Influence of the synthetic method on the properties of two-photon-sensitive mesoporous organosilica nanoparticles

International audienceHerein we report the modulation of the properties of mesoporous silica nanoparticles (NPs) via various synthetic approaches. Three types of elaborations were compared, one in aqueous media at 25 °C, and the other two at 80 °C in water or in a water–ethanol mixture. For all these methods, an alkoxysilylated two-photon photosensitizer (2PS) was co-condensed with tetraethylorthosilicate (TEOS) in the presence of cetyltrimethylammonium bromide (CTAB), leading to five two-photon-sensitive mesoporous silica (M2PS) NPs. The M2PS NP porous structure could be tuned from radial to worm-like and MCM-41 types of organization. Besides, the 2PS precursor spatial dispersion was found to be highly dependent on both the 2PS initial concentration and the elaboration process. As a result, two-photon properties were modulated by the choice of the synthesis, the best results being found in aqueous media at 25 or 80 °C. Finally, the M2PS NPs were used for in vitro two-photon imaging of cancer cells

Modulating the photoluminescence of bridged silsesquioxanes incorporating Eu(3+)-complexed n,n '-diureido-2,2 '-bipyridine isomers: application for luminescent solar concentrators

Two new urea-bipyridine derived bridged organosilanes (P5 and P6) have been synthesized and their hydrolysis-condensation under nucleophilic catalysis in the presence of Eu(3+) salts led to luminescent bridged silsesquioxanes (M5-Eu and M6-Eu). An important loading of Eu(3+) (up to 11%(w)) can be obtained for the material based on the 6,6'-isomer. Indeed the photoluminescence properties of these materials, that have been investigated in depth (photoluminescence (PL), quantum yield, lifetimes), show a significantly different complexation mode of the Eu(3+) ions for M6-Eu, compared with M4-Eu (obtained from the already-reported 4,4'-isomer) and M5-Eu. Moreover, M6-Eu exhibits the highest absolute emission quantum yield value (0.18 +/- 0.02) among these three materials. The modification of the sol composition upon the addition of a malonamide derivative led to similar luminescent features but with an increased quantum yield (026 +/- 0.03). In addition, M6-Eu can be processed as thin films by spin-coating on glass substrates, leading to plates coated by a thin layer (similar to 54 nm) of Eu(3+)-containing hybrid silica exhibiting one of the highest emission quantum yields reported so far for films of Eu(3+)-containing hybrids (0.34 +/- 0.03) and an interesting potential as new luminescent solar concentrators (LSCs) with an optical conversion efficiency of similar to 4%. The ratio between the light guided to the film edges and the one emitted by the surface of the film was quantified through the mapping of the intensity of the red pixels (in the RGB color model) from a film image. This quantification enabled a more accurate estimation of the transport losses due to the scattering of the emitted light in the film (0.40), thereby correcting the initial optical conversion efficiency to a value of 1.7%.FCT - PTDC/CTM/101324/2008COMPETEFEDE

Click Approaches in Sol-Gel Chemistry

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Synthesis of highly modular bis(oxazoline) ligands by Suzuki cross-coupling and evaluation as catalytic ligands

International audienceNew bis(oxazoline) ligands (BOXs) containing biaryl substitutents at the C-4 position and H or CH2OR substituents at the C-5 position have been synthesized using Suzuki cross-coupling as the main tool for structural diversity. Copper, zinc, and palladium complexes of the prepared BOXs have been evaluated in the following catalytic asymmetric processes: Acylation with kinetic resolution of trans-1,2-cyclohexanediol (Cu), enantioselective Friedel–Crafts alkylation of indole (Zn), and enantioselective alkylation of 3-acetoxy-1,3-diphenylpropene (Pd)

Amino-carbénes (réarrangements originaux, complexation)

L'introduction récapitule tous les carbènes stables (et persistants) connus, ainsi que leurs méthodes de préparation. Nous avons montré que le bis(triméthylsilyl)mercure réagit avec des chlorures de chloroiminium pour donner des diaminocarbènes cycliques et acycliques libres (sans métal), et aussi des aryl, alcoxy, chloro, hydrogéno et alkyl-aminocarbènes. Les aryl, chloro et hydrogéno-aminocarbènes sont formés intermédiairement puis se dimérisent. Les alkyl et les alcoxy aminocarbènes ont été seulement observés par RMN C13. Des sels d'iminium substitués par un groupement triméthylsilyle ont e té préparés. Nous avons ainsi pu montrer que ces composés silylés ne constituaient pas des intermédiaires pour la formation des carbènes. Dans la deuxième partie, nous avons essayé de synthétiser le cation pentaméthylcyclo-pentadiènyle. En fait, la réaction entre un triphénylcarbénium de tétrafluoroborate et le pentaméthylcyclopentadiène mène à la formation du cation pentaméthylcyclopentényle.TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Stable Noncyclic Singlet Carbenes

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Periodic mesoporous organosilica nanoparticles: Morphology control and sorption properties

International audienceThe synthesis of various periodic mesoporous organosilica nanoparticles (nanoPMOs) from the corresponding organo-bridged bis(triethoxy)silanes is described. A strong influence of the sodium hydroxide concentration is observed, leading to various sizes or morphologies depending on the precursor. In particular, in the case of the ethenylene linker, the morphology evolves from small flakes to elongated particles, while in the case of the phenylene precursor, small well-organized arms start to form at high base concentration. A mechanistic study shows that in all cases the nanoparticles nucleate before the condensation reaction commences and at very low conversions of the hydrolysis reaction of ethoxysilanes. The resulting hybrid nanoPMOs were compared for their adsorption properties towards rhodamine B (RB), which highlights large differences between the nanoPMOs with different linkers, and evidences a very strong affinity of the phenylene PMO with the poly-aromatic dye. Similarly, the sorption of cyclohexane and water revealed a much higher lipophilicity of the phenylene-bridged nanoPMO compared to the other studied linkers, despite a similar hydrophilicity. These results should help to better design nanoPMOs as nanovectors for drugs

A kinetic approach to the mechanism of formation of mesoporous silica nanoparticles

International audienceThe synthesis of mesoporous silica nanoparticles (MSNs), widely investigated for application in nanomedicine, depends on many experimental factors and lacks reproducibility. Furthermore, its mechanism is not fully understood, in particular for the chemistry of the hydrolysis and condensation of tetraethoxysilane (TEOS). We coupled simple pH measurements with light diffusion monitoring directly within the reaction vessel in order to understand the early stages of the synthesis until the formation of nanoparticles. We found that two regimes of hydrolysis can be detected before the nanoparticles are formed. At the turning point, only 28% of the TEOS molecules are singly hydrolyzed and the condensation reaction only starts after the aggregation of the silicate-surfactant micelles. Experimental factors such as stirring strength or presence of carbonates of sodium hydroxide exert a strong influence on the kinetics of MSNs formation and on their size, and must be carefully controlled for reproducibility. Based on all our experimental evidence and on previous literature reports, a formation mechanism was proposed in order to highlight the importance of the interplay between chemical and physicochemical processes in such a complex system

Recyclable Mesoporous Organosilica Nanoparticles Derived from Proline-Valinol Amides for Asymmetric Organocatalysis

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Clickable organic@inorganic core-shell nanoparticles obtained by a one-step spray drying process for biophotonics

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