Full protonation and also metal cation affinity of adenine in gas andsolution phases; a theoretical study

Adenine is a purine nucleobase. Purine is a heterocyclic aromatic organic compound thatconsists of two heterocylic rings (pyrimidine and imidazole) fused togther [۱]. In this work, wereport a theoretical study on protonation and metal cation affinity (Na+, K+ , Mg۲+, Ca۲+, Fe۲+ andZn۲+) of adenine molecule at M۰۶-D۳ level of theory, with def۲-TZVPP basis set usingGAUSSIAN ۰۹ program. The possibility of the protonation of different nitrogen atoms of theabove molecule in both gas phase and aqueous solution was studied.The microprotonationconstants for all different nitrogen atoms of adenine in solution was also computed. The completeprotonation of this molecule was also investigated threough our previously known methodology[۲-۴] and the most stable isomers for adenineH+, adenineH۲۲+, adenineH۳۳+, and adenineH۴۴+ weredetermined in the gas phase. The possibility of the binding of adenine and its protonated form tometal ions through its different nitrogen atoms has been also studied (see Figure ۱).

Keywords:

Adenine , Proton affinity , Metal cation affinity , Gibbs free energy