On theB andJ/ψ cross section measurements at UA1 and CDF

We analyse the implications of the measurement ofB andJ/ψ inclusivep _t distributions performed in \(p\bar p\) collisions by the UA1 and CDF experiments.     

Molecular switches of fluorescence operating through metal centred redox couples

Three-component molecular systems (redox active subunit)-spacer-(light-emitting fragment) can operate as fluorescence switches, following the alternate addition of an oxidizing agent and a reducing agent (or the adjustment of the potential of the working electrode in an electrolysis experiment). The redox active subunit typically consists of a metal centred redox couple (M⁽ⁿ⁺¹⁾⁺/Mⁿ⁺), encircled by a macrocyclic receptor, and switching efficiency requires that one of the two oxidation states quenches the proximate fluorophore and the other does not. Four ON/OFF systems, based on either the Cu^II/Cu^I or Ni^III/Ni^II couple, will be discussed. The nature of the quenching process responsible for the OFF state, either electron transfer or energy transfer, is related to the length and to the flexibility-rigidity of the spacer.     

Sorption kinetics: measurement of surface resistance

Adsorption - The problem of measuring sorption kinetics in microporous adsorbents and distinguishing experimentally between surface resistance and internal diffusion is discussed and reviewed with...     

Diffusion mechanism of CO2 in 13X zeolite beads

A systematic study of the diffusion mechanism of CO₂ in commercial 13X zeolite beads is presented. In order to gain a complete understanding of the diffusion process of CO₂, kinetic measurements with a zero length column (ZLC) system and a volumetric apparatus have been carried out. The ZLC experiments were carried out on a single bead of zeolite 13X at 38 °C at a partial pressure of CO₂ of 0.1 bar, conditions representative of post-combustion capture. Experiments with different carrier gases clearly show that the diffusion process is controlled by the transport inside the macropores. Volumetric measurements using a Quantachrome Autosorb system were carried out at different concentrations. These experiments are without a carrier gas and the low pressure measurements show clearly Knudsen diffusion control in both the uptake cell and the bead macropores. At increasing CO₂ concentrations the transport mechanism shifts from Knudsen diffusion in the macropores to a completely heat limited process. Both sets of experiments are consistent with independent measurements of bead void fraction and tortuosity and confirm that under the range of conditions that are typical of a carbon capture process the system is controlled by macropore diffusion mechanisms.     

M and P double helical complexes of copper(I) with bis-imino bis-quinoline enantiomerically pure chiral ligands

The enantiomerically pure bis-imino bis-quinoline ligands R,R-ImQ and S,S-ImQ have been prepared by Schiff condensation of 2-quinoline carboxyaldehyde with the pure R,R and S,S enantiomers of trans-1,2-diaminocyclohexane. Both ligands form 2:2 helical complexes with CuI perchlorate, and the crystal and molecular structure of [Cu2(R,R-ImQ)2]ClO4.H2O have been determined by X-ray diffraction methods: the [Cu2(R,R-ImQ)2]2+ molecular cation is a chiral double helix of M handedness, in which the two ligands are entertwined in such an arrangement that half of each ligand is not equivalent to the other half of the same ligand. Coupled circular dichroism and 1H NMR studies reveal that in CH3CN solution a rearrangement takes place toward a more symmetric helical structure (in which the two halves of the same ligand become equivalent), which maintains the same handedness found in the solid state and is a pure M isomer. Solid state and CH3CN solution CD experiments confirm that [Cu2(S,S-ImQ)2]ClO4.H2O, both in solution and in the solid state, is a pure double helix of P handedness, i.e., the enantiomer of the species containing the R,R ligand.