Role of cetyltrimethylammonium bromide (cationic surfactant) on the tryptophan-MnO4(-) reaction.
Upon addition of permanganate to a solution of tryptophan (Trp), yellow-brown color species appears within the time of mixing of tryptophan in absence and presence of cetyltrimethylammonium bromide (CTAB), which was stable for some days. Spectroscopic and kinetic evidences suggest the formation of water-soluble colloidal MnO(2) as the most stable reduction product of MnO(4)(-). Carbon dioxide and ammonia are not formed as the oxidation products. Carbon-carbon double bond of indole moiety of Trp is responsible for the fast reduction of permanganate. Cetyltrimethylammonium bromide catalyses the permanganate oxidation of Trp with a rate enhancement of ca. 200-fold. Sub- and postmicellar catalytic effect of CTAB ascribed to the association/incorporation/solubilization of both reactants (MnO(4)(-) and Trp) with the CTAB aggregates and into the Stern layer of cationic micelles. Quantitative kinetic analysis of the rate constant-[CTAB] data has been performed on the basis of modified pseudo-phase model of the micelles. A comparison was made of the oxidation rates of different amino acids by permanganate. The order of the effectiveness was as follows: tryptophan>>tyrosine>>phenylalanine.
Malik
Maqsood Ahmad
MA
Department of Chemistry, Jamia Millia Islamia (Central University), Jamia Nagar, New Delhi 110025, India.
Khan
Zaheer
Z
D002384:Catalysis; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D017895:Manganese Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry; D013501:Surface-Active Agents / Q000138:chemical synthesis*; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry
D002593:Cetrimonium Compounds; D017895:Manganese Compounds; D010087:Oxides; D013501:Surface-Active Agents; C048856:permanganic acid; D014443:Tyrosine; D010649:Phenylalanine; D014364:Tryptophan; D000077286:Cetrimonium