Ferrocene, construction

Mesomorphic dendrimers containing electroactive units have potential for construction of dendrimer based molecular switches. Deschenaux et al. reported [154] the synthesis and liquid-crystalline properties of a novel dendrimer containing six mesomorphic ferrocene units. Apart from exhibiting a broad enantiotropic smectic A phase as determined by polarized optical microscopy, DSC, and XRD studies, thermogravimetry revealed the excellent thermal stability of the macromolecule. 

Decafunctionalization of ferrocene with allyl units has been used to construct a dendrimer (7) having a ferrocene-type core and ten ferrocene-type... 

With regard to biosensor applications, a wide variety of electrochemically active species (ferrocene, ruthenium complexes, or carbon and metal (Pt, Pd, Au...) [185,186] were also introduced into the sol-gel matrices or adsorbed to improve the electron transfer from the biomolecules to the conductive support [187,188]. For instance, glucose oxidase has been trapped in organically modified sol-gel chitosan composite with adsorbed ferrocene to construct a low-cost biosensor exhibiting high sensitivity and good stability [189]. 

P.C. Pandey, S. Upadhayay, H.C., Pathak, and C.M.D. Pandey, Studies on ferrocene immobilized sol-gel glasses and its application in the construction of a novel solid-state ion sensor. Electroanalysis 11, 950-956 (1999). 

FIGURE 5.25. Avidin-biotin construction of a monolayer glucose oxidase electrode with an attached ferrocenium cosubstrate and cyclic voltammetric response in a phosphate buffer (pH 8) at 25°C and a scan rate of 0.04 V/s. a attached ferrocene alone, h In the presence of 0.5 M glucose, c Variation of the inverse of the plateau current with the inverse of substrate concentration. Adapted from Figure 1 in reference 24, with permission from the American Chemical Society. 

Nature uses globular protein domains to bind sulfate and phosphate anions using respectively 7 and 12 complementary anion-hydrogen bond arrangements. With this in mind we decided to construct new, neutral ferrocene derivatives that contain various hydrogen bond donor and acceptor sites for anion recognition. 

The same reasons for the interest in incorporating ferrocene units into polymers also provided motivation for the synthesis of dendritic macromolecules of well-defined size and structure containing ferrocenyl units. An important additional rationale for the construction of ferrocenyl dendrimers is provided by the fact that such macromolecules raise the possibility of combining the unique and valuable redox properties associated with the ferrocene nucleus with the highly structured macromolecular chemistry. This may provide access to materials of nanoscopic size possessing unusual symmetrical architectures, as well as specific physical and chemical properties which would be expected to differ from those of the ferrocene-based materials prepared to date. 

It has then to be concluded that the charge transfer in the ferrocene/ferroci-nium couple in this specific solvent is a fast process at the timescale of the hole diffusion in the semiconductor space charge layer. However, at the present time, it seems that the constraints arising from the construction of a perfectly tight device will hinder the development of these electrochemical photovoltaic cells. 

Biosensors constructed for ethanol and D-glucose measurements in beverages were built using ferrocene compounds as electron transfer mediators between the coenzyme PQQ of immobilized enzymes glucose (GDH) and alcohol (ADH) dehydrogenases and a carbon electrode surface <2003JOM(668)83>. 

The palladium based catalyst systems were also effective in the construction of carbon-nitrogen bonds on benzannulated five membered heterocycles. The 4-chloroindole derivative shown in 6.78. was coupled with piperazine in excellent yield, using a ferrocene based ligand.109 The analogous 5-bromo-benzimidazole derivative gave similar results (6.79.),110... 

Functionalisation of the carbosiloxane dendrimers is just as versatile as the above possibility of using different core units. Thus various metallo-carbosilox-ane dendrimers can be constructed, for example with titanocene dichloride end groups [93], ferrocene [94], or dicobalthexacarbonyl units [95]. 

Due to the high degree of conjugation, oh go(thiophene)s advanced as attractive candidates for molecular bridges. For instance, Sato et al. [34] constructed hexyl-sexithiophene and methoxy-terthiophene derivatives bearing two terminal ferrocenyl groups. These served as model compounds for molecular wires. In the hexyl-sexithiophene derivative, the resultant oxidized states spread over both the ferrocene and the sexithiophene moieties. Similarly, in the methoxy-terthiophene derivative, the oxidized species spreads over the entire molecule containing the terthiophene and the other ferrocene moiety. In both cases, CT between the terminal units is inferred as it is mediated via the oh go(thiophene)s. 

Glutamate Sensors. The glutamate sensors were constructed using graphite rods (Ultracarbon, Bay City, MI), which were polished to a smooth finish and coated with a small amount of redox polymer (0.033 Mmole of polymer-bound ferrocene) dissolved in chloroform. After evaporation of the solvent, a 5 m1 aliquot of glutamate oxidase (Yamasa Shoyu Co., Japan) solution (100 units/ml in pH 7.0 phosphate buffer) was added to the surface and allowed to dry at room temperature. The electrodes were stored under dry conditions at 5°C. 

Electron-Mediated Biosensor. Electropolymerization of 1,3-diaminobenzene (1,3-DAB), followed by adsorption of l,r-dimethylferrocene (1,1 -DMF), and immobilization of glucose oxidase, results in an easily and quickly (<2 h) constructed glucose biosensor with excellent linearity and stability (>3 months). Figure 5 shows a proposed schematic of the sensing layer consisting of film/mediator/enzyme. The ferrocene is depicted as circles... 

In conclusion, a ferrocene-mediated glucose sensor was constructed by all-chemical means. They are easily and quickly constructed (<2 h) and show excellent linearity and stability. Also, this construction method is applicable to any graphite electrode, regardless of shape or size. Future work will focus on applying electron mediators to ultramicrobiosensors. 

---