Identification of Living Legionella pneumophila Using Species‐Specific Metabolic Lipopolysaccharide Labeling

Legionella pneumophila is a pathogenic bacterium involved in regular outbreaks characterized by a relatively high fatality rate and an important societal impact. Frequent monitoring of the presence of this bacterium in environmental water samples is necessary to prevent these epidemic events, but the traditional culture‐based detection and identification method requires up to 10 days. Reported herein is a method allowing identification of Legionella pneumophila by metabolic lipopolysaccharide labeling which targets, for the first time, a precursor to monosaccharides that are specifically present within the O‐antigen of the bacterium. This new approach allows easy detection of living Legionella pneumophila, while other Legionella species are not labeled.     

Students' use of STEM content in design justifications during engineering design‐based STEM integration

Engineering design‐based STEM integration is one potential model to help students integrate content and practices from all of the STEM disciplines. In this study, we explored the intersection of two aspects of pre‐college STEM education: the integration of the STEM disciplines, and the NGSS practice of engaging in argument from evidence within engineering. Specifically, our research question was: While generating and justifying solutions to engineering design problems in engineering design‐based STEM integration units, what STEM content do elementary and middle school students discuss? We used naturalistic inquiry to analyze student team audio recordings from seven curricular units in order to identify the variety of STEM content present as students justified their design ideas and decisions (i.e., used evidence‐based reasoning). Within the four disciplines, fifteen STEM content categories emerged. Particularly interesting were the science and mathematics categories. All seven student teams used unit‐based science, and five used unit‐based mathematics, to support their design ideas. Five teams also applied science and/or mathematics content that was outside the scope of the units' learning objectives. Our results demonstrate that students integrated content from all four STEM disciplines when justifying engineering design ideas and solutions, thus supporting engineering design‐based STEM integration as a curricular model.     

A Modified Synthesis of Retinoates

Retinoates are obtained in high yield by the reaction of N-retinylimidazolium p-toluenesulfonate with alcohols.     

Uncertainty analysis of theoretical methods for adiabatic temperature rise determination in calorimetry

The main methods for the determination of the temperature rise in calorimetric experiments corrected of heat losses to surroundings (called adiabatic temperature rise) are described thereafter. This corrected temperature rise is obtained analytically from experimental temperature–time curves. The general scheme reported by Henri Régnault and Leopold Pfaundler for the first time in the 19th century is considered as the basis for all methods elaborated afterwards. A bibliographical study raised five methods including Régnault–Pfaundler’s. These methods have been applied on five experimental temperature–time curves obtained with an isoperibolic reference gas calorimeter at the French national metrology and testing institute (LNE) on combustion of pure methane. This paper deeply details a new analytical method elaborated at LNE exposing best heat transfer phenomena representation occurring in the water bath calorimeter. A comparative study of the five methods of the temperature rise determination and of their associated uncertainties is here presented.     

AC and DC percolative conductivity of single wall carbon nanotube polymer composites

The equations needed to correctly interpret both AC and DC conductivity results of single wall carbon nanotube (SWNT) polymer composites and the scaling of these results onto a single master curve are presented. Brief discussions on the factors that determine the critical volume fraction (?_c) and the percolation exponent (t) are also given. The results for a series of SWNT–polyimide composites are presented and the parameters obtained from fitting these results are discussed. The critical volume fraction for electrical percolation of the present composite was about 0.0005. Results obtained from previous work on SWNT (MWNT)–polymer composites and other percolation systems and the modeling (interpretation) of these results are also discussed and compared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3273–3287, 2005     

Systematic investigation of functional core variation within hyperbranched polyglycerols

A novel series of hyperbranched polyether polyols with various n‐alkyl amine cores (mono‐ and bifunctional) and photoactive cores (benzylamine and 1‐naphthylmethylamine) have been prepared. Polymerization of glycidol was carried out in two ways, starting directly from primary amine initiators and from bisglycidolized amine initiators. NMR spectroscopy and size exclusion chromatography (SEC) showed good control over the molecular weights only, when bisglycidolized amines were used. Molecular weights and polydispersity of the hyperbranched polyglycerols prepared with these initiator‐cores were in the range of 1600 to 8400 g/mol and of 1.5 to 2.5, respectively. MALDI‐ToF mass spectrometry confirmed covalent attachment of the functional cores to the hyperbranched polymers. When using the bis‐glycidolized amine‐initiators, only functionally initiated polymers could be observed. In contrast, the direct amine‐initiated polymers always showed the presence of nonfunctionalized PG homopolymer. Steady‐state and time‐resolved fluorescence measurements further support covalent attachment and site isolation of the functional initiators within the hyperbranched structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2049–2061, 2008     

