Highly selective and water-soluble peptidyl chemosensors for copper(ii) and mercury(ii) ions based on a β-hairpin structure

Abstract

Based on a β-hairpin structure, two new water-soluble peptidyl chemosensors, HP7-H2H11 and HP7-H1H12, were designed and synthesized. In the peptides we implanted histidine as a metal-binding unit and tryptophan as a reporting unit. These two peptides are sensitive and selective to the detection of Cu²⁺ and Hg²⁺ with a detection limit in the range of 0.6 to 1 μM. The dissociation constants (K_d) of Cu²⁺ binding are smaller than those of Hg²⁺ binding in HP7-H2H11 and HP7-H1H12, indicating that the peptides have a higher affinity to Cu²⁺ than Hg²⁺. pH-dependent fluorescence measurements could be used to discriminate between Cu²⁺ and Hg²⁺ in solution due to the fact that these two metal ions had significantly different quenching effects on the fluorescence of HP7-H2H11 and HP7-H1H12 under alkaline conditions. Circular dichroism (CD) measurements further showed that Cu²⁺ and Hg²⁺ have distinct effects on the secondary structure of the peptides, providing a complimentary means to differentiate Cu²⁺ from Hg²⁺.