Cationic,Methylene‐Bridged,Intramolecular Donor‐Acceptor Systems Based on Zirconium and Hafnium and Phosphino‐methanides

A new access to cationic zirconium and hafnium compounds [L₂MCH₂PR₂][MeB(C₆F₅)₃] (L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf) exhibiting an intramolecular donor‐acceptor system was established by treating the precursors L₂M(Me)CH₂PR₂ with B(C₆F₅)₃ (BCF). Precursors 1 – 6 [L₂M(Me)CH₂PR₂ with L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf] were fully characterized. The crystal structures of these compounds revealed large M–CH₂–P bond angles with values of about 134° indicating the absence of interactions between the Lewis‐acid and Lewis‐base. The cationic compounds [L₂MCH₂PR₂][MeB(C₆F₅)₃] ( 7 – 12 ) were obtained by treatment of 1 – 6 with BCF. They were characterized by NMR spectroscopy, mass spectrometry, and elemental analyses; in H/D‐scrambling experiments with H₂/D₂ mixtures 7 – 12 disclosed their reactivity towards cleavage of hydrogen.     

Hierarchical Archimedean Dependence in Common Shock Models

Methodology and Computing in Applied Probability - In this paper we show how to extend a simple common shock model with Archimedean dependence of the hidden variables to the non-exchangeable case....     

The Greatest Lower Bound of a Boros–Moll Sequence

Mathematical Notes - The Boros–Moll polynomials $$P_m(a)$$ arise in the evaluation of a quartic integral. In the past few years, there has been some remarkable research on the properties of...     

Sierpiński graphs as spanning subgraphs of Hanoi graphs

Hanoi graphs H _p ⁿ model the Tower of Hanoi game with p pegs and n discs. Sierpinski graphs S _p ⁿ arose in investigations of universal topological spaces and have meanwhile been studied extensively. It is proved that S _p ⁿ embeds as a spanning subgraph into H _p ⁿ if and only if p is odd or, trivially, if n = 1.     

Molecular organization and syn ? anti conformational equilibria in ethane-bridged bis(zinc porphyrin) floating films at the air-water interface

The behavior of the symmetrical ethane-bridged bis(Zn porphyrin) (1) has been investigated at the air-water interface. The molecular organization of floating films of pure 1 and its mixture with amphiphilic substances, such as arachidic acid and n-octadecylamine, was inspected by means of surface pressure-area isotherms, Brewster angle microscopy and reflection spectroscopy in the UV-Vis region. The overall results suggest the presence in all cases of mainly the anti conformer of 1 even when the dimer was spread on pure water, through the ligation of water molecules to the zinc atoms in the axial positions. It was also demonstrated for the first time that the syn-to-anti conformational transition of the porphyrin dimer can be accelerated by the ligation of suitable amphiphiles even at the liquid-air interface. In particular, it is noted that n-octadecylamine, and arachidic acid (to a lesser extent), added to the system as amphiphiles, drive the syn ? anti equilibrium of 1 towards the anti form through the axial ligation of the amino or carboxylate group to the zinc atoms.     

Step-selective measurement by grating-based lateral shearing interferometry for segmented telescopes

We present an original step-selective mode which allows to measure only the steps and not the slowly varying aberrations of a wave front. This mode can be implemented when measuring segmented wave front by a diffraction-grating-based lateral shearing interferometer. This set-up rests on the different chromatic response of these interferometers depending on the rate of change of the impinging wave front: for smooth defects, the response is classically achromatic whereas it is chromatic for a step variation, which was to our knowledge overlooked. The interest of this mode for astronomical measurements is highlighted. First we present theoretical considerations to show how this mode of measure is possible; then a numerical simulation illustrates them.     

Synthesis of BODIPY Derivatives Substituted with Various Bioconjugatable Linker Groups: A Construction Kit for Fluorescent Labeling of Receptor Ligands

The goal of the present study was to design small, functionalized green-emitting BODIPY dyes, which can readily be coupled to target molecules such as receptor ligands, or even be integrated into their pharmacophores. A simple two-step one-pot procedure starting from 2,4-dimethylpyrrole and ω-bromoalkylcarboxylic acid chlorides was used to obtain new ω-bromoalkyl-substituted BODIPY fluorophores (1a–1f) connected via alkyl spacers of different length to the 8-position of the fluorescent dye. The addition of radical inhibitors reduced the amount of side products. The ω-bromoalkyl-substituted BODIPYs were further converted to introduce various functional groups: iodo-substituted dyes were obtained by Finkelstein reaction in excellent yields; microwave-assisted reaction with methanolic ammonia led to fast and clean conversion to the amino-substituted dyes; a hydroxyl-substituted derivative was prepared by reaction with sodium ethylate, and thiol-substituted BODIPYs were obtained by reaction of 1a–1f with potassium thioacetate followed by alkaline cleavage of the thioesters. Water-soluble derivatives were prepared by introducing sulfonate groups into the 2- and 6-position of the BODIPY core. The synthesized BODIPY derivatives showed high fluorescent yields and appeared to be stable under basic, reducing and oxidative conditions. As a proof of concept, 2-thioadenosine was alkylated with bromoethyl-BODIPY 1b. The resulting fluorescent 2-substituted adenosine derivative 15 displayed selectivity for the A₃ adenosine receptor (ARs) over the other AR subtypes, showed agonistic activity, and may thus become a useful tool for studying A₃ARs, or a lead structure for further optimization. The new functionalized dyes may be widely used for fluorescent labeling allowing the investigation of biological targets and processes.