Microhydration of the magnesium(II) acetate cation in the gas phase

Electrospray ionization of aqueous solutions of magnesium(II) acetate leads to microhydrated magnesium acetate cations of the type [(CH(3)COO)(2m-1)Mg(m)(H(2)O)(n)](+) with m = 1-4 and n = 0-4, which are characterized by mass spectrometry and, for the cluster with three water molecules, also by infrared multiphoton dissociation spectroscopy. Density functional theory is used to determine the energies of microhydration for the mononuclear species [(CH(3)COO)Mg(H(2)O)(n)](+) with n = 0-6 and the associated changes in molecular structure. While bidentate coordination of the acetato ligand is generally preferred, at higher values of n, a switch to a monodentate coordination becomes energetically competitive.     

Ultrafast intersystem crossing and spin dynamics of zinc meso-tetraphenylporphyrin covalently bound to stable radicals

tert-Butylphenylnitroxide (BPNO(?)) and α,γ-bisdiphenylene-β-phenylallyl (BDPA(?)) stable radicals are each attached to zinc meso-tetraphenylporphyrin (ZnTPP) at a fixed distance using one of the ZnTPP phenyl groups. BPNO(?) and BDPA(?) are oriented para (1 and 3, respectively) or meta (2 and 4, respectively) relative to the porphyrin macrocycle. Following photoexcitation of 1-4, transient optical absorption spectroscopy is used to observe excited state quenching of (1)*ZnTPP by the radicals and time-resolved electron paramagnetic resonance (TREPR) spectroscopy is used to monitor the spin dynamics of the paramagnetic product states. The presence of BPNO(?) or BDPA(?) accelerates the intersystem crossing rate of (1)*ZnTPP about 10- to 500-fold in 1-4 depending on the structure compared to that of (1)*ZnTPP itself. In addition, the lifetime of (3)*ZnTPP in 1 is shorter than that of (3)*ZnTPP itself as a result of enhanced intersystem crossing (EISC) from (3)*ZnTPP to the ground state. The TREPR spectra of the three unpaired spins produced within 1 and 2 show spin-polarized excited doublet (D(1)) and quartet (Q) states and subsequent formation of a spin-polarized ground state radical (D(0)). All three signals are absorptive for 1 and emissive for 2. Polarization inversion of the Q state is observed on a tens of nanoseconds time scale in 2, while no polarization inversion is observed for 1. The lack of polarization inversion in 1 is attributed to the short lifetime of the doublet-quartet manifold as a result of the very large exchange interaction. The TREPR spectra of 3 and 4 show ground state radical polarization at X-band (9.5 GHz) at room temperature, but not at 85 K, and similarly no polarization is observed at W-band (94 GHz). No evidence of excited doublet or quartet states is observed, indicating that the exchange interaction is both weak and temperature dependent. These results show that although ultrafast EISC produces (3)*ZnTPP within 1-4, the magnitude of the exchange interactions between the three relevant spins in the resulting (3)*ZnTPP-BPNO(?) and (3)*ZnTPP-BDPA(?) systems dramatically alters their spin dynamics.     

Design, synthesis and evaluation of new α-nucleophiles for the hydrolysis of organophosphorus nerve agents: application to the reactivation of phosphorylated acetylcholinesterase

A series of new α-nucleophiles including oximes and amidoximes have been synthesized, and their ability to efficiently and selectively cleave the P-S bond of organophosphorus nerve agents has been evaluated. The relationship between the chemical structure of the α-nucleophiles and their reactivity towards PhX hydrolysis is reported. A significant effect induced by an ortho-hydroxyl group of aryl- and pyridyl-oximes, amidoximes on their organo-phosphono-thioase reactivity was discovered. The evaluation of the initial rates of PhX hydrolysis reaction in the presence of α-nucleophiles allowed the discovery of new uncharged molecules with increased reactivity compared to positively charged 2-pralidoxime used as antidote. The mechanism of their action was studied in details by kinetic analysis, HPLC and LC-MS methods. The most promising structures were then considered as potent in vitro reactivators of phosphylated acetylcholinesterase (AChE), which was confirmed by the preliminary results of AChE reactivation initially inhibited by VX.