Abstract
Heavy metals are hazardous environmental contaminants, often highly toxic even at extremely low concentrations. Monitoring their presence in environmental samples is an important but complex task that has attracted the attention of many research groups. We have previously developed a fluorescent peptidyl sensor, dH3w, for monitoring Zn2+ in living cells. This probe, designed on the base on the internal repeats of the human histidine rich glycoprotein, shows a turn on response to Zn2+ and a turn off response to Cu2+. Other heavy metals (Mn2+, Fe2+, Ni2+, Co2+, Pb2+ and Cd2+) do not interfere with the detection of Zn2+ and Cu2+. Here we report that dH3w has an affinity for Hg2+ considerably higher than that for Zn2+ or Cu2+, therefore the strong fluorescence of the Zn2+/dH3w complex is quenched when it is exposed to aqueous solutions of Hg2+, allowing the detection of sub-micromolar levels of Hg2+. Fluorescence of the Zn2+/dH3w complex is also quenched by Cu2+ whereas other heavy metals (Mn2+, Fe2+, Ni2+, Co2+, Cd2+, Pb2+, Sn2+ and Cr3+) have no effect. The high affinity and selectivity suggest that dH3w and the Zn2+/dH3w complex are suited as fluorescent sensor for the detection of Hg2+ and Cu2+ in environmental as well as biological samples.
Highlights
Heavy metal ions when present in excess are toxic for all organisms [1]
According to Wuthrich [31], identification of amino-acid spin systems was performed by comparison of total correlation spectroscopy (TOCSY) and DQF-COSY, while sequential assignment was obtained by the analysis of nuclear Overhauser effect spectroscopy (NOESY) and rotating frame Overhauser effect spectroscopy (ROESY) spectra
The second binding event likely involves the direct participation of the sulphonamide moiety of the fluorophore and is accompanied by relevant changes in the emission spectrum i.e. a blue shift of the λmax and an increase of the emission intensity
Summary
Heavy metal ions when present in excess are toxic for all organisms [1]. They are difficult to remove from the environment and unlike many other pollutants cannot be chemically or biologically degraded, heavy metals constitute a global environmental hazard [2]. Monitoring mercury (II) by fluorescent peptide dH3w samples Many of these Hg2+ sensors are based on colorimetric and/or fluorometric detection [6,7,8,9,10,11,12,13], but very sensitive sensors based on surface enhanced Raman spectroscopy (SERS) [14], chiroptical signal and electrical conductivity [15] have been developed. Some colorimetric and fluorometric sensors exploit metal catalyzed reactions like spirocyclic ring opening in rhodamine derivatives [7] or deprotection of dithioacetals ([8] and references therein) Major drawbacks of these sensors can be difficult synthesis, limited solubility in water or the fact that they undergo an irreversible reaction with the analyte. With the exception of Cu2+ no other heavy metal is able to displace Zn2+, dH3w complex with Zn2+ could be used as selective probes for environmental monitoring of Hg2+ and Cu2+
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