Ferrocene units, attaching

Fig. 6-1. Schematic representation of a ferrocene-containing macrocycle with the ferrocene moiety appended to the macrocycle. Fc = 1-substituted or l,l -disubstituted ferrocene x = O, S, or NR m,n,p= 1, 2, or 3 y = number of ferrocene units attached (usually between 1 and 4).

Other types include crown ether (coronands) modified by ferrocene units attached as side groups. These are illustrated by compounds in which the ferrocene is sepa-... 

Scheme 6. Steps involved in attaching ferrocene units to GO (98).

A further approach to electrically wire redox enzymes by means of supramolecular structures that include CNTs as conductive elements involved the wrapping of CNTs with water-soluble polymers, for example, polyethylene imine or polyacrylic acid.54 The polymer coating enhanced the solubility of the CNTs in aqueous media, and facilitated the covalent linkage of the enzymes to the functionalized CNTs (Fig. 12.9c). The polyethylene imine-coated CNTs were covalently modified with electroactive ferrocene units, and the enzyme glucose oxidase (GOx) was covalently linked to the polymer coating. The ferrocene relay units were electrically contacted with the electrode by means of the CNTs, and the oxidized relay mediated the electron transfer from the enzyme-active center to the electrode, a process that activated the bioelectrocatalytic functions of GOx. Similar results were observed upon tethering the ferrocene units to polyacrylic acid-coated CNTs, and the covalent attachment of GOx to the modifying polymer. 

Complex 2 also proved valuable in attaching the ferrocene unit to chloromethylated polystyrene. Treatment of chloromethylated styrene (18% of the phenyl rings modified) with 2 under basic conditions afforded polymer 6. Polymer 7 was then prepared and found to have UV-Vis spectroscopic data analogous to monomer 4 and polymer 5. 

The last three compounds (30-32) all comprise three macrocyclic rings with cobaltocenium units attached to a terminal ring and in one case (32) with ferrocene at the other end. 

Much of the interest in PVFc arises from the presence of redox-active iron sites attached to the polymer chain. Cyclic voltammetry experiments " have revealed that the iron sites are non-interacting, as a single reversible oxidation wave is observed as the iron centers interconvert between Fe(ii) and Fe(iii) states (Figure 2). The intensity of the current per molecule is directly proportional to the molecular weight of the polymer sample. The observation of a single cyclic voltammetric wave in low dielectric constant solvents is in contrast to the situation for polymers where the ferrocene units are in close proximity in the polymer backbone, such as PFSs (see Section 3.4). For the latter materials, evidence for communication between iron centers is provided by the presence of two reversible oxidation waves. This has been explained in terms of the oxidation of one Fe center making the neighboring Fe centers more difficult to oxidize. 

The observed eledron-transfer mediating role of the ferrocenes tethered to CyDs is of importance for biosensor applications (Fig. 10.5.10). The presence of several ferrocene units on one CyD molecule may enhance the fundioning of these molecules as electron mediators. Eledroactive monolayers of CyDs to be used as surface binding sites are usually prepared by attaching a ferrocene unit far from the cavity and close to the eledrode surface [43, 71]. Compounds 1 and 2 (Fig. 10.5.10) are examples of such systems [71]. 

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