Electron affinity for the most toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD): A density functional theory study

The electron affinity (EA) of the most toxic dioxin, 2,3,7,8-tetrachlorinat ed dibenzo-p-dioxin (TCDD), has been obtained along with that of two other toxic TCDDs using density functional theory (DFT) for the first time. The v ertical electron affinity calculated for 1,2,3,4- TCDD at the B3LYP/aug'-cc -pVDZ level agrees with the recently obtained (J. Am. Chern. Sec. 1999, 121 , 2561) experimental electron energy, which produced a maximum anion intens ity in electron-capture negative-ion mass spectrometry. The adiabatic EAs o f 0.259 and 0.265 eV for 2,3,7,8-TCDD obtained using B3LYP and B3PW91 funct ionals, respectively, suggest that anionic TCDDs are stable with respect to the detachment of electrons and indicate that TCDDs act as electron accept ers in the reaction with receptors in living cells. Because of the large di fference in geometry between the neutral and the anionic 1,2,3,4-TCDD, the calculated adiabatic EA differs considerably from the vertical electron aff inity. Anionic 1,3,6,8- and 2,3,7,8-TCDD are planar like their neutral coun terparts; on the other hand, anionic 1,2,3,4-TCDD is nonplanar although its neutral counterpart is planar.