細胞受到氧化破壞後，DNA (deoxyribonucleic acid) 鹼基中的鳥糞嘌呤 (guanine)會形成黃嘌呤 (xanthine)，黃嘌呤與正常鹼基配對之後會導致點突變。鹼基對的分子間氫鍵會影響整個核酸的結構和穩定，因此本實驗室利用Gaussian軟體對黃嘌呤二聚物 (XX) 、胸線嘧啶二聚物(TT) 和兩者的配對錯合物 (XT) 進行一系列的計算研究。
本研究利用密度泛涵理論(DFT)計算雙氫鍵錯合物中的一組氫鍵的拉長破壞，並使用天然鍵性軌域(NBO)，搭配 GaussView 軟體來分析分子穩定能及空間中的結構變化。
我們發現在其中一組氫鍵拉長後，錯合物的兩個單元會以另一組氫鍵為橋樑而旋轉。且隨著錯合物雙氫鍵兩旁未鍵結氫鍵官能基的不同，分子有可能旋轉或翻轉成之前算出來的同一鹼基對的其他最佳化結構。如TT6轉換成TT4，以及XX6與XX3的互相轉換。之後並確定了透過旋轉，形成含其他類型氫鍵之雙氫鍵錯合物的可能性。

The noncanonical nucleobases xanthine that is formed from the canonical base guanine by nitrogen loss when a cell is under oxidative stress is an important lesion that leading to point mutations. Hydrogen-bonded base pairs of nucleic acids substantially contribute to the structure and stability of nucleic acids. We do a series of calculating researches in xanthine dimers (XX)、thymine dimers (TT) and pairing complexs of xanthine and thymine (XT) with the help of Gaussian98.
Our research on the issue is using density functional theory (DFT) to draw apart one of the two hydrogen bonds of the complex containing double hydrogen bonds, then analyzes the variation of stabilization energy and structures with natural bond orbital (NBO) analysis and GaussView software.
We found that after drawing apart one of the two hydrogen bonds, the two units of the complex will rotate by the other hydrogen bond. Molecules may rotate or overturn to the other optimized structures of the same base pairs, such as TT6 change to TT4, and the interchange between XX6 and XX3. We also confirm that the complex may change to the other structure with different kind of hydrogen bond through rotating.

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