Ferrocene Dimethanol Research Articles

The Effect of Ionic Liquid Covalent Bonding to Sol‐Gel Processed Film on Ion Accumulation and Transfer

AbstractAccumulation of electroactive anions into a silicate film with covalently bonded room temperature ionic liquid film deposited on an indium tin oxide electrode was studied and compared with an electrode modified with an unconfined room temperature ionic liquid. A thin film containing imidazolium cationic groups was obtained by sol‐gel processing of the ionic liquid precursor 1‐methyl‐3‐(3‐trimethoxysilylpropyl)imidazolium bis(trifluoromethylsulfonyl)imide together with tetramethylorthosilicate on the electrode surface. Profilometry shows that the obtained film is not smooth and its approximate thickness is above 1 μm. It is to some extent permeable for a neutral redox probe – 1,1′‐ferrocene dimethanol. However, it acts as a sponge for electroactive ions like Fe(CN)63−, Fe(CN)64− and IrCl63−. This effect can be traced by cyclic voltammetry down to a concentration equal to 10−7 mol dm−3. Some accumulation of the redox active ions also occurs at the electrode modified with the ionic liquid precursor, but the voltammetric signal is significantly smaller compare with the bare electrode. The electrochemical oxidation of the redox liquid t‐butyloferrocene deposited on silicate confined ionic liquid film is followed by the expulsion of the electrogenerated cation into an aqueous solution. On the other hand, the voltammetry obtained with the electrode modified with t‐butyloferrocene solution in the ionic liquid precursor exhibits anion sensitive voltammetry. This is explained by anion insertion into the unconfined ionic liquid deposit following t‐butylferricinium cation formation.

Mass Transport and Electrode Accessibility Through Periodic Self-Assembled Nanoporous Silica Thin Films

Ordered nanoporous silica films have attracted great interest for their potential use to template nanowires for photovoltaics and thermoelectrics. However, it is crucial to develop films such that an electrode under the nanoporous film is accessible to solution species via facile mass transport through well-defined pores. Here, we quantitatively measure the electrode accessibility and the effective species diffusivity for nearly all the known nanoporous silica film structures formed by evaporation-induced self-assembly upon dip-coating or spin-coating. Grazing-angle of incidence small-angle X-ray scattering was used to verify the nanoscale structure of the films and to ensure that all films were highly ordered and oriented. Electrochemical impedance spectroscopy (EIS) was then used to assess the transport properties. A model has been developed that separates the electrode/film kinetics and the film transport properties from the film/solution interface and bulk solution effects. Accounting for this, the accessible area of the nanoporous film coated FTO electrode (1-theta) is obtained from the high-frequency data, while the effective diffusivity of the ferrocene dimethanol (D(FDM)) redox couple is obtained from intermediate frequencies. It was found that the degree of order and orientation in the film, in addition to the symmetry/topology, is a dominant factor that determines these two key parameters. The EIS data show that the (211) oriented double gyroid, (110) oriented distorted body center cubic, and (211) distorted primitive cubic silica films have significant accessibility (larger than 26% of geometric area). However, the double-gyroid films showed the highest diffusivity by over an order of magnitude. Both the (10) oriented 2D hexagonal and (111) oriented rhombohedral films were found to be highly blocking with only small accessibility due to microporosity. The impedance data were also collected to study the stability of the nanoporous silica films in aqueous solutions as a function of pH. The distorted primitive silica film showed much faster degradation in pH 7 solution when compared to a blocking film such as the 2D hexagonal. However, silica films maintained their structure at pH 2 for at least 12 h.

