Fluorinated squaraine as near-IR label with improved properties for the labeling of oligonucleotides

A new squaraine dye with fluorinated benzothiazole rings was synthesized. This new label possesses improved photophysical properties and chemical stability as compared to the corresponding non-fluorinated and the dicyanosquaraines. These squaraines were used for the labeling of a series of oligonucleotides with various sequences, lengths, and chemistries. The conjugates involving the fluorinated squaraine possess the best properties: emission wavelength >670 nm, high quantum yields (0.27-0.39).     

Meson photoproduction on the nucleon with polarized photons

Meson photoproduction with polarized photons has proved to be a powerful tool to identify contributions of baryon resonances that are not evident in the differential cross-sections. It provides information that are complementary to those extracted using pion-nucleon scattering data. Extensive results have been produced in the past on beam asymmetries by the Graal collaboration for η and π ⁰ on the proton. New results are now available for the same reactions on the quasi-free neutron and for the K⁺ photoproduction on the proton. Contributions from hitherto undetected baryon resonances may be important to understand the results.     

Phenomenology of photon-e ± collisions

The physical interest ofγe ^± collisions is examined. A basic formalism is established. Crosssections are computed with general couplings and polarization states. Illustrations are given for QED tests, Z⁰ andW ^± production, various electro-weak processes including γγ collisions and the search for new currents and particles.     

Inclusive properties of the ee annihilation into hadrons

The reaction e⁺e⁻ → hadrons is described on the basis of an hadronic structure for the photon. The structure functions of the inclusive reaction e⁺e⁻ → h + anything describe then the parton constitution of the photon in the scaling limit. Various types of couplings and models are considered (global couplings with vector mesons, fundamental photon-parton-antiparton couplings with formation of jets or fans). Precise shapes for the inclusive spectra and multiplicity distributions are deduced. Detailed comparisons with hadronic collisions A + B → h + anything are proposed in the fragmentation, the phase space boundary and the pionisation regions which could determine the nature of the partons and their interactions.     

Charge density wave transport in (TaSe4)2I

We report non linear transport properties below the metal-insulat transition temperature T_° = 263 K in the halogened metal transition tetrachalcogenide (TaSe₄)₂I. These non linear properties are similar to those of NbSe₃ and TaS₃ and indicate that (TaSe₄)₂I is a new compound exhibiting charge density wave transport.     

Superficial migration of tritium physisorbed on monocrystalline nickel (111)

The aim of this study is the measurement of superficial migration coefficient of tritium physisorbed on monocrystalline nickel without chemisorbed sublayer. The chosen crystalline orientation was (111) because it offers the greatest concentration of adsorption sites per square centimeter. A clean surface sample is obtained by mechanical polishing, chemical etching and finally ionic bombardment by high purity argon gas. The pressure in the experimental vessel is maintained below 10^?9 torr, by liquid helium cryopumping after zeolite sorption pumping.A little spot of adsorbed tritium is produced by introduction of a finite amount of tritium gas on the clean surface of the nickel sample through a stainless steel tube. Temperatures of nickel and of the gas introduction tube are respectively regulated at 5 K and 35 K. Tritium is used as a radioactive marker and its 10 keV β-radiation is measured by a channeltron type detector which permits the localization of the deposit without acting on the surface. We observed that tritium sorbed at 5 K is quite immobile (at the time scale of our experiment). After heating up to a fixed temperature T chosen between 10 K and 20 K, the deposite profile variation in function of time is observed to determine the superficial diffusion coefficient D. For the values of T from 13 K to 20 K, D varies from 10×10^?6 to 150×10^?6 cm² sec^?1. A diffusion activation energy of 200 cal mole^?1 is deduced from the exponential increase of the curve. A vibrational frequency can be evaluated to 3×10¹² sec^?1. The rate of desorption permits the evaluation of sorption energy at about 1800 cal mole^?1 in good agreement with usual results concerning physorption of H₂ on metals.     

Magnetic filaments in resistive manganites

The magnetic phase separation in single crystals of the Pr0.67Ca0.33MnO3 manganites is studied using polarized small angle neutron scattering. The measured spectra give a fractal dimension consistent with a configuration in ferromagnetic filaments of nanometric diameter. We argue here that localized charge carriers hop in a random walk fashion mediating a ferromagnetic "hopping exchange" which coexists with superexchange to create the filamentary phase separation. The arguments for this physical picture are validated by Monte Carlo simulations, where magnetism and transport are treated in a self-consistent manner.     

Design and synthesis of chemiluminescent probes for the detection of cholinesterase activity

Acetylcholinesterase is one of the most widely used and studied enzymes. Not only does this enzyme regulate neurotransmission (and thus play a key role in neurodegenerative processes) but it is also a prime target for pest control agents and warfare agents. Above all, due to its particularly high turnover rate, acetylcholinesterase is among the most efficient reporter enzymes yet described (for use as enzymatic tracer in immunoassays, for instance). However, its activity is detected through a colorimetric reagent, the Ellman reagent, which displays low detection limits and is often subject to background perturbations. In the course of our search for a more sensitive detection assay, we describe here a first-generation 1,2-dioxetane chemiluminescent probe, based on chemically induced electron exchange luminescence, which has an approximately 10 times lower detection limit than the Ellman colorimetric assay (2.5 x 10(-19) mol for Electrophorus electricus AChE in its tetrameric form).     

Fluorogenic Behaviour of the Hetero‐Diels–Alder Ligation of 5‐Alkoxyoxazoles with Maleimides and their Applications

Fluorogenic reactions are largely underrepresented in the toolbox of chemoselective ligations despite their tremendous potential, particularly in chemical biology and biochemistry. In this respect, we have investigated in full detail the fluorescence behaviour of the azaphthalamide, a scaffold which is generated through a hetero‐Diels–Alder reaction of 5‐alkoxyoxazole and maleimide derivatives under mild conditions that are compatible with, among others, peptide chemistry. The scope and limitations of such a fluorogenic labelling strategy were examined through four distinct applications, which target enzymatic activities or bioorthogonal reactions.