The application of solid phase extraction to the analysis of tobacco-specific nitrosamines.

A new isolation and separation method has been developed for the alkaloid-related nitrosamines in tobacco, called tobacco-specific nitrosamines (TSNA). The improved isolation procedure involves the extraction by sonication of TSNA from cured tobacco with toluene and an aqueous citrate buffer solution, while purification is achieved by solid phase extraction on small silica cartridges. Interfering extract materials are eluted from the silica cartridges with the toluene and a chloroform-methylene chloride solvent, while subsequent elution with chloroform yields the TSNA in a purified fraction. Gas chromatographic analyses on an SE-54-coated glass capillary column and detection by a nitrogen-phosphorous detector produce very good data on the four TSNAs, which include N-nitrosanatabine (NATB), N-nitrosoanabasine (NAB), 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (called NNK), and N-nitrosonornicotine (NNN). The method is shown to be quantitative, reproducible, and applicable to the determination of TSNA in various tobacco samples, such as stems and lamina of cured tobacco leaves, as well as to smokeless tobacco.     

Polymerization of lactide with zinc and magnesium beta-diiminate complexes: stereocontrol and mechanism.

A series of zinc(II) and magnesium(II) alkoxides based upon a beta-diiminate ligand framework has been prepared. [(BDI-1)ZnO(i)Pr](2) [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] exhibited the highest activity and stereoselectivity of the zinc complexes studied for the polymerization of rac- and meso-lactide to poly(lactic acid) (PLA). [(BDI-1)ZnO(i)()Pr](2) polymerized (S,S)-lactide to isotactic PLA without epimerization of the monomer, rac-lactide to heterotactic PLA (P(r) = 0.94 at 0 degrees C), and meso-lactide to syndiotactic PLA (P(r) = 0.76 at 0 degrees C). The polymerizations are living, as evidenced by the narrow polydispersities of the isolated polymers in addition to the linear nature of number average molecular weight versus conversion plots and monomer-to-catalyst ratios. The substituents on the beta-diiminate ligand exert a significant influence upon the course of the polymerizations, affecting both the degree of stereoselectivity and the rate of polymerization. Kinetic studies with [(BDI-1)ZnO(i)Pr](2) indicate that the polymerizations are first order with respect to monomer (rac-lactide) and 1.56 order in catalyst. Polymerization experiments with [(BDI-1)MgO(i)Pr](2) revealed that this complex is extremely fast for the polymerization of rac-lactide, polymerizing 500 equiv in 96% yield in less than 5 min at 20 degrees C.     

Zum qualitativen Nachweis der Salpeters?ure

Ohne Zusammenfassung     

The initial development of a jet caused by fluid, body and free surface interaction. part 3. an inclined accelerating plate

The free surface and flow field structure generated by the uniformacceleration of a rigid plate, inclined at an angle      

Interactions and reactions of transition metal clusters with the interior of single-walled carbon nanotubes imaged at the atomic scale

Clusters of transition metals, W, Re, and Os, upon encapsulation within a single-walled carbon nanotube (SWNT) exhibit marked differences in their affinity and reactivity with the SWNT, as revealed by low-voltage aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly with the SWNT, Re creates localized defects on the sidewall, and Os reacts readily causing extensive defect formation and constriction of the SWNT sidewall followed by total rupture of the tubular structure. AC-HRTEM imaging at the atomic level of structural transformations caused by metal-carbon bonding of π- and σ-character demonstrates what a crucial role these types of bonds have in governing the interactions between the transition metal clusters and the SWNT. The observed order of reactivity W < Re < Os is independent of the metal cluster size, shape, or orientation, and is related to the metal to nanotube bonding energy and the amount of electronic density transferred between metal and SWNT, both of which increase along the triad W, Re, Os, as predicted by first-principles density functional theory calculations. By selecting the appropriate energy of the electron beam, the metal-nanotube interactions can be controlled (activated or precluded). At an electron energy as low as 20 keV, no visible transformations in the nanotube in the vicinity of Os-clusters are observed.     

An efficient route to the synthesis of symmetric and asymmetric diastereomerically pure fullerene triads

A new synthetic route based on the stepwise functionalisation of fullerene cages allows the facile formation of linear, diastereomerically pure triads incorporating two different fullerene cages linked by an organic spacer group. The critical coupling step of two fullerene cages via activation by N,N′-dicyclohexylcarbodiimide was systematically investigated to reveal that the yield of the coupling is maximised in o-dichlorobenzene at high concentrations of the reactant fullerene nucleophile, while in more polar solvents or at lower concentrations of reactants the formation of unwanted side-products (such as guanidine-, N-acylurea- and anhydride-functionalised fullerenes) is favoured. The resultant triads possess an atypically good solubility for this class of compound, which enabled full detailed characterisation by ¹H and ¹³C NMR, IR and UV–vis spectroscopies and by MALDI-TOF mass spectrometry.     

Prion protein self-peptides modulate prion interactions and conversion

Background  

Molecular mechanisms underlying prion agent replication, converting host-encoded cellular prion protein (PrP^C) into the scrapie associated isoform (PrP^Sc), are poorly understood. Selective self-interaction between PrP molecules forms a basis underlying the observed differences of the PrP^C into PrP^Sc conversion process (agent replication). The importance of previously peptide-scanning mapped ovine PrP self-interaction domains on this conversion was investigated by studying the ability of six of these ovine PrP based peptides to modulate two processes; PrP self-interaction and conversion.