Proton Transfer —

The meanderings of the proton may appear a long way from standard understanding of nutrition but my belief is that Nutrition is a science based in Chemistry, Physiology and Biochemistry. It is important to retain an sense of basic sciences so as not to be overwhelmed by spurious claims.

Proton transfer is central to the chemistry of acids and bases in solution, enzyme activity, and transport mechanisms in biological membranes and photosystems. Our understanding of how protons are transferred between acids and bases in aqueous solution came from studies in the 1950s and 1960s. Now Mohammed et al add more detail. They have shown more of the myriad, sometimes indirect, molecular pathways between acid and base that a proton can follow.

An acid is a substance that donates protons; a base is a substance that accepts them. Mohammed et al, used laser excitation to ‘trigger’ the movement of a proton from the light-sensitive acidic molecule pyranine. This acid can be written ROH, where R is an organic group and OH a hydroxyl group. As a proton is simply a hydrogen atom stripped of its electron, its progress can be tracked by identifying, through spectroscopv, where the ‘H’ appears in the chemical products of the subsequent reactions.

Using spectroscopy the authors could follow the movement of the proton after leaving ROH, leaving behind the base RO~, and travelling to the negatively charged base molecule, BH. Protonation to form BH is incomplete even after 700 picoseconds — more than 1,000 times longer than it takes for ROH to be deprotonated. The proton appears to make intermediate stops at water molecules. Evidently, ROH is losing protons through more complicated, time-consuming pathways than just the simple confinement of the proton in a loose complex. It seems that the proton is not transferred directly to the base R in the loose complex, but follows an indirect route to its final destination, shuttling stepwise over one or more additional water molecules in its quest for the base. This process is termed a solvent switch. A meandering proton passing through assorted pathways.

You may ask what has all this to do with anything related to nutrition, who knows but|I find it interesting and it will encroach on us some day.

James T. Hynes Nature 446, March 2007, pp 270-273

And Mohammed O Angew Chem Int Edn 46, 1458-1461 , 2007