Franck Bertorelle

Compared Behavior of Hydrophobic Fluorescent NBD Probes in Micelles and in Cyclodextrins

Four hydrophobic NBD derivatives, differing by the length of the fatty chain, were introduced in micelles of Triton X100 as well as in α- and β-cyclodextrins. The spectroscopic data indicated that the probes were more efficiently protected from water in micelles than in cyclodextrins. The insertion of the probes in both media was discussed.

Spectrophotometric study of the incorporation of NBD probes in micelles: is a long alkyl chain on the fluorophore an advantage?

Abstract Fluorescence spectroscopy is widely used as a tool for elucidating the structure and dynamics of the micellar medium. A prerequisite commonly encountered for quantitative approaches is that the fluorophore resides exclusively in the micellar phase. Providing the fluorophore with a long alkyl chain may appear advantageous with regard to fixing the probe into the micelle. The present work was aimed at determining which are the consequences of this process from a spectroscopic viewpoint. The nitrobenzoxadiazolyl (NBD) moiety, which leads to well known fluorescent probes, was directly grafted on three fatty amines, the chain length of which varied from 8 to 18 carbon atoms. The spectroscopic properties of these NBD derivatives were investigated in three different micellar media: SDS, CTAB and TX100. The dyes were incorporated into micelles, where they were located in the interfacial region, whatever the chain length. When the dyes were previously dissolved in ethanol, and subsequently placed in the presence of the surfactant solution, complete solubilization was obtained. However, when the surfactant solution was used to dissolve directly a thin film of dye, a certain amount of dye remained non-incorporated and formed microcrystals, whose quantity and size increased with chain length. These microcrystals were mainly detected by UV/Vis-absorption and fluorescence microscopy. They induced drastic errors in the determination of fluorescence quantum yields, although they hardly interfered with other steady-state measurements and with dynamical fluorescence measurements. In conclusion, it appeared that for a small, non-ionic fluorophore such as NBD, the presence of a long alkyl chain is not an advantage. It slows down the incorporation process, unless some alcohol is introduced in the medium. Short-chain probes are therefore best suited for the study of the micellar medium.

Microcrystals of an organic fluorescent dye grown in the presence of various PAMAM dendrimers: Control of the morphology and optical properties

Microcrystals of a fluorescent dye, 4-n-octylamino-7-nitrobenzoxadiazole, were prepared by the reprecipitation method. Poly(amidoamine)dendrimers bearing anionic, cationic or neutral terminating groups were used as additives in the recrystallization medium. They directed the formation of thin plates or spindle- like microcrystals. The UV/vis absorption and emission properties were investigated on the microcrystal suspensions.

Free-standing microcrystals of a fluorescent organic dye: Preparation and spectroscopic study

Suspensions of microcrystals were obtained from an organic fluorescent dye, 4-n-octylamino-7-nitrobenz-2-oxa-1,3-diazole, by reprecipitation in water in the presence of various macromolecules: anionic or cationic PAMAM dendrimer, poly(acrylic acid, sodium salt), poly(acrylamide), and calf thymus DNA. The use of these additives allowed the size and shape of the microcrystals to be controlled. A study by UV/vis absorption and fluorescence spectroscopy revealed some common points, but also some interesting differences, in the optical behaviour of the five samples.

4-Hydroxycoumarin Derivatives in Micelles: An Approach to Detect a Structural Transition Using Fluorescent Viscosity Probes

The spectroscopic behavior of three coumarin derivatives was investigated in water and in different micellar media. In SDS, the fluorescence intensity of two of the dyes increased upon addition of sodium chloride. This effect was tentatively related to a sphere-to-rod transition occurring in the micelles.

Morphology Control of Organic Luminescent Microcrystals Grown in the Presence of Ionic and Nonionic PAMAM Dendrimers

ABSTRACT Poly(amidoamine)dendrimers bearing different terminating groups were used as additives in the reprecipitation of a fluorescent nitrobenzoxadiazole (NBD) derivative and directed the formation of thin plates or needle-like microcrystals. The optical properties of the microcrystals were investigated.