Semiempirical Approach to the Fukui Function Analysis of Uric Acid under Different pH Conditions

Analytic Fukui functions calculated at a first-principles level are combined with experimental pK(a) values and the calculation of tautomerization energies to obtain the effective regioselectivity of uric acid toward electron-transfer reactions under different pH conditions. Second-order electron binding energies are also computed to determine which of the tautomers is more likely to participate in the electron transfer. A comparison of vertical and adiabatic proton detachment energies allows us to conclude that tautomerization is not mediating deprotonation and that two monoanionic species are of comparable relevance. The main difference between these monoanionic species is the ring that has been deprotonated. Both monoanionic species are produced from a single neutral tautomer and mainly produce a single dianionic tautomer. As a method for the analysis of systems affected by pH such as uric acid, we propose to plot condensed Fukui functions versus pH, allowing us to draw the effect of pH on the regioselectivity of electron transfer in a single image.

Automated summary

Analytic Fukui functions calculated at a first-principles level are used to study the regioselectivity of uric acid towards electron-transfer reactions under different pH conditions. Experimental pK(a) values and tautomerization energies are combined to obtain effective regioselectivity, while second-order electron binding energies are computed to determine the likelihood of tautomers participating in electron transfer. Comparisons of proton detachment energies suggest that tautomerization does not mediate deprotonation and two monoanionic species are equally relevant. A proposed method for analyzing pH-affected systems, such as uric acid, involves plotting condensed Fukui functions against pH to visualize the effect of pH on electron transfer regioselectivity.