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红色桃子: 金币+50, 翻译EPI+1, ★★★很有帮助, 非常受用！ 2015-10-26 19:02:16
The mercapto group-contained Pyrimidine compounds possess anti-tumor activity and immunological enhancement function. Due to the difference of outer electron structure, the 3p electrons of sulfur atom are bonded with nucleus in less degree as the 2p electrons of oxygen atom are, therefore, after delocalization, the electrons on big ring are conjugatedly distributed, which enhances the conjugated effect. Electrons in sulfur atom may transit from 3p to 3d, the electronic energy level of sulfur atom 3p orbital is higher than that of oxygen atom 2p orbital, which the electronic energy level of sulfur atom 3d orbital is merely higher than that of 2π* orbital of carbanyl group C=O, therefore, the energy needed for the 3p→3d electron stransition of thiocarbonyl C=S is smaller, which is positive for 3p electron excitation. For the thiocarbonyl-added nucleosides, after the oxgen atom on 4- carbonyl is replaced by sulfur atom, its absorbance will be enlarged, the maximum absorption peak will be red shifted, making it extremely sensitive to light[3]. As a result, the low dosage of near ultraviolet, which creates no harm to normal cells, can
stimulate the electron transition of sulfur atom in thiocarbonyl group, thus destroying the compound structure, and easily killing the proliferating cells which contain 4 - sulfur thymidylic DNA. |
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