of Green Tea Extracts on Gene Expression in HepG2 and Cal-27 Cells

Abstract: Green tea extract is known to contain compounds that are able to produce antioxidant effects in many types of living cells. Treatment of cultured human hepatoma (HepG2) cells with green tea extract resulted in dramatically increased expression of at least 15 genes that are present on a commercial human drug metabolism gene array. RT-PCR was used to confirm the microarray results, and analysis of the 5'-flanking region of each of these genes revealed potential electrophile/antioxidant response elements. Members of the acetyl transferase, epoxide hydrolase, sulfotransferase and glutathione transferase gene families were strongly induced. In addition, the human tongue carcinoma cell line Cal-27 did not respond to green tea extract in the same way, as none of the induced genes in the HepG2 cells were induced in the Cal-27 cells. The lack of induction of detoxification enzymes in the Cal-27 cell line may help to explain the previously observed increased cytotoxicity of green tea catechins on this cell line

The unusual and the unexpected in an old reaction. The photochlorination of alkanes with molecular chlorine in solution

Peer reviewed: YesNRC publication: Ye

Selectivity in the photochlorination of 2,3-dimethylbutane with molecular chlorine in noncomplexing solvents

The factors affecting changes in the measured selectivity for the photochlorination of 2,3-dimethylbutane (DMB) in alkane solvents and in CCl 4 have been identified. At low chlorine concentrations in CCl 4 as solvent, the selectivities, S m = [2-ClDMB]/[1-ClDMB], are dramatically enhanced because of CCl 4 and Cl 3C \u2022 participation in the overall chain process. In the absence of CCl 4, the selectivities may also increase at very low chlorine concentrations because residual O 2 and peroxyl radicals participate in the overall chain process. In the absence of either of the above phenomena, S m was calculated to be 0.64, a value that compares well with a value of 0.62, which we have measured in the gas phase.Peer reviewed: YesNRC publication: Ye

Influence of aromatic solvents on the selectivity for photochlorination of 2,3-dimethylbutane with molecular chlorine

The effect of benzene and a wide variety of substituted benzenes upon the photochlorination of 2,3-dimethylbutane (DMB) has been investigated under standard conditions (0.15 M DMB, 2.0 M arene in CCl 4 at room temperature). The standard selectivities, S std m, are given by the product ratios [2-ClDMB]/[1-ClDMB] under these conditions. For arenes which are less electron rich than benzene, log S std m values decrease monotonically with the increase in the arenes' ionization potentials and with the decrease in the arenes' \u3c0-basicities. For arenes which are more electron rich than benzene, S std m values are greater than for benzene only for the mono- and dialkylated benzenes and 1,3,5-tri-tert-butylbenzene. Chlorination in the presence of trimethylbenzenes, more highly methylated benzenes, and anisole afforded less selective mixtures of DMB chlorides than benzene. The reduced selectivities of the most electron-rich arenes is attributed to the low reactivities of their Cl \u2022/arene \u3c0-complexes and the low yields of DMB chlorides, much of which are formed by hydrogen abstraction by the free Cl \u2022 atom. Ipso substitution occurs with bromo- and iodobenzene and these two arenes are more selective than would be predicted. It has also been demonstrated by laser flash photolysis that Cl \u2022/arene and Br \u2022/arene \u3c0-complexes will appear to react with O 2 only if the arene contains substituents which can donate hydrogen to the halogen atom and/or complex, viz., CH 3, C(CH 3) 3 and OCH 3 substituents for chlorine but only CH 3 and OCH 3 for bromine. This apparent reaction is due to interference by O 2 in the process which otherwise would very rapidly "regenerate" the halogen atom/arene complex following such hydrogen abstraction. Published 1989 by the American Chemical Society.Peer reviewed: YesNRC publication: Ye

Kinetic analysis of alkane polychlorination with molecular chlorine. Chlorine atom/monochloride geminate pairs and the effect of reactive "cage walls" on the competition between monochloride rotation and chlorine atom escape

The free-radical chlorination of alkanes produces polychlorides even at low conversions. These are formed by reaction of chlorine atom/monochloride (or dichloride) geminate pairs. This process has been studied in detail in various solvent systems, and a kinetic scheme has been proposed. Deviations from this scheme have been rationalized as being due to competition between monochloride rotation and reaction of the chlorine atom with reactive molecules in the "cage walls" surrounding the chlorine atom/chloride geminate pair. Analysis of the dichloride products supports the suggestion that monochloride rotation is not completely "free" within the lifetime of the geminate pair.Peer reviewed: YesNRC publication: Ye

Ultraviolet/visible spectra of halogen molecule/arene and halogen atom/arene \u3c0-molecular complexes

Ultraviolet/visible spectra have been recorded for chlorine, bromine, and iodine atom \u3c0-molecular complexes with a number of aromatic compounds. The visible spectra of the I \u2022/arene complexes show charge-transfer (CT) bands whose transition energy correlates linearly with the vertical ionization potential of the corresponding arene. Comparison of the spectra of these complexes with the spectra of the corresponding Cl 2/arene, Br 2/arene, and I 2/arene complexes leads to the conclusion that the I \u2022/arene complexes are classical hexahapto \u3c0-molecular complexes. The CT transition energies of the Cl \u2022/arene and the Br \u2022/arene complexes correlate well with one another, yet the CT transition energies of these complexes are seemingly independent of the vertical ionization potential of the arene.Peer reviewed: YesNRC publication: Ye