Characterization of partially transesterified poly(beta-hydroxyalkanoate)s by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used for the characterization of a partially transesterified poly(beta-hydroxyalkanoate) (PHA), a polymer produced by the bacterial strain Alcaligenes eutrophus with saponified vegetable oils as the sole carbon sources. The transesterification was carried out separately under acidic and basic conditions to obtain PHA oligomers weighing <10 kDa. The intact oligomers were detected in their cationized forms, [M + Na]+ and [M + K]+, by MALDI-TOFMS. A composition analysis, using the MALDI-TOF spectra, indicated that the oligomers obtained via acid catalysis contained a methyl 3-hydroxybutyrate end group, and those obtained by base catalysis had a methyl crotonate (olefinic) end group. In addition to hydroxybutyrate (HB), the oligomers were found to contain a small percentage of hydroxyvalerate, which was independently confirmed by gas chromatography/mass spectrometry. In comparison, analysis of a commercial PHA polymer, transesterified under identical conditions, showed only the presence of HB, i.e., a pure poly(HB) homopolymer.     

Uptake of Tm(III) ions onto polyurethane foam from H2O - ethanol mixture containing 1-(2-pyridylazo)-2-naphthol (PAN)

Summary The sorption of microquantities of Tm(III) ions on washed polyurethane foam (PUF) from a mixture of aqueous solution and ethanol containing PAN was examined. The maximum sorption of 3.18^. 10^-6M solution of Tm(III) ions was observed at pH 8 with 30-minute equilibration time. The optimum ratio of aqueous-ethanol phase for the sorption of Tm(III) ions was found to be 3:1 v/v, respectively. The sorption rate of metal ions on PUF is followed a first order kinetics and obeyed the equation for an intra particle diffusion process. The equilibrium concentration data of Tm(III) ions could be described satisfactorily by several adsorption isotherms. The Freundlich adsorption isotherm constants 1/nand K_Fare 0.66±0.02 and (5.7±0.3)^. 10^-3mol^. g^-1, respectively. The Langmuir isotherm constants for monolayer coverage (Q) and binding strength of sorption (b) are (2.5±0.7)^. 10^-5mol^. g^-1and (1.6±0.1)^. 10⁴l^. mol^-1, respectively. The sorption capacity derived from Dubinin-Radushkevich (D-R) isotherm is (1.7±0.2)^. 10^-4mol^. g^-1and the sorption free energy (E) is 9.8±0.2 kJ^. mol^-1indicating chemisorption phenomena. The thermodynamic parameters indicate that the sorption of Tm(III) ions onto PUF is endothermic, entropy driven and spontaneous in nature.     

Co-activation of Gi and Gq proteins exerts synergistic effect on human platelet aggregation through activation of phospholipase C and Ca2+ signalling pathways

Our previous studies have shown that subthreshold concentrations of two platelet agonists exert synergistic effects on platelet aggregation. Here we studied the mechanism of synergistic interaction of 5-hydroxytryptamine (5-HT) and epinephrine mediated platelet aggregation. We show that 5-HT had no or little effect on aggregation but it did potentiate the aggregation response of epinephrine. The synergistic interaction of 5-HT (1-5 microM) and epinephrine (0.5-2 microM) was inhibited by alpha2-adrenoceptor blocker (yohimbine; IC50= 0.4 microM), calcium channel blockers (verapamil and diltiazem with IC50 of 10 and 48 mM, respectively), PLC inhibitor (U73122; IC50=6 microM) and nitric oxide (NO) donor, SNAP (IC50=1.6 microM)). The data suggest that synergistic effects of platelet agonists are receptor-mediated and occur through multiple signalling pathways including the activation PLC/Ca2+ signalling cascades.     

Depolymerization Study of Pakistani Lignite Coal Influence of Pre‐treatments on Product Slate

Influence of pretreatments, i.e., demineralization and pre‐soaking in some solvents on the yields of liquefied products obtained from hydro‐depolymerization of Pakistani coal in a pool of hydrogen has been discussed. Results of hydrogenation experiments demonstrated that demineralizing the coal sample prior to liquefaction caused the yields to decrease compared with the virgin coal samples. The contribution of mineral matter of coal has been evaluated by comparing the yields of liquid products of virgin and leached samples. Increase in the yields obtained from the hydrogenation experiments of swollen coal samples was not satisfactorily significant.     

