Kinetic and Mechanistic Study on the Reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ with l-Cysteine and S-Methyl-l-cysteine

Biljana V. Petrović; Živadin D. Bugarčić

doi:10.1071/CH05033

RESEARCH ARTICLE

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Kinetic and Mechanistic Study on the Reactions of [Pd(dien)H₂O]²⁺ and [Pt(dien)H₂O]²⁺ with l-Cysteine and S-Methyl-l-cysteine

Biljana V. Petrović ^A and Živadin D. Bugarčić ^A ^B

+ Author Affiliations

- Author Affiliations

^A Department of Chemistry, Faculty of Science, University of Kragujevac, 34000 Kragujevac, Serbia.

^B Corresponding author. Email: bugi@kg.ac.yu

Australian Journal of Chemistry 58(7) 544-550 https://doi.org/10.1071/CH05033
Submitted: 21 January 2005 Accepted: 10 May 2005 Published: 21 July 2005

Abstract

The reactions of [Pd(dien)H₂O]²⁺ and [Pt(dien)H₂O]²⁺ (dien = diethylenetriamine or 1,5-diamino-3-azapentane) with l-cysteine and S-methyl-l-cysteine were studied in an aqueous 0.10 M NaClO₄ solution using stopped-flow and conventional UV-vis spectrophotometry. The second-order rate constants for the reactions of [Pd(dien)H₂O]²⁺ at pH 1.0 are k₁²⁹⁸ = (9.11 ± 0.11) × 10² M⁻¹ s⁻¹ for l-cysteine, and k₁²⁹⁸ = (33.79 ± 0.63) × 10² M⁻¹ s⁻¹ for S-methyl-l-cysteine. The second-order rate constants for the reactions of [Pt(dien)H₂O]²⁺ at pH 1.0 with l-cysteine is k₁²⁹⁸ = (1.28 ± 0.08) × 10⁻² M⁻¹ s⁻¹ and for S-methyl-l-cysteine is k₁²⁹⁸ = (3.87 ± 0.02) × 10⁻² M⁻¹ s⁻¹. Activation parameters were determined for all reactions, and the negative values of entropy of activation support an associative complex formation mechanism. Substitution reactions were also studied at pH 0.5, 1.0, and 1.5. The rate constants increase with increase in pH. These results are discussed in terms of protolitic equilibrium.

Acknowledgment

The authors thank the Ministry of Science and Technology, Republic of Serbia, for financial support (Project No. 1254).

References

Kinetic and Mechanistic Study on the Reactions of [Pd(dien)H2O]2+ and [Pt(dien)H2O]2+ with l-Cysteine and S-Methyl-l-cysteine

Abstract

Acknowledgment

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Kinetic and Mechanistic Study on the Reactions of [Pd(dien)H₂O]²⁺ and [Pt(dien)H₂O]²⁺ with l-Cysteine and S-Methyl-l-cysteine