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Kinetics and mechanism for reduction of halo- and haloam(m)ine platinum(IV) complexes by L-ascorbate

In English

Författare

Summary, in English

Reduction of the model platinum(IV) complexes cis-[PtCl4(NH3)(2)] (1), trans-[PtCl4(NH3)(2)] (2). trans-[PtCl2(en)(2)](2+) (3), trans-[PtBr2(NH3)(4)](2+) (4), [PtCl6](2-) (5), and [PtBr6](2-) (6) with L-ascorbic acid (H(2)Asc) in 1.0 M aqueous medium at 25 degreesC in the region 1.75 less than or equal to pH less than or equal to 7.20 has been investigated using stopped-flow spectrophotometry. The redox reactions follow the rate law: -d[Pt(IV]/dt = k[H(2)Asc](tot)[Pt(IV)] where k is a pH-dependent second-order rate constant and [H(2)Asc](tot), the total concentration of ascorbic acid. The pH-dependence of k is attributed to parallel reduction of Pt(IV) by the protolytic species HAsc(-) and Asc(2-). Analysis of the kinetics data reveals that the ascorbate anion Asc(2-) is up to seven orders of magnitude more reactive than HAsc(-) while H(2)Asc is unreactive. Electron transfer from HAsc(-)/Asc(2-) to the Pt(IV)) compounds is suggested to take place by a mechanism involving a reductive attack on any one of the mutually trans-halide ligands by Asc(2-) and/or HAsc(-) forming a halide-bridged activated complex, The rapid reduction of these complexes supports the assumption that ascorbate Asc(2-) might be an important reductant at physiological conditions for anticancer active Pt(IV) pro-drugs capable of undergoing reductive trans elimination. The parameters DeltaH(not equal) and DeltaS(not equal) for reduction of Pt(IV) with Asc(2) hake been determined from the study of the temperature dependence of k. (C) 2002 Elsevier Science B.V. All rights reserved.

Publiceringsår

2002-03-28

Språk

Engelska

Sidor

98-108

Publikation/Tidskrift/Serie

Inorganica Chimica Acta

Volym

331

Dokumenttyp

Artikel i tidskrift

Förlag

Elsevier

Ämne

  • Inorganic Chemistry

Nyckelord

  • L-ascorbic acid
  • Reduction
  • Kinetics
  • Platinum(IV) complexes
  • Reaction mechanism

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 0020-1693