Time-resolved pulse radiolysis has been used to study the reactions of etoposide (VP16) with N~3^., (SCN)~2^.^-, e~a~q^- in aqueous solution. The absorption spectra of reaction products were investigated, and a series of rate constants were determined to be 2. 7×10^9, 3.2×10^9, 2.5×10^8dm^3.mol^-^1.s^-^1 for reactions of e~a~q^-, N~3^., (SCN)~2^.^- with etoposide, respectively. Using laser flash photolysis techniques, it is demonstrated that VP16 in aqueous solution is ionized by 248nm photon to give hydrated electron and neutral radical resulting from rapid deprotonation of radical cation of etoposide. The pK value of VP16 is found to be 10.6, and the rate constants for reaction of VP16 with SO~4^.6- is 2.8× 10^9dm^3.mol^- ^1.s^-^1.

Key words: OXIDATION REDUCTION REACTION, FREE RADICALS