New approach to a collodion membrane composite via fluorocarbon polymer (Nafion) blending in terms of a diffusion coefficient of redox substances and transport properties

Nafion (fluorocarbon polymer) and collodion blended with Nafion in the ratio of CN5:5 composite solutions were used to produce thin membrane films on Au electrodes. It was found that the transport properties of water and KCl, such as the filtration coefficient, Lp, reflection coefficient, σ and salt permeation, ω, across the two composite collodion (C) and Nafion (N) membranes depended on the quantities of the Nafion component. Moreover, the study indicated that a better diffusion coefficient of redox substances can be achieved by blending the Nafion solution with an ionic group to collodion solution compared to Nafion only. The uptake of neutral species of ferrocenedimethanol (FcDM), positively charged species of methyl viologen (MV 2+), and negatively charged potassium ferrocyanide [Fe(CN) 6] 4− ions were studied by cyclic voltammetry and chronopotentiometry. The diffusion coefficient of MV 2+ and FcDM in blended Nafion:collodion showed higher values compared to that in Nafion alone. The diffusion of positively charged species, MV 2+, was decreased in the membrane matrix compared to the neutral species, FcDM. This may be attributed to the existence of an interaction between SO 3 − functional groups of the fluorocarbon polymer and MV 2+ that led to mobility restriction of MV 2+ compared to FcDM. The diffusion of the [Fe(CN) 6] 4− species was not clearly observed due to the electrostatic repulsion effect between SO 3 − functional groups of the flourocarbon polymer and the negative species, [Fe(CN) 6] 4−.

Characterization of an organic phase peroxide biosensor based on horseradish peroxidase immobilized in Eastman AQ

Due to their frequent occurrence in food, cosmetics and pharmaceutical products, and their poor solubility in water, the detection of peroxides in organic solvents has aroused significant interest. For diagnostics or on-site testing, a fast and specific experimental approach is required. Although aqueous peroxide biosensors are well known, they are usually not suitable for nonaqueous applications due to their instability. Here we describe an organic phase biosensor for hydrogen peroxide based on horseradish peroxidase immobilized in an Eastman AQ 55 polymer matrix. Rotating disc amperometry was used to examine the effect of the solvent properties, the amount and pH of added buffer, the concentration of peroxide and ferrocene dimethanol, and the amount of Eastman AQ 55 and of enzyme on the response of the biosensor to hydrogen peroxide. The response of the biosensor was limited by diffusion. Linear responses (with detection limits to hydrogen peroxide given in parentheses) were obtained in methanol (1.2 microM), ethanol (0.6 microM), 1-propanol (2.8 microM), acetone (1.4 microM), acetonitrile (2.6 microM), and ethylene glycol (13.6 microM). The rate of diffusion of ferrocene dimethanol was more constrained than the rate of diffusion of hydrogen peroxide, resulting in a comparatively narrow linear range. The main advantages of the sensor are its ease of use and a high degree of reproducibility, together with good operational and storage stability.

Characterization of charged film of fluorocarbon polymer (Nafion) and blended fluorocarbon polymer (Nafion)/Collodion composite membranes by electrochemical methods in the presence of redox substances. V

In order to get a better understanding regarding the structure of charged film of membranes, two kinds of the composite Collodion membrane (C), and Nafion one (N) were prepared and characterized by systematic and comparative studies. The Nafion (fluorocarbon polymer) and Collodion blended with Nafion in the ratio of (CN5:5) composite solutions were used to produce thin membrane films on Au electrodes. The present study indicated that better diffusion coefficient of redox substances can be achieved by blending the Nafion solution with ionic group to Collodion solution compared Nafion only. Diffusion coefficient of MV 2+ and FcDM in the blended Nafion/Collodion showed higher values compared to that Nafion. The uptake of neutral species of ferrocenedimethanol (FcDM), positively charged species of methyl viologen (MV 2+) and negatively charged of potassiumferrocyanide, [Fe(CN) 6] 4− ions were studied by cyclic voltammetry (CV), chronopotentiometry (CP) and chronocoulometry (CC). The diffusion coefficient values of MV 2+ of the blended composite, CN5:5 membranes are about twice (0.43 × 10 −6 cm 2/s) that of Nafion based membrane (0.27 × 10 −6 cm 2/s). While the diffusion coefficients of FcDM of the blended, CN5:5 and Nafion based membranes are in the order of 2.4 and 1.8 × 10 −6 cm 2/s, respectively. This means that the diffusion of positively charged species, MV 2+ was decreased in the membrane matrix compared to neutral species, FcDM. It also indicates that the concentrations of the MV 2+ are higher than that of the neutral species, FcDM, in both blended (CN5:5) and Nafion membranes. This may attributed to the existence of interaction between SO 3 − functional groups of fluorocarbon polymer and MV 2+ that led to mobility restriction of MV 2+compared to neutral FcDM one, i.e. diffusion of MV 2+ was decreased. It was found that the negatively species, [Fe(CN) 6] 4− exist in surface of the blended membrane (CN5:5) slightly, but not in Nafion one due to the electrostatic repulsion effect between SO 3 − functional groups of flourocarbon polymer and negatively species, [Fe(CN) 6] 4−. This means that diffusion of [Fe(CN) 6] 4− species was not clearly observed. As a whole, the blended membranes indicated membrane performance comparable to the commercial ion-exchange membranes.

