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| 題名: | 胞嘧啶及鳥嘌呤於金（111）電極上吸附-陰陽離子pH值及電位控制的影響 |
| 作者: | 吳哲愷;Wu, Che-Kai |
| 貢獻者: | 化學學系 |
| 關鍵詞: | 胞嘧啶;鳥嘌呤;金（111）;界面電化學;電位控制 |
| 日期: | 2021-08-11 |
| 上傳時間: | 2021-12-07 11:21:34 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | 文獻指出鳥嘌呤（Guanine, G）具有治療腫瘤的能力，經過修飾的四聚體層狀結構，會影響細胞端粒?的複製，後續研究也指出添加高濃度的鉀離子可以使G四聚體結構更加穩定，近期對G分子的結構研究大多在超高真空系統中進行。
本研究利用電位控制掃描式穿隧電子顯微鏡（STM）觀察G分子在不同陰陽離子、pH值及電位控制下，於金電極上的吸附結構。本研究皆以Ag/AgCl參考電極為電位標示。在酸性溶液中，陰離子的共吸附會造成不同G的吸附結構。在負電位時，G分子以平躺式物理吸附在金電極上，但隨著電位越正，轉變成直立型的化學吸附。STM結果顯示在物理吸附時，G分子以平躺式的構型吸附並形成整齊的二維結構，而化學吸附時，G分子直立於金電極上形成線性結構，更正的電位會造成吸附量增加，導致線性結構的扭曲，類似指紋形狀。G分子在中性溶液的溶解度下降，只有在負電位剛添加時能夠看到結構外，在較正電位分子的吸附量增加，從單層變為多層，而表面會變得粗糙。在鹼性溶液中G的溶解度明顯提升，在負電位是無序的分子吸附，但在正電位會出現指紋狀的結構。陽離子也會和G分子共吸附，從硫酸與過氯酸中吸附時，鉀離子和G分子形成一整齊的線型結構，從分子解析的STM圖像，可以看到分子與鉀離子以1：1的比例，可能以陰陽離子對的型態共吸附在電極表面。
後續也研究胞嘧啶（Cytosine, C）分子在金上的吸附，在高真空中C分子形成無序的結構，但在有電位控制下，不同電解液中發現數種整齊的C結構。在過氯酸的中，的CV圖在C分子吸附前後圖形變化不大，僅電流有所下降， pH值得測試發現在酸性條件中，C吸附很可能為兩個分子共用一個氫離子的特殊結構。在STM觀察時，C分子會迅速在金電極上吸附形成一整齊的分子結構-（3√3 × √13），此一結構穩定存在於(0~0.4 V)的電位區間，在正電位時，吸附C分子轉換成（3√3 × √19）結構。
在了解C及G分子各別的吸附結構後，將兩者同時配置於同一溶液中觀察，藉此想探討兩分子是否會共同吸附在金電極上，也同時研究電位控制及陰離子影響。在過氯酸條件下，以1：1的比例混合均勻後添加，CV的環境下，結果與單一的G分子吸附相似，在STM的實驗中，負電位的結構和G分子無異，但在正電位載體時，分子吸附量增加而形成二層的結構，位於上層分子形成一鏈狀結構，它的長度為5-20 nm寬度約為0.7 nm，此一分子寡聚體可能是兩種分子以氫鍵結合而成，C和G在STM圖像中明顯有亮度的差異，鏈狀特徵的量和電位有關，在0.1V時形成最多分子鏈條。
;Some literature pointed out that guanine (G) can be used as a drug to treat tumors. It is thought that cage-like tetramer structure of G can inhibit the replication of cell telomerase. The G tetramer has been prepared in vacuum after annealing. This is followed by more research to show that co-adsorption of potassium ions can facilitate the formation of G tetramer, which show improved structural stability. But again these studies were performed in ultra-high vacuum systems, which differ markedly from physiological condition.
In this study, a potential-controlled scanning tunneling electron microscope (STM) was used to study the adsorption structure of G molecules on the gold electrode as a function of anion and cation, pH of the media, and electrochemical potentials. In acidic solutions, the co-adsorption of anions resulted in different adsorption structures. G molecules were physically adsorbed on the gold electrode at negative potentials, but transformed to chemisorption as the potential was made more positive. The orientation of G admolecule changed from horizontal to upright and the surface coverage increased with more positive potential. This was the first stage of G adsorption, leading to ordered G adlayers on Au(111) electrode, as revealed by molecular resolution STM imaging. The second stage of G adsorption yielded crooked linear structure, having morphology similar to the shape of a fingerprint. In neutral phosphoric solutions only one ordered structure was seen at negative potential and deposition of G to give multilayer. The solubility of G in alkaline solution is significantly higher, but protracted STM imaging showed that G adlayer was disordered at negative potential, and transformed into a fingerprint-like structure at positive potential. The effect of potassium ions on G admolecules on Au(111) was examined with samples prepared by immersing in sulfuric and perchloric acids containing equal concentration G and K+. In sir STM imaging showed that G and potassium ions were co-adsorbed in an ordered structure with a 1:1 ratio. The degree of ordering deteriorated with solutions with different G/K+ ratios.
The adsorption of cytosine (C) molecule on Au(111) electrode was also examined. In contrast to disordered C structure formed in high vacuum, several C structures were found, depending on the chemical identity of the electrolyte. Aided by the CV results obtained in perchloric acid, partial deprotonation occurred at some positive potential. STM imaging revealed a (3√3 × √13)–C structure in a wide potential range, but transformed into (3√3 × √19) at more positive potential.
Finally, the co-adsorption of C and G molecules on Au(111) was investigated. The obtained STM results are used to understand the hydrogen bond formation within the adlayer potential control and anion co-adsorption. The CV recorded in perchloric acid containing1:1 C/G had the same characteristics as that of pure G. STM imaging showed that ordered structures the same as that of G molecule was formed at negative potential, but a bi-layer film was formed with the upper layer forming molecular chains 5-20 nm long and 0.7 nm wide. This structure is ascribed to mixed C and G adlayer linked by intermolecular hydrogen bonds. C and G admolecules could be differentiated by their STM intensities; C was lower than G by 0.01 nm. The mixed adlayer was most populated at 0.1V. |
| 顯示於類別: | [化學研究所] 博碩士論文
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