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This communication presents a novel truncated NiII-containing metbalamin and describes its reversible one electron reduction to a catalytically active NiI species, that features cofactor F430 model character. Our results strikingly demonstrate that stabilization of NiI is not restricted to the related hydroporhyrinoid ligands and is of relevance to the application of metallocorrins in (biomimetic) catalysis.

Horseradish peroxidase isoenzyme C (HRPC) is often used as catalyst for the preparation of the conductive emeraldine salt form of polyaniline (PANI-ES) from aniline and hydrogen peroxide (H2O2) in the presence of anionic templates in aqueous solution. Here, a direct comparison of three types of soft templates was made, (i) the sodium salt of sulfonated polystyrene (SPS), (ii) micelles from sodium dodecylbenzenesulfonate (SDBS), and (iii) vesicles from either a 1:1 molar mixture of SDBS and decanoic acid or from AOT (sodium bis(2-ethylhexyl)sulfosuccinate). Based on UV/vis/NIR, EPR and Raman spectroscopy measurements all three types of templates are similarly suitable, with advantages of the two vesicle systems in terms of aniline conversion degree and radical content in the final PANI-ES product. First experiments with sulfated cellulose nanocrystals (CNCs) indicate that they are promising rigid templates for the preparation of electroconductive PANI-ES-coated cellulose materials or devices.

Many previous studies have shown that (i) the oxidation of aniline or the aniline dimer p-aminodiphenyl-amine (PADPA) in a slightly acidic aqueous solution can be catalyzed with heme peroxidases or multicopper laccases and that (ii) subsequent reactions lead to oligomeric or polymeric products, which resemble chemically synthesized polyaniline in its conductive emeraldine salt form (PANI-ES), provided that (iii) an anionic "template" is present in the reaction medium. Good templates are anionic polyelectrolytes, micelles, or vesicles. Under optimal conditions, their presence directs the reactions in a positive way toward the desired formation of PANI-ES-type products. The effect of four different types of anionic templates on the formation of PANI-ES-like products from PADPA was investigated and compared by using Trametes versicolor laccase (TvL) as a catalyst in an aqueous pH 3.5 solution at room temperature. All four templates contain sulfonate groups: the sodium salt of the polyelectrolyte sulfonated polystyrene (SPS), micelles from sodium dodecylbenzenesulfonate (SDBS), vesicles from a 1:1 molar mixture of SDBS and decanoic acid, and vesicles from sodium bis(2-ethylhexyl) sulfosuccinate (AOT). Although with all four templates, stable, inkjet-printable solutions or suspensions consisting of PANI-ES-type products were obtained under optimized conditions, considerably higher amounts of TvL were required with SDBS micelles to achieve comparable monomer conversion to PANI-ES-like products during the same time period when compared to those with SPS or the two types of vesicles. This makes SDBS micelles less attractive as templates for the investigated reaction. In situ UV/vis/near-infrared, electron paramagnetic resonance (EPR), and Raman spectroscopy measurements in combination with an high-performance liquid chromatography analysis of extracted reaction products, which were deprotonated and chemically reduced, showed seemingly small but significant differences in th

Horseradish peroxidase isoenzyme C (HRPC) is often used as catalyst for the preparation of the conductive emeraldine salt form of polyaniline (PANI-ES) from aniline and hydrogen peroxide (H2O2) in the presence of anionic templates in aqueous solution. Here, a direct comparison of three types of soft templates was made, (i) the sodium salt of sulfonated polystyrene (SPS), (ii) micelles from sodium dodecylbenzenesulfonate (SDBS), and (iii) vesicles from either a 1:1 molar mixture of SDBS and decanoic acid or from AOT (sodium bis(2-ethylhexyl)sulfosuccinate). Based on UV/vis/NIR, EPR and Raman spectroscopy measurements all three types of templates are similarly suitable, with advantages of the two vesicle systems in terms of aniline conversion degree and radical content in the final PANI-ES product. First experiments with sulfated cellulose nanocrystals (CNCs) indicate that they are promising rigid templates for the preparation of electroconductive PANI-ES-coated cellulose materials or devices.

