Safranine bleaching

Fig. 17. Kinetics of la-catalyzed bleaching of Safranine 0 (4.3 x 10-5M) by 0.012 M H2O2. Initial concentration of la (7.5 x 10-8 M) aliquots of the same amount of la were added after complete inactivation of the catalyst giving rise to the stepped dependence. The dashed line shows that addition of 0.012 M H2O2 does not resume the catalytic bleaching. Inset shows linearization of the data obtained after each addition of la in terms of Eq. (6) to give consistent values of k ( 3.3 x 10 3s 1). Conditions pH 11, 25°C. From Ref. (52).

The rate constants of kn and kx obtained using Eq. (24) reveal that (i) the activity of Fem-TAMLs in bleaching Safranine O (k ) increases more than 10-fold when the tail ethyl groups of la are replaced by fluorine atoms in lk. The rate constant kn for lk equals l(rM 1s 1 at 25°C, a value that corresponds to those found for the reactivity of horseradish peroxidase Compound II... 

Fig. 18. LFER between the rate constants k for bleaching Safranine 0 and ki for intramolecular inactivation in the series of head -substituted Fem-TAML catalysts with methyl tail groups. Conditions [H202] 0.012 M, 25°C, pH 11.0. The data point for la was ignored in the linear regression. From Ref. (52).

Fig. 19. (A) Simulated bleaching of a hypothetical dye using Eq. (24) at different concentrations of Feni-TAML catalyst (in M) with the rate constants ki (in s-1) and ku (in M-1s-1). The numerical values are indicated on the graph. (B) Normalized experimental and simulated bleaching of Safranine O (4.3 x 10-5M) by H202 (0.012 M) catalyzed by la at pH 11 and 25°C. Experimental data are shown as a and. The simulations, shown as solid lines, were made as in (A). From Ref. (52).

Fig. 19B shows the la-catalyzed bleaching of Safranine O at different [la] for comparison. The experimental and calculated curves agree and prove that complete bleaching of the dye is achievable by just increasing the la concentration. The required amount is still very low, specifically, 10-6 M for the difficult-to-oxidize dye Safranine O. 

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