How acidic are corroles and why?

The pH-dependent absorption and emission spectra of the water-soluble 2,17-disulphonato-5,10,15-tris(pentafluorophenyl)corrole revealed that its inner-core nitrogen atoms can be both protonated and deprotonated, with acidity constants of 2.5 and 5.2, respectively. An analysis of the structural features of free-base corroles suggests that the quite limited pH range at which corroles remain neutral is reminiscent of the instability of mono-protonated porphyrins.     

Coverage dependence of neopentane trapping dynamics on Pt(111)

Adsorption probabilities for neopentane on Pt(111) were measured directly using supersonic molecular-beam techniques at coverages ranging from zero to monolayer saturation, incident translational energies between 18 and 110 kJ mol⁻¹ and incident angles between 0° and 60° at a surface temperature of 105 K. The adsorption probability was found to increase with coverage up to near monolayer saturation at all incident translational energies and incident angles. The coverage dependence of the adsorption probability predicted by a modified Kisliuk model with enhanced trapping into the second layer exhibits good quantitative agreement with the experimental values. The angular dependence of the adsorption probability decreases with increasing coverage, suggesting that the effective corrugation of the gas–surface interaction potential increases with the adsorbate coverage. The initial adsorption probability into the second layer onto the covered surface decreases from 0.95 to 0.75 with increasing energy over the energy range studied, and exhibits total energy scaling. A comparison with second-layer trapping data of simpler molecules onto covered Pt(111) indicates that the structural complexity of adsorbed neopentane molecules facilitates collisional energy transfer during adsorption.     

Coupling real-time surface-enhanced raman spectroscopy with linear-sweep voltammetry : Application to elucidation of electrochemical mechanisms

The broad-based utilization of real-time surface-enhanced Raman spectra, obtained by using an intensified diode-array detector, to examine interfacial redox transformations under cyclic voltammetric conditions is exemplified for the oxidation at gold electrodes of irreversibly adsorbed benzidine and the reduction of adsorbed azoxybenzene. The first reaction, involving a pair of irreversible one-electron oxidation steps, enabled a quantitative comparison to be made between the extent of oxidation of the adsorbed layer during the potential sweep and the simultaneous spectral response. Although relatively slow (10–50 mV s^?1) sweeps are required in order to yield spectral sequences having a suitably narrow (?50 mV) potential interval, the spectral data acquisition requires only a single potential perturbation. This “single-shot” spectroelectrochemical approach, desirable for the examination of irreversible interfacial systems, differs from conventional time-resolved methods that involve signal integration over numerous repetitive perturbations.     

Electronic structure and bonding in CaH2: Experiment and theory

Synchrotron radiation photoemission studies of Ca and CaH₂ reveal changes in the electronic structure and bonding which directly reflect metal-hydrogen interactions. The results indicate similarities between the saline dihydrides and the transition metal dihydrides, particularly the energy location and width of the bonding band states. Combined with APW band calculations for CaH₂ in the CaF₂ structure, they provide new insight regarding bonding in hydrides.