Polymer multilayer films obtained by electrochemically catalyzed click chemistry.

We report the covalent layer-by-layer construction of polyelectrolyte multilayer (PEM) films by using an efficient electrochemically triggered Sharpless click reaction. The click reaction is catalyzed by Cu(I) which is generated in situ from Cu(II) (originating from the dissolution of CuSO(4)) at the electrode constituting the substrate of the film. The film buildup can be controlled by the application of a mild potential inducing the reduction of Cu(II) to Cu(I) in the absence of any reducing agent or any ligand. The experiments were carried out in an electrochemical quartz crystal microbalance cell which allows both to apply a controlled potential on a gold electrode and to follow the mass deposited on the electrode through the quartz crystal microbalance. Poly(acrylic acid) (PAA) modified with either alkyne (PAA(Alk)) or azide (PAA(Az)) functions grafted onto the PAA backbone through ethylene glycol arms were used to build the PEM films. Construction takes place on gold electrodes whose potentials are more negative than a critical value, which lies between -70 and -150 mV vs Ag/AgCl (KCl sat.) reference electrode. The film thickness increment per bilayer appears independent of the applied voltage as long as it is more negative than the critical potential, but it depends upon Cu(II) and polyelectrolyte concentrations in solution and upon the reduction time of Cu(II) during each deposition step. An increase of any of these latter parameters leads to an increase of the mass deposited per layer. For given buildup conditions, the construction levels off after a given number of deposition steps which increases with the Cu(II) concentration and/or the Cu(II) reduction time. A model based on the diffusion of Cu(II) and Cu(I) ions through the film and the dynamics of the polyelectrolyte anchoring on the film, during the reduction period of Cu(II), is proposed to explain the major buildup features.journal articleresearch support, non-u.s. gov't2010 Feb 16importe

Electrochemically Triggered Assembly of Films: A One-Pot Morphogen-Driven Buildup:

Polymers that “click”: A polymer film is obtained by the CuI-catalyzed Sharpless click reaction between two polymers, bearing either azide or alkyne groups, both present simultaneously in a CuII solution (see picture). The CuI morphogen is generated at an electrode by applying an adequate potential. This concept can be extended to supramolecular films formed by coordination complexes

Urgent preliminary assessment of ornithological data relevant to the spread of Avian Influenze in Europe

In the course of 2005 the highly pathogenic Avian Influenza Asian lineage HPAI H5N1 virus spread from Southeast Asia to SW Siberia, Kazakhstan and the Southern Urals. Migratory birds were suspected of playing a role in the spread of the disease. This meant that the EU could be under direct threat as a number of waterbirds (geese, ducks and shorebirds in particular) were known to migrate through the infected areas to the EU in winter. The European Commission (DG Environment) therefore asked Wetlands International and EURING to undertake the present study. The aims of the project were: (1) to identify species which pose a relatively high risk of spreading H5N1 along their migration routes to the European Union, (2) to analyse the migration routes of these socalled Higher Risk Species on the basis of recoveries of ringed birds, (3) to identify wetland sites where Higher Risk Species concentrate in large numbers during migration and wintering and (4) to develop and test a format for the rapid assessment of ornithological data at the level of wetland sites, in order to prepare wetland managers for an outbreak of H5N1