Pyrrolic tripodal receptors for carbohydrates. Role of functional groups and binding geometry on carbohydrate recognition

The contribution from several H-bonding groups and the impact of geometric requirements on the binding ability of benzene-based tripodal receptors toward carbohydrates have been investigated by measuring the affinity of a set of structures toward octyl β-D-glucopyranoside, selected as a representative monosaccharide. The results reported in the present study demonstrate that a judicious choice of correct geometry and appropriate functional groups is critical to achieve the complementary hydrogen bonding interactions required for an effective carbohydrate recognition.     

Beta spectra deconvolution for liquid scintillation counting

This study presents the first results of a deconvolution method for Liquid Scintillation complex spectra. The method has been developed by means of the software MATLAB and is based on the utilization of Fourier Transforms. Its main target is to obtain a fast calculation procedure capable to unfold complex spectra without requiring any preliminary knowledge of the peak shapes of the component nuclides. Experimental tests have been carried out by means of a Perkin Elmer Wallac Quantulus 1220. Distinctive features of Quantulus have not been used, the instrument was only utilized to generate spectra in numerical form that subsequently were uploaded to a PC and analyzed by MATLAB. Results show acceptable capabilities of the method both for fitting convoluted spectra and for unfolding single nuclide shapes. Further experimentation is scheduled, in order to take account of quenching effects; it will be carried out by adding to the calculation algorithm another step, capable of performing a self-choice of the number of harmonics. The final aim is to fit any kind of beta spectra also when quenching influences the shape deeply.     

Viscosity of concentrated solutions of ethylene-vinylacetate copolymers in paraffin at three molecular weights and at three temperatures

Summary Measurements of the viscosity of concentrated solutions of the ethylene-vinyl-acetate copolymer (EVA) in paraffin were carried out at a temperature 80°C; 120.5°C; 150°C, at molecular weights of the EVA,M ₂ = 150 000; 200 000; 250 000, and at concentrationsc ₂ up to 11 g/100 cm³ solution.The equation ofBueche andKelley and its extension to the lower concentrations (both related to the free-volume theory) and the semiempirical equations ofOnogi et al. and ofWeissberg et al., were considered with the aim of correlating the values of vs.c ₂ in the most general way possible. The numerical elaboration of the data made it possible to calculate the value of (root-mean-square deviation between calculated and experimental ln) in the various cases, and it emerged that when curves ln vs.c ₂ are considered atT andM ₂ constant, the best interpolation is obtained withBueche's equation with three parameters (,f ₁,f₂), while if all the experimental points are considered withT andM ₂ variableWeissberg's equation gives the best interpolation. The behaviour ofOnogi's equation is intermediate, however the master curves atT = constant make it possible to assemble the data with limited dispersion.The comparison of our viscosity data with the ones calculated by means of the free-volume theoretical expressions leads to the conclusion that the paraffin-EVA system has been studied in a concentration region below the critical value of the polymer concentration above which the chain entanglements prevail.

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Zusammenfassung Viskositätsmessungen an konzentrierten Lösungen von Äthylen-Vinylacetat-Copolymer (EVA) mit MolekulargewichtenM ₂ von 150 000; 200 000 und 250 000 in Paraffin wurden bei Temperaturen von 80; 120,5 und 150°C für Konzentrationenc ₂ bis zu 11 g/100 cm³ durchgeführt.Die aus der Theorie des Freien Volumens abgeleitete Gleichung vonBueche undKelley und ihre Modifikation für niedrige Konzentrationen sowie die halbempirischen Gleichungen vonOnogi et al. und vonWeissberg et al. werden in möglichst allgemeiner Weise mit den experimentellen Kurven(c ₂) korreliert. Die numerische Auswertung mit der Methode der kleinsten Quadrate ergibt, daß für konstant gehaltenesT undM ₂ die beste Interpolation von ln gegenc ₂ durch die drei-parametrige Bueche-Gleichung gegeben wird, wohingegen für die Gesamtheit der experimentellen Werte mit variabler TemperaturT und KonzentrationM ₂ die Weissberg-Gleichung die beste Korrelation liefert. Die Onogi-Gleichung liegt in ihrem Verhalten zwischen den beiden genannten Gleichungen, doch ermöglichen es die Master-Kurven fürT = const, alle Daten mit begrenzter Streuung zusammenzufassen.Ein Vergleich der hier gemessenen Viskositätswerte mit den aus der Theorie des Freien Volumens berechneten führt zu dem Schluß, daß das Paraffin-EVA-System in einem Konzentrationsbereich untersucht worden ist, der unterhalb der kritischen Polymerkonzentration liegt, bei dem der Einfluß der Kettenverhängungen die Oberhand gewinnt.

