ADESIYAN, Funmilayo Aderonke
The oxidation of malachite green (a triphenylmethane dye) was studied in aqueous solutions of two cationic surfactants, hexadecyltrimethylammonium bromide (HDTAB), hexadecylpyridinium bromide (HDPB) with the view of investigating the effects of surfactant head group modification on the kinetic parameters of the reaction.
The reaction was studied by measuring the decrease in absorbance of the dye as a function of time at the wavelength of maximum absorption (λmax), 617nm at 25°C using an Ultra-violet- Visible (UV-VIS) spectrophotometer. Kinetic parameters such as maximum rate constant in the micellar phase, km and the substrate (dye) binding constant, 1/KD, were obtained by fitting the pseudo-first order rate constant versus surfactant concentration curve to the Piszkiewicz model. The catalytic factors km/kw (the ratio of the maximum rate constant in micellar medium to that in the pure water) of 12 and 22 were obtained for HDTAB and HDPB respectively.
The pseudo-first order rate constant variation with surfactant concentration shows a sigmoid-shaped curve, which is analogous to the positive cooperativity in enzymatic reactions. It was observed that the maximum reaction rate constant, km and the binding constant, 1/KD were higher in the presence of HDPB than in HDTAB. These observations could be attributed to the difference in the head-group of the two surfactants.
The study concluded that the difference in surfactant head group played a significant role in the catalytic behaviour of the two surfactants used.
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