Molecular redox-active molecule

Second, in designing new molecule-based electronic devices, one of the major goals is the precise control of the current flowing between the terminals. Electrochemical molecular junctions allow for control of the potentials of the electrodes with respect to the redox potential of incorporated redox-active molecules with well-defined, accessible, tunable energy states. These junctions represent unique systems able to predict precisely at which applied potential the current flow will take off. Even though the presence of a liquid electrolyte represents a detriment towards possible applications, they provide the concepts for designing molecular devices that mimic electronic functions and control electrical responses. 

A recent development in SPM technology is the combination of SECM and AFM to produce a hybrid high-resolution microscope that allows simultaneous topographic and electrochemical imaging.22 Figure 19 shows an example of this measurement in which pore structure and molecular transport of a redox-active molecule (Ru(NH3)e2+) were simultaneously imaged at l-nm resolution. Inspection of this image clearly shows a correlation between transport rates and pore structure. 

In contrast, a new type of redox polymer-coated electrode has recently been fabricated using the bottom-up method, in which redox-active molecules are connected with molecular wires, and the wires act as the current collector.11-13 In this case, electrons can be transported through the wires, and control of the electron transfer pathway is possible by changing the structure of the molecular wires. If the wire has a linear structure, redox active molecules with the wire connections exhibit a structure similar to that of a beaded curtain (Fig. lb), in which the electron transfers in a straightforward manner along each line. Furthermore, when the wire is composed of redox active molecules, we observe the promising phenomenon that the electron transfers via the redox process in the wire, whose mechanism would... 

Coupling between a biologically catalyzed reaction and an electrochemical reaction, referred to as bioelectrocatalysis, is the constructional principle for enzyme-based electrochemical biosensors. This means that the flow of electrons from a donor through the enzyme to an acceptor must reach the electrode in order for the corresponding current to be detected. In case a direct electron transfer between the active site of an enzjane and an electrode is not possible, a small molecular redox active species, e.g. hydrophobic ferrocene, meldola blue and menadione as well as hydrophilic ferricyanide, can be used as an electron transfer mediator. This means that the electrons from the active site of the enzyme reduce the mediator molecule, which, in turn, can diffuse to the electrode, where it donates the electrons upon oxidation. When these mediator molecules are employed for coupling of an enzymatic redox reaction to an electrode at a constant potential, the resulting application can be referred to as mediated amperometry or mediated bioelectrocatalysis. 

In a recent development novel nano-cluster based devices enabled to switch the conductivity of a non-junction by changing the oxidation state of a bridging molecule. Some redox-active molecules contain a molecular center where reduction or oxidation can be achieved more or less reversibly supporting quite large currents. A fundamental prerequisite is the overlapping of the electron energy bands of the molecule with those of... 

The preparation of crystalline low-dimensional molecular solids, commonly is performed by electrocrystallization techniques wherein redox active molecules are reduced or oxidized at a working electrode in the presence of appropriate counterions. Very little is known, however, about the effect of electrochemical parameters and interfacial structure on the self assembly processes that lead to crystallization on the electrode surface. This work will describe the electrocrystallization of various crystalline molecular solids, focusing on the control of nucleation, growth, morphology and stoichiometry of these materials through manipulation of the electrochemical growth conditions and interfacial properties of the electrode. 

Apart from electron promoters a large number of electron mediators have long been investigated to make redox enzymes electrochemically active on the electrode surface. In the line of this research electron mediators such as ferrocene and its derivatives have successfully been incorporated into an enzyme sensor for glucose [3]. The mediator was easily accessible to both glucose oxidase and an electron tunnelling pathway could be formed within the enzyme molecule [4]. The present authors [5,6] and Lowe and Foulds [7] used a conducting polymer as a molecular wire to connect a redox enzyme molecule to the electrode surface. 

Studies in the area of electrochemical molecular recognition deal with bifunctional receptor molecules that contain not only binding sites but also one or more redox-active centres whose electron transfer reaction is coupled to the receptor s complexation. Such systems can be described by the scheme of squares as shown in Scheme 1. 

Although in humans only MsrBl is a selenoprotein, the depletion of selenium from the diet of mice led to increases in both R and S stereoisomers. This was not initially explained, yet a subsequent study has shown that small molecule selenols (organic selenocysteine homologues) could act as efficient electron donors in vitro for MsrA enzymes. ° This effect has only been shown in vitro, but the possibility that small molecular selenium reductants, or more likely that some selenoproteins that contain reduced selenols (in redox-active motifs) is quite intriguing. Several small selenoproteins do not have real roles and reside in nearly all subcompartments of the cell (mitochondria, ER) where electron donors for Msr enzymes are probably critical to maintain protein stability. Low selenium nutritional status would then have a significant impact on all methionine oxidation, as Future studies to address selenium nutrition and methionine oxidation could prove to be... 

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