探討胞嘧啶與甲基胞嘧啶在金(111)電極上的吸附結構

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题名:	探討胞嘧啶與甲基胞嘧啶在金(111)電極上的吸附結構
作者:	許飴軒;Hsu, Yi-Hsuan
贡献者:	化學學系
关键词:	胞嘧啶;甲基胞嘧啶;掃描式穿隧電子顯微鏡;分子自組裝;界面電化學;DNA甲基化;cytosine;methylcytosine;Scanning Tunneling Microscope，STM;Molecular self-assembly;interfacial electrochemistry;DNA methylation
日期:	2021-08-11
上传时间:	2021-12-07 11:21:58 (UTC+8)
出版者:	國立中央大學
摘要:	本論文利用掃描式穿隧電子顯微鏡（STM）和循環伏安法（CV）來探討胞嘧啶（Cytosine, C）與甲基胞嘧啶（Methylcytosine, mC）在金（111）電極上的結構，雖然已有一些相關的研究報導，但對於分子間作用力、金載體結構、分子濃度以及pH值等變因還沒有系統性地完整探討。超高真空環境中，胞嘧啶分子會透過分子間氫鍵在金（111）載體上形成鋸齒狀的鏈條和圓環，而在電化學環境中，胞嘧啶分子存在多種互變異構物及酸鹼平衡，導致帶電界面上其豐富的結構變化，STM結果顯示胞嘧啶分子在負電位為物理吸附，在正電位會以酮-亞胺異構物的型態鍵結在金表面，形成一直立式化學性吸附分子層，且較正的電位會與陰離子共吸附在金表面。更特別的是，胞嘧啶分子在金表面的覆蓋度會隨著電位越正而越高，甚至形成雙層胞嘧啶膜。在分子結構上，5號位的甲基官能基導致甲基胞嘧啶與胞嘧啶和金（111）的作用力大不相同，甲基胞嘧啶甚至能從金（111）載體的平台拔起金原子，之後再與金原子形成有序吸附結構。當溶液含等比例胞嘧啶與甲基胞嘧啶時，CV結果展現甲基胞嘧啶的特徵，但STM的結果顯示，在負電位時兩分子共吸附在金（111）表面，而正電位則以甲基胞嘧啶為主，甲基展現出一推電子的效應，其強度足以讓甲基胞嘧啶和金電極有較強的作用力。 DNA序列中胞嘧啶甲基化程度牽涉到腫瘤與不孕症的發生，而DNA鹼基在金電極上的吸附是生物表面科學研究的模型系統，也是生物電化學、生物傳感器和納米材料發展的一個重要課題，透過本次實驗，更進一步瞭解胞嘧啶與甲基胞嘧啶在金電極上的吸附行為。 ;This study focus on using in situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) to investigate the structure of cytosine（C）and methylcytosine（mC）on Au（111）electrodes. Although similar studies have been conducted by using in situ STM and vibrational spectroscopy, many critical issues such as intermolecular interaction, substrate structure, and concentration of C are yet to be explored. Using gold as the substrate is a way to mitigate the adsorbate-and-substrate interaction and to highlight intermolecular interaction between adsorbed C molecules. Indeed, intermolecular hydrogen bond guides the organization of C molecules into zigzagged chains and circular rings on Au(111) in vacuum. In comparison, controlling the potential of Au electrode can influence the adsorption strength and the binding mode of C. In addition, the tautomerization and acid-base equilibrium of C molecule in the aqueous media endow a rich structural variation at the electrified interface. From the perspective of molecular structure, mC and C differ by one methyl group at the 5-position of a pyrimidine ring. The methyl group exerted a notable electronic effect, rendering a stronger interaction between MC and gold. This effect could be strong enough to cause mining of the Au(111) surface, where gold atoms were liberated from the terrace, and form an ordered structure with mC molecule. The adsorption strength of C and mC on Au(111) was conducted in a solution containing equal amount of mC and C. The obtained results show that they were co-adsorbed on the gold surface at negative potential, but mC adsorption prevailed at positive potential. The degree of cytosine methylation in the DNA sequence is related to tumors and infertility. The adsorption of DNA base on gold electrode is considered as a model system to the study of biological surface science, which represents an important aspect in the development of bioelectrochemistry, biosensors, and nanomaterials. This study can make us further understand the adsorption behavior of C and mC on the gold electrode.
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