Redox reactions of etoposide in aqueous solution - A pulse radiolysis and laser flash photolysis study

Time - resolved pulse radiolysis has been used to study the reactions of etoposide (VP 16) with N-3(.) , (SCN)2(. -), e(aq)(-) in aqueous solution. The absorption spectra of reaction products were investigated, and a series of rate constants were determined to be 2 . 7 x 10(9), 3 . 2 x 10(9), 2 . 5 x 10(8) dm(3) . mol (- 1) . s (- 1) for reactions of e(aq)(-) N-3(.) , (SCN)(2)(. -) with etoposide, respectively. Using laser flash photolysis techniques, it is demonstrated that VP16 in aqueous solution is ionized by 248 nm 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 SO4. - is 2 . 8 x 10(9) dm(3) . mol (- 1). s (- 1).