A novel, cysteine-containing fluorescent hexapeptide, Nacetyl-Tyr-Cys-Ser-Ser-Cys-Tyr( YY), targeting Cd(II) ion sensing, was synthesized on various solid supports including two resins, as well as glass and quartz surfaces. The synthesis was based on the Fmoc (9-fluorenylmethoxycarbonyl) and the APTES (3-aminopropyltriethoxysilane) methodologies on the resin and silica supports, respectively. The immobilized ligand, except when coupled to a hydrophobic benzhydrylamine resin, showed a remarkably efficient, pH-dependent Cd(II) capturing ability with a maximum binding capacity around neutral pH. The effect of contact time and metal ion concentration was also studied with a hydrophilic resin supported peptide (YY-NTG). The interaction of YY-NTG with Cd(II) was investigated by pH-potentiometric titrations in aqueous samples containing the resin beads and Cd(II). These studies, together with metal ion capturing experiments under buffer-controlled pH, prove that each immobilized peptide can bind one Cd(II) ion at pH 7.0 in the presence of one equivalent metal ion or metal ion excess. For Cd(II) binding to YY-NTG a notably high, K = 1.3 × 1010 apparent stability constant was determined (1:1 metal-to-ligand ratio, pH 7.0). Analytical results suggest that the concentration of Cd(II) can be measured below 200nM with this silicasupported peptide. The usefulness of the probe was demonstrated by fluorescence spectroscopy.
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