Abstract: M06/6­31＋＋G** method was applied to investigate the proton transfer mechanism of [Mg2＋•Ala]．Eight optimized stable configurations are obtained.The most stable configuration I is amphoteric and the rest seven are neutral.The eight stable configurations converts via seven transition states.Mg2＋ coordinates to alanine with bis­dentate and mono­dentate coordination modes.The most stable amphoteric configuration I and neutral configuration II adopt bis­dentate mode with binding energies of －687.0 and －656.6 kJ•mol－1，respectively.In addition，the rotation of intramolecular single bond leads to the neutral configuration conversion，in which the rotation energy barriers of C—C single bonds are lower than 16.0 kJ•mol－1，and those of C—O single bonds are lower than 60.0 kJ•mol－1.On the other hand，the proton transfers among the carboxylic oxygen atoms can also result in the neutral configuration conversion，whose energy barriers of forward/back reaction are 194.9 and 105.6 kJ•mol－1，respectively.In detail，the proton transfers from carboxylic group to amino lead to their configuration conversion from neutral to amphoteric，in which the energy barrier is 0.2 kJ•mol－1.The binding energies of all stable structures seem high(larger than 492.1 kJ•mol－1)，which are much higher than those in the configuration conversions.So，the configuration conversion is thermodynamic control rather than dynamic control.after the Mg2＋ interacts with alanine，the positive charge on Mg2＋ decreases larger than 0.14，suggesting that the electronic cloud tends to the Mg center，and the dipole moments of all the systems increase by over 6.0 Debye.The reaction pathway from the most stable neutral structure to the most stable zwitterionic structure is Ⅱ→Ⅱ－Ⅲ→Ⅲ→Ⅲ－Ⅶ→Ⅶ→Ⅵ－Ⅶ→Ⅵ→Ⅵ－Ⅷ→Ⅷ→Ⅴ－Ⅷ→Ⅴ→Ⅰ－Ⅴ→Ⅰ，and the highest energy barrier of this reaction pathway is 139.9 kJ•mol－1.