Comparison of the interaction of dihydrocholesterol and cholesterol with sphingolipid or phospholipid Langmuir monolayers

We report here a study of the interaction of dihydrocholesterol (DChol) with palmitoyl-oleoyl-phosphatidylcholine (POPC) or sphingomyelin (SM) in Langmuir monolayers. DChol and cholesterol (Chol) have very close chemical structures, and DChol is often used in place of Chol because of its better stability. Surface pressure measurements and experiments of desorption induced by beta-cyclodextrin show that POPC-DChol monolayers behave similarly to POPC-Chol ones: condensing effects of DChol and Chol on POPC and desorption percentages are in the same range. Moreover Brewster angle microscopy (BAM) experiments performed on these monolayers show that on the whole they are both homogenous. The analysis of mean molecular areas versus DChol percentage shows that this sterol is also able to induce SM condensation at low surface pressure. The condensation of SM molecules is particularly strong at 30 mol% of DChol. At higher surface pressure, the condensation efficiency of DChol decreases and monolayers behave more ideally, even if an inflection point is always observed at 30 mol% of DChol. However, desorption percentages, clearly lower than those obtained with POPC-DChol monolayers, show that DChol is kept at the interface. At last BAM images show also differences in the behaviour of SM-DChol and SM-Chol monolayers. These differences could be due to the different compressibility and conformation of the A/B rings in the two sterols and the rigidity of the sphingosine chain. They suggest that the use of DChol in place of Chol has to be done carefully in the presence of SM.     

Liquid crystalline formulations containing modified surface TiO2 nanoparticles obtained by sol–gel process

Titanium dioxide (TiO₂) is an inorganic compound used as sunscreen in cosmetic/pharmaceutical formulations as a way to prevent the skin cancer. In this work we have used surface modified titania nanoparticles obtained by thermo-reversible sol?Cgel transition showing transparency in the range of temperature typical for sunscreen use (between 20 and 45?°C). The goal of this work was to develop and characterize liquid crystalline cosmetic formulations containing surface modified titania nanoparticles. We have analyzed the citotoxicity of the nanoparticles, their zeta potential and the liquid crystalline phase behavior of the formulations. The violet crystal assay has shown no citotoxicity associated to the presence of surface modified groups on the two cell lines tested, human keratinocytes and fibroblasts, presenting more than 70% of cell viability for all analyzed nanoparticles. The zeta potential measurements revealed a negative charged surface for TiO₂ nanoparticles at pH values in the range of 6.5?C7.0, preventing the aggregation and maintaining the final transparency of the liquid crystalline sunscreen formulations. The polarized light microscopy, associated to SAXS, have shown the presence of liquid crystalline phases both with and without TiO₂ nanoparticles. The charged surface of TiO₂ nanoparticles maintains the stability of the formulations and the liquid crystalline structure. This renders this system a good candidate for being used simultaneously as sunscreen and as controlled release system of anti cancer drugs.     

Ionic core-shell dendrimers with an octacationic core as noncovalent supports for homogeneous catalysts

Ionic core-shell dendrimers with an octacationic core have been applied as noncovalent supports for homogeneous catalysts. Catalytically active arylpalladium complexes, which bear a tethered sulfato group, were noncovalently attached to the ionic core-shell dendritic supports via a straightforward ion-exchange reaction under mild conditions. Diagnostic shifts in (1)H NMR and Overhauser contacts show that the sulfato groups of the catalysts are located close to the octacationic core of the dendritic support in the resulting assemblies. The location of the catalytic Pd(II) sites has been varied via two strategies: by increasing the dendrimer generation and/or by shortening of the sulfato tether. In addition, a metallodendritic assembly was prepared, which bears an alternative shell of apolar dodecyl groups. Both the dendrimer size and the nature of the dendritic shell have no influence on the binding properties of the dendritic supports, i.e., the octacationic dendrimers of generations 1-3 form discrete 1:8 assemblies with the arylpalladium complexes. The structural aspects and the nature of the metallodendritic assemblies have been studied by means of pulse gradient spin-echo NMR diffusion methods, Overhauser spectroscopy, and electron microscopy (TEM). These techniques showed that the dendritic supports and arylpalladium complexes are strongly associated in solution to give unimolecular assemblies of nanoscopic dimensions. Membrane dialysis can recover these metallodendritic assemblies due to their nanoscopic size. The catalytic performances of the metallodendritic assemblies are comparable, but slightly lower than the performance of the unsupported catalyst.     

