Ruthenium-SYNPHOS-catalyzed asymmetric hydrogenations: an entry to highly stereoselective synthesis of the C15-C30 subunit of dolabelide A

An efficient construction of the C15-C30 segment of the cytotoxic macrolide dolabelide A is described. The synthesis relies on ruthenium-SYNPHOS-mediated asymmetric hydrogenation reactions of beta-keto esters to generate the C19, C21, and C27 hydroxyl-bearing stereocenters with very high levels of enantio- and diastereoselectivity.     

Local existence and uniqueness of the mild solution to the 1D Vlasov–Poisson system with an initial condition of bounded variation

We propose a result of local existence and uniqueness of a mild solution to the one‐dimensional Vlasov–Poisson system. We establish the result for an initial condition lying in the space W^1,1(?²), then we extend it to initial conditions lying in the space BV(?²), without any assumption of continuity, boundedness or compact support. Copyright © 2010 John Wiley & Sons, Ltd.     

Rapid Legionella pneumophila determination based on a disposable core–shell Fe3O4@poly(dopamine) magnetic nanoparticles immunoplatform

A novel amperometric magnetoimmunoassay, based on the use of core–shell magnetic nanoparticles and screen-printed carbon electrodes, was developed for the selective determination of Legionella pneumophila SG1. A specific capture antibody (Ab) was linked to the poly(dopamine)–modified magnetic nanoparticles (MNPs@pDA-Ab) and incubated with bacteria. The captured bacteria were sandwiched using the antibody labeled with horseradish peroxidase (Ab-HRP), and the resulting MNPs@pDA-Ab-Legionella neumophila-Ab-HRP were captured by a magnetic field on the electrode surface. The amperometric response measured at −0.15 V vs. Ag pseudo-reference electrode of the SPCE after the addition of H₂O₂ in the presence of hydroquinone (HQ) was used as transduction signal. The achieved limit of detection, without pre-concentration or pre-enrichment steps, was 10⁴ Colony Forming Units (CFUs) mL⁻¹. The method showed a good selectivity and the MNPs@pDA-Ab exhibited a good stability during 30 days. The possibility of detecting L. pneumophila at 10 CFU mL⁻¹ level in less than 3 h, after performing a membrane-based preconcentration step, was also demonstrated.     

The application of Rosenbrock-Wanner type methods with stepsize control in differential-algebraic equations

Summary Two Rosenbrock-Wanner type methods for the numerical treatment of differential-algebraic equations are presented. Both methods possess a stepsize control and an index-1 monitor. The first method DAE34 is of order (3)4 and uses a full semi-implicit Rosenbrock-Wanner scheme. The second method RKF4DA is derived from the Runge-Kutta-Fehlberg 4(5)-pair, where a semi-implicit Rosenbrock-Wanner method is embedded, in order to solve the nonlinear equations. The performance of both methods is discussed in artificial test problems and in technical applications.     

Comportement de quelques Arylbenzo[b]-furannes sous l'Impact électronique

A fragmentation mechanism for arylbenzo[b]furans is proposed to account for the similarity of the spectra of isomers with substituents in the 2 and 3 positions. This mechanism implies the migration of the aryl group during the decomposition of the 2-substituted species.     

Direct solid-phase synthesis and fluorescence labeling of large, monodisperse mannosylated dendrons in a peptide synthesizer

Fluorophore-labeled glycodendrimers have potential use in the study of carbohydrate-protein interactions by fluorescence spectroscopy and imaging methods. The current solution-phase methods for preparation of such glycoconjugates are labour intensive. On the other hand, the intrinsically more efficient solid-phase methods have been explored only at low generations. Herein we disclose a direct, expedient glycodendrimer synthesis from commercially available or easily prepared building blocks by machine-assisted solid-phase peptide synthesis (SPPS). Large, monodisperse 4th- and 5th-generation polylysine dendrons are prepared and capped with 16 and 32 mannose residues, respectively, in a single synthetic operation. Incorporation of a C-terminal lysine residue in the 4th-generation dendron allows fluorescence labelling with a number of common labels on resin, in organic solvent or in aqueous buffer, as required. A single HPLC purification is sufficient in all cases to obtain a homogeneous sample. The monodispersity of the glycodendrons is confirmed by MALDI-TOF. FITC-labeled 4th-generation glycodendron is an excellent probe for the imaging studies of mannose-receptor-mediated entry of into dendritic cells by confocal fluorescence microscopy.     

