對金屬離子具有高選擇性的偶氮 Calix[4]arenes 之感測研究

Abstract

本論文中我們探討一系列偶氮 calix[4]arenes 對鹼金、鹼土族及過渡金屬離子感測性的研究，觀察 UV/Vis 吸收光譜來辨別其對特別金屬離子的選擇性，利用 Job plot 及 Benesi-Hildebrand plots 可求出錯合物的錯合比例和結合常數 (Ka)。結果顯示 (1) 下緣無取代的偶氮 calix[4]arenes 33a-b、34a-b 及 35a-b 對過渡金屬離子有好的選擇性，雙偶氮取代效應較單偶氮取代好，其中又以偶氮對位為甲氧基取代的 33b 錯合 Hg2+ 的能力最強 (Ka = 235000 M-1)，而偶氮對位為硝基取代的 33c 和 34c 對金屬離子卻沒有錯合效應。(2) 下緣四醚酯基取代之偶氮 calix[4]arenes，偶氮對位為甲氧基取代的 42a 對 Hg2+ 的選擇性最好 (Ka = 18700 M-1)，偶氮對位為硝基取代的 42b-c 與 Li+、Na+ 的錯合能力較強，Ka值介於 11700-45100 M-1 之間。(3) 下緣三醚酯基取代之偶氮 calix[4]arene 12 在氯仿溶劑中對鹼金、鹼土族及過渡金屬皆有效應，對 Pb2+ 的選擇性最好 (Ka = 156000 M-1)，但是乙腈溶劑中，對過渡金屬的錯合效應相對較差。 本論文將探討在氯仿和乙腈兩種溶劑中，影響偶氮 calix[4]arenes 之 UV/Vis 吸收光譜變化及錯合金屬離子的效應，另外我們也利用 1H-NMR 滴定光譜推測 33b 和 12 錯合金屬離子時的構形變化。

In this work, we studied a series of azo-calix[4]arenes on their optical-sensing properties of alkali, alkaline, and transition metal ions. UV/Vis spectroscopy was used to monitor the complexation of these calix[4]arenes with metal ions. Job plot and Benesi-Hildebrand plots allowed us to determine the binding ratios and association constants (Ka) of the complexes. We found that (1) azo-calix[4]arenes 33a-b, 34a-b, and 35a-b, without substituent in the lower rim had high selectivity for transition metal ions, and the binding ability of diazo-calix[4]arenes were stronger than that of monoazo-calix[4]arenes. The azo group with para-methoxy aromatic ring 33b showed a very high selectivity for Hg2+ (Ka = 235000 M-1), but that with para-nitro aromatic ring 33c, and 34c, showed no effect for metal ion complexation. (2) For azo-calixarenes with tetraester substituents in the lower rim, the azo group with para-methoxy aromatic ring 42a had high selectivity for Hg2+ (Ka = 18700 M-1), and that with para-nitro aromatic ring 42b-c exhibited better binding ability for Li+ and Na+, and the association constants Ka were between 11700-4100 M-1 for the latter hosts. (3) Azo-calix[4]arene 12 with triester substituents in the lower rim had selectivity not only for alkali and alkaline but also for transition metal ions in chloroform. Especially 12 is an excellent sensor for Pb2+. When the complexation experiments for 12 were carried out in acetonitrile lower binding constants for transition metal ions were observed. Factors affecting the UV/Vis spectra, ability of binding metal ions of these azo-calix[4]arenes in chloroform and acetonitrile are discussed. Further more 1H-NMR titration studies allowed us to propose possible conformations of 33b and 12 upon metal ion complexation.