On-line dynamic extraction and automated determination of readily bioavailable hexavalent chromium in solid substrates using micro-sequential injection bead-injection lab-on-valve hyphenated with electrothermal atomic absorption spectrometry

A novel and miniaturized micro-sequential injection bead-injection lab-on-valve (microSI-BI-LOV) fractionation system was developed for on-line microcolumn soil extraction under simulated environmental scenarios and accurate monitoring of the content of easily mobilisable hexavalent chromium in soil environments at the sub-low parts-per-million level. The flow system integrates dynamic leaching of hexavalent chromium using deionized water as recommended by the German Standard DIN 38414-S4 method; on-line pH adjustment of the extract by a 0.01 mol L(-1) Tris-HNO(3) buffer solution; isolation of the chromate leached from the matrix constituents onto a Q Sepharose strong anion-exchanger freshly packed into the microconduits of the microSI-assembly; air-segmented elution of the sorbed species by a 40 microL plug of 0.5 mol L(-1) NH(4)NO(3) (pH 8) eluent; and detection by electrothermal atomic absorption spectrometry (ETAAS). The effect of simulated acidic rain on the accessibility of chromate forms for plant uptake was also investigated. The proposed approach offers several advantages over conventional speciation/fractionation protocols in the batch mode, including immediate separation with concomitant preconcentration of the released chromate, minimization of Cr(vi) to Cr(iii) interconversion risks, enhanced accuracy, and non-existence of re-adsorption/re-distribution problems along with a detailed pattern of the kinetics of the leaching process. The reliability of the proposed method was evaluated via spiking of a moderately polluted agricultural soil material (San Joaquin Soil-Baseline Trace Element Concentrations) with water-soluble Cr(vi) salts at different concentration levels. The potential of the microSI-BI-LOV set-up with renewable surfaces for flame-AAS determination of high levels of readily bioavailable chromate in contaminated soils is also addressed.     

The mechanistic puzzle of transition-metal-catalyzed skeletal rearrangements of enynes

Three pathways actually compete in metal-catalyzed cyclizations of enynes in which the metal selectively activates the alkyne: an endocyclic process and two exo-cyclizations, one proceeding by anti attack of the alkene and a second one resulting in a syn addition. Although cyclobutenes may be formed in transition-metal-catalyzed cyclization of some enynes, particularly, 1,7-enynes, these compounds are not necessarily the intermediates in the skeletal rearrangement. Cyclobutenes are formed by ring expansion of syn-cyclopropyl metal-carbenes formed in the syn pathway.     

Synthesis of Pd3Tl and Pd6Tl2 complexes based on a trinuclear aryl-palladium(II) complex acting as a metallaligand toward thallium(I) through Tl-arene and Tl-I bonds

The metallaligand [(PdIL(2))(3)(C(6)Me(3)-1,3,5)] (L(2) = 4,4'-di-tert-butyl-2-2'-bipyridine = tbbpy) reacts with TlOTf to afford the complex [{(PdIL(2))(3)C(6)Me(3)-1,3,5}Tl]OTf, which exists in the solid state as a 2:1 mixture of monomer and dimer, both showing Tl(I)-I and Tl(I)-η(6)-mesitylene bonds. In solution, only the monomer is observed. Heating of toluene solutions of [(PdIL(2))(3)(C(6)Me(3)-1,3,5)] affords the dinuclear complex [(PdIL(2))(2)(C(6)HMe(3)-1,3,5)].     

Electrochemical Modification of Gold Electrodes with Azobenzene Derivatives by Diazonium Reduction

An electrochemical study of Au electrodes electrografted with azobenzene (AB), Fast Garnet GBC (GBC) and Fast Black K (FBK) diazonium compounds is presented. Electrochemical quartz crystal microbalance, ellipsometry and atomic force microscopy investigations reveal the formation of multilayer films. The elemental composition of the aryl layers is examined by X‐ray photoelectron spectroscopy. The electrochemical measurements reveal a quasi‐reversible voltammogram of the Fe(CN)₆^3?/4? redox couple on bare Au and a sigmoidal shape for the GBC‐ and FBK‐modified Au electrodes, thus demonstrating that electron transfer is blocked due to the surface modification. The electrografted AB layer results in strongest inhibition of the Fe(CN)₆^3?/4? response compared with other aryl layers. The same tendencies are observed for oxygen reduction; however, the blocking effect is not as strong as in the Fe(CN)₆^3?/4? redox system. The electrochemical impedance spectroscopy measurements allowed the calculation of low charge‐transfer rates to the Fe(CN)₆^3? probe for the GBC‐ and FBK‐modified Au electrodes in relation to bare Au. From these measurements it can be concluded that the FBK film is less compact or presents more pinholes than the electrografted GBC layer.     

Value reducts and bireducts: A comparative study

In Rough Set Theory, the notion of bireduct allows to simultaneously reduce the sets of objects and attributes contained in a dataset. In addition, value reducts are used to remove some unnecessary values of certain attributes for a specific object. Therefore, the combination of both notions provides a higher reduction of unnecessary data. This paper is focused on the study of bireducts and value reducts of information and decision tables. We present theoretical results capturing different aspects about the relationship between bireducts and reducts, offering new insights at a conceptual level. We also analyze the relationship between bireducts and value reducts. The studied connections among these notions provide important profits for the efficient information analysis, as well as for the detection of unnecessary or redundant information.