Nickel und Kobalt

Ohne Zusammenfassung     

Elucidation of the collision induced dissociation pathways of water and alcohol coordinated complexes containing the uranyl cation

Multiple-stage tandem mass spectrometry was used to characterize the dissociation pathways for complexes composed of (1) the uranyl ion, (2) nitrate or hydroxide, and (3) water or alcohol. The complex ions were derived from electrospray ionization (ESI) of solutions of uranyl nitrate in H2O or mixtures of H2O and alcohol. In general, collisional induced dissociation (CID) of the uranyl complexes resulted in elimination of coordinating water and alcohol ligands. For undercoordinated complexes containing nitrate and one or two coordinating alcohol molecules, the elimination of nitric acid was observed, leaving an ion pair composed of the uranyl cation and an alkoxide. For complexes with coordinating water molecules, MS(n) led to the generation of either [UO2(2+)OH-] or [UO2(2+)NO3(-)]. Subsequent CID of [UO2(2+)OH-] produced UO2(+). The base peak in the spectrum generated by the dissociation of [UO2(2+)NO3(-)], however, was an H2O adduct to UO2(+). The abundance of the species was greater than expected based on previous experimental measurements of the (slow) hydration rate for UO2(+) when stored in the ion trap. To account for the production of the hydrated product, a reductive elimination reaction involving reactive collisions with water in the ion trap is proposed.     

STEREOCHEMISTRIES OF SOME REACTIONS OF CYCLIC STEREOISOMETRIC PHOSPHITES

Abstract

The reaction of the isomeric phosphites, 1 and 2, with ozone have been shown to be stereospecific and to proceed with retention of configuration about phosphorus. Similarly ozonization of mixtures of 3 and 4 were found to be stereospecific or very nearly so with retention of configuration about phosphorus. The mechanistic implications of these findings are discussed. Reactions of 1 and 2 with neopentyl and t-butyl hypochlorites proceed in a stereochemically random manner. The formation of a pentacoordinated intermediate is implicated. Reactions of a mixture of 1 and 2 with ethyl thiyl radicals provided phosphorothionates with complete retention of configuration.     

PSEUDOROTATION IN MONOCYCLIC OXYPHOSPHORANES WHICH CONTAIN CHIRAL CENTERS

Abstract

Phenylbis[2-methyl-1-butoxy]phosphine has been allowed to react with butanedione to produce 2,2-bis[2-methyl-1-butoxy]-2-phenyl-4,5-dimethyl-1,3,2-dioxaphophol-4-ene. This material is a mixture of three diastereomers. It has been reported that 2,2-bis[tetrahydrofurfuyloxy]-2-phenyl-4,5-dimethyl-1,3,2-dioxaphosphol-4-ene is a mixture of only two diastereomers. The present work suggest that two of the diastereomers of the tetrahydrofurfuryloxy compound interconvert via hexacoordinated zwitterionic intermediates which involve addition of the oxygen of the tetrahydrofuran ring to phosphorus.     

CONFORMATION OF EIGHT-MEMBERED DIOXATHIASILOCIN HETEROCYCLES IN SOLUTION

Abstract

The dibenzo[d,g][1,3,6,2]dioxathiasilocin derivatives 3a-f were prepared by the reaction of the thiobisphenols 1a-b with the corresponding dichlorosilanes 2a-e using triethylamine as an acid acceptor. The free energy of activation for ring inversion of the 2,4,8,10-tetra-tert-butyl-substituted 3a was determined by variable temperature ¹H NMR to be 13.9 kcal/mol. The ¹H NMR spectral data of 3a requires that the ring conformer possess a σ plane of symmetry passing through the silicon and bridging sulfur atoms. In the variable temperature ¹H NMR spectra of the 2,4,8,10-tetramethyl-substituted 3b no evidence was observed for the slowing of ring inversion at-55^oC, suggesting that the energy of activation for ring inversion is less than 10.9 kcal/mol. The ¹H NMR spectral data of 3e-f indicates the presence of equilibrating conformational isomers. The results of this study supports the suggestion that steric factors are a major contributor to the barrier of ring inversion for the dibenzo-[d, g][1,3,6,2]dioxathiasilocin ring system.     

