This minireview deals with the recent advances on the synthetic strategies for the immobilization of enzymes in metal–organic frameworks.

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Two crystal structures are described in this article: (a) the structure of a monomeric MnII complex with the tridentate N‐centered N3 ligand tris[(1‐methyl‐2‐imidazolyl)methyl]amine (TMIMA) ([MnII(TMIMA)2]2+); and (b) the structure of a monomeric MnIII complex with the tridentate N‐centered N2O ligand 2‐{[(1‐methyl‐2‐imidazolyl)methyl]amino}phenolate (PI–)2 ([MnIII(PI)2]+) (5). The latter was isolated both in the MnII and in the MnIII state, although only MnIII crystals were successfully grown. They are part of a series of Mn complexes prepared as SOD mimics, namely [Mn(BMPG)(H2O)]+ (2) {BMPG = N,N‐bis[(6‐methyl‐2‐pyridyl)methyl]glycinate}, [Mn(IPG)(MeOH)]+ (3) {IPG = N‐[(1‐methyl‐2‐imidazolyl)methyl]‐N‐(2‐pyridylmethyl)glycinate}, [Mn(BIG)(H2O)2]+ (4) {BIG = N,N‐bis[(1‐methyl‐2‐imidazolyl)methyl]glycinate}. The reactivity of MnII complexes 1 and 2 in an anhydrous medium is described and compared to that of complexes 3 and 4, the data for which was previously published. The cyclic voltammograms of the whole complex series were recorded in an aqueous medium (collidine buffer). Their SOD‐like activities were estimated by the McCord–Fridovich test (IC50 with 22 μM cytc FeIII: 1.6 ± 0.1 μMol L–1 for 1, 1.2 ± 0.5 μmol L–1 for 2, 3.0 ± 0.2 μmol L–1 for 3, 3.7 ± 0.6 μmol L–1 for 4, 0.8 ± 0.1 μmol L–1 for 5). IC50 values were converted into the corresponding kinetic constant kMcCF values. A linear correlation between Ea and log(kMcCF) was obtained, indicating that in this series the conversion to MnIII is probably the rate‐limiting step. This is of substantial importance for further Mn–SOD mimic design in this series. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Microperoxidase-8, a small, peroxidase-type enzyme was successfully immobilized into nanoparticles of the mesoporous and ultra-stable . The immobilized enzyme retained fully its catalytic activity and exhibited enhanced resistance to acidic conditions. The biocatalyst was reusable and showed a long-term stability. By exploiting the properties of the MOF's framework, we demonstrated, for the first time, that the MOF matrix could act in synergy with the enzyme (Microperoxidase-8) and enhance selectivity the oxidation reaction of dyes. The oxidation rate of the harmful negatively charged dye (methyl orange) was significantly increased after enzyme immobilization, most likely due to the preconcentration of the methyl orange reactant due to a charge matching between this dye and the MOF.Enzymes are biomolecules with remarkable catalytic properties essential for specific applications, such as production of biochemicals and biofuels, and for biosensing and bioremediation purposes. [1] Despite many advances in enzyme engineering, they remain expensive and/or fragile entities. As a result, their use in industrial context often requires their immobilization on a solid support to increase their stability and recovery. Many supports have been developed in the last decades, including, but not limited to, biopolymers/synthetic polymers, sol-gel materials, mesoporous silica, carbon materials, [2] and recently Metal-Organic Frameworks (MOFs). [3] These latter are a class of crystalline hybrid porous materials characterized by a vast chemical functionality, exhibiting a large variety of structural features (surface area, pore size, shape, flexibility…). These have sparked a great interest in many applications such as gas storage and separation, heat transfer, biomedicine, sensing and catalysis, among others. [4] As immobilization matrices, they seem promising since the

Here we report the best artificial metalloenzyme to date for the selective oxidation of aromatic alkenes; it was obtained by noncovalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into a host protein, xylanase 10A from Streptomyces lividans (Xln10A). Two metallic complexes-N,N'-ethylene bis(2-hydroxybenzylimine)-5,5'-dicarboxylic acid Mn(III) [(Mn-salen), 2-Mn] and 1-Mn-were associated with Xln10A, and the two hybrid biocatalysts were characterised by UV-visible spectroscopy, circular dichroism and molecular modelling. Only the artificial metalloenzyme based on 1-Mn and Xln10A was studied for its catalytic properties in the oxidation of various substituted styrene derivatives by KHSO(5): after optimisation, the 1-Mn-Xln10A artificial metalloenzyme was able to catalyse the oxidation of para-methoxystyrene by KHSO(5) with a 16 % yield and the best enantioselectivity (80 % in favour of the R isomer) ever reported for an artificial metalloenzyme.

