A rapid one‐step method for the characterization of membrane lipid remodeling in Francisella using matrix‐assisted laser desorption ionization time‐of‐flight tandem mass spectrometry

Lipids are essential components of all bacterial membranes. The most common membrane‐associated lipids in Gram‐negative bacteria are phospholipids and lipid A, the hydrophobic anchor of lipopolysaccharide. Diversity in these lipids arises through structural modifications that include changes in the length and location of fatty acids, and the addition of phosphate and carbohydrate moieties. Analysis of individual structural modifications normally requires large quantities of starting material and multiple methods for the isolation, hydrolysis, and analysis. In this study, we developed a novel one‐step protocol for the combined isolation of phospholipids and lipid A from Francisella subspecies followed by analysis using matrix‐assisted laser desorption ionization time‐of‐flight tandem mass spectrometry. The total time for lipid isolation and analysis was approximately 15 min and with a lower limit of detection of approximately 100 ng of purified lipid. This protocol identified the major lipid structures using both wild‐type Ft subspecies strains and lipid A biosynthesis mutants. We also determined the relative levels of individual lipid A and phospholipids after growth under conditions that mimic the mammalian infection process. This analysis showed that the bacterial membranes remodeled rapidly to adapt to changes in environmental growth conditions and may be important for Francisella pathogenesis. Copyright © 2011 John Wiley & Sons, Ltd.     

Activation of Isocyanates and Carbon Dioxide by a Monomeric Aluminium Hydrazide as an Active Lewis Pair

The monomeric aluminium hydrazide H₁₀C₅N? N(AltBu₂)? Ad ( 4 ; Ad=adamantyl, NC₅H₁₀=piperidinyl) was obtained in high yield by hydroalumination of the corresponding hydrazone derivative 1 . Compound 4 has a strained AlN₂ heterocycle formed by a donor–acceptor bond between the β‐nitrogen atom of the hydrazide group and the aluminium atom. Opening of this bond resulted in the formation of an active Lewis pair that was able to cooperatively activate carbon dioxide or isocyanates. Insertion of the heterocumulenes into the Al? N bond selectively afforded a carbamate and two urea derivatives in high yield. In the first step, phenyl isocyanate gave the adduct 6 , which has the oxygen atom coordinated to the aluminium atom and its central carbon atom bound to the nitrogen atom of the piperidine moiety. Adduct 6 represents a reasonable intermediate state for these activation processes. The applicability of hydroaluminated compounds, such as 4 , in organic synthesis was demonstrated by the reaction with an imidoyl chloride, which gave the corresponding amidrazone derivative 9 .     

Acoustic emission localization in beams based on time reversed dispersion

The common approach for the localization of acoustic emission sources in beams requires at least two measurements at different positions on the structure. The acoustic emission event is then located by evaluating the difference of the arrival times of the elastic waves. Here a new method is introduced, which allows the detection and localization of multiple acoustic emission sources with only a single, one point, unidirectional measurement. The method makes use of the time reversal principle and the dispersive behavior of the flexural wave mode. Whereas time-of-arrival (TOA) methods struggle with the distortion of elastic waves due to phase dispersion, the method presented uses the dispersive behavior of guided waves to locate the origin of the acoustic emission event. Therefore, the localization algorithm depends solely on the measured wave form and not on arrival time estimation. The method combines an acoustic emission experiment with a numerical simulation, in which the measured and time reversed displacement history is set as the boundary condition.     

Generic Hahn–Banach results

Given f:X→R∪{+∞}$f:X\to \mathbb{R}\cup \{+\infty \}$ a convex and lower semi-continuous function defined on a reflexive Banach space X, and L, a closed linear manifold of X over which f takes at least a real value, the aim of this note is to prove the following Baire category result: in the Euclidean setting, the set of affine functions dominated by f on L for which there is no dominated extension to X is always of first Baire category, but this set can be as large as a residual set, provided that X is a reflexive Banach space of infinite dimension.