Effect of axially coordinated pi-acid ligands on photovoltaic properties of Zn-tetraphenylporphyrin

Following our earlier observations that the well known doping effect of oxygen and water on electrical properties of porphyrin and phthalocyanine films may be attributed to a pi-acid axial interaction throughout the film in the case of PdTPP, we have compared Zn-TPP films supported on transparent n-doped SnO₂ electrodes which had been treated with several pi-acids in contact with an electrolyte to give photoelectrochemical cells. Photovoltages obtained in contact with a series of solution couples were used to obtain approximate photo flat band potentials. The doped films were examined by magnetic circular dichroism (MCD) spectroscopy so that the electronic effect of the dopant could be diagnosed. It was found that pi-acid dopants cause shifts to low energy in the band which indicates “hole stabilization” in the order pyridine < CO < triphenylarsine. The potentials of zero photopotential ‘E_FB’, correlate approximately with spectral shifts. It is concluded that manipulation of axial ligand dopants is a promising method for design of metal porphyrin and perhaps phthalocyanine films with desired photovoltaic properties.     

Reactive absorption of nitrogen dioxide by pulmonary epithelial lining fluid

In a previous study (J. Appl. Physiol. 68: 594-603, 1990) in isolated rat lungs, we suggested that the rate of pulmonary air space absorption of inhaled NO2 is limited, in part, by chemical reaction(s) rather than by physical solubility. Because the initial site of primary absorption interactions involves the epithelial lining fluid (ELF), we investigated whether ELF-NO2 interactions could account for pulmonary NO2 reactive absorption. Rat ELF, obtained by bronchoalveolar lavage (BAL), was compared with a model chemical system (reduced glutathione, GSH). In vitro exposures (NO2-air) used constant gas flow and planar gas-liquid interfaces. 1) Solvent pH notably altered NO2 uptake by GSH but to a lesser extent by BAL. 2) Uptake displayed [GSH]-dependent saturation. [ELF] in BAL was augmented by sequential lavage (lavagate reuse) of multiple lungs. Uptake was proportional to [ELF] but did not saturate under these exposure conditions. 3) The uptake rate exhibited [NO2] dependence. However, relative to increasing [NO2], fractional uptakes decreased for BAL and 1 mM GSH but not for 10 mM GSH. 4) Altered convective gas flow produced nonlinear increments in uptake (10 mM GSH) and substantial decrements in fractional uptake. 5) Arrhenius plots [ln(r) vs. 1/T, where r is reaction rate and T is absolute temperature (degree K)] for BAL and 1 mM GSH yielded respective activation energies of 4,952 and 4,149 kcal.g-1.mol-1 and degree of change in the rate of NO2 uptake per 10 degrees C (Q10) of 1.32 and 1.25. These results imply that the rate of NO2 uptake into rat ELF, like intact lung, is limited, in part, by chemical reaction(s).(ABSTRACT TRUNCATED AT 250 WORDS)