Recent developments and on-line tests of uranium carbide targets for production of nuclides far from stability

The capacity of uranium carbide target materials of different structure and density for production of neutron-rich and heavy neutron-deficient nuclides have been investigated. The yields of Cs and Fr produced by a 1 GeV proton beam of the PNPI synchrocyclotron and release properties of different targets have been measured. Yields and release efficiencies of Cs and Fr produced from a high density UC target material and from low density UCx prepared by the ISOLDE method at IRIS in the collaboration with PARRNe group from Orsay are compared. The yields from ISOLDE original target are presented for comparison as well.     

A KAM phenomenon for singular holomorphic vector fields

Let X be a germ of holomorphic vector field at the origin of Cⁿ and vanishing there. We assume that X is a good perturbation of a “nondegenerate” singular completely integrable system. The latter is associated to a family of linear diagonal vector fields which is assumed to have nontrivial polynomial first integrals (they are generated by the so called “resonant monomials”). We show that X admits many invariant analytic subsets in a neighborhood of the origin. These are biholomorphic to the intersection of a polydisc with an analytic set of the form “resonant monomials = constants”. Such a biholomorphism conjugates the restriction of X to one of its invariant varieties to the restriction of a linear diagonal vector field to a toric variety. Moreover, we show that the set of “frequencies” defining the invariant sets is of positive measure.     

A straightforward synthesis of ynones by reaction of dimethylalkynylaluminum reagents with acid chlorides

Alkynyldimethylaluminum reagents react with various aromatic and aliphatic acid chlorides in a fast and efficient way. This reaction provides a simple entry to numerous ynones, using readily available, inexpensive, and nontoxic metalating agent, and does not require any transition metal as a catalyst.     

Analysis of carbohydrates in plants by high-performance anion-exchange chromatography coupled with electrospray mass spectrometry

A mass spectrometer was coupled to high-performance anion-exchange chromatography (HPAEC) with the help of electrochemical neutralization of the eluent and post-column addition of lithium chloride for carbohydrate analysis. Parallel selective channels (single ion monitoring) were used to decrease the detection limits and separate unresolved peaks. The mass specific detection allowed the simultaneous analysis of a wide range of sugar alcohols, mono-, di- and oligosaccharides. Carbohydrates extracted from leaves of poplar submitted to drought stress were analyzed using pulsed amperometric detection (PAD), then mass spectrometry. It allowed the confirmation of peak attribution and the identification of salicin as a major compound in the extracts. Different responses to water deficit and re-hydration were obtained for several carbohydrates, suggesting different roles in osmoprotection processes.     

Optical properties of donor-acceptor phenylene-ethynylene systems containing the 6-methylpyran-2-one group as an acceptor

Donor-acceptor phenylene ethynylene systems containing the 6-methylpyran-2-one group, synthesized via classic or microwave-assisted Sonogashira cross-coupling, exhibit pronounced solvatochromism in fluorescence suggesting a highly polar excited state; 4-[4-(4-N,N-dihexylaminophenylethynyl)phenylethynyl]-6-methylpyran-2-one has a fluorescence quantum yield >0.9 in cyclohexane.     

Synthesis of Novel Fluorogenic L-Fmoc Lysine Derivatives as Potential Tools for Imaging Cells

Two coumarin-labeled lysines were conveniently prepared as fluorescent probes. 7-Methoxy and 7-diethylamino coumarin-3-carboxylic acids were synthesized according to a modification of known procedures. Labeling at lysine was achieved in solution via the active N-hydroxysuccinimide ester of the carboxylic acid coumarin derivatives to give the target compounds in good yield. Spectroscopic data (UV-vis and fluorescence) were recorded for all compounds.     

Short-pulse laser ablation of solids: from phase explosion to fragmentation

The mechanisms of laser ablation in silicon are investigated close to the threshold energy for pulse durations of 500 fs and 50 ps. This is achieved using a unique model coupling carrier and atom dynamics within a unified Monte Carlo and molecular-dynamics scheme. Under femtosecond laser irradiation, isochoric heating and rapid adiabatic expansion of the material provide a natural pathway to phase explosion. This is not observed under slower, nonadiabatic cooling with picosecond pulses where fragmentation of the hot metallic fluid is the only relevant ablation mechanism.     

Measurement of long range H,C couplings in natural products in orienting media: a tool for structure elucidation of natural products

In this paper we show that water insoluble compounds dissolved in poly-gamma-benzyl-glutamate are amenable to the measurement of a number of homo- and heteronuclear dipolar couplings. The sensitivity and experimental precision of dipolar couplings are sufficient to obtain a good match with the structure. In order to achieve the necessary precision for H,C dipolar couplings between protons and carbons that are not directly bound a new method for the measurement of heteronuclear long range couplings is introduced that allows a one-parameter fit to a HSQC-based experiment as reference experiment. The methodology is applied to menthol (1R, 3S, 4R).     

Highly cooperative formation of bis-urea based supramolecular polymers

Eleven bis-ureas have been synthesized, and some of their properties are reported. Several of these compounds form supramolecular polymers in organic solvents. The self-association is shown by FTIR spectroscopy to display cooperativity at two levels. The first level of cooperativity is due to the synergistic association of the two urea functions of a single molecule. The second level of cooperativity is revealed by the fact that the formation of dimers is less favored than that of long oligomers.