銅離子化學感測分子之設計與合成 (一)以NBD為基底 (二) 以 HGGG 胜肽為基底

Abstract

(一) 以NBD 為基底之銅離子化學感測分子之合成 以NBD 為基底，設計並成功合成出對過渡金屬離子具有辨識能力的化學感測分子1 及 2。在 pH = 7，甲醇和水體積比為 1：1 的混合溶劑中，化合物 1 可對Cu2+、Ni2+ 及Co2+ 離子分別作辨識，產生不同的溶液顏色變化；化合物 2 則可專對Cu2+ 離子作選擇性辨識，導致螢光淬熄現象的發生。由氫核磁共振實驗研究發現，當化學感測分子與金屬離子錯合後，醯胺基上 NH 訊號會消失，顯示醯胺基上的氫在錯合過程中會脫去；在 pH 值的影響研究中，Cu2+ 離子存在下，pH 值大於 4.5 時，吸收光譜或螢光放射光譜開始產生改變，Co2+ 及Ni2+ 離子則在 pH 值大於 5.5之後始有影響。藉由醯胺基上的氮、吡啶環上及NBD環上NH官能基的氮原子，化合物 1 及 2 可與金屬離子形成 1：1 或 2：1 的錯合。化合物 2 在結構上旋轉自由度較佳，造成對金屬離子的結合力較弱，卻也提升了對於金屬離子的選擇能力，可選擇性的只與 Cu2+ 離子形成 1：1 錯合。 (二) 以HGGG 胜肽為基底之銅離子螢光化學感測分子之合成 利用 9-fluorenylmethoxycarbonyl (Fmoc) 固相合成法，以胺基酸序列 HGGG 為基底結構，修飾上螢光基團 fluorescein，成功合成可溶於水的螢光化學感測分子 4。當Cu2+ 離子存在時，會造成螢光化學感測分子 4 螢光的淬熄，其他金屬離子 Ag+、Ca2+、Cd2+、Co2+、Ni2+、Fe2+、Fe3+、Mg2+、Mn2+、Hg2+ 及 Zn2+ 則無明顯影響。化學感測分子 4 與 Cu2+ 離子結合間的解離常數Kd為：37 □M；在 pH 值 7 至 8 之間，螢光淬熄效果最顯著，為化學感測分子 4 偵測 Cu2+ 離子的最佳 pH 值範圍。

(1)Synthesis of chemosensors based on 7-nitrobenz-2-oxa-1,3- diazole (NBD) for the detection of Cu2+. Two chemosensors 1 and 2 based on 7-nitrobenz-2-oxa-1,3-diazole (NBD) have been designed and successfully synthesized for detecting transition metal ions. For chemosensor 1, the different optical responses were observed: Cu2+ (yellow to blue), Ni2+ (yellow to violet) and Co2+ (yellow to green). For chemosensor 2, significant fluorescence quenching was observed on selective detection of Cu2+. In 1H NMR titration studies,the disappearance of amide hydrogen signal indicates the deprotonation of amide nitrogen upon metal ion bonding. pH effects on metal ion sensing were also investigated. In the presence of Cu2+, color change in chemosensor 1 and fluorescence quenching in chemosensor 2 occurred at pH > 4.5. For Ni2+ and Co2+, significant color changes were observed in chemosensor 1 as pH value was higher than 5.5. Chemosensors 1 and 2 form complexes with transition metal ions in 1:1 or 2:1 ratio by participation of deprotonated amide nitrogen, pyridine nitrogen, and an amine nitrogen attached to NBD. Chemosensor 2 is more flexible than chemosensor 1, resulting lower binding affinity for Cu2+. (2)Synthesis of the fluorescent chemosensor based on tetrapeptide Histidyl-Glycyl-Glycyl-Glycine (HGGG) for the detection of Cu2+. A water-soluble fluorescent chemosensor 4 has been synthesized by modifying a tetrapeptide histidyl-glycyl-glycyl-glycine (HGGG) with fluorescein via standard solid-phase 9-fluorenylmethoxycarbonyl (Fmoc) chemistry. In the presence of Cu2+, significant fluorescence quenching is observed with chemosensor 4. Other metal ions including (Ag+, Ca2+, Cd2+, Co2+,Ni2+, Fe2+, Fe3+, Mg2+, Mn2+, Hg2+, and Zn2+) causes only minor changes in the fluorescence intensity. The dissociation constant (Kd) of Cu2+ binding in chemosensor 4 is estimated to be 37 μM. The maximum fluorescence quenching caused by Cu2+ binding in 4 is observed over the pH range 7 ~ 8, providing the optimal pH range for the detection of Cu2+ by chemosensor 4.