Pierre Labbe

Effect of the Supporting Electrolyte Anion on the Thickness of PSS/PAH Multilayer Films and on Their Permeability to an Electroactive Probe

Quartz crystal microbalance and cyclic voltammetry are used to investigate the influence of the supporting salt of polyelectrolyte solutions on the buildup and the structure of PSS/PAH polyelectrolyte multilayers (PSS: poly(4-styrene sulfonate); PAH: poly(allylamine hydrochloride)). This film constitutes a model polyelectrolyte multilayer system. The supporting electrolytes were sodium salts where the nature of the anion was changed by following the Hofmeister series from cosmotropic to chaotropic anions (F-, Cl-, NO3-, ClO4-). For all the investigated anions, the film thickness increases linearly with the number of deposition steps.Wefind that chaotropic anions lead to larger thickness increments per bilayer during the film buildup than cosmotropic ones, confirming results found on PSS/PDADMA multilayers (PDADMA:poly(diallyldimethylammonium)). Films constituted by more than nine PSS/PAH bilayers are still permeable to hexacyanoferrate(II) ions, Fe(CN)(6)4-, whatever the nature of the supporting salt anion. On the other hand, these films are impermeable to ruthenium(II) hexamine ions, Ru(NH3)(6)2+, after the third PAH layer in the presence of NaF, NaCl, or NaNO3. These results are explained by the presence of an excess of positive charges in the film, which leads to a positive Donnan potential. We find that this potential is more positive when more chaotropic anions are used during the film buildup. We also find that a film constructed in the presence of chaotropic anions swells and becomes more permeable to Fe(CN)(6)4- ions when the film is brought into contact with a solution containing more cosmotropic anions. All our experimental findings can be explained by a strong interaction between chaotropic anions with the NH3+groups of PAH that is equivalent, as far as the multilayer buildup and electrochemical response is concerned, to a deprotonation of PAH as it is observed when the film is constructed at a higher pH. We thus arrive to a coherent explanation of the effect of the nature of the anions of the supporting electrolyte on the polyelectrolyte multilayer. We also find that great care must be taken when investigating polyelectrolyte multilayer films by electrochemical probing because electrochemical reactions involving the probes can appreciably modify the multilayer structure.

Electrochemical behavior of clay modified electrodes in the presence of cationic surfactant

Influence dun agent de surface cationique sur le comportement electrochimique dune electrode modifiee par une argile (laponite). Oxydoreduction de lhexacyanoferrate (III) en milieu salin (Na 2 SO 4 )

Possible analytical application of laponite clay modified electrodes

Abstract Laponite clay modified electrodes (LCME) have been used to detect trace amounts of neutral or cationic organometallic substances, including ferrocene (Fc) and cobaltocenium (Cc+), two molecules covalently attached to cobaltocenium, and a molecule labelled by ferrocene (N-amphetaminecarbonylferrocene) as an electroactive organic test species. During an ion-exchange preconcentration step, the cationic species (cobaltocenium derivatives) are collected in the laponite film from their dilute solutions under open-circuit conditions whereas the procationic species (ferrocene derivatives) are collected in their cationic form by applying a positive potential. Quantification of the surface bound cations is then carried out by applying a negative scan using voltammetry or square wave voltammetry. In the case of the two molecules labelled by Cc+, a detection limit of 4 × 10−8 mol l−1 and a linear calibration range from 1 × 10−7 to 2 × 10−5 mol l−1 are obtained reproducibly by using a new LCME for each measurement. Conversely with small redox molecules such as ferrocene and cobaltocenium, the same LCME can be used repeatedly because applying a negative potential leads to the exclusion of the resulting neutral molecule which can be rinsed efficiently from the film.

Molecular engineering of biomolecules for nanobio-sciences

Biologically programmed molecular recognition provides the basis of all natural systems and supplies evolution optimised functional materials from self-assembly of a limited number of molecular building blocks. Biomolecules such as peptides, nucleic acids and carbohydrates represent a diverse supply of structural building blocks for the chemist to design and fabricate new functional nanostructured architectures. In this context, we review here the chemistry part of our Nanobio program, we have developed in Grenoble to manipulate such biomolecules, and organic molecules, as well as assemble combinations thereof using a template assembled approach. With this methodology, we have prepared new integrated functional systems exhibiting designed properties in the field of nanovectors, biosensors as well as controlled peptide self-assembly. Thus this molecular engineering approach allows for the rational design of systems with integrated tailor-made properties and paves the way to more elaborate applications by bottom-up design in the domain of nanobiosciences.

Immobilization of redox anions in poly(amphiphilic pyrrolylalkylammonium) using a simple and monomer-saving one-step procedure in pure water electrolyte

The pyrrolylalkylammonium tetrafluoroborate monomer 1 can be electropolymerised in aqueous electrolytes when adsorbed on an electrode surface and electroactive bulky anions can be incorporated either in polymer films of 1, or by electropolymerisation of a coating containing the anion along with 1; cyclic voltammetry peak splittings suggest a regular surface arrangement.