Analysis of perfluoroalkyl anion fragmentation pathways for perfluoroalkyl carboxylates and sulfonates during liquid chromatography/tandem mass spectrometry: evidence for fluorine migration prior to secondary and tertiary fragmentation

It is known that under liquid chromatography/electrospray tandem mass spectrometry (LC/ES-MS/MS) conditions, the perfluorocarboxylate anion [R(F)CO(2)](-) first loses CO(2) to give a perfluoroalkyl anion R(F)(-), [(M-H)-CO(2)](-), which can subsequently fragment to give inter alia lower mass carbanions. It has been suggested in a previous study that such secondary fragmentation involves cleavage of C(n)F(2n) segments. Our study of the LC/ES-MS/MS of a series of (13)C-labeled perfluoroalkyl carboxylic acids (PFCAs) indicates that fragmentation of the R(F)(-) anion does not involve simple 'unzipping' of a primary perfluoroalkyl anion of the type F(3)C(CF(2))(x)CF(2)(-). For example, we have discovered that the secondary transition for the mass-labeled PFOA, perfluoro-1,2,3,4-(13)C(4)-octanoic acid (MPFOA), gives two signals of equal intensity at m/z 169 and 172. We propose a mechanism of fragmentation that involves rapid fluorine shifts, after the initial decarboxylation, which generate a series of new anions prior to secondary and tertiary fragmentation.     

Solvable potentials with exceptional orthogonal polynomials

Classes of solvable potentials are presented within an standard application of supersymmetric quantum mechanics. Sets of exceptional orthogonal polynomials generated by these solvable potentials are introduced and examined in detail. Several properties of these polynomials including orthogonality conditions, weight functions, differential equations, the Wronskains, possible recurrence relations are also investigated.

     

Block copolymers under periodic, strong three-dimensional confinement

In this communication we study the influence of strong 3D confinement on the self-assembly of diblock copolymers containing a polyferrocenylsilane metallopolymer segment. Both silica colloidal crystals and silica inverse colloidal crystals, having nanometer-scale interconnected pore networks, are used as molds to direct the self-assembly. Unusual morphologies, such as concentric shells and branched lamellae, result from the interaction of the polymer with the high surface area topologically periodic templates.     

Photochemically and thermally tunable planar defects in colloidal photonic crystals

We report a bottom-up synthesis of a photochemically and thermally active azobenzene-based polyelectrolyte multilayer (PEM) planar defect embedded in a colloidal photonic crystal (CPC). Both photoisomerization and thermal cycling lead to a precise tuning of an intragap transmitting state induced by the PEM structural defect.     

Ground Layer Adaptive Optics

We will introduce the present knowledge of the turbulence profile and in particular we will emphasise the existence of a turbulence layer close to the ground. Then we will present the concept of Ground Layer Adaptive Optics and will provide estimates of performance expected from such systems and their potential for astronomical applications. Finally we will provide practical implementation concepts for two instruments at the VLT, MUSE and HAWK-I using multi-Laser Guide Stars and a large Deformable Secondary Mirror. The latter will also be described as its use is optimum for GLAO systems. To cite this article: N. Hubin et al., C. R. Physique 6 (2005).     

Synthesis and characterization of zinc complexes and reactivity with primary phosphines

Zinc complexes of chelating monoanionic N-donors and neutral diphosphine ligands were synthesized by reaction of diethylzinc with 1,3-diketimine, diazabutadiene, and diphosphine ligand precursors. These complexes were reacted with primary phosphines in an attempt to solicit phosphine dehydrocoupling reactivity. In most cases, insoluble zinc-containing precipitates were formed and ligands were liberated. For the most sterically encumbered complex, (^DippL)ZnEt (3, ^DippL = [(2,6-ⁱPrC₆H₃)NC(CH₃)]₂CH^?), a product assigned as the zinc-phosphide (^DippL)ZnPHPh (6) was observed but could not be isolated as a pure compound. A new, less bulky β-diketiminate complex (^TolL)ZnEt (2, ^TolL = [(p-CH₃C₆H₄)NC(CH₃)]₂CH^?) was reacted with primary phosphines to give a precipitate and the bis(β-diketiminate)zinc complex (^TolL)₂Zn (5), an apparent product of comproportionation. (^MesAI)ZnEt (1, ^MesAI = MesNC(Me)(Et)C(Me) = NMes) and 2 were structurally characterized.     

