1129294-89-8Relevant academic research and scientific papers
Platinum complexes of vitamin C: Reaction chemistry of carbon-bound cis-[(diamine)(ascorbato-C2,O5)platinum] chelates
Hollis, L. Steven,Stern, Eric W.
, p. 2826 - 2831 (2008/10/08)
The reaction between a series of cis-[Pt(RNH2)2(ascorbato-C2,O5)] chelates, where (RNH2)2 is ethylenediamine (en), [1,2-15N]en, (15NH3)2, trans-(R,R)-, trans-(S,S)- or cis-(R,S)-diaminocyclohexane (dach), and various acids (HX = HNO3, HCl, CH3SO3H) were studied in an attempt to prepare monodentate ascorbate complexes of the form cis-[Pt(RNH2)2(ascorbato-C2)(L)]+/0 (1a), where L is an anionic or neutral ligand such as Cl-, ascorbate-O3, or S-Me2SO. 195Pt and 13C NMR studies of the reaction of the 15N-labeled ascorbate chelate [Pt(15en)(C2,O5-Asc)] (1) with aqueous acids show that, in the absence of a nucleophile, the protonated chelate [Pt(15en)(C2,O5-HAsc)]+ (2) is favored over the ring-opened complex [Pt(15en)(C2-HAsc)(H2O)]+ (3). Protonation occurs at the O5 site of the ascorbate ligand, and the pKa of the resulting complex is ～2.0 in water. While the protonated chelate 2 can be isolated from nonaqueous solvents, the complex decomposes to ascorbic acid and [Pt(15en)(H2O)2]2+ in aqueous solution. The ring-opened complex 3 was observed as an intermediate in the hydrolysis reaction of the protonated chelate 2. Similar behavior is observed with the dach and cis-diammine analogues. When the ascorbate chelates are protonated in the presence of a nucleophile in aprotic solvents, ring-opened complexes of the form 1a are obtained. In the two cases where these complexes were isolated (L = Cl- or S-Me2SO), both compounds were unstable in aqueous solutions; the chloro complex undergoes ring closure, re-forming the C2,O5 chelate, and the Me2SO complex isomerizes to the oxygen-bound ascorbate complex cis-[Pt(diamine)(O3-HAsc)(S-Me2SO)]+. Ring-opened complexes of form 1a, containing weak donors such as NO3-, SO42-, CH3CO2-, and O3-HAsc-, are also unstable when prepared from the C2,O5 chelate. In general, the monodentate C2-bound ascorbate complexes prefer the ring-closed structure when platinum is bound to the re face of the ascorbate ligand.
Outer-Sphere Electron-Transfer Reactions of Ascorbate Anions
Williams, Nicola H.,Yandell, John K.
, p. 1133 - 1144 (2007/10/02)
Rate constants for the one-electron oxidation of ascorbate dianion (A2-) by bis(terpyridine)cobalt(III) ion (8.5*106 dm3 mol-1 s-1) and pentaammine(pyridine)ruthenium(III) ion (6.0*109 dm3 mol-1 s-1), and of the monoanion (HA-) by tetraammine(bipyridine)ruthenium(III) ion (2.1*105 dm3 mol-1 s-1) have been determined in aqueous solution at 25 deg C and ionic strength 0.1 (NaNO3 or NaClO4).It is shown that these rate constants, and other published rate constants for oxidation of HA- and A2-, are consistent with the Marcus cross relation, on the assumption that the self-exchange rate constants for both the HA-/HA. and A2-/A-. couples are 106 dm3 mol-1 s-1.One-electron redox potentials for the ascorbate/dehydroascorbate system have been derived from scattered literature data.
