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| 含有巰基的嘧啶環(huán)系列化合物具有抗癌活性和免疫增強(qiáng)作用,硫原子較氧原子的外層電子的不同,硫原子的3p電子受原子核的束縛比氧原子的2p電子小,離域后與大環(huán)上的電子共軛,使共軛效應(yīng)增強(qiáng);硫原子上的電子可通過3p→3d 躍遷,硫原子3p軌道的電子比氧原子中2p軌道的電子的能級高,而硫原子的3d軌道能級比羰基C=O的2π* 軌道提高不多,故硫羰基C=S的3p→3d 躍遷所需能量小,有利于3p電子的激發(fā),含有硫羰基的核苷類化合物其4-位羰基氧被硫取代后吸光度變大,最大吸收峰紅移,對光極其敏感[3]。因此,對正常細(xì)胞無害的低劑量近紫外光可以激發(fā)硫羰基中硫原子的電子躍遷,破壞其化合物的結(jié)構(gòu),很容易地將含有4-硫胸苷的DNA的增生細(xì)胞殺死。 |
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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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