Stable hysteretic reflection of light at a nonlinear interface

We have observed a hysteretic (bistable) reflection of a Gaussian laser beam at the interface between glass and a liquid solution of polystyrene microspheres as nonlinear medium with both branches of the hysteretic curve being stable, in contrast to the results of previous experiments.     

Partial regularity for minimisers of certain functionals having nonquadratic growth

We prove partial regularity results for local minimisers of

Selective infrared photodissociation of protonated para-fluorophenol isomers: substitution effects in oxonium and fluoronium ions

Isomer-selective infrared photodissociation (IRPD) spectra are obtained for the first time for protonated polyfunctional aromatic molecules isolated in the gas phase. IRPD spectra of the oxonium and fluoronium isomers of protonated para-fluorophenol (C6H6FO+) were separately obtained by monitoring resonant photo-induced H2O and HF loss, respectively. Analysis of the F-H, O-H, and C-H stretch wave numbers provides valuable spectroscopic information on the chemical properties of these reactive intermediates, in particular on the substitution effects of functional groups.     

Amphiphilic cyclodextrin carriers embedding porphyrins: charge and size modulation of colloidal stability in heterotopic aggregates

The interaction between the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin (TPPS) and cationic vesicles formed by heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-cyclodextrin (SC6CDNH2) has been investigated in detail through a combination of elastic light scattering (ELS), quasi-elastic light scattering (QELS), zeta potential measurements, and time-resolved fluorescence anisotropy. ELS experiments provided the first structural characterization of these cationic vesicles both in the absence and in the presence of TPPS porphyrin, modeling the system as a spherical particle described by a single thin shell form factor. The structure of mixed hetero-aggregates is modulated by charge and size of the two components as function of different porphyrin/cyclodextrin (CD) molar ratios. At the limiting molar ratio studied, the absolute value of zeta potential (/zeta/ = 12.5 mV) seems to be a reference value for the formation of stable colloidal CD vesicular aggregates at thermodynamic equilibrium. New insights on the structure of these heterotopic colloids have been obtained by analysis of rotational correlation times at different molar ratios exploiting time-resolved fluorescence anisotropy experiments. At high porphyrin loads, the anisotropy decays behave as monoexponentials and the rotational correlation times (1-2 ns) together with the r(0) values close to zero suggest the presence of small amounts of TPPS embedded in a hydrophobic environment either in monomeric or in aggregated form. At the lower porphyrin/CD molar ratios, the anisotropy decays exhibit a double-exponential behavior showing a predominant component with a slow rotational correlation time (20-25 ns) and limiting anisotropy values of approximately 0.15. This component has been assigned to molecules that are more stabilized onto the CD vesicles, that is, porphyrins embedded into the oligo-ethylene "wall" of the CD vesicles. Scanning near-field optical microscopy of the samples evaporated on glass surfaces gave further insights on the morphology and optical properties of these systems, confirming the embedding of TPPS on the vesicles and evidencing the role of the solvent.     

The oxidation of water by cerium(IV) catalysed by nanoparticulate RuO2 on mesoporous silica

Mesoporous silicates are prepared by templating on the hexagonal (H1) mesophase of surfactant bipyridine complexes of ruthenium(II) using a true liquid-crystal templating approach. On calcination, the surfactant template is removed except for the central metal ion that is oxidised, forming nanoparticles of RuO2 that deposit within the pores. RuO2 is a known oxidation catalyst and, despite its anhydrous nature in these silicates, is found to be very active in catalyzing the oxidation of water by acidic CeIV.     

Separation of Escherichia coli 055:B5 lipopolysaccharide and detoxified lipopolysaccharide by high-performance capillary electrophoresis

A rapid, highly sensitive and reproducible high-performance capillary electrophoresis (HPCE) method (electrokinetic chromatography with sodium dodecyl sulfate) is described for the determination of the lipopolysaccharide (LPS) and detoxified LPS (D-LPS), produced by both alkaline treatment in anhydrous conditions and mild acid hydrolysis, from Escherichia coli 055:B5 bacteria. LPS and D-LPS are separated and readily determined within 25 min on an uncoated fused-silica capillary using normal polarity at 20 kV and detection at 200 nm. A linear relationship (correlation coefficient greater than about 0.97) was found for the LPS and the two D-LPS species over a wide range of concentrations, from approximately 120 to 360 ng, with a detection sensitivity less than about 100 ng. Furthermore, HPCE was able to separate several molecular species mainly due to the presence of populations with O-specific polysaccharides of distinct and increasing mean chain lengths. This approach could be of great importance for the quantitative determination of LPS and D-LPS during the purification and preparation processes, also considering the importance of D-LPS in the preparation of human vaccines, and for the qualitative evaluation of the heterogeneity of LPS and the O-polysaccharide components.     

Synthesis of 4H-3,1-benzoxazines, quinazolin-2-ones, and quinoline-4-ones by palladium-catalyzed oxidative carbonylation of 2-ethynylaniline derivatives

An effective and straightforward approach to the synthesis of 4H-3,1-benzoxazines 3 and 4, quinazolin-2-ones 5, and quinoline-4-one derivatives 6 and 7 is provided by palladium-catalyzed cyclization-alkoxycarbonylation of variously substituted 2-(trimethylsilanyl)ethynylaniline amide or urea derivatives 2. Reactions are carried out in 7:1 MeCN/MeOH at 65 or 75 degrees C in the presence of catalytic amounts of 10% Pd/C in conjunction with Bu(4)NI and KF and under 2.4 MPa of a 3:1 mixture of CO and air. Anti and syn 6-exo-dig cyclization modes account for the formation of the two stereoisomers. Isomerization of the vinylpalladium intermediate may occur as well. Formation of a double carbonylation product 7r and of a gem-dimethoxycarbonylation product 6s, whose structures have been determined by X-ray diffraction analysis, is justified through an unusual type of rearrangement.     

Recovery of pyridine from aqueous solution by membrane pervaporation

Three different membranes, based on poly(dimethylsiloxane) (PDMS), cation-exchange material and poly(vinyl alcohol) (PVA) respectively, were tudied for the separation of pyridine-water mixtures by pervaporation. The PDMS membrane was preferentially permeable to pyridine and the other two were selective towards water. Three membranes showed different permeation performance, allowing the application of the technique to the separation of feeds of different composition. The temperature profile of the permeability suggests that it is possible to carry out the operation at an elevated temperature in order to achieve high productivity. A combination of the three types of membranes was designed for the production of anhydrous pyridine from dilute pyridine aqueous solution by pervaporation.     

Mass spectrometric identification of a candidate biomarker peptide from the in vitro interaction of epichlorohydrin with red blood cells

The reaction products of epichlorohydrin with human alpha- and beta- globins, obtained through in vitro incubation of these compounds and red blood cells, were determined by using reversed-phase high-performance liquid chromatography (RP-HPLC), electrospray ionization mass spectrometry and matrix-assisted laser desorption/ionization tandem mass spectrometry. The alpha-globin was much more reactive than the beta-globin. At low incubation ratios, approximating the order of magnitude of epichlorohydrin concentration as found in workplaces, the only modified peptide still detectable was the 62-90 belonging to the alpha-chain and carrying an incremental mass of 92 u on either His72 or His89. Given that the two peptides co-eluted in a single chromatographic peak during RP-HPLC separation, they could be chosen as suitable biomarkers for quantification in the setting up of a new methodology for the biological monitoring of persons occupationally exposed, replacing currently known procedures.