Study of the Reactions of Platinum Macrocyclic Complex Ions with Free Radicals Formed by Pulse Radiolysis of Aqueous Media

Abstract

The near-diffusion-controlled reactions of hydroxyl radical, hydrated electron, and hydrogen atom with platinum macrocyclic complex ions in aqueous media have been studied using pulse radiolysis in conjunction with UV-visible absorption and conductivity detection. The hydrated electron and hydrogen atom react with trans-[Pt(cyclam)(Cl)(2)](2+) where cyclam is 1,4,8,11-tetraazacyclotetradecane to yield platinum(III) transients that exhibit intense absorption peaks in the 280-300 nm region; however in the case of the H-atom, the reaction involves a competition between chloride abstraction and a minor process, suggested to be attack on the organic ligand. The platinum(III) products are kinetically labile toward loss of chloro ligands, but these reactions are reversible in the presence of added KCl. The reactions of hydroxyl radical with [Pt(cyclam)](2+) and with [Pt(tmc)](2+), where tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, lead to platinum(III) intermediates absorbing in the 250-300 nm region. Depending on the presence or absence of added KCl and on the pH, the platinum(III) cyclam systems can react to form a product(s) exhibiting absorption peaks near 330 and 455 nm, and this species is proposed to be a long-lived amidoplatinum(III) complex. In support of this proposal is the observation that the tmc system does not give rise to a similar visible-absorbing product. The interrelations of the cyclam-based transients through acid-base, chloro-substitution and water-elimination processes are discussed.

Radiosensitization of DNA by Cisplatin Adducts Results from an Increase in the Rate Constant for the Reaction with Hydrated Electrons and Formation of PtI

“…This may occur through exchange of the ligands with water upon reduction of Pt II to Pt I . Although this has been demonstrated for certain Pt complexes, the stability and propensity for ligand exchange of Pt I under our conditions is not known . Alternatively, Pt I complexes may undergo a redox reaction with the ligand thereby releasing G radicals.…”

“…Although this has been demonstrated for certain Pt complexes, the stability and propensity for ligand exchange of Pt I under our conditions is not known. 31 Alternatively, Pt I complexes may undergo a redox reaction with the ligand thereby releasing G radicals. The latter species may undergo further reactions with H 2 O or radicals in the reaction mixture.…”

Palladium(II) and Platinum(II) Complexes of a Tetraphosphamacrocycle. X-ray Crystal Structures of Phosphorus Analogs of a (Tetramethylcyclam)metal Complex1

“…1 is a phosphorus analog of a tetramethylcyclam (tmc 1 ) metal complex which is one of the typical N 4 macrocycle complexes whose structures and reactivities have been drawing considerable interest. − , Although the first preparation of the macrocycle metal complexes with a 1,4,8,11-tetraphosphacyclotetradecane ([14]aneP 4 ) 1 framework, 2 and 3 , was carried out by Stelzer and co-workers, these complexes have the hydroxyl groups on the alkyl chains . A 14-membered macrocycle complex 4 having no such hydroxyl group was prepared by the same group, but its chain system is an unsymmetrical C 3 PC 3 PC 2 PC 2 P type.…”

7 Radiation chemistry

“…The reactions of the OH Á radical lead to Pt III by oxidation of Pt II . 193 The mechanism of CO 2 and H reduction by Ni(cyclam) studied by pulse radiolysis involves Ni(cyclam)(CO 2 ) or Ni(cyclam)(H) 2 . 194 The redox chemistry of Cu I/II (TTCN) 2 is interesting because the change in oxidation state of the copper ion is accompanied by substantial geometric changes in the coordination sphere of the metal ion as well as one of the ligands.…”