Vapour—liquid equilibrium of the square-well fluid of variable range via a hybrid simulation approach

The equilibrium between vapour and liquid in a square-well system has been determined by a hybrid simulation approach combining chemical potentials calculated via the Gibbs ensemble Monte Carlo technique with pressures calculated by the standard NVT Monte Carlo method. The phase equilibrium was determined from the thermodynamic conditions of equality of pressure and chemical potential between the two phases. The results of this hybrid approach were tested by independent NPT and μPT calculations and are shown to be of much higher accuracy than those of conventional GEMC simulations. The coexistence curves, vapour pressures and critical points were determined for SW systems of interaction ranges λ = 1.25, 1.5, 1.75 and 2. The new results show a systematic dependence on the range λ, in agreement with results from perturbation theory where previous work had shown more erratic behaviour.     

Imidazolium-Based Dicationic Cyclophanes. Solid-State Aggregates with Unconventional (C–H)+···Cl− Hydrogen Bonding Revealed by X-ray Diffraction

The first single-crystal X-ray crystallographic diffraction analysis of a dicationic heterophane showed a non-classic (C–H)⁺···Cl^?  hydrogen bond between the imidazolium rings and halide anions and the formation of unconventional charged assisted hydrogen bonds, which were the non-covalent forces driving the anion interactions shown by the dications 4·2X. Here is reported the halide-templated controlled synthesis and chemical response in basic media of 4·2X. Their structural properties were examined at the gas phase by electrospray ionization mass spectrometry in the negative-ion mode and in the solid-state by X-ray crystallography. Thus, the negative-ion ESI-MS response showed that the formation of non-covalent self-aggregates of macrocyclic dications is a consequence of hydrogen-bonded complexes with halide anions. Notably, X-ray diffraction of dication 4a·2Cl·2H₂O provides evidence for the H-bonding network, which has a crucial role in crystal packing. The solid-state aggregates showed that chloride anions and water molecules formed channels among dications 4a⁺.     

POLYMER BOUND PYRROLE COMPOUNDS–VI. PHOTOPHYSICAL PROPERTIES OF MONOMERIC MODELS FOR POLYSTYRENE-BOUND PORPHYRINS

Abstract— Several porphyrin esters used as models for polystyrene-bound porphyrins have been prepared and their excited states have been studied by laser flash photolysis, IR phosphorescence of singlet molecular oxygen, O₂(¹Δ_g), and steady-state fluorescence. The photophysical properties of the porphyrin esters in solution are affected by the presence of nitro group(s) in the chain. In this case, an important decrease in φ_f, φ_T and φ_δ (to ca 0.7–0.4 of the value for the parent dimethyl ester) is observed. This is mainly due to intramolecular electron-transfer quenching [by the nitro group(s)] of the first excited singlet state of the porphyrin. The thermodynamic feasibility of this deactivation pathway has been confirmed polarographically. Quenching of the porphyrin triplet state and of O₂(¹Δ_g) by the nitro groups is negligible. The present conclusions explain also the results obtained previously for the photooxidation of bilirubin sensitized by the parent insoluble polystyrene-bound porphyrins. In that case the photooxidation rates were correlated directly with the quantum yield of O₂(¹Δ_g) production by the sensitizer. The consequences of these results for the use of polystyrene-bound porphyrins in sensitized photooxidation processes are discussed.