Misleading information on homogeneity and heterogeneity obtained from sorption isotherms

In this paper, the applications and the differences among the widely applied sorption isotherms (Langmuir isotherm for adsorption, competitive adsorption, ion exchange, Freundlich isotherm) are shown. The misleading information obtained by the formal applications of the isotherms is demonstrated using a simple mathematical model of homovalent ion exchange on homogeneous surface. This model calculation clearly reveals that when studying surface accumulation processes, the mechanism of the sorption process has to be determined. The correct thermodynamic interpretation of the data of sorption experiments is possible only if the isotherm is adapted to the sorption mechanism. It is emphasized that the regression values of the applied models themselves provide correct information neither on the surface heterogeneity nor the interactions among the sorbed species. The curved shape of an inadequate applied isotherm gives no information about the heterogeneity. In order to study the energy distribution of surface sites, the thermodynamic equations, including isotherms, has to be selected on the basis of sorption mechanism. All variable quantities involved in the given model (concentrations of the competing substances in all phases) have to be measured experimentally and included into the isotherm.     

Anomeric information obtained from a series of synthetic trisaccharides using energy resolved mass spectra

The majority of structural investigations of oligosaccharides based on mass spectrometry use naturally occurring oligosaccharides, which do not allow extracting any common feature associated with anomeric structures and linkage positions. In order to address the issue to find such characteristics possibly contained in oligosaccharide structure, a synthetic combinatorial trisaccharide library was analyzed. The trisaccharides used in the analysis consisted of L-fucose, D-galactose and D-glucose, in which individual glycosidic linkages existed in either alpha- or beta-anomers. The analysis of energy-resolved mass spectra (ERMS) and the scattered plot analysis of some parameters obtained from ERMS for a series of trisaccharides revealed that lower activation energy was required for the dissociation of alpha-glycosides of these sugars compared to those of the corresponding beta-anomers. It is suggested that this finding may be useful in structural analysis of natural oligosaccharides.     

Studying the distribution pattern of selenium in nut proteins with information obtained from SEC-UV-ICP-MS and CE-ICP-MS

In this work, size exclusion chromatography (SEC) with UV and inductively coupled plasma mass spectrometry (ICP-MS) detection was used to study the association of selenium to proteins present in Brazil nuts (Bertholletia excelsa) under five different extraction conditions. As expected, better solubilization of proteins was observed using 0.05 mol L⁻¹ sodium hydroxide and 1% sodium dodecylsulfate (SDS) in Tris/HCl buffer (0.05 mol L⁻¹, pH 8) as compared to 0.05 mol L⁻¹ HCl, 0.05 mol L⁻¹ Tris/HCl or hot water (60 °C). Due to non-destructive character of Tris-SDS treatment, this was applied for studying molecular weight (MW) distribution patterns of selenium-containing nut proteins. Three different SEC columns were used for obtaining complete MW distribution of selenium: Superdex 75, Superdex Peptide, and Superdex 200 were tested with 50 mmol L⁻¹ Tris buffer (pH 8), 150 mmol L⁻¹ ammonium bicarbonate buffer (pH 7.8), phosphate (pH 7.5), and CAPS (pH 10.0) mobile phases. Using Superdex 200 column, the elution of at least three MW fractions was observed with UV detection (200-10 kDa) and ICP-MS chromatogram showed the co-elution of selenium with the two earlier fractions. The apparent MWs of these selenium-containing fractions were respectively about 107 and 50 kDa, as evaluated from the column calibration. For further characterization of individual selenium species, the defatted nuts were hydrolyzed with proteinase K and analyzed by capillary electrophoresis (CE) with ICP-MS detection. The suitability of CE for the separation of selenite, selenate, selenocystine and selenomethionine in the presence of the nut sample matrix is demonstrated. Complete separation of the above mentioned selenium species was obtained within a migration time of 7 min. In the analysis of nut extracts with CE-ICP-MS, selenium was found to be present mainly as selenomethionine.     

Gastric anti-ulcer activity of leaf fractions obtained of polar extract from Wilbrandia ebracteata in mice

Leaf fractions of Wilbrandia ebracteata were investigated for anti-ulcerogenic effects in ethanol and indomethacin-induced gastric ulcer assays in mice. Protective anti-ulcer effects were detected only in the ethanol-induced ulcer assay effects after pre-treatment with MeOH extract, MeOH chlorophyll-free, chlorophyll residue, HEX, DCM, aqueous MeOH fraction, ethyl acetate (EtOAc) and aqueous fractions. A potent anti-ulcerogenic effect was determined after pre-treatment of animals with EtOAc fraction, which was fractionated for isolation of active constituents. Seven flavonoids, 3',4',5,6,7,8-hexahydroxyflavonol, orientin, isoorientin, vitexin, isovitexin, luteolin, 6-methoxi-luteolin were isolated from the leaves of W. ebracteata (Cucurbitaceae) by chromatographic methods and identified by their spectral data. The data suggest that flavonoids are active anti-ulcerogenic compounds from leaves of W. ebracteata. The ability of scavenging free radicals was evaluated by DPPH reduction assay by TLC of flavonoids isolated.     

