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| 含有巯基的嘧啶环系列化合物具有抗癌活性和免疫增强作用，硫原子较氧原子的外层电子的不同，硫原子的3p电子受原子核的束缚比氧原子的2p电子小，离域后与大环上的电子共轭，使共轭效应增强；硫原子上的电子可通过3p→3d 跃迁，硫原子3p轨道的电子比氧原子中2p轨道的电子的能级高，而硫原子的3d轨道能级比羰基C=O的2π* 轨道提高不多，故硫羰基C=S的3p→3d 跃迁所需能量小，有利于3p电子的激发，含有硫羰基的核苷类化合物其4-位羰基氧被硫取代后吸光度变大，最大吸收峰红移，对光极其敏感[3]。因此，对正常细胞无害的低剂量近紫外光可以激发硫羰基中硫原子的电子跃迁，破坏其化合物的结构，很容易地将含有4-硫胸苷的DNA的增生细胞杀死。 |
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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
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
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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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