Ferrocinium

Ferrocene/ferrocinium (reference electrode) activity coefficient (also in use y)... 

Strehlow standard ferrocene-ferrocinium+ electrode and obtained a value of - 0.228 V, i.e., a positive pH shift of 3.85. Theoretically the pH range of pyridine is unlimited on the basic side, but in practice it is limited somewhere in that area as a consequence of the protogenic effect of contaminating traces of water. 

This means, in agreement with Fig. 4.17, that a negative Eh+/h2 value yields an additional increase in the Eredo range. Finally, solvation in itself contributes to extending the E OI range, as a more solvated ion is less accessible to electrolysis however, it is doubtful whether separate consideration of this effect makes any sense provided that E nodic and E +/h2 have been determined absolutely, i.e., versus the ferrocene-ferrocinium+ electrode. 

Single electron transfer to dialkylzirconocenes Single-electron oxidation of dialkylzirco-nocenes, e. g. with a ferrocinium [13] or silver salt [14,15], induces the following reaction leading to a cationic zirconocene [13] ... 

V, in acetonitrile with respect to the ferrocene/ferrocinium couple. " " Peroxodisulfate oxidation of [Fe(ttcn)2] does not give the Fe + complex the major product is [Fe(ttcn)(ttcn-1-oxide)]. Oxidation by lead dioxide does however yield [Fe(ttcn)2]. " The Fe—S bond... 

The transfer of charge from the metal to the ligand caused by back-donation can also be seen from a comparison of the ionization potentials of chromium in different complexes. The ionization potential of complex compounds is higher than that of the uncomplexed coordination center (6.76 eV), e.g. for dibenzenechromium ) 7.07 eV, and for hexacarbonyl-chromium 8.03 eV 43). It may be expected that a decrease in the net positive charge at the coordination center will give rise to an increase in ti-EPD properties. Hence the Fe-C distance will be shorter in [Fe(CO) 4] than in Fe(CO) 5. Likewise iron is more strongly coordinated in ferrocene than in the ferrocinium ion. 

A stable configuration can only be achieved when nonaqueous solvents are involved. For example, a photoelectro-chemical cell can be operated using the ferrocene/ferrocinium couple at an n-type Si electrode in a pure methanol solvent. This system is of special interest because the rate-determining steps can be analyzed in detail. Using Si as an electrode in CH3OH or CH3CN requires that the solvent is completely water free in order... 

Fig. 37.6. Experimental example of an unintended feedback imaging, (a) Schematic showing (1) the intended GC imaging of HRP activity (2) hindered diffusion above a densely packed monolayer using the ferrocinium derivative (Fc+) as mediator. Fc+ is present in low concentration possibly due to partial chemical oxidation by 02 or H202 (3) the regeneration of Fc+ at the gold electrode surface under a less-organized monolayer, (b) Experimental line scan in the presence of ferrocene methanol (and traces of Fc+) and H202. (c) Same as (b) but in absence of H202.

Along this line Matsue et al. [37,45,78,79] have developed a number of biochips. Among them are multi-analyte assays for human placental lactogen (HPL) and human chorionic gonadotropin (HCG) [45] and leukocidin, a toxic protein produced by methicillin-resistant Staphylococcus aureus [79]. Figure 37.8 shows an example of a dual immunoassay with SECM detection. The analyte is defined by the position on the chip and the amount of analyte is quantified via the collection current at the UME. The current originates from the reduction of ferrocinium methanol (Fc+) at the UME. Fc+ is produced locally at the chip surface by the enzyme HRP under consumption of H202. 

The process implies a first electrochemical step with a very fast conversion of the ferroceno/ferrocinium couple, due to the short length of the alkyl chain, and a second chemical step with a simple electron transfer between the iron complex in solution and that of the monolayer. Moreover, the thiols block the gold surface in such a way that the Fe(CN)g- oxidation will take place due solely to the ferrocene mediation at the monolayer, and with a very high efficiency (i.e., the catalytic way is observed at potentials 500 mV lower than those corresponding to a gold electrode with a C6SH monolayer). 

Another way to assess ion channel conductance is to use artificial phospholipid vesicles (liposomes) as cell models. These structures (described in more detail in the next chapter) are commonly used to transport vaccines, drugs, enzymes, or other substances to target cells or organs. The vesicles, which are several hundred nanometres in diameter, do not suffer from interference from residual natural ion channel peptides or ionophores, unlike purified natural cells. A liposome model was used to test the ion transport behaviour of the redox-active hydraphile 12.36. The compound transports Na+ and the process can also be monitored using 23Na NMR spectroscopy.26 The presence of the ferrocene-derived group in the central relay allows the ion transport to be redox-controlled - oxidation to ferrocinium completely prevents Na+ transport for electrostatic reasons. Some representative data from a planar bilayer measurement is shown for hydraphile 12.36 in Figure 12.16. 

The ferrocene-exchanged ZSM-5 zeolite shows a Mossbauer spectrum that when analyzed gives a 40% ferrocinium ion signal with an isomer shift of 0.53 mm/second. It is likely that water in the zeolite is being reduced as the ferrocene is oxidized. Reduction of this sample in hydrogen causes a complete loss of both the ferrocinium ion and the ferrocene Mossbauer features and a new appearance of alpha iron(0) metal and a new quadrupole split doublet of 0.4 mm/second and a quadrupole splitting of... 

The agreement between BPC(0/I), foc/fic", and Parson s data is not remarkably good. For example a deviation of AG (CP) referred to foc/fic" reference couple in highly aqueous acetone solutions was already mentioned previously in the case of other highly aqueous solvent mixtures This has been claimed to be due to specific interactions between ferrocinium 4i, 42) ferrocene with water. 

A chiral C2-symmetric bridged ferrocene was constructed from a synthetic ligand containing two cyclopentadiene units (Fig. 4-12d). The key step in the synthesis of the ligand is a diastereoselective Diels — Alder reaction of anthracene with bis[(S)-l-ethoxycarbonylethyl]fumarate. When oxidized to the ferrocinium salt, the ferrocene derivative has Lewis acid properties and catalyzes Diels — Alder reactions with some enantioselectivity [85]. 

C5H5)2M(IV)X2]), and ferrocinium complexes ([(C5H5)2Fe(III)]+) exhibit systemic activity against numerous other experimental tumors (Table IX) 100,101). Examples are the red complex (C5H5)2Ti(IV)Cl2 and its green V(IV) analog. Titanocene complexes are readily hydro-... 

Fig. 7.60 Photoluminescence decay characteristics for p-GaAs passivated with Na2S measured under the following conditions a) in air b) in acetonitrile c) upon addition of 1 mM cobaltoce-nium as an electron acceptor d) the same as c) but with 1 mM ferrocinium as an electron acceptor. (After ref. [82])...

Fig. 10.9 SNIFTIR spectra obtained in the 1700-700 regionfora2mM [Cr(DMSO)g] (0104)3 solution in dimethylacetamide at an Au electrode. The reference potential was 0.16 V against an internal ferrocene-ferrocinium couple spectra were recorded at more negative potentials at intervals of 100 mV (From reference 17, with permission.)...

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