Experimental cluster structures: What quantitative information can be obtained from a single rotational data set?

The accuracy of a simple method to obtain an approximative position of the centre of mass of a molecule in a binary complex is discussed. It is shown that this method yields useful results if the second molecule in the complex is much smaller and lighter than the first one.     

Photobiological characteristics and photosynthetic UV responses in two Ulva species (Chlorophyta) from southern Spain

The effect of different wavebands of artificial UV (UVB and UVA) and photosynthetically active radiation (PAR) was assessed in two species of the genus Ulva, U. olivascens and U. rotundata, from southern Spain in order to test for possible differences in acclimation of photosynthesis. Both species share similar morphology but are subject to different light environments: U. rotundata is an estuarine alga, inhabiting subtidal locations, while U. olivascens is an intertidal, sun-adapted organism. Algae were exposed to three different UV conditions, PAR+UVA+UVB, PAR+UVA and PAR for 7 d. Short-term exposure (6 h) was also carried out, using two PAR levels, 150 and 700 micromolm(-2)s(-1). Pigment contents and photosynthesis vs. irradiance curves from oxygen evolution were used to contrast sun- and shade adaptation between these species. O2-based net photosynthesis (Pmax) and PAM-chlorophyll fluorescence (optimal quantum yield, Fv/Fm) were used as parameters to evaluate photoinhibition of photosynthesis in the experiments. The results underline different photobiological characteristics among species: the subtidal U. rotundata had higher contents of pigments (Chl a, Chl b and carotenoids) than the sun-adapted U. olivascens, which resulted in higher thallus absorptance and P-I parameters characterized by higher photosynthetic efficiency at limiting irradiances (alpha) and lower saturating points for photosynthesis (Ek). After 7 d exposure, photoinhibition of Fv/Fm was close to 40-45% in both species. Differences between UV treatments were seen in U. rotundata after 5 d and after 7 d in U. olivascens, in which PAR+UVA impaired strongly photosynthesis (80%). Such patterns were correlated with a progressive decrease in pigment contents, specially chlorophylls. In short-term (6 h) exposures, combinations of UVA+UVB and high PAR level resulted in high rates of photoinhibition of chlorophyll fluorescence (68-92%) in U. rotundata, whereas in U. olivascens photoinhibition ranged between 42% and 53%. Photoinhibition under low PAR combined to UV radiation was lower than observed under high PAR. Net O2-Pmax revealed similar response among the species, with maximal photoinhibition rates close to 60% in algae incubated under high PAR+UVA+UVB. In the case of UV exposure in combination with low PAR, the highest photoinhibition rates were measured in U. rotundata.     

Radiocesium tracer obtained from mushrooms

Some species of higher fungi growing at localities with increased contamnation by fission products from radioactive fallout /about 10–20 kBq¹³⁷Cs m^–2 and more/ contain up to 200 kBq of radiocesium-¹³⁷Cs and¹³⁴Cs, per kilogram d. m. Simple isolation of the rationcesium preparation of fruittbodies of suchn mushroom accumlators of radiocesium is described.     

Polymers from intermediates obtained from hydrogen cyanide

The recent demonstration of an easy synthesis of diiminosuccinonitrile (DISN) from hydrogen cyanide and cyanogen, the reduction of DISN to diaminomaleonitrile (DAMN), and the use of these compounds to form difunctional heterocycles has made several new polyamide intermediates accessible. The 1- and 2-methyl-1,2,3-triazole-4,5-dicarbonyl chlorides have been polymerized interfacially to form high-melting polyamides of good heat stability. Interfacial polymerization of 1-methylimidazole-4,5-dicarbonyl chloride and trans-2,5-dimethylpiperazine has given a polyamide that is water-soluble. The 2,6- and 2,3-pyrazinedicarbonyl chlorides have been similarly converted to high-melting polyamides. 2,6-Dicyano-3,5-dipiperazinylpyrazine has been prepared from tetracyanopyrazine and piperazine and reacted with toluene diisocyanate to form a strong, stiff polyurea. Polyamides were also made from 2,3-diaminoquinoxaline, 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, and DAMN.     

