Dan A. Lerner

Synthesis and characterisation of ibuprofen-anchored MCM-41 silica and silica gel

A non-steroidal anti-inflammatory drug (ibuprofen) has been anchored inside the mesoporous channels of MCM-41-type silica and on a silica gel surface. The relevant anchoring procedure through an ester function has been investigated. It uses the epoxide ring opening of 3-glycidoxypropylsilane grafted on the silica surface by the carboxylic-group-containing ibuprofen. The control of the surface modification and of the anchoring efficiency was achieved by comparison of spectroscopic data with those obtained using homogeneous counterparts. The use of nanostructured silica allowed an accurate verification of the different surface modifications and also a higher drug loading.

Photoresponsive ordered hybrid materials containing a bridged azobenzene group

This paper describes the synthesis of 4,4′-[(triisopropoxysilyl)propyloxy]azobenzene and the preparation of the ordered hybrid material containing the bridged azobenzene moieties within the framework by using the direct liquid crystal templating approach. We show that a sizable fraction of the azobenzene groups is reversibly photoisomerized though the chromophore is covalently linked to the silica matrix at both ends. In contrast, the photoisomerization did not occur in the corresponding material prepared in the absence of template. This is explained by a regular dilution of the chromophores into silica thanks to the template used for the preparation of the material.

Azoic Dye Hosted in Layered Double Hydroxide: Physicochemical Characterization of the Intercalated Materials

Intercalation compounds were obtained by introduction of guest methyl orange (MO) into the interlayer space of host Mg/Al and Ni/Al layered double hydroxides (LDHs). Three synthesis methods of organic anion-LDH intercalation compounds, i.e., coprecipitation, reconstruction of the MII(Al)O mixed oxides, and anion exchange of LDH, were compared. The former method gives rise to a highly organized MO-intercalated Mg/Al LDH with an interlayer spacing of 2.43 nm and up to seven (00l) reflection orders. Reconstruction of the mixed oxide by intercalation with MO in the restored LDH was only achieved with Mg(Al)O. In this case, a competitive adsorption of MO on the external surface of the crystals was also seen. On the other hand, intercalation compounds exhibiting interlayer spacing of 2.43 nm were obtained with both Mg- and Ni-containing LDH using the anionic exchange method. The equilibrium and kinetic adsorption properties of the compounds were analyzed by UV-visible spectroscopy in anionic exchange experiments. According to the pseudo-second-order adsorption model, the amounts of adsorbed MO reach 3.82 and 2.83 mequiv/g for Mg- and Ni-containing LDHs, respectively, which are close to their respective anionic exchange capacity. The adsorption rates are on the same order of magnitude for the two LDHs (0.10-0.44 g mmol(-1) min(-1)), the equilibrium being reached in less than 60 min. The decomposition of MO by combustion of the organic moieties under an oxidizing atmosphere is delayed in Mg-containing MO-LDH hybrids when compared to the free MO molecule, showing that the thermal stability of MO species is enhanced after intercalation. In Ni-containing LDH, the main decomposition step of MO occurs 300 degrees C below that of Mg-containing LDH. This was rationalized in terms of a catalysis by the Ni-containing oxides formed during the thermal treatment. So these materials exhibit several advantages useful for the development of eco-friendly processes for the removal of dyes from effluents of textile, plastic, and paper industries.

Preparation and characterization of siliceous material using liposomes as template

Material synthesis using unilamellar liposomes with a high sol-gel temperature transition phase as a template leads to a new silica material.

Analytical applications of retinoid-cyclodextrin inclusion complexes. 1. Characterization of a retinal-β-cyclodextrin complex

In studies in these laboratories on the supramolecular chemistry of the retinoids, it has been recently confirmed that inclusion of these substances within the cavity of cyclodextrins protects their excited states, thus improving their photochemical stability. In the present paper, the isolation is described of a crystalline stable complex between retinal and beta-cyclodextrin, which has been characterized by means of several techniques including atomic force microscopy (AFM). The complex shows distinct spectroscopic differences from both retinal and beta-cyclodextrin. Thus, it absorbs at lambda(max) = 380 nm in water whereas retinal is insoluble; it shows room-temperature luminescence, which retinal does not; finally, it give 1H-NMR and 13C-NMR spectra in d6-DMSO with clear differences in chemical shifts with respect to those of beta-cyclodextrin. Besides these studies in solution, the behaviour of the complex in the solid state has been compared with that of physical mixtures of retinal and beta-cyclodextrin. IR spectroscopy shows clear differences, particularly a shift in the retinal carbonyl absorption (1644-1672 cm-1). AFM studies reveal the existence of aggregates; X-ray diffractometry also supports the formation of a cyclodextrin-retinal complex.

