Subatomic Physics in Your Medicine Cabinet

Aspirin’s Form I has a structure that is more robust all-around, whereas Form II is strongest along one axis and weaker on others, making the second version less stable.

Scientists in Berlin have just cracked the case on a recently-raised question about one of the world’s most popular medicines: aspirin. By taking into account previously-overlooked forces, which only have significant effects at distances not much greater than the size of an atom, the team was able to explain why aspirin’s molecules favor one crystal structure over another. 

Speculation began in the early 2000s when calculations were published claiming that, although aspirin has a unique and well-known structure, known as Form I, there is a second possible arrangement which should occur just as often called Form II. This result caused some dismay in the scientific community, since the second form of the drug had never been observed.

Different versions of seemingly identical molecules have caused medical disasters in the past, when a subtle property of the morning sickness medication thalidomide caused nightmarish birth defects in the late 1950s. For a drug employed as widely and indiscriminately as aspirin, any unaccounted-for discrepancies might be a cause for serious concern.  Researchers were later able to create the predicted alternative crystal structure under special conditions, allaying medical concerns when it was found that Form II turns back into Form I when subjected to significant heat or pressure. However, the reason why the unusual, surprisingly brittle new arrangement isn’t as common as Form I remained a mystery until this year.

In the new research, this preference was found to be attributable  to subatomic forces that lose strength quickly with distance, which is why they had been ignored or overlooked by previous investigators; other recent research has shown these same forces to be responsible for the gecko’s miraculous clinging and climbing abilities.  Taking into account the behavior of charges within the molecule's constituent atoms, rather than treating them as purely neutral particles on the basis of equal proton and electron numbers, the team found significant differences in the predicted favorability of Forms I and II.

This tale brings to mind the (probably apocryphal) story of the physicist at a dinner party who calculates to everyone’s amazement that, according to the laws of aerodynamics, bumblebees shouldn’t be able to fly. Here, as in that story, the lesson appears to be that when discrepancies arise between mathematical predictions and the observed universe, it’s usually the math that needs revision.