Voltammetry and redox charge storage capacity of ferrocene-functionalized silica nanoparticles

Composites and Copolymers Containing Redox-Active Molecules and Intrinsically Conducting Polymers as Active Masses for Supercapacitor Electrodes—An Introduction

In this introductory report, composites and copolymers combining intrinsically conducting polymers and redox-active organic molecules, suggested as active masses without additional binder and conducting agents for supercapacitor electrodes, possibly using the advantageous properties of both constituents, are presented. A brief overview of the few reported examples of the use of such copolymers, composites, and comparable combinations of organic molecules and carbon supports is given. For comparison a few related reports on similar materials without intrinsically conducting polymers are included.

Delivery of Doxorubicin from Hyaluronic Acid-Modified Glutathione-Responsive Ferrocene Micelles for Combination Cancer Therapy

A combination of different chemotherapy approaches can obtain the best response for many cancers. However, the greatest challenge is the development of a nanoparticle formulation that can encapsulate different chemotherapeutic agents to achieve the proper synergetic chemotherapy for the tumor. Here, amphiphilic ferrocenium-tetradecyl (Fe-C₁₄) was constructed to form cationic micelles in an aqueous solution via self-assembly. Then, it was coated by hyaluronic acid (HA) through electrostatic interactions to generate HA-Fe-C₁₄ micelles. The HA-Fe-C₁₄ micelles were used to deliver doxorubicin (DOX), and it showed that the DOX could be released rapidly under a high-GSH tumor environment. The HA-Fe-C₁₄/DOX micelles were able to accumulate efficiently in tumor and showed significant anticancer effect both in vitro and in vivo. These results suggest that HA-Fe-C₁₄/DOX micelles are a useful drug delivery system that enhances synergic antitumor treatment effects.

Design of an inherently-stable water oxidation catalyst

While molecular water-oxidation catalysts are remarkably rapid, oxidative and hydrolytic processes in water can convert their active transition metals to colloidal metal oxides or hydroxides that, while quite reactive, are insoluble or susceptible to precipitation. In response, we propose using oxidatively-inert ligands to harness the metal oxides themselves. This approach is demonstrated by covalently attaching entirely inorganic oxo-donor ligands (polyoxometalates) to 3-nm hematite cores, giving soluble anionic structures, highly resistant to aggregation, yet thermodynamically stable to oxidation and hydrolysis. Using orthoperiodate (at pH 8), and no added photosensitizers, the hematite-core complex catalyzes visible-light driven water oxidation for seven days (7600 turnovers) with no decrease in activity, far exceeding the documented lifetimes of molecular catalysts under turnover conditions in water. As such, a fundamental limitation of molecular complexes is entirely bypassed by using coordination chemistry to harness a transition-metal oxide as the reactive center of an inherently stable, homogeneous water-oxidation catalyst.

A current challenge in the development of molecular water oxidation catalysts is to overcome their inherent susceptibilities to oxidative or hydrolytic degradation under turnover conditions in water. Here, the authors design an inherently-stable water oxidation catalyst using oxidatively-inert ligands to harness a reactive metal oxide.

Current response for a single redox moiety trapped in a closed generator-collector system: the role of capacitive coupling

A theoretical model is proposed to describe the steady-state average limiting current associated with a single redox moiety (ox or red) trapped in a closed generator-collector system along with excess supporting electrolyte. By "closed" we mean that neither solvent nor solutes can enter or leave the system. The potential difference, EOE - ERE, between the oxidizing electrode (OE) and the reducing electrode (RE) is maintained constant with the values of EOE and ERE chosen so that the operative faradaic electrode processes are very fast, i.e., red = ox + nETe(-) (kox = ∞) at the OE and ox + nETe(-) = red (kred = ∞) at the RE. Because there is only a single redox moiety the faradaic process occurs at only one electrode at a time while current at the other electrode is purely capacitive (we refer to this as capacitive coupling). We propose that a two-step process is required to transfer nETqe coulombs (qe is the absolute value of the elemental electronic charge). The first step is associated with diffusion (approximated as a random walk) of a single red moiety to the OE where it is oxidized to ox with a concomitant transfer of qstep1 (= nETqe/(1 + AOECOE/ARECRE)) coulombs; the second step is associated with the diffusion (random walk) of the newly formed single ox moiety to the RE with the concomitant transfer of qstep2 (= nETqe/(1 + ARECRE/AOECOE)) coulombs (ARE,AOE andCRE,COEare the areas (cm(2)) and differential capacitances (farads cm(-2)) of the corresponding electrodes). The total charge transferred in the two steps is nETqe(= qstep1 + qstep2). Transport of the redox moiety from one electrode to the other is accomplished by a random walk. The probability density function (pdf) and cumulative density function (CDF) for the duration of a full redox cycle are presented as the analytical solution to a 1-dimensional bounded random-walk problem (confirmed by numerical simulation). These show that tfull, the average time for the full redox cycle (step 1 + step 2), is equal to L(2)/D where L is the intraelectrode distance and D is the diffusion coefficient. The average steady-state limiting current is shown to be described by the familiar expression for a generator-collector system: ilim = (qstep1 + qstep2)/tfull = nETqe/tfull = nETqeD/L(2).