Parametric analysis of the extraction of depth profile information from ARXPS data obtained on a silicon wafer sample

In this study a silicon wafer was analysed by angle‐resolved x‐ray photoelectron spectroscopy and the data compared with a calculation based upon a simple model of the sample surface. The parameters in the mathematical model were varied in groups of three and the sum‐squared difference between the calculation and the experimental results was plotted as an error surface. Most of the error surfaces were found to exhibit a well‐constrained minimum, indicating an optimum set of values for the parameters in question, but important examples of co‐dependency were also noted. Copyright © 2003 John Wiley & Sons, Ltd.     

Quantitative information in decay curves obtained with a pulsed ion mobility spectrometer

Ion mobility spectrometry (IMS) is well known for its very high sensitivity, and thus IMS spectra are commonly used in the identification of trace gases. Extracting quantitative information from IMS spectra is, in contrast, difficult, especially regarding the reproducibility due to the nature of the processes involved in the measurement of the spectra. Here we present data extracted from signal decay curves obtained with a pulsed IMS, which can support the determination of substance concentrations in the lower ppb range with good stability.     

Enzymatic hydrolysis of mannoglucans obtained from cellulose

Conclusions The mannoglucans obtained by the reduction of ketocelluloses are easily cleaved by cellulase preparations, in which connection, depending on the activity ratio of the exo and endo enzymes in the cellulase complex, the predominant hydrolysis products are either monosaccharides (glucose and mannose) or oligosaccharides, in which the residues of these sugars are connected by -(1 4) linkages.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2622–2625, November, 1979.     

Hybrid/porous materials obtained from nano-emulsions

Nano-emulsions known also as mini-emulsions, ultrafine emulsions or submicron emulsions are a specific kind of emulsions that have a sub-micrometer droplet size and a low polydispersity. Nano-emulsions, being kinetically stable systems, require energy input in order to be formed, either from mechanical devices or from the intrinsic physicochemical potential of the components. The properties of the nano-emulsions make them suitable for applications in various domains such as drug delivery, cosmetics, pesticides and in particular for the preparation of inorganic or hybrid nanostructured materials. This review discusses the recent progresses made in this latest field. We focus on inorganic or hybrid nanoparticles, nanocapsules, hollow spheres or composites prepared by combining the nano-emulsion technique and the sol–gel process. In that case nano-emulsions act as template. We also outline the most recent development, which consists in using the nano-emulsions as imprints to get hierarchical porous silica materials.     

Intermolecular potentials obtained from high-energy alkali scattering

Intermolecular potentials have been obtained from high-energy total cross sections for several alkali metal systems: CS + He, Ne, Ar, CH₃NO₂; K + CH₄, C(CH₃)₄, C₆H₆, c-C₆H₁₂, CH₃I, CCl₄, SF₆, N₂. For the CS-rare gas cases and K + N₂ only the repulsive part was determined. For the rest both attractive and repulsive parts were seen.     

Adsorption characteristics of activated carbons obtained from corncobs

Dried, crushed, corncobs were carbonized at 500°C and steam activated (in one- or two-step schemes), or activated with H₃PO₄. The products were characterized by N₂ adsorption at 77 K, using the BET, _s and DR methods. Adsorption capacity was demonstrated by the iodine and phenol numbers, and the isotherms of methylene blue and Pb²⁺ ions, from aqueous solutions. A distribution of porosity in the carbons was estimated within the various ranges (ultra-, super-, meso- and macropores). Simple carbonization yields a poor adsorbing carbon; only its uptake for iodine was high and proposed to be due to an addition reaction on residual unsaturation of the parent lignocellulosic structures. Enhanced porosity was best associated with chemical activation and/or steam pyrolysis at 700°C. These activated carbons proved highly porous and rich in mesopores, and showed high adsorption capacity for methylene blue and Pb²⁺ ions. Phenol uptake was found to depend on surface chemical nature of the carbon rather than its porous properties. Corncobs were postulated to be feasible as feedstock to produce good adsorbing carbons, under the one-step activation schemes outlined here.     

Fragment momentum distributions obtained from coupled electron-nuclear dynamics

We theoretically investigate fragmentation processes induced by femtosecond laser pulses within a model which incorporates electronic and nuclear motion. Single-pulse excitation leads to diffraction patterns in the electron momentum distribution which depend on the nature of the electronic state and also on the nuclear charge distribution. Additional structures appear in the nuclear momentum distribution if two time-delayed pulses produce fragments in the same dissociation channel. It is shown that these functions are modified by the electronic degree-of-freedom. A simultaneous excitation of two different electronic states results in further interferences which are related to electronic wave-packet dynamics on the attosecond time-scale.     

Structures of two oxidation products obtained from palytoxin

The structures of two oxidation products of N-(p-bromobenzoyl)palytoxin were unambiguously determined by means of X-ray crystallographic analysis.