利用密度泛函理論探討碳鏈長度與不同陽離子對磺基甜菜鹼周圍水分子氫鍵網路的影響

兩性離子型分子聚合物材料(Zwitterionic)，由於它具備優良的水合能力並且能夠阻抗蛋白質的沾粘，使其成為抗汙領域不可或缺的一環。較為常見的兩性離子型材料包含磺基甜菜鹼(Sulfobetaine,SB)、羧基甜菜鹼(Carboxybetaine,CB)以及磷脂酰膽鹼(Phosphobetaines,PB)。而兩性離子型材料在不同碳鏈長度與不同陽離子的存在下都有可能對整個系統的親水性造成影響。本次研究目的為使用量子化學原理之計算針對磺基甜菜鹼分子(SB)於不同碳鏈長度(CSL=2~4)以及於不同碳鏈長度下加入不同陽離子對水合能力的影響。首先，我們將前面提到的系統分別撒上15顆隨機分布的水分子並且生成各自50種相異的構型，接著使用半經驗法、密度泛函PBEPBE與M06-2X逐步篩選出能量最低之結構。最後再透過分析其氫鍵網路與構型來探討上述因素對水和能力之影響。根據研究結果發現SB分子於不同碳鏈長度下，透過分析其氫鍵長度與氫鍵角度，我們可以發現其氫鍵網路強度的排序為CSL= 2 > 3 > 4 。而SB分子加入鈉離子和加入鎂離子的系統中，從氫鍵網路被嚴重破壞不論碳鏈長短。加入鉀離子和鈣離子的系統在CSL=3時呈現了較好的氫鍵網路。透過結構優化完的結構，其中比較特別的是加入鉀離子的系統，此系統中大部分水分子位於鉀離子與SB上硫離子之間。其餘的金屬離子系統，我們發現到金屬離子吸引大部分水分子的情形發生。所以我們暫時地推測在鈉、鎂、與鈣離子的系統，磺基甜菜鹼分子的親水性會降低。但也有可能目前的含有金屬離子的兩性離子模型中金屬離子的濃度過高而造成的結果偏差。預期能在未來能在模型上做修正來獲得更確切的結論。

關鍵字

氫鍵網路；兩性離子；抗汙

並列摘要

Zwitterionic polymer material have excellent hydration ability and resistance to protein adhesion. These advantages make them to be an indispensable part in the field of anti-fouling. The common zwitterionic materials such as Sulfobetaine (SB), Carboxybetaine (CB) and Phosphobetaines (PB). In the presence of different carbon chain lengths and different cations, zwitterionic materials may affect the hydrophilicity of the entire system. The purpose of this study is to use the calculation of quantum chemistry principles to investigate the effect of adding different cations on water and capacity of sulfobetaine molecules (SB) with different carbon chain lengths (CSL=2~4) and different carbon chain lengths. First, we spread 15 randomly distributed water molecules around the aforementioned systems and generated 50 different configurations, and then we used semi-empirical methods, density functional PBEPBE and M06-2X to gradually screen out the lowest energy structure. Finally, the influence of the above factors on water and capacity is discussed by analyzing its hydrogen bond network and configuration. According to the results, it is found that under different carbon chain lengths of SB molecules, by analyzing the hydrogen bond length and hydrogen bond angle, we can find that the order of the hydrogen bond network strength is CSL= 2 > 3 > 4 . When the SB molecule coordinated to the sodium and magnesium ions, the hydrogen bond network is destroyed by the cations no matter what the carbon space length were compared to the SB molecule without coordinating any cation. Interestingly, the system included potassium and calcium ions showed a strong hydrogen bond network at CSL=3. The hydrogen bond network in the system contained potassium ion showed different feature than the other system containing sodium, magnesium, and calcium ions. The water molecules were sandwiched between SB molecule and potassium ion based on the optimized structure. For the other systems containing metal ions, we found that the metal ions attracted most of the water molecules. Based on these calculation results, we temporarily suspect that sodium, magnesium, and calcium ions would make the water affinity of SB decrease. However, the calculation result could be biased by the high concentration of metal ion the models. It should be tested more realistic models in the near future.

並列關鍵字

anti-fouling ； hydrogen bond network ； zwitterion

參考文獻

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