in the Web FAQ section: "Chlorine is present naturally in many of the foods and beverages that we eat and drink every day ranging from lettuce, mushrooms and table salt." Quite true. Another argument that could have been made—that selective chlorination changes sucrose essentially, so that the properties of sucralose may not at all resemble those of sugar—would not fit in with Splenda's advertising.




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