Abstract
Four new peptide-based chemosensors derived from a β-hairpin have been synthesized via solid phase peptide synthesis (SPPS) and Fmoc chemistry. The Trp fluorescence of HP7-H2H11 (Lys-His-Trp-Asn-Pro-Ala-Thr-Gly-Lys-Trp- His-Glu), HP7-H4H9 (Lys-Thr-Trp-His-Pro-Ala-Thr-Gly-His-Trp-Thr-Glu), HP7- H2H4H9H11 (Lys-His-Trp-His-Pro-Ala-Thr-Gly-His-Trp-His-Glu) and HP7-H1H12 (His-Thr-Trp-Asn-Pro-Ala-Thr-Gly-Lys-Trp-Thr-His) peptides was significantly quenched in the presence of Cu2+and Hg2+, while adding Al3+, Ba2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, Mg2+, Mn2+, Ni2+, Sr2+ and Zn2+dose not cause significant fluorescence changes. Also, pH dependent measurements indicate that Cu2+ has a more profound quenching effect than Hg2+ on the fluorescence at high pH, which could be used to discriminate Cu2+ and Hg2+. Besides, circular dichroism (CD) spectra show that Cu2+ and Hg2+ induce different structural changes on the peptides. At pH 7.5, the dissociation constants (Kd) of Cu2+ binding to HP7-H2H11, HP7-H4H9, HP7-H2H4H9H11 and HP7-H1H12 are 6.7 μM, 20.3 μM, 6.0μM and, 8.1μM respectively. For Hg2+ binding, the Kd is 50.3 μM to HP7-H2H11, 34.4 μM to HP7-H4H9, 29.0 μM to HP7-H2H4H9H11 and 35.9 μM to HP7-H1H12. The detection limit of HP7-H2H11 is 0.55 μM for Cu2+ and 0.54 μM for Hg2+, and that of HP7-H4H9 is 0.79 μM for Cu2+ and 0.97 μM for Hg2+. For HP7-H2H4H9H11, the detection limit of HP7-H2H4H9H11 is 0.68 μM for Cu2+ and 1.34 μM for Hg2+, and that of HP7-H1H12 is 0.62 μM for Cu2+ and 1.04 μM for Hg2+ . Our results demonstrate that these four new water-soluble peptides can be good chemosensors for the detection of Cu2+ and Hg2+.