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Stability, Tautomerism and Acidity of Xanthine by the Density Functional Theory (DFT)

Assoma BA, Bede LA, N Guessan RB, Kone S, Bamba SE* and N Guessan TY (France)

 This work is a contribution of theoretical chemistry to the knowledge of xanthine's properties. Its aim first consists in checking the chemistry's results related to the exploitation of semi-empirical methods, it provides theoretical data on the acidity of xanthine tautomers. To do this, the DFT method with the B3LYP functional, associated with the 6-311+G (d, p) basis set was used. The aqueous phase was modeled with the polarizable continuum model (PCM). The results show that in the gas one, xanthine can exist as a mixture of two tautomers, in decreasing order of stability, it is X (1,3,7) and X (1,3,9). In the aqueous one, four are identified, in the same order, those are X (1,3,7), X (1,3,9), X (1,7,10) and X (1,9,10). This work establishes that the tautomer X (1,9,10) comes from the X (1,3,7) via the X(1,3,9) one. It demonstrates that the acidity of the most stable tautomer’s nitrogen X (1,3,7) decreases in the order 7>3>1 regardless of its physical state. It provides data to elucidate the mechanisms to understand biological activities of xanthine.