Local Observation of Field Polarity Dependent Flux Pinning by Magnetic Dipoles

A scanning Hall probe microscope is used to study flux pinning in a thin superconducting Pb film covering a square array of single-domain Co dots with in-plane magnetization. We show that single flux quanta of opposite sign thread the superconducting film below T(c) at the opposite poles of these dipoles. Depending on the polarity of the applied field, flux lines are attracted to a specific pole of the dipoles, due to the direct interaction with the vortexlike structures induced by the local stray field.     

Annelated piperazinyl-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidines

Tricyclic analogs of piperazinylthiopyrano[3,2-d]pyrimidine hypoglycemic agents were prepared. The angular tricyclic systems, 8,9-dihydro-7H-thiopyrano[2,3-e][1,2,4]triazolo[4,3-a]pyrimidine and 8,9-dihydro-7H-tetrazolo[1,5-a]thiopyrano[2,3-e]pyrimidine derivatives were synthesized from 2,4-dichloro-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine in three step sequences. Derivatives of the linear tricyclic system, 5,6-dihydro-7H-thiopyrano[3,2-d][1,2,4]triazolo[2,3-a]pyrimidine, were prepared by condensation of 3-amino-1,2,4-triazole with ethyl 3-oxo-tetrahydropyran-2-carboxylate. The tricyclic heteroaryl-piperazines lacked significant hypoglycemic activity.     

17O NMR spectroscopy of nucleoside derivatives; bonding characteristics of pyrimidine carbonyls

Various uridine derivatives have been selectively enriched (≈ 50%) at the 04 and 02 oxygens, and the ¹⁷O chemical shifts and linewidths measured. The chemical shifts, which are primarily dependent on π-bond-order and hydrogen bonding, show effects that are selective for the 02 and 04 oxygens. In particular, significantly more H-bonding to D₂O and higher π bond order are found for the 04 oxygen.     

Fast and Accurate Protein False Discovery Rates on Large-Scale Proteomics Data Sets with Percolator 3.0

Percolator is a widely used software tool that increases yield in shotgun proteomics experiments and assigns reliable statistical confidence measures, such as q values and posterior error probabilities, to peptides and peptide-spectrum matches (PSMs) from such experiments. Percolator’s processing speed has been sufficient for typical data sets consisting of hundreds of thousands of PSMs. With our new scalable approach, we can now also analyze millions of PSMs in a matter of minutes on a commodity computer. Furthermore, with the increasing awareness for the need for reliable statistics on the protein level, we compared several easy-to-understand protein inference methods and implemented the best-performing method—grouping proteins by their corresponding sets of theoretical peptides and then considering only the best-scoring peptide for each protein—in the Percolator package. We used Percolator 3.0 to analyze the data from a recent study of the draft human proteome containing 25 million spectra (PM:24870542). The source code and Ubuntu, Windows, MacOS, and Fedora binary packages are available from http://percolator.ms/ under an Apache 2.0 license.

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The elusive 8-fluoroadenosine: a simple non-enzymatic synthesis and characterization

The only successful synthesis of 8-fluoroadenosine reported until now relied on an enzymatic removal of the acetate protecting groups using thermally resistant hydrolases. In the present communication we describe the first non-enzymatic synthesis of 8-fluoroadenosine. According to this, the C₈-fluorine atom was introduced in a halogen-exchange process performed at elevated temperature. The chief obstacle in the synthesis of 8-fluoroadenosine, the removal of the protecting groups in the presence of the labile C₈-F bond, was addressed by judicious choice of acid-labile protecting groups. Their deprotection in the presence of C₈-F is described. Using this newly developed procedure, significant quantities of 8-fluoroadenosine were synthesized and, for the first time, its physicochemical properties including pH-dependent stability, examined in detail. The intermediate generation of 8-fluoroadenosines as a tool to increase the reaction rates of nucleophilic substitutions was briefly examined and successfully demonstrated with the example of 8-cyanoadenosine. The presented procedure is applicable to the synthesis of various adenosine analogs with potential pharmacological significance.