Redox active biomolecules

While many redox transformations of pesticide compounds can occur abioticaUy, virtually all such reactions in namral systems are facilitated, either directly or indirectly, by biological processes (Wolfe and Macalady, 1992). Some pesticide compounds may be taken up by living organisms and directly oxidized or reduced through the involvement of a variety of redox-active biomolecules (Bollag, 1982). Enzymes that have been found to be responsible for the biological oxidation of pesticide compounds... 

Since the pioneering work of Davies and Brink [7] in 1942 that measured the concentration of oxygen in animal muscle, microelectrodes have been instrumental in providing information about the concentration and temporal release of redox-active biomolecules. This research is becoming more important in the light of evidence that not only is the absolute concentration... 

Impedance spectroscopy has been extensively used to follow changes of the interfacial properties of electrodes upon immobilization of enzymes and to characterize biocatalytic processes at enzyme-modified electrodes. Faradaic impedance spectroscopy can be used to study the kinetics of the electron transfer originating from bioelectrocatalytic reactions. It should be noted, that for characterizing redox-active biomolecules by impedance spectroscopy no additional redox probe is added to the electrolyte solution, and the measured electron-transfer process corresponds to the entire bioelectrocatalytic reaction provided by the biocatalyst. Under the condition that the enzyme is not saturated by the substrate, the electron-transfer resistance of the electrode is also controlled by the substrate concentration. Thus, the substrate concentration can be analyzed by the impedance spectroscopy following values [9]. 

Redox active biomolecules have been smdied by open cell thermoelectro-chemistiy. By potentiometry of cytochrome C at a gold electrode, thermodynamic quantities like AG have been identified [170]. Important thermodynamic constants, among them the entropic term of the redox processes in an immobilised myoglobin layer, have been determined in a similar way [171]. 

Another potential advantage of binding MFCs to redox-active biomolecules is current amplification. The Schiffrin groups used MFCs as a linker between the Cu metal center of glucose oxidase and the electrode surface, enabling electrochemical detection and study of the metalloenzyme. They were able to quantify the rate of ET between the electrode and the metal center, as well as the pH dependence of the formal potentials of the two processes involved, which are oxidation/ reduction of the tyrosyl radical and the Cu redox couple. The metalloenzyme-Au MFC complex showed effective electrocatalysis for O2 reduction as well. The possibilities for bioconjugated MFCs are extensive and will be discussed further in the sensors section. 

A number of different types of nanostructured electrodes, mostly used in conjunction with biomolecule films, have emerged for bioanalytical applications. These include metal nanoparticle films prepared by casting or electrodeposition, films of randomly oriented carbon nanotubes (CNTs), vertically aligned CNT forests, and graphene films (Figure 13.2). Such nanostructured electrodes have been found to serve as excellent platforms for electrochemical studies involving redox-active biomolecules. ° The following section describes how nanostructured electrodes, electrodes with... 

The techniques described herein demonstrate the breadth of invaluable information that can be derived by analyzing the morphology and electrochemical properties of enzymes, redox-active biomolecules, and other polymers on conductive materials. Many of these techniques offer rapid and relatively noninvasive methods to monitor bioelectrode constmction and assembly. By combining complementary analysis, we are able to characterize nearly any type of electrode surface, including biological and inert components, and understand the interfacial interactions between the two. The ability to conduct analysis in a liquid environment (such as an AFM fluid cell) provides information that can be correlated to electrocatalytic activity. In-depth analysis at the range of scale described herein will increasingly become a complementary and indispensable tool to elucidate and understand surface electrochemistry and bioelectrochemical interface chemistry. 

Linares F, Quartapelle Procopio E, Galindo MA, Angustias Romero M, Navarro JAR, Barea E (2010) Molecular architecture of redox-active half-sandwich Ru(II) cyclic assemblies. Interactions with biomolecules and anticancer activity. Cryst Eng Comm 12 2343-2346... 

Many simple complexes have been prepared as models of active sites of biomolecules. For example, a reactive five-coordinate thiolate Co complex (Figure 24) was prepared to model the active site of nitrile hydratase, a Co or Fe metalloenzyme that promotes the conversion of nitriles to amides. The synthesized model complex is facile in its uptake and release of azide and thiocyanate, indicating that an appropriate nonleaving group environment enhances ligand displacement sufficiently for catalytic paths in non-redox active Co metalloenzymes. Other examples have appeared earlier in this report. 

A vast amount of literature exists on enzyme-modified metal nanopartides. Crumbliss and co-workers pioneered the use of metal nanopartides for enzymatic sensors for various analytes such as H2O2, glucose, xanthine and hypoxanthine [156-158]. GCE or Pt electrodes are modified with enzyme-capped Au colloids, either by simple evaporation or electrodeposition. The nanopartides act as mediators, transferring electrons between the redox-active site on the immobilized biomolecule and the electrode and thus eliminating the need for external mediators. These sensors are classified as third generation biosensors . 

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