Characterization of perylene diimide dye self-assemblies and their use as templates for the synthesis of hybrid and supermicroporous nanotubules

The self-organizing structures formed by a water-soluble perylene diimide dye (PDI) have been studied by several experimental techniques as potential templates for the preparation of hybrid nanomaterials. The dye forms chromonic-nematic and hexagonal liquid crystals in water. The aggregates in liquid crystals consist of one-molecule-wide stacks. From the changes in the solution proton NMR chemical shifts with concentration, it appears that adjacent molecules are twisted. There is significant broadening of the aromatic resonances at higher concentrations, arising from nonmotionally averaged dipole-dipole coupling between adjacent aromatic hydrogens. This is attributed to slow overall rotation of the aggregates in solution, suggesting that they grow up to several tens of nanometers. Dye aggregates serve as templates for the formation of silica tubules (1-5 μm length, average diameter ≈300 nm), with aligned and very thin (1-2 nm) dye nanostripes embedded in the walls. The silica tubes precipitated from solution are formed by the cooperative interaction between PDI and silica species during the sol-gel reaction. Upon calcination, silica nanotubules with supermicroporous walls are obtained. In comparison with conventional surfactant systems, the use of π-π stacked chromonic aggregates brings new possibilities for the templated fabrication of pores with sizes below the mesoporous range. Materials could find applications in photovoltaics as well as in shape selective catalysis and adsorption.     

Surfactants Based on Bis-Galactobenzimidazolones: Synthesis, Self-Assembly and Ion Sensing Properties

A series of new non-ionic amphiphiles based on bis-galactobenzimidazolones have been synthesized by grafting alkyl bis-benzimidazolone units as hydrophobic tails on hydroxypropyloxygalacto-pyranose moieties as hydrophilic heads. Their surface and self-aggregation properties in water were evaluated. The compounds show very low critical micellar concentrations (CMCs) that decrease with increasing chain length; values for the minimal area per molecule at the interface (A _min) follow the same trend. The synthesized compounds also form hexagonal liquid crystals in water for a certain range of hydrophobic tail lengths. On the other hand, the new amphiphiles show characteristic UV?CVis absorption and fluorescence emission bands associated with the benzimidazolone moiety. The fluorescence emission is quenched with a certain degree of selectivity by cations, due to their strong affinity towards the benzimidazolone group, which shows ion complexation properties. Hence, the reported new amphiphiles are candidates as self-assembling chemosensors. The quenching efficiency and also ion sensing sensitivity is higher in the monomeric state as compared to the micellar state. The fluorescence emission intensity is higher for compounds with a shorter alkyl chain.     

Preparation,characterization, and release properties of hydrogels based on hyaluronan for pharmaceutical and biomedical use

Hyaluronic acid (HA) is a natural polysaccharide that is widely distributed in the human body. Its physicochemical properties and high biocompatibility make it a good candidate for biomedical and pharmaceutical uses. In the present work, we report HA‐based hydrogels that could be applied as drug delivery systems or as implants for the treatment of joint diseases. We use butanediol diglycidyl ether as a chemical crosslinker to obtain HA hydrogels. Using a new dissolution tester and ketoprofen (KP) as a model drug, we study the release properties of the hydrogels. We obtain homogeneous and transparent hydrogels with high strength and elasticity. The swelling ratio (SR) depends on the crosslinker concentration and pH of the medium. We also reveal differences between the release profile of KP from swollen and unswollen hydrogels. The characteristics and differences in KP release profiles depending on the SR suggest the possibility of obtaining controlled release from HA‐based hydrogels. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1377‐1382, 2013     

A Concise Review on Nano-emulsion Formation by the Phase Inversion Composition (PIC) Method

Nano-emulsion formation by the phase inversion composition method is reviewed. The relationship between phase behavior and nano-emulsion formation is revised with emphasis on the key role of phase transitions involving changes in the sign of the curvature of the surfactant layer (inversion) via zero-average-curvature structures such as bicontinuous microemulsions or lamellar liquid crystalline phases. The different low-energy methods that can be involved in a nano-emulsification process at constant temperature are also discussed.     

Composition effects on the mechanical properties of microemulsion-made core/shell polymers

The synthesis of hard-core/soft-shell and soft-core/hard-shell polymers by a two-stage semi-continuous microemulsion polymerization process is reported here. In the first stage, high-solid polymer seeds (>30 wt%) of slightly crosslinked polystyrene or poly(butyl acrylate) were obtained; then, the other monomer was added semi-continuously to form the shell. The effects on the mechanical properties (Young's modulus, ultimate properties, hardness and impact energy) of the ratio of rigid-to-soft and soft-to-rigid polymers were studied. It was found that the material becomes stiffer and presents a lower elongation at break as the amount of the rigid polymer increases. The mechanical properties also depend on the location of the hard and soft polymers. Experimental mechanical properties were compared with the predictions of the Kerner and the equivalent box models. Comparison with the predictions of the Kerner model suggests that phase inversion occurred in the case of hard-core/soft-shell materials. Phase inversion was corroborated by transmission electron microscopy. The thermodynamically preferred morphology, according to theory, is that of soft-core/hard-shell, regardless of the order of addition of monomers. Experimental data follow closely the predictions of the equivalent box model only for soft-core/hard-shell polymers.     

Synthesis, characterization and biological activity of trans-platinum(II) and trans-platinum(IV) complexes with 4-hydroxymethylpyridine

The synthesis and chemical characterization of two new trans platinum complexes, trans-[PtCl(2)NH(3)(4-hydroxymethylpyridine)] (1) and trans-[PtCl(4)NH(3)(4-hydroxymethylpyridine)] (2) are described. Their ability to interact with 5'-GMP by themselves and in the presence of reducing agents in the case of trans-[PtCl(4)NH(3)(4-hydroxymethylpyridine)] were tested. Circular dichroism, electrophoretic mobility in agarose gel, and atomic force microscopy studies showed that the interaction of complex 1 with DNA is stronger than that of complex 2. Cytotoxicity tests against HL-60 tumor cells also showed higher activity for trans-[PtCl(2)NH(3)(4-hydroxymethylpyridine)] than for trans-[PtCl(4)NH(3)(4-hydroxymethylpyridine)]. Complex 1 presents similar behavior to cisplatin, but with a lower IC(50) at 24 h. Complex 1 also showed high apoptosis induction.     

Surface and Self-Aggregation Properties of Bis-Benzimidazolones Derivatives of <Emphasis Type="SmallCaps">d</Emphasis>-Glucose

The surface and self-aggregation properties in water of a new series of amphiphilic homologues, bis-benzimidazolone derivatives of d-glucose, were investigated. Parameters such as the maximal surface excess concentration, minimal area per molecule at the interface, and critical micelle concentration (CMC) were found to be significantly dependent on the hydrophobic alkyl chain length. The synthesized compounds form micelles at remarkably low concentrations, and CMCs derived from surface tension measurements show a minimum as a function of the alkyl chain length; this unusual trend can be attributed to the formation of submicellar aggregates in compounds with long alkyl chains, as evidenced from fluorescence probe spectroscopy data. At high surfactant concentrations, lyotropic liquid crystalline phases with hexagonal structure are formed. Small angle X-ray scattering measurements indicate that the characteristic nanoscopic lengths increase with water swelling and alkyl chain length.