Oxygen reaction with ferrocene

The reaction scheme used in the first commercial electrochemical test strip from MediSense (now Abbott Diabetes Care) is shown later. Electron transfer rates between the reduced form of glucose oxidase and ferricinium ion derivatives are very rapid compared with the unwanted side reaction with oxygen (Cass et al. 1984 Forrow et al. 2002). The Abbott Diabetes Care Precision QID strip includes the l,l -dimethyl-3-(2-amino-l-hydroxyethyl) ferrocene mediator, which has the desirable characteristics of high solubility in water, fast electron-shuttling (bimolecular rate constant of 4.3 X 10 M s ), stability, and pH independence of the redox potential (Heller and Feldman 2008). Electrochemical oxidation of the ferrocene derivative is performed at 0.6 V. Oxidation of interferences, such as ascorbic acid and acetaminophen present in blood, are corrected for by measuring the current at a second electrode on the strip that does not contain glucose oxidase. 

The quenching of the trans dimer with oxygen and ferrocene indicates that this product is formed almost entirely from the triplet state. It is possible to calculate the amount of triplet-derived product in benzene by subtracting the amount of product obtained in the presence of oxygen from the amount of product obtained in the absence of oxygen. Such a calculation indicates that acenaphthylene triplets in benzene give both trans and cis dimers in the ratio of 74 26. The triplet state accounts for almost all of the trans product and about 10% of the cis product. The break in the slope of the Stem-Volmer plot for the trans dimer (Figure 10.3) may be attributed to the presence of two excited species which are quenched at different rates. These two species could be (a) two different monomeric acenaphthylene triplet states 7 and T2 or (b) a monomeric acenaphthylene triplet state 7 and a triplet excimer. This second triplet species is of relatively minor importance in the overall reaction since less than 5% of the total product in an unquenched reaction is due to this species. 

Polychloromethanes can take part in photochemical electron-transfer reactions with aromatic compounds, leading (in alcohol as solvent) to products with oxygenated one-carbon substituents. It is reported that ruthenocene (95), like ferrocene, gives the corresponding ethoxycarbonyl, formyl, or ethoxymethyl compounds when irradiated with carbon tetrachloride, chloroform, or dichloro-methane, respectively. Carbazole (96) behaves in a similar way with CCI4, and the... 

The dianion COT " is very stable because of its aromaticity with its 10 Jt electrons (Hiickel s rule, 4n -i- 2 with n = 2), but pyrophoric (very sensitive to oxygen). It is decomposed only slowly by water, acetic acid or electrophiles. The reactions of the latter cannot lead to ring functionalization, contrary to the case of ferrocene. Given the marked ionic character of the actinide complexes and the stability of the oxidation state IV, it is not surprising that uranocene is stable in its structure with aromatic planar rings. One may observe that, remarkably, uranocene is a homolog of ferrocene, but with/orbitals. 

The condensation reactions described above are unique in yet another sense. The conversion of an amine, a basic residue, to a neutral imide occurs with the simultaneous creation of a carboxylic acid nearby. In one synthetic event, an amine acts as the template and is converted into a structure that is the complement of an amine in size, shape and functionality. In this manner the triacid 15 shows high selectivity toward the parent triamine in binding experiments. Complementarity in binding is self-evident. Cyclodextrins for example, provide a hydrophobic inner surface complementary to structures such as benzenes, adamantanes and ferrocenes having appropriate shapes and sizes 12) (cf. 1). Complementary functionality has been harder to arrange in macrocycles the lone pairs of the oxygens of crown ethers and the 7t-surfaces of the cyclo-phanes are relatively inert13). Catalytically useful functionality such as carboxylic acids and their derivatives are available for the first time within these new molecular clefts. 

Attempts to reduce interference and minimize the effect of variations in oxygen tension have resulted in the development of biosensors with improved linear ranges which operate at lower electrode potentials. They incorporate artificial electron acceptors, called mediators, to transfer electrons from the flavoenzyme (e.g. glucose oxidase) to the electrode and thus are not dependent on oxygen. Ferrocene (bis(i75-cyclopentadienyl)iron) and its derivatives are examples of redox mediators for flavoenzymes. The reaction now becomes... 

Starting from the alcohols,/erroceno/ (Fe(C5H5)(C5H4-OH), Fc-OH) and l,T-ferro-cenediol (Fe(C5pl4-OH)2, Fc((3H)2), a series of new ferrocene derivatives has been prepared, in which the oxygen is directly connected with the ferrocene unit. The reactions... 

In the following, the outline of the redox reaction between O2 in W and decamethyl-ferrocene in O catalysed by flavin mononucleotide (FMN) in W evolving CO2, which was elucidated by applying VCTIES, will be introduced [12,13]. The selective ion transfer controlled by the redox reaction will also be discussed. The respiration mimetic reactions such as the redox reactions between -nicotinamide adenine dinucleotide and ascorbic acid or oxygen in W and quinone derivatives or hydroquinone derivatives, respectively, were also investigated with the aid of VCTIES [14,15], though they are not introduced here. 

The flexibility of the sol-gel process allows multiple approaches to enzymatic activity monitoring. The formation of hydrogen peroxide can be followed by optical measmements using another enzymatic reaction in which the oxidation of an organic dye is catalyzed by a peroxidase (HorseRadish Peroxidase HRP), coentrapped with GOD. The presence of glucose in the solution can also be detected via electrochemical means by following the redox reactions at the active site of GOD. However, because of the steric hindrance of the protein molecule, a ferrocene mediator has to be used in order to transfer electrons from the hidden active site to the electrode. Alternatively, oxygen consumption can be measmed with a Clark electrode. The hybrid gel is deposited on a Pt cathode... 

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