利用半胱胺酸與銅離子反應產生不均相辨識特定濃度範圍銅離子

Abstract

本論文以目視觀察相變化(phase segregation)偵測特定濃度範圍銅離子。利用半胱胺酸(cysteine, Cys)與銅離子反應產生棉絮狀聚合物(polymer)，使溶液變為不均相。實驗發現當[Cu2+]0/[Cys]0介於0.4~0.5時，不均相於3分鐘之內產生，當[Cu2+]0/[Cys]0小於0.4時，不均相產生所需時間隨[Cu2+]0減少而增加，當[Cu2+]0/[Cys]0大於0.5時，不產生不均相。加入奈米金可吸附於棉絮狀聚合物，藉以突顯相變化；或應用廷得耳效應(Tyndall effect)，使相變化容易以肉眼觀察。觀察3分鐘內不均相出現與否，判斷銅離子濃度範圍。 藉由半胱胺酸的硫醇官能基(-SH)與二價銅離子(Cu2+)發生氧化還原反應，半胱胺酸被氧化為胱胺酸(cystine)，二價銅離子被還原成ㄧ價銅離子(Cu+)，Cu+與溶液中未被氧化的半胱胺酸形成1:1錯合物(Cu+Cys)，此錯合物將進一步形成如棉絮狀的聚合物[Cu+Cys]n，而使原來均勻溶液相變為不均相。當[Cu2+]0/[Cys]0大於0.5時，將還原出無法與半胱胺酸形成Cu+Cys之過量free Cu+，此free Cu+於溶液中進行自身氧化還原後生成Cu2+及Cu0，Cu2+氧化Cu+Cys錯合物中之Cys影響聚合物之生成，而使溶液維持均相。

Visual and rapid determination of whether an analyte falls within or outside of a concentration range has been validated. The target analyte demonstrated in this study is Cu2+ which, among other transition metal ions, receives considerable attention of its biological and environmental importance. Concerning the reactions of cysteine (Cys) and Cu2+ under proper conditions, the colloidal gold solution with Cys and Cu2+ becomes fluffily flocculated in 3 minutes. The fluffy floccules appear reddish and the solution between the floccules becomes colorless owing to the adsorption of gold nanoparticles on the floccules. According to our experimental results and literature studies, the mercapto group from Cys is oxidized due to reducing Cu2+ into Cu+ which be bound with excess Cys and generates Cu+Cys. These Cu+Cys complexes will further form μ-thiolato complex polymers [Cu+Cys]n ascribed to the fluffy floccules and phase segregation. The visualization of the polymerization takes less than 3 minutes for [Cu2+]0/[Cys]0 ranging from 0.4 to 0.5. When [Cu2+]0/[Cys]0 > 0.5, the solution exhibits free Cu+ because of the limited amount of Cys. The Cu2+ is regenerated by the disproportionation of free Cu+. The Cu2+ oxidizes Cys from Cu+Cys monomer. As a result, no phase segregation is observed when [Cu2+]0/[Cys]0 > 0.5. As [Cu2+]0/[Cys]0 < 0.4, the time required for fluffy floccules formation is over 3 minutes.