Dynamic Stability Analysis of Shells Using a Finite Element Based Reduction Method

A finite element formulation of a reduction method for dynamic stability analysis of imperfection-sensitive shell structures is presented. The reduction method makes use of a perturbation approach, initially developed for static buckling and later extended to dynamic buckling analysis. The single mode dynamic buckling analysis and its extension to parametric excitation analysis are described. The approach is available within a general purpose finite element code. Characteristic results for the parametric excitation analysis of a composite cylindrical shell are shown. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Separation of polysorbates by liquid chromatography on a HILIC column and identification of peaks by MALDI-TOF MS

Polysorbates can be separated according to their functionality and architecture by liquid chromatography on a hydrophilic interaction chromatography (HILIC) column in acetone–water mobile phases containing 90–97% acetone. The different polymer homologous series are separated according to the number of terminal hydroxy groups and elute as narrow peaks. The hydrophilic part (ethoxylates of sorbitan, isosorbide, and poly(ethyleneglycol)) and amphiphilic funtionalites (ethoxylated mono-, di-, tri-, and tetraesters) were separated by HILIC mode of high-performance liquid chromatography (HPLC). All these separated functionaities are identified and confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS). This combination of HPLC and MALDI-TOF MS has been proven to be an excellent tool for the characterization of heterogenous complex samples.     

Two new triterpenoids from Zygophyllum eurypterum

Two new triterpenoids trivially named as atriplicoide A and B were isolated from the n-BuOH extract of the whole plant of Zygophyllum eurypterum. Based on EI-MS, IR, 1H- and 13C-NMR, and 2D-NMR (HMQC, HMBC, COSY and NOESY) data, the structures of the new compounds were determined as 30-carboxy-3beta,24-dihydroxy-urs-28,13beta-lactam-N-acetate (1) and 3beta,24-dihydroxyursan-28,13beta-olide (2).     

Pregnane derivatives from Potentilla evestita

A new pregnane derivative, 2,6beta,7beta-trihydroxy-4-methyl-19-norpregna-1,3,5(10)-trien-17-one, has been isolated from the ethyl acetate soluble fraction of Potentilla evestita along with a pregnane derivative, 11alpha,17alpha,21-trihydroxypregna-4,16(22)-diene-3,20-dione, that is reported for the first time as a natural product. Their structures were elucidated with the aid of 1H and 13C NMR spectra and by COSY, HMQC, HMBC and NOESY experiments.     

Chemical constituents of Cichorium intybus and their inhibitory effects against urease and alpha-chymotrypsin enzymes

Phytochemical investigation of the aerial parts of Cichorium intybus L. resulted in the isolation and identification of two new natural metabolites, 2,6-di[but-3(E)-en-2-onyl]naphthalene (1), and 3,3',4,4'-tetrahydroxychalcone (2), along with nine known compounds. Their structures were determined by spectroscopic techniques including 1D and 2D NMR. The known compounds were identified as scopoletin (3), 4-hydroxyphenylacetic acid (4), 3-hydroxy-4-methoxybenzoic acid (5), 4,4'-dihydroxychalcone (6), 6,7-dihydroxycoumarine (7), 1-triacontanol (8), lupeol (9), beta-sitosterol (10), and beta-sitosterol-3-O-beta-glucopyranoside (11). Compounds 4-6 and 8 are reported for the first time from C. intybus. Compounds 2 and 3 showed weak inhibitory activities against urease and alpha-chymotrypsin enzymes, respectively.     

Characterization of complex copolymers by two-dimensional Liquid Chromatography

Complex polymers were characterized by combinations of different chromatographic separation mechanisms: liquid adsorption chromatography (LAC), liquid chromatography under critical conditions (LCCC), and liquid exclusion-adsorption chromatography (LEAC). These techniques were combined off-line and on-line in two-dimensional separations. Fatty acid ethoxylates, fatty esters of polyethylene glycol (PEG) and polysorbates were analyzed by two-dimensional liquid chromatography with normal phase LAC as the first and liquid chromatography at critical conditions (LCCC) or liquid exclusion adsorption chromatography (LEAC) as the second dimension. A full separation of all oligomers to the baseline could be achieved in both dimensions. In two-dimensional separations, the offline approach is compared to comprehensive chromatography, and the scope and limitations of both techniques are discussed.     

Two new 3-C-carboxylated flavones from the rhizomes of Caragana conferta

Confertins A (1) and B (2), new 3-C-carboxylated flavones, have been isolated from the ethyl acetate soluble fraction of the rhizomes of Caragana conferta. Their structures have been assigned on the basis of spectroscopic studies.