Characterization of proteins by means of their buffer capacity, measured with an ISFET-based coulometric sensor-actuator system

Proteins form the specific selector in many biochemical sensors. A change in one of the properties of such a protein has to be detected by an appropriate transducer, which completes the biochemical sensor. One of these properties is the buffer capacity of a protein. If the binding of a substance to a protein can significantly change the proton binding, which accounts for the buffer capacity of proteins, the detection of this changed buffer capacity enables the construction of a new type of biosensor.\ud \ud It will be shown that the buffer capacity can be measured with an ISFET-based sensor—actuator device. The alternating generation of protons and hydroxyl ions by alternating current coulometry at a porous noble metal actuator electrode causes an associated small pH perturbation, which is detected by the underlying pH-sensitive ISFET. The amplitude of the measured signal is a function of the buffer capacity of the solute, in which proteins can be present (or these proteins can be adsorbed in the porous actuator electrode of the device). A model describing the transfer function from the electrical input signal of the actuator to the resulting chemical output, which is subsequently detected by the ISFET pH sensor, is presented. Preliminary results of the measured buffer capacity of ribonuclease and lysozyme are presented

Determination of water in organic solvents by flow-injection analysis with Karl Fischer reagent and a biamperometric detection system

A flow-injection system with a biamperometric flow-through detector provided with two platinum plate electrodes was tested for the determination of water with a two-component pyridine-free Karl Fischer reagent. The response was shown to be linear in the concentration range 0.03–0.11% water in methanol, ethanol or 2-propanol, with methanol as the carrier solvent. The maximum sampling frequency was about 150 samples per hr. It appeared to be possible to introduce a membrane separation step, thus allowing for the determination of water in fouled process streams. To avoid direct contact between the Karl Fischer solution and the pumping tubes, and thus extend the lifetime of the tubes, an indirect delivery system, based on replacement of the solution by pumped silicone oil, was also applied

The Electrochemical Oxidation of Substituted Catechols

The oxidation of substituted catechols was studied by cyclic voltammetry, chronoamperometry, rotating ring‐disk electrode, and coulometry. The results showed that the quinones that were formed from the oxidation of substituted catechols reacted with the basic forms of the starting material to yield the dimeric product. These products were generally unstable and rapidly polymerized or underwent some other irreversible reaction to form an electroinactive product. For 3,4‐dihydroxyacetophenone and propriophenone, the intermediate was stable long enough to be observed in cyclic voltammetry. The rate of the coupling reaction was found to correlate well with the Hammett ρ‐σ parameters and indicated that there was substantial negative charge in the transition state. Finally, an analysis of the coulometric n‐values along with the iat1/2/C values indicated that the initial coupling product was a diphenyl ether. Analysis of the coulometry products showed extensive polymerization

Switchable Imbibition in Nanoporous Gold

Spontaneous imbibition enables the elegant propelling of nano-flows because of the dominance of capillarity at small length scales. The imbibition kinetics are, however, solely determined by the static geometry of the porous host, the capillarity, and the fluidity of the imbibed liquid. This makes active control particularly challenging. Here, we show for aqueous electrolyte imbibition in nanoporous gold that the fluid flow can be reversibly switched on and off through electric potential control of the solid-liquid interfacial tension, i.e. we can accelerate the imbibition front, stop it, and have it proceed at will. Simultaneous measurements of the mass flux and the electrical current allow us to document simple scaling laws for the imbibition kinetics, and to explore the charge flow dynamics in the metallic nanopores. Our findings demonstrate that the high electric conductivity along with the pathways for ionic and/or fluid transport render nanoporous elemental gold a versatile, accurately controllable electro-capillary pump and flow sensor for minute amounts of liquids with exceptionally low operating voltages.Comment: 12 pages, 5 figure

Prussian Blue-coated interdigitated array electrodes for possible analytical application

Thin films of iron(III) hexacyanoferrate(II) (Prussian Blue) were electrochemically deposited on interdigitated array (IDA) electrodes, yielding systems which can be considered as chemiresistors in sensing alkali metal ion concentrations in an adjacent electrolyte. This is due to the fact that the conductivity of the film being measured by a steady-state current on application of a voltage to the two-fingered electrodes of the IDA depends on both the redox stare of the film and the cation concentration in the electrolyte. From the dependence of the steady-state current on the electrode (bias) potential at variable cation concentrations for different alkali metal ions and for mixtures of alkali metal ions, the possibilities of analytical application were elucidated. In addition, by using the methods of staircase coulometry and scanning conductivity, the electron diffusion coefficient De was determined as a function of the redox state of Prussian Blue. It is concluded that Prussian Blue-coated IDA electrodes are, in principle, suitable as chemiresistors for the determination of alkali metal ion concentrations with increasing selectivity in the series Li < Na < K < Rb < Cs

The anodic oxidation of bases in the solvent m-cresol

The oxidation of bases in the solvent m-cresol was investigated by polarography, voltammetry at the rotating platinum disc electrode and by chronopotentiometry. It was shown that the m-cresolate ion is the electroactive species in this reaction. The oxidation is a one-electron process giving a phenoxy radical. This phenoxy radical is converted in a chemical reaction of higher than first order, most likely to the dimer

金属置換クーロメトリーによる高感度タンパク質検出

この博士論文は内容の要約のみの公開（または一部非公開）になっています筑波大学 (University of Tsukuba)201

Catalytic Reduction of Bisulfite by Myoglobin/Surfactant Films

The voltammetry of bisulfite at a film formed with myoglobin was studied in aqueous solutions. A broad wave was observed for the reduction of bisulfite. Using controlled potential electrolysis, the reduction at potentials positive of the FeII/FeIwave formed dithionite exclusively. As the potential approached the region for the FeII/FeI reduction, bisulfite was reduced primarily to HS−. Even at the negative potentials, some dithionite was still formed, which could then be electrochemically reduced to thiosulfate. Analysis of the formation of HS−, dithionite and thiosulfate during the electrolysis was consistent with the parallel formation of HS−and dithionite, the latter of which was reduced to thiosulfate. Thiosulfate was verified by chemical analysis of the products from controlled potential electrolysis of the solution, and dithionite was observed spectroscopically using spectroelectro−chemistry

Simultaneous Ejection of Six Electrons at a Constant Potential by Hexakis(4-ferrocenylphenyl)benzene

A simple synthesis of a dendritic hexaferrocenyl electron donor (5) is described in which six ferrocene moieties are connected at the vertices of the propeller of the hexaphenylbenzene core. The molecular structure of 5 is confirmed by X-ray crystallography. An electrochemical analysis along with redox titrations (which are tantamount to coulometry) confirmed that it ejects six electrons at a single potential

Catalysis of the Electroreduction of Allyl Chloride by Cobalt 2,2'-Bipyridine Complexes

The electrochemical reduction of allyl chloride is strongly catalyzed in the presence of cobalt complexes of 2,2′‐bipyridine. A prominent reaction product of the catalyzed reduction is 1,5‐hexadiene. Voltammetry, coulometry, and gas chromatographic data are presented and analyzed and a mechanistic scheme proposed to account for the catalytic action of the cobalt‐2,2′‐bipyridine complexes