Diffusion Coefficient Of Fc Research Articles

Macrocycles Bearing Ferrocenyl Pendants and their Electrochemical Properties upon Binding to Divalent Transition Metal Cations.

Metal complexes of Cu2+ , Co2+ , Cd2+ , Zn2+ , and Ni2+ formed with the ligands [Fc(cyclen)] (1) and [Fc(cyclen)2 ] (2) (Fc=ferrocene, cyclen=1,4,7,10-tetraazacyclododecane) are synthesised and characterised. The X-ray structure of the Cu2+ complex of 2, Fc([Cu(cyclen)(CH3 CN)]2 (ClO4 )4 , is reported, and shows that the two positively charged Cu2+ -cyclen units have a coordination number of five, adopting a distorted trigonal-bipyramidal configuration. The Cu2+ -cyclen units are arranged in a trans-like configuration with respect to the Fc group, presumably to minimise electrostatic repulsion. The voltammetric oxidation of the free ligands 1 and 2 in a CH2 Cl2 /CH3 CN (1:4) solvent mixture yields two closely spaced oxidation processes. Both electron-transfer steps are associated with the ferrocenyl moiety, implying strong communication between the cyclen nitrogen atoms and the ferrocenyl group. In contrast, cyclic voltammograms display only a simple reversible one-electron process if 1 and 2 are complexed with Cd2+ , Cu2+ , Zn2+ , Ni2+ , or Co2+ . Binding of these metal ions produces a significant shift in the reversible midpoint potential (Em ). Except for Ni2+ , Em is linearly proportional to the charge density of the transition metal ion, demonstrating that 1 and 2 may undergo redox switching. The diffusion coefficients of Fc, DmFc, 1 and 2, and their metal ion complexes correlate well with their molecular weights.

Electrochemical Study of Ferrocene and Anthracene using Ultramicroelectrode in Chloroform over the Temperature Range of 25–50°C

In this study, electrochemical experiments were carried out in chloroform using ferrocene (Fc) or anthracene (An). We performed cyclic voltammetry (CV) on Fc and An in chloroform containing either tetrabutylammonium perchlorate (TBAP) or tetrabutylammonium hexafluoro‐phosphate (TBAPF6 ) over the temperature range of 25 to 50°C. The resulting pattern of CVs, half‐wave potential ( E 1 /2), diffusion coefficient of Fc and An, steady‐state current, solution viscosity, and long‐term stabilities were studied.

Electrochemical behaviour of ferrocene in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate, EMIMBF4, at 298 K

Electrochemical oxidation of ferrocene (Fc) at platinum and glassy carbon electrodes in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate, EMIMBF4, has been studied by cyclic voltammetry (CV), convolutive potential sweep voltammetry (CPSV), chronopotentiometry (CP) and chronoamperometry (CA).On both electrodes, the electro-oxidation of ferrocene to ferrocenium (Fc+) takes place in a quasi-reversible electrochemical mode. The intrinsic rate constant of charge transfer, k0, and the charge transfer coefficient, α, have been calculated for the first time in the mentioned ionic liquid, by simulation of the cyclic voltammograms, logarithmic analysis of the convoluted curves and from the steady-state current potential curves by applying the Gauss–Newton non-linear square method. The diffusion coefficient of Fc has been also calculated by CV, CPSV, CP and CA. A two-way analysis of variance, ANOVA, has shown that with a 95% confidence level, there are no significant differences between the diffusion coefficients obtained with both electrodes by the different techniques.

Consistent diffusion coefficients of ferrocene in some non-aqueous solvents: electrochemical simultaneous determination together with electrode sizes and comparison to pulse-gradient spin-echo NMR results

Cyclic voltammetry data recorded at disk macro- (millimeter dimension) and microelectrodes (10 and 100 μm) at various scan rates are used to simultaneously determine the diffusion coefficient D of ferrocene (fc) and the electroactive surfaces A and/or radii r of the electrodes. A case study with three electrodes of different sizes in CH3CN- and propylene carbonate (PC)-based electrolytes shows the possibly large effect of incorrect D values. Diffusion coefficients of fc are determined for PC, CH3CN, CH2Cl2, DMF, and DMSO electrolytes and (except for PC) compared to those from pulse-gradient spin-echo nuclear magnetic resonance experiments in the presence of supporting electrolyte in the respective deuterated solvents. The dependence of D fc on solvent viscosity is shown to follow the Stokes–Einstein relation.

