Das Spermin-Alkaloid Chaenorpin

The Spermine Alkaloid Chaenorpine Chaenorpine ( 1 ) was isolated from Chaenorhinum minus (Scrophulariaceae). Its structure elucidation was achieved on the basis of chemical degradation and spectroscopic measurements in comparison to the known alkaloid chaenorhine ( 2 ). Structure 1 displays the absolute configuration.     

Analytical approach to very large benzenoid polymers

We consider rigorous evaluation of conjugated-circuit resonance energies for families of structurally related benzenoid hydrocarbons of increasing size. Local and global aromatic properties of such molecules are investigated with particular interest in modeling high polymers. Using the algebra of large numbers, exact formulas for contributions from individual benzene rings of polymers with up to 25,000 repeating units (close to half a million carbon atoms) were derived. All arithmetic procedures were carried out in terms of whole numbers retaining all digits, of which there were sometimes more than 10⁵. © 1995 by John Wiley & Sons, Inc.     

Diels-alder reactions of hexafluoro-2-butyne with 2-heterosubstituted furans: A facile and general synthesis of 1, 4-disubstituted 2,3-Di(trifluoromethyl)benzenes

An electron-donating heteroatom substituent at position-2 of a furan promotes regiospecific opening of the 7-oxa bridge of the Diels-Alder cycloadduct with hexafluoro-2-butyne, producing a 4-heterosubstituted 2,3-di(trifluoromethyl)phenol building block in a single step. The phenol and heteroatom substituent are easily transformed to the corresponding iodide or triflate that readily undergoes Heck, Suzuki, and Stille reactions to install a variety of substituents in high yields. This methodology provides a facile and general synthesis of 1,4-disubsituted 2, 3-di(trifluoromethyl)benzenes.     

Can TMS and DSS be used as NMR references for cyclodextrin species in aqueous solution?

Tetramethylsilane (TMS) can be included by -cyclodextrin (-CD), and sodium 2,2-dimethylsilapentane-5-sulphonate (DSS) can form inclusion complexes with - and -CD. The NMR chemical shifts are changed considerably as a result of the strong interaction between CD and the guest compound in the inclusion complexes. A downfield shift of as much as 0.63 ppm shift downfield has been observed for the protons of external TMS in CD aqueous solution. In view of this, the question arises of whether TMS and DSS can be used as internal references. DSS in D₂O is suggested as an external reference for aqueous cyclodextrin solution in NMR measurements.     

A study of laser ablation and slurry nebulisation sample introduction for the analysis of geochemical materials by inductively coupled plasma spectrometry

Summary The performances of two alternative sample introduction methods for use with Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) have been evaluated for the analysis of the same sample material. The laser ablation sample introduction system is based on a Nd:YAG laser to which an x-y-z translational sampling head had been added. A study has been made of a number of parameters which affect the performance of the system to find the optimum operating conditions. The slurry introduction system involved aspirating the slurries into the plasma using a de Galan nebuliser and a Scott-type spray chamber arrangement. A study has been made of the parameters which control the production of stable homogeneous slurries. Initial particle size measurements have been carried out on the slurried samples to show how this affects this method of sample introduction. Results are presented for the analysis of a South African reference material rock sample (SARM 5) by ICP-OES with both laser ablation and slurry nebulisation sample introduction and some preliminary results for the analysis by ICP-MS with laser ablation introduction. Semi-quantitative results are obtained for laser ablation ICP-OES as only one matrix matched standard is used. However, the agreement between the results obtained for slurry nebulisation and the certificate value is poor. It is suggested by comparison with previous studies that this may be due to particle size effects. Encouraging results were obtained for the determination of trace elements by laser ablation ICP-MS.     

Fabrication of beta-Ni(OH)2 and NiO hollow spheres by a facile template-free process

Ni(OH)2 hollow microspheres with beta-Ni(OH)2 nanosheets as the in situ formed building units were fabricated via a novel template-free approach in a strong alkaline solution of glycine, and can be converted into NiO hollow microspheres by a thermal decomposition process.     

