This work provides spectroscopic, catalytic, and stability fingerprints of two new bacterial dye-decolorizing peroxidases (DyPs) from Bacillus subtilis (BsDyP) and Pseudomonas putida MET94 (PpDyP). DyPs are a family of microbial heme-containing peroxidases with wide substrate specificity, including high redox potential aromatic compounds such as synthetic dyes or phenolic and nonphenolic lignin units. The genes encoding BsDyP and PpDyP, belonging to subfamilies A and B, respectively, were cloned and heterologously expressed in Escherichia coli. The recombinant PpDyP is a 120-kDa homotetramer while BsDyP enzyme consists of a single 48-kDa monomer. The optimal pH of both enzymes is in the acidic range (pH 4-5). BsDyP has a bell-shape profile with optimum between 20 and 30 °C whereas PpDyP shows a peculiar flat and broad (10-30 °C) temperature profile. Anthraquinonic or azo dyes, phenolics, methoxylated aromatics, and also manganese and ferrous ions are substrates used by the enzymes. In general, PpDyP exhibits higher activities and accepts a wider scope of substrates than BsDyP; the spectroscopic data suggest distinct heme microenvironments in the two enzymes that might account for the distinctive catalytic behavior. However, the Bs enzyme with activity lasting for up to 53 h at 40 °C is more stable towards temperature or chemical denaturation than the PpDyP. The results of this work will guide future optimization of the biocatalytis towards their utilization in the fields of environmental or industrial biotechnology.

The complexes (η5-C5R5)MoO2Cl (R = H, CH3 (Me), CH2Ph (Bz)) are readily prepared from the parent carbonyls (η5-C5R5)Mo(CO)3Cl upon reaction with t-BuOOH (TBHP) in n-decane. The compounds are characterized by vibrational spectroscopy, 1H, 13C, and 95Mo NMR spectroscopy, and elementary analysis and are compared to their (η5-C5R5)ReO3 homologues. The Mo−C5R5 force constants have been determined. (η5-C5Bz5)MoO2Cl can be stored and handled at room temperature without decomposition, in contrast to the more temperature sensitive Cp (R = H) and Cp* (R = Me) analogues. The (η5-C5R5)MoO2Cl complexes catalyze the epoxidation of cyclooctene, styrene, and 1-octene with TBHP as oxidizing agent. The highest activity is found for (η5-C5Bz5)MoO2Cl:  TOF 21000 mol/(mol × h) for cyclooctene in CH2Cl2 at 55 °C with a ratio catalyst:substrate:TBHP = 0.0001:1:2.5. This activity even surpasses that of the well-known MeReO3/H2O2 system. The stable parent carbonyls (η5-C5R5)Mo(CO)3Cl can be used as catalyst precursors since they are transformed into (η5-C5R5)MoO2Cl under the operating catalytic conditions.

Complexes of the general formula [MoO2X2L2] (X=Cl, Br, Me; L2=bipy, bpym) have been prepared and fully characterized, including X‐ray crystallographic investigations of all six compounds. Additionally, the highly soluble complex [MoO2Cl2(4,4′‐bis(hexyl)‐2,2′‐bipyridine)] has been synthesized. The reaction of the complexes with tert‐butyl hydroperoxide (TBHP) is an equilibrium reaction, and leads to MoVI η1‐alkylperoxo complexes that selectively catalyze the epoxidation of olefins. Neither the Mo−X bonds nor the Mo−N bonds are cleaved during this reaction. These experimental results are supported by theoretical calculations, which show that the attack of TBHP at the Mo center through the X‐O‐N face is energetically favored and the TBHP hydrogen atom is transferred to a terminal oxygen of the Mo=O moiety. After the attack of the olefin on the Mo‐bound peroxo oxygen atom, epoxide and tert‐butyl alcohol are formed. The latter compound acts as a competitive inhibitor for the TBHP attack, and leads to a significant reduction in the catalytic activity with increasing reaction time.

Methyltrioxorhenium(vii) (MTO) forms trigonal-bipyramidal adducts with pyridines and related Lewis bases. These complexes have been isolated and fully characterized, and two single-crystal X-ray structures are reported. The complexes react with H 2 O 2 to form mono-and bisperoxo complexes which were examined in situ by 1 H and 17 O NMR spectroscopy. A clear increase in electron deficiency at the Re center can be observed from the MTO complexes to the bisperoxo complexes in all cases examined. The activity of the bisperoxo complexes in olefin epoxidation depends on the Lewis bases, the redox stability of the ligands, and the excess of Lewis base used. Density functional calculations show that when the ligand is pyridine or pyrazole there are significantly stabilized intermediates and moderate energies of the transition states in olefin epoxidation. This ultimately causes an acceleration of the epoxidation reaction. In contrast, the catalytic performance is reduced when the ligand was a nonaromatic nitrogen base. The frontier orbital interaction between the olefin HOMO p(C ± C) and orbitals with s*(O ± O) character in the LUMO group of the Re-peroxo moiety controls the olefin epoxidation.