In order to create a heme environment that permits biomimicry of heme-containing peroxidases, a number of new hemin-peptide complexes--hemin-2(18)-glycyl-L-histidine methyl ester (HGH), hemin-2(18)-glycyl-glycyl-L-histidine methyl ester (HGGH), and hemin-2,18-bis(glycyl-glycyl-L-histidine methyl ester) (H2GGH)--have been prepared by condensation of glycyl-L-histidine methyl ester or glycyl-glycyl-L-histidine methyl ester with the propionic side chains of hemin. Characterization by means of UV/vis- and 1H NMR spectroscopy as well as cyclic- and differential pulse voltammetry indicates the formation of five-coordinate complexes in the case of HGH and HGGH, with histidine as an axial ligand. In the case of H2GGH, a six-coordinate complex with both imidazoles coordinated to the iron center appears to be formed. However, 1H NMR of H2GGH reveals the existence of an equilibrium between low-spin six-coordinate and high-spin five-coordinate species in solution. The catalytic activity of the hemin-peptide complexes towards several organic substrates, such as p-cresol, L-tyrosine methyl ester, and ABTS, has been investigated. It was found that not only the five-coordinate HGH and HGGH complexes, but also the six-coordinate H2GGH, catalyze the oxidation of substrates by H2O2. The longer and less strained peptide arm provides the HGGH complex with a slightly higher catalytic efficiency, as compared with HGH, due to formation of more stable intermediate complexes.

An ambient and high-pressure stopped-flow kinetic study of the halogen-bridge cleavage reaction in the pallada-and platina-cycles [{M(o-C,H,RCH,NMe,)X},] ( M = Pd or Pt; R = H, 4-Me0, 5-Me or 5-F; X = CI or I) by a series of substituted pyridines in chloroform as solvent revealed that it is a

In order to investigate the ability of the Vitreoscilla hemoglobin (VHb) to act as a peroxidase, the protein was overexpressed in Escerichia coli and purified using a 6xHis-tag. The peroxidase activity of VHb was studied using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferrocene carboxylic acid (FcCOOH) dopamine and L-dopa as substrates. The effects of external agents such as pH, salt concentration/ionic strength, and the thermal stability of VHb on the catalytic activity were assessed. The optimum pH for VHb using ABTS as a substrate was estimated to be 6-7. The VHb protein proved to be stable up to 80 degrees C, as judged by its peroxidase activity. Furthermore, NaCl concentrations up to 100 mM did not exert any significant effect on the activity. The catalytic activity against ABTS and FcCOOH was similar to that measured for horseradish peroxidase, whereas in the case of the phenolic substrates dopamine and L-dopa the activity was several orders of magnitude lower. The Michaelis constants, KmH2O2, were in good agreement with the data for human and bovine hemoglobin. No activity could be detected for the negative controls lacking VHb. These results demonstrate that VHb exhibits peroxidase activity, a finding in line with the hypothesis that VHb has cellular functions beyond the role as an oxygen carrier.

Catalytically and electrocatalytically very active and stable are the complexes Ru(LL)‐GO, which are extremely readily accessible from glucose oxidase (GO) and the RuII complexes cis‐[Ru(LL)2Cl2] (LL=bpy, phen). These provide an unprecedentedly high amplification coefficient I/Io (see cyclic voltammograms) even at high scan rates and, correspondingly, very high rates of intramolecular electron transfer.

/k(R)-1 are 1.7 and 1.6, respectively. Based on the known X-ray structural data for the active site of GO, it has been tentatively suggested that the enantioselectivity originates from the hydrophobic contact between the enzyme tyr-68 residue and the h 5 -C 5 H 5 ring of 1 , and a hydrogen bond network formed by his-516 and/or his-559 residues and the carboxylic group of the ferrocene derivative. The findings reported confirm the existence of enantioselective electron transfer between oxidoreductases and organometallic compounds with a planar chirality. The lack of kinetic enantioselectivity may be a result of i) the incorrect ratelimiting step, ii) unfavorable pH region, and iii) the deficit of charged groups attached to ferrocenes.