Extended X-ray absorption fine structure study on reaction of anti-tumor platinum complexes with reduced glutathione

Reactions of cis-diamminedichloroplatinum(II) (cisplatin) and 1,1-cyclobutanedicarboxylatodiammineplatinum(II) (carboplatin) with reduced glutathione, a tripeptide that is abundant in cells, were studied by means of X-ray absorption spectroscopy. Back-scattering amplitudes F(i)(k) and phase shifts Phi(i)(k) were theoretically derived, and validated by applying them to calculate extended X-ray absorption fine structure (EXAFS) oscillations of cisplatin and K(2)[Pt(SCN)(4)] in the solid state. EXAFS oscillations of reaction mixtures of cisplatin or carboplatin with reduced glutathione were fitted to the standard EXAFS equation using the F(i)(k) and Phi(i)(k) functions to give the coordination numbers of N or O atoms (N(N/O)) and of Cl or S atoms (N(Cl/S)). For both cisplatin and carboplatin, the N(N/O) value decreased and the N(Cl/S) values increased monotonically as the reaction proceeded. However, the reaction rate for carboplatin was significantly slower than that for cisplatin.