A new peptide-based fluorescent probe selective for mercury(II)

Introduction Mercury is a hazardous environmental contaminant, highly toxic even at low concentrations.We have previously developed a fluorescent peptidyl sensor named dH3w(dansyl-HPHGHW-NH2) based on an internal repeat of... [ view full abstract ]

Introduction

Mercury is a hazardous environmental contaminant, highly toxic even at low concentrations.We have previously developed a fluorescent peptidyl sensor named dH3w(dansyl-HPHGHW-NH2) based on an internal repeat of human histidine rich glycoprotein (Donadio et al. 2016 J. Mater. Chem. B, 4, 6979). dH3w showed a turn on response to Zn²⁺ and a turn off response to Cu²⁺.Other heavy metals (Mn²⁺, Fe²⁺, Ni²⁺, Co²⁺,Pb²⁺ and Cd²⁺) did not interfere with the detection of Zn²⁺and Cu²⁺. Here we report that dH3w has an affinity for Hg²⁺considerably higher than those for Zn²⁺ and Cu²⁺, thus it could be used as a fluorescent probe for Hg²⁺.

Methods

Steady-statefluorescence measurements were performed in 20 mM MOPS pH 7.0 with thepeptide at a fixed concentration (7 μM). The dansyl fluorophore was excited at 340 nm. Emission spectra wererecorded in the range 450–630 mm. In the displacement experiments Zn²⁺and dH3w were kept at fixed concentrations (100 or 200 μM and 7 μM, respectively) whereas the concentration of Hgwas gradually increased up to 100 uM.

Results

Theaddition of Hg²⁺ to dH3w atconcentrations lower than 10 μM induced a reduction of the emission without changes to the spectrumfeatures. However at concentrations higher than 15 μM Hg²⁺ induced a noteworthy blue-shiftof the λ_max, from 560 to 510 nm (Fig.1) and anincrease of the fluorescence intensity. Very interestingly Hg²⁺ wasable to displace Zn²⁺ (Fig. 2) and Cu²⁺ even when these metalswere present in large excess. Also in the presence of Zn²⁺, low Hg²⁺concentrations induced a reduction of the fluorescence intensity, whereas athigher concentrations a blue-shift in the λ_max was observed.

Discussion

This behaviour strongly suggests that at least two complexes forms at different Hg²⁺/dH3w ratios, possibly with different stoichiometries and/or geometries. The significant blue-shift of the maximum emission could be tentatively attributed to the deprotonation of the dansyl-sulfonamide moiety upon binding to the strongly electrophilic Hg²⁺ ion. The determination of the nature of the two Hg²⁺/dH3w complexes will require further investigations.