A chemical inhibitor reveals the role of Raf kinase inhibitor protein in cell migration

Raf kinase inhibitor protein (RKIP) is a modulator of cell signaling that functions as an endogenous inhibitor of multiple kinases. We demonstrate here a positive role for RKIP in the regulation of cell locomotion. We discovered that RKIP is the relevant cellular target of locostatin, a cell migration inhibitor. Locostatin abrogates RKIP's ability to bind and inhibit Raf-1 kinase, and it acts by disrupting a protein-protein interaction, an uncommon mode of action for a small molecule. Small interfering RNA-mediated silencing of RKIP expression also reduces cell migration rate. Overexpression of RKIP converts epithelial cells to a highly migratory fibroblast-like phenotype, with dramatic reduction in the sensitivity of cells to locostatin. RKIP is therefore the compound's valid target and a key regulator of cell motility.     

Experimental verification of a predicted, previously unseen separation selectivity pattern in the capillary electrophoretic separation of noncharged enantiomers by octakis(2,3-diacetyl-6-sulfato)-gamma-cyclodextrin

The capillary electrophoretic separation of noncharged enantiomers with single-isomer anionic resolving agents is reexamined here with the help of the charged resolving agent migration model. Two general model parameters have been identified that influence the effective mobility, separation selectivity and mobility difference curves of the enantiomers: parameter b, called binding selectivity (K(RCD)/K(SCD)), and parameter s, called size selectivity (mu(o)RCD/mu(o)SCD). Analysis of the model in terms of these parameters indicates that in addition to the known, previously observed separation selectivity vs. resolving agent concentration patterns, a new pattern, increasing separation selectivity with increasing resolving agent concentration, is also possible provided that (i) K(RCD)/K(SCD)<1 and mu(o)RCD/mu(o)SCD>1 and (K(RCD)mu(o)RCD)/(K(SCD)mu(o)SCD)>1, or (ii) K(RCD)/ K(SCD)>1 and mu(o)SCD/mu(o)SCD<1 and (K(RCD)mu(o)RCD)/(K(SCD)mu(o)SCD)<1. This hitherto unseen separation selectivity pattern was experimentally verified during the capillary electrophoretic separation of the enantiomers of O-isopropyl p-nitrophenyl methylphosphonate with the single-isomer octakis(2,3-diacetyl-6-sulfato)-gamma-cyclodextrin as resolving agent.     

Amino acid analysis by micellar electrokinetic chromatography with laser-induced fluorescence detection: application to nanolitre-volume biological samples from Arabidopsis thaliana and Myzus persicae

Amino acids were derivatised with 4-fluoro-7-nitrobenzo-2,1,3-oxadiazol (NBD-F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon-ion (488 nm) laser-induced fluorescence. The optimised MEKC background electrolyte conditions were: 40 mM sodium cholate, 5 mM beta-cyclodextrin in 20 mM aqueous borate buffer, pH 9.1, with 7% v/v acetonitrile. Using these conditions, 19 amino acids were separated within 17 min. The limits of detection were in the range of 7.6-42.2 pmol/mL and limits of quantitation from 0.05-0.14 nmol/mL. The method was systematically validated for injection volume error, migration time variation, calibration linearity, accuracy, precision, and recovery. Nanolitre volume samples of phloem sap of individual sieve element cells from the plant Arabidopsis thaliana and honeydew from the aphid Myzus persicae were directly analysed with this method. Quantitative amino acid concentrations in these two biological matrices were profiled for the first time. This method is particularly important because it allows the complete profile of the amino acids obtained from individual phloem elements, allowing cell to cell and plant to plant variation to be quantified, which to date has not been possible with Arabidopsis thaliana.     

Polymer-enzyme conjugates can self-assemble at oil/water interfaces and effect interfacial biotransformations

Native water-soluble enzymes were transformed into interface-binding enzymes via conjugation with hydrophobic polymers, thus enabling interesting interfacial biocatalysis between immiscible chemicals at oil/water interfaces. Such interfacial biocatalysis demonstrated a significantly improved catalytic efficiency as compared to traditional biphasic reactions with enzymes contained in the bulk aqueous phase. Particularly, polystyrene-conjugated beta-galactosidase showed a catalytic efficiency that was more than 145 times higher than that of the native enzyme for a transgalactosylation reaction. It is believed that the improved accessibility of the biocatalysts to chemicals held in both phases across the interface is the key driver for the enhancement of enzyme activity.