Conformational dependence of hemoglobin reactivity under high viscosity conditions: the role of solvent slaved dynamics

The concept of protein dynamic states is introduced. This concept is based on (i) protein dynamics being organized hierarchically with respect to solvent slaving and (ii) which tier of dynamics is operative over the time window of a given measurement. The protein dynamic state concept is used to analyze the kinetic phases derived from the recombination of carbon monoxide to sol-gel-encapsulated human adult hemoglobin (HbA) and select recombinant mutants. The temperature-dependent measurements are made under very high viscosity conditions obtained by bathing the samples in an excess of glycerol. The results are consistent with a given tier of solvent slaved dynamics becoming operative at a time delay (with respect to the onset of the measurement) that is primarily solvent- and temperature-dependent. However, the functional consequences of the dynamics are protein- and conformation-specific. The kinetic traces from both equilibrium populations and trapped allosteric intermediates show a consistent progression that exposes the role of both conformation and hydration in the control of reactivity. Iron-zinc symmetric hybrid forms of HbA are used to show the dramatic difference between the kinetic patterns for T state alpha and beta subunits. The overall results support a model for allostery in HbA in which the ligand-binding-induced transition from the deoxy T state to the high -affinity R state proceeds through a progression of T state intermediates.     

Confirmation,Increase in Probability,and the Likelihood Ratio Measure: a Reply to Glass and McCartney

Bayesian confirmation theory is rife with confirmation measures. Zalabardo (2009) focuses on the probability difference measure, the probability ratio measure, the likelihood difference measure, and the likelihood ratio measure. He argues that the likelihood ratio measure is adequate, but each of the other three measures is not. He argues for this by setting out three adequacy conditions on confirmation measures and arguing in effect that all of them are met by the likelihood ratio measure but not by any of the other three measures. Glass and McCartney (2015), hereafter “G&M,” accept the conclusion of Zalabardo’s argument along with each of the premises in it. They nonetheless try to improve on Zalabardo’s argument by replacing his third adequacy condition with a weaker condition. They do this because of a worry to the effect that Zalabardo’s third adequacy condition runs counter to the idea behind his first adequacy condition. G&M have in mind confirmation in the sense of increase in probability: the degree to which E confirms H is a matter of the degree to which E increases H’s probability. I call this sense of confirmation “IP.” I set out four ways of precisifying IP. I call them “IP1,” “IP2,” “IP3,” and “IP4.” Each of them is based on the assumption that the degree to which E increases H’s probability is a matter of the distance between p(H | E) and a certain other probability involving H. I then evaluate G&M’s argument (with a minor fix) in light of them.     

Aharonov-Bohm conductance modulation in ballistic carbon nanotubes

We report on magnetoconductance experiments in ballistic multiwalled carbon nanotubes threaded by magnetic fields as large as 55 T. In the high temperature regime (100 K), giant modulations of the conductance, mediated by the Fermi level location, are unveiled. The experimental data are consistently analyzed in terms of the field-dependent density of states of the external shell that modulates the injection properties at the electrode-nanotube interface, and the resulting linear conductance. This is the first unambiguous experimental evidence of Aharonov-Bohm effect in clean multiwalled carbon nanotubes.     

Selective fluorescence turn-on of a prefluorescent azomethine with Zn

A prefluorescent conjugated azomethine (4) was prepared by condensing 8-hydroxyquinoline-5-carbaldehyde with 2-amine thiophene. The fluorescence of the azomethine was quenched in organic solvents including dichloromethane, methanol, DMSO, and DMF. However, the fluorescence of 4 was selectively revived in the presence of zinc and an absolute quantum yield Φ_fl = 0.15 was measured.