The structural, vibrational and electronic properties of nitrotyrosine and 8-nitroguanine have been investigated theoretically by performing the molecular mechanics (MM+ force field), the semi-empirical self-consistent-field molecular-orbital (PM3), and density functional theory calculations. The geometry of the nitrotyrosine and 8-nitroguanine molecules have been optimized, the vibrational dynamics and the electronic properties calculated in their ground states in the gas phase.