Ab initio theoretical study of dipole-bound anions of molecular complexes. Water molecule inhibits or enhances electron affinity of N-methylaminoadenine

Ab initio calculations have been performed to determine the electron affinity of the water complex of N-methylaminoadenine (NMA). This complex has been chosen for this study because it can form three different isomeric structures with a water molecule hydrogen-bonded at three different NMA sites, and only two of these structures have sufficient dipole moments to form dipole-bound states with an excess electron. In the third structure, which according to the calculations should be the most stable form, the dipole moments of NMA and the water molecule oppose each other resulting in an almost null dipole moment of the complex, so the complex has no ability to form a stable dipole-bound anion. This determination offers an interesting possibility for an experimental investigation of whether the NMA.H₂O complex forms an stable anion. If such an anion is detected, it will mean that an electron attachment can increase the gas- phase concentration of the complex, which is thermodynamically less stable in its neutral form.