Ferrocenes, electrochemical behavior

The electrochemical behavior of ferrocene-based polymers [15] and of complexes containing a large, well defined number of ferrocene-type units [16] had already been reported when several groups became interested in dendrimer research. In the past few years several dendrimers of different chemical nature and structure carrying ferrocene-type units in the periphery have been synthesized... 

Mixed-metal dendrimers containing up to 6 Pt(IV)-based organometallic species in the branches and 12 peripheral ferrocene units (8) have recently been synthesized and their electrochemical behavior investigated [13]. As in the previously discussed examples, multi-electron reversible oxidation processes, assigned to the equivalent, non-interacting ferrocene units, have been observed. The authors point out that cyclic voltammetry is a powerful tool to support the structure of the dendrimers containing ferrocene units. 

It should be noted that Lay and coworkers [12] have made a comparative study of the electrochemical behavior of ferrocene, 1,2,3,4,5-pentamethylferrocene and decamethylferrocene in 29 solvents and have concluded that increasing substitution on ferrocene reduces the solvent dependence of the ferrocene potential. Accordingly, they recommend that decamethylferrocene be adopted as a preferred reference standard for electrochemical measurements in nonaqueous... 

Because of the peculiar electrochemical behavior (a single cyclic voltammetric wave characterized by remarkable electrochemical and chemical reversibility), dendrimers terminated with ferrocene-type units can be profitable used as exoreceptors, provided that they contain a group able of interacting through noncovalent bonds with the species to be recognized. Furthermore, such a group has to be located near the ferrocene units to sufficiently perturb their electrochemical response as a consequence of the interaction with the guest species. 

Fe2(III,III)2+ states. By considering that organometallic dendrimers based on conjugated ferrocene units are of special importance since mixed-valence states have interesting electrical, redox, and magnetic properties, recently three generations of polypropylene amine) dendrimers, decorated at their periphery with 4, 8, and 16 (compound 6, Fig. 6.6a) BFc units, respectively, have been synthesized and the electrochemical behavior of the dendrimers complexed with (3-cyclodextrins ([3-CD) and adsorbed at self-assembled monolayers (SAMs) of heptathioether-functionalized [3-CD on gold (molecular printboard) has been studied.40... 

The ubiquitous electrochemical behavior of ferrocene and its relative chemical stability have made this organometallic complex a useful group for the preparation of redox-active devices. The incorporation of ferrocene-modified amino acids into larger polypeptide structures can therefore lead to electrochemically active de novo designed proteins. In addition, the attachment of ferrocene derivatives to peptides make them electroactive and eligible to electrochemical detection. Hence, it is not surprising that the first synthesis of a ferrocene-modified amino acid dates back to the 1950s. 

The electrochemical behavior of the ferrocenediyl complex has also been studied and from its cyclic voltammetric profile it can be deduced that it exhibits a ferrocene-centered one-electron oxidation, followed by the decomposition of the electrogenerated cation [Fc,(AuPPh3)2]+. 

When a ferrocene derivative loaded Pt/Nafion-GOD electrode is transferred to a phosphate buffer solution containing no ferrocene derivatives, the observed redox waves reflect their electrochemical behavior in the film. The scan rate dependence of the cyclic voltammetry for the Pt/Nafion-GOD incorporated with different ferrocene derivatives was studied. A linear plot of the anodic peak current against the square root of the scan rate was obtained in all cases, which is indicative of diffusion controlled redox process. Typical chronoamperometric... 

Studies on the electrochemical behavior of ferrocene encapsulated in the hemi-carcerands 61 and 62, indicated that encapsulation induces substantial changes in the oxidation behavior of the ferrocene subunit [98]. In particular, encapsulated ferrocene exhibits a positive shift of the oxidation potential of c. 120 mV, probably because of the poor solvation of ferrocenium inside the apolar guest cavity. Lower apparent standard rate constants were found for the heterogeneous electron transfer reactions, compared to those found in the uncomplexed ferrocene under identical experimental conditions. This effect may be due to two main contributions (i) the increased effective molecular mass of the electroactive species and (ii) the increased distance of maximum approach of the redox active center to the electrode surface. 

The electrochemical behavior of ferrocene is relatively simple, giving rise to a reversible monoelectronic oxidation process at a very accessible potential. Most commonly, ferrocene has been used to functionalize the periphery of dendrimers, along the scheme illustrated in Figure 2b. Dendrimers 1 [42] and 2 [55] exemplify the commonly observed electrochemical behavior ... 

A first class of heteronuclear ferrocene-rhodium complexes, the electrochemical behavior of which has been studied, is shown in Scheme 7-26. 

Due to its rich electronic and electrochemical behavior, and to its versatile chemical reactivity, fullerene Cgo has been considered as the ideal partner in photo-induced processes [28, 111, 112]. Cgo>in fact, is a good electron-acceptor, and has a low reorganization energy [113]. For these reasons, an increasingly high number of donors have been covalently linked to Cgo > for potential use as novel electronic materials and for applications in artificial photosynthesis. Many classes of donor units have been attached to Cgo > including aromatics [ 12, 13, 114-118], porphyrins [11, 119-125] and phthalocyanins [126, 127], rota-xanes [128,129],tetrathiafulvalenes [130-133],carotenes [125],Ru-bipy- [134, 135] and Ru-terpy- [135,136] complexes, as well as ferrocene [130,137]. 

Indirect transduction relies on the use of indicators or labels. The first ones are based on the differences in the electrochemical behavior of indicators that interact in a different extension with dsDNA and ssDNA. The indicators for hybridization detection can be anticancer agents, organic dyes, or metal complexes, and are not generally covalently joined to DNA. The latter strategies include the use of labels covalently joined to DNA such as ferrocene, enzymes, or metal nanoparticles. 

Evans and coworkers have published an interesting study of the electrochemical behavior of a ferrocene-carboxylic acid derivative in the presence of BCD [18] and a summary of general guidelines on the electrochemical methodology that can be used to assess the complexation of redox-active molecules by cyclodextrin hosts [19]. However, the amphiphilic character of the surfactant viologens used in this work prevented us from applying most of these methods because the voltammetric... 

The presence of at least one alkyl group on the cyclopentadienyl motif is required to induce solubility in these poly(ferrocenylene persulfide)s. These polymers show two reversible oxidations. This type of electrochemical behavior is fairly common in ferrocene polymers where the ferrocene units are separated by short spacers as will be pointed out in the next section. 

Poly(ferrocenylsilane)s have been investigated extensively in terms of their electrochemical behavior. The general observation of these investigations is that under cyclic voltammetric conditions these polymers show two reversible oxidation (Fe(II)/Fe(III)) peaks separated by a AE1/2 that varies from about 0.16 to 0.29 V. The observation of two oxidation peaks has been explained as two successive events where the first oxidation involves a set of alternate ferrocene units followed by the second oxidation of the other alternate set. The second oxidation occurs at a higher potential than the first one [3,7]. 

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