Shell-cross-linked cylindrical Polyisoprene-b-polyferrocenylsilane (PI-b-PFS) block copolymer micelles: one-dimensional (1D) organometallic nanocylinders

We report the creation and properties of colloidally stable shell-cross-linked cylindrical organometallic block copolymer micelles with adjustable length and swellability. The one-dimensional (1D) structures with semicrystalline polyferrocenylsilane (PFS) cores and polyisoprene (PI) coronas were initially self-assembled from PI-b-PFS block copolymers in a PI-selective solvent such as hexane. The length of the cylinders could be varied from hundreds of nanometers to several tens of micrometers by adjusting solution conditions, using various solvents such as hexane, decane, or hexane/THF (or toluene) mixtures. The cylindrical micelles with vinyl groups in the PI corona were cross-linked through a Pt(0)-catalyzed hydrosilylation reaction using 1,1,3,3-tetramethyl disiloxane as a cross-linker at room temperature. The shell cross-linking significantly increased the stability of the micelles relative to the un-cross-linked precursors as no fragmentation was observed upon sonication in solution. In addition, the structural integrity of the micelles was also enhanced after solvent removal; a solid sample was successfully microtomed and then examined using TEM, which revealed circular cross-sections for the PI-b-PFS micelles with an average diameter of ca. 15 nm. We also discovered that shell cross-linking is a prerequisite for generating ceramic replicas through the pyrolysis of PI-b-PFS aggregates. Moreover, we were able to pattern the cross-linked micelles on a flat substrate by microfluidic techniques, generating perpendicularly crossed lines of aligned micelles. In short, the shell-cross-linked PI-b-PFS 1D organometallic aggregates are a promising new type of nanomaterial with intriguing potential applications.     

Bis(Iminophosphorano)-Substituted Pyridinium Ions and their Corresponding Bispyridinylidene Organic Electron Donors

Optimized synthetic procedures for pyridinium ions featuring iminophosphorano (−N=PR₃; R=Ph, Cy) π-donor substituents in the 2- and 4- positions are described. Crystallographic and theoretical studies reveal that the strongly donating substituents severely polarize the π-electrons of the pyridyl ring at the expense of aromaticity. Moreover, the pyridinium ions are readily deprotonated to generate powerful bispyridinylidene (BPY) organic electron donors. Electrochemical studies show exceptionally low redox potentials for the two-electron BPY/BPY²⁺ couples, ranging from −1.71 V vs the saturated calomel electrode for 3PhPh (with four Ph₃P=N− groups) to −1.85 V for 3CyCy (with four Cy₃P=N− groups). These new compounds represent the most reducing neutral organic electron donors (OEDs) currently known. Some preliminary reductions involving 3CyCy showed enhanced capability owing to its low redox potential, such as the thermally activated reduction of an aryl chloride, but purification challenges were often encountered.     

Functional polymer laminates from hyperthermal hydrogen induced cross-linking

The use of a hyperthermal hydrogen induced cross-linking process to prepare laminates comprising polypropylene, poly(isobutylene-co-isoprene), and poly(vinyl acetate) is described. In this new, milder alternative to conventional plasma techniques, neutral molecular hydrogen projectiles were used to create carbon radicals on impacted surfaces by collision-induced dissociation of C-H bonds, and this process was used to cross-link polymers on a polypropylene surface. It was demonstrated that multiple layers of cross-linked materials could be added, creating polymer laminates with each layer introducing new functionalities and properties. In particular, the present work shows that the process is largely nondestructive toward ester functionalities. First, the esters were grafted to become nonleachable. Then, the esters were subsequently hydrolyzed to convert the surface from hydrophobic to hydrophilic. Afterward, the esters could be recovered by simple esterification demonstrating that further chemical transformations were possible.     

Les effets causes par les dimensions de la source dans les systemes optiques eclaires en lumiere spatialement incoherente

It has been shown recently that in order for an incoherent optical system to be linear and space invariant, the image of the source at the filter plane must be larger than the filter aperture. We show in this paper that the source image must be larger than the filter by an amount equal to twice the highest spatial frequency of the object, the frequency being measured in the filter plane.