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With 5 figures and 5 tables     

Diffusion of quinidine sulphate through polydimethylsiloxane membranes containing silica filler : II. Evaluation of the permeability of neutral quinidine at various ph values and at 37°c

In this paper, experimental data on the diffusion of quinidine sulphate through a polydimethylsiloxane film containing SiO₂ filler are reported at pH = 1.18, 4, 7.6, 8, 10 and 11; all at T = 37°C. When these data are correlated with the theoretical equation of Part I for large times, a least squares procedure gives the values of the permeability and of the fraction of quinidine adsorbed onto the filler as a function of pH. The quinidine flux is compared with that in a glass porous disc cell. The behaviour of the two ceils considered is similar only for higher values of pH. The adsorption of quinidine onto the SiO₂ phase leads to permeabilities quite different from those obtained from simpler models.     

Synthetic aminopyrrolic receptors have apoptosis inducing activity

We report two synthetic aminopyrrolic compounds that induce apoptotic cell death. These compounds have been previously shown to act as receptors for mannosides. The extent of receptor-induced cell death is greater in cells expressing a high level of high-mannose oligosaccharides than in cells producing lower levels of high-mannose glycans. The ability of synthetic receptors to induce cell death is attenuated in the presence of external mannosides. The present results provide support for the suggestion that the observed cell death reflects an ability of the receptors to bind mannose displayed on the cell surface. Signaling pathway studies indicate that the synthetic receptors of the present study promote JNK activation, induce Bax translocation to the mitochondria, and cause cytochrome c release from the mitochondria into the cytosol, thus promoting caspase-dependent apoptosis. Such effects are also observed in cells treated with mannose-binding ConA. The present results thus serve to highlight what may be an attractive new approach to triggering apoptosis via modes of action that differ from those normally used to promote apoptosis.     

Toxic metal species and food regulations--making a healthy choice

As a safeguard for human health, guidelines and regulations stipulating maximum permissible concentrations (MPCs) of metals in foods have been set to limit our dietary exposure to toxic metals. It is now well accepted, however, that the chemical form of the metal must be considered when assessing the possible human health consequences of exposure, and this in turn has led to discussion on the incorporation of speciation data in the setting of MPCs for metals in foods. Some practical aspects and implications of framing food legislation in terms of metal species are presented.     

(31)P magic angle spinning NMR spectroscopy for probing local environments in paramagnetic europium-substituted wells-dawson polyoxotungstates

A series of europium-substituted Wells-Dawson polyoxotungstates were addressed by 31P magic angle spinning (MAS) NMR spectroscopy. The electron-nuclear dipolar interaction dominates the 31P spinning-sideband envelopes. The experimental electron-nuclear dipolar anisotropies were found to be in good agreement with those calculated based on the known crystallographic coordinates and effective magnetic moments and assuming a point-dipole approximation. These electron-nuclear dipolar anisotropies directly report on the anion stoichiometry and on the positional isomerism, indicating that 31P MAS NMR spectroscopy may be a useful and quick analytical probe of the local environment in Wells-Dawson solids containing localized europium paramagnetic centers.     

Determination of ‘arsenosugars’ in algae with anion-exchange chromatography and an inductively coupled plasma mass spectrometer as element-specific detector

The retention behavior of four naturally occurring dimethylarsinoylribosides with –CH₂-CHOH-CH₂X (X = OH, HO₃POCH₂CHOHCH₂OH, SO₃H, OSO₃H) as aglycones, of arsenous acid, arsenic acid, methylarsonic acid, and dimethylarsinic acid was investigated on a Hamilton PRP-X100 anion-exchange column with aqueous solutions of ammonium dihydrogen phosphate (20 mmol/L) in the pH range of 3.8–9.0 as mobile phase. A HP 4500 inductively coupled plasma mass spectrometer (ICP-MS) served as arsenic-specific detector. The influence of pH, temperature, and the concentration of methanol in the mobile phase on the retention times of these arsenic compounds was explored. An aqueous 20 mM ammonium dihydrogen phosphate solution at pH 5.6 at a column temperature of 40?°C was considered optimal as it allowed ¶the separation of seven of the arsenic compounds within 16 min. Only arsenous acid and the ribose with the glycerol aglycone have overlapping signals with both migrating almost with the solvent front. At a concentration of 0.50 ng As mL^–1 the relative standard deviations (n = 3) of the signal areas of the eight arsenic compounds was in the range from 3.5 to 8.1%. The linear calibration curves (peak areas) from 0.5 to 10 ng/mL had correlation coefficients ¶> 0.997. Extracts obtained from the brown algae Fucus spiralis and Halidrys siliquosa were chromatographed under the optimized conditions. Both species contained the sulfate riboside as the major arsenic compound (～55% of total extractable arsenic) together with the sulfonate- and phosphate riboside. Arsenic acid was a significant constituent of Halidrys siliquosa (～6.5%), but was not detected in Fucus spiralis.