光熱測卡計在蛋白質折疊與共軛高分子光物理上的應用

Application of Time-resolved Photothermal Calorimetry on Protein Folding and Photophysics of Conjugated Polymer

陳信良(Hsin-Liang Chen)

指導教授 ： 范文祥

國立臺灣大學/理學院/物理研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.01987

摘要

高分子之結構變化與其發光機制、電荷傳遞、或生物高分子之功能皆有其重要的相關性。我們利用時間解析光熱測卡計，觀測高分子因光激發引發的結構改變行為與能量變化。
探討的樣品主要包含兩類:發光共軛高分子與蛋白質。在共軛高分子方面，我們比較以芴(fluorene)為單體、不同鏈長的小分子與PFO，在光激發後所產生的單體與單體間扭轉運動。並以TSBF當作標準物，因其在光激發後的能量衰減過程無伴隨單體間之扭轉運動。從這些實驗結果，我們提出四個步驟的運動模型，來解釋光激發後的扭轉運動，依此模型，單體與單體間扭轉的角度為35度。相對於PFO，另一具高規則性的共軛高分子聚3-烷基噻吩(Poly(3-dodecylthiophene))雖然似PFO的光譜變化但並沒有觀測到單體間之扭轉運動，其原因，可能為此高分子主鏈具有高規則性(>98%)，以頭對尾方式進行耦合排列之共軛高分子，易到達共平面結構，加上其支鏈較長，更不利於扭轉運動。
另一方面，我們利用易光解斷鍵的化學物質，將其連結到β摺板蛋白質上，固定β摺板的初始結構，利用光熱測卡計量測β摺板因光解斷鍵物質受破壞而引發的構形再折疊運動，經由替換β摺板轉折處的氨基酸，我們歸結出轉折處的氨基酸在蛋白質折疊上扮演一個重要的角色。

關鍵字

高分子結構變化 ； 光熱測卡計 ； 芴 ； β摺板 ； 單體間之扭轉運動

並列摘要

Conformations play important roles in electronic properties of conjugated polymers, and functionalities of bio-molecules. Studies on conformational changes upon electronically excited or performing functions always inspire scientists. Changes in photophysics of these macro-molecules, such as Stokes shifts, spectrum and etc. are sensitive to conformational changes, and serve as appropriate indicators. In this thesis, we apply time-resolved photothermal spectroscopy to focus on two kinds of macromolecules: proteins and conjugate polymers.
In the first part, photothermal techniques are used to visualize the photo induced backbone torsional motion and the corresponding energy flows of polyfluorene (PFO) and poly(3-dodecylthiophene) (P3DT). Systematically comparing photo-excited twisting motions among PFO with different numbers of monomer units has been done in this work. Based on the fact that the photo induced torsional motion can not be detected directly, Ter(9,9'-spirobifluorene) (TSBF) is adopted as a reference for comparison. A four-state model is proposed to correlate the observed energy flow change and volume expansion to photo-induced twisting motions according to the experimental results. The torsional angle can be accordingly estimated. On photo-excited PFO reveals ~ 35° twisting motions between monomer units while P3DT is quite rigid and does not show apparent backbone changes though it has similar spectrum dynamics to PFO. One of the reasons is that high regioregularity (>98%) and long effective conjugated length result in highly coplanar conformations of P3DT. In addition, the long side chain group of P3DT might also block the torsional motion.
In the study on proteins, we focus on kinetics of conformational refolding. It is strongly related to the functions of protein molecules. We use photolysis cages labeled on β-sheet peptides to force deformations of peptides at initial state. By combining laser flash photolysis of cages with photoacoustic calorimetry, we study the effects of different turns on the kinetics of β-hairpin upon refolding in nanosecond timescale. Our observations suggest that the turn formation of β-sheet is vital in directing protein conformational searching at the first place of refolding.

並列關鍵字

Conformational change ； Photothermal calorimetry ； Fluorene ； β-hairpin ； Torsional motion

參考文獻

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