Photolysis of pure solid O3 and O2 films at 193 nm.

We studied quantitatively the photochemistry of solid O(3) and O(2) films at 193 nm and 22 K with infrared spectroscopy and microgravimetry. Photolysis of pure ozone destroyed O(3), but a small amount of ozone remained in the film at high fluence. Photolysis of pure O(2) produced O(3) in an amount that increased with photon fluence to a stationary level. For both O(2) and O(3) films, the O(3):O(2) ratio at large fluences is ∼0.07, about two orders of magnitude larger than those obtained in gas phase photolysis. This enhancement is attributed to the increased photodissociation of O(2) due to photoabsorption by O(2) dimers, a process significant at solid-state densities. We obtain initial quantum yield for ozone synthesis from solid oxygen, Φ(O(3)) = 0.24 ± 0.06, and quantum yields for destruction of O(3) and O(2) in their parent solids, Φ(-O(3)) = 1.0 ± 0.2 and Φ(-O(2)) = 0.36 ± 0.1. Combined with known photoabsorption cross sections, we estimate probabilities for geminate recombination of 0.5 ± 0.1 for O(3) fragments and 0.88 ± 0.03 for oxygen atoms from O(2) dissociation. Using a single parameter kinetic model, we deduce the ratio of reaction cross sections for an O atom with O(2) vs. O(3) to be 0.1-0.2. The general good agreement of the model with the data suggests the validity of the central assumption of efficient energy and spin relaxation of photofragments in the solid prior to their reactions with other species.

Characterization of porosity in vapor-deposited amorphous solid water from methane adsorption.

We have characterized the porosity of vapor-deposited amorphous solid water (ice) films deposited at 30-40 K using several complementary techniques such as quartz crystal microgravimetry, UV-visible interferometry, and infrared reflectance spectrometry in tandem with methane adsorption. The results, inferred from the gas adsorption isotherms, reveal the existence of microporosity in all vapor-deposited films condensed from both diffuse and collimated water vapor sources. Films deposited from a diffuse source show a step in the isotherms and much less adsorption at low pressures than films deposited from a collimated source with the difference increasing with film thickness. Ice films deposited from a collimated vapor source at 77 degrees incidence are mesoporous, in addition to having micropores. Remarkably, mesoporosity is retained upon warming to temperatures as high as 140 K where the ice crystallized. The binding energy distribution for methane adsorption in the micropores of ice films deposited from a collimated source peaks at approximately 0.083 eV for deposition at normal incidence and at approximately 0.077 eV for deposition at >45 degrees incidence. For microporous ice, the intensity of the infrared bands due to methane molecules on dangling OH bonds on pore surfaces increases linearly with methane uptake, up to saturation adsorption. This shows that the multilayer condensation of methane does not occur inside the micropores. Rather, filling of the core volume results from coating the pore walls with the first layer of methane, indicating pore widths below a few molecular diameters. For ice deposited at 77 degrees incidence, the increase in intensity of the dangling bond absorptions modified by methane adsorption departs from linearity at large uptakes.

Low density solid ozone.

We report a very low density ( approximately 0.5 g/cm(3)) structure of solid ozone. It is produced by irradiation of solid oxygen with 100 keV protons at 20 K followed by heating to sublime unconverted oxygen. Upon heating to 47 K the porous ozone compacts to a density of approximately 1.6 g/cm(3) and crystallizes. We use a detailed analysis of the main infrared absorption band of the porous ozone to interpret previous research, where solid oxygen was irradiated by UV light and keV electrons.

Compaction of microporous amorphous solid water by ion irradiation.

We have studied the compaction of vapor-deposited amorphous solid water by energetic ions at 40 K. The porosity was characterized by ultraviolet-visible spectroscopy, infrared spectroscopy, and methane adsorption/desorption. These three techniques provide different and complementary views of the structural changes in ice resulting from irradiation. We find that the decrease in internal surface area of the pores, signaled by infrared absorption by dangling bonds, precedes the decrease in the pore volume during irradiation. Our results imply that impacts from cosmic rays can cause compaction in the icy mantles of the interstellar grains, which can explain the absence of dangling bond features in the infrared spectrum of molecular clouds.

The Saccharomyces cerevisiae YFR041C/ERJ5 gene encoding a type I membrane protein with a J domain is required to preserve the folding capacity of the endoplasmic reticulum.

