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运用分子力学方法研究了 3个含溴代胞嘧啶的分子内三螺旋及相应的未溴代分子内三螺旋DNA .理论结果表明 :当分子内三螺旋Hoogsteen嘧啶链的胞嘧啶被溴代胞嘧啶取代后其稳定性最强 ;而当分子内三螺旋 2条嘧啶链的胞嘧啶同时被溴代后 ,其稳定性最差 .从分子力学计算得到 ,4种分子内三螺旋的碱基以C3′ endo糖环构象为主 .在三螺旋YTCY( 2条嘧啶链中的胞嘧啶均被溴代胞嘧啶取代 )中 ,也含有一定数量的C2′ endo糖环构象 .因此 ,分子内三螺旋YTCY是A DNA和B DNA的综合体 ,而其他 3种三螺旋则是典型的A DNA .
Three intramolecular triple helixes containing bromocytosine and the corresponding uncooled intramolecular triple helical DNA were studied by molecular mechanics. The theoretical results show that when cytosine in the intramolecular triple helix Hoogsteen pyrimidine chain is replaced by bromocytosine The stability is the strongest when it is substituted, while the cytosine with two pyrimidine chains in the intramolecular triple helix is the most stable when it is brominated.From the molecular mechanics calculations, the three intramolecular triple helix bases are C3 ’Endo sugar ring conformation in the three helix YTCY (two pyrimidine chain cytosine are replaced by bromocytosine), also contains a certain number of C2’ endo sugar ring conformation.Therefore, the intramolecular triple helix YTCY Is a combination of A DNA and B DNA, while the other three types of triple helix are typical A DNAs.