Horseradish peroxidase isoenzyme C (HRPC) is often used as catalyst for the preparation of the conductive emeraldine salt form of polyaniline (PANI-ES) from aniline and hydrogen peroxide (H2O2) in the presence of anionic templates in aqueous solution. Here, a direct comparison of three types of soft templates was made, (i) the sodium salt of sulfonated polystyrene (SPS), (ii) micelles from sodium dodecylbenzenesulfonate (SDBS), and (iii) vesicles from either a 1:1 molar mixture of SDBS and decanoic acid or from AOT (sodium bis(2-ethylhexyl)sulfosuccinate). Based on UV/vis/NIR, EPR and Raman spectroscopy measurements all three types of templates are similarly suitable, with advantages of the two vesicle systems in terms of aniline conversion degree and radical content in the final PANI-ES product. First experiments with sulfated cellulose nanocrystals (CNCs) indicate that they are promising rigid templates for the preparation of electroconductive PANI-ES-coated cellulose materials or devices.

We present a comprehensive investigation of main-chain scission processes affecting peripherally charged and neutral members of a class of dendronized polymers (DPs) studied in our laboratory. In these thick, sterically highly congested macromolecules, scission occurs by exposure to solvents, in some cases at room temperature, in others requiring modest heating. Our investigations rely on gel permeation chromatography and atomic force microscopy and are supported by molecular dynamics simulations as well as by electron paramagnetic resonance spectroscopy. Strikingly, DP main-chain scission depends strongly on two factors: first the solvent, which must be highly polar to induce scission of the DPs, and second the dendritic generation g. In DPs of generations 1 # g # 8, scission occurs readily only for g ¼ 5, no matter whether the polymer is charged or neutral. Much more forcing conditions are required to induce degradation in DPs of g s 5. We propose solvent swelling as the cause for the main-chain scission in these individual polymer molecules, explaining in particular the strong dependence on g: g < 5 DPs resemble classical polymers and are accessible to the strongly interacting, polar solvents, whereas g > 5 DPs are essentially closed off to solvent due to their more closely colloidal character. g ¼ 5 DPs mark the transition between these two regimes, bearing strongly sterically congested side chains which are still solvent accessible to some degree. Our results suggest that, even in the absence of structural elements which favour scission such as cross-links, solvent swelling may be a generally applicable mechanochemical trigger. This may be relevant not only for DPs, but also for other types of sterically strongly congested macromolecules., Peer Reviewed, Postprint (published version)

The Trametes versicolor laccase (TvL)-catalysed oligomerisation of the aniline dimer p-aminodiphenylamine (PADPA) was investigated in an aqueous medium of pH = 3.5, containing 80-100 nm-sized anionic vesicles formed from AOT, the sodium salt of bis(2-ethylhexyl)sulfosuccinic acid. If run under optimal conditions, the reaction yields oligomeric products which resemble the emeraldine salt form of polyaniline (PANI-ES) in its polaron state, known to be the only oxidation state of linear PANI which is electrically conductive. The vesicles serve as "templates" for obtaining products with the desired PANI-ES-like features. For this complex, heterogeneous, vesicle-assisted, and enzyme-mediated reaction, in which dissolved dioxygen also takes part as a re-oxidant for TvL, small changes in the composition of the reaction mixture can have significant effects. Initial conditions may not only affect the kinetics of the reaction, but also the outcome, i.e., the product distribution once the reaction reaches its equilibrium state. While a change in the reaction temperature from T approximate to 25 to 5 degrees C mainly influenced the rate of reaction, increase in enzyme concentration and the presence of millimolar concentrations of chloride ions were found to have significant undesired effects on the outcome of the reaction. Chloride ions, which may originate from the preparation of the pH = 3.5 solution, inhibit TvL, such that higher TvL concentrations are required than without chloride to yield the same product distribution for the same reaction runtime as in the absence of chloride. With TvL concentrations much higher than the elaborated value, the products obtained clearly were different and over-oxidised. Thus, a change in the activity of the enzyme was found to have influence not only on kinetics but also led to a change in the final product distribution, molecular structure and electrical properties, which was a surprising find. The complementary analytical methods which w