Characterization of a phospholipid bilayer entrapped into non-porous silica nanospheres

Using liposomes as templates is one of the paths leading to the synthesis of silica spherical particles. In these particles, the silica wall is assembled onto the external surface of the liposome. Generally, the walls of the resulting silica spheres are porous and in the specific case of liposome templating, the exact state of the trapped lipids is undocumented. In this work we describe the characterization of a new non-porous silica material obtained by templating liposomes. We show that the liposomes trapped in the nanospheres retain most of the structural and dynamic properties of the free liposomes. Also, as a consequence of the non-porous nature of the silica cladding the inner aqueous pool is permanently retained. To the best of our knowledge, silica nanospheres with such promising properties have so far not been obtained. These properties make these hybrid silica nano-spheres, referred to as liposils, potentialy good candidates for the storage and delivery of drugs.

Room temperature luminescence of a retinal complex of cyclodextrin

Abstract Retinal, which is normally insoluble in an aqueous medium and not fluorescent in solution at room temperature, emits a luminescence in the region of 450 nm, even in air-saturated aqueous solutions, when complexed to β or γ-cyclodextrin. The intensity decreases in the order β> γ and the quantum yields of luminescence are in the range 10−3–10−4. Further, retinal molecules in the inclusion complexes are subject to a bleaching process. Solubilization in micellar sodium dodecyl sulphate solutions also allows emission, albeit in smaller yield.

Use of micellar media for the fluorimetric determination of ellipticine in aqueous solutions.

Ellipticine is a pyridocarbazole alkaloid with interesting antitumour activity. Use of neutral ellipticine is hampered by its very low water solubility and therefore this compound has been administered as a salt; however, nitrogen quaternization modifies the antitumour properties of ellipticine. Potential alternatives to quaternization include the use of cyclodextrins, and also the use of micellar media. The latter possibility is explored in this work as an analytical tool. The results obtained with model anionic (SDS), cationic (CTAB) and neutral (Brij-35) surfactants are described. Fluorimetric analysis shows that ellipticine solubilizes completely in the presence of all these compounds, as a result of its aromatic, planar structure. The use of micellar media considerably increases the slopes of the calibration curves with improved correlation coefficients (e.g. 0.8904 in water and 0.9982 with SDS). Micellar media also modify proton transfer processes, as a consequence of the apolar environment of the micellar phase. Deprotonation of ellipticine is hampered in SDS because of the relationship between this process and the surface charge of the micelles. Finally, fluorescence quenching in micellar media has been studied, it being found that surfactants provide protection towards this phenomenon.

Immobilisation of a biological chelate in porous mesostructured silica for selective metal removal from wastewater and its recovery

This study represents a preliminary stage in the development of a process aimed at the selective uptake and release of metal ions from wastewater. The process involves the immobilisation of highly selective natural chelates secreted by bacteria or other living species inside mesoporous micelle-templated silicas (MTS) that could be used as usual resins. To demonstrate the feasibility of the concept, a model system was used. It involves pyoverdin, a natural Fe(III) chelator from a Pseudomonas fluorescens strain, covalently anchored to a glycidoxypropyl linker into the large pores (13 nm) of a MTS material. The hybrid material obtained is very stable as no leaching of the pyoverdin complex was observed during repeated washings and repeated uses. The native fluorescence of the pyoverdin allows a simpler follow-up and quantification of the iron uptake and release processes. The pyoverdin-anchored MTS is very selective towards Fe(III) if a multi-metallic solution is used. MTS materials allow a higher density of pyoverdin anchoring and consequently a higher metal uptake, compared to a high-grade silica gel.

Single-Step Dispersion of Functionalities on a Silica Surface

A new process for coating a mesoporous silica gel with a mixture of the grafting reagents para-aminophenyltrimethoxysilane and phenyltrimethoxysilane is thoroughly analyzed. The dilution of para-aminophenylsilane with phenylsilane at different ratios allows the density of the functional amino groups present on the silica surface to be controlled, while keeping constant the overall number of grafts. Furthermore, the choice of a rigid linker prevents undesirable interactions between the active function and the inorganic support that could alter the function reactivity. This simple and new method, which results in the improvement of the dispersion of a functionality in a one-pot synthesis, could be particularly interesting in the field of supported catalysis and molecular recognition. The dispersion of the functional groups of the synthesized hybrid solids is investigated using a pyrene derivative covalently linked to the free amino groups of the para-aminophenylsilanes by analyzing the excimer and monomer fluorescence properties of the probe.