三唑取代香豆素衍生物之合成與其對於金屬離子及陰離子之螢光感測研究

Abstract

本論文的設計構想為：以7-甲氧基香豆素作為螢光基團，以三唑雜環取代基作為離子辨識基團，再透過不同的架橋來連接這兩個基團，組合成「香豆素-架橋-雜環取代基」型態的螢光感測分子12b、16、17、27和30。 使用三種不同的架橋連接螢光基團和離子辨識基團，分別以 (a) 直接連接 (12b) (b) 亞甲基連接 (16) (c) 乙醯基連接 (17和27) 做為架橋來連接三唑雜環取代基。化合物12b、16及17在MeOH/CHCl3 (9:1, v/v) 混合溶液中，只有化合物17對Hg2+有選擇性，其螢光強度增加1.8倍。經由氫核磁共振光譜滴定實驗得知化合物17與Hg2+是以1:1及1:2的比例進行錯合，推測第一個Hg2+與架橋乙醯基及三唑雜環2號氮螯合，然後第二個Hg2+才與三唑雜環3號氮及t-butylphenol上的氧原子螯合。 為了證實第二個Hg2+是與三唑雜環3號氮及t-butylphenol上的氧原子螯合，合成三唑雜環連接苯甲基基團的控制化合物27，在相同溶液條件下，化合物27對Hg2+有選擇性，其螢光強度增加3.3倍。經由氫核磁共振光譜滴定實驗得知化合物27與Hg2+是以1:1比例進行錯合，推測Hg2+與架橋乙醯基及三唑雜環2號氮螯合。化合物27與Hg2+錯合後螢光增強倍率比化合物17與Hg2+錯合後來的大，原因有二： (a) Hg2+本身是淬熄劑 (quencher)，因化合物17與2個Hg2+錯合，使得錯合物螢光增強倍率較27與1個Hg2+錯合低；(b) 在溶液中，有部分的17只與1個Hg2+錯合，未錯合的t-butylphenoxy 基團因為有loose bolt 效應可自由轉動，能量被消耗使得螢光減弱。 化合物30為具有多羥基及三唑基團的香豆素衍生物，在HEPES緩衝溶液中 (20 mM, pH 7.3, 3.3% DMSO, v/v)，化合物30只對Cu2+有選擇性，並造成螢光淬熄，以1:1的比例進行錯合，且此錯合現象在加入EDTA後具有可逆性。另外，化合物30對四級銨鹽陰離子進行篩選，只對CN□有選擇性。CN□會進行Michael addition反應攻打到香豆素4號位置上，導致破壞芳香性而造成螢光淬熄，為一化學劑量計。

Based on our design, 7-methoxycoumarin was chosen as the fluorophore, and 1,2,3-triazole as the heterocyclic group, was ultilized as the ionophore for ions. The two units of fluorophore and the 1,2,3-triazole group ionophore were joined with different spacers to afford a series of coumarin fluorescent sensors 12b, 16, 17, 27 and 30. In this work, we used three different ways to combine the fluorophore and the triazole groups: (a) by direct conjugation (12b), (b) by inserting a methylene bridge (16), and (3) by inserting a carbonyl methylene group (17 and 27). Among 12b, 16, and 17, only 17 was capable of selectively detecting Hg2+ by enhancing the fluorescence intensity by 1.8 fold in polar protic solvents MeOH/CHCl3 (v/v, 9:1). Based on 1H-NMR titration studies provide evidences of the 1:1 and 1:2 complexes of 17 and Hg2+. We propose that the first Hg2+ was coordinated with carbonyl and nitrogen (N2) atom of the 1,2,3-triazole to result in a more rigid conformation leading to the increase in fluorescence intensities. The second Hg2+ was proposed to coordinate with the nitrogen (N3) atom of the triazole and the oxygen atom of the t-butylphenol group. In order to confirm that the chelation of the second equiv of Hg2+ by 17 was indeed through the binding of the triazole and the phenoxy ether groups, we also synthesized coumarin 27, where the 4-position of the triazole unit was replaced by a benzyl group instead of the 4-t-butylphenoxymethyl. To our surprise, the fluorescence intensity of 27 was enhanced by 3.3-fold after addition of Hg2+ ions s compared to that of 1.8-fold enhancement by 17 under similar conditions. Based on 1H-NMR titration studies provide evidences of the 1:1 complexes of 27 and Hg2+. When complexed with Hg2+, the larger fluorescence enhancement factors by 27 than by 17 might be owing to two major reasons: (1) In general, Hg2+ tends to quench the fluorescence of a fluorophore by spin-orbit coupling, thus the complexation of 17 with two Hg2+ may reduce part of the fluorescence intensity; (2) In solution, part of the 17 was bound with only one Hg2+, the un-chelated t-butylphenoxy group in 17•Hg2+ was quite flexible and was therefore efficient in radiationless decay processes. Compound 30, in a coumarin derivatives that contains polyhydroxy is a highly selective fluorescent chemosensor (turn-off) for Cu2+ over other cations in HEPES buffer (20 mM, pH 7.3, 3.3% DMSO). Based on the 1H-NMR titration spectra, compound 30 was proposed to coordinate Cu2+ by triazole, carbonyl and hydroxyl groups. The coordination between 30 and Cu2+ can be reversed by the addition of EDTA. Furthermore, compound 30 also behaves as a selective fluorescent chemodosimeter for CN□ over other anions under same condition. Based on the 1H-NMR titration spectra, CN□ through the Michael addition to the 4-position of compound 30.