以紅外線光譜探討2-(三氯乙醯基)吡咯的自結合及與甲苯之異結合現象

Abstract

由於生物科技方面的議題在全球受到矚目，而許多生物反應牽涉到蛋白質，其中氫鍵具有穩定蛋白質結構的功能。因為2-(三氯乙醯基)吡咯分子有N-H•••O=C鍵結與蛋白質結構中的鍵結相似，故本文選擇2-(三氯乙醯基)吡咯為研究對象，以FTIR為研究工具探討N-H•••O=C氫鍵所衍生出的熱力學性質。本文中將討論2-(三氯乙醯基)吡咯溶於非極性或低極性溶劑時的氫鍵自結合及異結合現象，透過改變系統的溫度、溶劑種類及樣品的濃度，利用FTIR來得到單體及雙體N-H基個別的總吸收度，代入本實驗室所推導的二條公式，即可求得單體總莫耳吸收係數(εm)、雙體總莫耳吸收係數(εd)及單雙體自結合平衡常數(K)。由於這二條公式皆可個別求出自結合平衡常數，所以求出的值可以相互對照印證，檢驗所求得的實驗數值是否可靠。根據平衡常數隨溫度的變化利用van’t Hoff 理論作圖，可求得自結合系統的標準焓( Ho)及標準熵( So)。由標準焓及標準熵可以判斷2-(三氯乙醯基)吡咯的自結合現象有伴隨著熱量釋出，且自結合系統的亂度也會變小。接著利用溶劑極性的不同探討對這些熱力學參數所造成的影響，此外我們也推導出公式可用來判斷2-(三氯乙醯基)吡咯雙體分子為環狀形式。最後，本文將討論2-(三氯乙醯基)吡咯與質子接受者所形成的氫鍵異結合系統，利用推導出的公式可以求得錯體總莫耳吸收係數(εx)和異結合平衡常數(Kx)。

The advent of biotechnology has drawn much attention to the public. In biotechnology, the function, structure, and reaction of proteins play a crucial role. As to the structure, it is the N-H•••O=C hydrogen bonding that is a major factor in stability. Due to the similar hydrogen bonding involved between 2-(trichloroacetyl)pyrrole molecular dimerization, it is chosen as a model for the investigation into the protein stability. The FTIR has been employed to this purpose. The fact that the spectra of associated dimer and free monomer N-H stretching modes appear concurrently allows, upon deconvolution, the data of the integrated absorbance of the monomer is to be fitted into the linear equation (2-9), page 14, to determine the monomer molar absorptivity, dimerization constant; and that of dimer is to be fitted into equation (2-12), page 15, to determine the dimer molar absorptivity and dimerization constant at various temperatures. Since the very same dimerization constant can be determined by different data sources, the disparity of the results provides a criterion for judging the consistency of the determination. The enthalpy and entropy of dimerization can be obtained via a van’t Hoff plot. Instead of in a linear form, the dimer is predominantly in a cyclic form, this is reasoned from a plot based on a linear equation (3-28), page 121. Also the hetero-association of the 2-(trichloroacetyl)pyrrole with toluene has been studied to obtain the complex molar absorptivity and complexation constant using equation (2-20), page 19. The enthalpy and entropy of complexation have also been determined.