Although used for more than a century to treat gastric discomfort, Pepto-Bismol remained a relatively unknown product. Indeed, the structure of bismuth subsalicylate – the active ingredient in Pepto-Bismol – has only recently been rigorously documented.
A structure unknown for 120 years
Since the commercialization of Pepto-Bismol in the early 1900s to the delight of fragile stomachs, the molecular structure of its active ingredient resisted analysis by scientists. According a statement of April 13, 2022, a team from the University of Stockholm (Sweden) succeeded in lifting the mystery surrounding the structure of this ingredient known as bismuth subsalicylate, or bismuth subsalicylate. The researchers achieved these results using advanced electron microscopy techniques.
Although he did not participate in the study, Alexandre Gagnon, professor of chemistry at the University of Quebec in Montreal (UQAM), was questioned on the subject by the magazine Quebec Science on September 6, 2022. According to the subject, the structure of bismuth subsalicylate has been the subject of speculations in chemistry books till today. The expert asserted that since bismuth subsalicylate is not soluble, traditional methods do not work for the analysis of its structure.
Let us mention in particular the X-ray crystallography, the most common method for determining the structure of molecules. This technique requires crystals of good quality and in large quantities, which is not possible with bismuth subsalicylate. Indeed, the ingredient tends to form very small crystals.
The use of two advanced techniques
The Swedish researchers then resorted to two advanced techniques : electron beam diffraction and scanning transmission electron microscopy. The first technique therefore used an electron beam instead of X-rays, which made it possible to study crystals of smaller size and of lower quality. Thus, the scientists were able to deduce the structure of the molecule by observing the interaction of electrons with crystals.
Next, scanning transmission electron microscopy generated an image showing the stacking of molecules. The researchers then discovered that bismuth subsalicylate has a multilayered structure, with variations in stacking sequence molecules. The ingredient has a nice polymeric structure, which explains why it is insoluble.
So following 120 years of marketing Pepto-Bismol, the drug is finally better understood. However, if this research will not change anything regarding its consumption, it may perhaps one day make it possible to develop a more effective drug.
