Ferrocene methanol

Ferrocene Methanol Ferrocene Carboxylate (Dimethylamino) Methylferrocenec ... 

PQQ-dependent glucose dehydrogenase, EC 1.1.99.17 50 mM glucose 0.05-2 mM ferrocene monocarboxylic acid, 0.05-2 mM ferrocene methanol, 0.05-2 mM p-amniophenol oxidation [35]... 

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.

All chemicals were of analytical grade and were used as received. All solutions were prepared with deionized water. 2.7, 5.4 and 10.8 mg ferrocene methanol (ABCR GmbH Co. KG, Karlsruhe, Germany) was dissolved in 0.5 ml ethanol and filled up to 25 ml with 0.1M sodium sulfate (Carl Roth GmbH Co, Karlsruhe, Germany). Three different concentrations of ferrocene methanol were used (in mM) 0.5, 1.0 and 2.0. 

Mount the UME on the SECM setup. Place a smooth glass surface (microscope slide) in the electrochemical cell bellow the UME and add the mediator solution (2mM ferrocene methanol (Fc) in 0.1 M sodium sulfate) to the electrochemical cell. 

Fig. 51.1. Schematic of the feedback method of measuring heterogeneous standard rate constant at titantium nitride thin film. The UME is poised at a potential where ferrocene methanol is oxidized at a diffusion-controlled rate (Et = 0.4 V). The substrate is biased at a potential so that it reduces the species being produced at the UME, thus controlling the feedback effect.

Fig. 51.4. Normalized feedback current-distance curves obtained with a 25 pm Pt UME in ImM ferrocene methanol in 0.1M Na2S04. The substrate potential was varied to control the feedback effect (1) 150 mV, (2) 100 mV, (3) 50 mV, (4) OmV, (5) —50 mV, (6) —100 mV, (7) —150 mV and (8) —200 mV vs. Ag/AgCl reference electrode. (9) and (10) are the limiting curves for conductor and insulator substrate, respectively. The tip was held at 0.4 V where the oxidation was diffusion-controlled.

Figure 17. Schematic representation of the affinity biosensor construction and the proposed operational principle and voltammetric traces for affinity sensor signalling a biotin-functionalized surface before (A) and after (B) target protein (antibiotin IgG-HRP) association and precipitation reaction steps. Voltammetric measurements were performed in 0.1 M phosphate buffer (pH 7.0),containing 0.1 mM ferrocene methanol as a signal tracer. Inset charge coupled device (CCD) camera images of a sensor surface upon signalling reactions (Adapted from Refs. [176] [177]).

Fig. 4 Scanning electrochemical microscopy images of 200 xm x 200 jjim areas on mi-cropatterned conductive glass slides the columns (from left to right) correspond to electrode areas featiming a thin-film overlayer of open or cavity-modified squares. The rows correspond to the following redox mediators (A) 2 mM ferrocene-methanol (diameter 4.5 A) (B) 3 mM RuCNHsle " (diameter 5.5 A) (C) 5 mM Fe(l,10-phenanthroline)3 (diameter 13A) piat = 1.0V, i = 3.5nA and (D) 10 mM Fe(4,7-phenylsulfonate-l,0-phenanthroline) (diameter 24A). All solutions contained 0.1 M KNO3 electrolyte. Adapted from [22]...

A photoswitchable bioelectrocatalytic device based on a similar azo-SAM with a PAA-g-CD coating was designed, able to catalyze the oxidation of glucose by glucose oxidase upon inclusion of ferrocene-methanol (Fc), as electron mediator, into the available free CD units of the PAA-g-CD film. Photoreversible activation and deactivation of the enzyme could be obtained by UV/Vis light irradiation. The immobilization and release of the redox polymer was driven by the trans-cis photoisomerization of the azobenzene units in the SAM. ... 

Fig. 1 Cyclic voltammetry of the catalysis of the electrochemical oxidation of / -D-glucose by glucose oxidase with ferrocene methanol as the cosubstrate. Dashed line ferrocene methanol (0.1 M) alone the same trace is obtained in the presence of glucose oxidase (27 pM) with no glucose present or in the presence of glucose (0.5 M) with no gl ucose oxidase present. Dotted and full lines ferrocene methanoi (0.1 mM) + giucose oxidase(27 pM) + glucose (0.5 M) at pH 4.5 (acetate buffer) and 6.5 (phosphate buffer), respectively. Ionic strength 0.1 M. Scan rate ...

Fig. 3 Cyclic voltammetric analysis of the kinetics of an homogeneous redox enzyme reaction using a reversible one-electron mediator as the cosubstrate, taking as example the catalysis of the electrochemical oxidation of j8-D-glucose by glucose oxidase (6.5 pM) with ferrocene methanol as the cosubstrate at pH = 7 (ionic strength 0.1 M, temperature ...

Repeat of the same land of experiments at other pHs shows that the rate constant 3 varies with pH in a sigmoid manner, as shown in Fig. 5 (whereas k2 and red practically insensitive to this factor). Figure 5 also displays the pH-dependent values ofks obtained with other cosubstrates than ferrocene methanol [35, 36], The dependency of k upon pH is due to the fact that, as with many redox enzymes, the prosthetic group of glucose oxidase does not merely exchange electrons with the cosubstrate but both electrons and protons. Analysis of the... 

