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91.
Perfluorocarboxylic acids and their anions (PFCAs), such as perfluorooctanate (C7F15C(O)O?), have been generally recognized to be global pollutants and are believed to persist in the environment. Kinetic data for reactions of sulfate anion radicals (SO4?) with PFCAs are needed to evaluate the residence times of PFCAs in the environment, but no kinetic data have been reported, except for the rate constant for the reaction of SO4? with trifluoroacetate (CF3C(O)O?) (k1). In this study, using the fact that PFCAs react with SO4? to form shorter chain PFCAs, we determined rates relative to k1 of the reactions of photolytically generated SO4? with two short‐chain PFCAs, pentafluoropropionate (C2F5C(O)O?; k2) and heptafluorobutyrate (C3F7C(O)O?; k3), along with conversion ratios for conversion of C2F5C(O)O? into CF3C(O)O? (α) and conversion of C3F7C(O)O? into C2F5C(O)O? (β) and CF3C(O)O? (γ) at 298 K. Values of k1, k2, or k3 might change over the course of reaction with increasing ionic strength. Nevertheless, if the values of k1/k2, k2/k3, α, β, and γ remain almost constant during the reaction, a simple equation involving relative rates, such as k1/k2, can be used to relate the concentrations of C3F7C(O)O?, C2F5C(O)O?, and CF3C(O)O?. We compared the relative rates, such as k1/k2, and the conversion ratios determined from various experimental runs with different initial conditions to check whether relative rates and conversion ratios remained almost constant during each experimental run. The values of k1/k2, k2/k3, α, β, and γ seemed to remain almost constant, which facilitated determination of k2/k1 = 0.89 ± 0.07, k3/k1 = 0.84 ± 0.08, α = 0.88 ± 0.05, β = 0.75 ± 0.05, and γ = 0.17 ± 0.02. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 276–288, 2007 相似文献
92.
Thermoelectric powers of Fe, Ni and Co dissolved in liquid Sn are measured and discussed in relation to resistivity and susceptibility by reference to the concept of virtual bound state. 相似文献
93.
Sound attenuattion constants are calculated for the one-dimensional ferro- and antiferromagnetic systems at finite temperatures. Their frequency dependences, in both cases, turn out to be , where ωc is a “cut-off” frequency related to the three-dimensional anisotropic interactions. 相似文献
94.
95.
POSSIBLE ROLE OF METALLOTHIONEIN IN THE CELLULAR DEFENSE MECHANISM AGAINST UVB IRRADIATION IN NEONATAL HUMAN SKIN FIBROBLASTS 总被引:1,自引:0,他引:1
Shizuko Kobayashi Yumiko Hirota Junko Sayato-Suzuki Makoto Takehana Hisao Nishimura Noriko Nishimura Chiharu Tohyama 《Photochemistry and photobiology》1994,59(6):650-656
Abstract: The role of metallothionein (MT) in protecting skin cells against UVB irradiation was investigated. Fibroblast strains from normal adult (HS-K) and neonatal (NB1RGB) human skins as well as keratinocyte strains from human skin (SV40-HSK) and newborn Balb/c mouse skin (Pam 212) were exposed to UVB irradiation.
The sensitivity of HS-K and NB1RGB cells to UVB irradiation was similar; those of SV40-HSK and Pam 212 cells were two- and six-fold as sensitive to UVB irradiation as HS-K cells, respectively. The HS-K cells contained the greatest cellular reduced form of glutathione (GSH) levels compared to the three other skin cells: the levels were 13-, 7- and 6-fold of those in NB1RGB, SV40-HSK and Pam 212 cells, respectively. These results indicated that the sensitivity of skin cells to UVB irradiation was not always associated with their endogenous GSH levels. In particular, despite the fact that NB1RGB cells contained a relatively small amount of GSH, they were less sensitive to UVB irradiation.
NB1RGB cells contained 4–30 times more MT than those in other skin cells examined. The sulfhydryl residues of MT molecules in the NB1RGB cells were estimated to be mostly unoccupied by metals, suggesting they act in a similar way to those of GSH. Moreover, NB1RGB cells in which the MT content was elevated by dexamethasone (1 μ M ) or Zn2+ (7 μg/mL) treatment were more resistant to UVB irradiation than nontreated ones.
These results suggest that, at least in neonatal human skin fibroblasts, MT may play a role in protection against UVB irradiation. 相似文献
The sensitivity of HS-K and NB1RGB cells to UVB irradiation was similar; those of SV40-HSK and Pam 212 cells were two- and six-fold as sensitive to UVB irradiation as HS-K cells, respectively. The HS-K cells contained the greatest cellular reduced form of glutathione (GSH) levels compared to the three other skin cells: the levels were 13-, 7- and 6-fold of those in NB1RGB, SV40-HSK and Pam 212 cells, respectively. These results indicated that the sensitivity of skin cells to UVB irradiation was not always associated with their endogenous GSH levels. In particular, despite the fact that NB1RGB cells contained a relatively small amount of GSH, they were less sensitive to UVB irradiation.
NB1RGB cells contained 4–30 times more MT than those in other skin cells examined. The sulfhydryl residues of MT molecules in the NB1RGB cells were estimated to be mostly unoccupied by metals, suggesting they act in a similar way to those of GSH. Moreover, NB1RGB cells in which the MT content was elevated by dexamethasone (1 μ M ) or Zn
These results suggest that, at least in neonatal human skin fibroblasts, MT may play a role in protection against UVB irradiation. 相似文献
96.
97.
98.
The phase diagram and the heat of transition of AgI-AgBr system have been determined by using the differential scanning calorimetry (DSC) with the help of X-ray diffraction patterns. It has been verified that the miscibility gap between β-AgI-type solid solution and AgBr-type one depends on the thermal history of the sample. From the thermodynamic point of view, it is likely that the variation of transition temperature with composition suggests the change of correlation among silver ions in superionic conducting phase. 相似文献
99.
Hisao Watanabe 《Letters in Mathematical Physics》1991,23(1):1-9
In this Letter, we show that the local time of self-intersections ofd-dimensional Brownian motions is a generalized Brownian functional in the sense of Hida. 相似文献
100.
The novel unnatural ring system, 1-phosphacephalosporin, was synthesized for the first time from 4-acetoxy-2-azetidinone. 相似文献