Rhodamine B oxidation promoted by P450-bioinspired Jacobsen catalysts/cellulose systems†
In this work, we investigated the preparation of P450-bioinspired Mn(III)-Schiff base complexes supported on DEAE-cellulose ((R,R)-Jacobsen/Cell(NEt2) and (S,S)-Jacobsen/Cell(NEt2), respectively) to oxidize substrates of biological interest. Catalysts were characterized by several physical techniques. UV-Vis spectroscopy with diffuse reflectance (DR/UV-Vis) analysis featured peculiar electronic transitions for both complexes. Fourier transform infrared (FTIR) spectra evidenced the characteristic band of imine groups (HCN) for bioinspired/Cell(NEt2) materials. Immobilization ratios in cellulose fibres were confirmed by atomic absorption spectroscopic (GF-AAS) analyses. Catalytic essays were conducted during rhodamine B (RhB) oxidation. Supported materials attained oxidative yields close to those of homogeneous systems, and cellulose may be stabilizing the active intermediate catalytic species. Reactions may be driven through two different intermediates: MnV(O) and MnIII(O–OH)salen. Homogeneous reactions suggest an asymmetric catalysis. Heterogeneous system reaction yields are similar, and salen complexes anchored on cellulose conformation would interfere on complex intermediate species configuration. The four possible RhB-oxidation products obtained by the reaction with the homogeneous (S,S)-Jacobsen catalyst and meta-chloroperoxybenzoic acid (m-CPBA) system were suggested by 1H NMR analysis, and a catalytic mechanism was proposed.