Visual Detection for a Concentration Range of Cu2+ by Phase Segregation of Cu-Cysteine Complex
Date Issued
2010
Date
2010
Author(s)
Liu, Yao-Min
Abstract
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.
Subjects
cysteine
Cu
phase segregation
Type
thesis
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