Chemische Modifizierung von Pyranopterinen und deren Metallkomplexe

Eine große Gruppe von Metalloenzymen benutzt "Molybdopterin" - eine hydrierte Pterinkomponente - im Molybdän Kofaktor (Moco) um Oxotransferreaktionen zu katalysieren. Die Molybdänenzyme steuern wichtige Lebensfunktionen, wobei Fehlfunktionen zu Krankheiten führen können. Mehrere Proteinkristallstrukturen zeigten, dass das Pterin im Moco als ein trizyklisches System mit einem zusätzlichen Pyranoring vorliegt. Trotzdem ist die letztendliche Funktion des Pyranopterins noch immer unklar. Daher wurden Untersuchungen über Wechselwirkungen von Metallionen mit hydrierten Pterinen durchgeführt. Ein erster solcher Komplex von Pyranopterin wies eine N, O-chelatisierende Koordination an Molybdän des Pterinfragments auf. Wir berichten nun von neuen Pyranopterinderivaten, in denen eine N, O-chelatisierende Koordination durch die Blockierung der N(5)-Position nicht mehr erfolgen kann. Erste Metallkomplexe mit einer Koordination durch die Hydroxygruppen des Pyranorings werden vorgestellt

A chloride resistant high potential oxygen reducing biocathode based on a fungal laccase incorporated into an optimized Os-complex modified redox hydrogel

A chloride-resistant high-potential biocathode based on Trametes hirsuta laccase incorporated into an optimized Os-complex modified redox hydrogel (80 mV potential difference to the T1 Cu) is described. The bioelectrocatalytic activity towards O2 reduction is due to an intimate access of the polymer-bound Os-complex to the T1 Cu site. The chloride resistance of the biocathode is due to the tight binding of the polymer-bound Os-complex to the T1 Cu site

Design of a bioelectrocatalytic electrode interface for oxygen reduction in biofuel cells based on a specifically adapted Os-complex containing redox polymer with entrapped Trametes hirsuta laccase

The design of the coordination shell of an Os-complex and its integration within an electrodeposition polymer enables fast electron transfer between an electrode and a polymer entrapped high-potential laccase from the basidiomycete Trametes hirsuta. The redox potential of the Os3+/2+-centre tethered to the polymer backbone (+720 mV vs. NHE) is perfectly matching the potential of the enzyme (+780 mV vs. NHE at pH 6.5). The laccase and the Os-complex modified anodic electrodeposition polymer were simultaneously precipitated on the surface of a glassy carbon electrode by means of a pH-shift to 2.5. The modified electrode was investigated with respect to biocatalytic oxygen reduction to water. The proposed modified electrode has potential applications as biofuel cell cathode

The Thermophilic CotA Laccase from Bacillus subtilis: Bioelectrocatalytic Evaluation of O2 Reduction in the Direct and Mediated Electron Transfer Regime

International audienc

Entrapment Of Tyrosinase In A Redox Polymer

An amperometric biosensor for the detection of phenolic compounds was developed based on the immobilization of tyrosinase within an Os-complex functionalized electrodeposition polymer. Integration of tyrosinase within the redox polymer assures efficient catechol recycling between the enzyme and the polymer bound redox sites. The non-manual immobilization procedure improves the reproducibility of fabrication process, greatly reduces the desorption of the enzyme from the immobilization layer, and, most importantly prevents fast inactivation of the enzyme by its substrate due to fast redox cycling. A two-layer sensor architecture was developed involving ascorbic acid oxidase entrapped within an electrodeposition polymer in a second layer on top of the redox polymer=tyrosinase layer. Using this sensor architecture it was possible to eliminate the current interference arising from direct ascorbate oxidation up to a concentration of 630 mM ascorbic acid. The effects of the polymer thickness, the enzyme=polymer ratio, and the applied potential were evaluated with respect to optimal sensor properties. The sensitivity of the optimized sensors for catechol was 6.1 nA mM_1 with a detection limit of 10 nM, and for phenol 0.15 nA mM_1 with a detection limit of 100 nM

Phenol biosensor based on electrochemically controlled integration of tyrosinase in a redox polymer

An amperometric biosensor for the detection of phenolic compounds was developed based on the immobilization of tyrosinase within an Os-complex functionalized electrodeposition polymer. Integration of tyrosinase within the redox polymer assures efficient catechol recycling between the enzyme and the polymer bound redox sites. The non-manual immobilization procedure improves the reproducibility of fabrication process, greatly reduces the desorption of the enzyme from the immobilization layer, and, most importantly prevents fast inactivation of the enzyme by its substrate due to fast redox cycling

Mutual enhancement of the current density and the coulombic efficiency for a bioanode by entrapping bi-enzymes with Os-complex modified electrodeposition paints

A bioanode with high current density and coulombic efficiency was developed by co-immobilization of pyranose dehydrogenase from Agaricus meleagris (AmPDH) with the dehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophiles (recDHCtCDH) expressed recombinantly in Escherichia coli. The two enzymes were entrapped in Os-complex modified electrodeposition polymers (Os-EDPs) with specifically adapted redox potential by means of chemical co-deposition. AmPDH oxidizes glucose at both the C2 and C3 positions whereas recDHCtCDH oxidizes glucose only at the Cl position. Electrochemical measurements reveal that maximally 6 electrons can be harvested from one glucose molecule at the two-enzyme anode via a cascade reaction, as AmPDH oxidizes the products formed from of the recDHCtCDH catalyzed substrate oxidation and vice versa. Furthermore, a significant increase in current density can be obtained by combining AmPDH and recDHCtCDH in a single modified electrode. We propose the use of this bioanode in biofuel cells with increased current density and coulombic efficiency. (C) 2012 Elsevier B.V. All rights reserved

Optimization of a membraneless glucose​/oxygen enzymatic fuel cell based on a bioanode with high coulombic efficiency and current density

After initial testing and optimization of anode biocatalysts, a membraneless glucose​/oxygen enzymic biofuel cell possessing high coulombic efficiency and power output was fabricated and characterized. Two sugar oxidizing enzymes, namely, pyranose dehydrogenase from Agaricus meleagris (AmPDH) and flavodehydrogenase domains of various cellobiose dehydrogenases (DHCDH) were tested during the pre-​screening. The enzymes were mixed, wired and entrapped in a low-​potential Os-​complex-​modified redox-​polymer hydrogel immobilized on graphite. This anode was used in combination with a cathode based on bilirubin oxidase from Myrothecium verrucaria adsorbed on graphite. Optimization showed that the c.d. for the mixed enzyme electrode could be further improved by using a genetically engineered variant of the non-​glycosylated flavodehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophilus expressed in E. coli (ngDHCtCDHC310Y) with a high glucose-​turnover rate in combination with an Os-​complex-​modified redox polymer with a high concn. of Os complexes as well as a low-​d. graphite electrode. The optimized biofuel cell with the AmPDH​/ngDHCtCDHC310Y anode showed not only a similar max. voltage as with the biofuel cell based only on the ngDHCtCDHC310Y anode (0.55 V) but also a substantially improved max. power output (20 μW​/cm2) at 300 mV cell voltage in air-​satd. physiol. buffer. Most importantly, the estd. half-​life of the mixed biofuel cell can reach up to 12 h, which is apparently longer than that of a biofuel cell in which the bioanode is based on only one single enzyme