Interactions between oppositely charged conjugated polyelectrolytes and surfactants

Nous étudions les complexes formés en solutions tamponnées très diluées à partir d'un polyanion conjugué, le poly(3-thiophène acide acétique), et des tensioactifs cationiques. Nous varions le rapport R = [tensioactif]/[monomère] (10-5 < R < 100) et la lonWe study the complexes formed in very dilute buffered solutions between a polyanion, poly(3-thiophen acetic acid) and cationic surfactants. We vary the ratio R = [surfactant]/[monomer] (10-5 < R < 100) and the length of the hydrophobic part of the surfac

Interactions between oppositely charged conjugated polyelectrolytes and surfactants

Nous étudions les complexes formés en solutions tamponnées très diluées à partir d'un polyanion conjugué, le poly(3-thiophène acide acétique), et des tensioactifs cationiques. Nous varions le rapport R = [tensioactif]/[monomère] (10-5 < R < 100) et la longueur des parties hydrophobes des tensioactifs. Nous mesurons l'absorption UV-visible et la fluorescence des complexes ainsi que leur taille. Nous montrons que l'absorption UV-visible permet de mesurer la concentration d'agrégation critique (cac) entre polyélectrolytes et tensioactifs dans des conditions très diluées, ce qui évite la précipitation de ces chaînes très hydrophobes. L'évolution de la cac avec l'hydrophobie du tensioactif n'obéit pas au comportement classique des solutions polyélectrolytes saturés/tensioactifs, probablement à cause de l'hydrophobie très marquée de notre squelette conjugué. Pour la première fois, nous corrélons une mesure de l'effondrement des chaînes avec l'évolution de leur absorption UV-visible. Après cet effondrement, à mesure que les complexes s'enrichissent en tensioactif, un nouveau pic de fluorescence, décalé vers le rouge de plus de 100 nm, apparaît et le pic de fluorescence initial disparaît. Ce phénomène rarement observé semble correspondre à la création de nouvelles structures tensioactifs/polymère qu'il reste à étudier.We study the complexes formed in very dilute buffered solutions between a polyanion, poly(3-thiophen acetic acid) and cationic surfactants. We vary the ratio R = [surfactant]/[monomer] (10-5 < R < 100) and the length of the hydrophobic part of the surfactants. We measure the UV-visible absorption, the fluorescence and the size of the complexes. We show that the UV-visible absorption can measure the critical agregation concentration (cac) between the polyelectrolytes and the surfactants in very dilute solutions, thus preventing their precipitation. The evolution of the cac with surfactant hydrophobicity does not follow the classical behaviour of systems based on saturated polyelectrolytes, probably because of the strong hydrophobic conjugated backbone. For the first time we can correlate a measure of the collapse of the complexes with the evolution of their UV-visible absorption. After the collapse, as the complexes get progressively richer in surfactants, a new fluorescence maximum appears, shifted to the red by more than 100 nm, and the original polymer peak disappears. This uncommon phenomenon is likely due to new polymer/sufactants structures that remain to be investigated

From Chain Collapse to New Structures: Spectroscopic Properties of Poly(3-thiophene acetic acid) upon Binding by Alkyl Trimethylammonium Bromide Surfactants

The binding of cationic surfactants with varying alkyl chain length to a regiorandom conjugated polyanion, poly­(3-thiophene acetic acid) (PTAA), is studied in an aqueous buffer by using absorption and emission spectroscopies, photon correlation spectroscopy, isothermal titration calorimetry, and cryogenic transmission electron microscopy. We study the mixed solutions as a function of composition ratio <i>R</i> of surfactant molecules to monomer units molar concentrations, at low polymer concentration and in a very wide composition range (10^–6 < <i>R</i> < 10²) below the critical micellar concentration. Upon surfactant binding, the molecularly dispersed chains first collapse progressively and then form new structures as the mixed aggregates get enriched in surfactant. The collapse leads to a strong decrease of the conjugation length and to a blue shift of the absorption spectra by 30 to 50 nm. The new structures are responsible for a new intense emission band at about 600 nm, red-shifted by nearly 130 nm from the initial emission maximum of the polymer (∼472 nm). As the surfactant tail becomes shorter, the blue shift of the absorption spectra and the intensity raise of the new emission are delayed to larger composition ratios while their variations become smoother functions of the surfactant concentration. These particular spectroscopic properties of PTAA seem related to its unique combination of a strongly hydrophobic backbone, a large ratio of contour length to persistence length, and an overall good aqueous solubility. Our results show that such features are well suited to design a colorimetric biosensor at small composition ratio, and a fluorescent biomarker at large composition ratio

A comparison of the degree of implementation of marine biodiversity indicators by European countries in relation to the Marine Strategy Framework Directive (MSFD)

The degree of development and operability of the indicators for the Marine Strategy Framework Directive (MSFD) using Descriptor 1 (D1) Biological Diversity was assessed. To this end, an overview of the relevance and degree of operability of the underlying parameters across 20 European countries was compiled by analysing national directives, legislation, regulations, and publicly available reports. Marked differences were found between countries in the degree of ecological relevance as well as in the degree of implementation and operability of the parameters chosen to indicate biological diversity. The best scoring EU countries were France, Germany, Greece and Spain, while the worst scoring countries were Italy and Slovenia. No country achieved maximum scores for the implementation of MSFD D1. The non-EU countries Norway and Turkey score as highly as the top-scoring EU countries. On the positive side, the chosen parameters for D1 indicators were generally identified as being an ecologically relevant reflection of Biological Diversity. On the negative side however, less than half of the chosen parameters are currently operational. It appears that at a pan-European level, no consistent and harmonized approach currently exists for the description and assessment of marine biological diversity. The implementation of the MSFD Descriptor 1 for Europe as a whole can therefore at best be marked as moderately successful