Synthesis and electrochemistry of 6 nm ferrocenated indium-tin oxide nanoparticles

Indium-tin oxide (ITO) nanoparticles, 6.1 ± 0.8 nm in diameter, were synthesized using a hot injection method. After reaction with 3-aminopropyldimethylethoxysilane to replace the initial oleylamine and oleic acid capping ligands, the aminated nanoparticles were rendered electroactive by functionalization with ferrocenoyl chloride. The nanoparticle color changed from blue-green to light brown, and the nanoparticles became more soluble in polar solvents, notably acetonitrile. The nanoparticle diffusion coefficient (D = 1.0 × 10(-6) cm(2)/s) and effective ferrocene concentration (C = 0.60 mM) in acetonitrile solutions were determined using ratios of DC and D(1/2)C data measured by microdisk voltammetry and chronoamperometry. The D result compares favorably to an Einstein-Stokes estimate (2.1 × 10(-6) cm(2)/s), assuming an 8 nm hydrodynamic diameter in acetonitrile (6 nm for the ITO core plus 2 nm for the ligand shell). The ferrocene concentration result is lower than anticipated (ca. 1.60 mM) based on a potentiometric titration of the ferrocene sites with Cu(II) in acetonitrile. Cyclic voltammetric data indicate tendency of the ferrocenated nanoparticles to adsorb on the Pt working electrode.

Linker-based control of electron propagation through ferrocene moieties covalently anchored onto insulator-based nanopores derived from a polystyrene-poly(methylmethacrylate) diblock copolymer

This paper reports the effects of linker length on electron propagation through ferrocene moieties covalently anchored onto insulator-based cylindrical nanopores derived from a cylinder-forming polystyrene-poly(methylmethacrylate) diblock copolymer. These nanopores (24 nm in diameter, 30 nm long) aligned perpendicular to an underlying gold electrode were modified via esterification of their surface COOH groups with OH-terminated ferrocene derivatives having different alkyl linkers (FcCO(CH(2))(n)OH; n = 2, 5, 15). Cyclic voltammograms were measured in 0.1 M NaBF(4) at different scan rates to assess the efficiency of electron propagation through the ferrocene moieties. The redox peaks of the anchored ferrocenes were observed at nanoporous films decorated with FcCO(CH(2))(15)OH and FcCO(CH(2))(5)OH, but not at those with FcCO(CH(2))(2)OH. Importantly, the higher electron propagation efficiency was observed in the use of the longer linker, as shown by the apparent diffusion coefficients (ca. 10(-12) cm(2)/s for n = 15; ca. 10(-13) cm(2)/s for n = 5; no electron propagation for n = 2). The observed electron propagation resulted from electron hopping across relatively large spacing that was controlled by the motion of anchored redox sites (bounded diffusion). The longer linker led to the larger physical displacement range of anchored ferrocene moieties, facilitating the approach of the adjacent ferrocene moieties within a distance required for electron self-exchange reaction. The linker-based control of redox-involved electron propagation on nanostructured, insulating surfaces will provide a means for designing novel molecular electronics and electrochemical sensors.

Electrochemistry and DFT simulation of optical spectra of N-ferrocenoyl-N'-ω-decenoyl-ethylenediamine

A new hybrid organic-inorganic chromophore based on ferrocene was synthesized. In addition to a detailed synthesis description the article describes complex quantum chemical and experimental (UV-VIS and electrochemical) studies of the redox and chromophore characteristics. The properties studied include the diffusion coefficient as well as solvatochromic effects in solvents differing in polarity, namely dichloromethane, propylene carbonate and acetonitrile. The experimental results are discussed within a framework of theoretical description at the DFT and TDDFT (6-31G(df,p)) levels of theory, with the PCM solvation model. Accuracy of B3LYP and BLYP functionals in reproducing orbital energy levels and optical transitions of the title molecule is briefly discussed.

Stöber silica particles as basis for redox modifications: particle shape, size, polydispersity, and porosity

The synthesis of Stöber silica particles as basis for redox modifications is optimized for desired properties, in particular diameter in a wide sub-micrometer range, spherical shape, monodispersity, the absence of porosity, and aggregation free isolability for characterization and later covalent modification. The materials are characterized by SEM, DLS, nitrogen sorption isotherms, helium as well as Gay-Lussac (water) pycnometry, and DRIFT spectroscopy. Particles with diameters between approximately 50 and 800 nm are obtained by varying the concentrations of the reagents and reactants, the type of solvent as well as the temperature. The use of high water concentrations and post-synthetic calcination at 600 °C results in silica particles that can be considered as nonporous with respect to the size of the active molecules to be immobilized. The effect of reaction temperature on size distribution is identified. Low polydispersity is achieved by performing the reaction in a temperature range in which a change in temperature has only a weak or no effect on the final particle diameter. Upon optimization of the sol-gel process, the shape of the particles is still spherical. The agreement between experimental and geometric data is within the expected precision of the characterization techniques.

Redox-active ferrocene-modified Cowpea mosaic virus nanoparticles

A naturally occurring nanoparticle, the plant virus Cowpea mosaic virus, can be decorated with ferrocene derivatives, of various linker lengths with amine and carboxylate groups, on the external surface using a range of conjugation strategies. The multiple, organometallic, redox-active ferrocene moieties on the outer surface of the virus are electrochemically independent with reduction potentials that span a potential window of 0.16 V that are dependent on the site of modification and the nature of the ferrocene derivative. The number of ferrocenes coupled to each virus ranges from about 100 to 240 depending upon the conjugation site and the linker length and these redox active units can provide multielectron reservoirs.