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Pill-Soon Song William W. Mantulin Dyna Mcinturff Ira C. Felkner Marian L. Harter 《Photochemistry and photobiology》1975,21(5):317-324
Abstract— Although psoralen and many substituted psoralens are potent skin-photosensitizing agents, hydroxypsoralens are not. A satisfactory molecular interpretation of this structural specificity has been given in terms of dissociation of the hydroxyl group of 5- and 8-hydroxypsoralens in their excited states. The dissociation process in the S1 state effectively competes with S1→T1 intersystem crossing, thus reducing the photoreactive T1 population. The T1 states of the anions are more delocalized than those of neutral psoralens so that they are less reactive toward photocycloaddition with pyrimidine bases of DNA. The lack of significant phosphorescence of hydroxypsoralens in ionizing solvent or in the presence of base at low temperatures (14–77 K.) indicates ineffective S1→T1 and/or effective T1→S0 intersystem crossing. These factors make hydroxypsoralens unreactive, electronically and kinetically, as skin photosensitizers, which are known to react with DNA. In correlation with the hydroxypsoralens' spectroscopic characterization, they are also found to be ineffective or less effective photosensitizers in Bacillus subtilis. 相似文献
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Cellular response to near-infrared femtosecond laser pulses in two-photon microscopes 总被引:2,自引:0,他引:2
The influence of femtosecond near-infrared (NIR) microirradiation on cell vitality and cellular reproduction has been studied. Chinese hamster ovary cells exposed to a highly focused 150-fs scanning beam at 730, 760, and 800 nm (80 MHz, 80-mus pixel dwell time) of =1 mW remained unaffected by the femtosecond microbeam. However, increased mean power led to impaired cell division. At >/=6 -mW mean power, cells were unable to form clones. They died or became giant cells. Complete cell destruction, including cell fragmentation, occurred at mean powers >10 mW. Cell death was accompanied by intense luminescence in the mitochondrial region. When we consider the diffraction-limited spot size in the submicrometer region, intensities and photon flux densities of 0.8-kW pulses (10-mW mean power) are of the order of terawatts per square centimeter (10(12)W/cm (2)) and 10(32) photons cm(-2) s(-1) , respectively. Extremely high fields may induce destructive intracellular plasma formation. The power limitations should be considered during NIR femtosecond microscopy of vital cells and in the design of compact NIR femtosecond solid-state lasers for two-photon microscopes. 相似文献
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EXCITED STATES AND REACTIVITY OF CARCINOGENIC BENZPYRENE; A COMPARISON WITH SKIN-SENSITIZING COUMARINS* 总被引:1,自引:0,他引:1
Thomas A. Moore ‡ William W. Mantulin ‡ Pill-Soon Song 《Photochemistry and photobiology》1973,18(3):185-194
Abstract— Significant spectroscopic difference was found between the 3 (π, π*) state of coumarins and the 3 La state of benzpyrene. No analogy of the partially localized triplet state associated with the coumarin chromophore was revealed in the case of the potent carcinogen, benzo[a]pyrene. Instead, the 3 La state of benzo[a]pyrene is characterized by more derealization than that of the non–carcinogenic benzo[e]pyrene. Therefore, the predominant photoreaction between benzo[a]pyrene and DNA bases does not seem to involve cycloaddition in contrast to the coumarin-pyrimidine system. Reactivity indices have been calculated, and results are consistent with recent experimental findings. In addition, spectroscopic properties of benzo[a]pyrene and benzo[e]pyrene have been comparatively described in terms of relatively high-resolution spectra, polarization measurements, and molecular orbital calculations. 相似文献
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