Voltammetric Currents in Room Temperature Ionic Liquids Can Reflect Solutes Other Than the Electroactive Species and Are Influenced by Carbon Dioxide

The effects of such solutes such as halides and water on the physical properties of room temperature ionic liquids (RTILs) have been extensively studied. This work examines the effect of the solute carbon dioxide on the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide ([C2mim][NTf2]) and its influence on the electrochemical characterization of the important redox couple ferrocene/ferrocenium (Fc/Fc+). The system was studied using cyclic voltammetry, chronoamperometry, and electron spin resonance (ESR) spectroscopy. Addition of 100% CO2 to a solution of Fc in [C2mim][NTf2] resulted in a substantial increase in both the limiting oxidative current and diffusion coefficient of Fc. Arrhenius plots of Fc diffusion coefficients in the pure and CO2-saturated ionic liquid revealed a decrease in activation energy of translational diffusion from 29.0 (+/- 0.5) kJ mol(-1) to 14.7 (+/- 1.6) kJ mol(-1), suggesting a reduction in the viscosity of the ionic liquid with addition of CO2. ESR spectroscopy was then used to calculate the rotational correlation coefficients of a probe molecule, 2,2,6,6-tetramethyl-1-piperinyloxyl (TEMPO), to add supporting evidence to this hypothesis. Arrhenius plots of rotational correlation coefficients in the pure and CO2-saturated ionic liquid resulted in a similar drop in activation energy from 28.7 (+/- 2.1) kJ mol(-1) to 18.2 (+/- 5.6) kJ mol(-1). The effect of this solute on the ionic liquid [C2mim][NTf2] and on the electrochemical measurements of the Fc/Fc+ couple emphasizes the necessity of fastidious sample preparation, as it is clear that the voltammetric currents of the electroactive species under study are influenced by the presence of CO2 in solution. The voltammetric response of the electroactive species in RTILs cannot be assumed to be independent of other solutes.

Cyclic voltammetry investigation of diffusion of ferrocene within propylene carbonate organogel formed by gelator

Propylene carbonate organogel containing LiClO 4 was formed in the presence of gelator bis-(4-stearoylaminophenyl) methane (BSAPM). The electrochemical behavior and diffusion of ferrocene (Fc) and ferricenium (Fc +) entrapped within the organogel was investigated by cyclic voltammetry. The Fc molecules still show redox activity within the organogels in comparison with corresponding solutions of propylene carbonate containing LiClO 4. The shape of the cyclic voltammograms of the Fc electrooxidation in organogel was similar to that in corresponding solutions. The results indicated that redox reactions of Fc/Fc + were a quasi-reversible process of diffusion-controlled single electron transfer in organogels. The diffusion coefficients of Fc and Fc + in organogels decreased with an increase of the concentration of gelator BSAPM, but increased with an increase of temperature. The temperature dependence of the diffusion coefficient in organogels followed classical Arrhenius equation. The activation energy in organogels was found of no difference from that in corresponding solutions.

Thermoresponsive Poly‐N‐isopropylacrylamide Gels Modified with Colloidal Gold Nanoparticles for Electroanalytical Applications. 1. Preparation and Characterization

AbstractPreparation and spectroscopic and electrochemical characterization of thermoresponsive poly‐N‐isopropylacrylamide (NIPA) hydrogels modified with gold colloidal nanoparticles is described. Gold nanoparticles of various sizes in the range from 2.7 to 18 nanometers in diameter were synthesized and introduced to NIPA polymeric gels during the polymerization process. Dry, ground polymers were reswelled by solutions of well‐known and well‐controlled composition. Such polymeric gels undergo discontinuous reversible volume phase transition in response to temperature increase; this results in a release of up to 90% of solvent from the polymeric matrix. The potential window was determined in NIPA gels modified with gold nanoparticles and compared to that in pure NIPA gels. Diffusion coefficients of electroactive probes in NIPA gels modified with gold and in expelled solutions were determined. It was found that diffusion coefficients of Fc(MeOH)2 in swollen neat NIPA and NIPA‐gel modified with gold nanoparticles are identical within experimental error and they are approximately 10–30% smaller than those in aqueous solutions. Concentration of Fc(MeOH)2 in expelled solutions was up to 30% smaller than in swollen gel. Mole fractions of electroactive probes in collapsed gels and expelled solutions were also determined.