Fig. 9 Binding of polyclonal antibody glucose oxidase conjugates (in the presence of0.1 M glucose and 0.1 mM ferrocene methanol) to a saturated monolayer of whole antigen deposited on the surface of a GC rotating disk electrode. Variation of the coverage with time at three rotation rates (G 1600,...

From the intercept of the secondary plot shown in Fig. 11(c), it follows that fcsFgCp = 5 X 10 mol cm sec . Eg may be derived from an experiment where the ferrocene methanol cosubstrate is added in the solution so as to render negligible the contribution of the attached cosubstrate to the catalytic current. Applying the analysis developed in Sect. 13.3.1 leads to Fg = 3.5 x 10 mol cm and... 

Once [Q] has been estimated, can be derived from the intercept of the primary plot (Fig. 12c). The value thus found, 1.5 x 10 sec, is smaller than the value for ferrocene methanol in solution, 1.2 x 10 sec (regardless of the presence of PEG chains in solution) and larger than in the case where the ferrocenes are... 

Fig. 14 Cyclic voltammetry of glucose oxidase coated glassy carbon electrodes with an increasing number (N) of monolayers in a pH 8 phosphate buffer (ionic strength 0.1 M) solution containing 0.5 Mglucose. Scan rate 0.04 V sec. Temperature 25 °C. (a) Voltammograms for 0.2 mM ferrocene methanol mediator from bottom to top N = 0,2, 4, 6, 8, and 10 (for clarity, the odd numbers of monolayers are not represented).

How the above treatment may be applied to the full analysis of experimental data is illustrated in Fig. 15 with the example of glucose oxidase with ferrocene methanol as the cosubstrate. The results obtained with three different electrode coatings are displayed in the figure, successively, 10 inactivated layers plus one active layer (Fig. 15a), 10 active layers (Fig. 15b) and a series with 5 inactivated plus 1-5 active layers (Fig. 15c). Several parameters are know independently, namely, the three rate constants, 3 = 1.2 X 10 sec , ki = 700 sec , and kjed = 10 M-l sec Fg is also known (see the pertinent values in the caption of Fig. 15). From the size of the various proteins involved, it can be estimated that fy = 5/6. The diffusion coefficient in the solution, D = 6.7 10 cm sec . ... 

Fig. 15 Variations of the catalytic plateau current in the cyclic voltammetry of ferrocene methanol in the presence of 0.5 M glucose in a phosphate buffer (pH = 8, ionic strength = 0.1 M), at 25 °C and a scan rate of 0.04 V sec at three different electrodes, (a) Electrode coated with 10 inactivated (Fg = 2.0 X 10 mol cm ) and 1 active (F° = 1.5 x 10 mol cm ) glucose oxidase monomolecular layers, (b) Electrode coated with 1-10 active glucose oxidase monomolecular layers (F = 1.5 x 10 mol cm ).

Fig. 16 Cyclic voltammetry of ferrocene methanol 0.2 mM in the absence of glucose and in pH 8 phosphate buffer (ionic strength 0.1 M) at a bare electrode ( ) and at a glucose oxidase electrode coated with 12 monolayers...

The products of the reaction they catalyze may inhibit many enzymes through Michaelis-Menten kinetic retroaction. Protons, which are involved as products or reactants in a number of cases, may also influence the enzymatic kinetics. The course of the reaction may therefore be altered by the attending production or depletion of protons. It is thus interesting to examine whether these phenomena may be revealed by the effect they might have on the electrochemical responses of immobilized enzyme films under appropriate conditions [92]. A first clue of the existence of such inhibition effects is the observation of hysteresis behaviors of the type shown in Fig. 18(a) where data obtained with 10 glucose oxidase monolayers with ferrocene methanol as cosubstrate have been taken as example. In the absence of inhibition, the forward and reverse traces should be exactly superimposed. Hysteresis increases to the point of making a peak appear on the forward trace as the scan rate decreases and as the concentration of the buffer decreases, as illustrated in Fig. 18c, c , c , c by comparison with Fig. 18(a). 

If the enzymatic reaction produces protons, as is often the case with oxidases, the local variations of pH due to insufficient buffering may locally modify the rate of the various reactions involved and therefore influence the electrochemical response of the system. For example, in the case of glucose oxidase with ferrocene methanol as cosubstrate, the main effect of pH is on 3 [35] ... 

Fig. 18 Cyclic voltammetry of the catalysis of glucose oxidation at a glassy carbon disk electrode coated with 10 glucose oxidase monolayers in the presence of glucose and ferrocene methanol in pH 8.0 phosphate buffer (ionic strength, 0.1 M). Temperature 25 °C.

Considering as example the case of glucose oxidase and ferrocene methanol, the problem is simplified by the fact that the diffusion coefficients inside and outside the film are the same except for P where 5p = Dp/D = 0.6. 

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