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To develop artificial hemoproteins that could lead to new selective oxidation biocatalysts, a strategy based on the insertion of various iron-porphyrin cofactors into Xylanase A (Xln10A) was chosen. This protein has a globally positive charge and a wide enough active site to accommodate metalloporphyrins that possess negatively charged substituents such as microperoxidase 8 (MP8), iron(III)-tetra-alpha4-ortho-carboxyphenylporphyrin (Fe(ToCPP)), and iron(III)-tetra-para-carboxyphenylporphyrin (Fe(TpCPP)). Coordination chemistry of the iron atom and molecular modeling studies showed that only Fe(TpCPP) was able to insert deeply into Xln10A, with a KD value of about 0.5 microM. Accordingly, Fe(TpCPP)-Xln10A bound only one imidazole molecule, whereas Fe(TpCPP) free in solution was able to bind two, and the UV-visible spectrum of the Fe(TpCPP)-Xln10A-imidazole complex suggested the binding of an amino acid of the protein on the iron atom, trans to the imidazole. Fe(TpCPP)-Xln10A was found to have peroxidase activity, as it was able to catalyze the oxidation of typical peroxidase cosubstrates such as guaiacol and o-dianisidine by H2O2. With these two cosubstrates, the KM value measured with the Fe(TpCPP)-Xln10A complex was higher than those values observed with free Fe(TpCPP), probably because of the steric hindrance and the increased hydrophobicity caused by the protein around the iron atom of the porphyrin. The peroxidase activity was inhibited by imidazole, and a study of the pH dependence of the oxidation of o-dianisidine suggested that an amino acid with a pKA of around 7.5 was participating in the catalysis. Finally, a very interesting protective effect against oxidative degradation of the porphyrin was provided by the protein.

meso -Tetraary I porp hyri n i ron (I 11) derivatives cata lyse t he Ntosylaziridi nation of aryl -su bst ituted styrenes by tosylimidoiodobenzene, PhlNTs, a nitrogen analogue of iodosylbenzene. Three secondary reactions were found to limit the yield of N-tosylaziridination: (i) the formation of toluene-psulphonamide, TsN H2, which is presumably derived from hydrolysis of a possible iron-nitrene, Fe=NTs, intermediate, (ii) the conversion of the Fe(TPP) (CI) (TPP = tetraphenylporphyrin) catalyst into an iron(ii1) complex where the NTs moiety is inserted into an iron-nitrogen bond of Fe(TPP) (CI), (iii) an oxidative degradation of the porphyrin catalyst. These secondary reactions were avoided to a great extent by using anhydrous conditions and Fe(TDCPP)(CIO,) (TDCPP = tetrakis-2,6-dichlorophenylporphyrin) as a catalyst instead of Fe(TPP) (CI) and Fe(TPP) (CIO,). Under these conditions, N-tosylaziridination of styrene, cis-and trans-stilbene, and 1 ,I -diphenylethylene was performed with yields between 40 and 90%. Fe(TDCPP)(CIO,) was also found to be the best catalyst for N-tosylaziridination of aliphatic alkenes such as hex-I -ene, cyclo-octene, and cis-and trans-hex-2-enes. Although N-tosylaziridination of the two latter alkenes catalysed by Fe(TPP) (CI) was not stereospecific, this reaction became stereospecific with Fe(TDCPP) (CIO,) as catalyst. These results show that by a proper choice of the porphyriniron catalyst, relatively good yields of Ntosylaziridination of alkenes by PhlNTs can be obtained. As for 1,2-disubstituted aliphatic alkenes, syn addition of the NTs moiety to the double bond takes place. A possible mechanism is presented.