兩性離子分子是一同時擁有正電荷及負電荷基團的電中性分子。通常正電荷基團為銨根，而負電荷基團則為酸根基團；構成蛋白質的胺基酸就是ㄧ個典型的例子。本計劃所要研究的兩性離子膠體包含由兩性離子界面活性劑所生成的微胞和兩性離子高分子。與一般的界劑相比較，兩性離子界劑對生物體不具刺激性，易被生物分解，同時能在高鹽濃度下穩定存在。由於上述優點，兩性界劑常用於化妝品和洗髮精等產品，此外也被應用於原油開採。電中性的兩性離子高分子溶於水中會同時帶有許多正電荷與負電荷基團，其結構與性質類似簡單的蛋白質。固體表面接枝兩性高分子後，表面具有親水性質。目前的實驗顯示蛋白質不容易吸附在兩性高分子所覆蓋的表面；對於發展生醫材料或細菌吸附研究而言，該性質是非常關鍵的因素。雖然兩性離子膠體外觀呈現電中性，但其親水作用是肇因於正、負電荷基團，所以兩性膠體溶液展現的性質與傳統的中性膠體非常不同。最明顯的差別是添加電解質(鹽類)後的變化。以高分子膠體而言，一般的聚電解質溶於水中會因單體之間的靜電斥力而膨脹，具有較大的迴旋半徑。但在加入鹽後，會因單體吸引反離子而產生靜電遮避效應。單體之間的靜電斥力減弱，使得高分子容易捲縮在一起，高分子半徑因而變小。但兩性高分子卻與一般聚電解質的行為相反，在其水溶液中添加鹽會導致高分子膨脹，稱為『反聚電解質效應』。目前的理論相信該效應緣自於兩性離子基團之間電偶極和電偶極的靜電吸引。然而仍有許多的實驗結果無法以該理論解釋。為瞭解兩性膠體的特性，並提高其應用價值和範疇，本計畫提出一個新的模型。與過去文獻的想法不同，我們以為兩性離子基團間的作用不僅是簡單的靜電偶極矩吸引，正、負電基團之間同時存作類似氫鍵的弱化學作用(較凡得瓦力強)。兩性離子膠體在溶液的特殊行為是偶極矩和類氫鍵的共同作用，缺一不可。本計畫是三年期，研究方法包含實驗和理論兩部份。在實驗部份，我們將透過輸送與熱力性質的量測，包括電泳動度、電導、及相互作用參數等，宏觀探討兩性膠體呈現反電解質效應的成因。在理論部份，我們將利用分子模擬與量子化學計算，微觀研究兩性離子基團間的作用及其如何影響兩性微胞的生成和兩性高分子的構形。透過宏觀實驗與微觀理論的相互配合，我們可以驗證模型的正確性並進行相應的修正。築基於該模型，我們將可以解釋並預測兩性離子膠體的目前及未來的應用。 A zwitterion is an electrically neutral molecule which has an anion and a cation in the one molecule chemically joined together. Usually, the former is protonated amine while the latter is acid group. A typical example is amino acid. In this project the zwitterionic colloids we intend to study include micelles formed by zwitterionic surfactants and zwitterionic polymers. Zwitterionic surfactants do not irritate the skin or eyes, and have good surfactant properties over a wide pH range. Moreover, they can exist stably even at high salt concentrations. As a result, they are very popular in skin-care products and cosmetic manufacture, and used in enhanced oil recovery. “Zwitterionic polymer” means a polymer composed from zwitterionic monomers. A substrate grafted by zwitterionic polymers exhibits hydrophilic characteristics. Present experimental results indicate they can resist the protein adsorption. Such a property is a key factor for successfully developing nonfouling biomaterials. Despite being electroneutral, the hydrophilicity associated with zwitterionic colloids comes from their ionic groups. Therefore, the solution property of zwitterionic colloids is quite different from that of the typical neutral colloids. The main difference is the response to salt addition. The radius of gyration of a charged polymer in salt-free solution is greater than that in salty solution (collape) because of the electrostatic repulsions among charged monomers. However, opposite to the polyelectrolyte solution, the zwitterionic polymer expands upon salt addition, so-called the antipolyelectrolyte effect. It is generally believed that dipole-dipole attractions between zwitterionic units lead to the collapse of zwitterionic polymers in salt-free condition. Salt addition results in electrostatic screening effect and results in swelling. However, some results cannot be explained by the current model. In order to understand the solution properties of zwitterionic colloids and thus promote their applications, we propose a new model which suggests a hydrogen bond like interaction between zwitterionic groups. Both experimental and theoretical approaches are adopted in this three-year project. The former include measurement of transport and thermodynamic properties (i.e., capillary electrophoresis and interaction χ-parameter) while the latter involve molecular simulation (Monte Carlo) and quantum chemistry calculation (Jaguar). Once the proposed model is examined and revised, we are able to explain experimental observations and indicate possible applications. 研究期間：9908 ~ 10007