Effect of the Volume Phase Transition on Diffusion and Concentration of Molecular Species in Temperature‐Responsive Gels: Electroanalytical Studies

AbstractEffect of the volume phase transition on the diffusion and concentration of molecular probes was studied in temperature‐responsive polymeric hydrogels. Results were compared for two gels, poly(N‐isopropylacrylamide), NIPA, and poly(N‐isopropylacrylamide‐co‐acrylic acid), NIPA‐AA. These gels undergo discontinuous, reversible volume phase transition as a response to temperature changes; this transition results in release of approximately 40% and 90% of the solution/solvent from NIPA‐AA and NIPA gel phases, respectively. 1,1′‐Ferrocenedimethanol, Fc(MeOH)2, served as an electroactive and spectroscopic probe. Diffusion of Fc(MeOH)2 was investigated using voltammetry and chronoamperometry with platinum disk electrodes, while UV‐vis supported electroanalytical techniques to determine the concentration of that probe in the gel. The diffusion coefficient of Fc(MeOH)2 was inversely proportional to the concentration of the polymer in both NIPA and NIPA‐AA swollen gels for temperatures below the volume phase transition, and differed from that in an aqueous solution. The diffusion coefficient was 16 and 46% smaller than that in an aqueous solution for 3% NIPA and NIPA‐AA gels at 25 °C, respectively. As a result of the volume phase transition, after the gel collapses, no significant changes in the diffusion coefficient values were observed for NIPA‐AA gels. However, for NIPA gels, the diffusion coefficient of a probe decreases approximately two orders of magnitude. The volume phase transition also resulted in a change of the concentration of a probe in the collapsed gel phase. The concentration of Fc(MeOH)2 in collapsed NIPA gel was as much as 4.5 times higher than that in the original swollen gel, while for NIPA‐AA gel that increase in concentration was only 20%.

Diffusion and Concentration of Molecular Probes in Thermoresponsive Poly(N-isopropylacrylamide) Hydrogels: Effect of the Volume Phase Transition

Poly(N-isopropylacrylamide), NIPA, thermoresponsive hydrogels with well-defined concentrations of an electroactive probe, 1,1'-ferrocenedimethanol, Fc(MeOH)2, were prepared. The discontinuous reversible volume phase transition of such gels occurs at 32 +/- 1 degrees C and results in a release of approximately 93% of the solution from the polymeric network. Transport of Fc(MeOH)2 in both swollen and collapsed gels was studied using steady-state voltammetry and chronoamperometry at platinum microelectrodes. The diffusion coefficient of Fc(MeOH)2 in collapsed gels was approximately 2 orders of magnitude smaller than that in swollen gels. UV/vis spectroscopic studies showed that for 3.0% NIPA gel, the concentration of Fc(MeOH)2 in the collapsed phase was approximately 6 times higher than that in released solution and 4.5 times higher than in the original swollen gel.

Mass Transport in Thermoresponsive Poly(N-isopropylacrylamide-co-acrylic acid) Hydrogels Studied by Electroanalytical Techniques: Swollen Gels

Steady-state voltammetry and chronoamperometry at microelectrodes were used to study mass transport properties of temperature sensitive poly(N-isopropylacrylamide-co-acrylic acid), NIPA-AA, hydrogels. 1,1‘-Ferrocenedimethylanol, Fc(MeOH)2, and 2,2,6,6-tetramethyl-1-piperidinyloxy, TEMPO, were used as electroactive probe molecules. The activation energy of diffusion of Fc(MeOH)2 in aqueous solutions and in NIPA-AA hydrogels was found to be in the range of 17−19 kJ/mol, which suggests that the local microscopic viscosity does not change significantly because of the gelation process, although the macroscopic viscosity of the gels is extremely large. It was found that the diffusion coefficients of Fc(MeOH)2 and TEMPO in NIPA-AA hydrogels in their swollen state are approximately 20%−50% smaller than those in aqueous solutions, and that the diffusion coefficient of probe molecules in these gels is inversely proportional to the concentration of copolymer in the hydrogels. The “obstruction effect” and “hydration ...