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The piperonal electron affinity was studied using pulse radiolysis technique. The electron transfer reaction process between piperonal and anthraquinone-2-sulfate was observed in the pH 7 phosphoric acid salt buffer. The transient absorption spectra of electron transfer reaction between piperonal and anthraquinone-2-sulfate were obtained, and the initial proof of the electron transfer between electron donor and acceptor was provided directly. The one-electron reduction potential of piperonal was determined to be -0.457 V.

The electron transfer reaction of triplet menadione (3MQ*) with polyguanylic acid (polyG) in CH3CN rich (97%) solution was investigated by 248 nm(KrF) laser flash photolysis. The transient absorption spectra and kinetics obtained from the interaction of 3MQ* with polyG demonstrated that the primary radical ion pair, radical cation of polyG and radical anion of menadione can be detected simultaneously. The results demonstrated that the reaction rate constant of 3MQ* with polyG is almost equal to that of 3MQ* with dGMP.

One-electron oxidation of N-4-desmethylwyosine (dYt), a derivative of rare tricyclic nucleoside wyosine with several oxidative radicals, has been studied by using pulse radiolysis. The transient spectra of the radicals dYt(.+) and dYt(-H)(.) and the pK(a) of the radical cation were measured. The rate constants of reactions of dYt with SO4.-, CO3.-, N-3(.) and (OH)-O-. radicals have been determined and related reaction mechanisms were discussed.

Time-resolved laser flash photolysis and pulse radiolysis have been used to study the chemical activity of podophyllotoxin(PPT) and etoposide(VP-16). The mechanism of photoionization of etoposide and podophyllotoxin has been confirmed and illustrated. It is demonstrated that VP-16 and PPT in aqueous solution can be photoionized at 248 nm to give hydrated electron and neutral radical resulting from rapid deprotonation of radical cation of VP-16 and PPT. The quantum yield for the photoionization of VP-16 and PPT with single-photo is 0.21 and 0.61, respectively. In addition, they can react with hydrated electron, hydrogen radical and hydroxyl radical. This will give chemists some advice on synthesizing new derivatives of podophyllotoxin in cancer treatment.

The electron transfer reaction between triplet anthraquinone-2-sulfonate and polyguanylic acid (5′) in CH3CN-H2O (97?3) has been investigated by 248 nm (KrF) laser flash photolysis. The transient absorption spectra and kinetics obtained from the interaction of triplet anthraquinone-2-sulfonate and poly[G] demonstrate that the primary ionic radical pair, radical ation of poly[G] and radical anion of anthraquinone-2-sulfonate have been detected simultaneously. The free energy changes in the process of the electron transfer were also calculated.

The antitumor mechanism of etoposide (VP-16) is investigated using pulse radiolysis technology. The oxidizing mechanism of VP-16 is studied by sodium persulfate, and the reaction rate constant is 4.04×109 L·mol−1·s −1. The electron-transfer between VP-16 and tyrosine is observed and the reaction rate constant is 1.1×108 L·mol −1·s −1.

By using time-resolved kinetic spectrophotometry and pulse radiolysis technique, the oxidation of Phe by SO4 - radical has been investigated both in aqueous and water/acetonitrile mixed solutions. The results reveal that attack of the oxidizing SO4 - radical on Phe leads directly to the formation of Phe cation radical 3 with a strong absorption peak at 310 nm, then it proceeds in three competitive reactions via either hydroxylation, deprotonation or decarboxylation, which were found to be strongly dependent upon the ionization state of the substitutes —COOH and —NH2 and the nature of the solvents. Decarboxylation takes place only when the carboxyl group is deprotonated. At high pH deprotonation of Phe cation radical 3 is much easier to occur than that in neutral or acid solutions. Moreover, with addition of acetonitrile, deprotonation is more predominant than hydroxylation, whereas in aqueous solutions hydroxylation is much easier to occur.

Actinomycin D (AMD) is an anticancer antibiotic that can bind selectively to both double-stranded and single-stranded DNA, and this binding greatly enhances DNA photosensitization. Using electron paramagnetic resonance (EPR) in combination with spin trapping techniques, a systematic study was carried out on the reactive oxygen species generated in the photosensitization process of AMD. It was found that 1O2 and $$O_2^{ - \cdot } $$ are important reactive intermediates either in solution or in DNA complexes, and the generation of these species is in competition. This finding suggests that the photodynamic action of AMD proceeds via two pathways: energy transfer (type I mechanism) and electron transfer (type II mechanism). 1O2 is the main product formed via energy transfer reaction in solution while electron transfer between the excited states of AMD and DNA becomes the predominant pathway in DNA complexes.