Synthesis of 1-deoxysphingosine derivatives with conformationally restricted pyrrolidinediol head groups

[structure: see text] A family of cyclic 1-deoxysphingolipid derivatives of structure 4 has been designed and synthesized, which may serve as tumorigenesis suppressors for various cancers. Compound 4 is a second-generation analogue developed from sphingosine (1), in which a hydroxyl substituent is moved from C1 to C5 and a methylene is added for conformational rigidity between the C2-nitrogen substituent and C4. The synthetic chemistry for pyrrolidine ring closure at C3-C4 features ring-closing metathesis followed by hydroboration-oxidation.     

Total synthesis of stephanotic acid methyl ester

[structure: see text]The methyl ester of the naturally occurring macrocyclic pentapeptide stephanotic acid, containing an unusual beta-substituted alpha-amino acid with a tryptophan C-6 to leucine beta-carbon link, has been synthesized. The key steps include the formation of this amino acid through a thioxo-oxazolidine intermediate and a Horner-Wadsworth-Emmons reaction using a phosphonoglycine, derived by a dirhodium(II)-catalyzed N-H insertion reaction, to give a dehydroamino acid and subsequent rhodium(I)-catalyzed asymmetric hydrogenation to introduce the modified tryptophan residue.     

The role of dislocation walls for nanoindentation to shallow depths

Dislocation events are seen as excursions or pop-in events in the load–displacement curve of nanoindentation experiments. Two nanoindenters have been used to examine the difference between quasi-static and dynamic loading during indentation. Yield excursions were present in the load–displacement curves of both the statically and dynamically loaded single crystal nickel samples. Only one major excursion occurred in each quasi-static indent, nominally loaded at 100 μN/s while staircase yielding was observed under dynamic loading indentation with a 45 Hz oscillation of 2 nm superimposed on a 60 μN/s loading rate. Thermal activation analysis is used to explain the arrest and reinitiation of the yielding with activation volumes being modeled. For nanoindentation experiments differences between quasi-static and dynamic loading are described by the models presented. It is proposed that insight into the plastic deformation mechanisms associated with such plastic instabilities will provide one of the keys to length scale effects necessary to understanding nanostructures.     

The Horner-Wadsworth-Emmons reaction in the synthesis of macrocyclic peptides: the Trp-His-Gly-Arg derived macrocycle of moroidin

The Trp-His-Gly-Arg derived macrocycle 4 of moroidin 1 containing the unusual tryptophan C-2 histidine N-1 link has been synthesised in protected form. The key steps are displacement of a 2-chloroindole with a histidine derived nucleophile, a Horner-Wadsworth-Emmons reaction followed by asymmetric hydrogenation to establish the tryptophan side chain, and incorporation of the Gly-Arg dipeptide by peptide coupling.     

Method validation for determination of alkaloid content in goldenseal root powder

A fast, practical ambient extraction methodology followed by isocratic liquid chromatography (LC) analysis with UV detection was validated for the determination of berberine, hydrastine, and canadine in goldenseal (Hydrastis canadensis L.) root powder. The method was also validated for palmatine, a major alkaloid present in the possible bioadulterants Coptis, Oregon grape root, and barberry bark. Alkaloid standard solutions were linear over the evaluated concentration ranges. The analytical method was linear for alkaloid extraction using 0.3-2 g goldenseal root powder/100 mL extraction solvent. Precision of the method was demonstrated using 10 replicate extractions of 0.5 g goldenseal root powder, with percent relative standard deviation for all 4 alkaloids < or = 1.6. Alkaloid recovery was determined by spiking each alkaloid into triplicate aliquots of neat goldenseal root powder. Recoveries ranged from 92.3% for palmatine to 101.9% for hydrastine. Ruggedness of the method was evaluated by performing multiple analyses of goldenseal root powder from 3 suppliers over a 2-year period. The method was also used to analyze Coptis root, Oregon grape root, barberry bark, and celandine herb, which are possible goldenseal bioadulterants. The resulting chromatographic profiles of the bioadulterants were significantly different from that of goldenseal. The method was directly transferred to LC with mass spectrometry, which was used to confirm the presence of goldenseal alkaloids tetrahydroberberastine, berberastine, canadaline, berberine, hydrastine, and canadine, as well as alkaloids from the bioadulterants, including palmatine, jatrorrhizine, and coptisine.     

PVC ion-selective electrodes based on calcium bis-[dialkyl- and di-(4-alkylphenyl) phosphates] and mixed solvent mediators

PVC calcium ion-selective electrodes based on either calcium bis-di(n-decyl)phosphate or calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate with various solvent mediators (alone or in pairs) have been evaluated with particular respect to interference from Na(+), K(+), Mg(2+), Sr(2+), Ba(2+), Mn(2+), Cu(2+), Ni(2+) and Zn(2+) ions. PVC calcium ion-selective electrodes based on calcium bis-di[4-(n-octyl)phenyl]phosphate with varied amounts of decan-l-ol plus di-n-octyl phenylphosphonate showed a continuous gradation in selectivity coefficients on going from a high fraction of decan-l-ol to a high fraction of the second mediator. Thus, k(pot)(Ca,Mg) changed from 1.6 for an electrode based exclusively on decan-l-ol to 4.9 x 10(-4) for one based completely on di-n-octyl phenylphosphonate. The corresponding k(pot)(Ca,Na) values were 7.0 x 10(-2) and 1.1 x 10(-3).     

Zur quantitativen Bestimmung von Aluminium, Eisen, Chrom, Zink, Kobalt, Nickel und Zinn

Ohne Zusammenfassung     

New techniques for the analysis of fine-scaled clustering phenomena within atom probe tomography (APT) data.

Nanoscale atomic clusters in atom probe tomographic data are not universally defined but instead are characterized by the clustering algorithm used and the parameter values controlling the algorithmic process. A new core-linkage clustering algorithm is developed, combining fundamental elements of the conventional maximum separation method with density-based analyses. A key improvement to the algorithm is the independence of algorithmic parameters inherently unified in previous techniques, enabling a more accurate analysis to be applied across a wider range of material systems. Further, an objective procedure for the selection of parameters based on approximating the data with a model of complete spatial randomness is developed and applied. The use of higher nearest neighbor distributions is highlighted to give insight into the nature of the clustering phenomena present in a system and to generalize the clustering algorithms used to analyze it. Maximum separation, density-based scanning, and the core linkage algorithm, developed within this study, were separately applied to the investigation of fine solute clustering of solute atoms in an Al-1.9Zn-1.7Mg (at.%) at two distinct states of early phase decomposition and the results of these analyses were evaluated.     

Circular Symmetry of Pinwheel Diffraction

A method is given for explicitly determining the autocorrelation of the pinwheel tiling by use of the substitution system generating the tiling. Using this a new proof of the circular symmetry of the diffraction of the pinwheel tiling is given. Communicated by Jean Bellissard Submitted: 8/10/2004 Accepted: 21/11/2005