Incorporation of 1,1′-ferrocenedimethanol into polyphenosafranin and a binding interaction between them

This paper describes the electrocatalytic effect of polyphenosafranin films on the oxidation of 1,1′-ferrocenedimethanol (FM). Electrode modification with the polymer raised the voltammetric current of FM in its dilute solutions markedly. This effect arose from the preconcentration of FM on electrode surfaces. A partition coefficient of about 2.3×10 4 was obtained for the FM distribution between the polymer film and an acidic aqueous solution. Although adding 1-propanol to the solution lowered it, a sharp drop observed at low 1-propanol concentrations cannot be ascribed to the medium effect on FM. A positive shift in the FM redox potential due to incorporation indicated that the partition coefficient of the oxidized form FM + was about 400 times lower than that of the uncharged form. Since the surface concentration of FM more than doubled upon reducing the polymer, no donor–acceptor interaction may play a major role in determining a binding interaction between FM and the polymer. The pH dependence of the surface concentration suggested that the protonated primary amino group of the polymer strengthens the chemical interaction. Since FM formed an insoluble 1:1 complex with monomeric phenosafranin in acidic solutions, one can safely state that the polymer interacts specifically with FM, thus reducing its activity coefficient in the polymer phase greatly.

Electrochemically mediated enzyme reaction of polyethyleneglycol-modified galactose oxidase in organic solvents

This paper describes an electrochemically mediated enzyme reaction of polyethyleneglycol (PEG)-modified galactose oxidase (GAO) in organic solvents as well as in an aqueous solution. Catalytic currents were investigated in the presence of ferrocene derivatives as mediators and PEG-modified GAO in several organic solvents. The catalytic current due to the mediated enzyme reaction was obtained in acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide and dimethylsulfoxide (DMSO). Stability tests of PEG-modified GAO in organic solvents demonstrated that the initial Ik/Id value was highest in acetonitrile; however, it gradually decreased. The PEG-modified GAO was more stable in DMSO. Reactivities of several mediators were investigated. Although a positively charged mediator indicated high reactivity in the aqueous solution, non-charged mediators such as ferrocene dimethanol and n-butyl ferrocene showed the highest activity in organic solvents. Substrate specificity demonstrated that the catalytic activity for benzyl alcohol in acetonitrile was greater than in aqueous solution. The effect of water content in acetonitrile was investigated. The catalytic activity decreased with the increase in water content.

Electrochemical Behaviors of Ferrocene Derivatives at an Electrode Modified with Terminally Substituted Alkanethiol Monolayer Assemblies

Abstract Self-assembled monolayers of 11-mercapto-1-undecanol (MUO), 11-mercaptoundecanoic acid (MUA), and 11-amino-1-undecanethiol (AUT) were formed on a gold disk electrode. The effects of the terminal charges of these monolayers on the redox responses of 1,1′ -ferrocenedimethanol (FcDM), (ferrocenylmethyl)trimethylammoniun bromide (FcMA) and ammonium ferrocenesulfonate (FcSA) were evaluated by using voltammetric (CV) techniques. The CV responses of FcDM and FcMA decreased in the order of MUA/Au (MUA modified gold electrode), MUO/Au, and AUT/Au. In contrast, the CV response of FcSA increased in the order of MUA/Au, MUO/Au, and AUT/Au. From these results, the effects of the terminal charges on the CV responses were measured in relation to the diffuse layer potential and the electrostatic interaction between the terminal unit and redox species.