雙面角與金屬化反應對遠距調控氫鍵之訊號轉換器的影響

Remote Control of Hydrogen Bond Strengths in Donor-bridge-Acceptor Systems: The Effects of Torsion and Metalation

黃怡螢(Yi-Ying Huang)

指導教授 ： 趙奕姼

共同指導教授 ： 蘇志明(Tzu-Min Su)

國立臺灣大學/理學院/化學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.00504

摘要

我們設計了一個三元件的訊號轉換器，來達到遠距離良好調控氫鍵
的能力，其中包含了氫鍵鍵結中心(pyrrole)，反應中心(imine)和連結前面兩者的架橋，當反應中心被質子化時，可誘發分子內的電荷轉移，而改變在遠端之氫鍵鍵結中心的鍵結能力。本篇研究是以理論計算的方式，對轉換器的設計上進行兩項探討，第一項討論是關於共軛系統平面性的問題，我們轉動鍵結中心周圍之雙面角，觀察其對三元件共軛系統的影響，結果顯示氫鍵鍵能和轉換器之敏感度皆會隨著扭轉角度的增加而下降，當扭轉角度在45°以內，氫鍵鍵能下降幅度相當小(<1 kcal/mol)，故分子輕微的扭轉，氫鍵控制系統仍能維持適當的訊號傳遞能力，所以在設計三元件系統時不需特別避免小角度之非平面狀況 ; 而在CH=CH 架橋系列和N=N 架橋系列的比較上，則發現原本在平面電荷轉移能力較強的N=N 架橋類型較不易受小角度扭轉的影響 ; 在α site 和β site 三元件系統的比較上可發現β site 鍵能受扭轉而下降的幅度略小於α site，但兩者的敏感度則相差不多。另一項討論則是利用金屬化反應來改變電荷的
狀態，以帶動分子內的電荷轉移，觀察其氫鍵鍵結改變的效果，並和質子化反應進行比較。計算的系統分別有以純CH=CH-CH=CH 鏈為架橋的系統A、加入CN 取代基於架橋上的系統B、加入兩個CN 取代基於反應中心上的系統C 以及四個CN 取代基於反應中心上的系統D。研究結果發現在四個系統當中二價的金屬(Ru2+, Zn2+, Mg2+)所引發的電荷轉移能力和轉換器敏感度近似於質子化反應，一價的金屬(Li+, Na+)所引發的電荷轉移能力和敏感度則相當微弱，幾乎接近中性系統 ; 而在四個系統中可發現同價數的金屬彼此間氫鍵鍵能的差異性並不大，大小順序分別為：+2 價的金屬 Ru2+ > Zn2+＝Mg2+ ; +1 價的金屬 Li+ > Na+，但不同價數的金屬其氫鍵鍵能的差異則相當大。在四個系統的比較上，金屬化後鍵能強弱的大小順序分別為：系統B >系統D >系統C >系統A ; 敏感度高低順序分別為系統D >系統C >系統B >系統A。另外在架橋之鏈長效應的比較上，可發現系統B 其分子內電荷轉移能力最不受鏈加長的影響，但對轉換器的敏感度而言，四個系統隨著鏈加長鍵能下降的程度相近。系統D 是最適合用為遠距離的轉換器，因在鏈未加長時時敏感度即
相當大。這些相關研究可讓我們瞭解在反應中心進行金屬化反應，一樣具有誘發訊號傳遞的能力。此兩項討論可使我們對三元件系統有更深入的了解亦可提供較完整資訊讓合成化學家參考。

關鍵字

氫鍵 ； 分子內電荷轉移

並列摘要

Remote control of hydrogen bond strengths can be modulated in a three-component system consisting of a hydrogen bonding site (pyrrole), a conjugated bridge and a reaction
center (imine). Protonation of the reaction center can trigger intramolecular charge transfer thus altering the binding ability of the remote hydrogen-bonding site. The signaltransduction from the reaction center to the hydrogen-bonding site can be easily observed.
In the first part of the study, we investigated the effect of non-planarity in the π-conjugated system has on the binding strength in the three-component system. Computational study showed that the torsion angle between the binding site and the bridging unit could greatly
influence the remote signal communication in our three-component system. Dihedral angle drive calculations on the hydrogen-bonding site were performed to show how the
binding energies behaved as the torsion angle is varied. The results showed decay in the binding strength and transduction sensitivity as the torsion angle is increased. Small decrease in the binding energies is observed when the torsion angle is within 45°, so that
intramolecular charge transfer is not seriously affected by small distortion in the torsion angle. When we compare the CH=CH bridge and N=N bridge, the N=N bridge, which
displays more efficient charge-transfer ability than the CH=CH bridge in planar configuration, is less affected by the variation of the torsion angle, as long as the torsion
angle is within 30°. In general, the decrease of binding energy in the α-systems is slightly more than the β-systems as the three-component systems become nonplanar. In the second part of the study, we observed the extent of charge transfer that was induced by metalation
and compared it with protonation-induced charge transfer. We studied four three-component systems: system A (pure CH=CH-CH=CH bridge), system B (with two substituted CN groups in the CH=CH-CH=CH bridge), system C (with two substituted CN groups in the reaction center), and system D (with four substituted CN groups in the
reaction center). The results showed that the abilities of charge transfer and sensitivity for metalation with M2+ ions are similar to protonation in all four systems. However, the abilities of charge transfer and sensitivity for metalation with M+ ions are very weak and
are similar to the neutral state. The binding energies of different metals with the same oxidation state are similar (Ru2+ > Zn2+ = Mg2+ ; Li+ > Na+). The strengths of binding
energies ordered from high to low observed in the four systems are system B > system D > system C > system A and sensitivities ordered from high to low in four systems are system D > system C > system B > system A. When we observed the bridge length effect on the four systems, the charge-transfer ability of system B is the least affected as the length of the bridge increase. Our studies have provided great insights in the understanding of
remote hydrogen bond communication in our three-component systems and they could provide guidelines for the synthetic design of these materials.

並列關鍵字

hydrogen bond ； intramolecular charge transfer

參考文獻

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