High-throughput lectin magnetic bead array-coupled tandem mass spectrometry for glycoprotein biomarker discovery

Alterations in protein glycosylation occur during development and progression of many diseases, hence glycomics and glycoproteomics have emerged as important tools in glycobiomarker discovery. High-throughput glycan profiling can now be achieved with the recent developments in MS-based techniques. To enable identification and rapid monitoring of glycosylation changes in serum proteins, we developed a semi-automated high-throughput glycoprotein biomarker discovery platform termed lectin magnetic bead array-coupled tandem mass spectrometry (LeMBA-MS) which includes (i) effective single-step serum glycoprotein isolation using a panel of 20 individual lectin-coated magnetic beads in microplate format, (ii) on-bead trypsin digestion, and (iii) nanoLC-MS/MS with lectin exclusion list. With use of appropriate sequence databases, LeMBA-MS can detect glycosylation changes regardless of the species. By spiking known amounts of titrated ovalbumin to a serum sample, we report nanomolar sensitivity, and linearity of response of LeMBA-MS using concanavalin A-coupled beads. Neuraminidase treatment led to reduction of binding to sialic acid-binding lectins. Interestingly, we found that desialylation caused increased binding of haptoglobin and hemopexin to mannose-specific lectins, pointing to the importance of identifying a signature of lectin-binding. High-throughput LeMBA-MS to generate glycosylation signatures will facilitate glycobiomarker discovery. LeMBA can be coupled to down-stream detection platforms for validation, making it a truly versatile platform.     

On bounds for the cutting number of a graph

The cutting number of a vertex v of a finite graph G = (V,E) is a natural measure of the extent to which the removal of v disconnects the graph. Precisely, the cutting number c(v) of v is defined as the number of pairs of vertices {u,w} of G such that u,w ≠ v and every u-w path contains v. The cutting number c(G) of G is the maximum value of c(v) over all vertices in V. We provide exact bounds on the cutting number of G in terms of order and diameter of the graph.     

Promoting productive mathematical classroom discourse with diverse students

Productive mathematical classroom discourse allows students to concentrate on sense making and reasoning; it allows teachers to reflect on students’ understanding and to stimulate mathematical thinking. The focus of the paper is to describe, through classroom vignettes of two teachers, the importance of including all students in classroom discourse and its influence on students’ mathematical thinking. Each classroom vignette illustrates one of four themes that emerged from the classroom discourse: (a) valuing students’ ideas, (b) exploring students’ answers, (c) incorporating students’ background knowledge, and (d) encouraging student-to-student communication. Recommendations for further research on classroom discourse in diverse settings are offered.     

HPLC quantification of 5‐hydroxyeicosatetraenoic acid in human lung cancer tissues

A simple and cost‐effective HPLC method was established for quantification of 5‐hydroxyeicosatetraenoic acid (5‐HETE) in human lung cancer tissues. 5‐HETE from 27 patients' lung cancer tissues were extracted by solid‐phase extraction and analyzed on a Waters Symmetry C₁₈ column (4.6 × 250 mm, 5 µm) with a mobile phase consisting of methanol, 10 mm ammonium acetate, and 1 m acetic acid (70:30:0.1, v:v:v) at a flow rate of 1.0 mL/min. The UV detection wavelength was set at 240 nm. The calibration curve was linear within the concentration range from 10 to 1000 ng/mL (r² > 0.999, n = 7), the limit of detection was 1.0 ng/mL and the limit of quantitation was 10.0 ng/mL for a 100 µL injection. The relative error (%) for intra‐day accuracy was from 93.14 to 112.50% and the RSD (%) for intra‐day precision was from 0.21 to 2.60% over the concentration range 10–1000 ng/mL. By applying this method, amounts of 5‐HETE were quantitated in human lung cancer tissues from 27 human subjects. The established HPLC method was validated to be a simple, reliable and cost‐effective procedure that can be applied to conduct translational characterization of 5‐HETE in human lung cancer tissues. Copyright © 2009 John Wiley & Sons, Ltd.