Reduction of [PtCl6]2？ by L-ascorbic acid (H2ASc) in 0.1？M aqueous acid medium has been investigated spectrophotometrically under pseudo-first order condition at [PtCl6]2？ = 0.005–0.007？mol？dm？3, 0.05 ≤ [H2ASc]/mol？dm？3 ≤ 0.3, 298？K ≤ ≤ 308？K, [H+] = 0.14？mol？dm？3, ？mol？dm？3. The redox reaction follows the rate law: d[Pt(IV)]/dt = [H2ASc][Pt(IV)], where is the second-order rate constant and [H2ASc] is the total concentration of ascorbic acid. Electron transfer from [H2ASc] to Pt(IV) center leading to the release of two halide ions and formation of the reaction products, square planner Pt(II) halide complex, and dehydrated ascorbic acid is suggested. This redox reaction follows an outersphere mechanism as Pt(IV) complex is substituted inert. Activation parameters were calculated corresponding to rate of electron transfer reaction . Activation parameters favor the electron transfer reaction. 1. Introduction The redox reaction of L-ascorbic acid is of fundamental interest in chemistry, biochemistry, pharmacology, and several areas of medicine. It is used as a reducing agent with one or two electron reductants in chemical and biological systems [1–7]. Rate of reduction by ascorbic acid depends on nature of oxidant and pH of the medium. Different mechanisms have been proposed for the reaction between ascorbic acid and metal complexes [5–13]. In recent years there has been significant interest in the chemistry of square planar platinum (II) complex for remarkable anticancer properties [14–16]. Several thousand potentially biological active Pt(IV) complexes have been reported for anticancer properties [16]. We report here the interaction of ascorbic acid with Pt(IV)(aq). Ascorbic acid is a good biological reducing agent. Pt(IV)(aq) appeared attractive because these octahedral complexes are usually substitution inert and require reduction to Pt(II) species to act as potential anticancer drugs. The anticancer activity of Pt(IV) complexes is likely to be due to effective platinum (IV) transport into the cell followed by reduction to the more reactive platinum (II) compounds. The knowledge of the reactivity of Pt(IV) compounds towards the reduction by potential bioreductant like ascorbic acid may be important for understanding the mechanism of where antitumor activity as well as for designing new compounds with the least side effect. Chois et al. [17] reported that there is a correlation between the rate of the reduction and anticancer activity in a series of homologous Pt(IV) complex without going into the details of reaction mechanism. The present study was
References
[1]
E. Pelizzetti, E. Mentasti, E. Pramauro, and I. Ihaliz, Chemistry, vol. 15, p. 2829, 1976.
[2]
E. Pelizzetti, E. Mentasti, and E. Pramauro, “Outer-sphere oxidation of ascorbic acid,” Inorganic Chemistry, vol. 17, no. 5, pp. 1181–1186, 1978.
[3]
D. H. Macartiney and A. Mc Auley, Canadian Journal of Chemistry, vol. 59, p. 132, 1981.
[4]
Z. Amjad, J. C. Brodovitch, and A. McAuley, “Metal-ion oxidations in solution. Part XXI. Kinetics and mechanism of the reaction of ascorbic acid, hydroquinone, and catechol with 12-tungstocobaltoate (III),” Canadian Journal of Chemistry, vol. 55, no. 20, pp. 3581–3586, 1977.
[5]
K. Tsuleahara and Y. Yamamota, Bulletin of the Chemical Society of Japan, vol. 54, p. 2642, 1981.
[6]
N. H. Williams and J. K. Yamdell, “Outer-sphere electron-transfer reactions of ascorbate anions,” Australian Journal of Chemistry, vol. 35, no. 6, pp. 1133–1144, 1982.
[7]
M. Kimura and S. Yamab, Journal of the Chemical Society, Dalton Transactions, p. 423, 1982.
[8]
P. Martinez, J. Zuluaga, J. Kralt, and R. Van Eldik, “Kinetics and mechanism of the oxidation of L-ascorbic acid by trisoxalatocobaltate(III) in basic aqueous solution,” Inorganica Chimica Acta, vol. 146, no. 1, pp. 9–12, 1988.
[9]
D. Pinnell and R. B. Jordan, “Kinetics of reduction of cobalt(III)-ammine complexes by dithionite,” Inorganic Chemistry, vol. 18, no. 11, pp. 3191–3194, 1979.
[10]
S. Abey Okada, H. Horic, and S. Taniguchr, Journal of the Chemical Society, Perkin Transactions, vol. 7, p. 5, 1987.
[11]
D. H. Macartney and N. Sutin, Inorganica Chimica Acta, vol. 74, p. 221, 1983.
[12]
E. Pelizzetti and E. Mentasti, Journal of the Chemical Society, Dalton Transactions, p. 61, 1978.
[13]
M. M. Taqui khan and R. S. Sukla, Inorganica Chimica Acta, p. 149, 1989.
[14]
N. Farrel, R. Ugo, and B. R. James, Eds., Catalysis By Metal Complexes, vol. 11, Kluwer, Dordrecht, The Netherlands, 1989.
[15]
R. B. Weiss and M. C. Christian, “New cisplatin analogues in development: a review,” Drugs, vol. 46, no. 3, pp. 360–377, 1993.
[16]
M. C. Keage, M. J. Kelland, L. R. Neidles, and M. J. Warning, Eds., Molecular Aspects of Anticover Drug DNA Interactions, vol. 1, CRC Press, New York, NY, USA, 1993.
[17]
Chois, C. Filotto, M. Bisanzo, et al., “Reduction and anticancer activity of platinum(IV) complexes,” Inorganic Chemistry, vol. 37, pp. 2500–2504, 1988.
[18]
K. Moribe, W. Limwikrant, K. Higashi, and K. Yamamoto, “Drug Nanoparticle Formulation Using Ascorbic Acid Derivatives,” Journal of Drug Delivery, vol. 2011, Article ID 138929, pp. 1–9, 2011.
[19]
K. Lemma, A. Sargeson, and L. I. Elding, “Kinetics and mechanism for reduction of oral anticancer platinum(IV) dicarboxylate compounds by L-ascorbate ions,” Journal of the Chemical Society, Dalton Transactions, no. 7, pp. 1167–1172, 2000.
[20]
T. Shi, J. Berglund, and L. I. Elding, “Kinetics and mechanism for reduction of trans-dichlorotetracyanoplatinate(IV) by thioglycolic acid, l-cysteine, dl-penicillamine, and glutathione in aqueous solution,” Inorganic Chemistry, vol. 35, no. 12, pp. 3498–3503, 1996.
[21]
T. Shi, J. Berglund, and L. I. Elding, “Reduction of trans-dichloro- and trans-dibromo-tetracyano-platinate(IV) by L-methionine,” Journal of the Chemical Society, Dalton Transactions, no. 12, pp. 2073–2077, 1997.
[22]
K. Lemma, T. Shi, and L. I. Elding, “Kinetics and mechanism for reduction of the anticancer prodrug trans,trans,trans-[PtCl2(OH)2(c-C6H11NH2)(NH3)] (JM335) by thiols,” Inorganic Chemistry, vol. 39, no. 8, pp. 1728–1734, 2000.
[23]
L. Kelemu, D. A. House, N. Retta, and L. I. Eldirs, “Kinetics and mechanism for reduction of halo- and haloam(m)ine platinum(IV) complexes by L-ascorbate,” Inorganica Chimica Acta, vol. 331, pp. 98–108, 2002.
