Impact of Micelle Media on the Kinetics of Oxidation of l-Lysine (An Essential Amino Acid) by N-Bromophthalimide

Abstract

The effect of cationic surfactant cetyltrimethylammonium bromide (CTAB) on the oxidation of L-lysine by N-bromophthalimide (NBP) has been studied at 308 K. The reaction exhibits first order dependence on NBP and L-lysine and negative and fractional order dependence on HClO₄. The effects of KCl, KBr, phthalimide, mercuric acetate, and dielectric constant of the medium have also been studied and summarized. CTAB strongly catalyzes the reaction and typical k _obs and CTAB profile was observed, that is, with a progressive increase in CTAB, the reaction rate increased and after achieving a peak k _obs decreased at higher concentrations of CTAB. The results are treated quantitatively in terms of ‘Menger-Portnoy’ and ‘Piszkiewicz’ models. The various activation parameters in presence and absence of CTAB have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed. The rate constant in micellar phase k _M, cooperativity index (n) and binding constant have been computed.

Keywords:

• L-lysine
• micellar kinetics
• n-bromophthalimide
• oxidation

Acknowledgments

N. Goyal thanks the Department of Science and Technology, New Delhi for granting her the Woman Scientist fellowship and the research project grant (SR/WOS-A/CS-63/2009).

Notes

Experimental conditions: 55% (v/v) acetic acid, [NBP] = 1.0 × 10⁻⁴ mol dm⁻³, [L-lysine] = 1.0 × 10⁻³ mol dm⁻³, [Hg⁺⁺] = 2.0 × 10⁻⁴ mol dm⁻³, [CTAB] = 1.0 × 10⁻⁴ mol dm⁻³, [H⁺] = 2.0 × 10⁻² mol dm⁻³.

Experimental conditions T = 308 K, 55% (v/v) acetic acid, [NBP] = 1.0 × 10⁻⁴ mol dm⁻³, [L-lysine] = 1.0 × 10⁻³ mol dm⁻³, [Hg⁺⁺] = 2.0 × 10⁻⁴ mol dm⁻³, [H⁺] = 2.0 × 10⁻² mol dm⁻³.