title: Thermodynamics and fluorescence studies of the interactions of cyclooctapeptides with Hg2+, Pb2+, and Cd2+.
abstract: The purpose of this work is to characterize the interactions of cyclooctapeptides (CP) containing glutamyl and/or cysteinyl residues with common heavy-metal ions in order to facilitate the design of cyclopeptides as sensors for metal ions. Isothermal titration calorimetry studies show that cyclooctapeptides containing glutamyl and/or cysteinyl residues bind these Hg(2+) and Pb(2+) over Cd(2+) and other common metal ions. Differential binding isotherms, in their interactions with Hg(2+), support a two-binding site model, whereas pertinent interactions with Pb(2+) support a 2:1 stoichiometry, suggesting a CP/Pb(2+)/CP mode of complexation. The cyclooctapeptide containing both glutamyl and cysteinyl residues shows a significant binding affinity for Hg(2+) (K(a)=7.6x10(7)M(-1)), which is both enthalpically and entropically driven. The fluorescence of these cyclooctapeptides showed pronounced fluorescence quenching responses to Hg(2+) over Pd(2+) and Cd(2+). Stern-Volmer analyses of the dependence of fluorescence intensity on Hg(2+) and Pb(2+) are reported. The observed trends are useful for the design of Hg(2+) sensors based on fluorophore-tagged cyclooctapeptides.
authors.affiliation: Department of Chemistry, Winston-Salem State University, 601 M.L. King, Jr. Drive, W.B. Atkinson Science Building, Winston-Salem, NC 27110, USA. Schwemleinmn@wssu.edu
authors.forename: Maria
authors.initials: M
authors.lastname: Ngu-Schwemlein
authors.forename: Willie
authors.initials: W
authors.lastname: Gilbert
authors.forename: Kshawna
authors.initials: K
authors.lastname: Askew
authors.forename: Stefanie
authors.initials: S
authors.lastname: Schwemlein
mesh_terms: D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry*; D002151:Calorimetry; D004566:Electrodes; D005453:Fluorescence; D007854:Lead / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D008968:Molecular Conformation; D010456:Peptides, Cyclic / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D010456:Peptides, Cyclic; D002104:Cadmium; D007854:Lead; D008628:Mercury