YFR041C/ERJ5 was identified in Saccharomyces cerevisiae as a gene regulated by the unfolded protein response pathway (UPR). The open reading frame of the gene has a J domain characteristic of the DnaJ chaperone family of proteins that regulate the activity of Hsp70 chaperones. We determined the expression and topology of Erj5p, a type I membrane protein with a J domain in the lumen of the endoplasmic reticulum (ER) that colocalizes with Kar2p, the major Hsp70 in the yeast ER. We identified synthetic interactions of Deltaerj5 with mutations in genes involved in protein folding in the ER (kar2-159, Deltascj1Deltajem1) and in the induction of the unfolded protein response (Deltaire1). Loss of Erj5p in yeast cells with impaired ER protein folding capacity increased sensitivity to agents that cause ER stress. We identified the ERJ5 mRNA and confirmed that agents that promote accumulation of misfolded proteins in the ER regulate its abundance. We found that loss of the non-essential ERJ5 gene leads to a constitutively induced UPR, indicating that ERJ5 is required for maintenance of an optimal folding environment in the yeast ER.

Experimental evidence of threshold effects in the energy loss of protons in carbon and aluminum due to inner shell ionization

We explore the contributions of inner shell ionization to the energy loss of 7 to 270 keV protons in C and Al foils under experimental conditions such that the product of the observation angle and the projectile energy is kept constant. By normalizing these energy loss measurements to the energy loss in the forward direction we observe a pronounced rising behavior with increasing energy. This effect appears in the same range of energies where the respective K- and L-shell ionization cross sections of these elements show a similar threshold behavior. Based also on various theoretical considerations we interpret these results as clear evidence of the inner shell ionization contribution to the energy loss.

Molecular mechanism of drug photosensitization. Part 3. Photohemolysis sensitized by diflunisal.

The lysis of red blood cells photosensitized by diflunisal (DFN) was investigated. Photohemolysis is inhibited by butylated hydroxyanisole and reduced glutathione, but is unaffected by mannitol and enhanced by sodium azide; the presence of oxygen markedly reduces the lysis which is accelerated in anaerobic conditions. These results contrast with those expected for a photodynamic mechanism. High lytic activity is observed for pre-irradiated solutions, mainly under anaerobic conditions. Direct irradiation of DFN in buffer solution at pH 7.4 leads to the formation, under anaerobic conditions, of compound 2'-(2''',4'''-difluoro-3''-carboxy-[1'',1'''-biphenyl]-4''-oxy)-4'- fluoro-4-hydroxy-[1,1'-biphenyl]-3-carboxylic acid (PhP), whereas under aerobic conditions formation of PhP is accompanied by unidentified photo-oxidation products; only compound PhP displays strong lytic activity. The overall results for DFN-photosensitized hemolysis suggest a mechanism involving a concerted action of free radicals, superoxide anion, singlet oxygen and sensitizer photoproducts.

Molecular mechanism of drug photosensitization--II. Photohemolysis sensitized by ketoprofen.

Red blood cell lysis photosensitized by ketoprofen (KPF) was investigated. The photohemolysis was inhibited by butylated hydroxyanisole, reduced glutathione, superoxide dismutase and mannitol, and was unaffected by sodium azide; the presence of oxygen markedly enhanced the lysis. Photohemolysis was also observed under anaerobic conditions. Ketoprofen, irradiated in aqueous buffer solution at pH 7.4, underwent a decarboxylation process via intermediate radicals, leading to the compounds (3-benzoylphenyl)ethane, (3-benzoylphenyl)ethyl hydroperoxide, (3-benzoylphenyl)ethanol and (3-benzoylphenyl)ethanone under aerobic conditions and only to the compound (3-benzoylphenyl)ethane under anaerobic conditions. The four photoproducts showed lytic activity, particularly high for the alcohol and hydroperoxide. The overall results suggest for KPF-photosensitized hemolysis a molecular mechanism involving free radicals, superoxide anion and sensitizer photodegradation products.

Molecular mechanism of naproxen photosensitization in red blood cells.

Red blood cell lysis photosensitized by naproxen was investigated. The photohemolysis rate was enhanced by deuterium oxide and inhibited by butylated hydroxyanisole, reduced glutathione, sodium azide and superoxide dismutase. Photohemolysis was also observed under anaerobic conditions. In the absence of red cells the irradiation of deaerated solutions underwent a decarboxylation process via intermediate radicals, while under aerobic conditions photo-oxidation leading to the photoproduct 6-methoxy-2-acetonaphthone occurred. A molecular mechanism involving free radicals and singlet oxygen as important intermediates and consistent with the overall results is proposed.