We report about the first Raman spectroscopy study of a vesicle-assisted enzyme-catalyzed oligomerization reaction. The aniline dimer N-phenyl-1,4-phenylenediamine (=p-aminodiphenylamine, PADPA) was oxidized and oligomerized with Trametes versicolor laccase and dissolved O-2 in the presence of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) vesicles (80-100 nm diameter) as templates. The conversion of PADPA into oligomeric products, poly(PADPA), was monitored during the reaction by in situ Raman spectroscopy. The results obtained are compared with UV/vis/NIR and EPR measurements. All three complementary methods indicate that at least some of the poly(PADPA) products, formed in the presence of AOT vesicles, resemble the conductive emeraldine salt form of polyaniline (PANI-ES). The Raman measurements also show that structural units different from those of "ordinary" PANI-ES are present too. Without vesicles PANI-ES-like products are not obtained. For the first time, the as-prepared stable poly(PADPA)-AOT vesicle suspension was used directly to coat electrodes (without product isolation) for investigating redox activities of poly(PADPA) by cyclic voltammetry (CV). CV showed that poly(PADPA) produced with vesicles is redox active not only at pH 1.1-as expected for PANI-ES-but also at pH 6.0, unlike PANI-ES and poly(PADPA) synthesized without vesicles. This extended pH range of the redox activity of poly(PADPA) is important for applications.

RATIONALE Hemolysis occurs in conditions such as sickle cell disease and malaria but also during transfusion of stored blood, extracorporeal circulation and sepsis. Cell-free hemoglobin (Hb) depletes nitric oxide (NO) in the vasculature, causing vasoconstriction and eventually cardiovascular complications. We hypothesize that Hb-binding proteins may preserve vascular NO signaling during hemolysis. OBJECTIVES Characterization of an archetypical function by which Hb scavenger proteins could preserve NO signaling during hemolysis. METHODS We investigated NO reactions kinetics, effects on arterial NO signaling and tissue distribution of cell-free Hb and its scavenger protein complexes. MEASUREMENTS AND MAIN RESULTS Extravascular translocation of cell-free Hb into interstitial spaces, including the vascular smooth muscle cell layer of rat and pig coronary arteries, promotes vascular NO resistance. This critical disease process is blocked by haptoglobin. Haptoglobin does not change NO dioxygenation rates of Hb; rather, the large size of the Hb:haptoglobin complex prevents Hb extravasation, which uncouples NO/Hb interaction and vasoconstriction. Size-selective compartmentalization of Hb functions as a substitute for RBCs following hemolysis and preserves NO signaling in the vasculature. We found that evolutionarily and structurally unrelated Hb binding proteins, such as PIT54 found in avian species, functionally converged with haptoglobin to protect NO signaling by sequestering cell-free Hb in large protein complexes. CONCLUSIONS Sequential compartmentalization of Hb by erythrocytes and scavenger protein complexes is an archetypical mechanism, which may have supported co-evolution of hemolysis and normal vascular function. Therapeutic supplementation of Hb scavengers may restore vascular NO signaling and attenuate disease complications in patients with hemolysis.

Peroxiredoxins are an ubiquitous family of peroxidases widely distributed among prokaryotes and eukaryotes. Peroxiredoxin 5, which is the last discovered mammalian member, was previously shown to reduce peroxides with the use of reducing equivalents derived from thioredoxin. We report here that human peroxiredoxin 5 is also a peroxynitrite reductase. Analysis of peroxiredoxin 5 mutants, in which each of the cysteine residues was mutated, suggests that the nucleophilic attack on the O-O bond of peroxynitrite is performed by the N-terminal peroxidatic Cys(47). Moreover, with the use of pulse radiolysis, we show that human peroxiredoxin 5 reduces peroxynitrite with an unequalled high rate constant of (7+/-3)x10(7) M(-1)s(-1).