Figure 9.

Final position for superoxide O₂^. π–π approaching to emodin at graphite separation, with associated DeltaG = −8.0 Kcal/mo.l. The d(O–O), 1.260 Å, has decreased from 1.373 Å, getting closer to that in an oxygen molecule (1.227 Å). The separation between the O–O species to the ring, 3.426 Å, is of the same order of graphite stacking distance, 3.35 Å. Marked differences in C–C bond distances in the quinone ring are due to the electron coming from superoxide. This demonstrates that the π–π approach is able to sequester superoxide.