Thermal synthesis and characterisation of N,N'-di(chlorobenzyl) ureas

The thermal stability of the Schiff base ethylacetoacetate-o-chlorobenzylamine (bdII), N-o-chlorobenzyl-C-benzoyl acetamide (bdIII), and N-p-chlorobenzyl-C-benzoyl acetamide (bdIV) were studied by thermogravimetric analysis. II Gave N,N'-di(o-chlorobenzyl) urea (bdIa) at 60° C, whereas the thermogravimetric curves of III and IV indicate that reactions other than formation of I may occur. The urea derivatives (I) have also been prepared from benzylamines and the corresponding β-ketoester and identified.     

Composition of the basic fraction of marijuana and tobacco condensates: A comparative study by capillary GC/MS

Summary Combined capillary gas chromatography/mass spectrometry has been used to characterize the basic fraction of Mexican marijuana and standard tobacco smoke condensates. A thermostable Superox-coated glass capillary column permitted elution of relatively large nitrogen-containing compounds. Substantial qualitative and quantitative differences between the two materials were noted.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday.     

Potentiodynamic and cyclic voltammetric behaviour of a lead electrode in NaOH solution

Summary The electrochemical behaviour of lead in NaOH solution was studied by potentiodynamic and cyclic voltammetric techniques in combination with X-ray diffraction analysis. The active dissolution of lead involves a small shoulderA1 followed by a peakA1 prior to a passive region. The shoulderA1 is assigned to the electroformation of a Pb(OH)₂ film, whereas peakA1 is due to the formation of PbO. Beyond the passive region, the current density increases again, forming a small shoulderA2 and a peakA2 prior to the oxygen evolution potential. The shoulderA2 and the peakA2 are correlated to the electrooxidation of PbO to Pb₃O₄ and PbO₂, respectively. The intensity of the anodic peaks increases with increasing alkali concentration, temperature and scan rate. In cyclic voltammetry, the reverse scan shows two cathodic peaksC1 andC2 which are correlated to the electroreduction of PbO and PbO₂ respectively, to Pb.

---

Potentiodynamisches und cyclovoltammetrisches Verhalten einer Bleielektrode in NaOH-Lösung

Zusammenfassung Das elektrochemische Verhalten von Blei in NaOH wurde mittels potentiodynamischer und cyclovoltammetrischer Techniken unter Zuhilfenahme der Röntgenbeugungsanalyse untersucht. Die aktive Auflösung von Blei verläuft über eine SchulterA1, die von einem einer passiven Region vorgelagerten PeakA1 gefolgt wird. Die SchulterA1 wird der elektrochemischen Bildung eines Pb(OH)₂-Films, der PeakA1 der Bildung von PbO zugeschrieben. Jenseits der passiven Region steigt die Stromdichte wieder an, und vor Erreichen des Sauerstoffpotentials treten eine kleine SchulterA2 und ein PeakA2 auf, die mit der Elektrooxidation von PbO zu Pb₃O₄ und PbO₂ korrelieren. Analog dazu beobachtet man in der cyclischen Voltammetrie zwei kathodische PeaksC1 undC2, die der Elektroreduktion von PbO und PbO₂ zu Pb entsprechen. Die Intensität der anodischen Peaks steigt mit steigender Alkalikonzentration, Temperatur und Scangeschwindigkeit.

     

Determination of uranium and thorium concentrations in some West Malaysian limestones using neutron activation and delayed neutron analysis

Concentrations of uranium and thorium in some West Malaysian limestones have been determined using neutron activation and delayed neutron analyses. These limestones are mainly calcium carbonates and contain uranium and thorium in concentrations of about a few parts per million.     

Reduction of effects of structured non-specific absorption in the determination of arsenic and selenium by electrothermal atomic absorption spectrometry

The presence of iron and phosphates in biological matrices causes deuterium arc background-correction systems to overcompensate at several arsenic and selenium resonance lines. The addition of platinum as matrix modifier has a significant effect on both the absorbance/time profile of iron and the formation of gaseous phosphate decomposition products. A nickel/platinum matrix modifier is shown effectively to control the problems in the determination of selenium arising both from thermal instability and spectral interferences. The same combination eliminates the spectral interferences found at the arsenic resonance lines. Remaining problems are the thermal stabilization of organometallic arsenic compounds present in biological samples. When radioactived-labelled ⁷⁴As compounds prepared in vivo were applied, none of the tested matrix modifiers (Ni, Cu, Ag, Pd, Zr, Ce, Ce + magnesium nitrate) showed a significant influence on the volatility of arsenic in whole blood and urine from rats.