A team at HZB has developed a novel method of experimentally unraveling tautomeric mixtures. Based on resonant inelastic X-ray scattering (RIXS) at BESSY II, the proportions of the tautomers can be deduced selectively. This technique may provide detailed information about molecules'' biological functions and the prototypical keto-enol equilibrium.
Several (organic) molecules are formed as a mixture of two almost identical molecules, with the same molecular formula but one significant difference: A single hydrogen atom sits in a different position. Many amino acids are tautomeric mixtures, and since they are forming blocks of proteins, they may influence their appearance and function as well as their biological functions in organisms.
Until now: Mission impossible
Bisher, it has been impossible to selectively investigate the electronic structure of such tautomeric mixtures experimentally: Classical spectroscopic methods see only the sum of the signals of each molecular form, and the details of the two distinct molecules cannot be determined.
Now at BESSY II: it works
Using an inelastic X-ray scattering (RIXS) and a data processing/evaluation method at HZB, the individual proportions of the tautomers can be clearly deduced from the measured data. Dr. Vinicius Vaz Da Cruz, the first author of the paper and postdoc, has now provided a method of experimentally dissolving tautomeric mixtures.
"We measure a pure spectrum of each tautomer, utilizing the element specificity and site selectivity of the method," Vaz Da Cruz explains. This allowed them to fully characterize the components in the tautomer mixture.
New insights into biological processes
In this study, the technique was applied to the prototypical keto-enol equilibrium of 3-hydroxypyridine in an aqueous solution. The data was obtained at the EDAX terminal station at BESSY II.
These results provide evidence for concepts that have previously only been discussed elsewhere in the literature. These are particularly useful to enlighten and understand important biological processes such as the interaction between nucleoid bases of the DNA, the metabolic conversion of fructose into glucose, or the folding of proteins.