Mechanistic Investigations of Ruthenium(III) Catalyzed Oxidation of L-Tryptophan by Diperiodatocuprate(III) in Aqueous Alkaline Media (Stopped Flow Technique): A Kinetic Study

Abstract

The kinetics of the oxidation of ruthenium(III) (Ru(III)) catalyzed oxidation of L-tryptophan (L-trp) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.20 mol dm-3 was studied spectrophotometrically. The reaction between L-tryptophan and DPC in alkaline medium in presence of [Ru(III)] exhibits 1:4 stoichiometry (L-trp:DPC). The reaction was of first order in [DPC], less than unit order in [L-trp] and negative fractional order in both [OH-] and [IO 4-]. The order in [Ru(III)] was unity. Intervention of free radicals was observed in the reaction. The oxidation reaction in alkaline medium has been shown to proceed via a Ru(III)-L-trp complex, which reacts with monoperiodatocuprate(III) to decompose in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, NMR and LC-MS. Probable mechanism is proposed and discussed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. The active species of catalyst and oxidant have been identified.

Kinetics and mechanistic approach to the chromic acid oxidation of l-tryptophan with a spectral detection of chromium(III) product

“…Other products were identified as discussed elsewhere [31,44]. Similar oxidation products with different experimental conditions have been also reported earlier [33][34][35][36]. On the other hand, the formation of Cr III species was confirmed by the decrease in the oxidation rate upon addition of manganese(II) sulfate to the reaction mixture [14,20].…”

“…There is also an indication that some amino acids may play an important role in the chemistry of chromium, especially in the environment, where Cr V1 may present a serious hazard because of its mutagenic and carcinogenic activity [1][2][3]. They have been oxidized by a variety of reagents under different experimental conditions and they often undergo oxidative decarboxylation and deamination [24][25][26][27][28][29][30][31][32][33][34][35][36].…”

“…Our literature survey reveals that the oxidation of tryptophan by different oxidants has received limited attention [33][34][35][36]. We are particularly interested to investigate the mechanism of the oxidation of such amino acid by chromium(VI) in acidic media.…”

Palladium(II)-catalyzed oxidation of l-tryptophan by hexacyanoferrate(III) in perchloric acid medium: a kinetic and mechanistic approach

“…A large number of kinetic investigations on the oxidation of amino acids are being carried out using various oxidants under different experimental conditions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] because of their biological significance, selectivity towards the oxidants and to understand the mechanism of such biological redox reactions. In many cases, [5][6][7][8][9][10][11][12][13][14] it was reported that amino acids undergo oxidative decarboxylation and deamination. L-Tryptophan (Trp) is one of the essential amino acids that is required in human diet.…”

Mechanistic investigation of osmium(VIII)catalyzed oxidation of brilliant green dye by chloramine-T in alkaline medium: a spectrophotometric kinetic study

“…In recent years either alone or binary mixtures, the use of transition metal ions, as catalysts in various redox processes have attracted considerable interest [28]. For different metal ion catalysts like Cr(III) [29], Ru(III) [30][31][32][33][34][35][36][37][38][39][40], Ir(III) [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55], Pd(II) [52,[56][57][58][59] and Os(VIII) [59][60][61][62][63], Au(II) [64] different oxidizing agents have been used in the oxidation of organic compounds. The mechanism of the reaction relies upon the nature of the substrate, oxidant and moreover upon the ways in which transition metal complex ions play their role in order to promote the reactant molecules to the activated state before finally changing into products under experimental conditions.…”