Space-age analysis

A survey is given of present-day analysis, from an editorial point of view, and suggests that though techniques have changed in order to meet the challenges of modern technological advances and materials, the fundamental character of analytical research and its publication has not.     

Taking the mystery out of Gauss's Theorem

Gauss's Theorem can be derived simply from the assumption that lines of flux begin and end only on charges; it need not be considered as a consequence of the inverse-square law. In a 3-dimensional world, the inverse-square law is itself a consequence of the same assumption.     

Time Window Expansion for HDX Analysis of an Intrinsically Disordered Protein

Application of typical HDX methods to examine intrinsically disordered proteins (IDP), proteins that are natively unstructured and highly dynamic at physiological pH, is limited because of the rapid exchange of unprotected amide hydrogens with solvent. The exchange rates of these fast exchanging amides are usually faster than the shortest time scale (10 s) employed in typical automated HDX-MS experiments. Considering the functional importance of IDPs and their association with many diseases, it is valuable to develop methods that allow the study of solution dynamics of these proteins as well as the ability to probe the interaction of IDPs with their wide range of binding partners. Here, we report the application of time window expansion to the millisecond range by altering the on-exchange pH of the HDX experiment to study a well-characterized IDP; the activation domain of the nuclear receptor coactivator, peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α). This method enabled mapping the regions of PGC-1α that are stabilized upon binding the ligand binding domain (LBD) of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ). We further demonstrate the method’s applicability to other binding partners of the IDP PGC-1α and pave the way for characterizing many other biologically important ID proteins.

S‐Alkylation of Soft Scorpionates

The alkylation reactions of soft scorpionates are reported. The hydrotris(S‐alkyl‐methimazolyl)borate dications (alkyl=methyl, allyl, benzyl), which were prepared by the reaction of Tm^Me anion and primary alkyl halides, have been isolated and structurally characterised. The reaction is, however, not universally successful. DFT analysis of these alkylation reactions (C?S versus B? H alkylation) indicates that the observed outcome is driven by kinetic factors. Extending the study to incorporate alternative imine thiones (mercaptobenzothiazole, bz; thiazoline, tz) led to the structural characterisation of di[aquo‐μ‐aquohydrotris(mercaptobenzothiazolyl)boratosodium], which contains sodium atoms in the κ³‐S,S,S coordination mode. Alkylation of Na[Tbz] and Na[tzTtz] leads to decomposition resulting in the formation of the simple S‐alkylated heterocycles. The analysis of the species involved in these reactions shows an inherent weakness in the B? N bond in soft scorpionates, which has implications for their use in more advanced chemistry.     

Structural study of spirolide marine toxins by mass spectrometry

The spirolides are a family of marine biotoxins derived from the dinoflagellate Alexandrium ostenfeldii, recently isolated from contaminated shellfish and characterized. A crude phytoplankton extract has been extensively studied for mass spectrometric determination and characterization of several known spirolides and previously unreported compounds. The complex sample was initially analyzed by full-scan mass spectrometry in an ion-trap instrument, enabling identification of several components. Subsequent analysis by selected-ion monitoring in a triple-quadrupole instrument resulted in the confirmation of the identities of the compounds detected in the ion trap. Purification of the crude extract was performed using an automated mass-based fractionation system, yielding several fractions with different relative contributions of the spirolide components. Collision-induced dissociation (CID) in the triple-quadrupole instrument produced significant fragment ions for all identified species. Selective enrichment of some minor compounds in certain fractions enabled excellent CID spectra to be generated; this had previously been impossible, because of interferences from the major toxins present. Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry was then performed for accurate determination of the masses of MH+ ions of all the species present in the sample. Additionally, infrared multiphoton dissociation in the FTICR instrument generated elemental formulae for product ions, including those formed in the previous collisional activation experiments. Collection of these results and the fragmentation scheme proposed for the main component of the extract, 13-desmethyl spirolide C, from part I of this study, enabled elucidation of the structures of some uncharacterized spirolides and some biogenetically related compounds present at previously unreported masses.     

Shock-bubble interactions : Generation and evolution of vorticity in two-dimensional supersonic flows

We present high resolution simulations with the PPM code of shock-bubble interactions coresponding to the recent Haas-Sturtevant experiments. VCR cinemas show and diagnostic interpretations quantify the variety of shock-vortex interactions     

Quantification of changes in oxygen release from red blood cells as a function of age based on magnetic susceptibility measurements

This study extends the in vitro understanding of the RBC storage lesion by serially analyzing the RBC's magneophoretic mobility, a property dependent on the content and oxygenation or oxidation state of hemoglobin (Hb) iron, during storage. Four prestorage leukoreduced, AS-5 preserved RBC units were stored between 1 and 6 °C for 42 days. Weekly starting on storage day 7, each unit was sampled, divided into 3 aliquots, each subjected to different reactions: one aliquot was exposed to room air to produce oxyhemoglobin (oxyHb), another aliquot was mixed with sodium nitrite to produce methemoglobin (metHb), while the third aliquot was desaturated of oxygen (deoxyhemoglobin, deoxyHb) using nitrogen gas. These aliquots were placed into a cell tracking velocimetry (CTV) apparatus which measured both the settling velocity (u(s)) of the RBCs as well as their magnetically induced velocity (u(m)). The u(m)/u(s) ratio depends on the oxygenation state of the hemoglobin and the quantity of iron within the RBC. The RBC density was measured by percoll centrifugation. There was a significant reduction in the u(m)/u(s) ratio for the deoxyHb RBC aliquot as storage time elapsed, with a smaller but still significant reduction in the u(m)/u(s) ratio for the metHb aliquot. The average RBC density decreased very slightly during storage, as determined by the percoll centrifugation technique, although the average settling velocity (another measure of cell density) seemed to fluctuate during storage. The decrease in magnetophoretic mobility of the deoxyHb portion is explicable either by Hb's increased affinity for oxygen during storage, or else a loss of iron from the cells.