In this paper the reaction enthalpies of three antioxidant action mechanisms, HAT, SETPT,
and SPLET, for mono-substituted Stobadines were calculated in gas-phase and water. Results
show that electron-withdrawing substituents increase the bond dissociation enthalpy (BDE),
ionization potential (IP), and electron transfer enthalpy (ETE), while electron-donating ones
cause a rise in the proton dissociation enthalpy (PDE) and proton a±nity (PA). In comparison
to gas-phase, water attenuates the substituent e®ect on all reaction enthalpies. Results show
that IP and BDE values can be successfully correlated with the indolic NH bond length after
electron abstraction, R(NHþ), and the partial charge on the indolyl radical nitrogen atom,
q(N). Furthermore, calculated IP and PA values for mono-substituted Stobadines show linear
dependence on the energy of the highest occupied molecular orbital (EHOMO) of studied mol-
ecules in the two environments. SPLET represents the thermodynamically preferred mechanism
in water.
