Blanca González

Redox-active ferrocenyl dendrimers and polymers in solution and immobilised on electrode surfaces

Abstract This article reviews the electrochemical properties of different families of redox-active silicon- and amine-based ferrocenyl polymers and dendrimers prepared in our laboratory over the last few years. The electrochemical behaviour of the ferrocenyl polymers both in solution and immobilised on the electrode depends on the polymer structure. Solution electrochemical studies of silicon-based ferrocenyl polymers showed that all the redox centres were electrochemically independent and that polymers containing pendant ferrocenyl moieties undergo oxidative precipitation, yielding polymer films on electrode surfaces. The application of electrodes modified with a ferrocenyl polymer containing octakis(dimethylsiloxy)-octasilsesquioxane as framework, as mediator in the electrocatalytic oxidation of ascorbic acid is described. The electrochemical behaviour of silicon- and amine-based dendrimers in which ferrocenyl moieties behave as electronically isolated centres, and also of dendritic macromolecules containing interacting ferrocenyl units has been studied. The feasibility of modifying electrode surfaces with these redox-active metallo-dendrimers containing a controlled number of metal centres has been demonstrated. The application of ferrocenyl dendrimers as electron transfer mediators in amperometric biosensors and in the electrochemical recognition of anions, as well as the use of dendritic terminal ferrocenyl groups for inclusion complexation by cyclodextrins has been outlined.

Functionalization via hydrosilylation of linear and cyclic siloxanes with appendent first generation dendrons containing electronically communicated ferrocenyl units

Abstract The synthesis, structural characterization and redox-properties of a new family of siloxane-based poly(ferrocenyl) dendronized molecules are described. Hydrosilylation reaction of the vinyl-functionalized silicon-bridged biferrocene, CH 2 CHSiMe[Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 5 )] 2 ( 1 ) with SiH-containing poly(siloxane) backbones afforded the novel copolymer 6 and homopolymer 7 . To understand the properties of these polymers more thoroughly, we also synthesized the well-defined, closely related tetraferrocenyl-functionalized disiloxane and octaferrocenyl-functionalized cyclotetrasiloxane model compounds 4 and 5 . Solution voltammetric studies of the siloxane-based poly(ferrocenyl) derivatives 4 – 7 showed two reversible redox processes with a wave separation (Δ E ) of 190–160 mV, indicating that significant electronic communication exists between the ferrocenyl moieties bridged by a pendant silicon atom. The neutral cyclotetrasiloxane-based octaferrocenyl 5 , as well as polymers 6 and 7 become insoluble upon complete oxidation to the corresponding polycationic species, yielding electroactive films onto platinum and glassy-carbon electrode surfaces. The well-defined and persistent redox waves of electrode coated with these films are characteristic of electrochemically stable, surface-confined reversible redox couples. The microstructure of these multimetallic electroactive films has been analyzed by scanning electron microscopy.

Electrodes modified with a siloxane copolymer containing interacting ferrocenes for determination of hydrogen peroxide and glucose

Abstract The electrochemical characterization of a hydrogen peroxide sensor based on a ferrocene-containing polymer electrochemically deposited onto a platinum electrode is described. The redox polymer consists of a siloxane-based copolymer, with pendant electronically communicated ferrocenyl moieties. Amperometric biosensors for glucose were prepared by immobilization of glucose oxidase (Gox) onto these modified electrodes. The effects of substrate concentration, the thickness of the polymer layer, interferences and storage on the response of the sensors were investigated.

Synthesis, electrochemistry and cyclodextrin binding of novel cobaltocenium-functionalized dendrimers

A series of novel poly(propyleneimine) dendrimers functionalized with 4, 8, 16 and 32 peripheral cobaltocenium subunits were prepared and characterized with a special focus on their electrochemical properties and binding interactions with β-cyclodextrin.

Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38-99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (-0.12 to -0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 x 10(-6) to 7 x 10(-8) S cm(-1).

Electronic, redox and charge transport properties of an unusual hybrid structure: a bis(septithiophene) bridged by a fused tetrathiafulvalene (TTF)

A hybrid tetrathiafulvalene–oligothiophene compound has been synthesised, in which the fulvalene unit is fused on both sides to an end-capped septithiophene oligomer. The compound (1) has been studied by cyclic voltammetry, UV-vis spectroelectrochemistry and X-ray crystallography. The properties of this material are compared to the half-unit (9), which lacks the TTF core and contains only one septithiophene chain. In the case of the larger molecule, there are multiple and complex redox processes leading to the loss of 6–8 electrons per molecule. Charge generation layer time-of-flight measurements give maximum hole mobilities of ca. 1 × 10−5 cm2 V−1 s−1.

Dendritic Macromolecules: New Possibilities for Advanced Bioceramics

Dendrimers are a relatively new class of molecules that display a variety of potentially useful architecture-induced properties. In this chapter, we firstly present a general description of this interesting class of macromolecules, making special emphasis in their current biomedical applications. The combination of dendrimers with ceramics, traditionally used in the biomedical field, provides synergistic features and functions to the resulting hybrid materials. After the dendrimers introduction, an overall description of mesoporous silicas, iron oxide nanoparticles and carbon nanotubes bioceramics, is presented. Finally, recent research examples of dendrimer-functionalized ceramics, both from the synthetic and biomedical applicative points of view, are reviewed.

Retratos des-compuestos: cinco peculiares caricaturas del Sexenio democrático

During the democratic Six-Years, five caricatures were published in the satirical weekly journals El Caos and El Lio that resemble, at least formally, the composite heads painted in the sixteenth century by Giuseppe Arcimboldo. This article examines the circumstances in which the five drawings appeared and are compared with the paintings of the Cinquecento artist through the study of the original composite heads made by the philosopher Roland Barthes. The objective underlying this exercise of equalization is the analysis of the process and the resources that could be used by the two authors of the cartoons.