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The thermal dissociation of fluoroethane has been studied using shock tube (ST)/time-of-flight mass spectrometry (TOF-MS) at 500 and 1200 Torr over the temperature range 1200–1550 K. The ST/TOF-MS experiments confirm that elimination of HF is the only reaction channel and rate coefficients for this reaction were extracted from concentration/time profiles derived from the mass spectra. Results from a novel diaphragmless shock tube coupled to the TOF-MS are also presented and demonstrate the unique ability of this apparatus to generate sufficiently reproducible shock waves that signal averaging can be performed over multiple experiments; something that is not possible with a conventional shock tube. The dissociation is also studied with ab initio transition state theory based master equation simulations. A modest increase in the calculated barrier height (i.e., by 1 kcal mol−1) yields predicted high pressure rate coefficients that are in good agreement with the existing literature data. The present pressure dependent observations are accurately reproduced for a downwards energy transfer for neon at 1200 to 1500 K of ∼270 cm−1, which is somewhat smaller than that found in previous studies on fluorinated ethanes with the same bath gases. [ABSTRACT FROM AUTHOR]

This paper reports measurements of the thermal dissociation of 1,1-difluoroethane in the shock tube. The experiments employ laser-schlieren measurements of rate for the dominant HF elimination using 10% 1,1-difluoroethane in Kr over 1500–2000 K and 43 < P < 424 torr. The vinyl fluoride product of this process then dissociates affecting the late observations. We thus include a laser schlieren study (1717–2332 K, 75 < P < 482 torr in 10 and 4% vinyl fluoride in Kr) of this dissociation. This latter work also includes a set of experiments using shock-tube time-of-flight mass spectrometry (4% vinyl fluoride in neon, 1500–1980 K, 500 < P < 1300 torr). These time-of-flight experiments confirm the theoretical expectation that the only reaction in vinyl fluoride is HF elimination. The dissociation experiments are augmented by laser schlieren measurements of vibrational relaxation (1–20% C2H3F in Kr, 415–1975 K, 5 < P < 50 torr, and 2 and 5% C2H4F2 in Kr, 700–1350 K, 6 < P < 22 torr). These experiments exhibit very rapid relaxation, and incubation delays should be negligible in dissociation. An RRKM model of dissociation in 1,1-difluoroethane based on a G3B3 calculation of barrier and other properties fits the experiments but requires a very large 〈ΔE〉down of 1600 cm−1, similar to that found in a previous examination of 1,1,1-trifluoroethane. Dissociation of vinyl fluoride is complicated by the presence of two parallel HF eliminations, both three-center and four-center. Structure calculations find nearly equal barriers for these, and TST calculations show almost identical k∞. An RRKM fit to the observed falloff again requires an unusually large 〈ΔE〉down and the experiments actually support a slightly reduced barrier. These large energy-transfer parameters now seem routine in these large fluorinated species. It is perhaps a surprising result for which there is as yet no explanation. [ABSTRACT FROM AUTHOR]

This article reports the results of investigations into the process of cell death induced in the Chinese hamster ovary cell K1 subclone (CHO K1) by okadaic acid (OA), a hydrophobic polyether produced by marine dinoflagellates. The IC50 was about 13 nM OA after 24 h of treatment, as determined using neutral red. With the MTT assay, the IC50 was 25 nM, although in this case 25% of the initial staining was still observed at 100 nM. Hoechst staining showed that mitotic figures accumulated at 12 nM OA after a 24- or 48-h treatment. In experiments limited to a 3-day treatment without changing the medium, CHO K1 cells were engaged in the death process at 50 nM OA after about 20 h and at 10 nM OA after 48 h. In many cells nuclear fragmentation that resulted in the apparent appearance of vesicles correlated with increasing cellular volume. But additional cell fragmentation was not observed with any treatment, and the chromatin material seemed to progressively disappear inside the cells. DNA fragmentation was analyzed by electrophoresis and with the TUNEL technique. With both techniques, the DNA was fragmented by 48 h in both 25 and 50 nM OA. Electrophoresis showed that both adherent and nonadherent cells were affected. Annexin-positive/ propidium iodide (PI)–negative cells were rarely observed after OA treatment. Some were seen under the scanning cytometer after 20 h at 50 nM OA or after 48 h at 10 nM OA, but they were never detected by flow cytometry. Most of the time scanning cytometry showed either unstained cells or PI-positive (annexin-positive or -negative) cells (48 h, 50 nM, or 72 h, 10 nM). Flow cytometry cytograms showed two cell subpopulations: one composed of a majority of smaller cells, the other of larger cells. The larger cells markedly decreased with time and OA treatment (50 and 100 nM). Stained-cell counting showed that all cells that stained were both annexin- and PI positive and that most PI-positive cells were smaller. Ki67 antigen labeling showed the proliferative activity of CHO K1 cultures but also demonstrated the loss of this activity in smaller cells treated with 50 nM OA for 48 h. We concluded that in our culture conditions the main OA target within CHO K1 cultures was dividing cells. Our results suggest that cells with disturbed metaphase–anaphase enter apoptosis, leading to necrotic daughter cells. © 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 383–394, 2003 [ABSTRACT FROM AUTHOR]