Selective diesterase-like activity of bioinspired FeIIINiII and FeIIIZnII complexes and their 3-aminopropyl silica composites: A homo- and heterogeneous catalytic study

The paper reports synthesis and characterization of two new mixed-valence complexes [FeIIIMII(BPPAMFF)] (M = Zn/Ni). These compounds were also immobilized on silica. Kinetic studies using the phosphodiester 2,4-BDNPP as substrate revealed higher catalytic activity for FeIIINiII species. Immobilized catalysts outperformed homogeneous ones, suggesting enhanced hydrolase activity due to second coordination sphere effects. [Display omitted] •Synthesis and crystal structure of heterodinuclear FeIIIMII (M = Zn, Ni) complexes.•These compounds were successfully immobilized in 3-aminopropyl silica.•The compounds are active to hydrolytic cleavage of the phosphodiester 2,4-BDNPP.•FeIIINiII species presented higher activity than the FeIIIZnII species.•The activity of the immobilized compounds was better than the homogeneous processes. In this study, the preparation and characterization of two new mixed-valence heterodinuclear complexes [FeIIINiII(BPPAMFF)(μ-OAc)2(H2O)]ClO4 (1) and [FeIIIZnII(BPPAMFF)(μ-OAc)2(H2O)]ClO4 (2) with the bioinspired ligand 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl)])-4-methyl-6-formylphenol (H2BPPAMFF) are reported. These compounds were immobilized in 3-aminopropyl silica (APS) to afford composites APS-1 and APS-2 successfully. The aldehyde-containing ligand provided a reactive functional group, which could serve as a cross-linking group to bind the complexes to the directly amino-modified SiO2 surface. The complexes’ chemical integrity on the APS inorganic platform were probed by spectroscopical techniques, such as FTIR, UV–Vis and EPR. Potentiometric and spectrophotometric titrations allowed the chemical species present in solution to be rationalized, and identified which of them were potentially active in the hydrolytic cleavage of phosphodiester 2,4-BDNPP. Kinetic studies showed that FeIIINiII species (1 and APS-1) presented higher catalytic efficiency (E = kcat/KM) than FeIIIZnII species (2 and APS-2). Catalytic mechanisms were proposed based on a series of kinetic experiments, in which all the catalysts tested behaved as selective phosphodiesterases. In addition, it was also demonstrated that the hydrolase activity of the immobilized catalytic centers, APS-1 and APS-2, was better than the homogeneous processes, where second coordination sphere effects may be involved in directing and stabilizing the transition state.