ICMUB - News

Vendredi 18 mai 2007 : Conf du Pr Piersandro Pallavicini, Dipartimento di Chimica Generale, Università di Pavia (Italie)

Coordination and acid base chemistry inside micelles for the construction of self-assembled devices

Micelles can be advantageously used as containers for the self-assembling of multicomponent devices in aqueous solutions, thanks to the micelle ability of including a number of different molecular components in a small-dimension space. Inside the micelle, the included components display their peculiar functions, interact, and as a result the whole system may display a new overall function, as in traditional supramolecular devices. Moreover, inclusion in micelles changes the properties of the molecular components with respect to the water bulk: lower solvation and an overall charge effect (for charged surfactants) strongly influence the acid-base and coordination properties of the micellized molecules. Playing on the properties of the included molecules (e.g. lipophilicity or shape), or on the average charge of the micelles, it is possible to finely tune the observed protonation and complexation constants of included molecules. In addition, a local, inside-micelle, reciprocal overconcentration effect must be taken into account for micelle-included species, that may lead to interaction processes (e.g. complexation) that are not effective in bulk water at the same analytical concentration. With this micellar multicomponent self-assembling approach we have so far prepared systems capable of selective fluorescent sensing for Cu2+, Ni2+, Hg2+, and pH windows. In this talk, new results will be presented about: i) the role of the lipophilicity and shape of the micellized components on the efficiency of the signalling process for fluorescent cation sensing; ii) the role of the overall charge of the micelle when neutral and charged surfactants are mixed, in tuning the protonation constants of included bases. An ON-OFF-ON fluorescent system for pH windows will be presented that can move the ON window at will all along the pH axis; iii) the role of overconcentration effects inside micelles, in preparing a multicomponent fluorescent syscoordinative competition, capable of directly evaluating the lipophilicity of a given molecule.

Contact : Franck Denat
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ICMUB (UMR 5260) - University of Burgundy - Dijon (France)