Monophotonic ionization of etoposide in aqueous solution by 248 nm laser light: identification of transient intermediates

Using 248 nm laser flash photolysis, it has been demonstrated that etoposid e (VP16, 4'-demethyl-epipodophyllotoxin ethylidene-beta-D-glucoside) in aqu eous solution is ionized via a monophotonic process giving a hydrated elect ron and neutral radical that results from rapid deprotonation of the radica l cation of etoposide. The quantum yield of photoionization is determined t o be 0.17 at room temperature with KI solution used as a reference. On the basis of comparison of the result with that obtained from pulse radiolysis, the reaction mechanism has been unambiguously identified. (C) 1999 Elsevie r Science S.A. All rights reserved.