PNNL

Abstract

We demonstrated that the 3.12 kcal/mol instability of the zwitterion form of neutral arginine in the gas phase relative to the canonical tautomer could be suppressed by attaching an excess electron. This solvation by an excess electron provides and extra stabilization of 7.3 kcal/mol for the zwitterion structure and only 3.7 kcal/mol for the canonical structure. Hence, the anions based on the zwitterionic and canonical structures become quasidegenerate with their electronic energies, determined at the CCSD level of theory and corrected for zero-point vibrational energies determined at the B3LYP level, differing by less than 0.4 kcal/mol. Higher-order treatment of electron correlation effects and more complete one electron basis sets may be required to identify the global minimum for the anion. Moreover, thermal effects will contribute significantly to the stability of different anionic tautomers and rotamers. The effect of electron attachment/detachment on tautomerization reactions is currently investigated.