The　influence　of　a　series　of　square　planar　metal　adducts　on　the　protonation　ability　of　adenine　has　been　investigated　using　ab　initio　calculation.　The　results　showed　that　the　protonation　ability　was　mainly　influenced　by　the　long-range　electrostatic　effect　in　gas　phase,　no　strong　influence　of　different　metals　has　been　detected　for　the　system　studied,　and　the　solvent　effect　calculations　showed　that　the　polar　solvent　could　efficiently　compensate　for　the　long-range　electrostatic　effect　dominant　in　gas　phase.　The　NBO　population　analysis　indicated　that　the　protonation　ability　was　mainly　affected　by　changes　of　the　electron　density　on　selected　atoms.