Rhodamine B oxidation promoted by P450-bioinspired Jacobsen catalysts/cellulose systems

Abstract

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: Mn^V(O) and Mn^III(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.